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Sample records for al ba ca

  1. New insights into the application of the valence rules in Zintl phases-Crystal and electronic structures of Ba7Ga4P9, Ba7Ga4As9, Ba7Al4Sb9, Ba6CaAl4Sb9, and Ba6CaGa4Sb9

    NASA Astrophysics Data System (ADS)

    He, Hua; Stoyko, Stanislav; Bobev, Svilen

    2016-04-01

    Crystals of three new ternary pnictides-Ba7Al4Sb9, Ba7Ga4P9, and Ba7Ga4As9 have been prepared by reactions of the respective elements in molten Al or Pb fluxes. Single-crystal X-ray diffraction studies reveal that the three phases are isotypic, crystallizing in the orthorhombic Ba7Ga4Sb9-type structure (space group Pmmn, Pearson symbol oP40, Z=2), for which only the prototype is known. The structure is based on TrPn4 tetrahedra (Tr=Al, Ga; Pn=P, As, Sb), connected in an intricate scheme into 1D-ribbons. Long interchain Pn-Pn bonds (dP-P>3.0 Å; dAs-As>3.1 Å; dSb-Sb>3.3 Å) account for the realization of 2D-layers, separated by Ba2+ cations. Applying the classic valance rules to rationalize the bonding apparently fails, and Ba7Ga4Sb9 has long been known as a metallic Zintl phase. Earlier theoretical calculations, both empirical and ab-initio, suggest that the possible metallic properties originate from filled anti-bonding Pn-Pn states, and the special roles of the "cations" in this crystal structure. To experimentally probe this hypothesis, we sought to synthesize the ordered quaternary phases Ba6CaTr4Sb9 (Tr=Al, Ga). Single-crystal X-ray diffraction work confirms Ba6.145(3)Ca0.855Al4Sb9 and Ba6.235(3)Ca0.765Ga4Sb9, with Ca atoms preferably substituting Ba on one of the three available sites. The nuances of the five crystal structures are discussed, and the chemical bonding in Ba7Ga4As9 is interrogated by tight-binding linear muffin-tin orbital calculations.

  2. X-ray crystal structures of Al-doped (Y,Ca)Ba2Cu3O(7-y) whiskers.

    PubMed

    Bertolotti, Federica; Calore, Leandro; Gervasio, Giuliana; Agostino, Angelo; Truccato, Marco; Operti, Lorenza

    2014-04-01

    Al(+3)-doped (Y,Ca)Ba2Cu3O(7-y) (YBCO) whiskers have been synthesized using a solid-state reaction technique. These materials are promising candidates for solid-state THz applications based on sequences of Josephson Junctions (IJJs). Alumina addition was systematically varied and the effect of aluminium incorporation on the structure has been investigated using single-crystal X-ray diffraction. Aluminium only replaces Cu atoms in the O-Cu-O-Cu chains and a gradual transition from orthorhombic to tetragonal space group occurs, thus increasing the Al content. A gradual modification of the coordination sphere of the copper site has also been observed. The Ca(2+) ion substitutes mainly the Y(3+) ion and also, to a small extent, the Ba(2+) ion. PMID:24675593

  3. Conductor-backed coplanar waveguide resonators of Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O on LaAlO3

    NASA Technical Reports Server (NTRS)

    Miranda, F. A.; Bhasin, K. B.; Stan, M. A.; Kong, K. S.; Itoh, T.

    1992-01-01

    Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from Tl-Ba-Ca-O (TBCCO) and Y-Ba-Cu-O (YBCO) thin films on LaAlO3. The resonators consist of a coplanar waveguide (CPW) patterned on the superconducting film side of the LaAlO3 substrate with a gold ground plane coated on the opposite side. These resonators were tested in the temperature range from 14 to 106 K. At 77 K, the best of our TBCCO and YBCO resonators have an unloaded quality factor (Qo) 7 and 4 times, respectively, larger than that of a similar all-gold resonator. In this study, the Qo's of the TBCCO resonators were larger than those of their YBCO counterparts throughout the aforementioned temperature range.

  4. Blue, yellow and orange color emitting rare earth doped BaCa2Al8O15 phosphors prepared by combustion method

    NASA Astrophysics Data System (ADS)

    Yerpude, A. N.; Dhoble, S. J.; Reddy, B. Sudhakar

    2014-12-01

    Eu2+, Dy3+, Sm3+ activated BaCa2Al8O15 phosphors were prepared by the combustion method. The phosphor powders were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and photoluminescence (PL) spectrophotometer. Photoluminescence spectra of BaCa2Al8O15:Eu2+ phosphors show emission wavelength at 435 nm that corresponds to 4f65d1→4f7 transition of Eu2+ ion by keeping excitation wavelength extending broad-band from 270 to 400 nm centered at 334 nm. The Dy3+ doped BaCa2Al8O15 phosphors shows blue emission (485 nm) and yellow emission (566 nm) under the excitation of 347 nm, corresponding to the 4F9/2→6H15/2 transition and 4F9/2→6H13/2 transition of Dy3+ ions, respectively. The Sm3+ doped BaCa2Al8O15 phosphors have shown strong orange emission at 604 nm corresponding to the 4G5/2→6H7/2 transition of Sm3+ with intense excitation wavelength at 406 nm. Scanning electron microscopy has been used for exploring the size and morphological properties of the prepared phosphors. The obtained results show that the phosphors have potential application in the field of solid state lighting.

  5. Optically stimulated luminescence (OSL) response of Al2O3:C, BaFCl:Eu and K2Ca2(SO4)3:Eu phosphors.

    PubMed

    Kumar, Pratik; Bahl, Shaila; Sahare, P D; Kumar, Surender; Singh, Manveer

    2015-12-01

    This paper investigates the optically stimulated luminescence (OSL) response of BaFCl:Eu and K2Ca2(SO4)3:Eu phosphors for different doses and bleaching durations. The results have also been compared with the commercially available Landauer Al2O3:C (Luxel®) dosemeter. Nanocrystalline K2Ca2(SO4)3:Eu is known to be a sensitive thermoluminescent phosphor, but its OSL response is hardly reported. At first, pellets of nanocrystalline K2Ca2(SO4)3:Eu powder were prepared by adding Teflon as a binder. Their OSL signal was compared with that of the material in pure form, i.e. without adding the binder (in 100:1 ratio). It was observed that adding the binder does not appreciably affect the OSL intensity. On comparison with the commercially available Al2O3:C from Landauer, it was found that K2Ca2(SO4)3:Eu is around 15 times less sensitive than Al2O3:C. 'Homemade' BaFCl:Eu phosphor has also been studied. The intensity of BaFCl:Eu was ∼20 times more than the standard Al2O3:C dosemeter and ∼200 times more sensitive than K2Ca2(SO4)3:Eu in the dose range of 13-200 cGy. OSL dosemeters are believed to give luminescence signal even if they are read before, i.e. multiple reading may be possible under suitable conditions after single exposure. This was also checked for all the prepared dosemeters and it was found that Al2O3:C showed the least decrease of <2 %, followed by BaFCl:Eu of 15 % and K2Ca2(SO4)3:Eu with 20 %. Finally, Al2O3:C and BaFCl:Eu phosphors were also studied for their optical bleaching durations to which the respective signals get completely removed so that the phosphor can be re-used. It was observed that BaFCl:Eu is bleached faster and more easily than Al2O3:C. PMID:25646524

  6. Hexagonal Ba-ferrite: a good model for the crystal structure of a new high-pressure phase CaAl 4Si 2O 11?

    NASA Astrophysics Data System (ADS)

    Gautron, Laurent; Gerald, John D. Fitz; Kesson, Sue E.; Eggleton, R. Anthony; Irifune, Tetsuo

    1997-07-01

    A new calcium aluminosilicate phase of composition CaAl 4Si 2O 11 has been encountered amongst the transformation products of CaAl 2Si 2O 8 (anorthite composition) at 14 GPa (Gautron et al., 1996). X-ray diffraction (XRD) confirms that its crystal structure is essentially the same as that of a new complex CaAl-silicate (abbreviated CAS phase) first reported by Irifune et al. (1994). The crystal structure of the CAS phase has been investigated by transmission electron microscopy (TEM). It has a hexagonal unit cell with lattice parameters a = 5.4Å and c = 12.7Å, and its space group is either P6 3mc , P overline62c or P6 3/mmc. It is proposed that this CAS phase has a six-layer, close-packed structure so that Z = 2 and density is 3.94 g cm -3, reasonable for a phase stable at transition-zone pressures. The most plausible model for the structure of this phase arises from published refinements of hexagonal Ba-ferrites. This postulated P6 3/mmc structure consists of octahedral layers, 3/4 occupied, separated by 12-coordinate Ca atoms, and by Al and Si in face-shared octahedra and in complex trigonal bipyramidal polyhedra, i.e. some Si would be five-fold coordinated. Observed TEM and XRD data are compared with calculated reflection intensities for this CAS model.

  7. High-pressure modifications of CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2}: Implications for Laves phase structural trends

    SciTech Connect

    Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Haeussermann, Ulrich

    2008-11-15

    High-pressure forms of intermetallic compounds with the composition CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2} were synthesized from CeCu{sub 2}-type precursors (CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}) and Ba{sub 21}Al{sub 40} by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl{sub 2} and BaAl{sub 2}), X-ray single-crystal diffraction (CaZn{sub 2}), and electron microscopy (SrZn{sub 2}). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu{sub 2} (C15) structure, the dizincides adopt the hexagonal MgZn{sub 2} (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. - Graphical abstract: CeCu{sub 2}-type polar intermetallics can be transformed to Laves phases upon simultaneous application of pressure and temperature. The observed structures are controlled by the valence electron concentration.

  8. NOx uptake on alkaline earth oxides (BaO, MgO, CaO and SrO) supported on γ-Al2O3

    SciTech Connect

    Verrier, Christelle LM; Kwak, Ja Hun; Kim, Do Heui; Peden, Charles HF; Szanyi, Janos

    2008-07-15

    NOx uptake experiments were performed on a series of alkaline earth oxide (AEO) (MgO, CaO, SrO, BaO) on γ-alumina materials. Temperature Programmed Desorption (TPD) conducted on He flow revealed the presence of two kinds of nitrate species: i.e. bulk and surface nitrates. The ratio of these two types of nitrate species strongly depends on the nature of the alkaline earth oxide. The amount of bulk nitrate species increases with the basicity of the alkaline earth oxide. This conclusion was supported by the results of infrared and 15N solid state NMR studies of NO2 adsorption. Due to the low melting point of the precursor used for the preparation of MgO/Al2O3 material (Mg(NO3)2), a significant amount of Mg was lost during sample activation (high temperature annealing) resulting in a material with properties were very similar to that of the γ-Al2O3 support. The effect of water on the NOx species formed in the exposure of the AEO-s to NO2 was also investigated. In agreement with our previous findings for the BaO/γ-Al2O3 system, an increase of the bulk nitrate species and the simultaneous decrease of the surface nitrate phase were observed for all of these materials.

  9. Influences of CaO on Crystallization, Microstructures, and Properties of BaO-Al2O3-B2O3-SiO2 Glass-Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Bo; Tang, Bo; Xu, Mingjiang

    2015-10-01

    We have developed BaO-CaO-Al2O3-B2O3-SiO2 glass-ceramics with high thermal coefficient of expansion (TCE) to overcome thermal mismatch at board level. The crystalline phases include quartz (major), cristobalite (minor), and bazirite BaZrSi3O9 (minor). Calculations from whole-pattern fitting show that the crystallinity varies slightly within the range of 33.48% to 34.89%, while the mass fraction of the phases changes remarkably with the CaO content. This indicates that CaO cannot promote crystallization of Ba-Al-B-Si glass, but effectively suppresses the phase transformation from quartz to cristobalite, making the thermal expansion curves linear. An empirical equation for the TCE versus the temperature and the amount of CaO is established. Furthermore, the densification mechanism of Ca modifiers is revealed. Due to its higher field strength than Ba, substitution of Ca increases the glass viscosity and inhibits ion diffusion. Excessive CaO is thus harmful to the density, bending strength, and electrical properties. The sample with 10 wt.% CaO sintered at 950°C exhibited high bending strength (154.1 MPa) and high TCE (12.38 ppm/°C) as well as good electrical properties ( ɛ = 6.2, tan δ = 5 × 10-4, ρ = 3.8 × 1012 Ω cm).

  10. Trace element proxies (Sr/Ca, Ba/Ca and Pb/Ca) in Bivalve shells: environmental signals or not?

    NASA Astrophysics Data System (ADS)

    Gillikin, D. P.; Dehairs, F.; Steenmans, D.; Meng, L.; Haifeng, T.; Navez, J.; Andre, L.; Baeyens, W.; Keppens, E.; Calmars Group,.

    2004-12-01

    Coral and sclerosponge skeletons have both been used as recorders of their environment. Sr/Ca, Ba/Ca and Pb/Ca have all shown to be useful in these substrates, giving insight into the past environment in which the skeleton grew (e.g., Lea et al., 1989, Nature 340, 373-376; Beck et al., 1992, Science 257, 644-647; Lazareth et al., 2000, Geology 28, 515-518; Rosenheim et al., 2004, Geology 32, 145-148). Although bivalves have not been studied as extensively as corals, these proxies are apparently not as reliable in bivalves (e.g., Vander Putten et al., 2000, GCA 64, 997-1011). We therefore investigate Sr/Ca and Pb/Ca in two species of aragonitic clams (Mercenaria mercenaria and Saxidomus giganteus) and Ba/Ca in the calcite layer of the mussel Mytilus edulis. Results indicate that Sr/Ca is primarily controlled by growth rate in S. giganteus whereas there was no relationship between these parameters in M. mercenaria. Pb/Ca is somewhat reproducible between specimens of S. giganteus, however long-term Pb/Ca records (1949-2003) in the shell of M. mercenaria did not show the expected curve of anthropogenically introduced lead, indicating that they are not recording environmental Pb concentrations. Therefore, Sr/Ca and Pb/Ca incorporation seem to be regulated by biological processes and not directly by environmental parameters. Ba/Ca in M. edulis shells on the other hand, does seem to be directly linked to the environment. Shells grown under laboratory and natural conditions both show the same linear relationship between dissolved Ba/Ca and shell Ba/Ca. Experiments involving manipulations of dissolved and particulate (i.e. food) Ba/Ca, suggest that the dominant pathway of barium into the shell is from the dissolved phase via the hemolymph. We were unable to explain the large peaks noted in the Ba/Ca profiles, however, they did not seem linked to phytoplankton blooms as has been previously suggested (Stecher et al., 1996, GCA 60, 3445-3456; Vander Putten et al., 2000

  11. High-temperature tribological properties of NiCoCrAlY-WSe2-BaF2·CaF2 solid lubricant coatings prepared by plasma spraying

    NASA Astrophysics Data System (ADS)

    Chen, X. H.; Yuan, X. J.; Xia, J.; Yu, Z. H.

    2015-12-01

    In this paper, NiCoCrAlY-WSe2-BaF2·CaF2 solid lubricant coatings were produced on a substrate by plasma spray and investigated at the high temperature, such as 500 °C and 800 °C. The structure of the coatings was characterized using XRD pattern and scanning electron microscopy. The TC1 (83wt% NiCoCrAlY) coating has a low friction coefficient at 500C, where the WSe2 is a good solid lubricant. The TC2 (65wt% NiCoCrAlY) coating has the low friction coefficient (0.279) at 800°C, due to the formation of BaCrO4 on the surfaces. As a result, the TC2 coating has the optimal tribological property in the wide temperature.

  12. Electronic structure of Ca, Sr, and Ba under pressure.

    NASA Technical Reports Server (NTRS)

    Animalu, A. O. E.; Heine, V.; Vasvari, B.

    1967-01-01

    Electronic band structure calculations phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure

  13. Preparation of Tl sub 2 Ba sub 2 CaCu sub 2 O sub 8 superconducting thin films on LaAlO sub 3 substrates from metalorganic-chemical-vapor-deposition-prepared precursor films

    SciTech Connect

    Ladd, J.A.; Collins, B.T.; Matey, J.R. ); Zhao, J.; Norris, P. )

    1991-09-09

    Single phase Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} thin films have been deposited on single-crystal LaAlO{sub 3} substrates, (100) orientation, via a two-step deposition process. First, Ba-Ca-Cu-O precursor films were deposited by metalorganic chemical vapor deposition (MOCVD) using barium, calcium, and copper-tetramethyl-heptanedionate, (tmhd){sub 2}, source materials under reduced pressure in an oxygen/argon atmosphere. Substrate temperatures were between 500 and 600 {degree}C. Thallium was then incorporated by heating the films in a confined surface configuration with an unfired pellet of Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub {ital x}} composition at 870 {degree}C for 0.1 h. The resultant films (0.5--1 {mu}m thick) showed a preferred orientation with the {ital c} axis normal to the substrate. The superconducting properties were characterized by resistance and mutual inductance versus temperature and by critical current measurements. Zero resistance temperatures as high as 98 K and {ital J}{sub {ital c}} values close to 1{times}10{sup 4} A/cm{sup 2} at 77 K were observed.

  14. Structural distortions in Sr{sub 3-x}A{sub x}MO{sub 4}F (A=Ca, Ba; M=Al, Ga, In) anti-Perovskites and corresponding changes in photoluminescence

    SciTech Connect

    Sullivan, Eirin; Avdeev, Maxim; Vogt, Thomas

    2012-10-15

    The ordered oxyfluoride family Sr{sub 3}-{sub x}A{sub x}MO{sub 4}F (A=Ca, Ba and M=Al, Ga) has formed the basis of several new inorganic phosphors, and shows great potential for use in phosphor-conversion LED lamp devices. This study examines the correlation between subtle structural changes and photoluminescent behaviour in some of these materials. In order to ascertain whether cation charge compensation has any influence on structure and subsequent photoluminescent behaviour, a comparison was carried out between phases with the nominal compositions Sr{sub 2.975}Ce{sub 0.025}AlO{sub 4}F and Sr{sub 2.95}Ce{sub 0.025}Na{sub 0.025}AlO{sub 4}F using structural characterisation based upon high-resolution neutron powder diffraction (NPD) data. Additionally, NPD data has been used to elucidate the role of different M cations in these materials, using Sr{sub 2.25}Ba{sub 0.6}Eu{sub 0.1}M{sub 0.95}In{sub 0.05}O{sub 4-{alpha}}F{sub 1-{delta}} (M=Al, Ga) to determine the effect M cation size has on structure and photoluminescent properties. - Graphical abstract: The structure of Sr3-xAxMO4F (A=Ca, Ba and M=Al, Ga) and excitation and emission spectra for Sr{sub 2.25}Ba{sub 0.6}Eu{sub 0.1}Ga{sub 0.95}In{sub 0.05}O{sub 4-{alpha}}F{sub 1-{delta}}. Highlights: Black-Right-Pointing-Pointer Correlation between structural changes and photoluminescence in Sr{sub 3-x}A{sub x}MO{sub 4}F (A=Ca, Ba, M=Al, Ga). Black-Right-Pointing-Pointer Comparison of Sr{sub 2.975}Ce{sub 0.025}AlO{sub 4}F and Sr{sub 2.95}Ce{sub 0.025}Na{sub 0.025}AlO{sub 4}F using high-resolution NPD. Black-Right-Pointing-Pointer Study of the effect of cation charge-compensation on structure and photoluminescent behaviour. Black-Right-Pointing-Pointer Examination of high-resolution NPD data for Sr{sub 2.25}Ba{sub 0.6}Eu{sub 0.1}M{sub 0.95}In{sub 0.05}O{sub 4-{alpha}}F{sub 1-{delta}} (M=Al, Ga). Black-Right-Pointing-Pointer Determination of the effect M cation size has on structure and photoluminescent properties.

  15. Pressure effects on resistive transition in (Cu,M)Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub y} (M = C,Al,Tl,Mg,Zn) superconductors

    SciTech Connect

    Tokiwa, K.; Kunugi, C.; Kashiwagi, H.

    1999-11-01

    Single phase samples with the composition of (Cu,M)Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub y}(CuM-1234; M = C,Al,Tl,Mg,Zn) have been synthesized using high pressure technique. The authors have measured the pressure dependence of superconducting transition temperature ({Tc}) through in situ resistivity measurements up to 8 GPa for these samples, reproducibly. These samples indicated almost the same {Tc}-enhancement by applied pressure, in spite of their different ambient {Tc} values. The enhancement values of 8--10 K at 8 GPa pressure for these samples are found to be comparable to those of Hg-system and (B,C)-system.

  16. Allometric constraints on Sr/Ca and Ba/Ca partitioning in terrestrial mammalian trophic chains.

    PubMed

    Balter, Vincent

    2004-03-01

    In biological systems, strontium (Sr) and barium (Ba) are two non-essential elements, in comparison to calcium (Ca) which is essential. The Sr/Ca and Ba/Ca ratios tend to decrease in biochemical pathways which include Ca as an essential element, and these processes are termed biopurification of Ca. The quantitative pathway of the biopurification of Ca in relation to Sr and Ba between two biological reservoirs ( Rn and R(n -1)) is measured with an observed ratio (OR) expressed by the (Sr/Ca) Rn /(Sr/Ca)( Rn-1) and (Ba/Ca) Rn /(Ba/Ca)( Rn-1) ratios. For a mammalian organism, during the whole biopurification of Ca starting with the diet to the ultimate reservoir of Ca which is the bone, the mean values for ORSr and ORBa are 0.25 and 0.2, respectively. In this study, published Sr/Ca and Ba/Ca ratios are used for three sets of soils, plants, and bones of herbivorous and carnivorous mammals, each comprising a trophic chain, to illustrate the biopurification of Ca at the level of trophic chains. Calculated ORSr and ORBa of herbivore bones in relation to plants and of bones of carnivores in relation to bones of herbivores give ORSr=0.30+/-0.08 and ORBa=0.16+/-0.08, thus suggesting that trophic chains reflect the Sr/Ca and Ba/Ca fluxes that are prevalent at the level of a mammalian organism. The slopes of the three regression equations of log(Sr/Ca) vs. log(Ba/Ca) are similar, indicating that the process of biopurification of Ca with respect to Sr and Ba is due to biological processes and is independent of the geological settings. Modifications of the logarithmic expression of the Sr/Ca and Ba/Ca relationship allow a new formula of the biopurification process to be deduced, leading to the general equation ORBa=ORSr(1.79+/-0.33), where the allometric coefficient is the mean of the slopes of the three regression equations. Some recent examples are used to illustrate this new analysis of predator-prey relations between mammals. This opens up new possibilities for the

  17. Synthesis and structural characterization of the ternary Zintl phases AE{sub 3}Al{sub 2}Pn{sub 4} and AE{sub 3}Ga{sub 2}Pn{sub 4} (AE=Ca, Sr, Ba, Eu; Pn=P, As)

    SciTech Connect

    He, Hua; Tyson, Chauntae; Saito, Maia; Bobev, Svilen

    2012-04-15

    Ten new ternary phosphides and arsenides with empirical formulae AE{sub 3}Al{sub 2}Pn{sub 4} and AE{sub 3}Ga{sub 2}Pn{sub 4} (AE=Ca, Sr, Ba, Eu; Pn=P, As) have been synthesized using molten Ga, Al, and Pb fluxes. They have been structurally characterized by single-crystal and powder X-ray diffraction to form with two different structures-Ca{sub 3}Al{sub 2}P{sub 4}, Sr{sub 3}Al{sub 2}As{sub 4}, Eu{sub 3}Al{sub 2}P{sub 4}, Eu{sub 3}Al{sub 2}As{sub 4}, Ca{sub 3}Ga{sub 2}P{sub 4}, Sr{sub 3}Ga{sub 2}P{sub 4}, Sr{sub 3}Ga{sub 2}As{sub 4}, and Eu{sub 3}Ga{sub 2}As{sub 4} crystallize with the Ca{sub 3}Al{sub 2}As{sub 4} structure type (space group C2/c, Z=4); Ba{sub 3}Al{sub 2}P{sub 4} and Ba{sub 3}Al{sub 2}As{sub 4} adopt the Na{sub 3}Fe{sub 2}S{sub 4} structure type (space group Pnma, Z=4). The polyanions in both structures are made up of TrPn{sub 4} tetrahedra, which share common corners and edges to form {sup 2}{sub {infinity}}[TrPn{sub 2}]{sub 3-} layers in the phases with the Ca{sub 3}Al{sub 2}As{sub 4} structure, and {sup 1}{sub {infinity}}[TrPn{sub 2}]{sub 3-} chains in Ba{sub 3}Al{sub 2}P{sub 4} and Ba{sub 3}Al{sub 2}As{sub 4} with the Na{sub 3}Fe{sub 2}S{sub 4} structure type. The valence electron count for all of these compounds follows the Zintl-Klemm rules. Electronic band structure calculations confirm them to be semiconductors. - Graphical abstract: AE{sub 3}Al{sub 2}Pn{sub 4} and AE{sub 3}Ga{sub 2}Pn{sub 4} (AE=Ca, Sr, Ba, Eu; Pn=P, As) crystallize in two different structures-Ca{sub 3}Al{sub 2}P{sub 4}, Sr{sub 3}Al{sub 2}As{sub 4}, Eu{sub 3}Al{sub 2}P{sub 4}, Eu{sub 3}Al{sub 2}As{sub 4}, Ca{sub 3}Ga{sub 2}P{sub 4}, Sr{sub 3}Ga{sub 2}P{sub 4}, Sr{sub 3}Ga{sub 2}As{sub 4}, and Eu{sub 3}Ga{sub 2}As{sub 4}, are isotypic with the previously reported Ca{sub 3}Al{sub 2}As{sub 4} (space group C2/c (No. 15)), while Ba{sub 3}Al{sub 2}P{sub 4} and Ba{sub 3}Al{sub 2}As{sub 4} adopt a different structure known for Na{sub 3}Fe{sub 2}S{sub 4} (space group Pnma (No. 62

  18. Theoretical electric quadrupole transition probabilities for Ca, Sr and Ba

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.; Langhoff, S. R.; Jaffe, R. L.; Partridge, H.

    1984-01-01

    The 1D-1S quadrupole transition probabilities for Ca, Sr and Ba have been computed using extended GTO and STO valence basis sets and configuration-interaction wavefunctions that include the important core-valence correlation effects. For Ba and Sr, the relativistic contraction of the core orbitals was accounted for in the GTO calculations by a relativistic effective-core potential. The computed Einstein coefficient for Ca of 39.6/s is in excellent agreement with the recent experimental value of 40 + or - 8/s. The best Einstein coefficients for Sr (44.7/s) and Ba (2.98/s) imply increasing quadrupole line strengths down the column. Relativistic effects substantially increase the quadrupole Einstein coefficient for Ba.

  19. Processing, electrical and microwave properties of sputtered Tl-Ca-Ba-Cu-O superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Kapoor, V. J.; Chorey, C. M.; Bhasin, K. B.

    1993-01-01

    A reproducible fabrication process has been established for TlCaBaCuO thin films on LaAlO3 substrates by RF magnetron sputtering and post-deposition processing methods. Electrical transport properties of the thin films were measured on patterned four-probe test devices. Microwave properties of the films were obtained from unloaded Q measurements of all-superconducting ring resonators. This paper describes the processing, electrical and microwave properties of Tl2Ca1Ba2Cu2O(x) 2122-plane phase thin films.

  20. Magnetic characterization of Ca substituted Ba and Sr hexaferrites

    NASA Astrophysics Data System (ADS)

    Asti, G.; Carbucicchio, M.; Deriu, A.; Lucchini, E.; Slokar, G.

    1980-04-01

    A magnetic characterization has been worked out for the solid solution from Ba and Sr hexaferrites (BaFe 1 2O 1 9, SrFe 1 2O 1 9) towards CaO- xFe 2O 3 (2 ⪕ x ⪕5.5). Measurements of Curie temperature, saturation magnetization, magnetic anisotropy, together with Mössbauer characterization indicate that the intrinsic properties of the studied compounds do not change appreciably with increasing Ca content. These results, together with the X-ray data, are consistent with the formation of an undistorted M-type cell with a low content of iron and oxygen vacancies.

  1. Synthesis of TlBaCaCuO superconductive films with Tl diffusion into BaCaCu precursors

    SciTech Connect

    Wang, X.W.; Leone, A.F.; Shen, C.Q.

    1994-12-31

    There exists several techniques to synthesize TlBaCaCuO from precursor films. Recently, a two zone furnace technique was developed by DeLuca. Based on the authors` experience on the two zone furnace technique, they systematically conducted a series of experiments in a tube furnace with a temperature gradient distribution. The BaCaCuO precursor films were fabricated by an ink method, and the Tl diffusion source was Tl{sub 2}O{sub 3}. Superconductive films were characterized by SQUID magnetization measurement, X-ray diffraction, SEM, and EDS. Experimental results will be summarized.

  2. Incorporation of Ba in Al and Fe pollucite

    NASA Astrophysics Data System (ADS)

    Vance, Eric R.; Gregg, Daniel J.; Griffiths, Grant J.; Gaugliardo, Paul R.; Grant, Charmaine

    2016-09-01

    Ba, the transmutation product of radioactive Cs, can be incorporated at levels of up to ∼0.07 formula units in Cs(1-2x)BaxAlSi2O6 aluminium pollucite formed by sol-gel methods and sintering at 1400 °C, with more Ba forming BaAl2Si2O8 phases. The effect of Ba substitution in pollucite-structured CsFeSi2O6 was also studied and no evidence of Ba substitution in the pollucite structure via cation vacancies or Fe2+ formation was obtained. The Ba entered a Fe-silicate glass structure. Charge compensation was also attempted with a Cs+ + Fe3+ ↔ Ba2+ + Ni2+ scheme but again the Ba formed a glass and NiO was evident. PCT leaching data showed CsFeSi2O6 to be very leach resistant.

  3. Computer simulation of the self-assembly of crystal structures of zeolites Ca64(Sr,K,Ba)48(Cu12(O,Cl))4[Si192Al192O786](H2O) n (tschoertnerite, TSC, V = 31 614 Å3) and Ca2K2[Al6Si6O24](H2O)10 (willhendersonite, cha, V = 804 Å3) from template nanocluster precursors K48 and K12

    NASA Astrophysics Data System (ADS)

    Ilyushin, G. D.; Blatov, V. A.

    2013-07-01

    The self-assembly of zeolites Ca64(Sr,K,Ba)48(Cu12(O,Cl))4[Si192Al192 O786](H2O) n (tschoertnerite, TSC-type framework, V = 31614 Å3) and Ca2K2[Al6Si6O24] (H2O)10 (willhendersonite, CHA-type framework, V = 804 Å3), which form paragenetic associations, has been simulated using computational methods (TOPOS program package). A new method for analyzing zeolites of any complexity has been used, which is based on the complete expansion of the three-dimensional structural graph (3 D factor graph) in tiles and the selection of nonintersecting tiles forming a packing. The code of self-assembly of 3 D structures from complementary linked nanocluster precursors is reconstructed: primary chain → microlayer → microframework. A supracluster precursor K48 with the symmetry bar 43 m, formed of four K12 clusters corresponding to the t-hpr tile, is established for TSC. The K48 cluster contains Ca template cations, which stabilize its local region in the stages of K12 → K24 → K48 self-assembly. Bifurcations of evolution paths (structural branching points) during the self-assembly of TSC and CHA microframeworks are established in the stage of formation of the K24 supracluster from invariant templated K12 clusters. The models under consideration explain the 100% localization of B = Ca cations, which play the role of templates, and the 50% occupation of the positions of K, Sr, and Ba spacer cations (in TSC) and K spacer cations (in CHA).

  4. Effects of Ba loading and calcination temperature on BaAl2O4 formation for BaO/Al2O3 NOx Storage and Reduction Catalysts

    SciTech Connect

    Szailer, Tamas; Kwak, Ja Hun; Kim, Do Heui; Szanyi, Janos; Wang, Chong M.; Peden, Charles HF

    2006-04-30

    The effect of thermal treatment on the structure and chemical properties of Ba-oxide-based NOx storage/reduction catalysts with different Ba loadings was investigated using BET, TEM, EDS, TPD and FTIR techniques. On the basis of the present and previously reported results, we propose that moderate (< ~873 K) temperature calcinations result in a single monolayer (ML) ‘coating’ of BaO on the alumina surface. At high Ba loading in excess of that required for a full monolayer ‘coating’ (> 8 wt.% BaO), small (~5 nm) particles of ‘bulk’ BaO are present on top of the 1 ML BaO/Al2O3 surface. We did not observe any detectable morphological changes upon higher temperature thermal treatment of 2 and 8 wt% BaO/Al2O3 samples, while dramatic changes occurred for the 20 wt% sample. In this latter case, the transformations included BaAl2O4 formation at the expense of the bulk BaO phase. In particular, we conclude that the surface (ML) BaO phase is quite stable against thermal treatment, while the bulk phase provides the source of Ba for BaAl2O4 formation.

  5. Sr/Ca and Ba/Ca variations in environmental and biological sources: A survey of marine and terrestrial systems

    NASA Astrophysics Data System (ADS)

    Peek, Stephanie; Clementz, Mark T.

    2012-10-01

    The relative concentrations of strontium to calcium (Sr/Ca) and barium to calcium (Ba/Ca) in mammalian bioapatite are common biogeochemical indicators for trophic level and/or dietary preferences in terrestrial foodwebs; however, similar research in marine foodwebs is lacking. This study combined environmental and biological Sr/Ca and Ba/Ca data from both terrestrial and marine settings from 62 published books, reports, and studies along with original data collected from 149 marine mammals (30 species) and 83 prey items (18 species) and found that variations in Sr/Ca and Ba/Ca ratios of biological and environmental samples are appreciably different in terrestrial and marine systems. In terrestrial systems, environmental sources account for most of the variations in Sr/Ca and Ba/Ca ratios. In contrast, environmental sources in marine systems (i.e., seawater) are comparatively invariant, meaning most of the variations in Sr/Ca and Ba/Ca ratios originate from biological processes. Marine consumers, particularly non-mammalian and mammalian vertebrates, show evidence of biopurification of Ca relative to Sr and Ba, similar to what is observed in terrestrial systems; however, unlike terrestrial systems, variations in Sr/Ca and Ba/Ca ratios of environmental sources are overprinted by bioaccumulation of Sr and Ba at the base of marine foodwebs. This demonstrates that in marine systems, spatial or temporal differences may have little to no effect on Sr/Ca and Ba/Ca ratios of marine vertebrates, making Sr/Ca, and to a lesser extent Ba/Ca, potentially useful global proxies for trophic level and dietary preferences of marine vertebrates.

  6. R3Au(6+x)Al26T (R = Ca, Sr, Eu, Yb; T = early transition metal): a large family of compounds with a stuffed BaHg11 structure type grown from aluminum flux.

    PubMed

    Latturner, Susan E; Bilc, Daniel; Mahanti, S D; Kanatzidis, Mercouri G

    2009-02-16

    A collection of new quaternary intermetallic compounds with a cubic, stuffed BaHg(11) structure type has been synthesized by the combination of a divalent rare earth or alkaline earth metal R, an early transition metal T, and gold in an excess of molten aluminum. Structural characterization of these R(3)Au(6+x)Al(26)T compounds by powder and single crystal X-ray diffraction indicates that the unit cell varies with the radii of the early transition metal T and the rare earth/alkaline earth R as expected. The element T (where T = group 4, 5, 6, and 7 element) appears to be responsible for the stabilization of up to 43 different members of the R(3)Au(6+x)Al(26)T family of compounds. Varying amounts of disorder and trends in partial occupancies of the Au stuffed site--the site that is vacant in the parent compound BaHg(11)--are also indicated by the diffraction studies of this family of compounds. Magnetic susceptibility data reveals that the transition metal atoms in these materials do not possess local magnetic moments. For the magnetic rare earth containing materials, the europium compounds undergo a ferromagnetic transition at 10 K, and the ytterbium analogues show mixed valent behavior. Band structure calculations also support a mixed valent state for Yb in these compounds. PMID:19146424

  7. Calculation of NMR lineshapes for Ba-Al-Ge clathrates

    NASA Astrophysics Data System (ADS)

    Rodriguez, Sergio; Gou, Weiping; Ross, Joseph

    2008-10-01

    Clathrates consist of Si, Ge, or Sn cages in a crystalline framework, with guest atoms inside the cages. They have gained interest due to thermoelectric properties suitable for potential device application. To understand Al substitutional configurations, we calculated Al NMR line shapes for several structures with compositions Ba8Ge46-x-yAlxy for x=3,8,11,12,16,24; y=2,3; where represents a vacancy. The results were obtained by calculating Electric Field Gradients (EFG) for Al sites of type-I clathrates assuming an ordered superstructure of vacancies and framework occupation. We used ab initio methods in the Generalized Gradient Approximation as implemented by the WIEN2k program, and used the results to simulate NMR lineshapes numerically. These were compared to our previously reported NMR lineshapes. In the case of Ba8Ge31Al123 four Al sites in the superstructure include two sites with small EFG where the vacancy is far away and two sites with large EFG with a vacancy adjacent to Al. Assuming a larger Knight shift for sites next to vacancies, we obtain good agreement with NMR experimental results for reduced-Al Ba8Ge34Al12, while for the Zintl phase Ba8Ge30Al16 we obtain good agreement with no spontaneous vacancies. We infer that Al prefers locations close to vacancies rather than random occupation. This work was supported by Robert A. Welch Foundation (Grant A-1526).

  8. Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters

    NASA Technical Reports Server (NTRS)

    Zukic, Muamer; Torr, Douglas G.; Spann, James F.; Torr, Marsha R.

    1990-01-01

    An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

  9. Piezoelectric and Dielectric Properties of Multilayered BaTiO3/(Ba,Ca)TiO3/CaTiO3 Thin Films.

    PubMed

    Zhu, Xiao Na; Gao, Ting Ting; Xu, Xing; Liang, Wei Zheng; Lin, Yuan; Chen, Chonglin; Chen, Xiang Ming

    2016-08-31

    Highly oriented multilayered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films were fabricated on Nb-doped (001) SrTiO3 (Nb:STO) substrates by pulsed laser deposition. The configurations of multilayered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films are designed with the thickness ratio of 1:1:1 and 2:1:1 and total thickness ∼300 nm. Microstructural characterization by X-ray diffraction indicates that the as-deposited thin films are highly c-axis oriented and large in-plane strain is determined in BaTiO3 and CaTiO3 layers. Piezoresponse force microscopy (PFM) studies reveal an intense in-plane polarization component, whereas the out-of-plane shows inferior phase contrast. The optimized combination is found to be the BaTiO3-(Ba0.85Ca0.15)TiO3-CaTiO3 structure with combination ratio 2:1:1, which displays the largest domain switching amplitude under DC electric field, the largest room-temperature dielectric constant ∼646, a small dielectric loss of 0.03, and the largest dielectric tunability of ∼50% at 400 kV/cm. These results suggest that the enhanced dielectric and tunability performance are greatly associated with the large in-plane polarization component and domain switching. PMID:27514235

  10. Method of forming superconducting Tl-Ba-Ca-Cu-O films

    DOEpatents

    Wessels, Bruce W.; Marks, Tobin J.; Richeson, Darrin S.; Tonge, Lauren M.; Zhang, Jiming

    1993-01-01

    A method of forming a superconducting Tl-Ba-Ca-Cu-O film is disclosed, which comprises depositing a Ba-Ca-Cu-O film on a substrate by MOCVD, annealing the deposited film and heat-treating the annealed film in a closed circular vessel with TlBa.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x and cooling to form said superconducting film of TlO.sub.m Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+2, wherein m=1,2 and n=1,2,3.

  11. Ordered BaAl4- Type Variants in the BaAuxSn4-x System: A Unified View on Their Phase Stabilities versus Valence Electron Counts

    SciTech Connect

    Lin, Qisheng; Miller, Gordon J.; Corbett, John D.

    2014-05-28

    Three ordered structures of the tetragonal BaAl4 type were identified in the Ba–Au–Sn system, from which a unified view of the interplay between the valence electron counts (VECs) and phase stabilities of these three types of derivatives can be developed. The BaNiSn3 (I4mm), ThCr2Si2 (I4/mmm), and CaBe2Ge2 (P4/nmm) type BaAuxSn4–x phases occurred respectively at x = 0.78(1)–1, 1.38(1)–1.47(1), and 1.52(1)–2.17(1), consistent with theoretical atomic “coloring” analyses that reveal an optimal VEC of 14 for the ThCr2Si2 type but larger and smaller values respectively for the BaNiSn3- and CaBe2Ge2-type structures.

  12. Cu/Ba/bauxite: an Inexpensive and Efficient Alternative for Pt/Ba/Al2O3 in NOx Removal

    PubMed Central

    Wang, Xiuyun; Chen, Zhilin; Luo, Yongjin; Jiang, Lilong; Wang, Ruihu

    2013-01-01

    Cu/Ba/bauxite possesses superior NOx storage and reduction (NSR) performances, high thermal stability, strong resistance against SO2 poisoning and outstanding regeneration ability in comparison with Pt/Ba/Al2O3. It can serve as a cheap and promising alternative for traditional Pt/Ba/Al2O3 in NOx removal from lean-burn engines. PMID:23536149

  13. Ba2+ induces contraction in swine carotid artery by mobilizing intracellular Ca2+.

    PubMed

    Hai, C M; Murphy, R A

    1987-04-01

    Recent data suggest that Ba2+ activates the smooth muscle contractile apparatus. However, in vitro studies indicate that Ba2+ activates Ca2+ calmodulin-dependent enzymes only at very high concentrations. These observations might suggest that Ba2+ activates the contractile apparatus by a mechanism independent of myosin phosphorylation. We tested this hypothesis using intact and Triton X-100 skinned swine carotid medial strips. In intact tissues, Ba2+ stimulated dose-dependent contractions in the absence of extracellular Ca2+. However, in skinned tissues, Ba2+ induced much lower stress development at concentrations more than three orders of magnitude greater than needed for Ca2+-induced contraction. Ba2+ also failed to maintain stress in skinned tissues previously contracted with 4 microM Ca2+. The Ba2+-induced contraction in intact strips was associated with gradual increases in myosin phosphorylation from a basal level of approximately 5% to a sustained level of 30.0 +/- 0.8%. Partial intracellular calcium depletion with 100 microM histamine, 25 mM caffeine, and 5 mM ethyleneglycol-bis(beta-aminoethyl-ether)-N,N'-tetraacetic acid (EGTA) failed to abolish Ba2+-induced contractions. However, repeated contractions with Ba2+ in the absence of extracellular Ca2+ led to decreases in stress development. These observations suggest that Ba2+ induces stress development by mobilizing intracellular Ca2+ that was not released by histamine and caffeine. PMID:3565557

  14. Luminescence and Site Occupancy of Eu2+ in Ba2 Ca(BO3)2

    NASA Astrophysics Data System (ADS)

    Li, Pan-Lai; Wang, Zhi-Jun; Yang, Zhi-Ping; Guo, Qing-Lin

    2011-01-01

    A green phosphor Ba2Ca(BO3)2:Eu2+ was synthesized by a high temperature solid-state reaction method under a reductive atmosphere. The luminescence and site occupancy of Eu2+ in Ba2Ca(BO3)2 are investigated. Ba2Ca(BO3)2:Eu2+ shows one green band (537 nm) under 400 nm near ultraviolet excitation which is suitable for UV LED. Ca2+ and Ba2+ ions in Ba2Ca(BO3)2 are replaced by Eu2+ ions, the Ba2Ca(BO3)2:Eu2+ shows a dissymmetrical emission band. The influence of Eu2+ doping concentrations on the emission intensity of Ba2Ca(BO3)2:Eu2+ is studied. It is found that the emission intensity is influenced by the Eu2+ concentration and reaches the maximum value at 2% Eu2+. According to the Dexter theory, the concentration quenching mechanisms of Eu2+ in Ba2Ca(BO3)2 are the d-dinteraction.

  15. The role of π-bonding on the high temperature structure of the double perovskites Ba2CaUO6 and BaSrCaUO6.

    PubMed

    Reynolds, Emily; Thorogood, Gordon J; Avdeev, Maxim; Brand, Helen E A; Gu, Qinfen; Kennedy, Brendan J

    2015-09-28

    The high temperature structural behaviour of the uranium perovskites Ba2CaUO6 and BaSrCaUO6 has been investigated using a combination of synchrotron X-ray and neutron powder diffraction. Ba2CaUO6 undergoes a complex sequence of structures associated with the progressive loss of cooperative octahedral tilting: P21/n → I2/m → I2/m → I4/m → Fm3[combining macron]m. The observation of the intermediate tetragonal structure, I4/m, in this, contrasts with the previously reported rhombohedral R3[combining macron] intermediate formed by the Ba2SrUO6 oxide. The importance of π-bonding in determining the structural sequence is discussed. PMID:26286063

  16. Effect of Ca incorporation on the dielectric nonlinear behavior of (Ba, Ca)TiO3 multi layer ceramic capacitors

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Park, Yunjung; Kim, Chang-Hoon; Kim, Doo-Young

    2014-12-01

    The difference in the dielectric nonlinearity was investigated by contrasting BaTiO3 and (Ba0.925Ca0.075)TiO3 multilayer ceramic capacitors utilizing the first order reversal curve (FORC) distribution based on the Preisach model. Ca incorporation caused a decrease of the dielectric constants in the low field but little differences in the high field region resulting in a steep ac field dependence, which became more significant with the decrease of temperature. Such behavior can be correlated with a decrease of the reversible and an increase of the irreversible FORC distribution near origin by Ca incorporation. These results suggest that Ca incorporation, which is known to cause the asymmetric off-center displacement at Ba-site, has the role of weakly pinning centers that increase the portion of irreversible domain walls that are immobile at low field but can contribute to polarization beyond a threshold field.

  17. The unusual chemical bonding and thermoelectric properties of a new type Zintl phase compounds Ba3Al2As4

    NASA Astrophysics Data System (ADS)

    Yang, Gui; Zhang, Guangbiao; Wang, Chao; Wang, Yuanxu

    2016-07-01

    Ba3Al2As4 exhibits an unusual anisotropic electrical conductivity, that is, the electrical conductivity along the chain is smaller than those along other two directions. The results is conflict with previous conclusion for Ca5M2Pn6. Earlier studies on Ca5M2Pn6 showed that a higher electrical conductivity could be obtained along the chain. The band decomposed charge density is used to explain such unusual behavior. Our calculations indicate the existence of a conductive pathway near the Fermi level is responsible for the electrons transport. Further, the Ba-As bonding of Ba3Al2As4 has some degree covalency which is novel for the Zintl compounds.

  18. Ba/Ca Reproducibility and Growth Banding in Gulf of Alaska Bamboo Corals

    NASA Astrophysics Data System (ADS)

    Serrato Marks, G.; LaVigne, M.; Hill, T. M.; Sauthoff, W.; Guilderson, T. P.; Roark, E. B.; Dunbar, R. B.

    2014-12-01

    Deep-sea bamboo corals have been proposed as deep-ocean paleoceanographic archives because of their longevity and radial growth bands. Previous work has shown that bamboo coral Ba/Ca is a promising proxy for seawater barium, however, validation of Ba/Ca reproducibility is required. In addition, the growth band formation mechanism is uncertain, with some proposing that crystal orientation causes banding visible under light microscopy. The objective of this study was to evaluate Ba/Ca reproducibility and characterize growth band crystal orientation. Visible bands measured with a petrographic microscope were used to align LA-ICP-MS data collected along three replicate radii of the calcitic internodes of two well-dated corals from the Gulf of Alaska (collected live at 720m and 643m; 48°3'N, 132°44'W). Ba/Ca signals smoothed to ~annual resolution were reproducible within each coral (r=0.6-0.7; p<0.0001; n=3 radii/coral), suggesting that Ba/Ca varies in response to the external environment on annual timescales. Ba/Ca in the 720m coral increased from 1977 to 1998, a warm Pacific Decadal Oscillation (PDO) regime, possibly due to increased export production. The shallower coral (634m) revealed the inverse trend, suggesting variability in seawater barium dynamics with depth. Electron backscatter diffraction analysis of visible growth bands showed a preferred crystal orientation that does not correspond to location of visible bands or elemental composition, suggesting that crystal orientation does not cause bamboo coral banding. Overall, results show that regional oceanic signals are recorded as reproducible Ba/Ca variability in these corals. Comparison of these data to other well-dated records from the northeast Pacific would determine whether the relationship between Ba/Ca and PDO is regional. Additional archives of trace element variability will strengthen our understanding of how rapid climate change impacts intermediate ocean biogeochemistry.

  19. Bamboo coral Ba/Ca: Calibration of a new deep ocean refractory nutrient proxy

    NASA Astrophysics Data System (ADS)

    LaVigne, Michèle; Hill, Tessa M.; Spero, Howard J.; Guilderson, Thomas P.

    2011-12-01

    It is poorly understood how intermediate water masses are affected by decadal scale climate via biogeochemical cycling, export production, and changes in circulation/ventilation. To this end, a geochemical nutrient proxy from deep-sea bamboo corals would provide decadal to centennial scale records of deep and intermediate-water nutrient dynamics. Seawater barium (Ba SW) has a nutrient-like distribution in the water-column (similar to silicate), so Ba/Ca records in foraminifera, shallow water surface corals, and other deep-sea corals have been used to trace refractory nutrients. Here we present the first calibration of a nutrient proxy from skeletal barium preserved in the calcitic internodes of deep-sea bamboo corals, collected from intermediate water depths. A calibration was calculated from a broadly distributed suite of Isidella and Keratoisis corals spanning a silicate and Ba SW gradient (n = 33 corals; 300-2800 m): Ba/Caμmol/mol=0.079±0.008∗Banmol/kg+4.205±0.870r=0.77;n=33 The strong linear correlation between Ba/Ca bamboo coral and Ba SW suggests that coral Ba/Ca is a reliable recorder of seawater barium (and, therefore, silicate). We find a distribution coefficient (D Ba) for Ba/Ca bamboo coral of 1.3 ± 0.2, similar to that of other corals (surface and deep-sea dwelling) and inorganic calcium carbonate precipitation experiments (D Ba = 1.2-1.5). This suggests that Ba incorporation is primarily driven by cationic substitution in bamboo corals and holds promise as a globally applicable refractory nutrient proxy. We find interannual-decadal scale variability in a Ba/Ca bamboo coral timeseries from a California Margin coral (San Juan Seamount; 1295 m). These data suggest that additional high-resolution Ba/Ca bamboo coral records may reveal a connection between regional-scale intermediate water biogeochemistry and low-latitude surface ocean/atmospheric climate.

  20. Ba/Ca Ratios in North Pacific Bamboo Corals Record Changes in Intermediate Water Biogeochemistry

    NASA Astrophysics Data System (ADS)

    Serrato Marks, G.; LaVigne, M.; Hill, T. M.; Sauthoff, W.; Guilderson, T. P.; Roark, E. B.; Dunbar, R. B.

    2015-12-01

    Trace elemental ratios preserved in the skeleton of bamboo corals, which live for hundreds of years at >500m depth, have been utilized as archives of deep-ocean conditions. However, it was previously unclear whether trace element data from these corals were internally reproducible and could therefore be used as reliable climate proxies. This study tests the internal reproducibility of Ba/Ca in the calcite of nine bamboo corals to further develop a new proxy for dissolved Ba in seawater (BaSW). Trace element LA-ICP-MS data were collected along three replicate radii of varying lengths of the calcitic internodes of well-dated corals collected live from the Gulf of Alaska (720m and 643m) and the California Margin (870m, 1012m, 1295m, 1500m, 1521m, 1954m, and 2054m; samples from 1295-1521m are not yet dated). Data were aligned using visible bands measured with a petrographic microscope to account for irregular growth. Ba/Ca data filtered with a 50μm (1.5-2 year) moving average were reproducible within each coral to 2.9 ± 2.1% (n=3 radii/coral, 9 corals), suggesting that regional geochemical signals are recorded as reproducible Ba/Ca signals on >annual timescales. Coral Ba/Ca presents an excellent proxy for BaSW, which has been found to be correlated with refractory nutrients (e.g. silicate) and oxygen minima. Increasing BaSW with depth and increased variability near 1000m suggests that BaSW is not constant with depth or with time. Several factors, including barite saturation state, particulate organic carbon (POC) remineralization rate, and particle sinking time, may be involved in the observed changes in BaSW. Further examination of such mechanisms could provide new insights into modern changes in deep-sea biogeochemistry.

  1. Climate, productivity, and intermediate water nutrients: new records from bamboo coral Ba/Ca

    NASA Astrophysics Data System (ADS)

    Lavigne, M.; Hill, T. M.; Spero, H. J.; Guilderson, T. P.

    2010-12-01

    A geochemical nutrient proxy from deep-sea corals would provide decadal to centennial scale records of intermediate-water nutrient dynamics. Such records could be used to determine how intermediate water masses (300-2000m) are affected by decadal scale climate change (e.g. Pacific Decadal Oscillation) via carbon cycling, export production, and intermediate water-mass circulation/ventilation. Because seawater barium (BaSW ) has a nutrient-like distribution in the water-column (similar to silicate), Ba/Ca records have been used to trace upwelled nutrient supply in shallow water surface corals isolated from terrestrial barium sources. Here we show the first calibration of a nutrient proxy from skeletal barium preserved in the calcitic internodes of bamboo corals. Our calibration was calculated from a depth transect (500-2000m) of Isidella and Keratoisis corals spanning a silicate and (BaSW ) gradient on the California Margin (Ba/Ca coral (µmol/mol) = 0.117 BaSW (nmol/kg ) + 0.835; R2 = 0.88; n = 29). The strong linear correlation between Ba/Ca coral and BaSW suggests that coral Ba/Ca is a reliable recorder of seawater barium (and, therefore, silicate). We find a distribution coefficient (DBa) for bamboo coral Ba/Ca of 1.3±0.1, similar to that of other corals (surface and deep-sea dwelling) and inorganic calcium carbonate precipitation experiments (DBa = 1.2-1.5). This implies that, as true for other carbonates, Ba incorporation is primarily driven by ionic substitution and holds promise as a globally applicable nutrient proxy in bamboo corals. High-resolution Ba/Ca timeseries records sampled via LA-ICP-MS in two co-located California Margin corals (Pioneer Seamount; 830m; 37°22’27”N) co-vary with ~decadal-scale variations in silicate and nitrate measured at 500m depth (CalCOFI line 80 sta. 60; 34°8’60”N). This suggests that high-resolution records of bamboo coral Ba/Ca can be used to reconstruct broad changes in intermediate water nutrients driven by

  2. High-pressure densified solid solutions of alkaline earth hexaborides (Ca/Sr, Ca/Ba, Sr/Ba) and their high-temperature thermoelectric properties

    SciTech Connect

    Gürsoy, M.; Takeda, M.; Albert, B.

    2015-01-15

    Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB{sub 6}, SrB{sub 6}, BaB{sub 6} and the ternary hexaborides Ca{sub x}Sr{sub 1−x}B{sub 6}, Ca{sub x}Ba{sub 1−x}B{sub 6}, Sr{sub x}Ba{sub 1−x}B{sub 6} (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB{sub 6} (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process. - Highlights: • Solid solutions of alkaline earth hexaborides were synthesized. • High-temperature thermoelectric properties of mixed calcium borides are excellent. • Spark plasma source densification results in high ZT values. • Borides are rare-earth free and refractory materials.

  3. [Structure and photoluminescence of ASnO3 (A = Ca, Sr and Ba) : Eu nanocrystalline].

    PubMed

    Fu, Xiao-Yan; Niu, Shu-Yun; Zhang, Hong-Wu; Xin, Qin

    2007-09-01

    The present paper reports the photoluminescence properties of nanocrytalline ASnO3 (A = Ca, Sr and Ba) : 1% Eu phosphor synthesized by the Pechini-type sol-gel method. The powder was characterized by X-ray diffraction (XRD), UV-Vis absorption spectra, transmission electron microscopy (TEM) and photoluminescence measurements. The experimental results show that BaSnO3 has the ideal cubic peroskite structure, while SrSnO3 and CaSnO3 are both distorted from cubic symmetry by an octahedral tilting distortion. The difference of structure in induced the different spectral properties of ASnO3 : 1% Eu. On the other hand, when A2+ changes from Ca2+ to Ba2+, the luminescence intensity becomes weak. So CaSnO3 : 1% Eu seems to be a good candidate for new phosphors. PMID:18051556

  4. Co2FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    NASA Astrophysics Data System (ADS)

    Rogge, J.; Hetaba, W.; Schmalhorst, J.; Bouchikhaoui, H.; Stender, P.; Baither, D.; Schmitz, G.; Hütten, A.

    2015-07-01

    We succeed to integrate BaO as a tunneling barrier into Co2FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co2FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  5. [Spectra characteristics of LiM (M = Ca, Sr, Ba) BO3 : Tb3+ phosphor].

    PubMed

    Wang, Zhi-Jun; Li, Pan-Lai; Yang, Zhi-Ping; Guo, Qing-Lin

    2009-11-01

    LiM (M = Ca, Sr, Ba) BO3 : Tb3+ phosphors were synthesized by solid state reaction. The starting materials CaCO3, SrCO3, BaCO3, H3 BO3, Li2 CO3, Na2 CO3, K2 CO3 and Tb4 O7 (99.99% in mass) in appropriate stoichiometric ratio were mixed in the alumina crucible, then the mixed powders were calcined at 700 degrees C for 2 h, and LiCaBO3 : Tb3+, LiSrBO3 : Tb3+ and LiB-aBO3 : Tb3+ phosphors were obtained. The emission and excitation spectra were measured by a Shimadzu RF-540 ultraviolet spectrophotometer. All the photoluminescence properties of these phosphors were measured at room temperature. The emission spectra of LiM (M = Ca, Sr, Ba) BO3 : Tb3+ phosphors show several bands, and the main emission peaks correspond to the 5D4 --> 7F6(486, 486, 488 nm), 5D4 --> F5 (544, 544, 544 nm), 5D4 --> 7F4 (590, 595, 593 nm) and 5D4 --> 7F3 (620, 620, 616 nm) typical transitions of Tb3+, and the typical transitions of Tb3+ happens to split because of the effects of LiM (M = Ca, Sr, Ba) BO3 crystals field. The excitation spectra for the 544 nm green emission of LiM (M = Ca, Sr, Ba)BO3 : Tb3+ phosphors illuminate that these kinds of phosphors can be effectively excited by ultraviolet (350-410 nm) light, and emit green light, therefore, they are promising phosphors for white light emitting diodes. Effects of activation and charge compensation on the luminescence intensities of LiM (M = Ca, Sr, Ba) BO3 : Tb3+ phosphors were studied, and the results show that the intensities were obviously effected. PMID:20101952

  6. Ca-Al-rich chondrules and inclusions in ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Bischoff, A.; Keil, K.

    1983-01-01

    Ca-Al-rich objects, hitherto mostly found in carbonaceous chondrites, are shown to be widespread, albeit rare, constituents of type 3 ordinary chondrites. Widespread occurrence and textural similarities of Ca-Al-rich chondrules to common, Mg-Fe-rich chondrules suggest that they formed by related processes. It is suggested in this article that Ca-Al-rich chondrules were formed by total melting and crystallization of heterogeneous, submillimeter- to submillimeter-sized dustballs made up of mixtures of high-temperature, Ca-Al-rich and lower-temperature, Na-K-rich components.

  7. Improved MCFC performance with Li/Na/Ba/Ca carbonate electrolyte.

    SciTech Connect

    Centeno, C.-J.; Kaun, T. D.; Krumpelt, M.; Schoeler, A.

    1999-07-21

    Earlier electrolyte segregation tests of Li/Na carbonate used chemical analysis such as inductively coupled plasma/atomic emission spectroscopy (ICP/AES) of matrix strips wetted with carbonate and exposed to 5- to 20-V potential gradients. A segregation factor was correlated to the Li/Na carbonate composition. While fairly substantial segregation occurs at the eutectic composition of 52% Li, it is minimal at 60% to 75% Li. Such lithium-rich Li/Na carbonates may not be practical because the melting points are too high (i.e., liquidus point is 625 C). By adding calcium and barium to the lithium/sodium carbonates, we were able to lower the melting point and maintain nonsegregating behavior. This work is directed at examining the long-term stability of the quaternary Li/Na/Ba/Ca electrolytes. Electrolyte optimization work evaluates Li/Na ratio and Ba/Ca level to improve cell performance at 320 mA/cm{sup 2} and reduce temperature sensitivity. A number of cells with quaternary Li/Na/Ba/Ca electrolytes ranging from 3 to 5% Ba/Ca have operated well with stable, long-term performance. Congruent melting carbonate is important for commercial development. The best so far is 3.5% Ba/Ca/Na/Li (3.5 mol%/3.5 mol% Ba/Ca) carbonate (m.p. 440 C). Performance at 160 mA/cm{sup 2} is increased up to 150mV as compared with the baseline cell containing the Li/Na eutectic composition. Life stability has been reproduced by a number of bench-scale MCFC test with operations of 2000-4300 h and the electrolyte composition across the matrix little changed.

  8. Critical currents of aligned grains of Tl-Ba-Ca-Cu-O compounds

    NASA Technical Reports Server (NTRS)

    Fang, M. M.; Finnemore, D. K.; Farrell, D. E.; Bansal, N. R.

    1989-01-01

    A study of irreversibility in the magnetization curves of Tl2Ba2Ca2Cu3O10 and Tl2Ba2Ca1Cu2O8 was undertaken to determine the intragranular critical currents and the effects of flux-creep in grain-aligned samples of these materials. For fields of greater than 0.3 T, and H parallel to c axis, the critical supercurrent falls approximately exponentially with both magnetic field and temperature. Flux-creep is found to be linear in the logarithm of time at low fields over a wide temperature range.

  9. Effect of Cr{sub 2}O{sub 3} on solubility and thermo-physical properties of BaO-CaO-Al{sub 2}O{sub 3}-B{sub 2}O{sub 3}-SiO{sub 2} g

    SciTech Connect

    Goswami, M.; Kumar, Rakesh; Patil, A. S.; Sahu, A. K.; Kothiyal, G. P.

    2012-06-05

    BaO-CaO-Al{sub 2}O{sub 3}-(10-x)B{sub 2}O{sub 3}-xCr{sub 2}O{sub 3} SiO{sub 2} (BCABS), where 1.0 {<=}x {<=} 3.5, (mol%) glasses were prepared by melt-quench technique. Glass samples were characterized for density, microhardness, thermal expansion coefficient and glass transition temperature. Scanning electron microscopy was used to see the homogeneity/solubility of Cr2O3 in this glass system. UV-VIS absorption measurements were carried out to see the Cr speciation in the glass samples. Density values were found to vary from 3.97 to 3.92 g/cc and microhardness values varied from 283 to 503 kg/mm{sup 2}. Glass transition temperature increased from 635 to 671 deg. C while TEC value found to varies from 8.3 to 11.1x10{sup -6}/ deg. C(30-300) with Cr{sub 2}O{sub 3} content. SEM study revealed phase separation in these glasses. From absorption studies we infer the presence of small amount of Cr (VI) along with Cr(III) oxidation state.

  10. Analysis of Ca in BaCl 2 matrix using laser-induced breakdown spectroscopy

    NASA Astrophysics Data System (ADS)

    Rinaldi, C. A.; Ferrero, J. C.

    2001-08-01

    The simplicity of the sample preparation and the use of an internal standardization method for the quantitative analysis of Ca has been investigated. The experimental set-up allowed the measurement of the intensity of ionic emission lines from Ca(II) and Ba(II), as a function of the composition in the matrix sample. The intensity ratios of the emission of Ca(II) to three different lines of Ba(II) were measured as a function of the distance (time) from the ablation point. With this information, the best experimental conditions for the analysis were determined. The method was then applied to the quantitative analysis of Ca in soils and baby food and the results compared with those obtained with conventional chemical and atomic absorption analysis.

  11. Antiferromagnetic Metallic State And Spin Valve Effect in Doped (Ca1-x Ax)3Ru2O7 (A = Sr, Ba) Single Crystals

    NASA Astrophysics Data System (ADS)

    Chikara, S.; Korneta, O. B.; Qi, T. F.; Parkin, S.; Cao, G.; Song, W. P.; Crummett, W. P.

    2009-03-01

    Bilayered Ca3Ru2O7 is a highly anisotropic system [1] characterized by orbitally-driven colossal magnetoresistance^2 and an unusual antiferromagnetic metallic (AFM-M) state [2]. We report transport and thermodynamic properties of (Ca1-x Ax)3Ru2O7 (A = Sr, Ba) single crystals as a function of temperature and applied magnetic field. While Ba doping shows a far stronger impact, both Sr and Ba substitution for Ca induce a large array of interesting phenomena. Among them, a bulk spin-valve effect occurs in the AFM-M range, which is largely broadened due to the doping. This effect in bulk crystals is a novel phenomenon first observed in Ca3(Ru1-xCrx)2O7 single crystals [3]. The spin-valve effect in (Ca1-xAx)3Ru2O7 single crystals opens new avenues to understand the underlying physics and realize the potential of spin valves in practical devices.[0pt] [1] G. Cao et al., PRL 78, 1751 (1997)[0pt] [2] X. N. Lin et al., PRL 95, 017203 (2005)[0pt] [3] G. Cao et al., PRL 100, 016604 (2008)

  12. Atomized BaF2-CaF7 for Better-Flowing Plasma-Spray Feedstock

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Stanford, Malcolm K.

    2008-01-01

    Atomization of a molten mixture of BaF2 and CaF2 has been found to be superior to crushing of bulk solid BaF2- CaF2 as a means of producing eutectic BaF2-CaF2 powder for use as an ingredient of the powder feedstock of a high-temperature solid lubricant material known as PS304. Developed to reduce friction and wear in turbomachines that incorporate foil air bearings, PS304 is applied to metal substrates by plasma spraying. The constituents of PS304 are: a) An alloy of 80 weight percent Ni and 20 weight percent Cr, b) Cr2O3, c) Ag, and d) The BaF2-CaF2 eutectic, specifically, 62 weight percent BaF2 and 38 weight percent CaF2. The superiority of atomization as a means of producing the eutectic BaF2-CaF2 powder lies in (1) the shapes of the BaF2-CaF2 particles produced and (2) the resulting flow properties of the PS304 feedstock powder: The particles produced through crushing are angular, whereas those produced through atomization are more rounded. PS304 feedstock powder containing the more rounded BaF2-CaF2 particles flows more freely and more predictably, as is preferable for plasma spraying.

  13. Is otolith microchemistry (Sr: Ca and Ba:Ca ratios) useful to identify Mugil curema populations in the southeastern Caribbean Sea?

    PubMed

    Avigliano, E; Callicó-Fortunato, R; Buitrago, J; Volpedo, A V

    2015-11-01

    The aim of the present study was to evaluate the potential use of otolith microchemistry (Sr:Ca and Ba:Ca ratios) to identify silver mullet, Mugil curema, populations in Southeastern Caribbean Sea. Fish samples were collected in 7 areas of Nueva Esparta State (Venezuela). The otolith Sr:Ca and Ba:Ca ratios and water Sr:Ca were determined (by ICP-OES and EDTA volumetric method). Otoliths Sr:Ca and Ba:Ca ratios and Sr:Ca partition coefficient of mullets in Cubagua island (south of the State) were significantly different from ratios in La Guardia (north of the State). A discriminant analysis of otolith Sr:Ca and Ba:Ca ratios separated Cubagua Island from La Guardia values. These results suggest the existence of different mullet groups in the Southeastern Caribbean Sea. For this, the simultaneous use of Sr:Ca and Ba:Ca ratios could be a potential tool to identify populations in the study area. PMID:26628220

  14. Ca, Sr and Ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence

    USGS Publications Warehouse

    Bullen, Thomas D.; Chadwick, Oliver A.

    2016-01-01

    Nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus (P) and calcium (Ca) from minerals at depth and concentrate those nutrients at the surface. Here we use soil chemistry and stable isotopes of the alkaline earth elements Ca, strontium (Sr) and barium (Ba) to test the hypothesis that biolifting of P has been an important pedogenic process across a soil climosequence developed on volcanic deposits at Kohala Mountain, Hawaii. The geochemical linkage between these elements is revealed as generally positive site-specific relationships in soil mass gains and losses, particularly for P, Ba and Ca, using the ratio of immobile elements titanium and niobium (Ti/Nb) to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials. At sites where P is enriched in surface soils relative to abundances in deeper soils, the isotope compositions of exchangeable Ca, Sr and Ba in the shallowest soil horizons (< 10 cm depth) are lighter than those of the volcanic parent materials and trend toward those of plants growing on fresh volcanic deposits. In contrast the isotope composition of exchangeable Ba in deeper soil horizons (> 10 cm depth) at those sites is consistently heavier than the volcanic parent materials. The isotope compositions of exchangeable Ca and Sr trend toward heavier compositions with depth more gradually, reflecting increasing leakiness from these soils in the order Ba < Sr < Ca and downward transfer of light biocycled Ca and Sr to deeper exchange sites. Given the long-term stability of ecosystem properties at the sites where P is enriched in surface soils, a simple box model demonstrates that persistence of isotopically light exchangeable Ca, Sr and Ba in the shallowest soil horizons requires that the uptake flux to plants from those near-surface layers is less than the recycling flux returned to the surface as

  15. High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O

    DOEpatents

    Ginley, David S.; Hietala, Vincent M.; Hohenwarter, Gert K. G.; Martens, Jon S.; Plut, Thomas A.; Tigges, Chris P.; Vawter, Gregory A.; Zipperian, Thomas E.

    1994-10-25

    A process for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO.sub.3 crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O.sub.3, followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry.

  16. High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O

    DOEpatents

    Ginley, D.S.; Hietala, V.M.; Hohenwarter, G.K.G.; Martens, J.S.; Plut, T.A.; Tigges, C.P.; Vawter, G.A.; Zipperian, T.E.

    1994-10-25

    A process is disclosed for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO[sub 3] crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O[sub 3], followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry. 8 figs.

  17. Structural and photoluminescence properties of Dy3+ co-doped and Eu2+ activated MAl2O4 (M = Ba, Ca, Sr) nanophosphors

    NASA Astrophysics Data System (ADS)

    Dejene, F. B.; Kebede, M. A.; Redi-Abshiro, M.; Kgarebe, B. V.

    2013-09-01

    Long afterglow alkaline earth aluminates MAl2O4:Eu, Dy (M: Ca, Sr, Ba) phosphors are generally synthesized by the solid-state process which is more feasible than other conventional processes in terms of operation and large-scale production. However, the constituents of phosphors synthesized using this process are usually not mixed well, the particles agglomerates and very high temperature requirement to synthesize the final powder make it undesirable. In order to circumvent these problems, MAl2O4:Eu, Dy (Ca, Ba, Sr) phosphors were prepared at low temperatures (500 °C) by the solution-combustion of corresponding metal nitrate-urea solution mixtures, over a time of 5-10 min. In order to elucidate the relationship between the constituent, structure and PL properties product's particle size, morphological and structural properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), while the characteristic luminescence properties were investigated using emission spectra. The low temperature monoclinic structure for both CaAl2O4 and SrAl2O4 and the hexagonal structure of BaAl2O4 were observed. The emission spectra of these phosphors indicated that all of them are broad band, and the only emission peaks around 448, 490 and 515 nm of CaAl2O4:Eu, Dy, BaAl2O4:Eu, Dy and SrAl2O4:Eu, Dy, respectively, are due to 5d → 4f transition of Eu2+. The decay curves implied that these phosphors contain fast, medium and slow-decay process. The Dy3+ trap levels may be considered to be responsible for the long afterglow phosphorescence at room temperature.

  18. Epitaxial thin films of ATiO(3-x)H(x) (A = Ba, Sr, Ca) with metallic conductivity.

    PubMed

    Yajima, Takeshi; Kitada, Atsushi; Kobayashi, Yoji; Sakaguchi, Tatsunori; Bouilly, Guillaume; Kasahara, Shigeru; Terashima, Takahito; Takano, Mikio; Kageyama, Hiroshi

    2012-05-30

    Epitaxial thin films of titanium perovskite oxyhydride ATiO(3-x)H(x) (A = Ba, Sr, Ca) were prepared by CaH(2) reduction of epitaxial ATiO(3) thin films deposited on a (LaAlO(3))(0.3)(SrAl(0.5)Ta(0.5)O(3))(0.7) substrate. Secondary ion mass spectroscopy detected a substantial amount and uniform distribution of hydride within the film. SrTiO(3)/LSAT thin film hydridized at 530 °C for 1 day had hydride concentration of 4.0 × 10(21) atoms/cm(3) (i.e., SrTiO(2.75)H(0.25)). The electric resistivity of all the ATiO(3-x)H(x) films exhibited metallic (positive) temperature dependence, as opposed to negative as in BaTiO(3-x)H(x) powder, revealing that ATiO(3-x)H(x) are intrinsically metallic, with high conductivity of 10(2)-10(4) S/cm. Treatment with D(2) gas results in hydride/deuteride exchange of the films; these films should be valuable in further studies on hydride diffusion kinetics. Combined with the materials' inherent high electronic conductivity, new mixed electron/hydride ion conductors may also be possible. PMID:22563869

  19. Structural, optical and electrical properties of GdAlO3:Eu3+Ba2+

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, T.; Tamilarasi, S.; Bose, A. Chandra

    2015-06-01

    Effect of Ba2+ ions concentration on the photoluminescence of GdAlO3:Eu3+ Ba2+ phosphor is investigated. The phosphors are synthesized by citrate-based sol-gel method and the formation of orthorhombic phase GdAlO3 is confirmed by XRD analysis. Kubelka-Munk function is used to estimate the band gap and the value varies with concentration of Ba2+ is observed. Photoluminescence spectra show a strong red emission peak at 616 nm corresponding to5D0→7F2 transition and its intensity increase with the addition of Ba2+ ions. The presence of Eu3+ and Ba2+ ions in GdAlO3 strongly influences the dielectric property of GdAlO3.

  20. Multi-colony calibrations of coral Ba/Ca with a contemporaneous in situ seawater barium record

    NASA Astrophysics Data System (ADS)

    LaVigne, Michèle; Grottoli, Andréa G.; Palardy, James E.; Sherrell, Robert M.

    2016-04-01

    The coral skeleton barium to calcium ratio (Ba/Cacoral), a proxy for seawater barium concentrations (BaSW), has been interpreted as a tracer of upwelling based on the characteristic "nutrient like" depth profile of BaSW. However, in some tropical regions, such as the Gulf of Panamá, substantial influence of terrestrial runoff inputs and differences between the vertical distribution of BaSW and that of the major nutrients (nitrate and phosphate) in the upper water column can complicate the interpretation of Ba/Cacoral as an upwelled nutrient proxy. In the Gulf of Panamá, contemporaneous Ba/Cacoral records from multiple colonies of Porites lobata, Pavona gigantea, and Pavona clavus corals record a nearly twofold change in surface water BaSW as a 20-70% increase in skeletal Ba/Ca with excellent correlation among Ba/Ca records from co-located colonies (r = 0.86-0.99). These results provide, for the first time, an absolute calibration of the coral Ba proxy with a contemporaneous BaSW record. Compiling the Ba/Cacoral records from three co-located colonies of each species into taxon-specific composite regressions reveals strong statistically significant correlations with the BaSW time-series record (p < 0.001). Differences among taxa in regression slope, y-intercept, and average distribution coefficient, as well as a demonstration of the application of the P. clavus calibration to a previously published Ba/Cacoral record, emphasize the necessity of using taxon-specific calibrations to reconstruct changes in BaSW with accuracy. These results support the application of Ba/Cacoral to reconstruct past changes in absolute BaSW concentrations, adding an important tool to the collection of geochemical proxies for reconstructing surface ocean biogeochemical processes in the past.

  1. Barium aluminides Ba{sub x}Al{sub 5}(x=3,3.5,4)

    SciTech Connect

    Jehle, Michael; Scherer, Harald; Wendorff, Marco; Roehr, Caroline

    2009-05-15

    Three aluminides of the series Ba{sub x}Al{sub 5}(x=3,3.5,4) were synthesized from stoichiometric ratios of the elements in Ta crucibles. The crystal structure of the new compound Ba{sub 7}Al{sub 10} was determined using single crystal X-ray data (space group R3-barm, a=604.23(9), c=4879.0(12)pm, Z=3, R1=0.0325). The compound exhibits Al Kagome (3.6.3.6.) nets in which half of the triangles form the basis of trigonal bipyramids Al{sub 5}. The apical Al are thus three-bonded assuming a charge of -2 ({sup 27}Al-NMR chemical shift delta=660pm), whereas the Al atoms of the basal triangle (i.e. of the Kagome net) are four-bonded and thus of formal charge -1(delta=490ppm). The total charge of the anion is thus exactly compensated by the Ba cations, i.e. the compound can be interpreted as an electron precise Zintl phase, exhibiting a distinct pseudo-band gap at the Fermi level of the calculated tDOS. According to the total formula, the structure displays a combination the stacking sequences of Ba{sub 3}Al{sub 5} and Ba{sub 4}Al{sub 5}, the structures of which have been redetermined with current methods (both hexagonal with space group P6{sub 3}/mmc; Ba{sub 3}Al{sub 5}: a=606.55(7), c=1461.8(2)pm, Z=2, R1=0.0239; Ba{sub 4}Al{sub 5}: a=609.21(7), c=1775.8(3)pm, Z=2, R1=0.0300). These three compounds with slightly different electron counts but similar polyanions allow to compare the bond lengths, the electronic structures and the overall bonding situation in dependence of positive or negative deviation of the electron count in relation to the novel formally electron precise Zintl compound Ba{sub 7}Al{sub 10}. - Al{sub 5} layers of Kagome nets in the new binary electron precise Zintl compound Ba{sub 3.5}Al{sub 5}, also found in Ba{sub 3}Al{sub 5} and Ba{sub 4}Al{sub 5}.

  2. Observations of Al, Fe and Ca(+) in Mercury's Exosphere

    NASA Technical Reports Server (NTRS)

    Bida, Thomas A.; Killen, Rosemary M.

    2011-01-01

    We report 5-(sigma) tangent column detections of Al and Fe, and strict 3-(sigma) tangent column upper limits for Ca(+) in Mercury's exosphere obtained using the HIRES spectrometer on the Keck I telescope. These are the first direct detections of Al and Fe in Mercury's exosphere. Our Ca(-) observation is consistent with that reported by The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft.

  3. Processing and properties of silver-clad Tl-Ba-Ca-Cu-O wires and tapes

    SciTech Connect

    Goretta, K.C.; Wu, C.T.; Lanagan, M.T.; Boling, M.A.; Shi, D.; Miller, D.J.; Chen, Nan; Hanewald, W.G.; Sengupta, S.; Wang, Z.; Poeppel, R.B.; Foong, F.; Liou, S.H.

    1992-03-01

    TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} powders were synthesized, loaded into Ag tubes, and worked into wires and tapes by drawing and rolling. All processing outside of furnaces was in a dry-N{sub 2} glovebox. All heat treatments were performed in O{sub 2}. The Ag-clad wires fabricated from these powders exhibited onset of superconductivity at {approx}118 K and critical current densities at 77K of 2{times}10{sup 3} to 4{times}10{sup 3} A/cm{sup 2}.

  4. Preparation of superconducting Tl-Ca-Ba-Cu thin films by chemical deposition

    SciTech Connect

    Olson, W.L.; Eddy, M.M.; James, T.W.; Hammond, R.B.; Gruner, G.

    1989-07-10

    The scientific revolution in superconductivity has been driven by the discovery of many metal oxides that exhibit this unique property at unusually high temperatures. At the time of submission of this article, the material showing the highest transition temperature is Tl2Ca2Ba2Cu3O10 (2223) which is superconducting below 122 K. For many potential applications of high Tc superconductors uniform thin films are required. There are a number of methods that might be employed for the preparation of such a film. These include electron beam (e-beam) coevaporation and sequential evaporation, sputtering, ion beam deposition, molecular beam epitaxy, laser ablation, spray, and spin-on techniques, all of which have been used to prepare thin and thick films of YBa{sub 2}CuO{sub 7}. Sequential e-beam, sputtering, and laser ablation have been shown to make superconducting films in the Tl-Ca-Ba-Cu oxide system.

  5. Crystal structure and superconductivity in (Cu,Hg)Ba2Ca4Cu5Oy

    NASA Astrophysics Data System (ADS)

    Akimoto, J.; Kawaguchi, K.; Sohma, M.; Hayakawa, H.; Gotoh, Y.; Oosawa, Y.; Tokiwa, K.; Iyo, A.; Ihara, H.

    1997-02-01

    A new solid-solution superconductor, (Cu,Hg)Ba2Ca4Cu5Oy with the tetragonal lattice parameters a = 3.849(2) Å and c = 21.496(3) Å, has been synthesized by the high-temperature and high-pressure technique. The structure refinement of the as-prepared (Cu,Hg)-1245 by the single-crystal X-ray diffraction method confirmed the substitutional composition (Cu0.76Hg0.24)Ba2Ca4Cu5O12.45, whose cationic composition was close to that obtained by chemical analysis. The additional Cu atoms at the mercury site construct the chain-like oxygen coordination. The superstructure observed in Cu-1245 disappeared by the partial substitution of mercury for copper in the present (Cu,Hg)-1245. The structure refinement of the as-prepared Hg-1245 revealed the mercury-site deficiency of about 20%.

  6. Stability of Tl-Ba-Ca-Cu-O Superconducting Thin Films

    SciTech Connect

    Siegal, M.P.; Overmyer, D.L.; Venturini, E.L.; Padilla, R.R.; Provencio, P.N.

    1999-08-23

    We report the stability of TlBa{sub 2}CaCu{sub 2}O{sub 7} (Tl-1212) and Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} (T1-2212) thin films and by inference, the stability of TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 9} (Tl-1223) and Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (Tl-2223) thin films, under a variety of conditions. In general, we observe that the stability behavior of the single Tl-O layer materials (Tl-1212 and Tl-1223)are similar and the double Tl-O layer materials (Tl-2212 and Tl-2223) are similar. All films are stable with repeated thermal cycling to cryogenic temperatures. Films are also stable in acetone and methanol. Moisture degrades film quality rapidly, especially in the form of vapor. Tl-1212 is more sensitive to vapor than Tl-2212. These materials are stable to high temperatures in either N{sub 2}, similar to vacuum for the cuprates, and O{sub 2} ambients. While total degradation of properties (superconducting and structural) occur at the same temperatures for all phases, 600 C in N{sub 2} and 700 C in O{sub 2}, the onset of degradation occurs at somewhat lower temperatures for Tl-1212 than for Tl-2212 films. In all cases, sample degradation is associated with Tl depletion from the films.

  7. Encapsulating MAl 2O 4:Eu 2+, Dy 3+ (M = Sr, Ca, Ba) phosphors with triethanolamine to enhance water resistance

    NASA Astrophysics Data System (ADS)

    Ji, Ping Ting; Chen, Xiang Ying; Wu, Ye Qin

    2011-12-01

    Traditional aluminates phosphors with persistent luminescence are chemically unstable to water or moisture. Thus, how to improve the water-resistance of these phosphors is becoming a key issue in their practical applications. In this work, a series of alkaline earth aluminate phosphors including MAl 2O 4:Eu 2+, Dy 3+ (M = Sr, Ca, Ba) have been prepared by a co-precipitation synthesis and postannealing approach, using 8-hydroxyquinoline and sodium oxalate as precipitants. The samples before and after encapsulation were well characterized by means of XRPD, FESEM, FT-IR, TGA-DTG and PL techniques as well as water resistance measurements. The precipitants involved can react with Al 3+ and Sr 2+ (or Ca 2+, Ba 2+) to form complex compounds in aqueous solution, which further convert into porous phosphors by postannealing method under reducing atmosphere. Next, triethanolamine encapsulation at room temperature was conducted onto their surfaces to improve the water resistance. The results reveal that the encapsulation of aluminate phosphors with triethanolamine can effectively enhance the water resistance, and minimally affect on persistent phosphorescence.

  8. Investigation on double perovskite Ba 4Ca 2Ta 2O 11

    NASA Astrophysics Data System (ADS)

    Baliteau, S.; Mauvy, F.; Fourcade, S.; Grenier, J. C.

    2009-09-01

    The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba 4Ca 2Ta 2O 11 have been investigated. Ba 4Ca 2Ta 2O 11 crystallizes in the cryolite structure (cubic, Fm3 m SG) with a = 8.4508(2) Å, under dry air. The compound can be partially hydrated up to a maximum water content of approximately 0.52 mol H 2O per mol Ba 4Ca 2Ta 2O 11. In moist air, the structure symmetry becomes monoclinic ( C2/ m) and the temperature dependence of total conductivity shows a different behavior because of changes in transport mechanism. Three regions can be observed as a function of temperature. For the low temperature range 200-400 °C, the protonic conduction is prevailing with an activation energy EA = 0.85 eV. In the intermediate temperature range (400-600 °C), O 2- anionic and protonic conductions are mixed with an activation energy EA = 0.45 eV and in the third region, for temperatures above 600 °C, O 2-conduction is prevailing with an activation energy EA = 0.85 eV.

  9. Itinerant magnetism in CaMn2Al10

    NASA Astrophysics Data System (ADS)

    Simonson, Jack; Steinke, Lucia; Zellman, Shelby; Kistner-Morris, Jedediah; Puri, Akshat; Andrews, Evon; Aronson, Meigan

    2015-03-01

    We report the synthesis and basic properties of CaMn2Al10, a new itinerant magnet that is nearly isostructural with the known quantum critical compound YFe2Al10. Magnetic susceptibility measurements performed on single crystals reveal a cusp at 2 K. Electrical resistivity measurements similarly have a maximum at this temperature, and heat capacity measurements show a broad peak with total entropy of ~ 10 % R ln2. These results together with those of neutron diffraction measurements suggest that CaMn2Al10 is weakly magnetic and potentially close to a quantum critical point. Research supported by a DOD National Security Science and Engineering Fellowship via the AFOSR.

  10. Thick film of HgBa 2Ca 2Cu 3O 8+δ via the sol-gel technique

    NASA Astrophysics Data System (ADS)

    Yoo, S. H.; Wong, K. W.; Xin, Y.

    1997-02-01

    We have prepared superconducting HgBa 2Ca 2Cu 3O 8+δ thick films on polycrystalline MgO substrate via the sol-gel technique together with a slow annealing method. A precursor film of Ba 2Ca 2Cu 3O 7 was annealed with a bulk mixture of unreacted HgBa 2Ca 2Cu 3O 8+δ and a precursor, Ba 2Ca 2Cu 3O 7, pellet that was employed to control the HgO vapor pressure. Our films show an onset superconducting transition temperature of 140 K and a zero resistance temperature of 130 K after oxygen annealing. The high Tc thick films are consistently reproducible.

  11. A first principles study on newly proposed (Ca/Sr/Ba)Fe2Bi2 compounds with their parent compounds

    NASA Astrophysics Data System (ADS)

    Sundareswari, M.; Jayalakshmi, D. S.; Viswanathan, E.

    2016-02-01

    The structural, electronic, bonding and magnetic properties of newly proposed iron-based compounds viz., CaFe2Bi2, SrFe2Bi2, BaFe2Bi2 with their Fermi surface topology are reported here for the first time by means of first principles calculation. All these properties of newly proposed compounds are compared and analysed along with their respective parent compounds namely (Ca,Sr,Ba)Fe2As2.

  12. The effect of Mn2+, Zn2+, Ba2+ and Ca2+ on spontaneous motility in sheep duodenum in vitro.

    PubMed

    Murillo, M D; Plaza, M A; Arruebo, M P

    1997-01-01

    1. The effects of several ions, Mn2+, Zn2+, Ba2+ and Ca2+, on spontaneous motility were investigated in longitudinal smooth muscle strips from sheep duodenum, in vitro. 2. Mn2+ (0.5-1.5 mM) and Zn2+ (0.5-5 mM) inhibited both the amplitude and frequency of motility in Krebs solution and in Ca(2+)-free medium. 3. Ba2+ (0.5-5 mM) evoked three types of contractile responses: (i) an increase in the frequency and a reduction of the amplitude of spontaneous contractions; (ii) a slight increase in muscle tone of the phasic contractions; and (iii) a rapid initial phasic contraction followed by slowly fading contraction. Ca2+ induced two kinds of responses in spontaneous motility: (i) a fast phasic contraction, followed by an increase in the amplitude and frequency of phasic contractions with no changes in its tone; and (ii) an increase in the amplitude of contractions. 4. The Ba(2+)-induced contractions were inhibited by EDTA, verapamil and diltiazem, but were not modified by sodium nitroprusside. The Ca(2+)-induced contractions were reduced by verapamil and diltiazem. 5. Our results show that Mn2+ and Zn2+ behave as inhibitors of sheep duodenum motility. In contrast, Ba2+ and Ca2+ stimulate motility. It is suggested that Ba2+ can penetrate the cells through voltage-dependent Ca2+ channels and behave as a partial substitute for Ca2+. PMID:9112079

  13. Comparison Study of Transition Temperature between the Superconducting Compounds Tl0.9 Pb0.1 Ba2Ca2Cu3O9-δ, Tl0.9Sb0.1Ba2Ca2Cu3O9-δ and Tl0.9Cr0.1Ba2Ca2Cu3O9-δ

    NASA Astrophysics Data System (ADS)

    Jasim, Kareem Ali; Makki, Sameer Atta; Almohsin, Alia abud

    Three high temperature superconductors namely Tl0.9Pb0.1Ba2Ca2Cu3O9-δ, Tl0.9Sb0.1Ba2Ca2Cu3O9-δ and Tl0.9Cr0.1Ba2Ca2Cu3O9-δ have been successfully prepared by three-step solid state reaction method. The sintering was within (1128-1133) K. Electrical resistively, using four probe techniques, is used to find the transition temperature Tc. The transition temperature at zero resistivity Tc(offset) were 110, 115 and 118K, onset superconducting transition temperature Tc(onset) were 128, 131 and 132 K for Tl0.9Cr0.1Ba2Ca2Cu3O9-δ, Tl0.9Sb0.1Ba2Ca2Cu3O9-δ and Tl0.9Cr0.1Ba2Ca2Cu3O9-δ respectively. All samples preparation with O2 flow. X-ray diffraction (XRD) analysis showed a pesudotetragonal structure with changes of lattice parameters for these samples.

  14. Interface enhanced functionalities in BaTiO3/CaTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Wu, Xifan

    2014-03-01

    Interface engineering of oxide thin films has led to the development of many intriguing physical properties and new functionalities, in which the oxygen rotation and tilting take an crucial role. The oxygen octahedral tilt has been considered to be a coherent motion in the oxide thin-films, based on which the tilt is often neglected in the modeling of ABO3 superlattices. However, combined with state-of-art experimental high-resolution electron microscopic image, our first-principles results clearly show that oxygen octahedral tilt should be more appropriately defined by the tilting angles of two individual pyramids. Each pyramid will tilt rather independently as a function of its local chemical environment. Considering the oxygen octahedral rotation at the same time, the new picture of oxygen octahedral tilting will induce a novel interface effect, in which an unstable structure in bulk CaTiO3 will be stabilized at the interface in BaTiO3/CaTiO3 superlattice. This novel interface effect induces large polarizations both in-plane and out-of-plane with a corresponding enhanced piezoelectricity. The above scenario successfully explains the recent experimental discoveries in BaTiO3/CaTiO3 superlattices by H. Lee's and P. Evan's groups respectively.

  15. Oxygen Octahedral Rotations in BaTiO3/CaTiO3 Superlattices

    NASA Astrophysics Data System (ADS)

    Cosgriff, Margaret; Chen, Pice; Corey, Nathaniel; Wu, Xifan; Mehta, Apurva; Tajiri, Hiroo; Lee, Ho Nyung; Evans, Paul

    2013-03-01

    Complex oxide superlattices have a wide range of electronic and magnetic properties, which are affected by the structure of the interfaces between different components of the superlattice. The magnitude, coherence, and electric field response of oxygen displacements in three different BaTiO3/CaTiO3 superlattice compositions are measured using x-ray diffraction. The displacements are greater in compositions with more consecutive CaTiO3 layers. The pattern of layer-by-layer alternating displacements is coherent over less than two superlattice unit cells. The net in-phase rotation of the oxygen octahedra gives rise to an x-ray reflection at (3/2 1/2 1). Density functional theory calculations for a 2(BaTiO3) /4(CaTiO3) composition predict a decrease in displacements of oxygen octahedra between barium and calcium layers when an electric field is applied, causing an intensity increase in this reflection. We found the intensity of this reflection for this composition increases by 1.6% when a 12.5 V pulse is applied, a weaker response than the 11% increase predicted. When a 20 V pulse is applied, the reflection intensity actually decreases by 3%, indicating a more complicated response.

  16. Electronic Structure of TlBa2CaCu2O(7-Delta)

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Novikov, D. L.; Freeman, A. J.; Siegal, M. P.

    1997-01-01

    The core levels of TlBa2CaCu2O(7-delta) (Tl-1212) epitaxial films have been measured with X-ray photoelectron spectroscopy (XPS). The valence electronic structure has been determined using the full-potential linear muffin-tin-orbital band-structure method and measured with XPS. The calculations show that a van Hove singularity (VHS) lies above the Fermi level (E(sub F)) for the stoichiometric compound (delta = 0.5), while for 50% oxygen vacancies in the Tl-O layer (delta = 0.5) E(sub F) is in close proximity to the VHS. Samples annealed in nitrogen (to reduce the hole overdoping by the removal of oxygen) exhibit higher core-level binding energies and a higher T(sub c), consistent with a shift of E(sub F) closer to the VHS. Comparisons are made to the core levels and valence bands of Tl2Ba2CaCu2O(8 + delta)(Tl-2212) and HgBa2CaCu2O)6 + delta) (Hg- 1212). The similarity of the Cu 2p(sub 3/2) spectra for Tl-1212 and Tl-2212 indicates that the number of Tl-O layers has little effect on the Cu-O bonding. However, the Tl-1212 and Hg-1212 Cu 2p(sub 3/2) signals exhibit differences which suggest that the replacement of T(sup 3+) with Hg(sup 2+) results in a decrease in the O 2p right arrow Cu 3d charge-transfer energy and differences in the probabilities of planar vs apical oxygen charge transfer and/or Zhang-Rice singlet-state formation. Differences between the Tl-1212 and the Tl-2212 and Hg-1212 measured valence bands are consistent with the calculated Cu 3d and (Tl,Hg) 6s/5d partial densities of states.

  17. Hydration and proton transport in solid solutions based on Ba2CaWO6

    NASA Astrophysics Data System (ADS)

    Animitsa, I. E.; Kochetova, N. A.; Denisova, T. A.; Zhuravlev, N. A.; Baklanova, I. V.

    2009-02-01

    Hydrated alkaline-earth metal tungstates Ba4Ca2 + x W2 - x O12 - 2 x with perovskite structure were studied by the thermogravimetry, 1H NMR, IR, and Raman spectroscopy methods. Electrical conductivity and transfer numbers were measured with varying T, p_{O_2 } and p_{H_2 O} . The solid solutions are capable of reversibly intercalating water and can exhibit high-temperature proton transport. The localization of protons on oxygen results in the appearance of energetically nonequivalent OH groups; a small fraction of protons are present in the form of H2O and H3O+.

  18. TiO2 controlling photoluminescence of AWO4 (A =Ca,Sr,Ba) nanofilms

    NASA Astrophysics Data System (ADS)

    Jia, Runping; Zhang, Guoxin; Wu, Qingsheng; Ding, Yaping

    2006-07-01

    AWO4 (A =Ca,Sr,Ba) nanofilms are prepared by a self-inventive technique using collodion to disperse nanoparticles and form film, and their photoluminescence (PL) properties are controlled by a nano-TiO2 doping method. This cannot only reach the results of uniform film and PL enhancement, but also realize a PL increase/decrease shift effect. The PL behaviors of AWO4 nanofilms doped by TiO2 are in good agreement with Gaussion function relation. In addition, there is a positive correlation between the critical concentrations of TiO2 in AWO4-TiO2 nanofilm series and A's ionic potential.

  19. Rare gases and Ca, Sr, and Ba in Apollo 17 drill-core fines

    NASA Technical Reports Server (NTRS)

    Pepin, R. O.; Dragon, J. C.; Johnson, N. L.; Bates, A.; Coscio, M. R., Jr.; Murthy, V. R.

    1975-01-01

    Trapped gas isotopic compositions and spallation gas concentrations as functions of depth in the Apollo 17 drill core were determined from mass spectrometer studies by means of correlation techniques. The distribution of He, Ne, Ar, Kr, and Xe as well as Ca, Sr, and Ba was investigated, and rare-gas spallation and neutron capture profiles are compared with attention to proposed depositional models for the Taurus-Littrow regolith. The data exclude a sedimentation pattern similar to that found at the Apollo 15 site but are possibly compatible with long-term continuous accretion models or models of very recent rapid accumulation of regolith.

  20. Fabrication and chemical composition of RF magnetron sputtered Tl-Ca-Ba-Cu-O high Tc superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Radpour, F.; Kapoor, V. J.; Lemon, G. H.

    1990-01-01

    The preparation of TlCaBaCuO superconducting thin films on (100) SrTiO3 substrates is described, and the results of their characterization are presented. Sintering and annealing the thin films in a Tl-rich ambient yielded superconductivity with a Tc of 107 K. The results of an XPS study support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca(2+) for Tl(3+), resulting in hole creation, and (2) charge transfer from Tl(3+) to the CuO layers, resulting in a Tl valence between +3 and +1.

  1. Strain-coupled ferroelectric polarization in BaTiO3-CaTiO3 superlattices

    SciTech Connect

    Seo, Sung Seok A; Lee, Ho Nyung

    2009-01-01

    We report on growth and ferroelectric (FE) properties of superlattices (SLs) composed of the FE BaTiO{sub 3} and the paraelectric CaTiO{sub 3}. Previous theories have predicted that the polarization in (BaTiO{sub 3})n/(CaTiO{sub 3})n SLs increases as the sublayer thickness (n) increases when the same strain state is maintained. However, our BaTiO{sub 3}/CaTiO{sub 3} SLs show a varying lattice-strain state and systematic reduction in polarization with increasing n while coherently strained SLs with n = 1 and 2 show a FE polarization of ca. 8.5 {micro}C/cm{sup 2}. We suggest that the strain coupling plays a more important role in FE properties than the electrostatic interlayer coupling based on constant dielectric permittivities.

  2. Magnetic behaviour of the MTbF6 fluoroterbates (M=Cd, Ca, Sr, (α/β)-Ba)

    NASA Astrophysics Data System (ADS)

    Josse, M.; El-Ghozzi, M.; Avignant, D.; André, G.; Bourée, F.; Isnard, O.

    2012-01-01

    Neutron powder diffraction has been performed on the MTbF6 fluorides (M=Cd, Ca, Sr, (α/β)-Ba). Four of these fluorides (Cd, Ca, Sr, β-Ba) are built of a (pseudo-) tetragonal packing of [TbF6]2- chains and only differs by the chains relative orientations. Thus this series represents a valuable opportunity to evaluate the Tb4+-Tb4+ magnetic interactions. All the compounds displayed antiferromagnetic order (TN=2.70 K (Cd), 2.15 K (Ca), 2.60 K (Sr), 2.10 K (β-Ba)), except for the α form of BaTbF6. The crystal structure of this latter fluoroterbate has also been investigated by means of high-resolution neutron powder diffraction. From Neutron Powder Diffraction data, CdTbF6 and β-BaTbF6 magnetic structures were determined, together with the metamagnetic behaviour of β-BaTbF6 as a function of an external magnetic field. A tentative phase diagram is then given for β-BaTbF6. Advantage was taken of the polymorphism of the BaTbF6 fluoroterbate to analyse, on the basis of topological parameters such as bond distances and angles, the magnetic behaviour of its α and β forms. It was shown that superexchange interactions are present in β-BaTbF6, and that these interactions may also rule the magnetic behaviour of the other MTbF6 (M=Ca, Sr, Cd) tetravalent terbium fluorides.

  3. A new (Ba, Ca) (Ti, Zr)O3 based multiferroic composite with large magnetoelectric effect.

    PubMed

    Naveed-Ul-Haq, M; Shvartsman, Vladimir V; Salamon, Soma; Wende, Heiko; Trivedi, Harsh; Mumtaz, Arif; Lupascu, Doru C

    2016-01-01

    The lead-free ferroelectric 0.5Ba(Zr0.2Ti0.8)O3 - 0.5(Ba0.7Ca0.3)TiO3 (BCZT) is a promising component for multifunctional multiferroics due to its excellent room temperature piezoelectric properties. Having a composition close to the polymorphic phase boundary between the orthorhombic and tetragonal phases, it deserves a case study for analysis of its potential for modern electronics applications. To obtain magnetoelectric coupling, the piezoelectric phase needs to be combined with a suitable magnetostrictive phase. In the current article, we report on the synthesis, dielectric, magnetic, and magnetoelectric characterization of a new magnetoelectric multiferroic composite consisting of BCZT as a piezoelectric phase and CoFe2O4 (CFO) as the magnetostrictive phase. We found that this material is multiferroic at room temperature and manifests a magnetoelectric effect larger than that of BaTiO3 -CoFe2O4 bulk composites with similar content of the ferrite phase. PMID:27555563

  4. A new (Ba, Ca) (Ti, Zr)O3 based multiferroic composite with large magnetoelectric effect

    PubMed Central

    Naveed-Ul-Haq, M.; Shvartsman, Vladimir V.; Salamon, Soma; Wende, Heiko; Trivedi, Harsh; Mumtaz, Arif; Lupascu, Doru C.

    2016-01-01

    The lead-free ferroelectric 0.5Ba(Zr0.2Ti0.8)O3 − 0.5(Ba0.7Ca0.3)TiO3 (BCZT) is a promising component for multifunctional multiferroics due to its excellent room temperature piezoelectric properties. Having a composition close to the polymorphic phase boundary between the orthorhombic and tetragonal phases, it deserves a case study for analysis of its potential for modern electronics applications. To obtain magnetoelectric coupling, the piezoelectric phase needs to be combined with a suitable magnetostrictive phase. In the current article, we report on the synthesis, dielectric, magnetic, and magnetoelectric characterization of a new magnetoelectric multiferroic composite consisting of BCZT as a piezoelectric phase and CoFe2O4 (CFO) as the magnetostrictive phase. We found that this material is multiferroic at room temperature and manifests a magnetoelectric effect larger than that of BaTiO3 −CoFe2O4 bulk composites with similar content of the ferrite phase. PMID:27555563

  5. Magnetic behaviour of the MTbF{sub 6} fluoroterbates (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba)

    SciTech Connect

    Josse, M.; El-Ghozzi, M.; Avignant, D.; Andre, G.; Bouree, F.; Isnard, O.

    2012-01-15

    Neutron powder diffraction has been performed on the MTbF{sub 6} fluorides (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba). Four of these fluorides (Cd, Ca, Sr, {beta}-Ba) are built of a (pseudo-) tetragonal packing of [TbF{sub 6}]{sup 2-} chains and only differs by the chains relative orientations. Thus this series represents a valuable opportunity to evaluate the Tb{sup 4+}-Tb{sup 4+} magnetic interactions. All the compounds displayed antiferromagnetic order (T{sub N}=2.70 K (Cd), 2.15 K (Ca), 2.60 K (Sr), 2.10 K ({beta}-Ba)), except for the {alpha} form of BaTbF{sub 6}. The crystal structure of this latter fluoroterbate has also been investigated by means of high-resolution neutron powder diffraction. From Neutron Powder Diffraction data, CdTbF{sub 6} and {beta}-BaTbF{sub 6} magnetic structures were determined, together with the metamagnetic behaviour of {beta}-BaTbF{sub 6} as a function of an external magnetic field. A tentative phase diagram is then given for {beta}-BaTbF{sub 6}. Advantage was taken of the polymorphism of the BaTbF{sub 6} fluoroterbate to analyse, on the basis of topological parameters such as bond distances and angles, the magnetic behaviour of its {alpha} and {beta} forms. It was shown that superexchange interactions are present in {beta}-BaTbF{sub 6}, and that these interactions may also rule the magnetic behaviour of the other MTbF{sub 6} (M=Ca, Sr, Cd) tetravalent terbium fluorides. - Graphical abstract: Powder neutron diffraction revealed magnetic order in four of the five investigated fluoroterbates, while crystal chemical analyses of {alpha} and {beta} forms of BaTbF{sub 6} evidenced the existence of superexchange interactions. Highlights: Black-Right-Pointing-Pointer Five fluoroterbates are investigated by Powder Neutron Diffraction (PND). Black-Right-Pointing-Pointer Four of them are antiferromagnetically ordered at 1.4 K. Black-Right-Pointing-Pointer Magnetic structures of {beta}-BaTbF{sub 6} and CdTbF{sub 6} are determined. Black

  6. Aluminian Low-Ca Pyroxene in a Ca-Al-rich Chondrule from the Semarkona Meteorite

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.

    2006-01-01

    A Ca-AI-rich chondrule (labeled G7) from the Semarkona LL3.0 ordinary chondrite (OC) consists of 73 vol% glassy mesostasis, 22 vol% skeletal forsterite. 3 vol% fassaite (i.e., Al-Ti diopside), and 2 vol% Al-rich, low-Ca pyroxene. The latter phase, which contains up to 16.3 wt% A1203, is among the most AI-rich, low-Ca pyroxene grains ever reported. It is inferred that 20% of the tetrahedral sites and 13% of the octahedral sites in this grain are occupied by Al. Approximately parallel optical extinction implies that the Al-rich, low-Ca pyroxene grains are probably orthorhombic, consistent with literature data that show that A1203 stabilizes the orthoenstatite structure relative to protoenstatite at low pressure. The order of crystallization in the chondrule was forsterite, AI-rich low-Ca pyroxene, and fassaite; the residual liquid vitrified during chondrule quenching. Phase relationships indicate that, for a G7-composition liquid at equilibrium, spinel and anorthite should crystallize early and orthopyroxene should not crystallize at all. The presence of AI-rich orthopyroxene in G7 is due mainly to the kinetic failure of anorthite to crystallize; this failure was caused by quenching of the G7 precursor droplet. Aluminum preferentially enters the relatively large B tetrahedra of orthopyroxene; because only one tetrahedral size occurs in fassaite, this phase contains higher mean concentrations of Al2O3 than the Al-rich orthopyroxene (17.8 and 14.7 wt%, respectively). Chondrule G7 may have formed by remelting an amoeboid olivine inclusion that entered the OC region of the solar nebula during an episode of chondrule formation.

  7. Hardness of CaF2 and BaF2 solid lubricants at 25 to 670 deg C

    NASA Technical Reports Server (NTRS)

    Deadmore, Daniel L.; Sliney, Harold E.

    1987-01-01

    Plastic deformation is a prominent factor in determining the lubricating value of solid lubricants. Little information is available and its direct measurement is difficult so hardness, which is an indirect measure of this property was determined for fluoride solid lubricant compositions. The Vickers hardness of BaF2 and CaF2 single crystals was measured up to 670 C in a vacuum. The orientation of the BaF2 was near the (013) plane and the CaF2 was about 16 degrees from the degrees from the (1'11) plane. The BaF2 has a hardness of 83 kg/sq mm at the 25 C and 9 at the 600 C. The CaF2 is 170 at 25 C and 13 at 670 C. The decrease in hardness in the temperature range of 25 to 100 C is very rapid and amounts to 40% for both materials. Melts of BaF2 and CaF2 were made in a platinum crucible in ambient air with compositions of 50 to 100 wt% BaF2. The Vickers hardness of these polycrystalline binary compositions at 25 C increased with increasing CaF2 reaching a maximum of 150 kn/sq mm near the eutectic. The polycrystalline CaF2 was 14% softer than that of the single crystal surface and BsF2 was 30% harder than the single crystal surface. It is estimated that the brittle to ductile transition temperature for CaF2 and BaF2 is less than 100 C for the conditions present in the hardness tester.

  8. Rate of reactions between D 2O and Ca xAl yO z

    NASA Astrophysics Data System (ADS)

    Christensen, A. Nørlund; Lehmann, M. S.

    1984-02-01

    The rate of the reaction between D 2O and the calcium aluminum oxides Ca 3Al 2O 6, Ca 5Al 6O 14, CaAl 2O 4, and CaAl 4O 7 was investigated by on-line neutron diffraction powder methods at temperatures from room temperature to 100°C. The rate of the reaction increases with increasing calcium content of the compounds and with increasing temperature for each of the compounds. The crystallographic stable hydrate Ca 3Al 2(OD) 12 is obtained from CaAl 4O 7 and CaAl 2O 4 at temperatures above 63°C, from Ca 5Al 6O 14 at temperatures above 49°C, and from Ca 3Al 2O 6 at temperatures as low as 7°C.

  9. Solid-state combinatorial screening of (Sr,Ca,Ba, Mg)₂Si₅N₈:Eu(2+) phosphors.

    PubMed

    Lee, Bonghyun; Lee, Sangjun; Jeong, Hyung Gon; Sohn, Kee-Sun

    2011-03-14

    We employed a solid-state combinatorial chemistry technique to screen 4 ternary phosphor systems: (Sr,Ca,Ba)(2)Si(5)N(8):Eu(2+), (Sr,Ca,Mg)(2)Si(5)N(8):Eu(2+), (Sr,Mg,Ba)(2)Si(5)N(8):Eu(2+), and (Ca,Ba,Mg)(2)Si(5)N(8):Eu(2+). The current pure nitride-based system did not allow for the use of conventional liquid solution-based high-throughput experimentation, so that a specially designed solid-state high-throughput powder-dispensing synthesis technique was employed. As a result, four well-defined ternary combinatorial libraries were developed in terms of photoluminescent (PL) intensity and color chromaticity with no skipped compositions, which provided a quantitative relationship between PL properties and the composition of AE(2)Si(5)N(8):Eu(2+) (AE = alkaline earth elements) phosphors. PMID:21275428

  10. The LO-BaFL method and ALS microarray expression analysis

    PubMed Central

    2012-01-01

    Background Sporadic Amyotrophic Lateral Sclerosis (sALS) is a devastating, complex disease of unknown etiology. We studied this disease with microarray technology to capture as much biological complexity as possible. The Affymetrix-focused BaFL pipeline takes into account problems with probes that arise from physical and biological properties, so we adapted it to handle the long-oligonucleotide probes on our arrays (hence LO-BaFL). The revised method was tested against a validated array experiment and then used in a meta-analysis of peripheral white blood cells from healthy control samples in two experiments. We predicted differentially expressed (DE) genes in our sALS data, combining the results obtained using the TM4 suite of tools with those from the LO-BaFL method. Those predictions were tested using qRT-PCR assays. Results LO-BaFL filtering and DE testing accurately predicted previously validated DE genes in a published experiment on coronary artery disease (CAD). Filtering healthy control data from the sALS and CAD studies with LO-BaFL resulted in highly correlated expression levels across many genes. After bioinformatics analysis, twelve genes from the sALS DE gene list were selected for independent testing using qRT-PCR assays. High-quality RNA from six healthy Control and six sALS samples yielded the predicted differential expression for 7 genes: TARDBP, SKIV2L2, C12orf35, DYNLT1, ACTG1, B2M, and ILKAP. Four of the seven have been previously described in sALS studies, while ACTG1, B2M and ILKAP appear in the context of this disease for the first time. Supplementary material can be accessed at: http://webpages.uncc.edu/~cbaciu/LO-BaFL/supplementary_data.html. Conclusion LO-BaFL predicts DE results that are broadly similar to those of other methods. The small healthy control cohort in the sALS study is a reasonable foundation for predicting DE genes. Modifying the BaFL pipeline allowed us to remove noise and systematic errors, improving the power of this

  11. Magnetic field penetration depth of superconducting aluminum-substituted Ba8Si42Al4 clathrate

    NASA Astrophysics Data System (ADS)

    Li, Yang; Garcia, Jose; Franco, Giogiovanni

    2014-03-01

    During past years, efforts have been made to explore the superconductivity of Group IV clathrates with particular attention to the sp3 hybridized networks. In the study, we report on the superconductivity of Al-substituted type-I silicon clathrates. Pure phase samples of the general formula Ba8Si46-xAlx with different values of x were synthesized. The magnetic susceptibility measurements show that Ba8Si42Al4 is a bulk superconductor, with an onset at Tc =6 K. Al substitution results in a large decrease of the electronic density of states at the Fermi level, which explains the decreased superconducting critical temperature within the BCS framework. To further characterize the superconducting state, we carried out magnetic measurements showing Ba8Si42Al4 to be a type II superconductor. The critical magnetic fields were measured to be Hc1 = 77 Oe and Hc2 = 40 kOe. We deduce the London penetration depth 2900 Å and the coherence length 90 Å. Our estimate of the electron-phonon coupling reveals that Ba8Si42Al4 is a moderate phonon-mediated BCS superconductor. NASA PRSG IDEAS-ER Program(Granted No. NNX10AM80H).

  12. Fluorescence and phosphorescence properties of the low temperature forms of the MAl{sub 2}Si{sub 2}O{sub 8}:Eu{sup 2+} (M=Ca, Sr, Ba) compounds

    SciTech Connect

    Clabau, Frederic; Garcia, Alain; Bonville, Pierre; Gonbeau, Danielle; Le Mercier, Thierry; Deniard, Philippe; Jobic, Stephane

    2008-06-15

    The fluorescence and phosphorescence properties of Europium-doped MAl{sub 2}Si{sub 2}O{sub 8} (M=Ca, Sr, Ba) are reinvestigated and discussed on the basis of the propensity of an activator to agglomerate with an oxygen vacancy. Due to a stronger attraction of the anion vacancy towards Eu{sup 2+} cations going from BaAl{sub 2}Si{sub 2}O{sub 8} to SrAl{sub 2}Si{sub 2}O{sub 8} and CaAl{sub 2}Si{sub 2}O{sub 8} host lattices, the interpretation of the fluorescence spectra turns out to be less trivial in the Ca and Sr host lattices than in the Ba one and requests the account for Eu{sup 2+} cations lying at alkaline-earth sites with or without vacancy in their neighborhood. Phosphorescence in these compounds is highlighted. - Graphical abstract: The Eu{sup 2+}-doped MAl{sub 2}Si{sub 2}O{sub 8} (M=Ca, Sr, and Ba) aluminosilicates exhibit a bluish white luminescence, which can last several minutes after the removal of the excitation. The account for Eu{sup 2+} cations coupled with defects is required to explain fluorescence spectra.

  13. Co{sub 2}FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    SciTech Connect

    Rogge, J.; Schmalhorst, J.; Hütten, A.; Hetaba, W.

    2015-07-15

    We succeed to integrate BaO as a tunneling barrier into Co{sub 2}FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co{sub 2}FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  14. Al-Ca and Al-Fe metal-metal composite strength, conductivity, and microstructure relationships

    SciTech Connect

    Kim, Hyong June

    2011-01-01

    Deformation processed metal-metal composites (DMMC’s) are composites formed by mechanical working (i.e., rolling, swaging, or wire drawing) of two-phase, ductile metal mixtures. Since both the matrix and reinforcing phase are ductile metals, the composites can be heavily deformed to reduce the thickness and spacing of the two phases. Recent studies have shown that heavily drawn DMMCs can achieve anomalously high strength and outstanding combinations of strength and conductivity. In this study, Al-Fe wire composite with 0.07, 0.1, and 0.2 volume fractions of Fe filaments and Al-Ca wire composite with 0.03, 0.06, and 0.09 volume fractions of Ca filaments were produced in situ, and their mechanical properties were measured as a function of deformation true strain. The Al-Fe composites displayed limited deformation of the Fe phase even at high true strains, resulting in little strengthening effect in those composites. Al-9vol%Ca wire was deformed to a deformation true strain of 13.76. The resulting Ca second-phase filaments were deformed to thicknesses on the order of one micrometer. The ultimate tensile strength increased exponentially with increasing deformation true strain, reaching a value of 197 MPa at a true strain of 13.76. This value is 2.5 times higher than the value predicted by the rule of mixtures. A quantitative relationship between UTS and deformation true strain was determined. X-ray diffraction data on transformation of Al + Ca microstructures to Al + various Al-Ca intermetallic compounds were obtained at the Advanced Photon Source at Argonne National Laboratory. Electrical conductivity was measured over a range of true strains and post-deformation heat treatment schedules.

  15. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure

    PubMed Central

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Do Kim, Keum; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-01

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization – voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization. PMID:26742878

  16. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure.

    PubMed

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Kim, Keum Do; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-01

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization - voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization. PMID:26742878

  17. Vortex fluctuation in HgBa 2Ca 3Cu 4O 10+δ

    NASA Astrophysics Data System (ADS)

    Kim, Mun-Seog; Kim, Wan-Seon; Lee, Sung-Ik; Yu, Seong-Cho; Itskevich, E. S.; Kuzemskaya, I.

    1997-08-01

    Reversible magnetization with the external magnetic fields of 1 T ≤ H ≤ 5 T parallel to the c-axis has been measured for the grain aligned HgBa2Ca3Cu4O10+δ. A strong vortex fluctuation effect was clearly observed and the magnetization is well described by the vortex fluctuation model. From this analysis, the penetration depth λab(0) = 1583 Å and the effective interlayer spacing s = 44.6 Å were estimated. However, the value of s is significantly larger than the lattice parameter c = 19 Å, which is different from the prediction of the vortex fluctuation model. From the model on superconducting fluctuations proposed by Koshelev, in which not only the critical fluctuations at the lowest Landau level but also the Gaussian fluctuations at higher Landau levels were considered, the different value of s = 15.4 Å was obtained.

  18. Liquid Be, Ca and Ba. An orbital-free ab-initio molecular dynamics study

    SciTech Connect

    Rio, B. G. del; González, L. E.

    2015-08-17

    Several static and dynamic properties of liquid beryllium (l-Be), liquid calcium (l-Ca) and liquid barium (l-Ba) near their triple point have been evaluated by the orbital-free ab initio molecular dynamics method (OF-AIMD), where the interaction between valence electrons and ions is described by means of local pseudopotentials. These local pseudopotentials used were constructed through a force-matching process with those obtained from a Kohn-Sham ab initio molecular dynamics study (KS-AIMD) of a reduced system with non-local pseudopotentials. The calculated static structures show good agreement with the available experimental data, including an asymmetric second peak in the structure factor which has been linked to the existence of a marked icosahedral short-range order in the liquid. As for the dynamic properties, we obtain collective density excitations whose associated dispersion relations exhibit a positive dispersion.

  19. Performance of TlCaBaCuO 30 GHz 64 element antenna array

    NASA Technical Reports Server (NTRS)

    Lewis, L. L.; Koepf, G.; Bhasin, K. B.; Richard, M. A.

    1993-01-01

    A 64-element, 30-GHz microstrip antenna array with corporate feed network was designed and built on a 0.254-mm (10-mil) thick lanthanum aluminate substrate. One antenna pattern was fabricated from gold film, and a second pattern used TlCaBaCuO high-temperature superconductor. Both antennas used gold ground planes deposited on the reverse side of the substrate. Gain and radiation patterns were measured for both antennas at room temperature and at cryogenic temperatures. Observations agree well with simple models for loss and microwave beam width, with a gain on boresight of 20.3 dB and beam width of 15 deg for the superconducting antenna. The antenna loss is only 1.9 dB.

  20. Transformation of Ba-Al-Si precursors to celsian by high-temperature oxidation and annealing

    NASA Astrophysics Data System (ADS)

    Schmutzler, Hans J.; Sandhage, Kenneth H.

    1995-02-01

    Celsian (monoclinic BaO · A12O3 · 2SiO2) is being considered as a matrix material for ceramic composites used in high-temperature structural applications. The present article describes the synthesis of celsian by the oxidation and annealing of solid, malleable, metallic Ba-Al-Si precursors. The phase and microstructural evolution after various stages of oxidation at 300 °C to 1260 °C in pure oxygen at 1 atm pressure have been examined by X-ray diffraction (XRD) and electron microprobe analyses (EPMA). Barium peroxide, BaO2, formed rapidly during oxidation at 300 °C, with aluminum and silicon remaining largely as unoxidized particles in a BaO2 matrix. Between 300 °C and 500 °C, barium orthosilicate, Ba2Si04, formed by a solid-state reaction between barium peroxide and unoxidized silicon. Further exposure to temperatures between 500 °C and 1200 °C resulted in the oxidation of aluminum and of residual silicon. The oxidized silicon reacted with the barium orthosilicate matrix to yield higher silica-containing barium silicates that, in turn, reacted with alumina or mullite to form metastable hexacelsian (hexagonal BaO-A12O3 · 2SiO2). Celsian was then obtained by further exposure to peak temperatures ≤1260°C.

  1. LiCaAl/sub 6/:Cr/sup 3+/

    SciTech Connect

    Payne, S.A.; Chase, L.L.; Newkirk, H.W.; Smith, L.K.; Krupke, W.F. )

    1988-11-01

    The authors report the discovery of a new laser, LiCaAIF/sub 6/:Cr/sup 3/ (Cr/sup 3+/ :LiCAF). The intrinsic (extrapolated maximum) slope efficiency was found to be 67 percent. For comparison, they also measured the intrinsic slope efficiencies of BeAl/sub 2/O/sub 4/:Cr/sup 3+/ (alexandrite), Na/sub 3/Ga/sub 2/Li/sub 3/F/sub 12/:Cr/sup 3+/, and ScBO/sub 3/:Cr/sup 3+/, and obtained values of 65,28, and 26 percent, respectively. The tuning range of LiCaAIF/sub 6/:Cr/sup 3+/ was determined to be at least 720-840 nm. The conventional spectroscopic properties, such as the absorption, emission, and emission lifetimes as a function of temperature, are reported as well.

  2. Polymorphic structure evolution and large piezoelectric response of lead-free (Ba,Ca)(Zr,Ti)O{sub 3} ceramics

    SciTech Connect

    Tian, Ye; Chao, Xiaolian E-mail: yangzp@snnu.edu.cn; Wei, Lingling; Liang, Pengfei; Yang, Zupei E-mail: yangzp@snnu.edu.cn; Jin, Li

    2014-03-17

    The polymorphic structure evolution of (Ba,Ca)(Zr,Ti)O{sub 3} piezoelectric ceramics was investigated by analysis of the in situ X-ray diffraction and dielectric spectra. The results indicated that a confined orthorhombic (O) phase region induced by the approach of the rhombohedral (R) and tetragonal (T) phases existed in an extremely narrow temperature range of (Ba{sub 0.85}Ca{sub 0.15})(Zr{sub 0.1}Ti{sub 0.9})O{sub 3} composition. The electric properties near the O–T phase boundaries of (Ba{sub 0.95}Ca{sub 0.05})(Zr{sub 0.05}Ti{sub 0.95})O{sub 3} and (Ba{sub 0.85}Ca{sub 0.15})(Zr{sub 0.1}Ti{sub 0.9})O{sub 3} were compared. The results suggested that the confined O phase region is an important factor that contributes to the extremely large piezoelectric response.

  3. Evaluation of minimum yields for planar channeling in CaF 2 and BaF 2

    NASA Astrophysics Data System (ADS)

    Saitoh, Kazuo; Kobayakawa, Mikio; Niwa, Hiroaki; Tanemura, Seita

    1980-04-01

    Minimum yields for planar channeling in CaF 2 and BaF 2 have been calculated using an average potential model. The use of the Lentz-Jensen ionic potential gives results consistent with the experimental data. The validity of the model and the dependence of the minimum yields on the potential are discussed.

  4. Dielectric properties of (CuO, CaO2, and BaO)y/CuTl-1223 composites

    NASA Astrophysics Data System (ADS)

    Mumtaz, M.; Kamran, M.; Nadeem, K.; Jabbar, Abdul; Khan, Nawazish A.; Saleem, Abida; Tajammul Hussain, S.; Kamran, M.

    2013-07-01

    We synthesized (CuO, CaO2, and BaO)y/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (y = 0, 5%, 10%, 15%) composites by solid-state reaction and characterized them by x-ray diffraction, scanning electron microscopy, dc-resistivity, and Fourier transform infrared spectroscopy. Frequency and temperature dependent dielectric properties, such as real and imaginary parts of the dielectric constant, dielectric loss, and ac-conductivity of these composites were studied by capacitance and conductance measurements as a function of frequency (10 kHz to 10 MHz) and temperature (78 to 300 K). X-ray diffraction analysis reveals that the characteristic behavior of the superconductor phase and the structure of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ are nearly undisturbed by doping with nanoparticles. Scanning electron microscopy images show the improvement in the intergranular linking between the superconducting grains occurring with increasing nanoparticle concentration. Microcracks are healed up with these nanoparticles, and superconducting volume fraction is also increased. Dielectric properties of these composites strongly depend on the frequency and temperature. Zero resistivity critical temperature and dielectric properties show opposite trends with the addition of nanoparticles to the Cu0.5Tl0.5Ba2Ca2Cu3O10-δ superconductor matrix.

  5. Relaxor behavior of (Ba,Bi)(Ti,Al)O3 ferroelectric ceramic

    NASA Astrophysics Data System (ADS)

    Cui, Lei; Hou, Yu-Dong; Wang, Sai; Wang, Chao; Zhu, Man-Kang

    2010-03-01

    Perovskite type (Ba0.9Bi0.1)(Ti0.9Al0.1)O3 (BBTA) ceramics have been prepared through solid state reaction route. The room temperature x-ray diffraction study suggests that BBTA ceramics have single phase tetragonal symmetry with space group P4mm. In contrast to the sharp dielectric transition of pure BaTiO3, a broad dielectric anomaly coupled with the shift in dielectric maxima toward a higher temperature with increasing frequency has been observed in BBTA. The quantitative characterization based on empirical parameters (ΔTm, γ, ΔTrelax, and ΔTdiffuse(1 kHz)) confirms its relaxor nature. The dielectric relaxation which follows the Vogel-Fulcher relationship with Eα=0.011 eV, Tf=356 K, and f0=1.38×1010 Hz, further supports spin-glass-like characteristics. In this system, the relaxor behavior can be attributed to the dynamic response of the polar clusters induced by the combined substitutions of Bi3+ and Al3+ on the Ba2+ and Ti4+ site. Moreover, the curie temperature of BBTA shows the decreasing trend compared to that of pure BaTiO3, which doesn't follow the normal Vegard's law, confirming that no BiAlO3 sublattice formed in BBTA. All these features indicate that BBTA is a promising candidate for lead-free relaxors.

  6. Temperature driven nano-domain evolution in lead-free Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 piezoceramics

    NASA Astrophysics Data System (ADS)

    Lu, Shengbo; Xu, Zhengkui; Su, Shi; Zuo, Ruzhong

    2014-07-01

    Hierarchical micro- and nanoscale domain structures in Pb-free Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 piezoceramics were investigated by transmission electron microscopy. In situ heating and cooling studies of domain structure evolution reveal an irreversible domain transformation from a wedge-shaped rhombohedral nanodomain structure to a lamellar tetragonal domain structure, which could be associated with strong piezoelectricity in Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 piezoceramics.

  7. Quantum Chemical Design of Doped Ca2MnAlO(5+δ) as Oxygen Storage Media.

    PubMed

    Ling, Chen; Zhang, Ruigang; Jia, Hongfei

    2015-07-01

    Brownmillerite Ca2MnAlO5 has an exceptional capability to robustly adsorb half-molecules of oxygen and form Ca2MnAlO5.5. To utilize this unique property to regulate oxygen-involved reactions, it is crucial to match the oxygen release-intake equilibrium with targeted reaction conditions. Here we perform a comprehensive investigation of the strategy of tuning the oxygen storage property of Ca2MnAlO5 through chemical doping. For undoped Ca2MnAlO5+δ, our first-principles calculation predicts that the equilibrium temperature at a pressure of 1 atm of O2 is 848 K, which is in excellent agreement with experimental results. Furthermore, the doping of alkaline earth ions at the Ca site, trivalent ions at the Al site, and 3d transition metal ions at the Mn site is analyzed. By the doping of 12.5% of Ga, V, and Ti, the equilibrium temperature shifts to high values by approximately 110-270 K, while by the doping of 12.5% of Fe, Sr, and Ba, the equilibrium temperature is lowered by approximately 20-210 K. The doping of these elements is thermodynamically stable, and doping other elements including Mg, Sc, Y, Cr, Co, and Ni generates metastable compounds. The doping of a higher content of Fe, however, lowers the oxygen storage capacity. Finally, on the basis of our calculated data, we prove that the formation energetics of nondilute interacting oxygen vacancy in doped Ca2MnAlO5.5 scale linearly with a simple descriptor, the oxygen p-band position relative to the Fermi level. The higher-oxygen p-band position leads to a lower vacancy formation energy and thus a lower oxygen release temperature. Understanding such a relationship between fundamental quantum chemical properties and macroscopic properties paves the road to the design and optimization of novel functional oxides. PMID:26066573

  8. Effect of reaction time and (Ca+Mg)/Al molar ratios on crystallinity of Ca-Mg-Al layered double Hydroxide

    NASA Astrophysics Data System (ADS)

    Heraldy, E.; Nugrahaningtyas, K. D.; Sanjaya, F. B.; Darojat, A. A.; Handayani, D. S.; Hidayat, Y.

    2016-02-01

    Ca-Mg-Al Layered Double Hydroxides (Ca-Mg-Al-LDH) compounds were successfully synthesized from brine water and AlCl3.6H2O as the starting materials by coprecipitation method. The product result was characterized by X-ray powder diffraction (XRD) and Fourier transform infrared (FT-IR). The effects of the reaction time and the molar ratios of the raw material on the crystallinity of Ca-Mg-Al-LDH were examining. Results show that increasing reaction time (30; 60 and 90 min.) could improve the crystallinity and monodispersity of layered double hydroxide compounds particles. The well-defined Ca-Mg- Al-LDH could be prepared with (Ca+Mg)/Al molar ratios 0.5.

  9. Light-Emitting Characteristics of Organic Light-Emitting Diodes with Ba/Al Cathode and Effect of Ba Thickness by Measuring their Built-in Potential

    NASA Astrophysics Data System (ADS)

    Lim, Jong Tae; Yeom, Geun Young

    2009-12-01

    The electronic nature of metal-organic semiconductor contacts is a fundamental issue in the field of organic semiconductor device physics, because these contacts control the charge injection. The built-in potential in organic light-emitting diodes (OLEDs) with a Ba/Al cathode was investigated by using the modulated photocurrent technique. To measure the built-in potential, a device with a glass/tin-doped indium oxide (ITO)/tris(8-quinolinolato)aluminum (III) (Alq3, 150 nm)/Ba (x nm, x=3, 2, 1, and 0)/Al (150 nm) structure was fabricated and encapsulated in a nitrogen atmosphere. The device with Ba/Al cathode showed a higher built-in potential, compared with the Al-only device, which reduced the barrier height for electron injection from the Ba/Al cathode to Alq3. For the device with a Ba thickness of 3 nm, the barrier height for electron injection showed a low value of 0.1 eV. On the basis of the built-in potential data, the device with the ITO/4,4',4''-tris(2-naphthylphenyl-1-phenylamino)triphenylamine (2-TNATA, 30 nm)/4,4'-bis(N-(1-napthyl)-N-phenyl-amino)-biphenyl (NPB, 18 nm)/Alq3 (62 nm)/Ba (3 nm)/Al (100 nm) structure showed the best characteristics with the highest luminance of 54,000 cd/m2 and the highest efficiency of 2.7 lm/W, as compared to the other devices with Ba thicknesses of less than 3 nm.

  10. Ca(AlH4)2, CaAlH5, and CaH2+6LiBH4: Calculated dehydrogenation enthalpy, including zero point energy, and the structure of the phonon spectra.

    PubMed

    Marashdeh, Ali; Frankcombe, Terry J

    2008-06-21

    The dehydrogenation enthalpies of Ca(AlH(4))(2), CaAlH(5), and CaH(2)+6LiBH(4) have been calculated using density functional theory calculations at the generalized gradient approximation level. Harmonic phonon zero point energy (ZPE) corrections have been included using Parlinski's direct method. The dehydrogenation of Ca(AlH(4))(2) is exothermic, indicating a metastable hydride. Calculations for CaAlH(5) including ZPE effects indicate that it is not stable enough for a hydrogen storage system operating near ambient conditions. The destabilized combination of LiBH(4) with CaH(2) is a promising system after ZPE-corrected enthalpy calculations. The calculations confirm that including ZPE effects in the harmonic approximation for the dehydrogenation of Ca(AlH(4))(2), CaAlH(5), and CaH(2)+6LiBH(4) has a significant effect on the calculated reaction enthalpy. The contribution of ZPE to the dehydrogenation enthalpies of Ca(AlH(4))(2) and CaAlH(5) calculated by the direct method phonon analysis was compared to that calculated by the frozen-phonon method. The crystal structure of CaAlH(5) is presented in the more useful standard setting of P2(1)c symmetry and the phonon density of states of CaAlH(5), significantly different to other common complex metal hydrides, is rationalized. PMID:18570508

  11. Crystallization kinetics of BaO-Al2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.

    1988-01-01

    Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

  12. Crystallization kinetics of BaO-Al2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.

    1989-01-01

    Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

  13. Anomalous phonon properties in the silicide superconductors CaAlSi and SrAlSi

    NASA Astrophysics Data System (ADS)

    Kuroiwa, S.; Hasegawa, T.; Kondo, T.; Ogita, N.; Udagawa, M.; Akimitsu, J.

    2008-11-01

    Lattice-dynamical properties of CaAlSi and SrAlSi with a similar layer structure to MgB2 have been first investigated by both Raman-scattering and ab initio calculations. All Raman-active phonons with E' symmetry have been clearly observed for both compounds. Their line shapes are asymmetric but their linewidths are ˜10cm-1 , which is very narrower than that of MgB2 . In addition to the Raman-active modes, several extra peaks have been observed below 160cm-1 . These low-energy extra modes can be assigned to the out-of-plane vibrations of Al perpendicular to Al-Si basal plane. Since these peak intensities are strongly affected by the incident energy (resonance Raman process), the electronic state is important for them. Moreover, in both crystals of CaAlSi and SrAlSi, we point out the energy difference for the different propagation directions along the c axis and the c plane, in spite of the very close wave vector to the Brillouin-zone center. This energy difference cannot be explained by a usual Raman-scattering scenario at this stage.

  14. Estimation Model for Electrical Conductivity of CaF2-CaO-Al2O3 Slags

    NASA Astrophysics Data System (ADS)

    Shi, Guan-yong; Zhang, Ting-an; Dou, Zhi-he; Niu, Li-ping

    2016-04-01

    Electrical conductivity is one of the most important properties of molten slags. It has an important influence on process parameter selection of the electroslag remelting process. In the present work, a new model for estimating electrical conductivity of high-temperature slags has been proposed via calculating the conductivity by electrical conductivity of pure substances and interaction parameters between the different components in the slag has been proposed. In this model, the Arrhenius law is used to describe the relationship between electrical conductivity and temperature of slags. This model has been successfully applied to the CaF2-Al2O3, CaF2-CaO, and CaO-Al2O3, as well as CaF2-CaO-Al2O3 systems, and the calculated results are in good agreement with the measured values.

  15. On the microstructure and symmetry of apparently hexagonal BaAl 2O 4

    NASA Astrophysics Data System (ADS)

    Larsson, A.-K.; Withers, R. L.; Perez-Mato, J. M.; Fitz Gerald, J. D.; Saines, P. J.; Kennedy, B. J.; Liu, Y.

    2008-08-01

    The P6 3 ( a=2 ap, b=2 bp, c= cp) crystal structure reported for BaAl 2O 4 at room temperature has been carefully re-investigated by a combined transmission electron microscopy and neutron powder diffraction study. It is shown that the poor fit of this P6 3 ( a=2 ap, b=2 bp, c= cp) structure model for BaAl 2O 4 to neutron powder diffraction data is primarily due to the failure to take into account coherent scattering between different domains related by enantiomorphic twinning of the P6 322 parent sub-structure. Fast Fourier transformation of [0 0 1] lattice images from small localized real space regions (˜10 nm in diameter) are used to show that the P6 3 ( a=2 ap, b=2 bp, c= cp) crystal structure reported for BaAl 2O 4 is not correct on the local scale. The correct local symmetry of the very small nano-domains is most likely orthorhombic or monoclinic.

  16. Energy transfer between Eu-Mn and photoluminescence properties of Ba0.75Al11O17.25-BaMgAl10O17:Eu2+,Mn2+ solid solution

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Wang, Yuhua; Liu, Bitao; Li, Feng

    2010-08-01

    In order to evaluate the energy transfer between Eu-Mn in Ba0.75Al11O17.25-BaMgAl10O17 solid solution, Ba0.75Al11O17.25-BaMgAl10O17:Eu2+,Mn2+ phosphors were prepared by flux method. The crystal structure and the morphology of the solid solution were demonstrated by x-ray dirrfactometer and scanning electron microscopy. The photoluminescence mechanisms were explained by the energy transfer of Eu2+ to Mn2+ and the Dexter theory. A redshift of green emission peak and a decrease in decay time with the increase in Mn2+ concentration were observed. These phenomena are attributed to the formation of Mn2+ paired centers after analysis by a method of Pade approximations.

  17. Actinide chemistry in Allende Ca-Al-rich inclusions

    NASA Astrophysics Data System (ADS)

    Murrell, M. T.; Burnett, D. S.

    1987-04-01

    Fission track radiography is used to investigate the U and Th microscale distribution in a set of Allende-meteorite Ca-Al-rich inclusions. In the Type B inclusions, the major phases melilite and fassaite are important actinide host phases, and on the rims of Type B inclusions and throughout all other inclusions studied, perovskite is the dominant actinide host phase. Results suggest that neither alteration nor loss or gain of an actinide-rich phase appears to have been an important Th/U fractionation mechanism, and that volatility differences may be the dominant factor. Th/U and rare earth element abundance patterns for the spinel and perovskite rim suggest rim formation by volatilization of interior material, and within the constraints of the brief time scale required for this heating, several mechanisms for spinel-perovskite rim formation are possible.

  18. Actinide chemistry in Allende Ca-Al-rich inclusions

    NASA Technical Reports Server (NTRS)

    Murrell, M. T.; Burnett, D. S.

    1987-01-01

    Fission track radiography is used to investigate the U and Th microscale distribution in a set of Allende-meteorite Ca-Al-rich inclusions. In the Type B inclusions, the major phases melilite and fassaite are important actinide host phases, and on the rims of Type B inclusions and throughout all other inclusions studied, perovskite is the dominant actinide host phase. Results suggest that neither alteration nor loss or gain of an actinide-rich phase appears to have been an important Th/U fractionation mechanism, and that volatility differences may be the dominant factor. Th/U and rare earth element abundance patterns for the spinel and perovskite rim suggest rim formation by volatilization of interior material, and within the constraints of the brief time scale required for this heating, several mechanisms for spinel-perovskite rim formation are possible.

  19. Enhanced high temperature performance of MgAl2O4-supported Pt-BaO lean NOx trap catalysts

    SciTech Connect

    Kwak, Ja Hun; Kim, Do Heui; Szanyi, Janos; Cho, Sung June; Peden, Charles HF

    2012-03-05

    The structural and chemical characteristics of Pt/BaO lean-NO{sub x} trap (LNT) catalysts supported on {gamma}-Al{sub 2}O{sub 3} and MgAl{sub 2}O{sub 4} are compared in this study. The Pt-BaO/MgAl{sub 2}O{sub 4} sample shows relatively low NO{sub x} uptake at temperatures below 300 C, and the temperature of maximum NO{sub x} uptake (T{sub max}) is shifted to 350 C in comparison to that of Pt-BaO/Al{sub 2}O{sub 3} (T{sub max} {approx}250 C). More importantly, the NO{sub x} uptake over the MgAl{sub 2}O{sub 4}-supported catalyst at 350 C is twice that of the alumina-based one. The shift toward the higher temperature NO{sub x} uptake is explained by the larger interfacial area between Pt and BaO, due to smaller Pt clusters as evidenced by TEM and Pt L3 EXAFS. In situ TR-XRD results demonstrate that the formation of a BaAl{sub 2}O{sub 4} phase in the BaO/MgAl{sub 2}O{sub 4} LNT catalyst occurs at a temperature about 100 C higher than on BaO/Al{sub 2}O{sub 3}, which may also represent a beneficial attribute of the BaO/MgAl{sub 2}O{sub 4} LNT with respect to catalyst stability.

  20. The effect of Al-substitution on superconducting type-I clathrate Ba8Si46

    NASA Astrophysics Data System (ADS)

    Liu, Lihua; Bi, Shanli; Chen, Ning; Li, Feng; Liu, Yang; Cao, Guohui; Li, Yang

    2014-11-01

    A series of samples with the chemical formula Ba8Si46-xAlx (x = 2, 3, 5, 6, 7 and 8) were prepared by arc melting, ball milling and washing with diluted HCl. The lattice parameter of Ba8Si46-xAlx increases linearly with the increase of nominal Al content x. The composition analysis by energy-dispersive X-ray spectroscopy (EDS) shown that the actual Al contents in clathrates are lager than the nominal compositions because the dilute Al-contained impurity phases were washed out. The experimental results show that the minimum incorporation of Al into clathrate structure is expected to be about 3 at ambient pressure, which is in agreement with a first-principle simulation. The Al substitution for Si results in the decrease of superconducting transition temperature TC, which can be explained on the BCS theoretical frame. The electron density of state at Fermi level N(EF) decreases with the increment of x except for an abnormal increase for the sample x = 6. Such sample has a higher spatial symmetry of the structure in which all the six Si atoms at 6c sites were substituted by Al atoms. Its higher N(EF) causes to a higher TC. In addition, we calculated the phonon-dispersion relations and vibrational density of states for Al-doped silicon clathrates. The high frequency acoustic branch has a red shift from 430 cm-1 to 420 cm-1 with the doping of Al. The decreased frequency of bond-stretching vibration modes is another reason for the suppression of TC induced by Al substitution.

  1. Resonant Ultrasound studies of double perovskites A2FeReO6 (A=Ba, Ca)

    NASA Astrophysics Data System (ADS)

    Li, Ling; Yan, Jiaqiang; Mandrus, David; Keppens, Veerle

    2013-03-01

    The elastic response as a function of temperature (50-380) K and magnetic field (0-2) T has been studied using Resonant Ultrasound Spectroscopy (RUS) for the polycrystalline double perovskites A2FeReO6 (A= Ba, Ca). An elastic softening over a wide temperature range is observed below the Curie temperature (Tc ~ 305K) of Ba2FeReO6, which is suppressed upon the application of a magnetic field. For Ca2FeReO6, both the longitudinal and shear modulus show a step-like softening starting around 140K, indicative of a structural transition. A large change in the magnetoelastic coupling constant is observed at this temperature, suggesting that this transition is strongly coupled to the magnetic properties of this material. Work at ORNL was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

  2. Structure and Properties of Egyptian Blue Monolayer Family: XCuSi4O10 (X = Ca, Sr, and Ba).

    PubMed

    Chen, Yu; Kan, Min; Sun, Qiang; Jena, Puru

    2016-02-01

    Motivated by the recent experimental advances in exfoliating Egyptian blue monolayers, we have carried out extensive calculations using density functional theory to understand their geometry, stability, mechanical properties, electronic structures, and magnetism. Upon exfoliation from the bulk, XCuSi4O10 (X = Ca, Sr, and Ba) monolayers are found to change symmetry from tetragonal to orthorhombic. They all satisfy Born criteria and are mechanically stable. Each Cu site carries a magnetic moment of 1.0 μB but with degenerate ferromagnetic and antiferromagnetic coupling states. From Ca to Sr and Ba, as the atomic number increases, the thickness, elastic constants, Young's moduli, and Poisson's ratios of the monolayers increase, while the band gaps decrease. Applying strain can tune the magnitude of energy band gaps, but the direct gap feature remains. Complementing the widely studied graphene, MXenes, black phosphorus, and dichalcogenide sheets, the Egyptian blue monolayers add additional features to the family of two-dimensional materials. PMID:26763651

  3. Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae=Ca,Sr,Ba, as thermoelectric materials

    SciTech Connect

    Parker, David S; Singh, David J

    2013-01-01

    We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2 Sn, Sr2 Sn and Ba2 Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli - roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.

  4. Electrochemical properties of mixed conducting (La,M)(CoFe) oxide perovskites (M=3DSr, Ca, and Ba)

    SciTech Connect

    Stevenson, J.W.; Armstrong, T.R.; Bates, J.L.

    1996-04-01

    Electrical properties and oxygen permeation properties of solid mixed-conducting electrolytes (La,M)(CoFe) oxide perovskites (M=3DSr, Ca, and Ba) have been characterized. These materials are potentially useful as passive membranes to separate high purity oxygen from air and as the cathode in a fuel cell. Dilatometric linear expansion measurements were performed as a function of temperature and oxygen partial pressure to evaluate the stability.

  5. Monte Carlo Simulation of Gamma-Ray Response of BaF2 and CaF2

    SciTech Connect

    Gao, Fei; Xie, YuLong; Wang, Zhiguo; Kerisit, Sebastien N.; Wu, Dangxin; Campbell, Luke W.; Van Ginhoven, Renee M.; Prange, Micah P.

    2013-12-01

    We have employed a Monte Carlo (MC) method to study intrinsic properties of two alkaline-earth halides, namely BaF2 and CaF2, relevant to their use as radiation detector materials. The MC method follows the fate of individual electron-hole (e-h) pairs and thus allows for a detailed description of the microscopic structure of ionization tracks created by incident γ-ray radiation. The properties of interest include the mean energy required to create an e-h pair, W, Fano factor, F, the maximum theoretical light yield, and the spatial distribution of e-h pairs resulting from γ-ray excitation. Although W and F vary with incident photon energy at low energies, they tend to constant values at energies higher than 1 keV. W is determined to be 18.9 and 19.8 eV for BaF2 and CaF2, respectively, in agreement with published data. The e-h pair spatial distributions exhibit a linear distribution along the fast electron tracks with high e-h pair densities at the end of the tracks. Most e-h pairs are created by interband transition and plasmon excitation in both scintillators, but the e-h pairs along fast electron tracks in BaF2 are slightly clustered, forming nanoscale domains and resulting in the higher e-h pair densities than in CaF2. Combining the maximum theoretical light yields calculated for BaF2 and CaF2 with those obtained for CsI and NaI shows that the theoretical light yield decreases linearly with increasing band gap energy.

  6. Cluster Chemistry in Electron-Poor Ae-Pt-Cd Systems (Ae=Ca, Sr, Ba): (Sr,Ba)Pt2Cd4, Ca6Pt8Cd16, and Its Known Antitype Er6Pd16Sb8

    SciTech Connect

    Samal, Saroj L.; Gulo, Fakhili; Corbett, John D.

    2013-02-18

    Three new ternary polar intermetallic compounds, cubic Ca6Pt8Cd16, and tetragonal (Sr, Ba)Pt2Cd4 have been discovered during explorations of the Ae–Pt–Cd systems. Cubic Ca6Pt8Cd16 (Fm-3m, Z = 4, a = 13.513(1) Å) contains a 3D array of separate Cd8 tetrahedral stars (TS) that are both face capped along the axes and diagonally bridged by Pt atoms to generate the 3D anionic network Cd8[Pt(1)]6/2[Pt(2)]4/8. The complementary cationic surface of the cell consists of a face-centered cube of Pt(3)@Ca6 octahedra. This structure is an ordered ternary variant of Sc11Ir4 (Sc6Ir8Sc16), a stuffed version of the close relative Na6Au7Cd16, and a network inverse of the recent Er6Sb8Pd16 (compare Ca6Pt8Cd16). The three groups of elements each occur in only one structural version. The new AePt2Cd4, Ae = Sr, Ba, are tetragonal (P42/mnm,Z = 2, a ≈ 8.30 Å, c ≈ 4.47 Å) and contain chains of edge-sharing Cd4 tetrahedra along c that are bridged by four-bonded Ba/Sr. LMTO-ASA and ICOHP calculation results and comparisons show that the major bonding (Hamilton) populations in Ca6Pt8Cd16 and Er6Sb8Pd16 come from polar Pt–Cd and Pd–Sb interactions, that Pt exhibits larger relativistic contributions than Pd, that characteristic size and orbital differences are most evident for Sb 5s, Pt8, and Pd16, and that some terms remain incomparable, Ca–Cd versus Er–Pd.

  7. Enthalpies of formation of CaAl4O7 and CaAl12O19 (hibonite) by high temperature, alkali borate solution calorimetry

    NASA Technical Reports Server (NTRS)

    Geiger, C. A.; Kleppa, O. J.; Grossman, L.; Mysen, B. O.; Lattimer, J. M.

    1988-01-01

    Enthalpies of formation were determined for two calcium aluminate phases, CaAl4O7 and CaAl12O19, using high-temperature alkali borate solution calorimetry. The aluminates were synthesized by multiple-cycle heating and grinding stoichiometric mixtures of CaCO3 and Al2O3, and the products were characteized by X-ray diffraction and SEM microbeam analysis. The data on impurities (CaAl4O7 was found to be about 89.00 percent pure by weight and the CaAl12O19 samples about 91.48 percent pure) were used to correct the heat of solution values of the synthetic products. The enthalpies of formation, at 1063 K, from oxides, were found to be equal to -(25.6 + or - 4.7) kJ/g.f.w. for CaAl4O7 and -(33.0 + or - 9.7) kJ/g.f.w. for CaAl12O19; the respective standard enthalpies of formation from elements, at 298 K, were estimated to be -4007 + or - 5.2 kJ/g.f.w. and -10,722 + or - 12 kJ/g.f.w.

  8. Microwave properties of a Y 0.7Ca 0.3Ba 2Cu 3O 7- δ microstrip ring resonator with various hole concentrations

    NASA Astrophysics Data System (ADS)

    Lai, L. S.; Juang, J. Y.; Wu, K. H.; Uen, T. M.; Lin, J. Y.; Gou, Y. S.

    2004-10-01

    Superconducting ring resonator with a Y 0.7Ca 0.3Ba 2Cu 3O 7- δ ground plane was fabricated by using Y 0.7Ca 0.3Ba 2Cu 3O 7- δ thin film deposited on both sides of a LaAlO 3 (LAO) substrate. The resonator exhibits a high quality factor Q > 10 4 at T < 30 K, and from empirical relation, Tc/ Tc,max = 1 - 82.6( p - 0.16) 2, we obtained the hole concentration p. By controlling the oxygen contents of the ring resonator, the hole concentration p was controlled from 0.218 to 0.088, determined by the empirical relation, in the same film. The temperature dependence of the resonance frequency, f( T), was then systematically studied. By using Chang’s inductive formula and taking a functional form ( λ(5 K)/ λ( T)) 2 = 1 - ( T/ Tc) 2 at T < 0.6 Tc, the London penetration depths λ(5 K) for various oxygen contents at 5 K were obtained, respectively. Finally, it allows us to test the Uemura relation 1/ λ2(5 K) ∝ Tc from the over- to the underdoped regime in the same sample.

  9. Ultracold magnetically tunable interactions without radiative-charge-transfer losses between Ca+, Sr+, Ba+, and Yb+ ions and Cr atoms

    NASA Astrophysics Data System (ADS)

    Tomza, Michał

    2015-12-01

    The Ca+, Sr+, Ba+, and Yb+ ions immersed in an ultracold gas of the Cr atoms are proposed as experimentally feasible heteronuclear systems in which ion-atom interactions at ultralow temperatures can be controlled with magnetically tunable Feshbach resonances without charge transfer and radiative losses. Ab initio techniques are applied to investigate electronic-ground-state properties of the (CaCr)+, (SrCr)+, (BaCr)+, and (YbCr)+ molecular ions. The potential energy curves, permanent electric dipole moments, and static electric dipole polarizabilities are computed. The spin-restricted open-shell coupled-cluster method restricted to single, double, and noniterative triple excitations and the multireference configuration-interaction method restricted to single and double excitations are employed. The scalar relativistic effects are included within the small-core energy-consistent pseudopotentials. The leading long-range induction and dispersion interaction coefficients are also reported. Finally, magnetic Feshbach resonances between the Ca+, Sr+, Ba+, and Yb+ ions interacting with the Cr atoms are analyzed. The present proposal opens the way towards robust quantum simulations and computations with ultracold ion-atom systems free of radiative charge-transfer losses.

  10. A Comparative Study of Si-BaSO4 and Si-CaSO4 Pyrotechnic Time-Delay Compositions

    NASA Astrophysics Data System (ADS)

    Tichapondwa, Shepherd M.; Focke, Walter W.; del Fabbro, Olinto; Gisby, John; Kelly, Cheryl

    2016-07-01

    Slow-burning Si-BaSO4 pyrotechnic delay compositions are employed commercially for intermediate to long-time delays. However, there is very little information on this composition available in open literature. The reactivity of this composition was therefore characterized and compared to that of Si-CaSO4. The Si-BaSO4 composition supported combustion in the range of 20-60 wt% Si in the bomb calorimeter. However, burning was only sustained between 20 and 40 wt% Si in rigid aluminum tubes, with burning rates of between 8.4 and 16 mm s-1. These values are comparable to those for the Si-CaSO4 system (6.9-12.5 mm s-1). However, the CaSO4-based formulations tended to have higher energy output and produced more transient pressure compared to the barium sulfate compositions. Both formulations were insensitive to impact, friction, and electrostatic discharge stimuli. The reaction products were a complex mixture that contained crystalline phases in addition to an amorphous phase. Although barium sulfate is insoluble in water and decidedly nontoxic, the reaction products produced by the Si-BaSO4 compositions were found to release soluble barium ions when contacted with water. This ranged from 50 to 140 mg per gram of barium sulfate reacted.

  11. Morphological Evolution of Ba(NO3)2 Supported on -Al2O3(0001): An In-Situ TEM Study

    SciTech Connect

    Wang, Chong M; Kwak, Ja Hun; Kim, Do Heui; Szanyi, Janos; Sharma, R; Thevuthasan, Suntharampillai; Peden, Charles HF

    2006-06-22

    One of the key questions for the BaO-based NOx catalyst system is the morphological evolution of Ba(NO3)2 to BaO upon heating for releasing of NOx or vice versa from BaO to Ba(NO3)2 upon uptaking of NOx. However, associated with the small crystallite size of high-surface area Al2O3, it can be difficult to extract structural and morphological features of Ba(NO3)2 supported on -Al2O3 by any direct imaging method including transmission electron microscopy. In this work, by choosing a model system of Ba(NO3)2 particles supported on single crystal -Al2O3, we have investigated the structural and morphological features of Ba(NO3)2 as well as the formation of BaO from Ba(NO3)2 during the release of NOx using ex-situ and in-situ TEM imaging, electron diffraction, energy dispersive spectroscopy (EDS), and Wulff shape construction. We find that Ba(NO3)2 supported on -Al2O3 possesses a platelet morphology, with the interface and facets being invariably the 8 {111} planes. Formation of the platelet structure leads to an enlarged interface area between Ba(NO3)2 and -Al2O3, indicating that the interfacial energy is lower than the Ba(NO3)2 surface free energy. In fact, Wulff shape constructions indicate that the interfacial energy is ~1/4 of the {111} surface free energy of Ba(NO3)2. The orientation relationship between Ba(NO3)2 and the -Al2O3 is: -Al2O3[0001]//Ba(NO3)2[111] and -Al2O3(1-2 10)//Ba(NO3)2(110).

  12. Growth of Tl2Ba2CaCu2O7 thin films on curved substrates for metamaterial applications

    NASA Astrophysics Data System (ADS)

    Speller, S. C.; Hao, T.; Stevens, C. J.; Edwards, D. J.; Grovenor, C. R. M.

    2008-02-01

    Recent developments in the field of magnetic metamaterials have shown that coupled split-ring resonator (SRR) structures can manipulate magnetic fields on a scale shorter than the wavelength of the electromagnetic radiation [1]. In particular, stacks of copper/dielectic SRR structures can be used as high Q filters or as waveguides in near field imaging applications [2]. However, major improvements in the sensitivity of such devices would be achieved by fabricating the SRR elements from high temperature superconducting (HTS) films on appropriate dielectric substrates. In order to produce a stack of superconducting/dielectric SRR structures, the ideal method involves patterning them into an HTS film grown on the curved surface of a dielectric cylinder. To our knowledge this has not previously been attempted on the small scale required for these applications. The desired feature sizes range from a few millimetres for filter applications down to about 10μm for high resolution imaging applications. We report here our initial attempts at the growth of Tl2Ba2CaCu2O7 (Tl-2212) thin films on the surface of LaAlO3 and MgO single crystal cylinders of diameter 3mm and length 5mm. Scanning Electron Microscopy, Electron Backscatter Diffraction and a novel X-ray Diffraction technique have been used to study the microstructure and analyse the growth morphology of the Tl-2212 films in this unusual geometry. Simulations have been carried out on an axial array of SRR structures that could be fabricated from these HTS/dielectric cylinders.

  13. Different binding sites for Bacillus thuringiensis Cry1Ba and Cry9Ca proteins in the European corn borer, Ostrinia nubilalis (Hübner).

    PubMed

    Hernández-Martínez, Patricia; Hernández-Rodríguez, Carmen Sara; Van Rie, Jeroen; Escriche, Baltasar; Ferré, Juan

    2014-07-01

    Binding studies using (125)I-Cry9Ca and biotinylated-Cry1Ba proteins showed the occurrence of independent binding sites for these proteins in Ostrinia nubilalis. Our results, along with previously available binding data, indicate that combinations of Cry1A or Cry1Fa proteins with Cry1Ba and/or Cry9Ca could be a good strategy for the resistance management of O. nubilalis. PMID:24799046

  14. Interfacial chemical reaction and multiple gap state formation on three layer cathode in organic light-emitting diode: Ca/BaF{sub 2}/Alq{sub 3}

    SciTech Connect

    Kim, Tae Gun; Kim, Jeong Won; Lee, Hyunbok; Yi, Yeonjin; Lee, Seung Mi

    2015-07-14

    A three layer cathode is a promising stack structure for long lifetime and high efficiency in organic light-emitting diodes. The interfacial chemical reactions and their effects on electronic structures for alkaline-earth metal (Ca, Ba)/Alq{sub 3} [tris(8-hydroxyquinolinato)aluminum] and Ca/BaF{sub 2}/Alq{sub 3} are investigated using in-situ X-ray and ultraviolet photoelectron spectroscopy, as well as molecular model calculation. The BaF{sub 2} interlayer initially prevents direct contact between Alq{sub 3} and the reactive Ca metal, but it is dissociated into Ba and CaF{sub 2} by the addition of Ca. As the Ca thickness increases, the Ca penetrates the interlayer to directly participate in the reaction with the underlying Alq{sub 3}. This series of chemical reactions takes place irrespective of the BaF{sub 2} buffer layer thickness as long as the Ca overlayer thickness is sufficient. The interface reaction between the alkaline-earth metal and Alq{sub 3} generates two energetically separated gap states in a sequential manner. This phenomenon is explained by step-by-step charge transfer from the alkaline-earth metal to the lowest unoccupied molecular orbital states of Alq{sub 3}, forming new occupied states below the Fermi level.

  15. Tracing Environmental Variation Over The Past 130 Years In The Barents Sea: Mineral Ratio (Mg/Ca, Sr/Ca, Ba/Ca, And Mn/Ca) Evidence In Shells Of The Circumpolar Greenland Cockle, Serripes groenlandicus

    NASA Astrophysics Data System (ADS)

    Henkes, G. A.; Ambrose, W. G.; Johnson, B. J.; Carroll, M. L.; McMahon, K. W.; Denisenko, S. G.; Thorrold, S. R.

    2007-12-01

    In order to quantify the impacts of human induced climate change on Arctic marine ecosystems it is crucial to establish high-resolution proxies to record regional environmental variability. The Barents Sea region is highly influenced by the annual recession and precession of Arctic sea ice and, as an ecosystem is extremely sensitive to seasonal to decadal climatic changes. Long-lived, sessile, marine bivalves have the potential to provide detailed oceanographic and biological proxy information from the Barents Sea in locations where historic, long- term data logging does not exist. Here, we present preliminary mineral ratio evidence (Mg, Sr, Ba, Mn) for Barents Sea environmental variation from shells of the circumpolar Greenland cockle, Serripes groenlandicus, over the past 130 years from 4 different locations in Norwegian and Russian waters. For all mineral ratios there are clear seasonal trends corresponding with dark winter growth checks on the external surface of each individual. The seasonal patterns of Mg and Sr show progressive change. On average for 9 individuals, Mg/Ca was 10.6 percent greater and Sr/Ca was 5.5 percent lower on the winter checks compared to other values, while Ba/Ca and Mn/Ca ratios show peaks during the middle of the summer growth period. Mineral patterns from the Pechora Sea region are particularly pronounced, which may be related to the influence freshwater from summer river discharge. While the mineral data are initially compelling enough to demonstrate clear seasonal periodicity and inter-annual variation, we believe that a multi-proxy approach to interpreting the information obtained from these bivalves is critical. Therefore, parallel to this study, we are examining external, incremental growth and organic carbon isotopes of shell material from the same collection of bivalves.

  16. BaCoCa--a heuristic software tool for the parallel assessment of sequence biases in hundreds of gene and taxon partitions.

    PubMed

    Kück, Patrick; Struck, Torsten H

    2014-01-01

    BaCoCa (BAse COmposition CAlculator) is a user-friendly software that combines multiple statistical approaches (like RCFV and C value calculations) to identify biases in aligned sequence data which potentially mislead phylogenetic reconstructions. As a result of its speed and flexibility, the program provides the possibility to analyze hundreds of pre-defined gene partitions and taxon subsets in one single process run. BaCoCa is command-line driven and can be easily integrated into automatic process pipelines of phylogenomic studies. Moreover, given the tab-delimited output style the results can be easily used for further analyses in programs like Excel or statistical packages like R. A built-in option of BaCoCa is the generation of heat maps with hierarchical clustering of certain results using R. As input files BaCoCa can handle FASTA and relaxed PHYLIP, which are commonly used in phylogenomic pipelines. BaCoCa is implemented in Perl and works on Windows PCs, Macs and Linux operating systems. The executable source code as well as example test files and a detailed documentation of BaCoCa are freely available at http://software.zfmk.de. PMID:24076250

  17. Structure, phase composition, and strengthening of cast Al-Ca-Mg-Sc alloys

    NASA Astrophysics Data System (ADS)

    Belov, N. A.; Naumova, E. A.; Bazlova, T. A.; Alekseeva, E. V.

    2016-02-01

    The structure and phase composition of Al-Ca-Mg-Sc alloys containing 0.3 wt % Sc, up to 10 wt % Ca, and up to 10 wt % Mg have been investigated in the cast state and state after heat treatment. It has been shown that only binary phases Al4Ca, Al3Sc, and Al3Mg2 can be in equilibrium with the aluminum solid solution. It has been found that the maximum strengthening effect caused by the precipitation of Al3Sc nanoparticles for all investigated alloys is attained after annealing at 300-350°C.

  18. Improvement of critical current density in thallium-based (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) superconductors

    NASA Technical Reports Server (NTRS)

    Ren, Z. F.; Wang, C. A.; Wang, J. H.; Miller, D. J.; Goretta, K. C.

    1995-01-01

    Epitaxial (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) ((Tl,Bi)-1223) thin films on (100) single crystal LaAlO3 substrates were synthesized by a two-step procedure. Phase development, microstructure, and relationships between film and substrate were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Resistance versus temperature, zero-field-cooled and field cooled magnetization, and transport critical current density (J(sub c)) were measured. The zero-resistance temperature was 105-111 K. J(sub c) at 77 K and zero field was greater than 2 x 10(exp 6) A/sq cm. The films exhibited good flux pinning properties.

  19. Ca(2+) and CaM are involved in Al(3+) pretreatment-promoted fluoride accumulation in tea plants (Camellia sinesis L.).

    PubMed

    Zhang, Xian-Chen; Gao, Hong-Jian; Wu, Hong-Hong; Yang, Tian-Yuan; Zhang, Zheng-Zhu; Mao, Jing-Dong; Wan, Xiao-Chun

    2015-11-01

    Tea plant (Camellia sinensis (L.) O. kuntze) is known to be a fluoride (F) and aluminum (Al(3+)) hyper-accumulator. Previous study showed that pre-treatment of Al(3+) caused a significant increase of F accumulation in tea plants. However, less is known about the intricate network of Al(3+) promoted F accumulation in tea plants. In this study, the involvement of endogenous Ca(2+) and CaM in Al(3+) pretreatment-promoted F accumulation in tea plants was investigated. Our results showed that Al(3+) induced the inverse change of intracellular Ca(2+) fluorescence intensity and stimulated Ca(2+) trans-membrane transport in the mature zone of tea root. Also, a link between internal Ca(2+) and CaM was found in tea roots under the presence of Al(3+). In order to investigate whether Ca(2+) and CaM were related to F accumulation promoted by Al(3+) pretreatment, Ca(2+) chelator EGTA and CaM antagonists CPZ and TFP were used. EGTA, CPZ, and TFP pretreatment inhibited Al(3+)-induced increase of Ca(2+) fluorescence intensity and CaM content in tea roots, and also significantly reduced Al(3+)-promoted F accumulation in tea plants. Taken together, our results suggested that the endogenous Ca(2+) and CaM are involved in Al(3+) pretreatment-promoted F accumulation in tea roots. PMID:26318146

  20. Phase, Dielectric and Ferroelectric Properties of Microwave Sintered La and Ca Modified BaTiO{sub 3} Ceramics

    SciTech Connect

    Sonia, S.; Patel, R. K.; Kumar, P.; Prakash, Chandra; Agrawal, D. K.

    2011-11-22

    Lanthanum and calcium modified barium titanate, Ba{sub (1-x)}La{sub x}Ti{sub (1-x/4)}O{sub 3}/BLT and Ba({sub 1-x})Ca{sub x}TiO{sub 3}/BCT, where x = 0.02, ferroelectric ceramic samples were synthesized in single perovskite phase by microwave processing technique. Sintering temperature was optimized at 1100 deg. C for 1h. Presence of pore free micron size uniform grains suggested the advantage of using microwave sintering process. Transition temperature (T{sub c}) decreases with the substitution of La content in BT system. Temperature coefficient of capacitance is negligible from RT temperature to 75 deg. C for BLT ceramic samples. Polarization vs. electric field (P-E) hysteresis loop study confirms the ferroelectric nature of the modified BT ceramic samples.

  1. ALS-like skin changes in mice on a chronic low-Ca/Mg high-Al diet.

    PubMed

    Kihira, Tameko; Yoshida, Sohei; Kondo, Tomoyoshi; Yase, Yoshiro; Ono, Seiitsu

    2004-04-15

    Epidemiologic studies of endemic foci of amyotrophic lateral sclerosis (ALS) have shown low concentrations of Ca/Mg and high concentrations of Al/Mn in the drinking water and garden soil, which may play a causative role in the pathogenesis of endemic ALS. We studied the effects of chronic exposure to a low-Ca/Mg high-Al maltol diet on the skin of experimental animals. In ALS patients, atrophy of the epidermis, edematous changes with separated collagen fibrils and an accumulation of amorphous materials between collagen bundles were regarded as pathognomonic skin changes of ALS. Mice chronically fed a low-Ca/Mg high-Al maltol diet showed neuronal degeneration and loss in the spinal cords and cerebral cortices, as well as skin changes including atrophy, separation of collagen fibrils and accumulation of amorphous materials, similar to the skin changes characteristic of ALS. This is the first report of skin changes in animal models similar to those of ALS. We speculate that environmental factors such as chronic low-Ca/Mg high-Al condition play some causative role in the pathogenesis of Kii-ALS. PMID:15050431

  2. Effect of sintering temperature on the luminescence properties of Ca0.8Ba0.2TiO3:Pr(3+) red-emitting phosphor.

    PubMed

    Mu, Yannan; Qiu, Min; Zhou, Xiaoming; Li, Qian; Sun, Meiling; Yang, Haibin; Fu, Wuyou; Yang, Lihua; Ma, Jinwen

    2015-08-01

    Nanoparticles with the nominal composition Ca0.8Ba0.2Ti03:Pr(3+) were prepared using the sol-gel process. Barium nitrate, 4-hydrated calcium nitrate and praseodymium oxide were used as raw materials. The structural evolution and decomposition processes of the precursors were investigated by powder X-ray diffraction, differential thermal analysis and thermogravimetric analysis. Crystalline Ca0.8Ba0.2Ti03:Pr(3+) could be obtained at 700°C. The photoluminescence properties of the samples were investigated using excitation and emission spectra. Ca0.8Ba0.2Ti03:Pr(3+) nanoparticles showed strong red emission, which could be assigned to the typical (1) D2 →(3) H4 transition of Pr(3+). Furthermore, the study found that sintering temperature and the introduction of Ba(2+) influence the decay time of persistent luminescence. PMID:25209628

  3. The Thermodynamic Behavior of Copper in the CaO-B2O3 and BaO-B2O3 Slag System

    NASA Astrophysics Data System (ADS)

    Jang, Dea Young; Min, Dong Joon

    2011-12-01

    The Cu solubility was measured in the CaO-B2O3 and BaO-B2O3 slag systems to understand the dissolution mechanism of Cu in the slags. The Cu solubility had a linear relationship with oxygen partial pressure in the CaO-B2O3 slag system, which corresponds with previous studies. Also, the Cu solubilities in slag decreased with increasing the slag basicity, which value of slope was close to -0.5 in logarithmic form. From the results of experiment, the Cu dissolution mechanism established as follows: {{Cu}} + 1/4{{O}}2 = {{Cu}}^{ + } + 1/2{{O}}^{2 - } To compensate the effects of oxygen partial pressure and chemical potential of Cu in alloy on the Cu solubility of slag, the concept of cuprous capacity was suggested as follows: C_{{Cu^{ + } }} = K/{f_{{Cu^{ + }} \\cdot a_{{O^{2 - } }}^{1/2} }} = {({{mass pct Cu}})}/{a{_Cu \\cdot p_{O_{2 }}^{1/4} }} The cuprous capacity showed decreasing tendency as the slag basicity increased in the B2O3 bearing slags as well as in CaO-SiO2-Al2O3(Satd.) and FeO-Fe2O3-SiO2(Satd.) slag systems. It is suggested that the proposed dissolution mechanism could be available in various slag systems.

  4. Continuous cross-over from ferroelectric to relaxor state and piezoelectric properties of BaTiO3-BaZrO3-CaTiO3 single crystals

    NASA Astrophysics Data System (ADS)

    Benabdallah, F.; Veber, P.; Prakasam, M.; Viraphong, O.; Shimamura, K.; Maglione, M.

    2014-04-01

    Optimal properties like piezoelectricity can be found in polarizable materials for which the structure changes sharply under small composition variations in the vicinity of their morphotropic phase boundary or the triple point in their isobaric temperature-composition phase diagram. In the latter, lead-free (Ba0.850Ca0.150)(Ti0.900Zr0.100)O3 ceramics exhibit outstanding piezoelectric coefficients. For the first time, we report the growth of piezoelectric lead-free single crystals in the BaTiO3-BaZrO3-CaTiO3 pseudo-ternary system. The stoichiometry control in the CaO-BaO-TiO2-ZrO2 solid solution led to single crystals with various compositions ranging from (Ba0.857Ca0.143)(Ti0.928Zr0.072)O3 to (Ba0.953Ca0.047)(Ti0.427Zr0.573)O3. We evidenced a continuous cross-over from a ferroelectric state at high titanium content to a relaxor one on increasing the zirconium content. Such a property tuning is rather seldom observed in lead-free ferroelectrics and confirms what was already reported for ceramics. Single crystal with (Ba0.838Ca0.162)(Ti0.854Zr0.146)O3 composition, which has been grown and oriented along [001] crystallographic direction, displayed electromechanical coefficients d31 and k31 of 93 pC.N-1 and 0.18, respectively, near the room temperature (T = 305 K).

  5. Continuous cross-over from ferroelectric to relaxor state and piezoelectric properties of BaTiO{sub 3}-BaZrO{sub 3}-CaTiO{sub 3} single crystals

    SciTech Connect

    Benabdallah, F.; Veber, P. Prakasam, M.; Viraphong, O.; Maglione, M.; Shimamura, K.

    2014-04-14

    Optimal properties like piezoelectricity can be found in polarizable materials for which the structure changes sharply under small composition variations in the vicinity of their morphotropic phase boundary or the triple point in their isobaric temperature-composition phase diagram. In the latter, lead-free (Ba{sub 0.850}Ca{sub 0.150})(Ti{sub 0.900}Zr{sub 0.100})O{sub 3} ceramics exhibit outstanding piezoelectric coefficients. For the first time, we report the growth of piezoelectric lead-free single crystals in the BaTiO{sub 3}-BaZrO{sub 3}-CaTiO{sub 3} pseudo-ternary system. The stoichiometry control in the CaO-BaO-TiO{sub 2}-ZrO{sub 2} solid solution led to single crystals with various compositions ranging from (Ba{sub 0.857}Ca{sub 0.143})(Ti{sub 0.928}Zr{sub 0.072})O{sub 3} to (Ba{sub 0.953}Ca{sub 0.047})(Ti{sub 0.427}Zr{sub 0.573})O{sub 3}. We evidenced a continuous cross-over from a ferroelectric state at high titanium content to a relaxor one on increasing the zirconium content. Such a property tuning is rather seldom observed in lead-free ferroelectrics and confirms what was already reported for ceramics. Single crystal with (Ba{sub 0.838}Ca{sub 0.162})(Ti{sub 0.854}Zr{sub 0.146})O{sub 3} composition, which has been grown and oriented along [001] crystallographic direction, displayed electromechanical coefficients d{sub 31} and k{sub 31} of 93 pC.N{sup −1} and 0.18, respectively, near the room temperature (T = 305 K)

  6. Preparation, photoluminescent properties and luminescent dynamics of BaAlF{sub 5}:Eu{sup 2+} nanophosphors

    SciTech Connect

    Zhang, Wei; Hua, Ruinian; Liu, Tianqing; Zhao, Jun; Na, Liyan; Chen, Baojiu

    2014-12-15

    Graphical abstract: Rice-shaped BaAlF{sub 5}:Eu{sup 2+} nanophosphors were synthesized via one-pot hydrothermal process. The as-prepared BaAlF{sub 5}:Eu{sup 2+} are composed of many particles with an average diameter of 40 nm. When excited at 260 nm, the sharp line emission located at 361 nm of Eu{sup 2+} was observed. The optimum doping concentration of Eu{sup 2+} was confirmed to be 5 mol%. The strong ultraviolet emission of Eu{sup 2+} ions in BaAlF{sub 5}:Eu{sup 2+} nanoparticles suggests that these nanoparticles may have potential applications for sensing, solid-state lasers and spectrometer calibration. - Highlights: • BaAlF{sub 5}:Eu{sup 2+} nanophosphors were synthesized via a mild hydrothermal process. • The Van and Huang models were used to research the mechanism of concentration quenching. • The optimum doping concentration of Eu2+ was confirmed to be 5 mol%. - Abstract: Eu{sup 2+}-doped BaAlF{sub 5} nanophosphors were synthesized via a facile one-pot hydrothermal method. The final products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. XRD results showed that the prepared samples are single-phase. The FE-SEM and TEM images indicated that the prepared BaAlF{sub 5}:Eu{sup 2+} nanophosphors are composed of many rice-shaped particles with an average diameter of 40 nm. When excited at 260 nm, BaAlF{sub 5}:Eu{sup 2+} nanophosphors exhibit the sharp line emissions of Eu{sup 2+} at room temperature. The optimum doping concentration of Eu{sup 2+} was confirmed to be 5 mol%. The Van and Huang models were used to study the mechanism of concentration quenching and the electric dipole–dipole interaction between Eu{sup 2+} can be deduced to be a dominant for quenching fluorescence in BaAlF{sub 5}:Eu{sup 2+} nanophosphors. The strong ultraviolet emission of Eu{sup 2+} in BaAlF{sub 5}:Eu{sup 2+} nanophosphors suggests that

  7. Magnetic exchange interactions and antiferromagnetism of ATcO3 (A= Ca, Sr, Ba) studied from first principles

    NASA Astrophysics Data System (ADS)

    Borisov, V. S.; Maznichenko, I. V.; Böttcher, D.; Ostanin, S.; Ernst, A.; Henk, J.; Mertig, I.

    2012-04-01

    The magnetic properties of ATcO3 (A = Ca, Sr, Ba) perovskites were studied from first principles using multiple-scattering theory. For each system, the most preferable magnetic order is antiferromagnetic where the magnetic moments of the nearest Tc atoms are aligned antiparallel to each other. In the case of CaTcO3 and SrTcO3, their recently observed antiferromagnetism is supported by our calculation of the Tc-Tc exchange coupling parameters. The Néel temperatures TN estimated for CaTcO3 and SrTcO3 are in a good agreement with experiment. For BaTcO3, which is not synthesized so far, we predict a fundamental band gap of 0.3 eV and TN below 900 K. In general, TN increases with volume expansion, whereas the presence of vacancies on both the oxygen and cation sites of ATcO3 should significantly suppress the critical temperature as well as the magnetic moment of Tc. Electronic correlations play a minor role in the formation of the magnetic state, although they may improve the calculated value of TN.

  8. Suppression of structural phase transition by Sr substitution in the improper ferroelectric BaAl2O4

    NASA Astrophysics Data System (ADS)

    Mori, Shigeo; Ishii, Yui; Tanaka, Eri; Tsukasaki, Hirofumi; Kawaguchi, Shogo

    2015-10-01

    To clarify lattice fluctuations and precursor phenomena accompanied by structural phase transition in stuffed tridymite compounds, changes in diffuse scattering as a function of temperature in Ba0.6Sr0.4Al2O4 have been carefully investigated by powder X-ray diffraction using synchrotron radiation, electron diffraction and transmission electron microscopy (TEM) experiments. In situ electron diffraction experiments revealed that Ba0.6Sr0.4Al2O4 exhibits lattice fluctuation manifested as a unique honeycomb-shaped diffuse scattering in the wide temperature range between 298 and 100 K. Unlike in the case of BaAl2O4, Ba0.6Sr0.4Al2O4 shows no structural phase transition to the ferroelectric structure with the hexagonal P63 space group in the temperature range. In contrast, it is revealed that the electron beam irradiation to the Ba0.6Sr0.4Al2O4 sample inside the transmission electron microscope induced structural change from the hexagonal P6322 structure to the modulated structure with double periodicity in the three equivalent <110> directions in the low-temperature region. This implies that the total energy difference between these two structures is small. The hexagonal P6322 structure transforms into the modulated one with short correlation length owing to some small external perturbations.

  9. Luminescent Characteristics of Ba(1--x)Al2Si2O8:xTb3+ Green Phosphors.

    PubMed

    Hakeem, D A; Kim, Y; Park, K

    2016-02-01

    Ba(1--x)Al2Si2O8:xTb3+ (0.03 < or = x < or = 0.12) green phosphors are prepared by solution combustion method. The photoluminescence properties of the Ba(1--x)Al2Si2O8:xTb3+ phosphors are studied as a function of Tb3+ concentration. The Ba(1--x)Al2Si2O8:xTb3+ phosphors crystallize in a hexagonal crystal structure. The excitation spectra consist of two broad bands with maxima at 238 nm and 265 nm and several weak peaks in the range of 310-500 nm. Strong emission peaks are observed at 484, 540, 589, and 612 nm due to the (5)D4 --> (7)F6, (5)D4 --> (7)F5, (5)D4 --> (7)F4, and (5)D4 --> (7)F3 tran- sitions of the Tb3+, respectively. The emission peak (540 nm) from the (5)D4 --> (7)F3 transition is dominant, indicating green light emission. Ba(1--x)Al2Si2O8:xTb3+ phosphor shows the strongest green emission intensity. The Ba(1--x)Al2Si2O8:xTb3+ can be considered a promising green phosphor for white LEDs applications. PMID:27433666

  10. Structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Cinthia, A. Jemmy; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Iyakutti, K.

    2015-04-01

    The structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba) in the cubic (B1, B2 and B3) phases and in the wurtzite (B4) phase are investigated using density functional theory calculations as implemented in VASP code. The lattice constants, cohesive energy, bulk modulus, band structures and the density of states are computed. The calculated lattice parameters are in good agreement with the experimental and the other available theoretical results. Electronic structure reveals that all the five alkaline earth metal oxides exhibit semiconducting behavior at zero pressure. The estimated band gaps for the stable wurtzite phase of BeO is 7.2 eV and for the stable cubic NaCl phases of MgO, CaO, SrO and BaO are 4.436 eV, 4.166 eV, 4.013 eV, and 2.274 eV respectively. A pressure induced structural phase transition occurs from wurtzite (B4) to NaCl (B1) phase in BeO at 112.1 GPa and from NaCl (B1) to CsCl (B2) phase in MgO at 514.9 GPa, in CaO at 61.3 GPa, in SrO at 42 GPa and in BaO at 14.5 GPa. The elastic constants are computed at zero and elevated pressures for the B4 and B1 phases for BeO and for the B1 and B2 phases in the case of the other oxides in order to investigate their mechanical stability, anisotropy and hardness. The sound velocities and the Debye temperatures are calculated for all the oxides using the computed elastic constants.

  11. Mechanism of particle growth of a BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor by firing with AlF{sub 3}

    SciTech Connect

    Oshio, Shozo; Matsuoka, Tomizo; Tanaka, Shosaku; Kobayashi, Hiroshi

    1998-11-01

    The mechanism of particle growth of the blue emitting BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor by firing with AlF{sub 3} has been clarified. It was found that the reaction between BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} and AlF{sub 3} during firing, on the basis of the following chemical equation, results in recreation of BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} with particle growth BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} + (4/3)AlF{sub 3} {l_reversible} BaMgF{sub 4}:Eu{sup 2+} + (17/3)Al{sub 2}O{sub 3}, the firing of Ba/MgAl{sub 10}O{sub 17}:Eu{sup 2+} with AlF{sub 3} first converts the phosphor into a mixture of the two compounds, BaMgF{sub 4}:Eu{sup 2+} and Al{sub 2}O{sub 3}, at around 1200 C. The BaMgF{sub 4}:Eu{sup 2+} melts at temperatures over 1000 C, then reacts with Al{sub 2}O{sub 3}, and participates in the recreation of both BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} and AlF{sub 3} through a chemical reaction between the two compounds at 1200 C in BaMgF{sub 4}:Eu{sup 2+} solutions. Recreated AlF{sub 3} appears to sublime immediately because it is a material which sublimates with heating. This paper proposes a mechanism for the growth of particle of recreated BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} by the melting of BaMgF{sub 4}:Eu{sup 2+}.

  12. Study of the electronic structure and half-metallicity of CaMnO3/BaTiO3 superlattice

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Jiang, Wei; Chen, Jun-Nan; Huang, Jian-Qi

    2016-09-01

    In this paper, the electronic structure, magnetic properties and half-metallicity of the CaMnO3/BaTiO3 superlattice are investigated by employing the first-principle calculation based on density functional theory within the GGA or GGA + U exchange-correlation functional. The CaMnO3/BaTiO3 superlattice is constructed by the cubic CaMnO3 and the tetragonal ferroelectric BaTiO3 growing alternately along (0 0 1) direction. The cubic CaMnO3 presents a robust half-metallicity and a metastable ferromagnetic phase. Its magnetic moment is an integral number of 3.000 μB per unit cell. However, the CaMnO3/BaTiO3 superlattice has a stable ferromagnetic phase, for which the magnetic moment is 12.000 μB per unit cell. It also retains the robust half-metallicity which mainly results from the strong hybridization between Mn and O atoms. The results show that the constructed CaMnO3/BaTiO3 superlattice exhibits superior magnetoelectric properties. It may provide a theoretical reference for the design and preparation of new multiferroic materials.

  13. The GW electronic structure of cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Syrotyuk, Stepan V.; Shved, Vira M.

    2015-09-01

    The electronic energy band spectra of cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba) have been evaluated within the projector augmented waves (PAW) approach by means of the ABINIT code. The Kohn-Sham single-particle states have been found in the LDA framework. Our parameters of the electron energy bands obtained in the LDA are in good agreement with the published results of other authors. The calculated GW band gaps and dielectric constants are well compared with the available experimental data. The quasiparticle energies and density of states of electrons as well as the dielectric constants were obtained in the approximation GW for the first time.

  14. Synthesis of a new layered cuprate, Gd 2CaBa 2Ti 2Cu 2O 12

    NASA Astrophysics Data System (ADS)

    Fukuoka, A.; Adachi, S.; Sugano, T.; Wu, X.-J.; Yamauchi, H.

    1994-10-01

    A new layered cuprate, Gd 2CaBa 2Ti 2Cu 2O 12, which has a perovskite-related structure, has been discovered. The crystal structure is investigated by powder X-ray diffraction, electron diffraction and Rietveld analysis. It has a tetragonal symmetry with lattice parameters a=3.894 Å and c=35.49 Å. In the crystal there are sheets consisting of CuO 5 pyramids, which is one of the common features of p-type high- Tc superconducting cuprates.

  15. Radio frequency surface resistance of Tl-Ba-Ca-Cu-O films on metal and single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Arendt, P. N.; Reeves, G. A.; Elliott, N. E.; Cooke, D. W.; Gray, E. R.; Houlton, R. J.; Brown, D. R.

    1990-01-01

    Films of Tl-Ba-Ca-Cu were dc magnetron sputtered from a single multielement target. The films were deposited onto substrates of: (1) magnesium oxide, (2) a silver based alloy (Consil 995), (3) a nickel based alloy (Haynes 230), and (4) buffer layers of barium fluoride or copper oxide on Consil. To form superconducting phases, post-deposition anneals were made on these films using an alumina crucible with an over pressure of thallium and flowing oxygen. After annealing, the film phases were determined using x-ray diffraction. The film surface resistances (Rs) were measured at 22 GHz in a TE011 cavity.

  16. Radio frequency surface resistance of Tl-Ba-Ca-Cu-O films on metal and single-crystal substrates

    SciTech Connect

    Arendt, P.N.; Reeves, G.A.; Elliott, N.E.; Cooke, D.W.; Gray, E.R.; Houlton, R.J.; Brown, D.R. )

    1990-01-25

    Films of Tl-Ba-Ca-Cu were dc magnetron sputtered from a single multielement target. The films were deposited onto substrates of: (1) magnesium oxide, (2) a silver based alloy (Consil 995), (3) a nickel based alloy (Haynes 230), and (4) buffer layers of barium fluoride or copper oxide on Consil. To form superconducting phases, post-deposition anneals were made on these films using an alumina crucible with an over pressure of thallium and flowing oxygen. After annealing, the film phases were determined using x-ray diffraction. The film surface resistances (Rs) were measured at 22 GHz in a TE{sub 011} cavity.

  17. Photoluminescence property of A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] phosphors.

    PubMed

    Singh, Roshani; Dhoble, S J

    2013-01-01

    A new efficient phosphor, A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] has been synthesized by the solid-state method at high temperature. X-ray diffraction analysis confirmed the formation of the compound. Photoluminescence excitation measurements show that the phosphor can be efficiently excited by near-ultraviolet light from 300 nm to 400 nm to realize emission covering the 397-647 nm region of visible spectrum. Therefore, newly synthesized novel phosphor may be useful as green-emitting phosphor in solid-state lighting. PMID:22961920

  18. Thermodynamical properties of ceramic fuel cell Ba0.2Ca0.8ZrO3

    NASA Astrophysics Data System (ADS)

    Shukla, Aarti; Parey, Vanshree; Bano, Amreen; Khare, Preeti; Gaur, N. K.

    2016-05-01

    We have investigated the elastic and thermal properties of proton conducting Ba0.8Ca0.2ZrO3 at temperature 20K ≤ T ≤ 700K by using the Modified Rigid Ion Model (MRIM). We have computed the Second Order Elastic Constants (SOECs) C11, C12, C44 in the cubic phase. The cohesive energy (ϕ), molecular force constant (f), reststrahlen frequency (v), Debye temperature (θD) and Gruneisen parameter (γ) are also discussed. In addition, the variation of specific heat and volume thermal expansion coefficient with temperature are reported below and above room temperature.

  19. Ba3Pt4Al4-Structure, Properties, and Theoretical and NMR Spectroscopic Investigations of a Complex Platinide Featuring Heterocubane [Pt4Al4] Units.

    PubMed

    Stegemann, Frank; Benndorf, Christopher; Bartsch, Timo; Touzani, Rachid St; Bartsch, Manfred; Zacharias, Helmut; Fokwa, Boniface P T; Eckert, Hellmut; Janka, Oliver

    2015-11-16

    Ba3Pt4Al4 was prepared from the elements in niobium ampules and crystallizes in an orthorhombic structure, space group Cmcm (oP44, a = 1073.07(3), b = 812.30(3), c = 1182.69(3) pm) isopointal to the Zintl phase A2Zn5As4 (A = K, Rb). The structure features strands of distorted [Pt4Al4] heterocubane-like units connected by condensation over Pt/Al edges. These are arranged in a hexagonal rod packing by further condensation over Pt and Al atoms with the barium atoms located inside cavities of the [Pt4Al4](δ-) framework. Structural relaxation confirmed the electronic stability of the new phase, while band structure calculations indicate metallic behavior. Crystal orbital Hamilton bonding analysis coupled with Bader effective charge analysis suggest a polar intermetallic phase in which strong Al-Pt covalent bonds are present, while a significant electron transfer from Ba to the [Pt4Al4](δ-) network is found. By X-ray photoelectron spectroscopy measurements the Pt 4f5/2 and 4f7/2 energies for Ba3Pt4Al4 were found in the range of those of elemental Pt due to the electron transfer of Ba, while PtAl and PtAl2 show a pronounced shift toward a more cationic platinum state. (27)Al magic-angle spinning NMR investigations verified the two independent crystallographic Al sites with differently distorted tetrahedrally coordinated [AlPt4] units. Peak assignments could be made based on both geometrical considerations and in relation to electric field gradient calculations. PMID:26536164

  20. Solidification Pathways of Alloys in the Mg-Rich Corner of the Mg-Al-Ba Ternary System

    NASA Astrophysics Data System (ADS)

    Bryan, Zachary L.; Hooper, Ryan J.; Henderson, Hunter B.; Manuel, Michele V.

    2015-04-01

    An experimental investigation of the solidification reactions and microstructures of alloys in the Mg-rich corner of the Mg-Al-Ba ternary system has been conducted. Four distinct exothermic reactions involving the formation of α-Mg, Mg17Ba2, Mg17Al12, and a fourth phase designated as τ were observed and their onset temperatures were recorded as functions of composition. Using compositional and microstructural analysis, the Mg17Ba2 intermetallic was found to have significant solubility of Al, up to 20 at. pct. The solidification pathways of the investigated alloys involved both a Class I and Class II equilibrium reaction. A flow block diagram that outlines the observed solidification reactions is presented and discussed in reference to cast microstructures.

  1. Crystal structure of oxygen deficient 16L hexagonal perovskites Ba 4(Ca,Cr,Mn) 4- yO 12- x

    NASA Astrophysics Data System (ADS)

    Floros, N.; Hervieu, M.; Michel, C.; Perez, O.; Raveau, B.; Suard, E.

    2002-04-01

    The crystal structure of Ba 4Ca 0.9Mn 3.1O 11.3 has been determined by neutron powder diffraction at room temperature. A chromium substituted phase, Ba 4Ca 0.85Mn 2.65Cr 0.5O 11.5, has also been isolated and studied by neutron diffraction. The two compounds exhibit the same close-packed structure built up from [BaO 3] (h,c) and [BaO 2] (c') layers in a (hhhccc'cc) 2 stacking sequence. They crystallize in an hexagonal symmetry, space group P 6¯m2, with the unit cell parameters a=5.8005(1) and c=38.954(1) Å for Ba 4Ca 0.9Mn 3.1O 11.3. Calcium is found in octahedral environment while part of the manganese is in tetrahedra inducing a high oxidation degree for these atoms. A single crystal X-ray diffraction study has shown the possibility to introduce cationic deficiency in such a structure leading to the composition Ba 4CaMn 2.5O 11+ δ.

  2. Structural changes and microstructures in stuffed tridymite-type compounds Ba1-xSrxAl2O4

    NASA Astrophysics Data System (ADS)

    Tanaka, Eri; Ishii, Yui; Tsukasaki, Hirofumi; Taniguchi, Hiroki; Mori, Shigeo

    2014-09-01

    Crystal structures and microstructures in Ba1-xSrxAl2O4 solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent <110> directions in the (001) plane, which appear in the P63 structure of Ba1-xSrxAl2O4 for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P21 structure in Ba1-xSrxAl2O4 with x = 0.7 was found to consist of a modulated structure with \\boldsymbol{{q}} = 0,1/2,0. The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P63 structure with a large structural fluctuation and a monoclinic P21 phase with the single-q modulated structure.

  3. [Synthesis and properties of nanorod-long afterglow BaAl2O4:Eu2+, Dy3+ phosphor].

    PubMed

    He, Chun-hui; Zheng, Shu-hui; Xiao, Yong; Liu, Ying-liang

    2010-01-01

    The present paper mainly reports a new method to synthesize long afterglow photoluminescent material BaAl2O4:Eu2+, Dy3+. Al(NO3)3.9H2O, Ba(NO3)2, urea, RE(NO3) 3(RE==Eu, Dy) were employed as raw materials, the admixture of H2O/n-butanol and H2O/n-butanol/SBS were used as medium, then BaAl2O4:Eu2+, Dy3+ phosphor was achieved by calcining the precursor, which was synthesized by hydrothermal method, at 130 degrees C under reduction atmosphere. The TEM and SEM were used to analyse the morphology and BaAl2O4:Eu2+, Dy3+ synthesized by annealing at 1300 degrees C are all nanorods. The excitation and emission spectra of the phosphor indicated that all of them are broad band, and the main emission peak is around 498 nm, which is due to 5d-->4f transition of Eu2+. The state-solid synthesis of the long afterglow phosphor BaAl2O4:Eu2+, Dy3+ generally requires a high calcination temperature, so the products are easily agglomerated, and in this paper the hydrothermal solvothermal synthesis was used, so the synthesized products calcined at 130 degrees degrees C still present well-dispersed rod structure, need not milling, and display well luminescence performance. The authors compared the two different conditions of experiment, and found that under the condition without surfactant the authors can still get well-dispersed rod structure of BaAl2O4:Eu2+, Dy3+. The method is hopeful to be used in synthesizing other alkali-earth aluminate and silicate and other luminescent materials. PMID:20302073

  4. P- T- X controls on Ca and Na distribution between Mg-Al tourmaline and fluid

    NASA Astrophysics Data System (ADS)

    Berryman, Eleanor J.; Wunder, Bernd; Rhede, Dieter; Schettler, Georg; Franz, Gerhard; Heinrich, Wilhelm

    2016-04-01

    Ca-Na partitioning between tourmaline and a coexisting fluid is investigated in the system CaO-Na2O-B2O3-Al2O3-MgO-SiO2-H2O-Cl between 0.2-4.0 GPa and 500-700 °C. The synthesis experiments produced a mineral assemblage of tourmaline, coesite/quartz, and in some cases additional phases, typically comprising <1 wt% of the solid product. The synthesized tourmalines are solid solutions of dravite [NaMg3Al6Si6O18(BO3)3(OH)3(OH)], "oxy-uvite" (i.e. "Ca-Mg-O root name") [CaMg3Al6Si6O18(BO3)3(OH)3O], and magnesio-foitite [☐(Mg2Al)Al6Si6O18(BO3)3(OH)3(OH)]. Starting materials comprised a fluid of constant ionic strength (2.00 m) and an oxide mixture with a constant Mg/Al ratio. As a result, the number of vacancies at the X site and the Mg/Al ratio of tourmaline crystals synthesized at the same temperature vary only slightly. The major solid solution is Ca-Na exchange at the X site via the exchange vector X Ca W O[ X Na W (OH)]-1, with the exchange vector X (Ca☐)[ X Na2]-1 serving as a secondary Ca-incorporation mechanism. Tourmaline's X-site composition reflects the fluid composition, whereby the Ca (or Na) concentration in the fluid corresponds with the Ca (or Na) content in tourmaline at each pressure and temperature. At 0.2 GPa, 700 °C, Ca preferentially partitions into tourmaline, producing the most Ca-rich tourmaline crystals synthesized here. At pressures >1.0 GPa, Ca partitions preferentially into the fluid, resulting in Na-dominant tourmaline compositions. Temperature has a secondary effect on Ca-Na partitioning, with higher temperatures correlating with increased Ca incorporation in tourmaline. Based on the experimental findings, tourmaline is expected to have Ca-rich compositions when it forms in low pressure, high-temperature Ca-rich rocks, consistent with the current record of tourmaline occurrence. The bulk Mg/Al ratio and the pH of the tourmaline-forming system may also affect Ca incorporation in tourmaline, but remain to be investigated experimentally.

  5. Theoretical survey on M@C80 (M = Ca, Sr, and Ba): Behavior of different alkaline earth metal impacting the chemical stability and electronic properties

    NASA Astrophysics Data System (ADS)

    Cui, Jin-Bo; Guo, Yi-Jun; Li, Qiao-Zhi; Zhao, Pei; Zhao, Xiang

    2016-08-01

    Structures of mono-metallofullerenes M@C80 (M = Ca, Sr, and Ba) that separated in early experiment are determined owning the C2v(31920)-C80 cage. The change rule of properties for M@C80 (M = Ca, Sr, and Ba) influenced by different inner metal are discussed. As the trapped metal changes from calcium to barium, performance of thermodynamic stabilities for M@C2v(31920)-C80, M@C2v(31922)-C80, and M@D5h(31923)-C80 are significantly different. Orbital analysis suggests that the lowest unoccupied molecular orbitals (LUMOs) of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 are mostly located on the trapped metal, whereas reduction reactions of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 occur on the fullerene cage. Natural electron configuration analyses demonstrates that the decentralized electron back-donation of Ba@C2v(31920)-C80 would take responsible for the instability of itself. Electronic properties such as electron affinities and ionization potentials are significantly affected by encapsulated metal are also found. Computational UV-visible-NIR spectra for M@C2v(31920)-C80 (M = Ca, Sr, Ba) are in perfect accord with the spectra obtained experimentally.

  6. CaFeAl mixed oxide derived heterogeneous catalysts for transesterification of soybean oil to biodiesel.

    PubMed

    Lu, Yongsheng; Zhang, Zaiwu; Xu, Yunfeng; Liu, Qiang; Qian, Guangren

    2015-08-01

    CaAl layered double oxides (LDO) were prepared by co-precipitation and calcined at 750°C, and then applied to biodiesel production by transesterification reaction between methanol and soybean oil. Compared with characteristics of CaFe/LDO and CaAl/LDO, CaFeAl/LDO had the best performance based on prominent catalytic activity and stability, and achieved over 90% biodiesel yield, which stayed stable (over 85%) even after 8 cycles of reaction. The optimal catalytic reaction condition was 12:1M-ratio of methanol/oil, reaction temperatures of 60°C, 270rpm stirring rate, 60min reaction time, and 6% weight-ratio of catalyst/oil. In addition, the CaFeAl/LDO catalyst is insoluble in both methanol and methyl esters and can be easily separated for further reaction, turning it into an excellent alternative for biodiesel synthesis. PMID:25740001

  7. Nonlinear-optical susceptibility of hilgardite-like borates MBOX(M=Pb,Ca,Sr,Ba; X=Cl,Br)

    NASA Astrophysics Data System (ADS)

    Plachinda, Paul A.; Dolgikh, Valery A.; Stefanovich, Sergey Yu.; Berdonosov, Petr S.

    2005-10-01

    Usage of non-centrosymmetric boron oxide derivative crystals as nonlinear elements may be a key solution of pressing problem of obtaining powerful radiation at shorter wavelengths via frequency multiplication of solid state laser radiations. It is shown that Pb 2B 5O 9Br and some other members of hilgardite-like borohalogenides demonstrate in powder form, high non-linear optical activity in the SHG experiments. An attempt is made using the Philips-Van Vechten-Levine-Xue bond theory to calculate second-order nonlinear coefficients for isostructural to mineral hilhardite noncentrosymmetric crystals MBOX with M=Pb, Sr, Ba, Eu, Ca and X=Cl, Br. Theoretically obtained values of nonlinear optical coefficients d only partly correlate with the results of SHG measurements. In particular, the experiments distinctively show sharp increase of nonlinear activity along the series Ca < Sr < Ba < Pb and Cl < Br of metal boro-halogenides, while theoretical estimations give substantially more slack composition dependences. Analysis of contribution of different boron-oxygen bonds to optical nonlinearities of the compounds reveals important role of planar BO 3 triangles, though this factor is yet unable to explain enormously high SHG output from Pb 2B 5O 9Br.

  8. Effect of particle size on the thermoluminescence properties of Ba0.97Ca0.03SO4:Cu

    NASA Astrophysics Data System (ADS)

    Bokolia, Renuka; Sahare, P. D.

    2013-02-01

    Copper doped Ba0.97Ca0.03SO4 in its nanocrystalline form has been prepared and its thermo-luminescence (TL) properties are studied. The nanoparticles of the phosphor were prepared by the chemical co-precipitation method. The formation of the compound was confirmed by X-Ray Diffraction (XRD). The particle size was calculated by the broadening of the XRD peaks using Scherrer's formula. The TL glow curve of the phosphor has been found to have a simple structure with a single peak at 466 K. Compared to the higher molar concentration solution of Ba0.97Ca0.03SO4:Cu (0.3M), the nano-sized phosphor of lower molar concentration (0.2M and 0.1M) has a lesser TL sensitivity. However, this reduction in TL sensitivity on decreasing the particle size from higher molar concentration to lower molar concentration gives a better understanding of the TL phenomenon. The decrease in the sensitivity is attributed to the particle size effect i.e., the volume-to-surface ratio.

  9. Thermoelectric Properties of Mn-Doped Ca5Al2Sb6

    NASA Astrophysics Data System (ADS)

    Zevalkink, Alex; Swallow, Jessica; Snyder, G. Jeffrey

    2012-05-01

    Ca5Al2Sb6 is a relatively inexpensive Zintl compound exhibiting promising thermoelectric efficiency at temperatures suitable for waste heat recovery. Motivated by our previous studies of Ca5Al2Sb6 doped with Na and Zn, this study focuses on doping with Mn2+ at the Al3+ site. While Mn is a successful p-type dopant in Ca5Al2Sb6, we find that incomplete dopant activation yields lower hole concentrations than obtained with either previously investigated dopant. High-temperature Hall effect and Seebeck coefficient measurements show a transition from nondegenerate to degenerate semiconducting behavior in Ca5Al2- x Mn x Sb6 samples ( x = 0.05, 0.1, 0.2, 0.3, 0.4) with increasing Mn content. Ultimately, no improvement in zT is achieved via Mn doping, due in part to the limited carrier concentration range achieved.

  10. Mechanism of X-ray excited optical luminescence (XEOL) in europium doped BaAl2O4 phosphor.

    PubMed

    Rezende, Marcos V Dos S; Montes, Paulo J R; Andrade, Adriano B; Macedo, Zelia S; Valerio, Mário E G

    2016-06-29

    This paper reports a luminescence mechanism in Eu-doped BaAl2O4 excited with monochromatic X-rays (also known as X-ray excited optical luminescence - XEOL) from synchrotron radiation. The material was prepared via a proteic sol-gel methodology. The X-ray absorption near edge structures (XANES) at the Ba LIII- and Eu LIII-edges exhibit typical absorption spectra. XEOL spectra recorded in energy ranges, either around the Ba LIII- or Eu LIII-edges, showed important differences concerning the intensity of the Eu(2+) or Eu(3+) emission bands. Nevertheless, the total area under the XEOL spectra increases as the energy of the X-ray photons increases in both ranges (Ba LIII- and Eu LIII-edges). PMID:27306425

  11. Nonlinear optical properties ofBaAlBO3F2 crystal.

    PubMed

    Zhou, Yong; Yue, Yinchao; Wang, Jianuo; Yang, Feng; Cheng, Xiankun; Cui, Dafu; Peng, Qinjun; Hu, Zhanggui; Xu, Zuyan

    2009-10-26

    We investigated the nonlinear optical properties of new BaAlBO(3)F(2)(BABF) crystal. The high quality BABF is nonhygroscopic and possesses a moderate birefringence suitable for UV light generation. On the basis of its refractive index dispersion curves, it is inferred that BABF has great potential applications nonlinear optical material, notably for UV light generation at 355 nm. In order to characterize its nonlinear optical properties, BABF samples were cut an oriented in phase matching conditions The optical conversion efficiency from 1064 nm to 532 nm was investigated for the first time: up to 49.0% were achieved. The external angular acceptance bandwidth of SHG and THG for 1064 nm pump light was measured. PMID:19997227

  12. Crystal structure of (Cu,C)Ba2Ca3Cu4O11+δ (Tc=117 K) by neutron-powder-diffraction analysis

    NASA Astrophysics Data System (ADS)

    Shimakawa, Y.; Jorgensen, J. D.; Hinks, D. G.; Shaked, H.; Hitterman, R. L.; Izumi, F.; Kawashima, T.; Takayama-Muromachi, E.; Kamiyama, T.

    1994-12-01

    The crystal structure of the newly discovered 117-K superconductor, (Cu,C)Ba2Ca3Cu4O11+δ, has been refined from time-of-flight neutron-powder-diffraction data. The structure has ``average'' tetragonal symmetry and is similar to that of Tl(or Hg)Ba2Ca3Cu4Oy. C atoms in CO3 groups substitute at the Cu site in the (Cu,C)O1+δ layer leading to a chemical composition of (Cu0.68C0.32)Ba2Ca3Cu4O11.06. This compound has two inequivalent kinds of CuO2 layers with pyramidal and square coordination of Cu to oxygen. The inner CuO2 layers with Cu in four coordination are less corrugated than the outer ones with Cu in five coordination, and exhibit a structure very similar to those of infinite-layer compounds.

  13. Surface modification of MAl2O4:Eu2+,Dy3+ (M = Sr, Ca, Ba) phosphors to enhance water resistance by combustion method

    NASA Astrophysics Data System (ADS)

    Deng, Suqing; Xue, Zhiping; Yang, Qu; Liu, Yingliang; Lei, Bingfu; Xiao, Yong; Zheng, Mingtao

    2013-10-01

    A facile combustion method was introduced into surface modification of MAl2O4:Eu2+,Dy3+ (M = Sr, Ca, Ba) phosphors to improve their water resistance. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), pH measurements and photoluminescence (PL) spectrophotometry were used to characterize the phosphors before and after modification, respectively. Experimental results showed that compact layer of MAl2B2O7 (M = Sr, Ca, Ba) substance was formed on the surface of aluminate phosphors by direct chemical reaction between aluminate and boracic acid. MAl2B2O7 (M = Sr, Ca, Ba) substance is chemically stable in water and could improve water resistance of aluminate phosphors effectively with little influence of luminescence property. It was considered that the versatility of combustion method for surface modification of aluminate phosphors has been confirmed.

  14. Defect-induced wetting on BaF 2(111) and CaF 2(111) at ambient conditions

    NASA Astrophysics Data System (ADS)

    Cardellach, M.; Verdaguer, A.; Fraxedas, J.

    2011-12-01

    The interaction of water with freshly cleaved (111) surfaces of isostructural BaF2 and CaF2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF2(111) two-dimensional water layers are formed after accumulation at step edges, CaF2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF2(CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level.

  15. Energy transfer and luminescence properties of Ba2CaMoO6:Eu3+ phosphors prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Li, Yuntong; Liu, Xiaohua

    2015-04-01

    Novel Ba2CaMoO6:Eu3+ reddish orange phosphors were synthesized by the sol-gel method. The XRD results indicate that the phosphors keep the cubic structure. The excitation spectra exhibit an intense broad charge transfer (CT) band centered at 380 nm, indicating the phosphors can be effectively excited by near UV (370-410 nm) light. The photoluminescence (PL) measurements demonstrate a strong red emission band centered at about 595 nm (5D0 → 7F1) under host excitation at 380 nm. A low concentration quenching occurs in Ba2CaMoO6:Eu3+ and the optimal doping concentration is about 6 mol%. The efficient energy transfer from host to Eu3+ ions in Ba2CaMoO6:Eu3+ phosphors has been discussed in this paper.

  16. Research and analysis on the thin films sputtered by the Ba-Al-S:Eu target fabricated by powder sintering

    NASA Astrophysics Data System (ADS)

    Zhang, Dongpu; Xu, Fang; Yu, Zhinong; Xue, Wei

    2014-11-01

    Europium-doped barium thioaluminate (BaAl2S4:Eu) is currently the most efficient blue phosphor for inorganic thin film electroluminescent (iEL) device. To produce the full-color EL device, several kinds of blue-emitting layer were attempted and tested. As a key point of blue-emitting layer fabrication, single target sputtering deposition is an effective method. In this work, new structural target is introduced and the fabricated process is expatiated. The PL spectra of as fabricated targets show that both of two, 3mol% and 5mol% europium-doped, have blue emitting property. According to the PL spectra excited by 290nm, 300nm and 320nm ultraviolet, emission peaks located in the region near 470nm. So the as-fabricated targets can be used in single target sputtering deposition on thin film of BaAl2S4:Eu. XRD pattern indicates that there are 4 different phases, barium tetraaluminum sulfide (BaAl4S7), barium sulfide (BaS), europium sulfide (EuS) and barium aluminum oxide (BaAl2O4), in target 1. Besides these four compounds, other two phases, aluminum sulfide (Al2S3) and barium thioaluminate (BaAl2S4), are detected in target 2. Considering the analysis results, especially the hydrolyzation of Al2S3, target 1 is more suitable for sputtering deposition of BaAl2S4:Eu thin film. XPS and X-ray Fluorescence patterns describe the precise molar ratio of each element. In target 1 the relative atom concentration of barium, aluminum, sulfur and oxygen can be calculated from the pattern and molar ratio is about 9:33:41:17. Molar ratio of barium and europium is about 1:0.03. In short, the barium thioaluminate doped by europium sputtering target 1 is better to be applied in the fabrication of blue-emitting layer in inorganic electro-luminescent devices.

  17. The microstructure-strength relationship in a deformation processed Al-Ca composite

    SciTech Connect

    Tian, Liang; Kim, Hyongjune; Anderson, Iver; Russell, Alan

    2013-02-07

    An Al-9 vol% Ca composite was produced by powder metallurgy and deformation processing. The Al–Ca composite was extruded, swaged and wire drawn to a deformation true strain of 13.8. Both Al and Ca are face-centered cubic, so the Ca second phase deformed into continuous, nearly cylindrical filaments in the Al matrix. The formation of intermetallic compounds, filament coarsening, and spheriodization at elevated temperature was observed by scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. Both the thickness and spacing of the Ca filaments decreased exponentially with increasing deformation. The ultimate tensile strength of the composite increased rapidly with increased deformation, especially at high deformation processing strains. The relation between deformation true strain and ultimate tensile strength is underestimated by the rule of mixtures; a modified Hall–Petch barrier strengthening model was found to fit the data better.

  18. Ca-rich Ca-Al-oxide, high-temperature-stable sorbents prepared from hydrotalcite precursors: synthesis, characterization, and CO2 capture capacity.

    PubMed

    Chang, Po-Hsueh; Chang, Yen-Po; Chen, San-Yuan; Yu, Ching-Tsung; Chyou, Yau-Pin

    2011-12-16

    We present the design and synthesis of Ca-rich Ca-Al-O oxides, with Ca(2+)/Al(3+) ratios of 1:1, 3:1, 5:1, and 7:1, which were prepared by hydrothermal decomposition of coprecipitated hydrotalcite-like Ca-Al-CO(3) precursors, for high-temperature CO(2) adsorption at 500-700 °C. In situ X-ray diffraction measurements indicate that the coprecipitated, Ca-rich, hydrotalcite-like powders with Ca(2+)/Al(3+) ratios of 5:1 and 7:1 contained Ca(OH)(2) and layered double hydroxide (LDH) phases. Upon annealing, LDH was first destroyed at approximately 200 °C to form an amorphous matrix, and then at 450-550 °C, the Ca(OH)(2) phase was converted into a CaO matrix with incorporated Al(3+) to form a homogeneous solid solution without a disrupted lattice structure. CaO nanocrystals were grown by thermal treatment of the weakly crystalline Ca-Al-O oxide matrix. Thermogravimetric analysis indicates that a CO(2) adsorption capacity of approximately 51 wt. % can be obtained from Ca-rich Ca-Al-O oxides prepared by calcination of 7:1 Ca-Al-CO(3) LDH phases at 600-700 °C. Furthermore, a relatively high CO(2) capture capability can be achieved, even with gas flows containing very low CO(2) concentrations (CO(2)/N(2) = 10 %). Approximately 95.6 % of the initial CO(2) adsorption capacity of the adsorbent is retained after 30 cycles of carbonation-calcination. TEM analysis indicates that carbonation-promoted CaCO(3) formation in the Ca-Al-O oxide matrix at 600 °C, but a subsequent desorption in N(2) at 700 °C, caused the formation CaO nanocrystals of approximately 10 nm. The CaO nanocrystals are widely distributed in the weakly crystalline Ca-Al-O oxide matrix and are present during the carbonation-calcination cycles. This demonstrates that Ca-Al-O sorbents that developed through the synthesis and calcination of Ca-rich Ca-Al LDH phases are suitable for long-term cyclic operation in severe temperature environments. PMID:22072595

  19. Laser soldering of sapphire substrates using a BaTiAl6O12 thin-film glass sealant

    NASA Astrophysics Data System (ADS)

    de Pablos-Martin, A.; Tismer, S.; Benndorf, G.; Mittag, M.; Lorenz, M.; Grundmann, M.; Höche, Th.

    2016-07-01

    Two sapphire substrates are tightly bonded through a BaTiAl6O12-glass thin film, by irradiation with a nanosecond laser. After the laser process, the composition of the glass sealant changes, due to incorporation of Al2O3 from the upper substrate. After annealing of the bonded samples (950 °C for 30 minutes) crystalline structures are observed by TEM which are attributed to crystalline BaTiAl6O12. These crystals together with Al2O3:Ti centers are the responsible of the observed strong blue luminescence of the laser irradiated region upon UV excitation. The structural and optical characterizations of the bonded samples clarify the laser soldering procedure as well as the origin of the luminescence. Bond quality and bond strength were evaluated by scanning acoustic microscopy (SAM) and tensile tests, which results in a tensile stress of nearly 13 MPa, which is an acceptable value for glass sealants.

  20. Combustion Synthesized Cr3+-doped-BaMgAl10O17 Phosphor: An Electron Paramagnetic Resonance and Optical Study

    NASA Astrophysics Data System (ADS)

    Singh, Vijay; Sivaramaiah, G.; Rao, J. L.; Srivastava, Anoop K.; Ravikumar, R. V. S. S. N.; Dhoble, S. J.; Singh, P. K.; Mohapatra, Manoj

    2016-01-01

    BaMgAl10O17 phosphors doped with Cr3+ ions were prepared by a combustion route at a furnace temperature of 773 K. The X-ray diffraction pattern revealed that the BaMgAl10O17 phosphor was in a hexagonal phase. Energy-dispersive X-ray mapping images demonstrated the presence of the dopant ion in the BaMgAl10O17 matrix. The bands observed in the optical absorption spectrum were characteristic of Cr3+ ions in octahedral geometry. Upon 555-nm excitation, an intense narrow red emission line centred at 690 nm due to the 2Eg → 4A2g transition of Cr3+ ions was observed. The electron paramagnetic resonance (EPR) spectrum of Cr3+ ions in BaMgAl10O17 phosphor showed multiple absorption bands having at least 6 g values. Based on the EPR data, various parameters such as the absolute number of spins, Gibbs potential, magnetic susceptibility and magnetic moments, Curie constant, etc., for the system were evaluated.

  1. [Influence of Eu2+ content on the spectral characteristics of BaMgAl10O17 : Eu2+ phosphors].

    PubMed

    Chen, Zhe; Xie, Hong; Yan, You-Wei

    2007-04-01

    Nanocrsytalline Ba(1-x)MgAl10O17 : xEu2+ (0.05 < or = x < or = 0.4) blue-emitting phosphor was successfully prepared by low-temperature combustion synthesis. The influence of different Eu content on the spectral characteristics of Ba(1-x) MgAl10O17 : xEu2+ was mainly investigated. The results of XRD and SEM analysis show that the sample is single phase and its average grain size is about 30 nm. The luminescence property of Ba(1-x)MgAl10O17 : xEu2+ phosphor is considerably influenced by Eu2+ concentration. In an appropriate Eu2+ doping concentration range, the intensity of the fluorescence of Ba(1-x)MgAl10O17 : xEu2+ was increased obviously with increasing the Eu2+ doping concentration, owing to adding the number of luminescent centers and enhancing the energy transfer between Eu2+ ions. The optimum emission intensity was reached at x = 0.2. However, as the Eu2+ doping concentration was higher than 0.2, the intensity of the fluorescence was reduced, due to the concentration quenching occurrence. PMID:17608168

  2. Synthesis and luminescence properties of red-emitting M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) phosphors by a simple nitrate reduction

    NASA Astrophysics Data System (ADS)

    Chen, ChangCheng; Xie, ErQing

    2014-03-01

    M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) red-emitting phosphors are fabricated at relatively low temperature (1200°C) and atmospheric pressure using a simple solid-state reaction process. Several processing parameters are systematically investigated to optimize the phosphors structural characterization and photoluminescence performance, including the amount of europium and the properties of the precursor materials. The as-prepared M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) phosphors are orange in color and are intensively emitted in the red region of 580-670 nm under 465 nm excitation.

  3. Dy3+-activated NaM4(VO4)3 (M = Ca, Ba, Sr) phosphor for near-UV solid-state lighting.

    PubMed

    Singh, Roshani; Dhoble, S J

    2011-01-01

    We report the photoluminescence characterization of Dy(3+)-activated NaM(4)(VO(4))(3) (M = Ca, Ba, Sr) phosphors prepared by a solid-state method. The synthesis was confirmed by X-ray diffraction (XRD) characterization and photoluminescence (PL) emission results showed sharp blue and yellow bands for NaM(4)(VO(4))(3) (M = Ca, Ba, Sr):Dy(3+) phosphors at the excitation wavelength of 323 nm, which is near-UV excitation. Thus, these phosphors could be applicable for near-UV excited solid-state lighting devices. PMID:21618681

  4. Electronic structure of TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}}

    SciTech Connect

    Vasquez, R.P.; Novikov, D.L.; Freeman, A.J.; Siegal, M.P.

    1997-06-01

    The core levels of TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}} (Tl-1212) epitaxial films have been measured with x-ray photoelectron spectroscopy (XPS). The valence electronic structure has been determined using the full-potential linear muffin-tin-orbital band-structure method and measured with XPS. The calculations show that a van Hove singularity (VHS) lies above the Fermi level (E{sub F}) for the stoichiometric compound ({delta}=0), while for 50{percent} oxygen vacancies in the Tl-O layer ({delta}=0.5) E{sub F} is in close proximity to the VHS. Samples annealed in nitrogen (to reduce the hole overdoping by the removal of oxygen) exhibit higher core-level binding energies and a higher T{sub c}, consistent with a shift of E{sub F} closer to the VHS. Comparisons are made to the core levels and valence bands of Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Tl-2212) and HgBa{sub 2}CaCu{sub 2}O{sub 6+{delta}} (Hg-1212). The similarity of the Cu 2p{sub 3/2} spectra for Tl-1212 and Tl-2212 indicates that the number of Tl-O layers has little effect on the Cu-O bonding. However, the Tl-1212 and Hg-1212 Cu 2p{sub 3/2} signals exhibit differences which suggest that the replacement of Tl{sup 3+} with Hg{sup 2+} results in a decrease in the O 2p{r_arrow}Cu 3d charge-transfer energy and differences in the probabilities of planar vs apical oxygen charge transfer and/or Zhang-Rice singlet-state formation. Differences between the Tl-1212 and the Tl-2212 and Hg-1212 measured valence bands are consistent with the calculated Cu 3d and (Tl,Hg) 6s/5d partial densities of states. {copyright} {ital 1997} {ital The American Physical Society}

  5. Crystal and Magnetic Structures of the Oxide Sulfides CaCoSO and BaCoSO.

    PubMed

    Salter, Edward J T; Blandy, Jack N; Clarke, Simon J

    2016-02-15

    CaCoSO, synthesized from CaO, Co, and S at 900 °C, is isostructural with CaZnSO and CaFeSO. The structure is non-centrosymmetric by virtue of the arrangement of the vertex-sharing CoS3O tetrahedra which are linked by their sulfide vertices to form layers. The crystal structure adopts space group P63mc (No. 186), and the lattice parameters are a = 3.7524(9) Å and c = 11.138(3) Å at room temperature with two formula units in the unit cell. The compound is highly insulating, and powder neutron diffraction measurements reveal long-range antiferromagnetic order with a propagation vector k = (1/3, 1/3, 1/2). The magnetic scattering from a powder sample can be modeled starting from a 120° arrangement of Co(2+) spin vectors in the triangular planes and then applying a canting out of the planes which can be modeled in the magnetic space group C(c)c (space group 9.40 in the Belov, Neronova, and Smirnova (BNS) scheme) with Co(2+) moments of 2.72(5) μ(B). The antiferromagnetic structure of the recently reported compound BaCoSO, which has a very different crystal structure from CaCoSO, is also described, and this magnetic structure and the magnitude of the ordered moment (2.75(2) μ(B)) are found by experiment to be similar to those predicted computationally. PMID:26824255

  6. A Fluctuating State in the Framework Compounds (Ba,Sr)Al2O4

    PubMed Central

    Ishii, Yui; Tsukasaki, Hirofumi; Tanaka, Eri; Mori, Shigeo

    2016-01-01

    The structural fluctuation in hexagonal Ba1−xSrxAl2O4 with a corner-sharing AlO4 tetrahedral network was characterized at various temperatures using transmission electron microscopy experiments. For x ≤ 0.05, soft modes of q ~ (1/2, 1/2, 0) and equivalent wave vectors condense at a transition temperature (TC) and form a superstructure with a cell volume of 2a × 2b × c. However, TC is largely suppressed by Sr-substitution, and disappears for x ≥ 0.1. Furthermore, the q ~ (1/2, 1/2, 0) soft mode deviates from the commensurate value as temperature decreases and survives in nanoscaled regions below ~200 K. These results strongly suggest the presence of a new quantum criticality induced by the soft mode. Two distinct soft modes were observed as honeycomb-type diffuse scatterings in the high-temperature region up to 800 K. This intrinsic structural instability is a unique characteristic of the framework compound and is responsible for this unusually fluctuating state. PMID:26758625

  7. A Fluctuating State in the Framework Compounds (Ba,Sr)Al2O4

    NASA Astrophysics Data System (ADS)

    Ishii, Yui; Tsukasaki, Hirofumi; Tanaka, Eri; Mori, Shigeo

    2016-01-01

    The structural fluctuation in hexagonal Ba1-xSrxAl2O4 with a corner-sharing AlO4 tetrahedral network was characterized at various temperatures using transmission electron microscopy experiments. For x ≤ 0.05, soft modes of q ~ (1/2, 1/2, 0) and equivalent wave vectors condense at a transition temperature (TC) and form a superstructure with a cell volume of 2a × 2b × c. However, TC is largely suppressed by Sr-substitution, and disappears for x ≥ 0.1. Furthermore, the q ~ (1/2, 1/2, 0) soft mode deviates from the commensurate value as temperature decreases and survives in nanoscaled regions below ~200 K. These results strongly suggest the presence of a new quantum criticality induced by the soft mode. Two distinct soft modes were observed as honeycomb-type diffuse scatterings in the high-temperature region up to 800 K. This intrinsic structural instability is a unique characteristic of the framework compound and is responsible for this unusually fluctuating state.

  8. Stabilization of metastable ferroelectric Ba1−xCaxTi2O5 by breaking Ca-site selectivity via crystallization from glass

    PubMed Central

    Masuno, Atsunobu; Moriyoshi, Chikako; Mizoguchi, Teruyasu; Okajima, Toshihiro; Kuroiwa, Yoshihiro; Arai, Yasutomo; Yu, Jianding; Inoue, Hiroyuki; Watanabe, Yasuhiro

    2013-01-01

    The thermal stability and dielectric and structural properties of ferroelectric Ba1−xCaxTi2O5 (0 ≤ x ≤ 0.30) prepared by crystallization from glass are investigated. The Ba1−xCaxTi2O5 compounds with x < 0.10 are thermally stable phases, while those with x ≥ 0.10 are metastable phases. The ferroelectric transition temperature drastically decreases from 470 to 220°C with increasing x. Crystal structure analyses reveal that one of two possible Ba sites is occupied by Ca in the stable phase region, while Ca-site selectivity is broken in the metastable phase region. The Ca-site selectivity introduces local distortion and makes the crystal lattice unstable. However, the local distortion is suppressed by the occupancy of Ca into both Ba sites. Accordingly, the metastable ferroelectric phase can be obtained beyond the substitution limit of Ca by crystallization from the glassy state. The stabilization mechanism provides possible wide control of the functionality of materials by expanding the composition range. PMID:24145958

  9. Ba/Ca in Planktonic Foraminifera as a Recorder of Freshwater Input to the Ocean: Proxy Refinement in the Gulf of Papua, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Gibson, K.

    2015-12-01

    In the study of paleoclimate, the past several decades have seen large strides in the advancement of proxies designed to reconstruct changes in sea surface temperature (SST); however, techniques for reconstructing ocean salinity are less well developed. The ratio of Ba/Ca in planktic foraminiferal tests has shown initial promise as a tool for reconstructing salinity in continental margin sites near river mouths. In these environments, Ba/Ca shows an inverse correlation with salinity, and often a less clear correlation to nutrients or indicators of productivity, as is more typical in open-ocean settings. An ideal area in which to apply and test foraminiferal Ba/Ca as a proxy for freshwater input is the Western Pacific Warm Pool (WPWP), where temperatures are relatively stable, but large variations in precipitation are today driven by the El Nino Southern Oscillation (ENSO) and strength of the Australian-Indonesian monsoon. Foraminiferal Ba/Ca in sediments proximal to a river mouth should therefore reflect changes in riverine input, which in turn reflect variations in precipitation on different timescales. We present here planktic foraminiferal δ18O, Ba/Ca, and Mg/Ca records spanning the last glacial-interglacial transition from marine sediment cores in the Gulf of Papua, located in the WPWP. The δ18O records show an increase in the magnitude of glacial-interglacial (G-IG) δ18O change (∆18O) moving away from the coastline and the mouth of the primary local freshwater source, the Fly River. The reduced amplitude in G-IG ∆18O in the cores closer to shore, manifested by more negative δ18O values before ~20 kyr ago, is likely due to freshwater input from the Fly River, with the effects diminishing with distance from the Fly River source. Temperature and sea level are also changing over the deglaciation, however, contributing to the signal recorded in the calcite δ18O. We use planktic Mg/Ca analyses and independent records of sea level change to isolate the

  10. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    DOE PAGESBeta

    Stoyko, Stanislav; Voss, Leonard; He, Hua; Bobev, Svilen

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e.,more » P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.« less

  11. Structural variation and recovery of superconductivity by Ca substitution in Y{sub 0.4}Pr{sub 0.6}Ba{sub 2-x}Ca{sub x}Cu{sub 3}O{sub 7-{sigma}}

    SciTech Connect

    Cao, G.; Qian, Y.; Wu, H.

    1996-02-01

    Y{sub 0.4}Pr{sub 0.6}Ba{sub 2{minus}x}Ca{sub x}Cu{sub 3}O{sub 7{minus}{delta}} polycrystalline samples were prepared and investigated. The Ca substitution led to a structural variation toward tetragonal symmetry, possibly due to the structural modification within the Cu(1)O layer. Superconductivity and metallic conduction were recovered when x{>=}0.2, giving one more evidence for the existence of the ion-size effect at the Ba site.

  12. Optically stimulated luminescence in K2SO4:AEu (A=Ca,Na,Al)

    NASA Astrophysics Data System (ADS)

    More, Y. K.; Patil, R. R.; Wankhede, S. P.; Kulkarni, M. S.; Kumar, Munish; Bhatt, B. C.; Moharil, S. V.

    2015-08-01

    Optically stimulated luminescence in doped K2SO4 is reported. K2SO4 was prepared by simple melt quenched process using readymade potassium sulphate. Samples were doped with Eu and AEu (A=Ca, Na and Al). Out of these samples K2SO4:Eu and K2SO4:Ca,Eu shows good OSL response to 470 nm optical stimulation. K2SO4:Eu and K2SO4:Ca,Eu have the sensitivities comparable with that of commercial phosphor Al2O3:C (Landauer).

  13. Normal pressure synthesis of (Tl1-yCy)Ba2Ca3Cu4O12-δ superconductor

    NASA Astrophysics Data System (ADS)

    Khan, Nawazish A.; Ahmad, Shakeel; Khurram, A. A.; Ahmad, Maqsood

    2012-10-01

    Single phase (Tl1-yCy)Ba2Ca3Cu4O12-δ (Tl1-yCy-1234) (y = 0, 0.25, 0.5 and 0.75) superconductor samples have been prepared by solid state reaction method. The FTIR absorption measurements have confirmed the substitution of carbon at thallium site in the charge reservoir layer, (Tl1-yCy)Ba2O4-δ. The electron micrographs of these samples have shown that the carbon substitution has improved the grain morphology of Tl0.75C0.25-1234 sample. The y = 0.25 was found to be the optimum carbon concentration to achieve higher superconducting transition temperature Tc[0] and improved grain morphology. The superconducting transition temperature of Tl0.75C0.25-1234 sample has been increased to 100 K whereas a decrease in the superconducting transition temperature of Tl1-yCy-1234 (y = 0.5 and 0.75) samples was observed. However, the magnitude of diamagnetism has been decreased in all the carbon substituted samples.

  14. Contrasting Effects of Ca{sup 2+} and Ho{sup 3+} Substitutions on Superconductivity and Excess conductivity of (Ho{sub 1-x}Ca{sub x})(Ba{sub 2-y}Ho{sub y})Cu{sub 3}O{sub 7-{delta}}

    SciTech Connect

    Maulud, M. F.; Hamidi, Z. S.; Yusof, A. A.; Yusof, M. I. M.; Yahya, A. K.

    2010-07-07

    Effects of Ho{sup 3+} and Ca{sup 2+} substitutions in (Ho{sub 1-x}Ca{sub x})(Ba{sub 2-y}Ho{sub y})Cu{sub 3}O{sub 7-{delta}}ceramics on normal and superconducting state behaviour were investigated. Electrical resistivity measurements showed increasing Ho{sup 3+} substitution at Ba{sup 2+} site (x = 0, 0.4, y = 0-0.4) caused normal state resistivity to change from metal-like to semimetal/semiconductor-like behaviour and suppressed T{sub c} from 89 K (y = 0) to 72 K (y = 0.4) while substitution of Ca{sup 2+} for Ho{sup 3+}((x = 0.2) 0.4, (y 0.4)) revives metallic behaviour of the normal state with increasing x. Excess conductivity analysis based on Asmalazov-Larkin theory showed 2D to 3D transition for all superconducting samples but with contrasting effects of the substitutions on AL{sub 2D} and AL{sub 3D} constants. The resistivity and excess conductivity results indicate effective hole filling Ho{sup 3+} and hole doping by by Ca{sup 2+} substitutions.

  15. Structural and Optoelectronic Properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) Anti-Perovskite Compounds

    NASA Astrophysics Data System (ADS)

    Ullah, Imran; Murtaza, G.; Khenata, R.; Mahmood, Asif; Muzzamil, M.; Amin, N.; Saleh, M.

    2016-01-01

    We employed first-principles calculations to predict the structural and optoelectronic properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) anti-perovskite compounds using an all-electron full-potential linearized augmented plane-wave method. Optimized structural parameters are found to be in good agreement with the available experimental measurements. The electronic band structure is calculated using different exchange-correlation potentials which reveal that the investigated compounds are narrow direct band gap semiconductors. A direct narrow band gap at the center of the Brillouin zone emphasises the optical activity of these compounds. Prediction of the optical properties, such as the real and imaginary parts of the dielectric function and refractive index along with reflectivity and optical conductivity, reveals the importance of these compounds in the visible and near UV optoelectronic devices industry.

  16. Fabrication and microwave properties of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman; Konopka, Janusz; Kula, Witold; Gierlowski, Piotr; Konopka, Anna

    1989-03-01

    Studies are reported of the interaction of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films with microwaves. The films were prepared on cubic zirconia and magnesium oxide substrates using a modified spray deposition technique. The tested films were about 1-3 microns thick and exhibited good superconducting properties. Several test structures have been designed by spraying a mixture of nitrate precursors on heated substrates through very thin stencil marks. The supercurrent dependence on millimeter wavelength microwave illumination was measured, and microwave detection and mixing experiments were performed. The films of both materials exhibited properties characteristic of granular superconductors, with Josephson-type coupling at the intergrain connections. The results also indicate that these materials can be successfully used as very sensitive millimeter radiation detectors operational at liquid-nitrogen temperatures.

  17. Anisotropy of Multilayered (cu, C)BA2CA3CU4OY Superconductors Studied by Torque Magnetometry

    NASA Astrophysics Data System (ADS)

    Tokiwa, K.; Koganezawa, T.; Mikusu, S.; Watanabe, T.; Iyo, A.; Tanaka, Y.

    The magnetic torque of (Cu,C)Ba2Ca3Cu4Oy ( (Cu,C)-1234) aligned samples with various carrier concentrations has been measured under a magnetic field of 9 T at 80 K and 90 K. The carrier concentration was determined by Hall effect measurements. From angular dependent torque measurements, the anisotropy ratio γ was estimated using the 3D anisotropic London model. The γvalues decreased from 23 to 10 with an increase in the average Hall number per CuO2 plane (nH); however, these samples showed a nearly constant Tc of about 117 K. These results indicate that the anisotropy of (Cu,C)-1234 strongly reflects the doping levels of the outer planes.

  18. Flux pinning in Tl1-xCxBa2Ca3Cu4O12-δ superconductor

    NASA Astrophysics Data System (ADS)

    Khurram, A. A.; Ahmad, Shakeel; Khan, Nawazish A.

    2012-10-01

    The dissipation mechanism in Tl1-xCxBa2Ca3Cu4O12-δ (x = 0, 0.25, 0.5 and 0.75) superconductor under the influence of external magnetic fields have been studied. The sample with x = 0.25 have shown strong flux pinning characteristic as compared to the Tl1-xCx-1234 (x = 0, 0.5 and 0.75) samples. The scanning electron micrographs of Tl1-xCx-1234 shows well connected grains in x = 0 and 0.25 samples. Whereas, x = 0.5 and 0.75 samples have relatively poor grain morphology, which shows that the source of pinning in Tl0.75C0.25-1234 sample is intrinsic one. The transition width data was also fitted to the thermally activated flux flow model. The apical phonon modes of vibrations were studied through FTIR absorption measurements.

  19. Structural and Optoelectronic Properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) Anti-Perovskite Compounds

    NASA Astrophysics Data System (ADS)

    Ullah, Imran; Murtaza, G.; Khenata, R.; Mahmood, Asif; Muzzamil, M.; Amin, N.; Saleh, M.

    2016-06-01

    We employed first-principles calculations to predict the structural and optoelectronic properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) anti-perovskite compounds using an all-electron full-potential linearized augmented plane-wave method. Optimized structural parameters are found to be in good agreement with the available experimental measurements. The electronic band structure is calculated using different exchange-correlation potentials which reveal that the investigated compounds are narrow direct band gap semiconductors. A direct narrow band gap at the center of the Brillouin zone emphasises the optical activity of these compounds. Prediction of the optical properties, such as the real and imaginary parts of the dielectric function and refractive index along with reflectivity and optical conductivity, reveals the importance of these compounds in the visible and near UV optoelectronic devices industry.

  20. (Hg, Sb)Ba2Ca2Cu3O8+δ thick films on YSZ substrates

    NASA Astrophysics Data System (ADS)

    Li, J. Q.; Lam, C. C.; Peacock, G. B.; Hyatt, N. C.; Gameson, I.; Edwards, P. P.; Shields, T. C.; Abell, J. S.

    2000-02-01

    Superconducting thick films of (Hg, Sb)Ba2Ca2Cu3O8+icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> have been fabricated on polycrystalline yttria-stabilized-zirconia substrates utilizing an Hg-free precursor film reacted with Hg vapour, released from a solid Hg source, in a sealed quartz tube. The resulting films have been studied by x-ray diffraction, scanning electron microscopy, ac susceptibility and resistance measurement techniques. A high quality Hg(Sb)-1223 superconducting thick film on YSZ can be fabricated by using a pre-melted Hg-free precursor film. The zero resistance superconducting transition temperature in the post-growth oxygenated thick film is in excess of 130 K and the transport critical current density for the film is 510 A cm-2 at 77 K.

  1. Critical current densities in neutron irradiated Tl 2Ca 2Ba 2Cu 3O 10 single crystals

    NASA Astrophysics Data System (ADS)

    Brandstätter, G.; Sauerzopf, F. M.; Weber, H. W.; Aghaei, A.; Schwarzmann, F.

    1994-12-01

    A Tl 2Ca 2Ba 2Cu 3O 10 single crystal with a transition temperature of 117.5 K was subjected to fast neutron irradiation to fluences of 2·10 21, 4·10 21, 8·10 21, and 1.6·10 22 m 2 (E>0.1 MeV). The superconducting transition temperatures T c, the hysteresis loops and the irreversibility lines were measured before and after each irradiation step. The critical current densities J c were calculated from the magnetization loops using an anisotropic Bean model. With increasing fluence we find a decrease of T c, as observed in YBCO-123 and other high temperature superconductors, and an increase of J c. The irreversibility line is shifted to higher fields and temperatures.

  2. The photo-catalytic activities of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) microparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Shi, Yuanji; Zhao, Zongshan; Song, Weijie; Cheng, Yang

    2014-02-01

    For the good performance of apatite-based materials in the removal of dyes and their environment-friendly advantage, five kinds of apatite microparticles of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) were synthesized by a simple precipitation method and their photo-catalytic properties were invested. Better performance in the decolorization of methyl orange (MO) under the assistance of H2O2 than that of TiO2 were obtained for all the MPs. The photo-catalytic activity was mainly affected by surface area, energy band, impurity, crystallinity and crystal structure. The DFT calculation results demonstrated that the 2p of O and 3p of P in PO43- played the main role in the photo-catalytic process. This work would be helpful to design and synthesize low cost apatite materials with good photo-catalytic performance.

  3. Compositional dependence of the crystal symmetry of Eu3+-doped (SrxBa1-x)2CaWyMo1-yO6 phosphors

    NASA Astrophysics Data System (ADS)

    Sletnes, M.; Valmalette, J. C.; Grande, T.; Einarsrud, M.-A.

    2016-01-01

    Two series of A-site and B-site Eu3+ doped (SrxBa1-x)2CaWyMo1-yO6 double perovskite phosphor materials were prepared via a modified Pechini sol-gel route; (SrxBa1-x)1.96Eu0.02K0.02CaWyMo1-yO6 and (SrxBa1-x)2Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, 1). The Sr/Ba ratio was the main determinant for the crystal symmetry of the series, while variation in the W/Mo ratio did influence the crystal symmetry significantly. The crystal structure evolved with Sr/Ba ratio from cubic Fm 3 bar m for x=0, via tetragonal I 4 / m for x=0.25, to monoclinic P 21 / n for x≥0.5, as verified by Rietveld refinement of X-ray diffractograms as well as by Raman spectroscopy. The reported boundaries for the compositionally induced phase transitions are in very good agreement with reported optical properties.

  4. Phosphate-sulfide assemblages and Al/Ca ratios in type-3 chondrites

    NASA Technical Reports Server (NTRS)

    Rubin, A. E.; Grossman, J. N.

    1985-01-01

    Electron microscopic examinations were carried out on various chondrites to re-examine previously reported anomalously high Al/Ca ratios. Polished thin sections of the three CV3, two CO3 and the Krymka LL3 chondrites were scanned to characterize the phosphate-sulfide inclusions. The formation of the assemblages was interpreted as proceeding in five steps, starting with the formation of metal grains with early nebular material and finishing with a reaction between schreibersite with Ca, O and Cl to form merrillite and chloropatite. The abundances of the observed assemblages were not high enough to imply Al/Ca ratios similar to whole-rocks. It is concluded that the specimens were originally examined with a broader electron beam than used to examine standard samples, and resulted in the anomalously high Al/Ca ratios.

  5. Fabrication and chemical composition of rf magnetron sputtered Tl-Ca-Ba-Cu-O high T sub c superconducting thin films

    SciTech Connect

    Subramanyam, G.; Radpour, F.; Kapoor, V.J.; Lemon, G.H. )

    1990-08-01

    High-temperature superconducing Tl-Ca-Ba-Cu-O (TlCaBaCuO) thin films were fabricated by rf magnetron sputtering on strontium titanate (SrTiO{sub 3}) substrates. Thin films of 0.5--0.7-{mu}m thickness were deposited by pure argon sputtering from a single composite powder target of Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub {ital x}} at an rf power of 250 W and a pressure of 5 mTorr. As-deposited thin films were sintered and annealed in a thallium-rich ambient to obtain superconductivity with a zero resistance temperature ({ital T}{sub {ital c}0}) at 107 K. X-ray diffraction results showed highly {ital c}-axis oriented films with Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub {ital x}} (2223) and Tl{sub 2}Ca{sub 1}Ba{sub 2}Cu{sub 2}O{sub {ital x}} (2122) phases present. Auger electron spectroscopy survey and depth profiles were performed to determine the compositional uniformity and impurity contents of the thin films. X ray photoelectron spectroscopy high-resolution spectra were obtained at the surface, in the bulk, and near the interface with the substrate. Our XPS results support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca{sup 2+} for Tl{sup 3+} and (2) charge transfer from Tl{sup 3+} to the CuO layers resulting in a valence of Tl between +3 and +1 states and the creation of holes in the CuO layers. In addition, a wet chemical etching process was developed for patterning the as-deposited TlCaBaCuO thin films. A 125-{mu}m-wide line was formed using standard photolithography and wet chemical etching which, after heat treatments, showed superconductivity with a {ital T}{sub {ital c}0} of 80 K.

  6. Formation Mechanism of CaS-Bearing Inclusions and the Rolling Deformation in Al-Killed, Low-Alloy Steel with Ca Treatment

    NASA Astrophysics Data System (ADS)

    Xu, Guang; Jiang, Zhouhua; Li, Yang

    2016-08-01

    The existing form of CaS inclusion in Ca-treated, Al-killed steel during secondary refining process was investigated with scanning electron microscopy and an energy-dispersive spectrometer (EDS). The results of 12 heats industrial tests showed that CaS has two kinds of precipitation forms. One form takes place by the direct reaction of Ca and S, and the other takes place by the reaction of CaO in calcium aluminates with dissolved Al and S in liquid steel. Thermodynamic research for different precipitation modes of CaS under different temperature was carried out. In particular, CaO-Al2O3-CaS isothermal section diagrams and component activities of calcium aluminates were calculated by the thermodynamic software FactSage. By thermodynamic calculation, a precipitation-area diagram of oxide-sulfide duplex inclusion was established by fixing the sulfur content. The quantity of CaS, which was precipitated in a reaction between [Al], [S] and (CaO), can be calculated and predicted based on the precipitation-area diagram of oxide-sulfide duplex inclusion. Electron probe microanalysis and EDS were used for observing rolling deformation of different types of CaS-bearing inclusions during the rolling process. Low modification of calcium aluminates wrapped by CaS has different degrees of harm to steel in the rolling process. A thick CaS layer can prevent some fragile calcium aluminates from being crushed during the rolling process. Some oxide-sulfide duplex inclusion contains little CaS performed better deformation during the rolling process, but when CaS in oxide-sulfide duplex inclusion becomes more, it will cause the whole inclusion to lose plastic yielding ability. The plastic deformation region of CaS-bearing inclusion in a CaO-Al2O3-CaS isothermal section diagram is confirmed.

  7. Formation Mechanism of CaS-Bearing Inclusions and the Rolling Deformation in Al-Killed, Low-Alloy Steel with Ca Treatment

    NASA Astrophysics Data System (ADS)

    Xu, Guang; Jiang, Zhouhua; Li, Yang

    2016-05-01

    The existing form of CaS inclusion in Ca-treated, Al-killed steel during secondary refining process was investigated with scanning electron microscopy and an energy-dispersive spectrometer (EDS). The results of 12 heats industrial tests showed that CaS has two kinds of precipitation forms. One form takes place by the direct reaction of Ca and S, and the other takes place by the reaction of CaO in calcium aluminates with dissolved Al and S in liquid steel. Thermodynamic research for different precipitation modes of CaS under different temperature was carried out. In particular, CaO-Al2O3-CaS isothermal section diagrams and component activities of calcium aluminates were calculated by the thermodynamic software FactSage. By thermodynamic calculation, a precipitation-area diagram of oxide-sulfide duplex inclusion was established by fixing the sulfur content. The quantity of CaS, which was precipitated in a reaction between [Al], [S] and (CaO), can be calculated and predicted based on the precipitation-area diagram of oxide-sulfide duplex inclusion. Electron probe microanalysis and EDS were used for observing rolling deformation of different types of CaS-bearing inclusions during the rolling process. Low modification of calcium aluminates wrapped by CaS has different degrees of harm to steel in the rolling process. A thick CaS layer can prevent some fragile calcium aluminates from being crushed during the rolling process. Some oxide-sulfide duplex inclusion contains little CaS performed better deformation during the rolling process, but when CaS in oxide-sulfide duplex inclusion becomes more, it will cause the whole inclusion to lose plastic yielding ability. The plastic deformation region of CaS-bearing inclusion in a CaO-Al2O3-CaS isothermal section diagram is confirmed.

  8. Investigation on photoluminescence properties and defect chemistry of GdAlO3:Dy3+ Ba2+ phosphors

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, Thangaraj; Sellaiyan, Selvakumar; Uedono, Akira; Semba, Takaaki; Bose, Arumugam Chandra

    2016-08-01

    GdAlO3:Dy3+ Ba2+ phosphors are synthesized by citrate-based sol-gel method. Photoluminescence and positron annihilation studies are used to investigate the emission and defect chemistry of the phosphors respectively. The strong yellow (Dy3+) emission properties of phosphors are discussed for various concentrations of Dy3+ ions. Upon the addition of Ba2+ ion, an enhancement in emission intensity is observed due to the lattice distortions around Dy3+ ion. The positron studies indicate the presence of defects at crystallite boundaries, vacancy clusters and large voids in the materials. The influence of Ba2+ ion on the photoluminescence and lattice distortion around Dy3+ is also explored.

  9. Determining Solute Sources and Water Flowpaths in a Forested Headwater Catchment: Advances With the Ca-Sr-Ba Multi-tracer

    NASA Astrophysics Data System (ADS)

    Bullen, T. D.; Bailey, S. W.; McGuire, K. J.; Zimmer, M. A.; Ross, D. S.

    2011-12-01

    Determining solute sources and water flowpaths in catchments is of critical importance to development of models that effectively describe catchment function. For solutes in soil water and stream water, simple mass balance models that compare precipitation input to catchment outlet compositions can predict average mineral weathering contributions for the catchment as a whole, but fail to provide information about either variability of contributions from different portions of the catchment and different soil depths or processes such as ion exchange and biological cycling. In order to better understand how forested headwater catchments function, we are interpreting concentration and isotope ratios of the alkaline earth elements Ca, Sr and Ba in streamwater, groundwater, the soil ion exchange pool and plants in a hydropedologic context at the 41 hectare hydrologic reference catchment (Watershed 3) at the Hubbard Brook Experimental Forest, New Hampshire, USA. This forested headwater catchment consists of a beech-birch-maple-spruce forest growing on vertically- and laterally-developed Spodosols and Inceptisols formed on granitoid glacial till that mantles Paleozoic metamorphic bedrock. Across the watershed in terms of the soil ion exchange pool, the forest floor has high Sr/Ba and Ca/Sr ratios, mineral soils have intermediate Sr/Ba and low Ca/Sr, and relatively unweathered till in the C horizon has low Sr/Ba and high Ca/Sr. Waters moving through these various compartments will obtain Sr/Ba and Ca/Sr ratios reflecting these characteristics, and thus variations of Sr/Ba and Ca/Sr of streamwater provide evidence of the depth of water flowpaths feeding the streams. 87Sr/86Sr of exchangeable Sr spans a broad range from 0.715 to 0.725, with highest values along the mid-to upper flanks of the catchment and lowest values in a broad zone along the central axis of the catchment associated with numerous groundwater seeps. Thus, variations of 87Sr/86Sr in streamwater provide

  10. Effect of Al3+ on Photoluminescence Properties of Eu3+-Doped BaZr(BO3)2 Phosphors

    NASA Astrophysics Data System (ADS)

    Li, Guang-Min; Li-Lan; Wang, Da-Jian; Zhang, Xiao-Song; Tao, Yi

    2006-08-01

    We discuss the influence of Al3+ on the charge transfer state (CTS) and the photoluminescence properties of BaZr(BO3)2:Eu. The results reveal that there is a red shift which is about 20 nm for the charge transfer state when doping with Al3+ and indicate the formation of `free' electrons due to the change of microstructures. In addition, the influence of Al3+ doping on the PPR is analysed and a new explanation is raised based on the photo luminescent mechanism. It is the CTS intensity rather than the CTS energy that influences the peak-peak ratio.

  11. Single Phase Melt Processed Powellite (Ba,Ca) MoO{sub 4} For The Immobilization Of Mo-Rich Nuclear Waste

    SciTech Connect

    Brinkman, Kyle; Marra, James; Fox, Kevin; Reppert, Jason; Crum, Jarrod; Tang, Ming

    2012-09-17

    Crystalline and glass composite materials are currently being investigated for the immobilization of combined High Level Waste (HLW) streams resulting from potential commercial fuel reprocessing scenarios. Several of these potential waste streams contain elevated levels of transition metal elements such as molybdenum (Mo). Molybdenum has limited solubility in typical silicate glasses used for nuclear waste immobilization. Under certain chemical and controlled cooling conditions, a powellite (Ba,Ca)MoO{sub 4} crystalline structure can be formed by reaction with alkaline earth elements. In this study, single phase BaMoO{sub 4} and CaMoO{sub 4} were formed from carbonate and oxide precursors demonstrating the viability of Mo incorporation into glass, crystalline or glass composite materials by a melt and crystallization process. X-ray diffraction, photoluminescence, and Raman spectroscopy indicated a long range ordered crystalline structure. In-situ electron irradiation studies indicated that both CaMoO{sub 4} and BaMoO{sub 4} powellite phases exhibit radiation stability up to 1000 years at anticipated doses with a crystalline to amorphous transition observed after 1 X 10{sup 13} Gy. Aqueous durability determined from product consistency tests (PCT) showed low normalized release rates for Ba, Ca, and Mo (<0.05 g/m{sup 2}).

  12. In vitro synthesis of amorphous Mg-, Ca-, Sr- and Ba-carbonates: What do we learn about intracellular calcification by cyanobacteria?

    NASA Astrophysics Data System (ADS)

    Cam, N.; Georgelin, T.; Jaber, M.; Lambert, J.-F.; Benzerara, K.

    2015-07-01

    Some cyanobacteria, including Candidatus Gloeomargarita lithophora, which was isolated from Lake Alchichica (Mexico), can form intracellular carbonates. This contradicts the common paradigm that cyanobacterial calcification is always extracellular and suggests that calcification might be controlled by these cyanobacterial species. Intracellular carbonates have several peculiar characteristics: they are relatively small (between 60 and 500 nm), they are poorly crystalline, and they have Sr/Ca and Ba/Ca ratios much higher than the solution in which the cells grow. It is therefore crucial to understand whether these unique features may indicate the involvement of specific biological processes. Here, in vitro abiotic syntheses were performed to synthesize Mg-, Ca-, Sr- and Ba-containing carbonates with compositions, crystallinities and sizes close to those observed in intracellularly calcifying cyanobacteria. Precipitates were characterized by scanning and transmission electron microscopies coupled with energy dispersive X-ray spectroscopy, thermogravimetric analysis and X-ray diffraction. The size and the poor crystallinity of cyanobacterial intracellular carbonates could be mimicked under these abiotic conditions. It was shown that similarly to Mg, elements such as Sr and Ba can favor stabilization of poorly crystalline carbonates. In contrast, the differential partitioning of Sr, Ba and Ca between the solution and the solids as observed in cyanobacteria could not be mimicked in vitro. This provides keys to a better understanding of biological processes involved in the formation of intracellular carbonates by some cyanobacteria, including the involvement of membrane transporters.

  13. Irreversibility line and flux pinning properties in a multilayered cuprate superconductor of Ba2Ca3Cu4O8(O,F)2 (Tc = 105 K)

    NASA Astrophysics Data System (ADS)

    Shirage, P. M.; Iyo, A.; Shivagan, D. D.; Tanaka, Y.; Kito, H.; Kodama, Y.

    2008-07-01

    Irreversibility line (IL) and flux pinning properties were investigated for a Ba2Ca3Cu4O8(O,F)2 (F-0234) multilayered cuprate superconductor with a Tc of 105 K. The intragrain critical current density (Jc) and irreversibility field (Birr) were determined by using Bean's critical state model for the grain-aligned sample (nominal composition Ba2Ca3Cu4O8.7F1.3). The irreversibility line (IL) of F-0234 is much lower than that of (Cu,C)Ba2Ca3Cu4Oy ((Cu, C)-1234) and HgBa2Ca3Cu4Oy (Hg-1234) in spite of the spacing between the superconducting blocks of F-0234 (7.3 Å) being much thinner. The double logarithmic plot of Birr field versus [1-(T/Tc) ] analysis hints that the flux line melting model has been adopted. An anisotropy factor of 65 was calculated from a 3D to 2D crossover field of about 0.95 T. Due to the high anisotropy of this system, a low IL has resulted. The flux pinning force density Fp ( ≈JcB) exhibits scaling behaviour when the magnetic field B is normalized by the Birr field. Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and the reduced magnetic field bmax = 0.2 agrees with surface pinning mechanism with closely spaced pins.

  14. Energy transfer in M₅(PO₄)₃  F:Eu²⁺,Ce³⁺ (M = Ca and Ba) phosphors.

    PubMed

    Shinde, K N; Dhoble, S J

    2014-08-01

    M5(PO4)3F:Eu(2+) (M = Ca and Ba) co-doped with Ce(3+) phosphors were successfully prepared by the combustion synthesis method. The introduction of co-dopant (Ce(3+)) into the host enhanced the luminescent intensity of the M5(PO4)3F:Eu(2+) (M = Ca and Ba) efficiently. Previously, we have reported the synthesis and photoluminescence properties of same phosphors. The aim of this article is to report energy transfer mechanism between Ce(3+) ➔Eu(2+) ions in M5(PO4)3F:Eu(2+) (M = Ca and Ba) phosphors, where Ce(3+) ions act as sensitizers and Eu(2+) ions act as activators. The M5(PO4)3F:Eu(2+) (M = Ca and Ba) co-doped with Ce(3+) phosphor exhibits great potential for use in white ultraviolet (UV) light-emitting diode applications to serve as a single-phased phosphor that can be pumped with near-UV or UV light-emitting diodes. PMID:23901019

  15. Thermal stability of the luminescence of Ca6Ba(PO4)4O:Eu2+ yellow phosphor for white light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Meng, Yingjun; Zhao, Weiren; Chen, Junhua; Wang, Nenghuo; Zhou, Yiyang; Zhang, Wei; Yi, Shuangping

    2016-07-01

    Yellow-emitting Ca6Ba(PO4)4O:Eu2+ phosphors were synthesized by solid-state reaction method. The phase composition was checked by X-ray powder diffraction. The photoluminescence properties of Ca6Ba(PO4)4O:Eu2+ and their thermal properties of photoluminescence were explored. The excitation spectra ranging from 230 to 450 nm and an intense broad yellow emission band centered at 530 nm can be observed under the excitation at 375 nm. Ca6Ba(PO4)4O:0.07Eu2+ phosphor maintains 45 % of the photoluminescence intensity of room temperature when heated up to 150 °C, exhibiting a relatively good thermal quenching resistance. The optimum concentration of Eu2+ in Ca6- x Ba(PO4)4O: xEu2+ was found with x = 0.07, and the concentration quenching mechanism was illustrated by configurational coordinate diagram. The luminescence decay of Eu2+ ions was also studied carefully, showing the decrease of the lifetime with the increase of Eu2+ concentration.

  16. Metal-semiconductor-transition observed in Bi{sub 2}Ca(Sr, Ba){sub 2}Co{sub 2}O{sub 8+δ} single crystals

    SciTech Connect

    Dong, Song-Tao; Zhang, Bin-Bin; Zhang, Lun-Yong; Yao, Shu-Hua E-mail: shyao@nju.edu.cn; Zhou, Jian; Zhang, Shan-Tao; Gu, Zheng-Bin; Chen, Yan-Feng; Chen, Y. B. E-mail: shyao@nju.edu.cn

    2014-07-28

    Electrical property evolution of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} single crystals (AE = Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+δ} and Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} demonstrates semiconductor-like properties. But Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} to semiconductor-like Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} can be attributed to Anderson localization. However the semiconductor behaviour of Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} and Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+δ} is related to electronic correlations effect that is inferred by large negative magnetoresistance (∼70%). The theoretical electronic structures and valence X-ray photoemission spectroscopy substantiate that there is a relative large density of state around Fermi level in Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} compared with other two compounds. It suggests that Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} is more apt to be metal in this material system.

  17. Luminescence properties of undoped LiBaAlF6 single crystals.

    PubMed

    Omelkov, S I; Kirm, M; Feldbach, E; Pustovarov, V A; Cholakh, S O; Isaenko, L I

    2010-07-28

    This paper presents the results of the study of electronic excitations in undoped LiBaAlF(6) single crystals by means of luminescence spectroscopy and complimentary optical methods. The intrinsic emission at 4.2 eV due to self-trapped excitons was identified. The fast nanosecond defect-related luminescence was revealed at 3.0 eV. Both emissions degrade under electron beam irradiation, the most probable reason of which is defect creation introducing an additional non-radiative relaxation channel prohibiting energy transfer to luminescence centers. These defects can be recovered and luminescence intensity restored at higher temperatures (>200 K). The permanent damage by electron beam irradiation results only in overall growth of the absorption coefficient in the whole 1.5-6.5 eV spectral region studied. The analysis of thermally stimulated luminescence glow curves in the temperature range of 5-410 K revealed two shallow charge carrier traps with the activation energies of 0.22 and 0.33 eV, respectively. The luminescence of an impurity peaked at 2.5 eV was found and tentatively assigned to an oxygen-related emission center. PMID:21399311

  18. Growth of Tl 2Ba 2CaCu 2O 8 superconducting thin films on curved substrates for metamaterials applications

    NASA Astrophysics Data System (ADS)

    Speller, S. C.; Dinner, R. B.; Grovenor, C. R. M.

    2008-08-01

    Recent developments in the field of magnetic metamaterials have shown that coupled resonator structures can manipulate magnetic fields on a scale shorter than the wavelength of the electromagnetic radiation [E. Shamonina, V.A. Kalinin, K.H. Ringhofer, L. Solymar, J. Appl. Phys. 92 (10) (2002) 6252]. Major improvements in the sensitivity of such devices could be achieved by fabricating the resonating elements from high temperature superconducting (HTS) films on appropriate dielectric substrates. In order to produce a stack of superconducting/dielectric resonator structures, the ideal method involves patterning them into an HTS film grown on the curved surface of a dielectric cylinder. We report here our initial attempts at the growth of Tl 2Ba 2CaCu 2O 8 (Tl-2212) thin films on the surface of LaAlO 3 and MgO single-crystal cylinders. We have found that Tl-2212 thin films grow epitaxially on LaAlO 3 cylinders with Tl-2212 [0 0 1] aligned with the closest LaAlO 3 pseudocubic <1 0 0> direction, resulting in abrupt changes in Tl-2212 plate orientation at four positions around the cylinder. In contrast, Tl-2212 films grow smoothly on MgO cylinders, with Tl-2212 [0 0 1] aligned roughly parallel to the surface normal at all positions around the cylinder. This smooth growth on MgO leads to higher critical current values than epitaxial growth, making HTS on MgO a promising candidate for metamaterial device applications.

  19. Effect of NiCr Clad BaF2·CaF2 Addition on Wear Performance of Plasma Sprayed Chromium Carbide-Nichrome Coating

    NASA Astrophysics Data System (ADS)

    Du, Lingzhong; Huang, Chuanbing; Zhang, Weigang; Zhang, Jingmin; Liu, Wei

    2010-03-01

    NiCr clad BaF2·CaF2 fluoride eutectic powders were added into chromium carbide-nichrome feedstock to improve the tribological properties of NiCr-Cr3C2 coating, and the structures, mechanical, and ball-on-disk sliding wear performance of the coating were characterized. The results show that NiCr cladding can effectively decrease the density and thermophysical difference between the feedstock components, while alleviate the decarburization and oxidization of the constituent phases, and form the coating with a uniform and dense microstructure. However, the addition of BaF2·CaF2 has a negative effect on mechanical properties of the coating. When the temperature reaches 500 °C, the BaF2·CaF2 eutectic is soften by the heat and smeared by the counterpart, thus the low shear stress lubricating film forms between the contact surface, that improves the tribological properties dramatically. At this temperature, the dominant wear mechanisms also change from splats spallation and abrasive wear at room temperature to plastic deformation and plawing by the counterpart. Within the temperature range from 600 to 800 °C, the friction coefficient, the wear rates of NiCr/Cr3C2-10% BaF2·CaF2 coating and its coupled Si3N4 ball are 20%, 40%, and 75% lower than those of the NiCr/Cr3C2 coating, respectively. The NiCr/Cr3C2-BaF2·CaF2 coating shows superior wear performance to the NiCr/Cr3C2 coating without lubricant additive.

  20. Synthesis, characterization and optical properties of ATiO{sub 3}–Pr thin films prepared by a photochemical method (where A = Ba and Ca)

    SciTech Connect

    Cabello, G.; Lillo, L.; Caro, C.; Seguel, M.; Buono-Core, G.E.; Huentupil, Y.; Chornik, B.; Carrasco, C.; Rodríguez, C.A.

    2015-10-15

    Highlights: • A method of photochemical deposition has been used to the preparation of (Ba,Ca)TiO{sub 3} thin films doped Pr(III). • The (Ba,Ca)TiO{sub 3}/Pr(III) films under 375 nm excitation shows emissions attributable to {sup 1}D{sub 2} → {sup 3}H{sub 4} transition of Pr ion. • These PL signals decreased above 10 mol% of Pr(III). • Analysis suggests the presence of intermediate energy levels in the band gap influences in the PL processes. - Abstract: This article reports the characterization and optical properties of (Ba,Ca)TiO{sub 3} thin films doped with Pr at different proportions (0–15 mol%). The films were deposited on Si (1 0 0) and quartz substrates using a photochemical method and post-annealed at 900 °C. The evaluation of photo-reactivity of the precursor complexes was monitored by UV–vis and FT-IR spectroscopy. The obtained films were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The results indicate that Ba, Ca, Ti, O and Pr are present in the form of perovskite. Under UV light excitation (375 nm) the (Ba,Ca)TiO{sub 3}–Pr films show the characteristic emissions ascribed to {sup 1}D{sub 2} → {sup 3}H{sub 4} transition of Pr{sup 3+} ion. The optical measurements show the presence of intermediate energy levels in the band gap which influence the emission processes.

  1. Chemical spray pyrolysis of Tl-Ba-Ca-Cu-O high-T(sub c) superconductors for high-field bitter magnets

    NASA Technical Reports Server (NTRS)

    Derochemont, L. Pierre; Zhang, John G.; Squillante, Michael R.; Hermann, A. M.; Duan, H. M.; Andrews, Robert J.; Kelliher, Warren C.

    1991-01-01

    The deposition of Tl-Ba-Ca-Cu-O thick films by spray pyrolyzing a Ba-Ca-Cu-O precursor film and diffusing thallium into the film to form the superconducting phase is examined. This approach was taken to reduce exposure to thallium and its health and safety hazards. The Tl-Ba-Ca-Cu-O system was selected because it has very attractive features which make it appealing to device and manufacturing engineering. Tl-Ba-Ca-Cu-O will accommodate a number of superconducting phases. This attribute makes it very forgiving to stoichiometric fluctuations in the bulk and film. It has excellent thermal and chemical stability, and appears to be relatively insensitive to chemical impurities. Oxygen is tightly bound into the systems, consequently there is no orthorhombic (conductor) to tetragonal (insulator) transition which would affect a component's lifetime. More significantly, the thallium based superconductors appear to have harder magnetic properties than the other high-Tc oxide ceramics. Estimates using magnetoresistance measurements indicate that at 77 K Tl2Ba2CaCu2O10 will have an upper critical field, H(sub c2) fo 26 Tesla for applied fields parallel to the c-axis and approximately 1000 Tesla for fields oriented in the a-b plane. Results to date have shown that superconducting films can be reproducibly deposited on 100 oriented MgO substrates. One film had a zero resistance temperature of 111.5 K. Furthermore, x ray diffraction analysis of the films showed preferential c-axis orientation parallel to the plane of the substrate. These results have now made it possible to consider the manufacture of a superconducting tape wire which can be configured into a topology useful for high-field magnet designs. The research which leads to the preparation of these films and plans for further development are reviewed.

  2. A 170-year Sr/Ca and Ba/Ca coral record from the western Pacific warm pool: 2. A window into variability of the New Ireland Coastal Undercurrent

    NASA Astrophysics Data System (ADS)

    Alibert, Chantal; Kinsley, Leslie

    2008-06-01

    A Porites coral from New Ireland (2.5°S, 150.5°E), at the heart of the Pacific warm pool, records variations of Ba/Ca back to the early 1820s. The New Ireland Coastal Undercurrent, which flows along the north coast and transports high-nutrient thermocline waters, is thought to be the main source of the Ba enrichment observed in the coral during El Niño. Between the 1850s and the 1960s, frequent large Ba peaks indicate that nutrients were available during both phases of El Niño-Southern Oscillation (ENSO). During La Niña, Ba could be advected along the South Equatorial Current. Also during this period, clusters of Ba/Ca peaks at nearly decadal timescale generally coincide with the return time of a strong El Niño, in accord with the high decadal variance of NINO3 sea surface temperatures. Ba enrichment in this coral primarily reflects the stratification in the thermocline that controls vertical mixing. The coral records long-term changes in those properties affecting nutrients in surface waters, with reduced Ba after the 1960s, and even less between 1823 and 1850. These reductions are tentatively attributed to the high rate of warming at the end of the Dalton Minimum and since the mid-20th century. An ensuing weakening of the trade winds may have produced a more stratified equatorial thermocline, hindering the transport of Ba and nutrients from the undercurrent to the shallow coastal waters north of New Ireland.

  3. Structural, dielectric and electrocaloric properties in lead-free Zr-doped Ba0.8Ca0.2TiO3 solid solution

    NASA Astrophysics Data System (ADS)

    Asbani, B.; Gagou, Y.; Dellis, J.-L.; Lahmar, A.; Amjoud, M.; Mezzane, D.; Kutnjak, Z.; El Marssi, M.

    2016-07-01

    We investigate in the present work the additional data points (x=0.02, 0.06 and 0.08) to the previous reported paper (Asbani et al., 2015) [21] that sufficiently enrich to understand the EC properties and underlying phase diagram of the lead-free Ba0.8Ca0.2Ti(1-x)ZrxO3 (xBCTZ) system. X-ray diffraction analysis performed at room temperature, confirms a continuous tetragonal solid solution with P4mm (No. 99) space group that evolved to pseudo-cubic symmetry for the high Zr-content compounds. Ferroelectric and paraelectric behaviors were highlighted using P-E hysteresis data versus temperature. Phase transition was confirmed by dielectric permittivity measurements versus temperature showing a decrease of the Curie temperature when Zr-content increases. From P-E hysteresis recording the electrocaloric temperature change (ΔT) was calculated that ranged in between 0.12 and 0.27 K and the electrocaloric responsivity (ξ) in 0.15 to 0.34×10-6 K·m/V under 7.95 kV/cm applied electric field. The zero-field entropy is compared to electrocaloric isothermal entropy to estimate the extent the EC is being under-driven.

  4. Effect of Ca addition on the corrosion behavior of Mg-Al-Mn alloy

    NASA Astrophysics Data System (ADS)

    Yang, Jiang; Peng, Jian; Nyberg, Eric A.; Pan, Fu-sheng

    2016-04-01

    The microstructures and corrosion resistance of magnesium-5 wt% aluminum-0.3 wt% manganese alloys (Mg-Al-Mn) with different Ca additions (0.2-4 wt%) were investigated. Results showed that with increasing Ca addition, the grain of the alloys became more refined, whereas the corrosion resistant ability of the alloys initially increased and then decreased. The alloy with 2 wt% Ca addition exhibited the best corrosion resistance, attributed to the effect of the oxide film and (Mg,Al)2Ca phases which were discontinuously distributed on the grain boundaries. These phases acted as micro-victims, they preferentially corroded to protect the α-Mg matrix. The oxide film formed on the alloy surface can hinder the solution further to protect the α-Mg matrix.

  5. Concentrations and ratios of Sr, Ba and Ca along an estuarine river to the Gulf of Mexico - implication for sea level rise effects on trace metal distribution

    NASA Astrophysics Data System (ADS)

    He, S.; Xu, Y. J.

    2015-11-01

    Strontium and barium to calcium ratios are often used as proxies for tracking animal movement across salinity gradients. As sea level rise continues, many estuarine rivers in the world face saltwater intrusion, which may cause changes in mobility and distribution of these metals upstream. Despite intensive research on metal adsorption and desorption in marine systems, knowledge of the spatiotemporal distribution of these elements along estuarine rivers is still limited. In this study, we conducted an intensive monitoring of Sr and Ba dynamics along an 88 km long estuary, the Calcasieu River in South Louisiana, USA, which has been strongly affected by saltwater intrusion. Over the period from May 2013 to August 2015, we collected monthly water samples and performed in-situ water quality measurements at six sites from the upstream to the river mouth, with a salinity range from 0.02 to 29.50 ppt. Water samples were analyzed for Sr, Ba, and Ca concentrations. In-situ measurements were made on salinity, pH, water temperature, dissolved oxygen concentration, and specific conductance. We found that the Sr and Ca concentrations and the Sr / Ca ratio all increased significantly with increasing salinity. The average Sr concentration at the site closest to the Gulf of Mexico (site 6) was 46.21 μmol L-1, which was about 130 times higher than that of the site furthest upstream (site 1, 0.35 μmol L-1). The average Ca concentration at site 6 was 8.19 mmol L-1, which was about 60 times higher than that of site 1 (0.13 mmol L-1). The average Sr / Ca ratio at site 6 (8.41 mmol mol-1) was about 3 times the average Sr / Ca ratio at site 1 (2.89 mmol mol-1). However, the spatial variation in Ba concentration was marginal, varying from 0.36 μmol L-1 at site 6 to 0.47 at site 5. The average Ba / Ca ratio at site 1 (4.82 mmol mol-1) was about 54 times the average Ba / Ca ratio at site 6 (0.09 mmol mol-1), showing a clear negative relation between the Ba / Ca ratio and increasing

  6. Catalyst Size and Morphological Effects on the Interaction of NO2 with BaO/γ-Al2O3 Materials

    SciTech Connect

    Mei, Donghai; Kwak, Ja Hun; Szanyi, Janos; Ge, Qingfeng; Peden, Charles HF

    2010-06-19

    The capability of NOx storage on the supported BaO catalyst largely depends on the Ba loading. With different Ba loadings, the supported BaO component exposes various phases ranging from well-dispersed nanoclusters to large crystalline particles on the oxide support materials. In order to better understand size and morphological effects on NOx storage over -Al2O3 supported BaO materials, the adsorption structures and energetics of single NO2 molecule, as well as NOx+NOy (NO2+NO2, NO+NO3 and NO2+NO3) pairs on the BaO/-Al2O3(100), (BaO)2/-Al2O3(100), and (BaO)5/-Al2O3(100) surfaces were investigated using first-principles density functional theory calculations. A single NO2 molecule prefers to adsorb at basic OBa site forming anionic nitrate species. Upon adsorption, a charge redistribution in the supported (BaO)n clusters occurs. Synergistic effects due to the interaction of NO2 with both the (BaO)n clusters and the  Al2O3(100) support enhances the stability of adsorbed NO2. The interaction between NO2 and the (BaO)n/ Al2O3(100) catalysts was found to be markedly affected by the sizes and morphologies of the supported (BaO)n clusters. The adsorption energy of NO2 increases from 0.98 eV on the BaO/-Al2O3(100) surface to 3.01 eV on (BaO)5/ Al2O3(100). NO2 adsorption on (BaO)2 clusters in a parallel configuration on the -Al2O3(100) surface is more stable than on dimers oriented in a perpendicular fashion. Similar to the bulk BaO(100) surface, a supported (BaO)n cluster-mediated electron transfer induces cooperative effects that dramatically increase the total adsorption energy of NOx+NOy pairs on the (BaO)n/-Al2O3(100) surfaces. Following the widely accepted NO2 storage mechanism of , our thermodynamic analysis indicates that the largest energy gain for this overall process of NOx uptake is obtained on the amorphous monolayer-like (BaO)5/-Al2O3(100) surface. This suggests that -Al2O3-supported BaO materials with ~ 6  12 wt

  7. Revised structural phase diagram of (Ba0.7Ca0.3TiO3)-(BaZr0.2Ti0.8O3)

    NASA Astrophysics Data System (ADS)

    Keeble, Dean S.; Benabdallah, Feres; Thomas, Pam A.; Maglione, Mario; Kreisel, Jens

    2013-03-01

    The temperature-composition phase diagram of barium calcium titanate zirconate (x(Ba0.7Ca0.3TiO3)-(1 - x)(BaZr0.2Ti0.8O3); BCTZ) has been reinvestigated using high-resolution synchrotron x-ray powder diffraction. Contrary to previous reports of an unusual rhombohedral-tetragonal phase transition in this system, we have observed an intermediate orthorhombic phase, isostructural to that present in the parent phase, BaTiO3, and we identify the previously assigned T-R transition as a T-O transition. We also observe the O-R transition coalescing with the previously observed triple point, forming a phase convergence region. The implication of the orthorhombic phase in reconciling the exceptional piezoelectric properties with the surrounding phase diagram is discussed.

  8. Revised structural phase diagram of (Ba{sub 0.7}Ca{sub 0.3}TiO{sub 3})-(BaZr{sub 0.2}Ti{sub 0.8}O{sub 3})

    SciTech Connect

    Keeble, Dean S.; Thomas, Pam A.; Benabdallah, Feres; Maglione, Mario; Kreisel, Jens

    2013-03-04

    The temperature-composition phase diagram of barium calcium titanate zirconate (x(Ba{sub 0.7}Ca{sub 0.3}TiO{sub 3})-(1 - x)(BaZr{sub 0.2}Ti{sub 0.8}O{sub 3}); BCTZ) has been reinvestigated using high-resolution synchrotron x-ray powder diffraction. Contrary to previous reports of an unusual rhombohedral-tetragonal phase transition in this system, we have observed an intermediate orthorhombic phase, isostructural to that present in the parent phase, BaTiO{sub 3}, and we identify the previously assigned T-R transition as a T-O transition. We also observe the O-R transition coalescing with the previously observed triple point, forming a phase convergence region. The implication of the orthorhombic phase in reconciling the exceptional piezoelectric properties with the surrounding phase diagram is discussed.

  9. Microstructural characterization of Ag-sheathed Tl-Ba-Ca-Cu-O and Bi-Sr-Ca-Cu-O superconducting tapes by analytical electron microscopy

    SciTech Connect

    Hu, J.G.; Miller, D.J.; Goretta, K.C.; Poeppel, R.B.

    1992-09-01

    The microstructures of Tl(1223) and Pb-doped Bi(2223) silver tapes produced by the powder-in-tube (PM) method have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The Tl tapes annealed below the melting point exhibited fine grains and a high density of pores while tapes subjected to partial melting prior to solid state annealing were fully dense with large grains. However, these tapes also showed an increase in the size and density of impurity particles, particularly CaO and a Ba-Cu rich phase. Silver powders added to the precursors tended to promote the growth of Tl(1223) at lower temperatures but also interfered with the development of texture by providing nucleation sites of random orientations. In contrast, the Bi(2223) tape exhibited a high degree of texture and alignment. The incorporation of silver within the superconducting phase was found to be negligible for both the Tl(1223) and Bi(2223) tapes.

  10. On the microstructure and symmetry of apparently hexagonal BaAl{sub 2}O{sub 4}

    SciTech Connect

    Larsson, A.-K. Withers, R.L.; Perez-Mato, J.M.; Fitz Gerald, J.D.; Saines, P.J.; Kennedy, B.J.; Liu, Y.

    2008-08-15

    The P6{sub 3} (a=2a{sub p}, b=2b{sub p}, c=c{sub p}) crystal structure reported for BaAl{sub 2}O{sub 4} at room temperature has been carefully re-investigated by a combined transmission electron microscopy and neutron powder diffraction study. It is shown that the poor fit of this P6{sub 3} (a=2a{sub p}, b=2b{sub p}, c=c{sub p}) structure model for BaAl{sub 2}O{sub 4} to neutron powder diffraction data is primarily due to the failure to take into account coherent scattering between different domains related by enantiomorphic twinning of the P6{sub 3}22 parent sub-structure. Fast Fourier transformation of [0 0 1] lattice images from small localized real space regions ({approx}10 nm in diameter) are used to show that the P6{sub 3} (a=2a{sub p}, b=2b{sub p}, c=c{sub p}) crystal structure reported for BaAl{sub 2}O{sub 4} is not correct on the local scale. The correct local symmetry of the very small nano-domains is most likely orthorhombic or monoclinic. - Graphical abstract: The electron diffraction pattern of BaAl{sub 2}O{sub 4} (left) is compatible with the 3-q superstructure corresponding to the conventional P6{sub 3}, a=2a{sub p} structure (p refers to the tridymite-related parent P6{sub 3}22 structure). Fast Fourier transforms (right) of small domains of lattice images, however, show that the local structure in fact is single q, and that true symmetry is monoclinic or orthorhombic.

  11. Photoluminescence properties of AlN-doped BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphors

    SciTech Connect

    Wang, Yong; Tang, Jianfeng; Ouyang, Xicheng; Liu, Buqiong; Lin, Rong Han

    2013-06-01

    Highlights: ► Ideal hexagonal shape particle size in 5 μm and 2.5–3 μm in thickness are obtained. ► The growth mechanism is studied by a computer simulation. ► The influence of introduced AlN on the sites of Eu{sup 2+} and photoluminescence properties was investigated. - Abstract: The AlN-doped BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphors were synthesized by conventional solid-state reaction. Powder X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectrum (PL) were used for characterization. The growth mechanism was carried out by computer simulation with CASTEP application, and revealed that an ideal hexagonal shape, particle size in 5 μm and 2.5–3 μm in thickness, could be obtained by AlN doping. Additionally, due to the low electronegativity of N{sup 3−}, the AlN-doped sample showed 35% increase in PL intensity and improvement of thermal stability. These fine particle size and better photoluminescence properties are expected to be applicable to industrial production of BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphors.

  12. Pedogeochemical mapping of Al, Ba, Pb, Ti and V in soils of the Barcelona Province (Catalonia, NE Spain): relationships with soil physico-chemical properties.

    NASA Astrophysics Data System (ADS)

    Bech, J.; Reverter, F.; Tume, P.; Sokolowska, M.; Sanchez, P.; Longan, L.; Bech, J.; Zhiyanski, M.; Lansac, A.; Oliver, M. T.

    2009-04-01

    Pedogeochemical mapping is a useful tool for estimating the local background of potentially toxic elements (PTE), wich is essential for environmental regulation. The aim of this study is to estimate the levels and distribution of Al, Ba, Pb, Ti and V in surface soils of the Barcelona province (Catalonia, NE Spain) and their relationships with administrative-geographic districts, texture, pH, organic carbon and CaCO3. The studied region has a surface area of 7731 Km2. The geology is varied: granites and Paleozoic shales predominate in SE-E. and Mesozoic and Cenozoic limestones, dolomites, marlstones, gypsum and sandstones in the remainder of the studied area. 319 top soil samples (0-20 cm) were collected at 5 km intervals on a regular grid, dried and sieved (2mm). General soil properties were analysed by standard methods. Aqua regia digests (DIN 38414-S7) of Al, Ba, Pb, Ti and V were determined by Inductively Coupled Plasma Spectrometry. Statistical data treatment was carried out using SPSS 12.0 and Statgraphics Plus 5.1. We applied Exploratory Data Analysis (EDA) techniques to statistically describe the data. The software used for mapping was ESRI's Arc Wiew 9.0, Desktop version. Analytical data is represented using growing dot maps. The values of every mapped variable were grouped into a few cartographic classes in order to produce limited legends. The limits for the cartographic classes were chosen by the percentile method (5th, 25th, 50th, 75th, 90th, and 98th). Some results are: Al mg kg-1min 4410.0, max 194786.0, mean 18145.6, sd 12112.1, med 16273.3 ; Ba mgkg-1min 7.32, max 1709.0, mean 128.4, sd 149.2, med 91.7; Pb mg kg-1min 2.76, max 485.7, mean 52.2, sd 46.3, med 46.0; Ti mg kg-1min 11.6, max 3540.0, mean 268.0, sd 421.6, med 132.2, and V mg kg-1min 2.15, max 289.2, mean 31.4, sd 25.7, med 26.0. . The highest mean value of Ba (328mkg-1), Pb (139.6 mgkg-1) and V (54.7 mgkg-1) corresponds to the Barcelonés district with mainly urban soils. The Al contents

  13. Ca and In co-doped BaFeO3-δ as a cobalt-free cathode material for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Lam, Kwun Yu; Saccoccio, Mattia; Gao, Yang; Chen, Dengjie; Ciucci, Francesco

    2016-08-01

    We report Ba0·95Ca0·05Fe0·95In0·05O3-δ (BCFI), a novel cobalt-free perovskite, as a promising cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). We synthesize this new material, and systematically characterize its lattice structure, thermal stability, chemical composition, electrical conductivity, and oxygen reduction reaction (ORR) activity. The cubic phase of BaFeO3-δ is stabilized by light isovalent and lower-valence substitution, i.e., 5% Ca2+ in the Ba2+ site and 5% In3+ in the Fe3+/Fe4+ site, in contrast with the typical approach of substituting elements of higher valence. Without resorting to co-doping strategy, the phase of BaFe0·95In0·05O3-δ (BFI) is rhombohedral, while Ba0·95Ca0·05FeO3-δ (BCF) is a mixture of the cubic phase together with BaFe2O4 impurities. The structure of BCFI is cubic from room temperature up to 900 °C with a moderate thermal expansion coefficient of 23.2 × 10-6 K-1. Thanks to the large oxygen vacancy concentration and fast oxygen mobility, BCFI exhibits a favorable ORR activity, i.e., we observe a polarization resistance as small as 0.038 Ω cm2 at 700 °C. The significantly enhanced performance, compared with BFI and BCF, is attributed to the presence of the cubic phase and the large oxygen vacancies brought by the isovalent substitution in the A-site and lower-valence doping in the B-site.

  14. Ca and In co-doped BaFeO3-δ as a cobalt-free cathode material for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Lam, Kwun Yu; Saccoccio, Mattia; Gao, Yang; Chen, Dengjie; Ciucci, Francesco

    2016-08-01

    We report Ba0·95Ca0·05Fe0·95In0·05O3-δ (BCFI), a novel cobalt-free perovskite, as a promising cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). We synthesize this new material, and systematically characterize its lattice structure, thermal stability, chemical composition, electrical conductivity, and oxygen reduction reaction (ORR) activity. The cubic phase of BaFeO3-δ is stabilized by light isovalent and lower-valence substitution, i.e., 5% Ca2+ in the Ba2+ site and 5% In3+ in the Fe3+/Fe4+ site, in contrast with the typical approach of substituting elements of higher valence. Without resorting to co-doping strategy, the phase of BaFe0·95In0·05O3-δ (BFI) is rhombohedral, while Ba0·95Ca0·05FeO3-δ (BCF) is a mixture of the cubic phase together with BaFe2O4 impurities. The structure of BCFI is cubic from room temperature up to 900 °C with a moderate thermal expansion coefficient of 23.2 × 10-6 K-1. Thanks to the large oxygen vacancy concentration and fast oxygen mobility, BCFI exhibits a favorable ORR activity, i.e., we observe a polarization resistance as small as 0.038 Ω cm2 at 700 °C. The significantly enhanced performance, compared with BFI and BCF, is attributed to the presence of the cubic phase and the large oxygen vacancies brought by the isovalent substitution in the A-site and lower-valence doping in the B-site.

  15. Luminescent nitridophosphates CaP2 N4 :Eu(2+) , SrP2 N4 :Eu(2+) , BaP2 N4 :Eu(2+) , and BaSr2 P6 N12 :Eu(2.).

    PubMed

    Pucher, Florian J; Marchuk, Alexey; Schmidt, Peter J; Wiechert, Detlef; Schnick, Wolfgang

    2015-04-20

    Nitridophosphates MP2 N4 :Eu(2+) (M=Ca, Sr, Ba) and BaSr2 P6 N12 :Eu(2+) have been synthesized at elevated pressures and 1100-1300 °C starting from the corresponding azides and P3 N5 with EuCl2 as dopant. Addition of NH4 Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single-crystal X-ray diffraction data (CaP2 N4 :Eu(2+) (P63 , no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) Å(3) , Z=24, 2033 observed reflections, 176 refined parameters, wR2 =0.096). Upon excitation by UV light, luminescence due to parity-allowed 4f(6) ((7) F)5d(1) →4f(7) ((8) S7/2 ) transition was observed in the orange (CaP2 N4 :Eu(2+) , λmax =575 nm), green (SrP2 N4 :Eu(2+) , λmax =529 nm), and blue regions of the visible spectrum (BaSr2 P6 N12 :Eu(2+) and BaP2 N4 :Eu(2+) , λmax =450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline-earth ions. The corresponding full width at half maximum values (2240-2460 cm(-1) ) are comparable to those of other known Eu(2+) -doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba3 P5 N10 Br:Eu(2+) , this investigation represents the first report on the luminescence of Eu(2+) -doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu(2+) -doped nitridophosphates may have the potential to be further developed into efficient light-emitting diode phosphors. PMID:25765825

  16. A possibility of substituting Ca2+ by Ba2+ or Mn2+ during the contractile processes of complex stomach smooth muscles.

    PubMed

    Milanov, M P; Stoyanov, I N

    1982-01-01

    In vitro experiments were carried out on muscle strips from different compartments of sheep complex stomach. The following conclusions were drawn: 1. In Ca2+-free medium containing EDTA (0.5 mM) proximal and antral abomasum preparations are mechanically inactive. The addition of BaCl2 (0.2-1 mM) induces phasic contractions in the rumen and antrum strips. In contrast to the simple stomach Ba2+ causes a significant increase in the tone of the rumen and proximal abomasum preparations. This tonic contraction is verapamil resistant and is completely suppressed by sodium nitroprusside. 2. The Ba2+ effect is not mediated by cholinergic or adrenergic systems. Ba2+ can substitute Ca2+ in generating both phasic and tonic contractions in complex stomach smooth muscles. 3. Compared with the simple stomach Mn2+ (0.2-0.8 mM) influences neither the ACh-induced activity in normal nutrient medium nor the tone of the rumen and proximal abomasum preparations in Ca2+-free solution. PMID:7152231

  17. Synthesis and Microwave Dielectric Properties of A16V18O61 (A = Ba, Sr and Ca) Ceramics for LTCC Applications

    NASA Astrophysics Data System (ADS)

    Suresh, E. K.; Prasad, K.; Arun, N. S.; Ratheesh, R.

    2016-06-01

    Low-temperature co-firable A16V18O61 (A = Ba, Sr, Ca) ceramics have been prepared through the solid state ceramic route. The structural features of these ceramics have been studied using the x-ray diffraction (XRD) technique. The existence of the A16V18O61 (A = Ba, Sr, Ca) ceramic phase was confirmed through laser Raman spectroscopic studies. Scanning electron microscopy analysis revealed a dense microstructure for the ceramics with closely packed polygonal grains. Among the samples studied, Ba16V18O61 ceramic was prepared in the ultralow sintering temperature of 620°C for 1 h, which can be co-firable with an aluminium electrode. XRD and electron dispersive spectroscopy analyses showed that the samples under study have excellent compatibility with metal electrodes. The microwave dielectric properties measured using a vector network analyzer revealed that A16V18O61 (A = Ba, Sr, Ca) ceramics have excellent unloaded quality factors.

  18. Microwave Dielectric Properties for Ba(Mg1/3Ta2/3)O3 A(Mg1/2W1/2)O3 (A=Ba, Sr, and Ca) Ceramics

    NASA Astrophysics Data System (ADS)

    Furuya, Mitsuru; Ochi, Atsushi

    1994-09-01

    For a high-Q dielectric resonator at microwave frequencies, complex perovskite-structured Ba(Mg1/3Ta2/3)O3 A(Mg1/2W1/2)O3 (A=Ba, Sr, and Ca) ceramics have been developed. A(Mg1/2W1/2)O3 effects on the crystal structure, microstructure, and microwave characteristic of Ba(Mg1/3Ta2/3)O3 (BMT) were investigated. Ba(Mg1/2W1/2)O3 (BMW) decreased the temperature coefficient of resonant frequency ( TCF) for BMT. Sr(Mg1/2W1/2)O3 (SMW) and Ca(Mg1/2W1/2)O3 (CMW) increased it. Zero TCF was obtained for the BMT/BMW=95/5 composition. With 0.5 mol% BMW content, dielectric loss quality, Q d, reached a maximum (40000 at 10 GHz).

  19. First principles study of magnetoelectric coupling in Co2FeAl/BaTiO3 tunnel junctions.

    PubMed

    Yu, Li; Gao, Guoying; Zhu, Lin; Deng, Lei; Yang, Zhizong; Yao, Kailun

    2015-06-14

    Critical thickness for ferroelectricity and the magnetoelectric effect of Co2FeAl/BaTiO3 multiferroic tunnel junctions (MFTJs) are investigated using first-principles calculations. The ferroelectric polarization of the barriers can be maintained upto a critical thickness of 1.7 nm for both the Co2/TiO2 and FeAl/TiO2 interfaces. The magnetoelectric effect is derived from the difference in the magnetic moments on interfacial atoms, which is sensitive to the reversal of electric polarization. The magnetoelectric coupling is found to be dependent on the interfacial electronic hybridizations. Compared with the Co2/TiO2 interface, more net magnetization change is achieved at the FeAl/TiO2 interface. In addition, the in-plane strain effect shows that in-plane compressive strain can lead to the enhancement of ferroelectric polarization stability and intensity of magnetoelectric coupling. These findings suggest that Co2FeAl/BaTiO3 MFTJs could be utilized in the area of electrically controlled magnetism, especially the MFTJ with loaded in-plane compressive strain with the FeAl/TiO2 interface. PMID:25987345

  20. Mössbauer spectroscopy study of Al distribution in BaAl{sub x}Fe{sub 12−x}O{sub 19} thin films

    SciTech Connect

    Przybylski, M. Żukrowski, J.; Harward, I.; Celiński, Z.

    2015-05-07

    Barium hexagonal ferrite (BaM) films grown on Si are a good candidate material for new-generations of on-wafer microwave devices operating at frequencies above 40 GHz. Doping BaM with Al increases the value of anisotropy field even more, and in combination with a large value of remanence, would allow one to create a self-biasing material/structure that would eliminate the need for permanent bias magnets in millimeter wave devices. To examine the occupation of Fe sublattices by Al ions, we carried out Conversion Electron Mössbauer Spectroscopy (CEMS) measurements at room temperature and zero magnetic field (after magnetizing the samples in a strong magnetic field). The spectra can be reasonably fitted with three components (sub-spectra) corresponding to different Fe sublattices. There are significant changes in the spectra with the addition of Al: The magnetic hyperfine field decreases for all three components, and their relative contributions also change remarkably. These observations are in agreement with the fact that the Al substitutes Fe, thus lowering the component contributions and the value of the hyperfine field. In addition, our previous XRD analysis indicates increasing grain misalignment with Al content, further supporting the CEMS data.

  1. Crystal Growth and Photoluminescence Properties of Truncated Cubic BaMgAl10O17:Eu2+ Phosphors for Three-Dimensional Plasma Display Panels.

    PubMed

    Liu, Bitao; Chen, Yuan; Peng, Lingling; Han, Tao; Yu, Hong; Tian, Liangliang; Tu, Mingjing

    2016-04-01

    Monodispersed, truncated cube BaMgAl10O17:Eu2+ phosphors were synthesized by the sol-gel process. Scanning electron microscope (SEM), photoluminescence spectrum, powder X-ray diffraction and decay curves were used to evaluate the truncated cubic BaMgAl10O17:Eu2+ phosphors. The crystal growth process and photoluminescence properties were discussed in detail. The results showed that this truncated cubic morphology can be achieved via a simple sinter process. These truncated cubic BaMgAl10O17:Eu2+ phosphors showed acceptable emission intensity and better thermal properties. This result indicates truncated cubic BaMgAl10O17:Eu2+ phosphors would meet the requirements of plasma display panels (PDPs). PMID:27451727

  2. [Effect of N+ (N = Li, Na, K) on the spectra of M3 (M = Ca, Sr, Ba) Y2 (BO3)4 : Eu3+ luminescent phosphor].

    PubMed

    Li, Pan-Lai; Wang, Zhi-Jun; Gao, Hui-Ying; Yang, Zhi-Ping

    2008-11-01

    The M3 (M = Ca, Sr, Ba) Y2 (BO3)4 : Eu3+ red phosphor was synthesized by firing twice at 800 and 1 050 degrees C each for 4 h and 4 h in air, respectively. Y2O3 (99.9%), Eu2O3 (99.9%), H3BO3 (99.9%), CaCO3 (99.9%), SrCO3 (99.9%), BaCO3 (99.9%), Li2CO3 (99.9%), Na2CO3 (99.9%) and K2CO3 (99.9%) were used as starting materials, and the doping Eu3+ concentration was 3 mol%. The excitation spectrum was measured by a SHIMADZU RF-540 ultraviolet spectrophotometer. The emission spectrum was measured by a SPEX1404 spectrophotometer. All the luminescence characteristics of the phosphors were investigated at room temperature. The emission spectrum of M3 (M = Ca, Sr, Ba) Y2 (BO3)4 : Eu3+ phosphor exhibited a 613 nm red emission corresponding to the electric dipole 55D0 - 7F2 transition of Eu3+ under 365 nm excitation. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet (UV) (254, 365 and 400 nm) and blue (470 nm) light. The effect of Li+ , Na+ and K+ on the excitation and emission spectra of M3 (M = Ca, Sr, Ba)Y2 (BO3)4 : Eu3+ phosphor was studied. The results show that the location of the excitation and emission spectrum of M3 (M = Ca, Sr, Ba) Y2 (BO3)4 : Eu3+ phosphor was not influenced by Li+, Na+ and K+. However, the excitation and emission spectrum intensities were greatly influenced by Li+, Na+ and K+, and the emission peak intensities were all enhanced. Under the condition of the same Li+, Na+ and K+ concentration, the emission peak intensities of M3 (M = Ca, Sr, Ba)Y2 (BO3)4 : Eu3+ phosphor were compared, and the result shows that the accretion effect of doping Li+ is the best. The effect of Li+ concentration on the emission peak intensity of Sr3 Y2 (BO3)4 : Eu3+ phosphor was studied. The results show that the emission peak intensity firstly increased with the increasing Li+ concentration, then decreased, and reached the maximum value at 5 mol% Li+, and the maximum value is about twice as much as the Li-undoped one

  3. M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion

    SciTech Connect

    Popa, Karin; Wallez, Gilles; Bregiroux, Damien; Loiseau, Pascal

    2011-10-15

    Three earth alkali-germanium monophosphates M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO{sub 4}){sub 2} and high-temperature {beta}-SrGe(PO{sub 4}){sub 2} (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO{sub 4}){sub 2} and low-temperature {alpha}-SrGe(PO{sub 4}){sub 2} (C2/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The thermal expansion, resulting from several structural mechanisms, is very anisotropic. - Graphical abstract: The superstructure of SrGe(PO{sub 4}){sub 2} at room temperature ({alpha}) results from the off-centering of cation Sr{sup II}. Highlights: > Crystal structures of yavapaiite-type M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) have been solved. > Distortion and superstructure result from Ca and Sr off-centering. > A global scheme for the polymorphism of yavapaiites is proposed.

  4. Preparation and Electrochemical Characterization of Aluminium Liquid Battery Cells With Two Different Electrolytes (NaCl-BaCl2-AlF3-NaF and LiF-AlF3-BaF2).

    PubMed

    Napast, Viktor; Moškon, Jože; Homšak, Marko; Petek, Aljana; Gaberšček, Miran

    2015-01-01

    The possibility of preparation of operating rechargeable liquid battery cells based on aluminium and its alloys is systematically checked. In all cases we started from aluminium as the negative electrode whereas as the positive electrode three different metals were tested: Pb, Bi and Sn. Two types of electrolytes were selected: Na(3)AlF(6) -AlF(3) - BaCl(2) - NaCl and Li(3)AlF(3) - BaF(2). We show that some of these combinations allowed efficient separation of individual liquid layers. The cells exhibited expected voltages, relatively high current densities and could be charged and discharged several times. The capacities were relatively low (120 mAh in the case of Al-Pb system), mostly due to unoptimised cell construction. Improvements in various directions are possible, especially by hermetically sealing the cells thus preventing salt evaporation. Similarly, solubility of aluminium in alloys can be increased by optimising the composition of positive electrode. PMID:26680707

  5. Microstructure and dielectric properties of (Ba 0.6Sr 0.4)TiO 3 thin films grown on super smooth glazed-Al 2O 3 ceramics substrate

    NASA Astrophysics Data System (ADS)

    Chen, Hongwei; Yang, Chuanren; Zheng, Shanxue; Zhang, Jihua; Zhang, Qiaozhen; Lei, Guanhuan; Lou, Feizhi; Yang, Lijun

    2011-12-01

    Modified substrates with nanometer scale smooth surface were obtained via coating a layer of CaO-Al2O3-SiO2 (CaAlSi) high temperature glaze with proper additives on the rough-95% Al2O3 ceramics substrates. (Ba0.6Sr0.4)TiO3 (BST) thin films were deposited on modified Al2O3 substrates by radio-frequency magnetron sputtering. The microstructure, dielectric, and insulating properties of BST thin films grown on glazed-Al2O3 substrates were investigated by X-ray diffraction (XRD), atomic force microscope (AFM), and dielectric properties measurement. These results showed that microstructure and dielectric properties of BST thin films grown on glazed-Al2O3 substrates were almost consistent with that of BST thin films grown on LaAlO3 (1 0 0) single-crystal substrates. Thus, the expensive single-crystal substrates may be substituted by extremely cheap glazed-Al2O3 substrates.

  6. Photoluminescence Properties of CaAlBO4:M (M: Pb2+, Dy3+, and Sm3+)

    NASA Astrophysics Data System (ADS)

    Erdoğmuş, E.; Pekgözlü, İ.

    2014-07-01

    Pb2+, Dy3+, and Sm3+ doped CaAlBO4 materials were synthesized by the conventional solid state reaction. The synthesized phosphors were characterized by X-Ray powder diffraction. The emission and excitation spectra of these phosphors were measured at room temperature. The emission band of CaAlBO4:Pb2+ appeared as a broad band at 339 nm upon excitation with 272 nm. The second phosphor, CaAlBO4: Dy3+, emits at 477, 570, and 670 nm upon 347 nm excitation. The third phosphor, CaAlBO4:Sm3+, emits at 563, 594, 643, and 705 nm upon 236 nm excitation.

  7. Characteristics of TlBa2Ca2Cu3O(9+delta) powder as-synthesized and after grinding

    NASA Astrophysics Data System (ADS)

    Kung, P. J.; Maley, M. P.; Wahlbeck, P. G.; Peterson, D. E.

    1993-04-01

    Crystal structure and superconductivity of the Tl-Ba-Ca-Cu-O powder prepared by a solid-state reaction were studied. The results of XRD, SEM, and TEM analyses indicate that the powder of a major single 1223 phase was synthesized with a cauliflower-like morphology; by grinding, the powder was partially transformed to an amorphous phase. The measurement of magnetic hysteresis was also performed in the temperature range of 7-75 K up to 5 T, from which the weak field-dependent behavior of critical current density was observed. The as-synthesized powder, with T(c) = 110 K measured from magnetometer and susceptometer, is considered to consist of weak-linked regions. The results obtained from comparing the as-synthesized and the ground powder imply that in the Tl-1223 system, the Ag-sheathed tapes fabricated by the powder-in-tube process may be benefited by forming other intermediate phases with plate-like morphologies to give better densification or grain alignment.

  8. Magnetoelectric effect and magnetic phase diagram of a polar ferrimagnet CaBaFe4O7

    NASA Astrophysics Data System (ADS)

    Kocsis, V.; Tokunaga, Y.; Bordács, S.; Kriener, M.; Puri, A.; Zeitler, U.; Taguchi, Y.; Tokura, Y.; Kézsmárki, I.

    2016-01-01

    The magnetic phase diagram of a polar ferrimagnet CaBaFe4O7 with a magnetic easy axis has been investigated by measurements of magnetization, specific heat, and magnetoelectricity. A ferrimagnetic transition takes place at TC 1=275 K within the orthorhombic phase followed by a second magnetic transition at TC 2=211 K. Below TC 2, successive metamagnetic transitions occur for magnetic fields applied perpendicular to the easy axis, implying a sequential emergence of magnetic states which are neither collinear nor coplanar. The observation of the static magnetoelectric effect was limited to temperatures below 120 K due to the conducting nature of the crystals at higher temperatures. The magnitude of the ferroelectric polarization shows large changes between the different field-induced magnetic phases. The low-field state is characterized by a large linear magnetoelectric coefficient of αc c=39 ps/m, while a gigantic polarization change of Δ P =850 μ C /m2 is observed for μoH =14 T applied along the easy axis.

  9. Thermoluminescent response of rare earth doped nanocrystalline Ba0.97Ca0.03SO4

    NASA Astrophysics Data System (ADS)

    Bahl, Shaila; Lochab, S. P.; Pandey, Anant; Kumar, Pratik

    2013-02-01

    The effects of Ce co-doping on the thermoluminescence (TL) characteristics of nanocrystalline Ba0.97Ca0.03SO4:Eu phosphor are studied. Formation of the compound and particle size was confirmed by XRD with particle size around 45 nm. The Eu doped phosphor has a simple TL glow curve structure with a single prominent peak at around 187°C with a small hump at around 250°C. Ce co-doping, decreases the TL intensity considerably, though the shape of the glow curve remains same. The photoluminescence (PL) emission spectrum has been examined and studied for the Co-doped sample to get an insight into the emission mechanism of the phosphor which involves transfer of energy from Eu2+ to Ce3+ to examine the decrease in peak intensity of the phosphor. The TL response for different doses has also been reported to check the linearity range and it is found that the phosphor is quite suitable for use in dosimetry of ionizing radiations.

  10. XPS study of thallium oxidation states in precursor TlBaCaCuO HTSC thin films

    NASA Astrophysics Data System (ADS)

    Young, K. H.; Smith, E. J.; Eddy, M. M.; James, T. W.

    1991-10-01

    The Tl oxidation state in the precursor of Tl 2Ba 2CaCu 2O 8 superconducting films plays an important role in the post-deposition process and has been carefully examined by X-ray photoelectron spectroscopy (XPS). The Tl4f 5/2 and Tl4f 5/2 peaks in the XPS spectra have been deconvoluted into several peaks corresponding to different oxidation states. Under normal deposition conditions for laser ablation, it is found that mixtures of Tl-I(+ 1 oxidation state) and Tl-III (+ 3) are present with various percentages. The study of time evolution and depth profile data suggests that the surface oxidation state is a function of time and 200 Å of film should be removed before collecting data. The Tl-oxidation state depends strongly on the oxygen background pressure during deposition and the optimal pressure is found to be about 180 mTorr. Negatively charged Tl (presumably due to alloying with other metal constituents) is found when deposited with no background oxygen pressure.

  11. A Josephson junction to FET high speed line driver made of TlCaBaCuO

    SciTech Connect

    Martens, J.S.; Dinley, D.S. ); Beyer, J.B.; Nordman, J.E. . Dept. of Electrical and Computer Engineering); Hohenwarter, G.K.G. )

    1991-03-01

    This paper reports on the use of a Tl-Ca-Ba- Cu-O superconducting flux flow transistor (SFFT) as an active impedance converter between Josephson and FET circuitry. The input of the flux flow device is a control line of low impedance that can be driven by a tunnel junction. The output is the signal across the SFFT which is made of a parallel array of weak links. The output impedance is typically greater than 5 {Omega} with a maximum voltage swing of over 100 mV into a 50 {Omega} system. The switching of an all-Nb junction induced a 90 mV voltage swing at the FET input and over 200 mV at the FET output. The line driver can operate anywhere between 4.2K and 85K with minor changes in speed ({plus minus}5 ps) and output level ({plus minus}10 mV). The switching time measured was about 100 ps and was fixture limited.

  12. Intrinsic Josephson properties in (Hg, Re)Ba 2Ca 3Cu 4O 10+δ single crystals

    NASA Astrophysics Data System (ADS)

    Ueda, S.; Okutsu, T.; Kubo, Y.; Ishii, S.; Tsuda, S.; Yamaguchi, T.; Horii, S.; Shimoyama, J.; Kishio, K.; Takano, Y.

    2008-09-01

    We have investigated the I- V characteristics of intrinsic Josephson junctions (IJJs) in (Hg, Re)Ba 2Ca 3Cu 4O 10+δ [Hg(Re)1234]. Two types of inline junctions with different dimensions were fabricated using a focused Ga + ion beam from Hg(Re)1234 single crystals grown by the flux method. In the I- V curves of the IJJs, multiple-branches with hysteresis structure similar to those of other HTS IJJs were successfully observed above 80 K. The IJJs with dimension of 1.2 × 0.65 μm 2 showed almost step by step switching, while the other with larger size showed uniform-stack switching, which indicated that the switching dynamics in the IJJs were affected by the coupling between junctions. The critical current density, Jc, of both IJJs were high ∼320 kA/cm 2 at 4.2 K due to its high Tc and relatively low anisotropy parameter γ=(mc∗/mab∗)∼25.

  13. Theory for the Spin State and Spectroscopic Modes of Multiferroic CaBaCo4O7

    NASA Astrophysics Data System (ADS)

    Fishman, Randy; Bordacs, Sandor; Kezmarki, Istvan; Kocsis, Vilmos; Nagel, Urmas; Room, Toomas; Tokunaga, Y.; Takahashi, Y.; Taguchi, Y.; Tokura, Y.

    With alternating Kagome and triangular lattices, the type I multiferroic CaBaCo4O7 is highly frustrated. Magnetic frustration produces a non-collinear, ferrimagnetic spin state with a net magnetic moment of about 1 mB along the b axis below 60 K. Based on the the field dependence of the three observed spectroscopic modes between 0.8 and 2.7 THz and on the field dependence of the magnetization up to 14 T, we construct a microscopic model for this compound. Using the symmetry of the crystal, the model is constructed in terms of eight independent nearest-neighbor exchange interactions as well as both in-plane and easy-axis anisotropies. With three observed Co species (spins 1.45, 1.0, and 1.2), the magnetic unit cell contains 16 spins. Our results indicate that the easy-plane and hexagonal anisotropy in the triangular layers is far larger than the anisotropy in the kagome layers. The observed spin-induced polarization along the c axis is produced by magnetostriction. We also predict other spin-wave modes outside the window of the spectroscopic measurements. Research Sponsored by the Department of Energy, Office of Sciences, Basic Energy Sciences, Materials Sciences and Engineering Division.

  14. Structural chemistry of M2Si5N8:Eu2+ (M = Ca, Sr, Ba) phosphor via structural refinement.

    PubMed

    Kim, Yong-Il; Kim, Kwang Bok; Lee, Yun-Hee; Kim, Ki-Bok

    2012-04-01

    Structural refinement using X-ray powder diffraction data and geometry energy calculations using quantum mechanics were used to investigate the preferential substitution sites and the amount of Eu2+ ions in the host lattice of alkaline earth elements co-doped M2Si5N8:Eu2+ (M = Ca, Sr, and Ba), which is a red color-emitting nitride phosphor prepared via a carbothermal reaction method. Of the possible preferential sites, the preferential site proposed by the structural refinement results, in which the Eu2+ ions might preferentially occupy nine coordinated sites with nitrogen in M2Si5N8:Eu2+, was confirmed via geometry energy calculations using a first-principle based on the density-functional theory. The final converged weighted R factor (R(wp)) and the goodness-of-fit indicator [S(= R(wp)/R(e))] were 9.51% and 1.77, respectively. Each occupancy of Eu2+ ions for the two non-equivalent M sites, M(1) and M(2), was 0.10(2) and 0.04(2), respectively. The final refined model described the crystal structure in a space group Pmn2, (No. 31) with Z = 2, a = 5.7424(1) angstroms, b = 6.8837(1) angstroms, c = 9.3586(1) angstroms, and alpha(= beta= gamma)= 90 degrees. PMID:22849142

  15. Optical absorption and TEM studies of silver nanoparticle embedded BaO-CaF2-P2O5 glasses

    NASA Astrophysics Data System (ADS)

    Narayanan, Manoj Kumar; Shashikala, H. D.

    2016-05-01

    Silver nanoparticle embedded 30BaO-20CaF2-50P2O5-4Ag2O-4SnO glasses were prepared by melt-quenching and subsequent heat treatment process. Silver-doped glasses were heat treated at temperatures 500 °C, 525°C and 550 °C for a fixed duration of 10 hours to incorporate metal nanoparticles into the glass matrix. Appearance and shift in peak positions of the surface plasmon resonance (SPR) bands in the optical absorption spectra of heat treated glass samples indicated that both formation and growth of nanoparticle depended on heat treatment temperature. Glass sample heat treated at 525 °C showed a SPR peak around 3 eV, which indicated that spherical nanoparticles smaller than 20 nm were formed inside the glass matrix. Whereas sample heat treated at 550 °C showed a size dependent red shift in SPR peak due to the presence of silver nanoparticles of size larger than 20 nm. Size of the nanoparticles calculated using full-width at half-maximum (FWHM) of absorption band showed a good agreement with the particle size obtained from transmission electron microscopy (TEM) analysis.

  16. Tl 2Ba 2CaCu 2O 8 thin film high frequency filters on 3 inch sapphire substrates

    NASA Astrophysics Data System (ADS)

    Schneidewind, H.; Manzel, M.; Stelzner, T.

    2002-08-01

    Modern communication systems require densely packed frequency channels in the expensive frequency bands. Therefore high temperature superconducting (HTS) high frequency filters are of increasing importance, taking advantage of their outstanding properties namely steep filter skirts, low insertion loss, and furthermore reduced mass and volume compared to conventional cavity or dielectric resonator systems. Within the framework of a German BMBF pilot project a HTS equiped satellite repeater will be developed to demonstrate the performance advantage of HTS. For that purpose we prepare filters on double-sided Tl 2Ba 2CaCu 2O 8 thin films on CeO 2 buffered 3 inch sapphire substrates. The HTS films are prepared in the two-step process by sputtering an amorphous thallium free precursor and following oxythallination. The critical temperature and spatial distribution of critical current density at 77 K, both measured by inductive techniques, show values above 100 K or 1 MA/cm 2, respectively. We use a dielectric resonator technique at 3.9 GHz and power levels up to some mT to determine the films surface resistance. We present measurements of input filters made from our double-sided 3 inch films.

  17. Experimental determination of the partition coefficient for Ba in Neogloboquadrina dutertrei suggests calcification occurs in a Ba-enriched microenvironment

    NASA Astrophysics Data System (ADS)

    Fehrenbacher, J. S.; Russell, A. D.; Davis, C. V.; Spero, H. J.; Chu, E.

    2015-12-01

    The Ba/Ca ratio in several spinose planktic foraminifer species varies as a function of the Ba/Ca concentration of seawater and is not affected by other parameters such as the seawater salinity, temperature and pH (Honisch et al., 2011). Since seawater Ba concentration is linearly related to Ba in nearshore environments, Ba/Ca ratios in spinose species shows promise as an indicator of past changes in monsoon strength and river runoff (e. g. Weldeab et al. 2007). In contrast, the non-spinose foraminifers often have intrashell variability in Ba/Ca, with Ba/Ca ratios much higher than expected for the range of Ba concentrations observed in the ocean. Furthermore, the Ba/Ca ratio can vary by over a factor of 10 within a single specimen. This suggests either 1) the partition coefficient for Ba in non-spinose species differs from that determined for spinose species, or 2) non-spinose species calcify in a micro-environment that is enriched in Ba. We conducted experiments on live specimens to determine the partition coefficient for Ba in the non-spinose foraminifer N. dutertrei. Specimens were collected via plankton net from the Southern California Bight and cultured at the Wrigley Marine Science Center, Santa Catalina Island during the summer of 2013-2015. We use isotopically labeled seawater (87Sr) to identify discrete portions of calcite that grew in culture. We use laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for trace element analyses and to identify ocean grown vs. culture grown calcite. We show that the partition coefficient is similar to the spinose species: N. dutertrei incorporates Ba as a function of seawater chemistry. We conclude from these observations that N. dutertrei forms its calcite from fluids enriched in Ba, and hypothesize that this process occurs via attachment to organic-rich particles such as marine snow.

  18. Morphology Control for Al2O3 Inclusion Without Ca Treatment in High-Aluminum Steel

    NASA Astrophysics Data System (ADS)

    He, Shengping; Chen, Gujun; Guo, Yintao; Shen, Boyi; Wang, Qian

    2015-04-01

    Nozzle blockage is a major problem during continuous casting of Al-containing steel. Herein, we analyzed the thermodynamic equilibrium behavior between aluminum and oxygen in steel at 1873 K (1600 °C) and demonstrated that, the dissolved [O] initially decreases with increasing the dissolved [Al] until approximately 0.1 wt pct [Al], and after that, the dissolved [O] increases with dissolved [Al]. Thus, for high-aluminum steel with 1.0 wt pct dissolved [Al], the precipitation of Al2O3 inclusion can be avoided during cooling from deoxidation temperature to the liquidus temperature, if the actual dissolved [O] can be kept from increasing when the dissolved [Al] further increases from 0.1 to 1.0 wt pct. Hence, a method of inclusion control for high-aluminum steel without traditional Ca treatment technology was proposed based on the thermodynamic analysis. Industrial tests confirmed that low-melting point Ca-aluminate inclusions were observed typically through a slag washing with SiO2-minimized high-basicity slag during tapping, accompanied by two-step Al-adding process for production of high-aluminum steel. Moreover, there was no nozzle clogging occurred for five heats of continuous casting.

  19. Optically stimulated luminescence in LiCaAlF6:Eu2+ phosphor.

    PubMed

    More, Y K; Wankhede, S P; Moharil, S V; Kumar, Munish; Chougaonkar, M P

    2015-09-01

    Results on optically stimulated luminescence (OSL) in LiCaAlF6:Eu(2+) are reported. Continuous wave OSL signal as recorded using blue (470 nm) stimulation was found to be ~31% that of standard phosphor lithium magnesium phosphate. The rate of OSL depletion for standard phosphor lithium magnesium phosphate is only three times less as compared with that of LiCaAlF6:Eu(2+). Strong photoluminescence (PL) in the near ultraviolet region is observed for LiCaAlF6:Eu(2+) with the characteristic Eu(2+) emission at 369 nm for 254 nm excitation. The thermoluminescence (TL) glow peak for LiCaAlF6:Eu(2+) was observed at around 180°C. The glow peak was about six times more intense compared with the dosimetric peak of the well known thermoluminescence dosimetric (TLD) phosphor LiF-TLD 100. Thus this phosphor deserves much more attention than it has received until now and may be useful as a dosimetric material in radiation dosimetry. PMID:25620581

  20. Pre-Accretionary Distribution of Ca and Al Between Matrix and Chondrules in CV Chondrites

    NASA Astrophysics Data System (ADS)

    Hezel, D. C.; Palme, H.

    2007-03-01

    Ca/Al-ratios in Y-86751 (CV) chondrules are super- and in matrix sub-chondritic. The opposite is true for Allende and Efremovka. Incorporation of spinel in Allende and Efremovka chondrule precursors in a nebular setting can explain this observation.

  1. The first observation of SRS in a trigonal LiCaAlF{sub 6} crystal

    SciTech Connect

    Kaminskii, Alexandr A; Eichler, H J; Gad, G M; Ueda, Ken-ichi; Reiche, P

    2000-12-31

    The Raman parametric generation is excited for the first time in a trigonal LiCaAlF{sub 6} fluoride crystal pumped by picosecond pulses. The energy of the {chi}{sup (3)}-active vibrational mode is determined and all Stokes and anti-Stokes components of SRS are detected for this crystal in the visible region. (letters)

  2. Multi-Centennial Record of North Atlantic Freshwater Variability since the Little Ice Age Archived in Coralline Algal Ba/Ca

    NASA Astrophysics Data System (ADS)

    Chan, P. T. W.; Halfar, J.; Adey, W.; Zack, T.

    2014-12-01

    Declining Arctic sea-ice cover in recent decades has driven large-scale freshwater transport into the North Atlantic, possibly influencing the strength of the Meridional Overturning Circulation and even global climate. However, due to the lack of long-term oceanographic observations, little is known about the natural freshwater variability of the Northwestern Atlantic. Crustose coralline algae Clathromorphum compactum are extremely long-lived shallow marine calcareous plants that are abundant along the subarctic eastern Canadian coastline. They are particularly well-suited as recorders of paleoclimate signals due to the formation of annual growth increments, allowing for the precise calendar dating and geochemical sampling of hard tissue. Here, we provide the first annually-resolved multi-centennial record of coralline algal Ba/Ca from Labrador, Canada, as a proxy for North Atlantic freshwater variability extending well into the Little Ice Age (LIA) (1665 AD). Barium-to-calcium ratios (Ba/Ca) from coralline algae have previously been used as an indicator of freshwater runoff. This is because barium-rich clay sediments are transported by terrestrial runoff into coastal waters, and barium is released from the clay minerals upon encountering more alkaline elements present in seawater. We observe higher algal barium concentrations during the LIA, followed by a steady decline to recent times. In addition, coralline algal Ba/Ca shows significant positive relationships to Hudson Strait runoff, as well as Canadian Arctic and North Atlantic sea-ice extent. This suggests that more riverine Ba is transported from the Hudson Strait into the Labrador Sea during periods of increased sea-ice cover. Multiyear sea-ice can block incoming solar radiation thereby diminishing the effects of nutrient scavenging by phytoplankton, resulting in a more conservative transport of Ba into northern Labrador. However as sea-ice continues to thin, more sunlight is able to penetrate through the

  3. Formation Mechanism of CaS-Al2O3 Inclusions in Low Sulfur Al-Killed Steel After Calcium Treatment

    NASA Astrophysics Data System (ADS)

    Xu, Jianfei; Huang, Fuxiang; Wang, Xinhua

    2016-04-01

    The laboratory experiments of alumina inclusions modified by calcium treatment in Al-killed steel were carried out at 1873 K (1600 °C), and the inclusions in steel samples were characterized at 1, 5, and 10 minutes after calcium addition. The results show that the type of inclusions after calcium treatment was determined by the sulfur and T.O contents of steel. CaS-Al2O3 inclusions were obtained in steels with high sulfur and low T.O contents. The mass ratio between CaS and Al2O3 was determined by T.Ca and T.O contents of steel. The influence of holding time after calcium addition on the composition of inclusions was negligible. The thermodynamics for the formation of CaS-Al2O3 inclusions after calcium treatment was discussed, and a simple formation mechanism was proposed. Moreover, the CaO, Al2O3, and CaS contents in the inclusions were predicted through the sulfur, total calcium (T.Ca), and T.O contents, and it was found that the CaO content decreases with increasing S/T.O, while (pctCaS)/(pctAl2O3)1/3 increases with increasing T.Ca/T.O.

  4. Self-organized homo-epitaxial growth in nonlinear optical BaAlBO3F2 crystal crossing lines patterned by laser in glass

    NASA Astrophysics Data System (ADS)

    Shinozaki, K.; Abe, S.; Honma, T.; Komatsu, T.

    2015-11-01

    Crystallization processing of glasses is important as a novel technique for the development of new optical materials, and laser-induced crystallization provides a new challenge in science and technology of materials. Nonlinear optical BaAlBO3F2 crystal lines with crossing, bending, and spiral shapes were patterned at the surface of 2NiO-49BaF2-24.5Al2O3-24.5B2O3 (mol%) and 2.9NiO-48.5BaF2-24.3Al2O3-24.3B2O3 (mol%) glasses by laser irradiation (Yb:YVO4 laser with a wavelength of 1080 nm) and the orientation state of BaAlBO3F2 crystals was examined from birefringence image observations. The birefringence images indicate that the growth of highly c-axis oriented BaAlBO3F2 crystals follows along the laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of BaAlBO3F2 crystals changes gradually at the crossing and bending points. The model of "self-organized homo-epitaxial growth" is proposed for the crystal orientation at the crossing and bending points, as a new crystal growth science and engineering beyond the wise providence of nature.

  5. Ca-,Al-rich inclusions in the unique chondrite ALH85085 - Petrology, chemistry, and isotopic compositions

    NASA Technical Reports Server (NTRS)

    Kimura, Makoto; El-Goresy, Ahmed; Palme, Herbert; Zinner, Ernst

    1993-01-01

    A comprehensive study is performed for the Ca-,Al-rich inclusions (CAIs) in the unique chondrite ALH85085. The ALH85085 inclusions are smaller (5-80 microns) and more refractory than their counterparts in carbonaceous chondrites. The study includes 42 inclusions for petrography and mineralogy, 15 for bulk major and minor element chemical composition, six for Mg-Al isotopic systematics, 10 for Ca isotopes, nine for Ti isotopes, and six for trace element abundances. In addition, oxygen-isotopic compositions were determined in minerals from a single inclusion. No correlation is found between mineralogy, major element chemistry, and trace element abundances. It is further shown that the high-temperature geochemical behavior of ultrarefractory trace elements is decoupled from that of the major elements Ca and Ti (Ti is correlated with the relatively volatile elements Nb and Yb) implying that perovskite is of only minor importance as carrier of ultrarefractories.

  6. Ca-,Al-rich inclusions in the unique chondrite ALH85085 - Petrology, chemistry, and isotopic compositions

    NASA Astrophysics Data System (ADS)

    Kimura, M.; El Goresy, A.; Palme, H.; Zinner, E.

    1993-05-01

    A comprehensive study is performed for the Ca-,Al-rich inclusions (CAIs) in the unique chondrite ALH85085. The ALH85085 inclusions are smaller (5-80 microns) and more refractory than their counterparts in carbonaceous chondrites. The study includes 42 inclusions for petrography and mineralogy, 15 for bulk major and minor element chemical composition, six for Mg-Al isotopic systematics, 10 for Ca isotopes, nine for Ti isotopes, and six for trace element abundances. In addition, oxygen-isotopic compositions were determined in minerals from a single inclusion. No correlation is found between mineralogy, major element chemistry, and trace element abundances. It is further shown that the high-temperature geochemical behavior of ultrarefractory trace elements is decoupled from that of the major elements Ca and Ti (Ti is correlated with the relatively volatile elements Nb and Yb) implying that perovskite is of only minor importance as carrier of ultrarefractories.

  7. The Density and Compressibility of BaCO3-SrCO3-CaCO3-K2CO3-Na2CO3-Li2CO3 Liquids: New Measurements and a Systematic Trend with Cation Field Strength

    NASA Astrophysics Data System (ADS)

    Hurt, S. M.; Lange, R. A.; Ai, Y.

    2015-12-01

    The volumetric properties of multi-component carbonate liquids are required to extend thermodynamic models that describe partial melting of the deep mantle (e.g. pMELTS; Ghiorso et al., 2003) to carbonate-bearing lithologies. Carbonate in the mantle is an important reservoir of carbon, which is released to the atmosphere as CO2 through volcanism, and thus contributes to the carbon cycle. Although MgCO3 is the most important carbonate component in the mantle, it is not possible to directly measure the 1-bar density and compressibility of MgCO3 liquid because, like other alkaline-earth carbonates, it decomposes at a temperature lower than its melting temperature. Despite this challenge, Liu and Lange (2003) and O'Leary et al. (2015) showed that the one bar molar volume, thermal expansion and compressibility of the CaCO3 liquid component could be obtained by measuring the density and sound speeds of stable liquids in the CaCO3-Li2CO3-Na2CO3-K2CO3 quaternary system at one bar. In this study, this same strategy is employed on SrCO3- and BaCO3-bearing alkali carbonate liquids. The density and sound speed of seven liquids in the SrCO3-Li2CO3-Na2CO3-K2CO3 quaternary and three liquids in the BaCO3-Li2CO3-Na2CO3-K2CO3 quaternary were measured from 739-1367K, with SrCO3 and BaCO3 concentrations ranging from 10-50 mol%. The density measurements were made using the double-bob Archimedean method and sound speeds were obtained with a frequency-sweep acoustic interferometer. The molar volume and sound speed measurements were used to calculate the isothermal compressibility of each liquid, and the results show the volumetric properties mix ideally with composition. The partial molar volume and compressibility of the SrCO3 and BaCO3 components are compared to those obtained for the CaCO3 component as a function of cation field strength. The results reveal a systematic trend that allows the partial molar volume and compressibility of the MgCO3 liquid component to be estimated.

  8. Effect of alloying elements Al and Ca on corrosion resistance of plasma anodized Mg alloys

    NASA Astrophysics Data System (ADS)

    Anawati, Asoh, Hidetaka; Ono, Sachiko

    2016-04-01

    Plasma anodizing is a surface treatment used to form a ceramic-type oxide film on Mg alloys by the application of a high anodic voltage to create intense plasma near the metal surface. With proper selection of the process parameters, the technique can produce high quality oxide with superior adhesion, corrosion resistance, micro-hardness, wear resistance and strength. The effect of alloying element Al on plasma anodizing process of Mg alloys was studied by comparing the anodizing curves of pure Mg, AZ31, and AZ61 alloys while the effect of Ca were studied on AZ61 alloys containing 0, 1, and 2 wt% Ca. Anodizing was performed in 0.5 M Na3PO4 solution at a constant current density of 200 Am-2 at 25°C. Anodic oxide films with lava-like structure having mix composition of amorphous and crystal were formed on all of the alloys. The main crystal form of the oxide was Mg3(PO4)2 as analyzed by XRD. Alloying elements Al and Ca played role in modifying the plasma lifetime during anodization. Al tended to extend the strong plasma lifetime and therefore accelerated the film thickening. The effect of Ca on anodizing process was still unclear. The anodic film thickness and chemical composition were altered by the presence of Ca in the alloys. Electrochemical corrosion test in 0.9% NaCl solution showed that the corrosion behavior of the anodized specimens depend on the behavior of the substrate. Increasing Al and Ca content in the alloys tended to increase the corrosion resistance of the specimens. The corrosion resistance of the anodized specimens improved significantly about two orders of magnitude relative to the bare substrate.

  9. Directionally solidified Eu doped CaF2/Li3AlF6 eutectic scintillator for neutron detection

    NASA Astrophysics Data System (ADS)

    Kamada, Kei; Hishinuma, Kousuke; Kurosawa, Shunsuke; Shoji, Yasuhiro; Pejchal, Jan; Ohashi, Yuji; Yokota, Yuui; Yoshikawa, Akira

    2015-12-01

    Eu doped CaF2/Li3AlF6 eutectics were grown by μ-PD method. The directionally solidified eutectic with well-aligned 600 nm diameter Eu:CaF2 scintillator fibers surrounded with Li3AlF6 was prepared. The grown eutectics showed an emission peak at 422 nm ascribed to Eu2+ 4f-5d transition from Eu:CaF2 scintillation fiber. Li concentration in the Eu:CaF2-Li3AlF6 eutectic is around 0.038 mol/cm3,which is two times higher than that of LiCaAlF6 single crystal (0.016 mol/cm3). The light yield of Eu:CaF2-Li3AlF6 eutectic was around 7000 ph/neutron. The decay time was about 550 ns (89%) and 1450 ns (11%).

  10. Luminescence Properties of Self-Activated Mm(VO4)2 (M = Mg, Ca, Sr, and Ba) Phosphors Synthesized by Solid-State Reaction Method.

    PubMed

    Min, Xin; Huang, Zhaohui; Fang, Minghao; Liu, Yan'gai; Tang, Chao; Wu, Xiaowen

    2016-04-01

    In this paper, M3(VO4)2 (M = Mg, Ca, Sr, and Ba) self-activated phosphors were prepared by a solid-state reaction method at 1,000 °C for 5 h. The phase formation and micrographs were analyzed by X-ray diffraction and scanning electron microscopy. The Ca3(VO4)2 phosphor does not show any emission peaks under excitation with ultraviolet (UV) light. However, the M3(VO4)2 (M = Mg, Sr, and Ba) samples are effectively excited by UV light chips ranging from 200 nm to 400 nm and exhibit broad emission bands due to the charge transfer from the oxygen 2p orbital to the vacant 3d orbital of the vanadium in the VO4. The color of these phosphors changes from yellow to light blue via blue-green with increasing ionic radius from Mg to Sr to Ba. The luminescence lifetimes and quantum yield decrease with the increasing unit cell volume and V-V distance, in the order of Mg3(VO4)2 to Sr3(VO4)2 to Ba3(VO4)2. The emission intensity decreases with the increase of temperatures, but presents no color shift. This confirms that these self-activated M3(VO4)2 phosphors can be suggested as candidates of the single-phase phosphors for light using UV light emitting diodes (LEDs). PMID:27451689

  11. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    SciTech Connect

    Stoyko, Stanislav; Voss, Leonard; He, Hua; Bobev, Svilen

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e., P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.

  12. Synthesis and characterisation of chloro-vanadato-apatites M5(VO4)3ClM5(VO4)3Cl (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Beck, Horst P.; Douiheche, Maoiheb; Haberkorn, Robert; Kohlmann, Holger

    2006-01-01

    The synthesis of chloro-vanadato-apatites M5(VO 4) 3Cl ( M = Ca, Sr, Ba) in a two step solid state procedure is reported. IR spectra show a considerable shift of the frequencies attributed to the tetrahedral group to lower energies compared with the phosphato-apatites. The structure of these compounds is determined by powder diffraction data and refined using Rietveld methods. An elaborate analysis of the data shows that the chloride anions are to be found at different positions along a channel along [001] with varying probability. They are fairly well localised in the case of the Sr and the Ba compound. In the Ca compound they are spread over a larger region along c. A refinement according to a new concept of "metric distortion" gives a good fit of the data and indicates that the delocalisation of electron density seen in a Difference-Fourier plot is best described by a static picture of disorder.

  13. Band alignment at epitaxial BaSnO3/SrTiO3(001) and BaSnO3/LaAlO3(001) heterojunctions

    NASA Astrophysics Data System (ADS)

    Chambers, Scott A.; Kaspar, Tiffany C.; Prakash, Abhinav; Haugstad, Greg; Jalan, Bharat

    2016-04-01

    We have spectroscopically determined the optical bandgaps and band offsets at epitaxial interfaces of BaSnO3 with SrTiO3(001) and LaAlO3(001). 28 u.c. BaSnO3 epitaxial films exhibit direct and indirect bandgaps of 3.56 ± 0.05 eV and 2.93 ± 0.05 eV, respectively. The lack of a significant Burstein-Moss shift corroborates the highly insulating, defect-free nature of the BaSnO3 films. The conduction band minimum is lower in electron energy in 5 u.c. films of BaSnO3 than in SrTiO3 and LaAlO3 by 0.4 ± 0.2 eV and 3.7 ± 0.2 eV, respectively. This result bodes well for the realization of oxide-based, high-mobility, two-dimensional electron systems that can operate at ambient temperature, since electrons generated in the SrTiO3 by modulation doping, or at the BaSnO3/LaAlO3 interface by polarization doping, can be transferred to and at least partially confined in the BaSnO3 film.

  14. Thermochemistry of glasses and liquids in the systems CaMgSi 2O 6-CaAl 2Si 2O 8-NaAlSi 3O 8, SiO 2-CaAl 2Si 2O 8-NaAlSi 3O 8 and SiO 2-Al 2O 3-CaO-Na 2O

    NASA Astrophysics Data System (ADS)

    Navrotsky, A.; Hon, R.; Weill, D. F.; Henry, D. J.

    1980-10-01

    Enthalpies of solution in 2PbO· B 2O 3 at 712°C have been measured for glasses in the systems albite anorthite diopside, NaAlO 2-SiO 2, Ca 0.5AlO 2-SiO 2 and albite-anorthite-quartz. The systems albite-anorthite and diopside-anorthite show substantial negative enthalpies of mixing, albite-diopside shows significant positive heats of mixing. For compositions up to NaAlO2 = 0.42 (which includes the subsystem albite-silica) the system NaAlO 2-SiO 2 shows essentially zero heats of mixing. A negative ternary excess heat of mixing is found in the plagioclase-rich portion of the albite-anorthite-diopside system. The join Si 4O 8-CaAl 2Si 2O 8 shows small but significant heats of mixing. In albite-anorthite-quartz. ternary glasses, the ternary excess enthalpy of mixing is positive. Based on available heat capacity data and appropriate consideration of the glass transition, the enthalpy of the crystal-glass transition (vitrification) is a serious underestimate of the enthalpy of the crystal-liquid transition (fusion) especially when the melting point, Tf, is many hundreds of degrees higher than the glass transition temperature, Tg. On the other hand, the same heat capacity data suggest that the enthalpies of mixing in albite-anorthite-diopside liquids are calculated to be quite similar to those in the glasses. The enthalpies of mixing observed in general support the structural models proposed by TAYLOR and BROWN (1979a, b) and others for the structure of aluminosilicate glasses.

  15. Synthesis and performance of Ca-α/β-SiAlON composites from tailings

    NASA Astrophysics Data System (ADS)

    Hao, Hong-shun; Yang, Yang; Lian, Fang; Gao, Wen-yuan; Liu, Gui-shan; Hu, Zhi-qiang

    2014-05-01

    Ca-α/β-SiAlON composites were prepared using Ca-α/β-SiAlON powder synthesized from gold ore tailings, which contained abundant Si and Al elements as the major raw materials together with minor additives, through a pressure-less sintering method. The influences of sintering temperature on the phase composition and microstructure of the composites were analyzed. The scanning electron microscopy images of the composites show the interlacing of grains with elongated columnar, short columnar and plate-like morphologies. The composites sintered at 1520°C for 6 h have a flexural strength of 352 MPa, Vickers hardness of 11.2 GPa, and fracture toughness of 4.8 MPa·m1/2. The relative content of each phase in the products is I(Ca-α-SiAlON): I(β-SiAlON): I(Fe3Si) = 23:74:3, where I i stands for the diffraction peak intensity of phase i.

  16. Hydrogen sorption behavior of CaAl1.5Li0.5

    NASA Astrophysics Data System (ADS)

    Bereznitsky, Matvey; Mogilyanski, Dmitry; Jacob, Isaac

    2016-04-01

    The hydrogen sorption properties of an alloy with nominal composition CaAl1.5Li0.5 have been investigated in a pursuit for hydrogen-absorbing Li-containing intermetallics. X-ray analysis of the original alloy indicated a coexistence of three closely related Laves phases. The maximum hydrogen capacity, recorded at about 6 MPa and 300 °C, was approximately 2.5 H atoms per formula unit (f.u.). Pressure-composition (p-c) isotherm measurements were taken in the temperature range between 350 and 450 °C up to pressures of 133 kPa. Thermodynamic parameters are derived for two plateau regions in the p-c isotherms. Analysis of these parameters and supporting evidence from X-ray patterns of hydrogenated and dehydrogenated samples suggest: (a) an initial irreversible disproportionation of the original alloy and (b) subsequent reversible hydrogenations, featuring reversible disproportionations of CaAl2 and LiAl intermetallic compounds. Attempts to form additional Li-containing intermetallics, namely CaAlLi, TiMn2- x Li x (x = 0.2, 0.3, 0.4, 0.6) and TiAl2- x Li x (x = 0.3, 0.5), and to hydrogenate them, are reported in brief.

  17. Levitation properties of the YBa sub 2 Cu sub 3 O sub x and Tl-Ba-Ca-Cu-O superconducting systems

    SciTech Connect

    Weeks, D.E. )

    1989-12-25

    A torsion balance is used to measure the levitation force on a magnet as a function of height above bulk samples of the YBa{sub 2}Cu{sub 3}O{sub {ital x}} ({ital T}{sub {ital c}}{similar to}90 K) and Tl-Ba-Ca-Cu-O ({ital T}{sub {ital c}}{similar to}110--120 K) superconducting systems. Measurements of magnetic shielding and trapped magnetic fields are also made.

  18. Thick c-axis textured (Tl,Pb)(Ba,Sr)2Ca2Cu3O9/Ag0.37 superconducting tapes by an ink spray pyrolysis method using a Tl-free precursor

    NASA Astrophysics Data System (ADS)

    Schulz, Douglas L.; Parilla, Philip A.; Ginley, David S.; Voigt, James A.; Roth, E. Peter

    1994-11-01

    In this letter we demonstrate a synthetic route to thick (5-20 μm) highly c-axis textured, nearly phase-pure superconducting (Tl,Pb)(Ba,Sr)2Ca2Cu3O9/Ag0.37 tapes. First, a Tl-free ink consisting of Pb0.5Ba0.4Sr1.6Ca2.0Cu3.0O9/Ag0.37 precursor powder in an ethanolic ethyl cellulose binder is sprayed onto a heated LaAlO3 substrate. After an intermediate oxygen anneal to remove the carbonaceous binder, a static 2-zone thallination anneal is performed to promote superconducting phase formation. Films exhibit excellent c-axis texturing as evidenced by x-ray diffraction θ/2θ and rocking curve characterization with morphological evidence for partial melting by scanning electron microscopy. Electrical characterization of these films give Tc onset values of 106-115 K with Tc zero reached by 99-101 K and transport Jc(77 K) up to 2.9×104 A/cm2. A mixed strong/weak-linked magnetic field dependence is observed for these films at 77 K and 0.4 T.

  19. Optically pumped cerium-doped LiSrAlF{sub 6} and LiCaAlF{sub 6}

    DOEpatents

    Marshall, C.D.; Payne, S.A.; Krupke, W.F.

    1996-05-14

    Ce{sup 3+}-doped LiSrAlF{sub 6} crystals are pumped by ultraviolet light which is polarized along the c axis of the crystals to effectively energize the laser system. In one embodiment, the polarized fourth harmonic light output from a conventional Nd:YAG laser operating at 266 nm is arranged to pump Ce:LiSrAlF{sub 6} with the pump light polarized along the c axis of the crystal. The Ce:LiSrAlF{sub 6} crystal may be placed in a laser cavity for generating tunable coherent ultraviolet radiation in the range of 280-320 nm. Additionally, Ce-doped crystals possessing the LiSrAlF{sub 6} type of chemical formula, e.g. Ce-doped LiCaAlF{sub 6} and LiSrGaF{sub 6}, can be used. Alternative pump sources include an ultraviolet-capable krypton or argon laser, or ultraviolet emitting flashlamps. The polarization of the pump light will impact operation. The laser system will operate efficiently when light in the 280-320 nm gain region is injected or recirculated in the system such that the beam is also polarized along the c axis of the crystal. The Ce:LiSrAlF{sub 6} laser system can be configured to generate ultrashort pulses, and it may be used to pump other devices, such as an optical parametric oscillator. 10 figs.

  20. Optically pumped cerium-doped LiSrAlF.sub.6 and LiCaAlF.sub.6

    DOEpatents

    Marshall, Christopher D.; Payne, Stephen A.; Krupke, William F.

    1996-01-01

    Ce.sup.3+ -doped LiSrAlF.sub.6 crystals are pumped by ultraviolet light which is polarized along the c axis of the crystals to effectively energize the laser system. In one embodiment, the polarized fourth harmonic light output from a conventional Nd:YAG laser operating at 266 nm is arranged to pump Ce:LiSrAlF.sub.6 with the pump light polarized along the c axis of the crystal. The Ce:LiSrAlF.sub.6 crystal may be placed in a laser cavity for generating tunable coherent ultraviolet radiation in the range of 280-320 nm. Additionally, Ce-doped crystals possessing the LiSrAlF.sub.6 type of chemical formula, e.g. Ce-doped LiCaAlF.sub.6 and LiSrGaF.sub.6, can be used. Alternative pump sources include an ultraviolet-capable krypton or argon laser, or ultraviolet emitting flashlamps. The polarization of the pump light will impact operation. The laser system will operate efficiently when light in the 280-320 nm gain region is injected or recirculated in the system such that the beam is also polarized along the c axis of the crystal. The Ce:LiSrAlF.sub.6 laser system can be configured to generate ultrashort pulses, and it may be used to pump other devices, such as an optical parametric oscillator.

  1. Half-metallic ferromagnetism in zinc-blende CaC , SrC , and BaC from first principles

    NASA Astrophysics Data System (ADS)

    Gao, G. Y.; Yao, K. L.; Şaşıoǧlu, E.; Sandratskii, L. M.; Liu, Z. L.; Jiang, J. L.

    2007-05-01

    Using the first-principles full-potential linearized augmented plane-wave method based on density functional theory, we have investigated the electronic structure and magnetism of hypothetical M C ( M=Mg , Ca, Sr, and Ba) compounds with the zinc-blende (ZB) crystal structure. It is shown that ZB CaC , SrC , and BaC are half-metallic ferromagnets with large half-metallic gaps (up to 0.83eV ). The half metallicity is found to be robust with respect to the lattice compression and is maintained up to the lattice-constant contraction of 14%, 13%, and 9% for CaC , SrC , and BaC , respectively. The exchange interactions in these compounds are studied using the augmented spherical wave method in conjunction with the frozen-magnon approach. The Curie temperature is estimated within both the mean field approximation and the random phase approximation. The predicted Curie temperatures of all three half-metallic compounds considerably exceed the room temperature. The large half-metallic gaps, the robustness of the half metallicity with respect to the lattice contraction, and the high Curie temperatures make these systems interesting candidates for applications in spintronic devices. The absence of the transition-metal atoms makes these compounds important model systems for the study of the origin and properties of the half-metallic ferromagnetism of s-p electron systems.

  2. Dielectric and electromechanical properties of LiNbO3-modified (BiNa)TiO3-(BaCa)TiO3 lead-free piezoceramics

    NASA Astrophysics Data System (ADS)

    Zaman, Arif; Hussain, Ali; Malik, Rizwan Ahmed; Maqbool, Adnan; Nahm, Sahn; Kim, Myong-Ho

    2016-05-01

    The dielectric and electromechanical properties of LiNbO3-modified (1-x) [0.91Na0.5Bi0.5TiO3-0.09Ba0.70Ca0.30TiO3]-xLiNbO3 (abbreviated as (BiNa)TiO3-(BaCa)TiO3-LN) lead-free piezoceramics were investigated. The electrical properties revealed that the addition of LiNbO3 (LN) induces a phase transition from a non-ergodic relaxor to an ergodic relaxor in the (BiNa)TiO3-(BaCa)TiO3-LN system. A large electrostrain of ~0.418% with a normalized strain of ~690 pm V-1 at 6 kV mm-1 was observed at the coexistence of the non-ergodic relaxor and ergodic relaxor phases for LN 0.020, where a field-assisted reversible phase transition between metastable ferroelectric and stable ergodic relaxor phases occurs. Subsequently, a gradual enhancement in the temperature stability of the dielectric constant was observed. At 3 mol.% LN, a nearly constant temperature and a frequency-invariant permittivity of ɛ r ~ 3300 over a broad temperature range of 147 °C-306 °C was observed along with small losses from room temperature up to 400 °C.

  3. Cation Loss of BaCa 0.393Nb 0.606O 2.91 in Aqueous Media: Amorphization at Room Temperature

    NASA Astrophysics Data System (ADS)

    Schober, T.; Szot, K.; Barton, M.; Kessler, B.; Breuer, U.; Penkalla, H. J.; Speier, W.

    2000-02-01

    The complex perovskite BaCa(1+x)/3Nb(2-x)/3O3-x/2 (here x=0.18), also referred to as BCN18, is a widely studied high-temperature proton conductor which has O-vacancies in the dry state accommodating highly mobile protonic defects in the wet state. Experimental evidence is given that BCN18 exposed to a very dilute acid (here HCl), or even hot water, undergoes a remarkable reaction to an amorphous state within a surface layer. The thickness of this layer ranges from tens of nm to several μm depending on exposure time. The amorphous layer is studied with TEM, XRD, XPS, SNMS, TRFA, and AFM. It is concluded that Ba and Ca are almost completely leached out of the surface layer. Protons penetrate into the solid, forming an intermediate, unstable solid acid, rich in Nb and O. The latter eventually collapses into an amorphous phase of Nb, O, and some water. A prerequisite of the above scheme inferred from the kinetics of the process is the presence of planar defects or channels of amorphous character in the initial BCN18 structure that allow rapid diffusion of Ba, Ca, and H. The present model assumes a block arrangement for the initial BCN18 with perfect perovskite structure inside the blocks, separated by thin amorphous slabs.

  4. Influence of simultaneous doping of Sb and Pb on phase formation, superconducting and microstructural characteristics of HgBa 2Ca 2Cu 3O 8+ δ

    NASA Astrophysics Data System (ADS)

    Giri, Rajiv; Tiwari, R. S.; Srivastava, O. N.

    2007-01-01

    We report systematic studies of structural, microstructural and transport properties of (Hg 0.80Sb 0.2- xPb x)Ba 2Ca 2Cu 3O 8+ δ (where x = 0.0, 0.05, 0.1, 0.15, 0.2) compounds. Bulk polycrystalline samples have been prepared by two-step solid-state reaction route at ambient pressure. It has been observed that simultaneous substitution of Sb and Pb at Hg site in oxygen deficient HgO δ layer of HgBa 2Ca 2Cu 3O 8+ δ cuprate high- Tc superconductor leads to the formation of Hg-1223 as the dominant phase. Microstructural investigations of the as grown samples employing scanning electron microscopy reveal single crystal like large grains embodying spiral like features. Superconducting properties particularly transport current density ( Jct) have been found to be sensitive to these microstructural features. As for example (Hg 0.80Sb 0.05Pb 0.15)Ba 2Ca 2Cu 3O 8+ δ compound which exhibits single crystal like large grains (∼50 μm) and appears to result through spiral growth mechanism, shows highest Jct (∼1.85 × 10 3 A/cm 2) at 77 K. A possible mechanism for the generation of spiral like features and correlation between microstructural features and superconducting properties have been put forward.

  5. Coral Ba/Ca records of sediment input to the fringing reef of the southshore of Moloka'i, Hawai'i over the last several decades

    USGS Publications Warehouse

    Prouty, N.G.; Field, M.E.; Stock, J.D.; Jupiter, S.D.; McCulloch, M.

    2010-01-01

    The fringing reef of southern Moloka’i is perceived to be in decline because of land-based pollution. In the absence of historical records of sediment pollution, ratios of coral Ba/Ca were used to test the hypothesis that sedimentation has increased over time. Baseline Ba/Ca ratios co-vary with the abundance of red, terrigenous sediment visible in recent imagery. The highest values at One Ali’i are near one of the muddiest parts of the reef. This co-varies with the lowest growth rate of all the sites, perhaps because the upstream Kawela watershed was historically leveed all the way to the nearshore, providing a fast-path for sediment delivery. Sites adjacent to small, steep watersheds have ∼decadal periodicities whereas sites adjacent to mangrove forests have shorter-period fluctuations that correspond to the periodicity of sediment transport in the nearshore, rather than the watershed. All four sites show a statistically significant upward trend in Ba/Ca.

  6. Aluminum-Magnesium and Oxygen Isotope Study of Relict Ca-Al-rich Inclusions in Chondrules

    NASA Astrophysics Data System (ADS)

    Krot, Alexander N.; McKeegan, Kevin D.; Huss, Gary R.; Liffman, Kurt; Sahijpal, Sandeep; Hutcheon, Ian D.; Srinivasan, Gopalan; Bischoff, Adolph; Keil, Klaus

    2006-03-01

    Relict Ca-Al-rich inclusions (CAIs) in chondrules crystallized before their host chondrules and were subsequently partly melted together with chondrule precursors during chondrule formation. Like most CAIs, relict CAIs are 16O enriched (Δ17O<-20‰) compared to their host chondrules (Δ17O>-9‰). Hibonite in a relict CAI from the ungrouped carbonaceous chondrite Adelaide has a large excess of radiogenic 26Mg (26Mg*) from the decay of 26Al, corresponding to an initial 26Al/27Al ratio [(26Al/27Al)I] of (3.7+/-0.5)×10-5 in contrast, melilite in this CAI and plagioclase in the host chondrule show no evidence for 26Mg* [(26Al/27Al)I of <5×10-6]. Grossite in a relict CAI from the CH carbonaceous chondrite PAT 91546 has little 26Mg*, corresponding to a (26Al/27Al)I of (1.7+/-1.3)×10-6. Three other relict CAIs and their host chondrules from the ungrouped carbonaceous chondrite Acfer 094, CH chondrite Acfer 182, and H3.4 ordinary chondrite Sharps do not have detectable 26Mg* [(26Al/27Al)I<1×10-5, <(4-6)×10-6, and <1.3×10-5, respectively]. Isotopic data combined with mineralogical observations suggest that relict CAIs formed in an 16O-rich gaseous reservoir before their host chondrules, which originated in an 16O-poor gas. The Adelaide CAI was incorporated into its host chondrule after 26Al had mostly decayed, at least 2 Myr after the CAI formed, and this event reset 26Al-26Mg systematics.

  7. The Al-Rich Part of the System CaO-Al 2O 3-MgO . Part I. Phase Relationships

    NASA Astrophysics Data System (ADS)

    Göbbels, M.; Woermann, E.; Jung, J.

    1995-12-01

    In the Al-rich part of the ternary system CaO-Al 2O 3MgO two new ternary phases Ca 2Mg 2Al 28O 46 (CAM-I) and CaMg 2Al 16O 27 (CAM-II) with limited solid solution ranges were found. Due to the fact that the compositions of the Mg-rich end members of these solid solutions lie on the join between hibonite (CaAl 12O 19) and spinel (MgAl 2O 4), the model of the crystal structures of these phases can be constructed by a suitable combination of hibonite and spinel units. Both phases, CAM-I and CAM-II, exhibit solid solution ranges described by a substitution mechanism also found in the binary spinel phase, MgAl 2O 4: 3 Mg 2+ = 2 Al 3+ + □. Thus the ternary phases can be expressed by the chemical formulas. Ca 2Mg 2-3 xAl 28+2 x□ xO 46 for CAM-I with 0 ≤ x ≤ 0.30 and CaMg 2-3 yAl 16+2 y□ yO 27 for CAM-II with 0 ≤ y ≤ 0.2.

  8. Al doped Ba hexaferrite (BaAlxFe12-xO19) thin films on Pt using metallo-organic decomposition

    NASA Astrophysics Data System (ADS)

    Harward, I.; Nie, Yan; Gardner, A.; Reisman, L.; Celinski, Z.

    2012-04-01

    We grew a series of aluminum-substituted M-type barium hexaferrite (BaAlxFe12-xO19) thin films on a Pt (111) template and Si wafer using metallo-organic decomposition technique. We varied the composition from x = 0 to x = 2 with 0.25 step increments. X-ray diffraction patterns confirm highly textured c-axis polycrystalline films while atomic force microscope measurements allow us to estimate the lateral grain sizes which range from 0.2-1 micron depending on Al content. The microwave properties of these films were studied using a broadband ferromagnetic resonance spectrometer from 35 to 70 GHz. The measured out of plane effective anisotropy field increases in a nearly linear fashion with increasing Al concentration, between 12.8 kOe for x = 0 and 25 kOe for x = 2. The measured ferromagnetic resonance linewidths were relatively low, on the order of 150-300 Oe for compositions below x = 1, increasing significantly up to 800 Oe for x = 2. The easy axis magnetic hysteresis loops exhibit high squareness.

  9. Crystal structure study of (Ca, Gd){sub 2}(Al, Ti)O{sub 4}

    SciTech Connect

    Sawada, Haruo; Marumo, Fumiyuki; Kodama, Nobuhiro

    1998-08-01

    The crystal structures of two crystals of (Ca, Gd){sub 2} (Al, Ti)O{sub 4} [tetragonal I4/mmm; Z = 4], one strongly fluorescent and the other weakly fluorescent, having minor differences in their precise compositions have been studied with single-crystal X-ray diffraction methods. The unit cell is significantly smaller for the weakly fluorescent crystal, which also shows alteration of the coordination polyhedraon around the (Ca, Gd) site, suggesting the formation of vacancies at an oxygen site.

  10. Low loss composition of BaxSryCa1-x-yTiO3: Ba0.12-0.25Sr0.35-0.47Ca0.32-0.53TiO3

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Takeuchi, Ichiro

    2001-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  11. Electronic structure and x-ray magnetic circular dichroism in A2FeReO6 (A =Ca ,Sr ,andBa ) oxides

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.; Bekenov, L. V.; Ernst, A.

    2016-07-01

    A systematic electronic structure study of A2FeReO6 (A =Ba ,Sr ,andCa ) has been performed by employing the local-spin-density approximation (LSDA) and LSDA +U methods using the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We investigated the effects of the subtle interplay between spin-orbit coupling, electron correlations, and lattice distortion on the electronic structure of double perovskites. Ca2FeReO6 has a large distortion in the Fe-O-Re bond, and the electronic structure is mainly determined by electron correlations and lattice distortion. In the Ba -Sr -Ca row, the correlation effects at the Fe site are increased. The correlations at the Re site are small in the Ba- and Sr-based compounds but significant in Ca2FeReO6 . Ca2FeReO6 behaves like an insulator only if considered with a relatively large value of Coulomb repulsion Ueff=2.3 eV at the Re site in addition to Ueff=3.1 eV at the Fe site. Ca2FeReO6 possesses a phase transition at 140 K where the metal-insulator transition (MIT) occurs between metallic high-temperature and insulating low-temperature phases. The spin and orbital magnetic moments are linear functions of temperature before and after the MIT but change abruptly at the point of the phase transition. From theoretically calculated magnetocrystalline anisotropy energy (MAE), we found that the easy axis of magnetization for the low-temperature phase is along the b direction, in agreement with experimental data. We found that the major contribution to the MAE is due to the orbital magnetic anisotropy at the Re site. X-ray-absorption spectra and x-ray magnetic circular dichroism at the Re, Fe, and Ba L2 ,3 and Fe, Ca, and O K edges were investigated theoretically in the frame of the LSDA +U method. A qualitative explanation of the x-ray magnetic circular dichroism spectra shape is provided by an analysis of the corresponding selection rules, orbital character, and occupation numbers of individual orbitals

  12. Solid-state combinatorial screening of ARSi4N7:Eu2+ (A = Sr, Ba, Ca; R = Y, La, Lu) phosphors.

    PubMed

    Park, Woon Bae; Son, Kyung Hyun; Singh, Satendra Pal; Sohn, Kee-Sun

    2012-10-01

    A double-ternary combinatorial chemistry (combi-chem) library was visualized in terms of structure, PL intensity, and color chromaticity for a nitride phosphor system, ARSi4N7:Eu(2+) (A = Sr, Ca, Ba; R = Y, La, Lu), so as to obtain a quantitative structure and property relationship (QSPR) in a systematic manner. Most of the samples constituting the double-ternary combi-chem library turned out to have ARSi4N7 structures with a P63mc space group. However, several phases such as Ca2Si5N8 with a Cc space group, LaSi3N5 with a P212121 space group, R6Si11N20O with a P31c space group, etc., coexisted. Aside from the green luminescence from the well-known SrYSi4N7:Eu(2+) and BaYSi4N7:Eu(2+) phosphors, their solid solutions (Sr,Ba)Si4N7:Eu(2+) proved to possess better PL properties. In addition, novel phosphors with an acceptable green PL intensity and color chromaticity were discovered in the ALuSi4N7:Eu(2+) side of the double-ternary combi-chem library. The Ca-rich side did not constitute a single-phase ARSi4N7 structure with a P63mc space group, and therefore the red emission in the Ca-rich side proved to originate from well-known Ca2Si5N8:Eu(2+) phosphors, which resided in the sample as a minor phase. PMID:22920282

  13. Photoluminescence of A- and B-site Eu3+-substituted (SrxBa1-x)2CaWyMo1-yO6 phosphors

    NASA Astrophysics Data System (ADS)

    Sletnes, M.; Lindgren, M.; Valmalette, J. C.; Wagner, N. P.; Grande, T.; Einarsrud, M.-A.

    2016-05-01

    The photoluminescence of two series of A- and B-site Eu3+ substituted (SrxBa1-x)2CaWyMo1-yO6 double perovskite phosphor materials, (SrxBa1-x)1.96Eu0.02K0.02CaWyMo1-yO6 and (SrxBa1-x)2Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, and 1), were studied systematically as a function of stoichiometry and crystal structure. The Eu3+ lattice sites controlled by co-doping with either K or Li were confirmed by Raman spectroscopy. The variation in integrated emission intensity and emission colour over the experimental matrix was examined using statistical tools, and the observed trends were rationalized based on the physical and electronic structure of the phosphors. Phosphors with Eu on B-site with maximum Sr content had remarkably higher emission intensities than all other materials, but the emission was more orange than red due to domination of the 5D0-7F1 (595 nm) transition of Eu3+. The relative intensities of the 5D0-7F2 (615 nm) and 5D0-7F1 transitions of Eu3+, and thus the red-shift of the emission, decreased linearly with increasing Sr content in the A-site Eu-substituted phosphors, and reached a maximum for Sr1.96Eu0.02K0.02CaW0.25Mo0.75O6. A maximum external quantum efficiency of 17% was obtained for the phosphor Sr2Ca0.7Eu0.15Li0.15W0.5Mo0.5O6 with Eu on B-site.

  14. Co-Dopant Influence on the Persistent Luminescence of BaAl2O4:Eu2+,R3+

    NASA Astrophysics Data System (ADS)

    Rodrigues, Lucas C. V.; Hölsä, Jorma; Carvalho, José M.; Pedroso, Cássio C. S.; Lastusaari, Mika; Felinto, Maria C. F. C.; Watanabe, Shigeo; Brito, Hermi F.

    2014-04-01

    The R3+ (rare earth) co-dopants may have a surprisingly important role in persistent luminescence - enhancement of up to 1-3 orders of magnitude may be obtained in the performance of these phosphor materials - depending strongly on the R3+ ion, of course. In this work, the effects of the R3+ co-dopants in the BaAl2O4:Eu2+,R3+ materials were studied using mainly thermoluminescence (TL) and synchrotron radiation XANES methods. In BaAl2O4, the conventional and persistent luminescence both arise from the 4f7→4f65d1 transition of Eu2+, yielding blue-green emission color. The former, in the presence of humidity, turns to more bluish because of creation of an additional Eu2+ luminescence centre which is not, however, visible in persistent luminescence. The trap structure in the non-co-doped BaAl2O4:Eu2+ is rather complex with 4-5 TL bands above room temperature. With R3+ co-doping, this basic structure is modified though no drastic change can be observed. This underlines the fact that even very small changes in the trap depths can produce significant modifications in the persistent luminescence efficiency. It should be remembered that basically the persistent luminescence performance is controlled by the Boltzmann population law depending exponentially on both the temperature and trap depth. Some mechanisms for persistent luminescence have suggested the presence of either divalent R2+ or tetravalent RIV during the charging of the Eu2+ doped materials. The present XANES measurements on BaAl2O4:Eu2+,R3+ confirmed the presence of only the trivalent form of the R3+ co-dopants excluding both of these pathways. It must thus be concluded, that the energy is stored in intrinsic and extrinsic defects created by the synthesis conditions and charge compensation due to R3+ co-doping. Even though the effect of the R3+ co-dopants was carefully exploited and characterized, the differences in the effect of different R3+ ions with very similar chemical and spectroscopic properties could

  15. Mechanisms of electromechanical response in (1 - x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Acosta, Matias; Novak, Nikola; Rossetti, George A.; Rödel, Jürgen

    2015-10-01

    Contributions to the piezoelectric response of (1 - x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ceramics are quantified by small signal measurements made as functions of bias field and temperature. The highest fraction of intrinsic contributions is observed far from phase boundaries, of extrinsic contributions around phase boundaries, and of irreversible switching in the orthorhombic phase. The largest piezoelectric response, d33 = 475 ± 85 pC/N, is found near the orthorhombic to tetragonal phase boundary due to both reversible and irreversible switching. A peak in reversible switching above the Curie temperature for all compositions suggests a line of critical points associated with first order phase transitions, indicating that concurrence of triple and tricritical points in the zero-field phase diagram is not the responsible mechanism of enhanced piezoelectricity.

  16. Microstructure basis for strong piezoelectricity in Pb-free Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Gao, Jinghui; Xue, Dezhen; Wang, Yu; Wang, Dong; Zhang, Lixue; Wu, Haijun; Guo, Shengwu; Bao, Huixin; Zhou, Chao; Liu, Wenfeng; Hou, Sen; Xiao, Ge; Ren, Xiaobing

    2011-08-01

    In this letter, we use transmission electron microscopy to study the microstructure feature of recently reported Pb-free piezoceramic Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 across its piezoelectricity-optimal morphotropic phase boundary (MPB) by varying composition and temperature, respectively. The domain structure evolutions during such processes show that in MPB regime, the domains become miniaturized down to nanometer size with a domain hierarchy, which coincides with the d33-maximum region. Further convergent beam electron diffraction measurement shows that rhombohedral and tetragonal crystal symmetries coexist among the miniaturized domains. Strong piezoelectricity reported in such a system is due to easy polarization rotation between the coexisting nano-scale tetragonal and rhombohedral domains.

  17. Phase transitions and phase diagram of Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 Pb-free system by anelastic measurement

    NASA Astrophysics Data System (ADS)

    Xue, Dezhen; Gao, Jinghui; Zhou, Yumei; Ding, Xiangdong; Sun, Jun; Lookman, Turab; Ren, Xiaobing

    2015-03-01

    The internal friction and storage modulus of Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) Pb-free ceramics have been measured by dynamic mechanical analysis. The anelastic properties show clear anomalies with regard to the transformations between cubic (C), tetragonal (T), orthorhombic (O), and rhombohedral (R) phases, which are all of ferroelastic in nature. The previous reported T-R transition region in the BZT-xBCT system can be divided into the T-O and O-R transitions, consistent with recent studies on the appearance of an intermediate O phase. Based on the internal friction and storage modulus results, a revisited version of BZT-xBCT phase diagram is proposed.

  18. Origin of Ca-Al-rich inclusions. II - Sputtering and collisions in the three-ph8se interstellar medium

    NASA Technical Reports Server (NTRS)

    Clayton, D. D.

    1981-01-01

    The theory put forward by Clayton (1977) for the formation of the Ca-Al-rich inclusions within C3 meteorites is extended to an evolutionary history in a three-phase interstellar medium. Widespread supersonic turbulence in the hot interstellar medium is maintained by supernova shock waves, giving rise to heavy sputtering of the refractory dust. Subsequent reaccumulation with varying dust/gas ratios or varying particle sizes produces isotopically fractionated Ca-Al-rich accumulates. It is thought that the Ca-Al-rich inclusions themselves are formed by the following sequence in the solar system: (1) cold accumulation of larger-than-average Ca-Al-rich particles containing supernova condensate cores into macroscopic (approximately 1 cm) Ca-Al-rich agglomerates, probably by sedimentation; and (2) fusion of the supernova condensates into macroscopic minerals by exothermic chemical reactions that begin when the accumulate has been warmed, thereby releasing energy from the unequilibrated forms accumulated from the interstellar medium.

  19. Advanced treatment of stabilized landfill leachate after biochemical process with hydrocalumite chloride (Ca/Al-Cl LDH).

    PubMed

    Chen, Hua; Sun, Ying; Ruan, Xiuxiu; Yu, Ying; Zhu, Minying; Zhang, Jia; Zhou, Jizhi; Xu, Yunfeng; Liu, Jianyong; Qian, Guangren

    2016-06-01

    This study investigated the effectiveness of Ca/Al-Cl LDH for the treatment of stabilized landfill leachate. Experiments were performed including different dosage of Ca/Al-Cl LDH and comparison with different reagents, such as CaCl2 and AlCl3. As a result, Ca/Al-Cl LDH efficiently removed organic matters in stabilized landfill leachate with the maximum removal (59.41% COD, 62.06% DOC and 70.56% UV254) at the dose of 30g/L. According to UV254 and EEM, it is remarkable that the formation of Ca/Al-LDH has a greater beneficial to organic removal than other reagents, especially for fulvic acid-like and humic acid-like compounds. Moreover, the removal of fulvic acid-like compounds was much better than humic acid-like compounds. The previous compounds had more carboxylic groups, thus had a better removal selectivity. PMID:26920626

  20. Photoluminescence and cathodoluminescence properties of Eu{sup 3+} ions activated AMoO{sub 4} (A = Mg, Ca, Sr, Ba) phosphors

    SciTech Connect

    Du, Peng; Yu, Jae Su

    2015-10-15

    Highlights: • Under 393 nm excitation, strong red emission located at 615 nm was observed in all the samples. • The Eu{sup 3+}-activated CaMoO{sub 4} phosphor exhibited the strongest PL properties. • The CIE chromaticity coordinate of Eu{sup 3+}-activated CaMoO{sub 4} phosphor was (0.647,0.352). • The color purity of Eu{sup 3+}-activated CaMoO{sub 4} phosphor was 92.8%. • Strong CL properties were observed in the Eu{sup 3+}-activated CaMoO{sub 4} phosphor. - Abstract: Eu{sup 3+}-activated AMoO{sub 4} (A = Mg, Ca, Sr, Ba) phosphors were synthesized by a solid-state reaction method. Photoluminescence and cathodoluminescence (CL) spectra as well as X-ray diffraction patterns were measured to characterize the fabricated samples. Under 393 nm excitation, strong red emissions located at ∼615 nm corresponding to the {sup 5}D{sub 0} → {sup 7}F{sub 2} transition of Eu{sup 3+} ions were observed in all the samples. Compared with other Eu{sup 3+} ions activated AMoO{sub 4} (A = Mg, Sr, Ba) phosphors, Eu{sup 3+}-activated CaMoO{sub 4} phosphor exhibited the strongest red emission intensity with better Commission Internationale de L’Eclairage chromaticity coordinate and higher color purity. Furthermore, the CL results indicated that the Eu{sup 3+}-activated CaMoO{sub 4} phosphor had excellent luminescence properties.

  1. Effect of divalent metal ion impurities (Ba2+, Ca2+ and Mg2+) on the growth, structural and physical properties of KAP crystals

    NASA Astrophysics Data System (ADS)

    Kanchana, P.; Elakkina Kumaran, A.; Hayakawa, Y.; Sekar, C.

    2013-02-01

    Single crystals of potassium hydrogen phthalate (KAP), a semi-organic compound, have been grown by slow evaporation method at room temperature from aqueous solution in the presence of divalent metal ionic impurities Ba2+, Ca2+ and Mg2+. Elemental analysis by inductively coupled plasma optical emission spectroscopy (ICP-OES) proves the incorporation of these impurities into the grown crystals. Powder X-ray diffraction studies confirmed the phase formation and metal ions doping into KAP crystals. Thermogravimetric-differential thermal analysis (TG-DTA) shows the onset decomposition temperatures to be 255, 238, 251 and 250 °C for pure, Ba2+, Ca2+ and Mg2+ doped KAP crystals respectively. Microhardness studies revealed that all the three doped crystals have improved hardness values than that of undoped KAP crystal. Ca-KAP crystal exhibited the highest second harmonic generation (SHG) conversion efficiency of 16 mV with the output power of nearly half of the standard potassium dihydrogen phosphate (KDP) crystal. The grown crystals were also subjected to Fourier transform infrared (FTIR) spectroscopy, ultra violet-visible-near infrared (UV-NIR) spectroscopy studies and dielectric studies. Among the three investigated metal ion impurities, Ca2+ ion seem to have positive influence on the growth, mechanical, thermal, dielectric and SHG characteristics of KAP which makes it suitable for applications.

  2. Eu(2+)-Activated Alkaline-Earth Halophosphates, M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) for NUV-LEDs: Site-Selective Crystal Field Effect.

    PubMed

    Kim, Donghyeon; Kim, Sung-Chul; Bae, Jong-Seong; Kim, Sungyun; Kim, Seung-Joo; Park, Jung-Chul

    2016-09-01

    Eu(2+)-activated M5(PO4)3X (M = Ca, Sr, Ba; X = F, Cl, Br) compounds providing different alkaline-earth metal and halide ions were successfully synthesized and characterized. The emission peak maxima of the M5(PO4)3Cl:Eu(2+) (M = Ca, Sr, Ba) compounds were blue-shifted from Ca to Ba (454 nm for Ca, 444 nm for Sr, and 434 nm for Ba), and those of the Sr5(PO4)3X:Eu(2+) (X = F, Cl, Br) compounds were red-shifted along the series of halides, F → Cl → Br (437 nm for F, 444 nm for Cl, and 448 nm for Br). The site selectivity and occupancy of the activator ions (Eu(2+)) in the M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) crystal lattices were estimated based on theoretical calculation of the 5d → 4f transition energies of Eu(2+) using LCAO. In combination with the photoluminescence measurements and theoretical calculation, it was elucidated that the Eu(2+) ions preferably enter the fully oxygen-coordinated sites in the M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) compounds. This trend can be well explained by "Pauling's rules". These compounds may provide a platform for modeling a new phosphor and application in the solid-state lighting field. PMID:27494550

  3. Observations of the minor species Al, Fe and Ca+ in Mercury's exosphere

    NASA Astrophysics Data System (ADS)

    Killen, R. M.; Bida, T. A.

    2015-12-01

    We report here on the first observational evidence of Al and Fe in the exosphere of Mercury, based on measurements of 4-5-σ resolved emission lines of these metals made with Keck-1/HIRES. AlI emission was observed on two separate runs, in 2008 and 2013, with tangent column densities of 2.4 and 3.0e+07 Al atoms cm-2 at altitudes of 1300 and 1850 km (1.1 and 1.5 RM), respectively. FeI emission has been observed once, yielding a tangent column of 6.2e+08 cm-2 at an altitude of 950 km (1.4 RM) in 2009. We also present observations of 3.5-σ CaII emission features near Mercury's equatorial anti-solar limb in 2011, from which a stringent column abundance upper limit of 4.0e+06 cm-2 is derived for the Ca ion. A simple model for zenith column abundances of the neutral species yields 2.0e+07 Al cm-2, and 8.2e+08 Fe cm-2. The observations appear to be consistent with production of these species by impact vaporization, with a large fraction of the Al ejecta in molecular form, and that for Fe in mixed atomic and molecular forms. The scale height of the Al gas is consistent with a kinetic temperature of 4800-8200 K while that of Fe is 5000-13000 K. The apparent high temperature and low density of the Al gas would suggest that it may be produced by dissociation of molecules. A large fraction of both Al and Fe appear to condense in a vapor cloud at low altitudes.

  4. Observations of the minor species Al, Fe and Ca+ in Mercury’s exosphere

    NASA Astrophysics Data System (ADS)

    Killen, Rosemary M.; Bida, Thomas A.

    2015-11-01

    We report here on the first observational evidence of Al and Fe in the exosphere of Mercury, based on measurements of 4-5-σ resolved emission lines of these metals with Keck-1/HIRES. AlI emission was observed on two separate runs, in 2008 and 2013, with tangent column densities of 2.4 and 3 x 107 Al atoms cm-2 at altitudes of 1300 and 1850 km (1.1 and 1.5 RM), respectively. FeI emission has been observed once, yielding a tangent column of 6.2 x 108 cm-2 at an altitude of 950 km (1.4 RM) in 2009. We also present observations of 3.5-σ Ca+ emission features near Mercury’s equatorial anti-solar limb in 2011, from which a stringent tangent column abundance of 4.0 x 106 cm-2 is derived for the Ca ion.A simple model for zenith column abundances of the neutral species yields 2.0 x 107 Al cm-2, and 8.2 x 108 Fe cm-2. The observations appear to be consistent with production of these species by impact vaporization, with a large fraction of the Al ejecta in molecular form, and that for Fe in mixed atomic and molecular forms. The scale height of the Al gas is consistent with a kinetic temperature of 4800-8200 K while that of Fe is 5000-13000 K. The apparent high temperature and low density of the Al gas would suggest that it may be produced by dissociation of molecules. A large fraction of both Al and Fe appear to condense in a vapor cloud at low altitudes.

  5. Observations of the Minor Species Al, Fe and Ca(+) in Mercury's Exosphere

    NASA Technical Reports Server (NTRS)

    Bida, Thomas A.; Killen, Rosemary M.

    2011-01-01

    We report the first detections of Al and Fe, and strict upper limits for Ca(+) in the exosphere of Mercury, using the HIRES spectrometer at the Keck I telescope. We report observed 4-sigma tangent columns of 1.5x10(exp 7) Al atoms per square centimeter at an altitude of 1220 km (1.5 Mercury radii (R(sub M)) from planet center), and that for Fe of 1.6 x 10 per square centimeter at an altitude of 950 km (1.4 R(sub M)). The observed 3-sigma Ca(+) column was 3.9x10(exp 6) ions per square centimeter at an altitude of 1630 km (1.67 R(sub M). A simple model for zenith column abundances of the neutral species were 9.5 x 10(exp 7) Al per square centimeter, and 3.0 x 10(exp 8) Fe per square centimeter. The observations appear to be consistent with production of these species by impact vaporization with a large fraction of the ejecta in molecular form. The scale height of the Al gas is consistent with a kinetic temperature of 3000 - 9000 K while that of Fe is 10500 K. The apparent high temperature of the Fe gas would suggest that it may be produced by dissociation of molecules. A large traction of both Al and Fe appear to condense in a vapor cloud at low altitudes.

  6. Sr isotopic fractionation in Ca-Al inclusions from the Allende meteorite

    USGS Publications Warehouse

    Patchett, P.J.

    1980-01-01

    True relative Sr isotopic compositions, determined by double spiking on Ca-Al inclusions from the Allende meteorite show up to 1.5??? per mass unit mass fractionation relative to the Earth and bulk chondrites. All abnormal inclusions are light-isotope enriched. A lack of isotopically heavy Sr in inclusions would place constraints on the time, place and mechanism of origin of these objects. ?? 1980 Nature Publishing Group.

  7. Crystallization of Ca-Al-Rich Inclusions: Experimental Studies on the Effects of Repeated Heating Events

    NASA Technical Reports Server (NTRS)

    Paque, Julie M.; Lofgren, Gary E.; Le, Loan

    2000-01-01

    The observed textures and chemistry of Ca-Al-rich inclusions (CAIs) are presumed to be the culmination of a series of repeated heating and cooling events in the early history of the solar nebula. We have examined the effects of these heating/cooling cycles experimentally on a bulk composition representing an average Type B Ca-Al-rich inclusion composition. We have tested the effect of the nature of the starting material. Although the most recent and/or highest temperature event prior to incorporation into the parent body dominates the texture and chemistry of the CAI, prior events also affect the phase compositions and textures. We have determined that heating precursor grains to about 1275 C prior to the final melting event increases the likelihood of anorthite crystallization in subsequent higher temperature events and a prior high temperature even that produced dendritic melilite results in melilite that shows evidence of rapid crystallization in subsequent lower temperature events. Prior low temperature pre-crystallization events produce final ran products with pyroxene compositions similar to Type B Ca-Al-rich inclusions, and the glass (residual liquid) composition is more anorthitic than any other experiments to date. The addition of Pt powder to the starting material appears to enhance the ability of anorthite to nucleate from this composition.

  8. Hibonite, Ca2/Al, Ti/24O38, from the Leoville and Allende chondritic meteorites.

    NASA Technical Reports Server (NTRS)

    Keil, K.; Fuchs, L. H.

    1971-01-01

    Hibonite was discovered in light-colored, Ca-Al-Ti-rich and Si-Fe-poor, achondritic inclusions of the Leoville and Allende HL-group chondrites. Two varieties of hibonite occur: one emits a bright red-orange luminescence under electron bombardment and has high amounts of Al2O3 (87.7; 87.9) and low amounts of MgO (0.65; 0.8) and TiO2 (0.68; 0.8). The other emits a bright blue luminescence and is low in Al2O3 (78.7; 79.2) and high in MgO (3.3; 3.7) and TiO2 (6.5; 7.9) (in wt. %). The oxide CaO is about the same in both varieties. It is suggested that the change in the color of the visible luminescence results from changes in composition. The origin of hibonite which occurs in complex mineral assemblages together with anorthite, gelhenite, wollastonite, aluminous diopside, andradite, Ca-pyroxene, perovskite, spinel, taenite, chromite, and pentlandite, and in close proximity to nodules containing calcite, whewellite, forsterite and many of the aforementioned phases, is discussed. The proposition that hibonite and associated phases originated by contact metamorphism and metasomatism of calcite-dolomite bearing assemblages cannot, at this time, be completely ruled out.

  9. Crystal growth, polarized spectra, and laser performance of Yb:CaGdAlO4 crystal

    NASA Astrophysics Data System (ADS)

    Di, J. Q.; Xu, X. D.; Xia, C. T.; Zheng, L. H.; Aka, G.; Yu, H. H.; Sai, Q. L.; Guo, X. Y.; Zhu, L.

    2016-04-01

    In this paper, the crystal growth, polarized spectra, and laser performance of Yb:CaGdAlO4 crystal were reported. The segregation coefficient of Yb3+ ions was calculated to be 0.47. The cell parameters were determined to be a  =  b  =  0.3658 nm, c  =  1.1985 nm. The peak absorption cross-section was calculated to be 2.65  ×  10-20 cm2 at 979 nm and the peak stimulated emission cross-section was 2.23  ×  10-20 cm2 at 980 nm for the π polarization. The continuous-wave (CW) laser operations of uncoated Yb:CaGdAlO4 crystals with 5  ×  5  ×  3 mm3 in size were demonstrated. A maximum output power of 1.6 W at 1048 nm was obtained with a slope efficiency of 28%. The results show that Yb:CaGdAlO4 crystal is a promising laser medium.

  10. Polymer Coated CaAl-Layered Double Hydroxide Nanomaterials for Potential Calcium Supplement

    PubMed Central

    Kim, Tae-Hyun; Lee, Jeong-A; Choi, Soo-Jin; Oh, Jae-Min

    2014-01-01

    We have successfully prepared layered double hydroxide (LDH) nanomaterials containing calcium and aluminum ions in the framework (CaAl-LDH). The surface of CaAl-LDH was coated with enteric polymer, Eudragit®L 100 in order to protect nanomaterials from fast dissolution under gastric condition of pH 1.2. The X-ray diffraction patterns, Fourier transform infrared spectroscopy, scanning electron and transmission electron microscopy revealed that the pristine LDH was well prepared having hydrocalumite structure, and that the polymer effectively coated the surface of LDH without disturbing structure. From thermal analysis, it was determined that only a small amount (less than 1%) of polymer was coated on the LDH surface. Metal dissolution from LDH nanomaterials was significantly reduced upon Eudragit®L 100 coating at pH 1.2, 6.8 and 7.4, which simulates gastric, enteric and plasma conditions, respectively, and the dissolution effect was the most suppressed at pH 1.2. The LDH nanomaterials did not exhibit any significant cytotoxicity up to 1000 μg/mL and intracellular calcium concentration significantly increased in LDH-treated human intestinal cells. Pharmacokinetic study demonstrated absorption efficiency of Eudragit®L 100 coated LDH following oral administration to rats. Moreover, the LDH nanomaterials did not cause acute toxic effect in vivo. All the results suggest the great potential of CaAl-LDH nanomaterials as a calcium supplement. PMID:25490138

  11. The crystal structure of bøgvadite (Na2SrBa2Al4F20)

    NASA Astrophysics Data System (ADS)

    Balić-Žunić, Tonči

    2014-08-01

    The crystal structure of bøgvadite, Na2SrBa2Al4F20, has been solved and refined to a R1 factor of 4.4 % from single-crystal data (Mo Kα X-ray diffraction, CCD area detector) on a sample from the cryolite deposit at Ivittuut, SW Greenland. Bøgvadite is monoclinic, P21/ n space group, with unit cell parameters a = 7.134(1), b = 19.996(3) and c = 5.3440(8) Å, β = 90.02(1)o. A close proximity of the crystal structure to an orthorhombic symmetry and the presence of the two twin components in a nearly 1:1 ratio suggest that the investigated bøgvadite crystal has originally formed as a high-temperature orthorhombic polymorph which on cooling transformed to the stable low temperature monoclinic structure. The bøgvadite crystal structure has groupings of cation-fluoride coordination polyhedra similar to those found in the crystal structures of the genetically closely associated minerals jarlite and jørgensenite. However, its structure type is different from the latter two. The fluoridoaluminate framework of bøgvadite consists of infinite zig-zag chains of cis-connected AlF6 coordination octahedra. The 1 ∞[AlF5] chains are interconnected by infinite chains of Na-F coordination polyhedra which extend in the same direction. Na is coordinated by nine F atoms if its full surrounding is taken in consideration, but makes significant chemical bonds only to closest five. The chains of AlF6 and NaF9 coordination polyhedra form double layers. In the centre of layers, relatively large voids in the form of pentagonal antiprisms are occupied by Sr atoms which make chemical bonds with the closest six F atoms. Between the SrF10 coordinations in the centre of layers run empty channels. The double layers are interconnected by Ba atoms which are coordinated by eight F atoms and fill the spaces between the layers. Bøgvadite belongs to the group of fluoridoaluminates with infinite chains of cis-connected AlF6 coordination octahedra, alike those found in the crystal structures of Ba-fluoridoaluminates.

  12. ABiO2X (A = Cd, Ca, Sr, Ba, Pb; X = halogen) Sillen X1 Series: Polymorphism Versus Optical Properties.

    PubMed

    Olchowka, Jacob; Kabbour, Houria; Colmont, Marie; Adlung, Matthias; Wickleder, Claudia; Mentré, Olivier

    2016-08-01

    The Sillen X1 series of Bi(3+)A(2+)O2X (A = Cd, Ca, Sr, Ba, Pb; X = Cl, Br, I) compounds is composed of three main crystallographic types, namely, the tetragonal form (space group (S.G.) I4/mmm), the orthorhombic form (S.G. Cmcm), and the monoclinic form (S.G. P21/m). Because of Bi(3+)/A(2+) disorder the Bi(3+) based photoluminescence (PL) of the tetragonal polytypes is quenched at room temperature (RT). In the two other ordered forms, the Bi-O-Bi connectivity is different but limited, such that bluish/greenish emission occurs at RT in the monoclinic CdBiO2Cl and CaBiO2Cl and orthorhombic SrBiO2Cl and BaBiO2Cl phases. The crystal structure of BaBiO2Br was refined in the orthorhombic Cmcm space group and also shows RT emission. Focusing on the RT luminescent activity as a key parameter, the PL active compounds were investigated by means of density functional theory calculations and UV-visible reflectance spectroscopy. The influence of A and X ions on the excitation energy is discussed by analyzing the A-O-Bi and Bi-X bonding schemes and gives some insights for rational tuning of both the excitation and emission energies. PMID:27414069

  13. [Luminescent properties of Eu3+ doped layered perovskite structure M2TiO4 (M = Ca, Sr, Ba) red-emitting phosphors].

    PubMed

    Lu, Zhou; Le, Zhang; Xu, Nai-Cen; Wang, Li-Xi; Zhang, Qi-Tu

    2012-10-01

    Series of Eu3+ doped layered perovskite structure M2TiO4: Eu3+ (M = Ca, Sr, Ba) red phosphors were prepared by the high-temperature solid state reaction method. Their phase compositions and photoluminescence properties were investigated by XRD, UV-Vis DRS and fluorescence spectra The results indicated that pure Sr2 TiO4 and Ba2 TiO4 powers could be prepared under 1 100 degrees C for 2 hours, but Ca2 TiO4 powers could not be synthesized even raising the calcination temperature and lengthening the calcination time. Ba2TiO4: Eu3+ phosphor emitted 594 nm (5D0 --> 7F1) and 615 nm (5D0 --> 7F2) orange-red light under the excitation of 395 nm. Sr2TiO4 : Eu3+ phosphor gave a unusual and strong orange-red emission of 578 nm (5D0 --> 7F0) and 626 nm (5 D0 --> 7F2) under the excitation of near ultraviolet or blue light, resulting in the better color purity and higher luminescent intensity. In addition, this phosphor had the highest luminous efficiency when excited by the charge migration excitation at 363 nm and it had the great potential to be a red phosphor for N-UV LED and blue light chip. PMID:23285854

  14. Improvement of critical current density in thallium-based (Tl,Bi)Sr{sub 1.6}Ba{sub 0.4}Ca{sub 2}Cu{sub 3}O{sub x} superconductors

    SciTech Connect

    Ren, Z.F.; Wang, C.A.; Wang, J.H.

    1994-12-31

    Epitaxial (Tl,Bi)Sr{sub 1.6}Ba{sub 0.4}Ca{sub 2}Cu{sub 3}O{sub x} (Tl,Bi)-1223 thin films on (100) single crystal LaAlO{sub 3} substrates were synthesized by a two-step procedure. Phase development, microstructure, and relationships between film and substrate were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Resistance versus temperature, zero-field-cooled and field-cooled magnetization, and transport critical current density (J{sub c}) were measured. The zero-resistance temperature was 105-111 K. J{sub c} at 77 K and zero field was > 2 x 10{sup 6} A/cm{sup 2}. The films exhibited good flux pinning properties.

  15. Soot oxidation and NO{sub x} reduction over BaAl{sub 2}O{sub 4} catalyst

    SciTech Connect

    Lin, He; Li, Yingjie; Shangguan, Wenfeng; Huang, Zhen

    2009-11-15

    This study addresses soot oxidation and NO{sub x} reduction over a BaAl{sub 2}O{sub 4} catalyst. By XRD analysis, the catalyst was shown to be of spinel structure. Temperature Programmed Oxidation (TPO) and Constant Temperature Oxidation (CTO) at 673 K show that the presence of O{sub 2} decreases the ignition temperature of soot, and it enhances the conversion of NO{sub x} to N{sub 2} and N{sub 2}O. The kinetic features of soot oxidation in the TPO test are similar to that in the TG-DTA analysis. Analysis by Diffuse Reflectance Fourier Infrared Transform Spectroscopy (DRIFTS) indicates that the nitrates formed from NO{sub x} adsorption and the C(O) intermediates from soot oxidation are the key precursors of the redox process between soot and NO{sub x} over surfaces of the BaAl{sub 2}O{sub 4} catalyst. Moreover, DRIFTS tests suggest that nitrates act as the principal oxidants for C(O) oxidation, through which nitrates are reduced to N{sub 2} and N{sub 2}O. The O{sub 2} in the gas mixture presents a positive effect on the conversion of NO{sub x} to N{sub 2} and N{sub 2}O by promoting the oxidation of nitrites into nitrates species. (author)

  16. Evolution of structure and physical properties in Al-substituted Ba-hexaferrites

    NASA Astrophysics Data System (ADS)

    Alex, Trukhanov; Larisa, Panina; Sergei, Trukhanov; Vitalii, Turchenko; Mohamed, Salem

    2016-01-01

    The investigations of the crystal and magnetic structures of the BaFe12-xAlxO19 (x = 0.1-1.2) solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12-xAlxO19 (x = 0.1-1.2) solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range (from 4.2 K to 150 K). It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFe12-xAlxO19 (x = 0.1-1.2) solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed. Project supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISiS” (Grant No. K4-2015-040). L. Panina acknowledges support under the Russian Federation State contract for organizing a scientific work.

  17. Structural and photoluminescent properties of nanosized BaMgAl10O17:Eu2+ blue-emitting phosphors prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Van Bui, Hao; Nguyen, Tu; Nguyen, Manh Cuong; Tran, Trong An; Le Tien, Ha; Tam Tong, Hao; Nguyen, Thi Kim Lien; Pham, Thanh Huy

    2015-09-01

    We report on the photoluminescent properties of Ba0.9Eu0.1MgAl10O17 (BAM) phosphors in correlation with the host crystalline structures. The phosphors were synthesized by citrate sol-gel process, followed by a sintering and a reduction step, both at elevated temperatures. We found that the phosphors were amorphous when sintered at temperatures below 900 °C. At 1000 °C, the crystalline structure was mainly that of BaAl2O4 phase. The BaMgAl10O17 phase appeared at 1100 °C, and became dominant with increasing temperature. At 1300 °C, the BaAl2O4 phase almost disappeared, and only BaMgAl10O17 features were found. The luminescent characteristics of the phosphors were closely related to the structures of the host lattice. Under the same reduction conditions, the phosphors sintered at 1000 °C showed the emission of both Eu3+ and Eu2+. For the phosphors sintered at higher temperatures, the main features were originated from the emission of Eu2+. We additionally observed the increase of emission intensity and the broadening of emission spectra with increasing reduction temperature.

  18. Effects of Ca and Zr substitution upon structure and properties of Ba{sub 5}LaTi{sub 3}Ta{sub 7}O{sub 30} low-loss dielectric ceramics

    SciTech Connect

    Sun, Y.H.; Chen, X.M

    2004-07-02

    Effects of Ca and Zr substitution upon the dielectric properties of Ba{sub 5}LaTi{sub 3}Ta{sub 7}O{sub 30} ceramics were investigated together with the structural characterization. All the samples of Ba{sub 5}La(Zr{sub x}Ti{sub 1-x}){sub 3}Ta{sub 7}O{sub 30} formed a filled tungsten-bronze structures, whereas the solid solution limit was determined as x=0.25 in (Ca{sub x}Ba{sub 1-x}){sub 5}LaTi{sub 3}Ta{sub 7}O{sub 30}. Beyond this limit secondary phase of CaTa{sub 2}O{sub 6} was detected and it would become the major phase for the Ca-rich compositions. The temperature coefficient of dielectric constant was improved with increasing Zr content while the dielectric constant decreased and the low dielectric loss varied little (in the order of 10{sup -4}). In the case of (Ca{sub x}Ba{sub 1-x}){sub 5}LaTi{sub 3}Ta{sub 7}O{sub 30}, small temperature coefficient of dielectric constant could be obtained with increasing Ca content while the dielectric constant decreased significantly, and a small amount substitution of Ca for Ba induced decrease in dielectric loss.

  19. Hydrothermal Transformation of the Calcium Aluminum Oxide Hydrates CaAl2O4 . 10H2O and Ca2Al2O. 8H2O to Ca3Al2(OH)12 Investigated by In Situ Synchrotron X-ray Powder Diffraction

    SciTech Connect

    Jensen,T.; Christensen, A.; Hanson, J.

    2005-01-01

    The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl{sub 2}O{sub 4}{center_dot}10H{sub 2}O converted to Ca{sub 3}Al{sub 2}(OH){sub 12} and amorphous aluminum hydroxide. Ca{sub 2}Al{sub 2}O{sub 5}{center_dot}8H{sub 2}O transformed via the intermediate phase Ca{sub 4}Al{sub 2}O{sub 7}{center_dot}13H{sub 2}O to Ca{sub 3}Al{sub 2}(OH){sub 12} and gibbsite, Al(OH){sub 3}. The phase Ca{sub 4}Al{sub 2}O{sub 7}{center_dot}19H{sub 2}O reacted via the same intermediate phase to Ca{sub 3}Al{sub 2}(OH){sub 12} and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.

  20. Luminescence and X-ray absorption studies on 0.5% Ce(3+) doped BaCa2MgSi2O8 phosphor.

    PubMed

    Hou, Dejian; Zhou, Weijie; Wu, Cen; Dorenbos, Pieter; Liang, Hongbin; Sham, Tsun-Kong; Zhang, Bingbing; Huang, Yan; Tao, Ye

    2015-09-14

    0.5% Ce(3+) doped BaCa2MgSi2O8 phosphor was prepared by a conventional solid state reaction method. Luminescence spectra as well as fluorescence decay were monitored in the VUV-UV range. Ce(3+) emissions are assigned to cerium ions on a Ba(2+) site, and the five 4f-5d excitation bands of Ce(3+) were determined at low temperature. The light yield is estimated to be around 10,600 ph MeV(-1) under X-ray excitation. X-ray absorption near-edge structure (XANES) was explored to study the energy transfer efficiency to optical centers from each element in the phosphor; the results show that the contributions to luminescence are not identical for each element. PMID:26234548

  1. Reoxidation of Aluminum in Fe- Al- M (M = C, Mn, and Ti) melts with CaO-Al2 O3-Fe t O (3 mass pct) slags

    NASA Astrophysics Data System (ADS)

    Lee, Kwang Ro; Suito, Hideaki

    1996-06-01

    An Fe-0.01 to 0.5 mass pct Al alloy and an Fe-0.003 to 0.71 mass pct Al-1 mass pct M (M = C, Mn, and Ti) alloy were reoxidized with the CaO-Al2O3-FetO (3 mass pct) slags at 1873 K in an Al2O3 or CaO crucible for 5 and 60 minutes. The contents of acid-insoluble Al, total O, and alloying element M in metal as well as those of M and FetO in slag were measured as a function of total Al content. On the basis of the present and previous results for Fe- Al- Te alloys, the effect of alloying elements on the degree of supersaturation with respect to the Al2O3 precipitation was studied. As a result, the supersaturation phenomenon was observed in all experiments at 5 minutes, but in the experiments at 60 minutes, it was observed only in Fe- Al and Fe- Al- Ti alloys. No supersaturation was observed in the reoxidation of Si in Fe-0.13 to 0.98 mass pct Si alloys with the CaO-SiO2-FetO (3 mass pct) slags in a CaO crucible at 5 and 60 minutes.

  2. Multiple Magnetic Transitions and Magnetocaloric Effect in (La,Pr,M)MnO3 (M = Ca, Sr, Ba) Mixed Phase Manganites

    NASA Astrophysics Data System (ADS)

    Lampen, P. J.; Bingham, N. S.; Phan, M. H.; Srikanth, H. S.; Phan, T. L.; Yu, S. C.; Cheong, S. W.

    2012-02-01

    The manganite compound (La,Pr,Ca)MnO3 is a well-studied system that is known to exhibit a complex phase diagram featuring ``strain liquid'' and ``strain glass'' regions in combination with competing ferromagnetic (FM) and charge-ordered antiferromagnetic (CO/AFM) phases. The balance of these phases is sensitive to various perturbations including magnetic and electric field, strain, bandwidth, and A-site cation disorder. The A-site disorder and bandwidth of this compound can be tuned through the replacement of Ca with larger Sr and Ba ions. We report here a systematic study of the influence of cation substitution on the magnetic and magnetocaloric properties of La0.35Pr0.275M0.375MnO3 (M = Ca, Sr, Ba). Structural properties, including lattice parameters and Mn--O--Mn bond angles, were determined from X-ray diffraction patterns. DC magnetometry studies reveal multiple magnetic transitions in each sample which are probed by magnetocaloric effect (MCE) and transverse susceptibility (TS) experiments. Increasing the average A-site cationic radius is found to strongly impact the magnetic properties and phase behavior of the system.

  3. Petrography, mineralogy, and Mg isotope composition of VICTA: A vigarano CaAl4O7-bearing type A inclusion

    NASA Technical Reports Server (NTRS)

    Greenwood, R. C.; Morse, A.; Long, J. V. P.

    1993-01-01

    Thermodynamic calculations predict that Ca-dialuminate (CaAl4O7) condenses from a cooling gas of solar composition after hibonite and before melilite. Although Ca-dialuminate has now been recorded from Ca Al-rich inclusions (CAI's) in at least 9 meteorites, compared to hibonite it is a relatively rare phase. As pointed out by Michel-Levy et al., the absence of Ca-dialuminate from most hibonite-bearing inclusions poses a serious problem for the condensation model of CAI formation. Here we describe an inclusion which contains abundant CA-dialuminate partially altered to a hercynite-rich (FeAl2O4) assemblage. The evidence from VICTA indicates that compared to all other phases in type A inclusions, Ca-dialuminate is the most susceptible to secondary alteration; a feature which may explain its restricted occurrence. Unaltered Ca-dialuminate and melilite in VICTA display excess Mg-26 indicative of in situ decay of Al-26.

  4. Low-temperature heat capacities of CaAl2SiO6 glass and pyroxene and thermal expansion of CaAl2SiO6 pyroxene.

    USGS Publications Warehouse

    Haselton, H.T., Jr.; Hemingway, B.S.; Robie, R.A.

    1984-01-01

    Low-T heat capacities (5-380 K) have been measured by adiabatic calorimetry for synthetic CaAl2SiO6 glass and pyroxene. High-T unit cell parameters were measured for CaAl2SiO6 pyroxene by means of a Nonius Guinier-Lenne powder camera in order to determine the mean coefficient of thermal expansion in the T range 25-1200oC. -J.A.Z.

  5. Observation of a Bulk Nodal-Gap in Overdoped Y $_{0.9} 0.9 Ca _{0.1} 0.1 Ba _{2} 2 Cu _{3} 3 O _{7-delta }$ 7 - δ Thin Films

    NASA Astrophysics Data System (ADS)

    Bachar, N.; Bechor, Y.; Gorshunov, B.; Farber, E.

    2015-04-01

    Complex conductivity of overdoped YCaBaCuO thin films was measured in Terahertz frequency using frequency and time domain methods. The films were measured in the frequency range of 3-100 cm and in the temperature range of 20-300 K. Results show a possible deviation from a pure -wave superconductor, indicated by the existence of an energy sub-gap in overdoped YCaBaCuO films. Evidence for this sub-gap appears as non-monotonic behavior of as a function of frequency followed by a sharp decrease at low frequencies, and a dip in the imaginary part of the optical conductivity multiplied by frequency, . The mentioned features were observed at energy of about 1.2 meV in 10 % Ca-doped YBCO thin films. Our complex conductivity spectra are in agreement with the theoretical prediction obtained by using a mixed symmetry order parameter within the Born limit, shown by Schürrer et al. We suggest that these observations are direct evidence for a nodal gap obtained in a -wave superconductor and can be theoretically clarified by adding an imaginary component as or to the main -wave order parameter.

  6. Theoretical studies of 63Cu2+ orbital Knight shifts of HgBa2Ca2Cu3O8+δ

    NASA Astrophysics Data System (ADS)

    Kuang, Min-Quan; Wu, Shao-Yi; Hu, Xian-Fen

    2014-08-01

    The orbital Knight shifts and g factors for the tetragonal 63Cu2+ site in HgBa2Ca2Cu3O8+δ at 133 and 115 K are theoretically investigated based on the high-order perturbation formulae of these quantities for a 3d9 ion situated into tetragonally elongated octahedra. The theoretical results reveal good agreement with the observed values. The significant anisotropies of the Knight shifts are illustrated as the considerable local tetragonal elongation distortions of the five-coordinated Cu2+ sites. The results at different temperatures are also discussed in view of the local structure of the Cu2+ sites.

  7. Characteristics of TlBa[sub 2]Ca[sub 2]Cu[sub 3]O[sub 9+][sub [delta

    SciTech Connect

    Kung, P.J.; Maley, M.P.; Wahlbeck, P.G.; Peterson, D.E. )

    1993-04-01

    Crystal structure and superconductivity of the Tl--Ba--Ca--Cu--O powder prepared by a solid-state reaction were studied. The results of x-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses indicate that the powder of a major single 1223 phase was synthesized with a cauliflower-like morphology; by grinding, the powder was partially transformed to an amorphous phase. The measurement of magnetic hysteresis was also performed in the temperature range of 7--75 K up to 5 T from which the weak field-dependent behavior of critical current density was observed. The as-synthesized powder, with [ital T][sub [ital c

  8. Studies on the new superconducting system (RE) Ba2Ca3Sr4Cu5Ox (RE=Gd, Ho & Dy)

    NASA Astrophysics Data System (ADS)

    Arumugam, S.

    1996-03-01

    Superconducting studies have been carried out in the new high TC (50-65K) system (RE)Ba2Ca3Sr4Cu5OX [(RE) 12345] with RE=Gd, Ho&Dy. The unit cell dimensions are of the order of a=5.44 °A, b=5.46°A and c=14.62°A. The data above the diamagnetic onset and below the upturn temperature due to ordering were analyzed to yield the effective magnetic moments (Peff) of the rare earth ions.

  9. Effect of Eu substitution on superconductivity in Ba{sub 8−x}Eu{sub x}Al{sub 6}Si{sub 40} clathrates

    SciTech Connect

    Liu, Lihua; Bi, Shanli; Peng, Bailu; Li, Yang

    2015-05-07

    The silicon clathrate superconductor is uncommon as its structure is dominated by strong Si-Si covalent bonds, rather than the metallic bond, that are more typical of traditional superconductors. To understand the influence of large magnetic moment of Eu on superconductivity for type-I clathrates, a series of samples with the chemical formula Ba{sub 8−x}Eu{sub x}Al{sub 6}Si{sub 40} (x = 0, 0.5, 1, and 2) were synthesised in which Eu occupied Ba sites in cage center. With the increase of Eu content, the cubic lattice parameter decreases monotonically signifying continuous shrinkage of the constituting (Ba/Eu)@Si{sub 20} and (Ba/Eu)@Si{sub 24} cages. The temperature dependence of magnetization at low temperature revealed that Ba{sub 8}Al{sub 6}Si{sub 40} is superconductive with transition temperature at T{sub C} = 5.6 K. The substitution of Eu for Ba results in a strong superconductivity suppression; Eu-doping largely decreases the superconducting volume and transition temperature T{sub C}. Eu atoms enter the clathrate lattice and their magnetic moments break paired electrons. The Curie-Weiss temperatures were observed at 3.9, 6.6, and 10.9 K, respectively, for samples with x = 0.5, 1.0, and 2.0. Such ferromagnetic interaction of Eu can destroy superconductivity.

  10. Femtosecond laser-induced subwavelength ripples on Al, Si, CaF2 and CR-39

    NASA Astrophysics Data System (ADS)

    Bashir, Shazia; Shahid Rafique, M.; Husinsky, Wolfgang

    2012-03-01

    The formation of self-organized subwavelength ripples on Al, Si, CaF2 and CR-39 induced by 25 fs laser pulses at central wavelength of 800 nm has been observed under certain experimental conditions. In case of Al subwavelength gratings with periodicities ranging from 20 to 220 nm are reported. For CaF2 the periodicity goes up to 625 nm. In case of Si, nano-gratings have the periodicity of 10-100 nm. The interspacing of these gratings is 60 nm in case of CR-39. These features which are significantly shorter than incident laser wavelength are observed at the irradiation fluence slightly higher than the ablation threshold regardless of the target material. In addition to these nanoripples, classical or microripples with an average spacing of 1-2 μm have also been registered on irradiated surfaces of Al and Si. These microripples have appeared at fluence higher than that is required for nanoripple-formation. It has been found that the formation of the laser-induced ripples is strongly dependent and quite sensitive to the incident laser fluence and the selection of material.

  11. Surface micromorphology of dental composites [CE-TZP]-[Al2O3] with Ca(+2) modifier.

    PubMed

    Berezina, Sofia; Il'icheva, Alla Alexandrovna; Podzorova, Lyudmila Ivanovna; Ţălu, Ştefan

    2015-09-01

    The objective of this study was to characterize the three-dimensional (3D) surface micromorphology of the ceramics produced from nanoparticles of alumina and tetragonal zirconia (t-ZrO2) with addition of Ca(+2) for sintering improvement. The 3D surface roughness of samples was studied by atomic force microscopy (AFM), fractal analysis of the 3D AFM-images, and statistical analysis of surface roughness parameters. Cube counting method, based on the linear interpolation type, applied for AFM data was used for fractal analysis. The morphology of non-modified ceramic sample was characterized by the rather big (1-2 μm) grains of α-Al2O3 phase with a habit close to hexagonal drowned in solid solution of t-ZrO2 with smooth surface. The pattern surfaces of modified composite content a little amount of elongated prismatic grains with composition close to the phase of СаСеAl3О7 as well as hexahedral α-Al2O3-grains. Fractal dimension, D, as well as height values distribution have been determined for the surfaces of the samples with and without modifying. It can be concluded that the smoothest surface is of the modified samples with Ca(+2) modifier but the most regular one is of the non-modified samples. A connection was observed between the surface morphology and the physical properties as assessed in previous works. PMID:26190812

  12. CaMn2Al10: Itinerant Mn magnetism on the verge of magnetic order

    DOE PAGESBeta

    Steinke, L.; Simonson, J. W.; Yin, W. -G.; Smith, G. J.; Kistner-Morris, J. J.; Zellman, S.; Puri, A.; Aronson, M. C.

    2015-07-24

    We report the discovery of CaMn2Al10, a metal with strong magnetic anisotropy and moderate electronic correlations. Magnetization measurements find a Curie-Weiss moment of 0.83μB/Mn, significantly reduced from the Hund's rule value, and the magnetic entropy obtained from specific heat measurements is correspondingly small, only ≈ 9% of Rln2. These results imply that the Mn magnetism is highly itinerant, a conclusion supported by density functional theory calculations that find strong Mn-Al hybridization. Consistent with the layered nature of the crystal structure, the magnetic susceptibility χ is anisotropic below 20 K, with a maximum ratio of χ[010]/χ[001] ≈ 3.5. A strong power-lawmore » divergence χ(T) ~ T–1.2 below 20 K implies incipient ferromagnetic order, an Arrott plot analysis of the magnetization suggests a vanishing low Curie temperature TC ~ 0. Our experiments indicate that CaMn2Al10 is a rare example of a system where the weak and itinerant Mn-based magnetism is poised on the verge of order.« less

  13. CaMn2Al10 : Itinerant Mn magnetism on the verge of magnetic order

    NASA Astrophysics Data System (ADS)

    Steinke, L.; Simonson, J. W.; Yin, W.-G.; Smith, G. J.; Kistner-Morris, J. J.; Zellman, S.; Puri, A.; Aronson, M. C.

    2015-07-01

    We report the discovery of CaMn2Al10 , a metal with strong magnetic anisotropy and moderate electronic correlations. Magnetization measurements find a Curie-Weiss moment of 0.83 μB/Mn , significantly reduced from the Hund's rule value, and the magnetic entropy obtained from specific heat measurements is correspondingly small, only ≈9 % of R ln 2 . These results imply that the Mn magnetism is highly itinerant, a conclusion supported by density functional theory calculations that find strong Mn-Al hybridization. Consistent with the layered nature of the crystal structure, the magnetic susceptibility χ is anisotropic below 20 K, with a maximum ratio of χ[010 ]/χ[001 ]≈3.5 . A strong power-law divergence χ (T ) ˜T-1.2 below 20 K implies incipient ferromagnetic order with a low Curie temperature TC<2 K . Our experiments indicate that CaMn2Al10 is a rare example of a system where the weak and itinerant Mn-based magnetism is poised on the verge of order.

  14. Geochemical modeling of leaching of Ca, Mg, Al, and Pb from cementitious waste forms

    SciTech Connect

    Martens, E.; Jacques, D.; Van Gerven, T.; Wang, L.; Mallants, D.

    2010-08-15

    Results from extraction tests on cement-waste samples were simulated with a thermodynamic equilibrium model using a consistent database, to which lead data were added. Subsequent diffusion tests were modeled by means of a 3D diffusive transport model combined with the geochemical model derived from the extraction tests. Modeling results of the leached major element concentrations for both uncarbonated and (partially) carbonated samples agreed well with the extraction test using the set of pure minerals and solid solutions present in the database. The observed decrease in Ca leaching with increasing carbonation level was qualitatively predicted. Simulations also revealed that Pb leaching is not controlled by dissolution/precipitation only. The addition of the calcite-cerrusite solid solution and adsorption reactions on amorphous Fe- and Al-oxides improved the predictions and are considered to control the Pb leaching during the extractions tests. The dynamic diffusive leaching tests were appropriately modeled for Na, K, Ca and Pb.

  15. Low Loss Composition of BA{sub X}SR{sub Y}CA{sub 1-X-Y}TIO{sub 3}:BA{sub 0.12-0.25}SR{sub 0.35-0.47}CA{sub 0.32-0.53}TIO{sub 3}

    SciTech Connect

    Xiang, Xiao-Dong; Chang, Hauyee; Takeuchi, Ichiro

    1999-10-19

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba{sub x}Sr{sub y}Ca{sub 1-x-y})TiO{sub 3}. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  16. Method of forming a dielectric thin film having low loss composition of Ba.sub.x Sr.sub.y Ca.sub.1-x-y TiO.sub.3 : Ba.sub.0.12-0.25 Sr.sub.0.35-0.47 Ca.sub.0.32-0.53 TiO.sub.3

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Takeuchi, Ichiro

    2000-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  17. Effect of Heat Treatment in Air on Thermoelectric Properties of Polycrystalline Type-I Silicon-Based Clathrate: Ba8Al15Si31

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Shirataki, Ritsuko

    2015-06-01

    The effect of heat treatment in air on the thermoelectric properties was investigated for polycrystalline Ba8Al15Si31, where the Al content is almost at the maximum in the Ba8Al x Si46- x system, to evaluate the thermal stability in air at high temperatures, which is indispensable for practical use in thermoelectric applications. Samples were prepared by combining arc melting and spark plasma sintering techniques. Heat treatments were performed in air at 873 K for 10 days and 20 days. The Seebeck coefficient, electrical conductivity, and thermal conductivity were measured before and after the heat treatments. The microstructure and chemical composition were also analyzed before and after the heat treatments, using scanning electron microscopy with energy-dispersive x-ray spectroscopy. Although an oxidation layer was formed on the surface by the heat treatment in air, the chemical composition of the interior of Ba8Al15Si31 was found to be stable in air at 873 K for 10 days and 20 days. The Seebeck coefficient, the electrical conductivity, and the thermal conductivity were found to be almost unchanged after the heat treatment, indicating that Ba8Al15Si31 clathrate is promising as a thermoelectric material with high thermal stability for use in air at 873 K.

  18. Partition coefficients for Al, Ca, Ti, Cr, and Ni in olivine obtained by melting experiment on an LL6 chondrite

    NASA Technical Reports Server (NTRS)

    Miyamoto, M.; Mikouchi, T.; Mckay, G. A.

    1994-01-01

    We report the partition coefficients for Ca, Al, Ti, Cr, and Ni in olivine obtained through a series of melting experiments on an LL6 chondrite under varying conditions of temperature and oxygen fugacity. It is necessary to examine the variation of partition coefficients up to extremely reducing conditions in order to study meteoritic olivines. For Ca, Al, and Cr, the partition coefficients tend to decrease as temperature increases, but do not change even under extremely reducing conditions.

  19. A diode pumped passively mode-locked Nd:CaGdAlO4 laser

    NASA Astrophysics Data System (ADS)

    Rao, H.; Cong, Z. H.; Qin, Z. G.; Feng, C.; Wang, Q. P.; Liu, Z. J.; Zhang, X. Y.; Zhang, S. S.; Liu, Y.; Men, S. J.; Xia, J. B.; Di, J. Q.; Xu, X. D.; Xu, J.

    2016-04-01

    A diode pumped passively mode-locked Nd:CaGdAlO4 (Nd:CGA) laser was demonstrated. By using a semiconductor saturable-absorber mirror (SESAM) as the modulator, stable mode-locked pulses with a duration of 6.0 ps and a repetition rate of 88.3 MHz have been achieved at a central wavelength of 1078.6 nm. The maximum output power of 452 mW was obtained under a pump power of 10 W.

  20. Electronic Properties of Lead-Free (Ba0.95Ca0.05)(Ti0.92Sn0.08)O3 Piezoceramic Nanofibers by Electrospinning

    NASA Astrophysics Data System (ADS)

    Sahoo, Benudhar; Panda, Prasanta Kumar

    2015-11-01

    Lead-free (Ba0.95Ca0.05)(Ti0.92Sn0.08)O3, (BCTS) piezoceramic nanofibers were prepared by electrospinning acetate precursor solutions in polyvinyl pyrrolidone, followed by calcining at 1150ºC for 2 h. X-ray diffraction of calcined nanofibers confirmed the formation of the BCTS phase and energy dispersive x-ray analysis confirmed the presence of Ca and Sn ions. The scanning electron microscope studies showed cylindrical fibers with a diameter in the range 80-275 nm. The dielectric constant and piezoelectric charge constant ( d 33) were 3485 at 100 Hz, RT and 398 pC/N, respectively.

  1. Acid precipitation and food quality: Effects of dietary Al, Ca and P on bone and liver characteristics in American black ducks and mallards

    USGS Publications Warehouse

    Sparling, D.W.

    1991-01-01

    American black ducks (Anas rubripes) and mallards (A. platyrhynchos) were fed diets varying in concentrations of aluminum (Al). calcium (Ca), and phosphorus (P) for 10 weeks to identify toxic effects of Al under conditions representative of areas with acid precipitation. Femur and liver tissues were analyzed for Al. Ca, and P concentrations and structural characteristics. At two weeks of age, both species demonstrated pronounced differences in femur Al and P concentrations and femur mass from dietary Al and interaction between Ca:P regimen and Al:Low Ca:Low P enhanced Al storage and decreased P and mass in femurs. Femur Ca was lowest in the Low Ca:Low P regimen but was not affected by dietary Al. At 10 weeks, femur and liver Al continued to vary with dietary Al. Elevated Al and reduced Ca lowered modulus of elasticity. Femur P increased with elevated dietary P in black ducks. Elevated dietary P negated some of the effects of dietary A! on femur mass in black ducks. Reduced Ca concentrations weakened bones of both species and lowered both Ca and P. An array of clinical signs including lameness, discoloration of the upper mandible, complete and greenstick fractures, and death were responses to elevated Al and Ca:P regimen. Black ducks seemed to display these signs over a wider range of diets than mallards. Diets of 1,000 mg/kg Al had toxic effects on both species, particularly when combined with diets low in Ca and P.

  2. Geoenvironmental weathering/deterioration of landfilled MSWI-BA glass.

    PubMed

    Wei, Yunmei; Saffarzadeh, Amirhomayoun; Shimaoka, Takayuki; Zhao, Chun; Peng, Xuya; Gao, Junmin

    2014-08-15

    Municipal solid waste incineration bottom ash (MSWI-BA) glass serves as a matrix of assorted bottom ash (BA) compounds. Deterioration of the BA glass phases is quite important as they regulate the distribution of a series of toxic elements. This paper studied landfilled MSWI-BA samples from the mineralogical and geochemical viewpoint to understand the deterioration behavior of the BA glass phases as well as mechanisms involved. Bulk analysis by PXRD as well as micro-scale analysis by optical microscopy and SEM/EDX was conducted for such purposes. The results revealed that dissolution of the BA glass phases has resulted in a deterioration layer of 10(0)-10(2)μm thickness after years of disposal. This rapid weathering process is highly relevant to the specific glass characteristics and solution pH. The BA glass phases with more embedded compounds and cracks/fissures tend to be more vulnerable. Moreover, the generally alkaline pH in ash deposit favors a rapid disruption of the glass phase. The weathering products are mainly gel phases (including Al-Si gel, Ca-Al-Si gel, Fe-Al-Si gel etc.) with iron oxide/hydroxide as accessory products. Breakdown of the BA glass phases triggers chemical evolution of the embedded compounds. Based on all the findings above, a model is proposed to illustrate a general evolution trend for the landfilled MSWI-BA glass phases. PMID:25043593

  3. Broadband photoluminescence in the (CaO-Al2O3-SiO2):Eu system

    NASA Astrophysics Data System (ADS)

    Gurin, N. T.; Paksyutov, K. V.; Terent'ev, M. A.; Shirokov, A. V.

    2009-08-01

    Phosphors of the (CaO-Al2O3-SiO2):Eu system obtained by direct solid-state synthesis in air at 1300°C produce broadband photoluminescence (PL) covering the entire visible range under excitation by a nitrogen laser. Upon vacuum annealing, the PL intensity in (CaO-Al2O3-SiO2):Eu and (CaO-Al2O3-2SiO2):Eu samples exhibits a several-fold increase and the latter phosphor yields blue emission according to the CIE color standard. The annealing of a (CaO-Al2O3):Eu composition leads to a change in the emission color from red (close to that according to the EBU scale) to blue (in the same scale). Vacuum-annealed (CaO-2Al2O3):Eu phosphor yields red emission (close to that according to the NTSC scale), while (2CaO-Al2O3):Eu composition exhibits intense purple luminescence.

  4. Comparison of Ba/Ca and δOWATER18 as freshwater proxies: A multi-species core-top study on planktonic foraminifera from the vicinity of the Orinoco River mouth

    NASA Astrophysics Data System (ADS)

    Bahr, André; Schönfeld, Joachim; Hoffmann, Julia; Voigt, Silke; Aurahs, Ralf; Kucera, Michal; Flögel, Sascha; Jentzen, Anna; Gerdes, Axel

    2013-12-01

    Past river run-off is an important measure for the continental hydrological cycle and the assessment of freshwater input into the ocean. However, paleosalinity reconstructions applying different proxies in parallel often show offsets between the respective methods. Here, we compare the established foraminiferal Ba/Ca and δOWATER18 salinity proxies for their capability to record the highly seasonal Orinoco freshwater plume in the eastern Caribbean. For this purpose we obtained a data set comprising Ba/Ca and δOWATER18 determined on multiple species of planktonic foraminifera from core tops distributed around the Orinoco River mouth. Our findings indicate that interpretations based on either proxy could lead to different conclusions. In particular, Ba/Ca and δOWATER18 diverge in their spatial distribution due to different governing factors. Apparently, the Orinoco freshwater plume is best tracked by Ba/Ca ratios of G. ruber (pink and sensu lato morphotypes), while δOWATER18 based on the same species is more related to the local precipitation-evaporation balance overprinting the riverine freshwater contribution. Other shallow dwelling species (G. sacculifer, O. universa) show a muted response to the freshwater discharge, most likely due to their ecological and habitat preferences. Extremely high Ba/Ca ratios recorded by G. ruber are attributed to Ba2+-desorption from suspended matter derived from the Orinoco. Samples taken most proximal to the freshwater source do not show pronounced Ba/Ca or δOWATER18 anomalies. Here, the suspension loaded freshwater lid developing during maximum discharge suppresses foraminiferal populations. Both proxies are therefore biased towards dry season conditions at these sites, when surface salinity is only minimally reduced.

  5. Increased Eu²⁺ content and codoping Mn²⁺ induced tunable full-color emitting phosphor Ba(1.55)Ca(0.45)SiO₄:Eu²⁺,Mn²⁺.

    PubMed

    Miao, Shihai; Xia, Zhiguo; Zhang, Jie; Liu, Quanlin

    2014-10-01

    We demonstrated that a new intermediate composition of Ba(1.55)Ca(0.45)SiO4 between the orthosilicates Ca2SiO4 and Ba2SiO4 yields the best phosphor hosts, and interesting luminescence properties can be found from the Eu(2+) singly doped and/or Eu(2+)/Mn(2+) codoped Ba(1.55)Ca(0.45)SiO4 phosphors. The phosphors can be excited by near-ultraviolet (nUV) light at wavelengths ranging from 200 to 450 nm matching well with the nUV light-emitting diode (LED) chips. As a result of fine-tuning the activators of different Eu(2+) content and Eu(2+)/Mn(2+) couples with different ratios, tunable full-color emission under UV light excitation can be realized by combining the blue emission (460 nm) and green emission (520 nm) originating from Eu(2+) with the red emission (595 nm) from Mn(2+) in the Ba(1.55)Ca(0.45)SiO4 host lattice. Energy-transfer efficiency between Eu(2+) and Mn(2+) increases and tunable emission can be obtained with increasing Mn(2+) doping content. These results indicate that the Ba(1.55)Ca(0.45)SiO4:Eu(2+),Mn(2+) phosphor will have potential use in nUV chip pumped white LED devices. PMID:25254295

  6. Network topology for the formation of solvated electrons in binary CaO–Al2O3 composition glasses

    PubMed Central

    Akola, Jaakko; Kohara, Shinji; Ohara, Koji; Fujiwara, Akihiko; Watanabe, Yasuhiro; Masuno, Atsunobu; Usuki, Takeshi; Kubo, Takashi; Nakahira, Atsushi; Nitta, Kiyofumi; Uruga, Tomoya; Weber, J. K. Richard; Benmore, Chris J.

    2013-01-01

    Glass formation in the CaO–Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO–Al2O3 glasses using combined density functional theory–reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O–Ca and O–Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al–O is stronger than that of Ca–O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71–74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass. PMID:23723350

  7. Anomalous vortex melting line in the two-component superconductor (Cu,C)Ba2Ca3Cu4O10+δ

    NASA Astrophysics Data System (ADS)

    Crisan, A.; Tanaka, Y.; Iyo, A.; Cosereanu, L.; Tokiwa, K.; Watanabe, T.

    2006-11-01

    Using the on-set of third-harmonic susceptibility we have measured vortex melting lines of high-pressure synthesized (Cu0.6C0.4)Ba2Ca3Cu4Oy [(Cu,C):1234] and (Cu0.5C0.5)Ba2Ca2Cu3Oy [(Cu,C):1223] with preferentially oriented crystallites and having various carrier concentrations. Vortex melting lines of all (Cu,C):1223 samples and of optimum-doped (Cu,C):1234 were very well described by the commonly accepted theory of melting lines within the two-fluid model. Overdoped (Cu,C):1234 proved to have an anomalous melting line, that was phenomenologically explained by the rather special gaps evolution, that is the significant opening of a second superconducting gap due to CuO2 outer planes at a temperature lower than the critical one, where the first superconducting gap due to inner planes opens. The experimental melting lines of overdoped (Cu,C):1234 were modelled theoretically by assuming an empirical formula for the temperature dependence of anisotropy factor.

  8. Structural studies of the rhombohedral and orthorhombic monouranates: CaUO4, α-SrUO4, β-SrUO4 and BaUO4

    NASA Astrophysics Data System (ADS)

    Murphy, Gabriel; Kennedy, Brendan J.; Johannessen, Bernt; Kimpton, Justin A.; Avdeev, Maxim; Griffith, Christopher S.; Thorogood, Gordon J.; Zhang, Zhaoming

    2016-05-01

    The structures of some AUO4 (A=Ca, Sr, or Ba) oxides have been determined using a combination of neutron and synchrotron X-ray diffraction, supported by X-ray absorption spectroscopic measurements at the U L3-edge. The smaller Ca cation favours a rhombohedral AUO4 structure with 8-coordinate UO8 moieties whilst an orthorhombic structure based on UO6 groups is found for BaUO4. Both the rhombohedral and orthorhombic structures can be stabilised for SrUO4. The structural studies suggest that the bonding requirements of the A site cation play a significant role in determining which structure is favoured. In the rhombohedral structure, Bond Valence Sums demonstrate the A site is invariably overbonded, which, in the case of rhombohedral α-SrUO4, is compensated for by the formation of vacancies in the oxygen sub-lattice. The uranium cation, with its flexible oxidation state, is able to accommodate this by inducing vacancies along its equatorial coordination site as demonstrated by neutron powder diffraction.

  9. Synthesis, spectroscopic characterization, thermal analysis and electrical conductivity studies of Mg(II), Ca(II), Sr(II) and Ba(II) vitamin B2 complexes

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; Moussa, Mohamed A. A.; Mohamed, Soha F.

    2011-05-01

    Riboflavin (RF) complexes of Mg(II), Ca(II), Sr(II) and Ba(II) were successfully synthesized. Structures of metal complexes obtained were confirmed and characterized by elemental analysis, molar conductance, and infrared spectra. DC electrical conductivity measurements indicated that the alkaline earth metal (II) complexes of RF ligand are non-electrolytes. Elemental analysis of chelates suggest that the metal(II) ligand ratio is 1:2 with structure formula as [M(RF) 2( X) 2]· nH 2O. Infrared assignments clearly show that RF ligand coordinated as a bidentate feature through azomethine nitrogen of pyrazine ring and C dbnd O of pyrimidine-2,4-dione. Thermal analyses of Mg(II), Ca(II), Sr(II) and Ba(II) complexes were investigated using (TG/DSC) under atmospheric nitrogen between 30 and 800 °C. The surface morphology of the complexes was studied by SEM. The electrical conductivities of RF and its metal complexes were also measured with DC electrical conductivity in the temperature range from room to 483 K.

  10. Structural and optical analysis on europium doped AZrO3 (A=Ba, Ca, Sr) phosphor for display devices application

    NASA Astrophysics Data System (ADS)

    Dubey, Vikas; Tiwari, Neha

    2016-05-01

    Behavior displayed by europium doped AZrO3 phosphor which was synthesized by solid state reaction method. For synthesis of BaZrO3, SrZrO3 and CaZrO3 phosphor with fixed concentration of europium ion was calcination at 1000°C and sintered at 1300°C following intermediate grinding. Synthesized sample was characterized by X-ray diffraction analysis and crystallite sized was calculated by Scherer's formula. From PL spectra of prepared phosphors shows intense emission centred at 612nm (red emission) with high intensity for SrZrO3:Eu3+. For europium doped BaZrO3 and CaZrO3 (613nm) phosphor shows less intense PL spectra as compared to SrZrO3:Eu3+. The strong emission peak of AZrO3:Eu3+ phosphor is due to forced electric dipole transition of 5D0 to 7F2 centered at 612 and 613nm. It is characteristic red emission for europium ion. The excitation spectra of AZrO3:Eu3+ phosphor mainly consists of the charge transfer and (CTB) of Eu3+ located in 200-350 nm centred at 254nm. The present phosphors can act as single host for red light emission in display devices. The CIE coordinates were calculated by Spectrophotometric method using the spectral energy distribution of the AZrO3:Eu3+ sample.

  11. Spectroscopy of laser properties of Nd(3+)-doped CaF2, SrF2, and BaF2

    NASA Astrophysics Data System (ADS)

    Payne, Stephen A.; Caird, John A.; Chase, L. L.; Smith, L. K.; Nielsen, N. D.; Krupke, William F.

    1990-03-01

    The optical properties of Nd(3+) in CaF2, SrF2, and BaF2 were investigated in order to determine if these materials are useful as laser-pumped amplifier media. The CaF2:Nd crystal was found to not be useful because the impurities tend to cluster at very low concentration, leading to the formation of nonluminescent centers. On the other hand, the Nd(3+) centers in BaF2 exhibit unacceptably low transition strengths. SrF2:Nd appears to have adequate absorption strength, and, in addition, to have a remarkably long emission lifetime of 1280 microns. A maximum doping of 0.20 atomic percent Nd(3+) can be tolerated in SrF2 without the occurrence of detrimental clustering. The peak emission cross section of SrF2:Nd is 1.7 x 10(exp -20) sq cm at 1036.5 nm. Direct measurement of the gain spectrum of SrF2:Nd(3+) reveals the presence of the F-4(sub 3/2) yields G-2(sub 9/2) excited state absorption lines, although the impact on the emission cross section is minor.

  12. Nanoscale polarisation switching and leakage currents in (Ba0.955Ca0.045)(Zr0.17Ti0.83)O3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Sreenivas Puli, Venkata; Pradhan, Dhiren K.; Adireddy, Shiva; Martínez, R.; Silwal, Punam; Scott, J. F.; Ramana, C. V.; Chrisey, Douglas B.; Katiyar, Ram S.

    2015-09-01

    This paper investigates the crystal structure, ferroelectric, temperature-dependent leakage current conduction mechanism and the piezoresponse force microscopy (PFM) behaviours of (Ba0.955Ca0.045) (Zr0.17Ti0.83)O3-BZT-BCT (x=0.15 ) films at the vicinity of the morphotropic phase boundary (MPB) of the [(1  -  x) BaZr0.20Ti0.80O3-xBa0.70Ca0.30TiO3] (x=0.50 ) composition. Epitaxial BZT-BCT thin films were grown on conductive La0.5Sr0.5CoO3 (LSCO) layers coated onto MgO (1 0 0) single-crystal substrates by pulsed laser deposition (PLD). High resolution x-ray diffraction (HR-XRD) reciprocal space maps (RSMs) confirmed the epitaxy with in-plane tetragonal symmetry (c  <  a), and Raman spectra also revealed a tetragonal perovskite crystalline lattice structure. Polarisation studies demonstrate that BZT-BCT films exhibit a high saturation polarisation of 148 µC cm-2 and a high recoverable (discharged) energy-storage density of 39.11 J cm-3 at 2.08 MV cm-1. Temperature-dependent P-E hysteresis loops resulted in a decrease in polarisation. Temperature-dependent leakage current behaviour was obtained and possible conduction mechanism is discussed. PPFM images revealed switchable ferroelectric piezoelectric contrasts after the application of a  ±9 V dc voltage on the conductive tip of the piezoresponse force microscope.

  13. Interfacial Reactions Between BaAl2Si2O8 and Molten Al Alloy at 1423 K and 1523 K (1150 °C and 1250 °C)

    NASA Astrophysics Data System (ADS)

    Adabifiroozjaei, E.; Koshy, P.; Pardehkhorram, R.; Rastkerdar, E.; Hart, J.; Sorrell, C. C.

    2016-06-01

    This work investigates the interfacial interactions of Al7075 alloy with BaAl2Si2O8 at high temperatures [1423 K and 1523 K (1150 °C and 1250 °C)]. X-ray diffraction, electron probe microanalysis, and scanning electron microscopy coupled with energy dispersive spectroscopy were used to identify the mineralogical and microstructural changes at the interfaces. The vaporization, migration, and subsequent oxidation of alloying constituents (Mg and Zn) in contact with BaAl2Si2O8 caused intense interfacial phase transformations, forming spinel solid solution, magnesia solid solution, celsian-based solid solution, and barium magnesium silicate solid solution. The driving force for these phase transformations at the reaction front is the interdiffusion processes between Al (or Mg/Zn)-Si and Mg (or Zn)-Ba that occurs owing to the relative elemental gradients. The rate-limiting step of corrosion kinetics was identified to be Ba substitution in the MgO structure. The corrosion mechanism (extensive phase transformation of Ba-celsian by interdiffusion processes) at high temperatures was found to be different from that observed at lower temperatures [1123 K (850 °C)].

  14. CO₂ sorbents with scaffold-like Ca-Al layered double hydroxides as precursors for CO₂ capture at high temperatures.

    PubMed

    Chang, Po-Hsueh; Lee, Tai-Jung; Chang, Yen-Po; Chen, San-Yuan

    2013-06-01

    A highly stable high-temperature CO₂ sorbent consisting of scaffold-like Ca-rich oxides (Ca-Al-O) with rapid absorption kinetics and a high capacity is described. The Ca-rich oxides were prepared by annealing Ca-Al-NO₃ layered double hydroxide (LDH) precursors through a sol-gel process with Al(O(i)P)₃ and Ca(NO₃)₂ with Ca(2+)/Al(3+) ratios of 1:1, 2:1, 4:1, and 7:1. XRD indicated that only LDH powders were formed for Ca(2+)/Al(3+) ratios of 2:1. However, both LDH and Ca(OH)₂ phases were produced at higher ratios. Both TEM and SEM observations indicated that the Ca-Al-NO₃ LDHs displayed a scaffold-like porous structure morphology rather than platelet-like particles. Upon annealing at 600 °C, a highly stable porous network structure of the CaO-based Ca-Al-O mixed oxide (CAMO), composed of CaO and Ca₁₂Al₁₄O₃₃, was still present. The CAMO exhibited high specific surface areas (up to 191 m(2)g(-1)) and a pore size distribution of 3-6 nm, which allowed rapid diffusion of CO₂ into the interior of the material, inducing fast carbonation/calcination and enhancing the sintering-resistant nature over multiple carbonation/calcination cycles for CO₂ absorption at 700 °C. Thermogravimetric analysis results indicated that a CO₂ capture capacity of approximately 49 wt% could be obtained with rapid absorption from the porous 7:1 CAMO sorbents by carbonation at 700 °C for 5 min. Also, 94-98% of the initial CO₂ capture capability was retained after 50 cycles of multiple carbonation/calcination tests. Therefore, the CAMO framework is a good isolator for preventing the aggregation of CaO particles, and it is suitable for long-term cyclic operation in high-temperature environments. PMID:23650194

  15. Phase relations for CaAl 2Si 2O 8 (anorthite composition) in the system CaOAl 2O 3SiO 2 at 14 GPa

    NASA Astrophysics Data System (ADS)

    Gautron, L.; Kesson, S. E.; Hibberson, W. O.

    1996-10-01

    Multi-anvil experiments at 14 GPa and 1500°C reveal that CaAl 2Si 2O 8 (anorthite composition) undergoes subsolidus disproportionation into grossular Ca 3Al 2Si 3O 12, stishovite SiO 2 and a calcium aluminosilicate phase of composition CaAl 4Si 2O 11. This last phase (CAS) was first synthesised by Irifune et al. (1994, Earth Planet. Sci. Lett., 126: 351-368) in a continental crust composition, at P, T conditions appropriate for the Transition Zone. In the system CaOAl 2O 3SiO 2, a new three-phase assemblage (grossular + stishovite + CAS) encountered at 14GPa replaces the grossular + stishovite + kyanite assemblage known to be stable at around 10GPa because of an univariant reaction between grossular and kyanite that yields stishovite and CAS. By 1600°C another univariant reaction between grossular and stishovite produces CAS plus liquid. Schreinemakers' analysis suggests that, given Ca,Al-rich lithologies, the CAS phase should be stable at transition-zone pressures.

  16. Magnesium doping on brownmillerite Ca{sub 2}FeAlO{sub 5}

    SciTech Connect

    Malveiro, J.; Ramos, T.; Ferreira, L.P.; Waerenborgh, J.C.

    2007-06-15

    Ca{sub 2}FeAl{sub 1-} {sub x} Mg {sub x} O{sub 5} (x=0, 0.05 and 0.1) compounds adopting the brownmillerite-type structure were prepared by a self-combustion route using two different fuels. Characterisation was performed using X-ray powder diffraction, Moessbauer spectroscopy, magnetisation measurements, chemical analysis, scanning electron microscopy and 4-point dc conductivity measurements. Global results indicate that the solubility limit was reached for x=0.1. An antiferromagnetic behaviour was detected for all studied compositions, with magnetic ordering temperatures of 340 and 290 K for x=0 and 0.05, respectively. Mg doping increases the number of iron cations in tetrahedral sites, which induces magnetisation enhancement at low temperatures through the coupling between octahedral iron cations in different octahedral planes. The compounds exhibit semiconductor behaviour and Mg{sup 2+} doping yields a significant enhancement of the total conductivity, which can be essentially attributed to the presence of Fe{sup 4+} ions. - Graphical abstract: Ca{sub 2}FeAl{sub 1-} {sub x} Mg {sub x} O{sub 5} (x=0, 0.05, 0.1) compounds with the brownmillerite structure were prepared and characterised. The paramagnetic Moessbauer spectra presented were obtained at T=363 K (x=0); T=297 K (x=0.05) and T=353 K (x=0.1)

  17. Tunable full-color emitting BaMg2Al6Si9O30:Eu2+, Tb3+, Mn2+ phosphors based on energy transfer.

    PubMed

    Lü, Wei; Hao, Zhendong; Zhang, Xia; Luo, Yongshi; Wang, Xiaojun; Zhang, Jiahua

    2011-08-15

    A series of single-phase full-color emitting BaMg(2)Al(6)Si(9)O(30):Eu(2+), Tb(3+), Mn(2+) phosphors has been synthesized by solid-state reaction. Energy transfer from Eu(2+) to Tb(3+) and Eu(2+) to Mn(2+) in BaMg(2)Al(6)Si(9)O(30) host matrix is studied by luminescence spectra and energy-transfer efficiency and lifetimes. The wavelength-tunable white light can be realized by coupling the emission bands centered at 450, 542, and 610 nm ascribed to the contribution from Eu(2+) and Tb(3+) and Mn(2+), respectively. By properly tuning the relative composition of Tb(3+)/Mn(2+), chromaticity coordinates of (0.31, 0.30), high color rendering index R(a) = 90, and correlated color temperature (CCT) = 5374 K can be achieved upon excitation of UV light. Thermal quenching properties reveal that BaMg(2)Al(6)Si(9)O(30): Eu(2+), Tb(3+), Mn(2+) exhibits excellent characteristics even better than that of YAG:Ce. Our results indicate our white BaMg(2)Al(6)Si(9)O(30):Eu(2+), Tb(3+), Mn(2+) can serve as a key material for phosphor-converted light-emitting diode and fluorescent lamps. PMID:21766885

  18. New oxyfluoride glass with high fluorine content and laser patterning of nonlinear optical BaAlBO{sub 3}F{sub 2} single crystal line

    SciTech Connect

    Shionozaki, K.; Honma, T.; Komatsu, T.

    2012-11-01

    A new oxyfluoride glass of 50BaF{sub 2}-25Al{sub 2}O{sub 3}-25B{sub 2}O{sub 3} (mol. %) with a large fraction of fluorine, i.e., F/(F + O) = 0.4, was prepared using a conventional melt-quenching method in order to synthesize new glass-ceramics containing nonlinear optical oxyfluoride crystals. The refractive index at 632.8 nm and ultra-violet cutoff wavelength of the glass were 1.564 and {approx}200 nm, respectively. Eu{sup 3+} ions in the glass showed a high quantum yield of 88% in the photoluminescence spectrum in the visible region. BaAlBO{sub 3}F{sub 2} crystals (size: 50-100 nm) showing second harmonic generations were formed through the crystallization of the glass. Lines consisting of BaAlBO{sub 3}F{sub 2} crystals were patterned successfully on the glass surface by laser irradiations (Yb:YVO{sub 4} laser with a wavelength of 1080 nm, laser power of 1.1 W, scanning speed of 8 {mu}m/s). High resolution transmission electron microscope observations combined with a focused ion beam technique indicate that BaAlBO{sub 3}F{sub 2} crystals are highly oriented just like a single crystal. The present study proposes that the new oxyfluoride glass and glass-ceramics prepared have a high potential for optical device applications.

  19. Self-reactivated mesostructured Ca-Al-O composite for enhanced high-temperature CO2 capture and carbonation/calcination cycles performance.

    PubMed

    Chang, Po-Hsueh; Huang, Wei-Chen; Lee, Tai-Jung; Chang, Yen-Po; Chen, San-Yuan

    2015-03-25

    In this study, highly efficient high-temperature CO2 sorbents of calcium aluminate (Ca-Al-O) mesostructured composite were synthesized using presynthesized mesoporous alumina (MA) as a porous matrix to react with calcium nitrate through a microwave-assisted process. Upon annealing at 600 °C, a highly stable mesoporous structure composed of poorly crystalline Ca12Al14O33 phase and the CaO matrix was obtained. The Ca-Al-O mesostructured sorbents with a Ca(2+)/Al(3+) ratio of 5:1 exhibit an enhanced increasing CO2 absorption kinetics in the CO2 capture capacity from 37.2 wt % to 48.3 wt % without apparent degradation with increasing carbonation/calcination cycling up to 50 at 700 °C due to the strong self-reactivation effect of the mesoporous Ca-Al-O microstructure. Remarkable improvements in the CaO-CaCO3 conversion attained from the mesostructured Ca-Al-O composite can be explained using the concept combined with available mesoporous structure and Ca12Al14O33 phase content. However, a high Ca(2+)/Al(3+) =8:1 Ca-Al-O composite causes degradation because the pores become blocked and partial sintering induces CaO agglomeration. PMID:25730384

  20. Sequence of phase transitions induced by chemical composition and high temperature in [Ba2CaWO6](1-x)[Sr2CaWO6]x double perovskite tungsten oxides

    NASA Astrophysics Data System (ADS)

    Mirinioui, F.; Manoun, Bouchaib; Tamraoui, Y.; Lazor, P.

    2015-12-01

    [Ba2CaWO6]1-x[Sr2CaWO6]x (0≤x≤1) materials were synthesized by the high temperature solid state reaction and firing methods, and characterized using techniques of X-ray diffraction and Raman spectroscopy. The crystal structures were determined by Rietveld refinements on the laboratory X-ray powder diffraction data. As a function of composition, upon increasing the strontium content, the samples exhibit a sequence of three phase transitions: from cubic (Fm 3 ̅m) to tetragonal (I4/m) to monoclinic structural phases (I2/m, P21/n). These transitions have been confirmed by Raman studies Fm 3 bar m x = 0 → I 4 / m 0.1 ≤ x ≤ 0.2 → I 2 / m 0.3 ≤ x ≤ 0.5 → P21 / n 0.6 ≤ x ≤ 1 Furthermore, increasing the temperature for the compositions [Ba2CaWO6]1-x[Sr2CaWO6]x (0.1≤x<1), manifests the P21/n to I2/m, the I2/m to I4/m and the I4/m to Fm 3 ̅m phase transitions. For the compositions (0.1≤x≤0.2) the tetragonal to cubic phase transition is well illustrated. For the room temperature I2/m monoclinic compositions, two phase transitions were observed for all the compositions with x ranging from 0.3 to 0.5: from the monoclinic (I2/m) to tetragonal (I4/m), and from I4/m to Fm 3 ̅m structures. Finally, for the room temperature P21/n monoclinic compositions, only two phase transitions are observed in the temperature range probed by Raman spectroscopy, the temperature was not high enough to reach the tetragonal-to-cubic phase transition.

  1. Atomistic and Ab initio modeling of CaAl2O4 high-pressure polymorphs under Earth's mantle conditions

    NASA Astrophysics Data System (ADS)

    Eremin, N. N.; Grechanovsky, A. E.; Marchenko, E. I.

    2016-05-01

    Semi-empirical and ab initio theoretical investigation of crystal structure geometry, interatomic distances, phase densities and elastic properties for some CaAl2O4 phases under pressures up to 200 GPa was performed. Two independent simulation methods predicted the appearance of a still unknown super-dense CaAl2O4 modification. In this structure, the Al coordination polyhedron might be described as distorted one with seven vertices. Ca atoms were situated inside polyhedra with ten vertices and Ca-O distances from 1.96 to 2.49 Å. It became the densest modification under pressures of 170 GPa (density functional theory prediction) or 150 GPa (semi-empirical prediction). Both approaches indicated that this super-dense CaAl2O4 modification with a "stuffed α-PbO2" type structure could be a probable candidate for mutual accumulation of Ca and Al in the lower mantle. The existence of this phase can be verified experimentally using high pressure techniques.

  2. Petrography and classification of Ca, Al-rich and olivine-rich inclusions in the Allende CV3 chondrite

    NASA Technical Reports Server (NTRS)

    Kormacki, A. S.; Wood, J. A.

    1984-01-01

    The results of a detailed, systematic petrographic survey of Ca, Al-rich and olivine-rich inclusions in the Allende CV3 chondrite are reported, and a new classification system based on clearly defined and readily applied petrographic criteria is presented. Most Allende inclusions are aggregates containing one or more of three distinct constituents: (1) rimmed concentric objects enriched in Al- and Ti-rich oxide minerals and various amounts of Ca-rich silicates; (2) porous, 'fine-grained' chaotic material enriched in Ca-rich silicates, especially clinopyroxenes and garnets; and (3) porous, 'fine-grained', mafic inclusion matrix, enriched in olivine, pyroxene, and feldspathoids. Two texturally distinct varieties of inclusions consist primarily of inclusion matrix: unrimmed olivine aggregates and rimmed olivine aggregates. Ca, Al-rich inclusions are classified on the basis of the size and abundance of their constituent concentric objects. Some fundamental relationships among Allende inclusions that previusly have not been emphasized are discussed.

  3. Significant increase of Curie temperature and large piezoelectric coefficient in Ba(Ti0.80Zr0.20)O3-0.5(Ba0.70Ca0.30)TiO3 nanofibers

    NASA Astrophysics Data System (ADS)

    Fu, Bi; Yang, Yaodong; Gao, Kun; Wang, Yaping

    2015-07-01

    Ba(Ti0.80Zr0.20)O3-0.5(Ba0.7Ca0.3)TiO3 (abbreviated as BTZ-0.5BCT) is a piezoelectric ceramic with a high piezoelectric coefficient d33 (˜620 pC N-1) and has been regarded as one of the most promising candidates to replace PZT-based materials (200-710 pC N-1). However, its Curie temperature TC is relatively low (93 °C) limiting its application. In this letter, we found a temperature dependent Raman spectrum in BTZ-0.5BCT nanofibers (NFs), demonstrating a diffused tetragonal-to-cubic phase transition at 300 °C. This means that the TC of the NFs is nearly 207 °C higher than that of the normal bulk material. The increased TC is considered to be associated with the size effect of BTZ-0.5BCT nanoceramic subunits and the nanoporous nature of the fiber, resulting in discontinuous physical properties. The variation of the ferro/piezoelectricity over the fiber surface is attributed to the polycrystalline structure. The d33 (173.32 pm V-1) is improved in terms of the decreased Q factor result in an increase in d33 of 236.54 pm V-1 after polarization. With a high TC and a very large d33, BTZ-0.5BCT NFs are capable of providing electromechanical behavior used in moderate temperatures.

  4. Lead-free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 nanowires for energy harvesting.

    PubMed

    Zhou, Zhi; Bowland, Christopher C; Malakooti, Mohammad H; Tang, Haixiong; Sodano, Henry A

    2016-03-01

    Lead-free piezoelectric nanowires (NWs) show strong potential in sensing and energy harvesting applications due to their flexibility and ability to convert mechanical energy to electric energy. Currently, most lead-free piezoelectric NWs are produced through low yield synthesis methods and result in low electromechanical coupling, which limit their efficiency as energy harvesters. In order to alleviate these issues, a scalable method is developed to synthesize perovskite type 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-BCT) NWs with high piezoelectric coupling coefficient. The piezoelectric coupling coefficient of the BZT-BCT NWs is measured by a refined piezoresponse force microscopy (PFM) testing method and shows the highest reported coupling coefficient for lead-free piezoelectric nanowires of 90 ± 5 pm V(-1). Flexible nanocomposites utilizing dispersed BZT-BCT NWs are fabricated to demonstrate an energy harvesting application with an open circuit voltage of up to 6.25 V and a power density of up to 2.25 μW cm(-3). The high electromechanical coupling coefficient and high power density demonstrated with these lead-free NWs produced via a scalable synthesis method shows the potential for high performance NW-based devices. PMID:26868967

  5. Resistive switching in ferroelectric lead-free 0.5Ba (Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Silva, J. P. B.; Kamakshi, K.; Sekhar, K. C.; Queirós, E. C.; Agostinho Moreira, J.; Almeida, A.; Pereira, M.; Tavares, P. B.; Gomes, M. J. M.

    2016-08-01

    In this work, resistive switching in pulsed laser deposited ferroelectric lead-free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (0.5BZT–0.5BCT) thin films was investigated. This study reveals that films grown at 5.5 J cm‑2 have shown optimal ferroelectric and resistive switching response, which are attributed to high tetragonality, large grain size and less defect concentration. Au/0.5BZT–0.5BCT/Pt capacitors show the electroforming free resistive switching that is explained based on the polarization modulation of the Schottky-like barrier at the 0.5BZT–0.5BCT/Au interface. The polarization induced resistive switching is evidenced by its disappearance as the temperature increases to the Curie temperature. The capacitor based on film grown at 5.5 J cm‑2 shows resistive switching characterized by high switching ratio of 106 at a low set/reset voltage  ≈1 V, and by a stable memory window, which are highly required for memory applications.

  6. Lead-free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 nanowires for energy harvesting

    NASA Astrophysics Data System (ADS)

    Zhou, Zhi; Bowland, Christopher C.; Malakooti, Mohammad H.; Tang, Haixiong; Sodano, Henry A.

    2016-02-01

    Lead-free piezoelectric nanowires (NWs) show strong potential in sensing and energy harvesting applications due to their flexibility and ability to convert mechanical energy to electric energy. Currently, most lead-free piezoelectric NWs are produced through low yield synthesis methods and result in low electromechanical coupling, which limit their efficiency as energy harvesters. In order to alleviate these issues, a scalable method is developed to synthesize perovskite type 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-BCT) NWs with high piezoelectric coupling coefficient. The piezoelectric coupling coefficient of the BZT-BCT NWs is measured by a refined piezoresponse force microscopy (PFM) testing method and shows the highest reported coupling coefficient for lead-free piezoelectric nanowires of 90 +/- 5 pm V-1. Flexible nanocomposites utilizing dispersed BZT-BCT NWs are fabricated to demonstrate an energy harvesting application with an open circuit voltage of up to 6.25 V and a power density of up to 2.25 μW cm-3. The high electromechanical coupling coefficient and high power density demonstrated with these lead-free NWs produced via a scalable synthesis method shows the potential for high performance NW-based devices.

  7. Water-Induced Morphology Changes in BaO/gamma-Al2O3 NOx Storage Materials: an FTIR, TPD, and Time-Resolved Synchrotron XRD Study

    SciTech Connect

    Szanyi,J.; Kwak, J.; Kim, D.; Wang, X.; Chimentao, R.; Hanson, J.; Epling, W.; Peden, C.

    2007-01-01

    The effect of water on the morphology of BaO/Al{sub 2}O{sub 3}-based NO{sub x} storage materials was investigated using Fourier transform infrared spectroscopy, temperature programmed desorption, and time-resolved synchrotron X-ray diffraction techniques. The results of this multispectroscopy study reveal that in the presence of water surface Ba-nitrates convert to bulk nitrates and water facilitates the formation of large Ba(NO{sub 3}){sub 2} particles. The conversion of surface to bulk Ba-nitrates is completely reversible (i.e., after the removal of water from the storage material a significant fraction of the bulk nitrates reconverts to surface nitrates). NO{sub 2} exposure of a H{sub 2}O-containing (wet) BaO/Al{sub 2}O{sub 3} sample results in the formation of nitrites and bulk nitrates exclusively (i.e., no surface nitrates form). After further exposure to NO{sub 2}, the nitrites completely convert to bulk nitrates. The amount of NO{sub x} taken up by the storage material, however, is essentially unaffected by the presence of water regardless of whether the water was dosed prior to or after NO{sub 2} exposure. On the basis of the results of this study, we are now able to explain most of the observations reported in the literature on the effect of water on NO{sub x} uptake on similar storage materials.

  8. Superconducting La 1.5- xBa 1.5 + x-yCa yCu 3O z solid solutions II. Oxygen content and crystal structure

    NASA Astrophysics Data System (ADS)

    Skakle, J. M. S.; West, A. R.

    1994-07-01

    The La 1.5- xBa 1.5 + x-yCa yCu 3O z solid solutions have properties that vary from semiconducting ( x= y=0) to super conducting with Tc=78 K ( x= y=0.5). The latter are of special interest since they are tetragonal. Rietveld refinement of powder X-ray diffraction data confirms that Ca substitutes onto the La sites, with concomitant displacement of La onto the Ba sites and that the solid solutions are based on the 336 formula, La 1.55Ba 1.5Cu 3O z rather than on 123, LaBa 2Cu 3O z. The oxygen con tents have been determined by H 2 reduction. With increasing x, the oxygen content is unchanged as Ba substitutes for La and therefore charge compensation is achieved by hole creation. With substitution of Ba by Ca, i.e. increasing y, additional oxygen is incorporated into the structure and, again, holes are created to preserve charge balance. A good correlation between TC and average Cu valence is found.

  9. Novel Magnetic and Charge Orders in Dimer-Chain Iridate Ba5AlIr2O11

    NASA Astrophysics Data System (ADS)

    Ye, Feng; Terzic, J.; Wang, J. C.; Song, W. H.; Yuan, S. J.; Aswartham, S.; Cao, G.

    2015-03-01

    We report a novel magnetic state coexisting with a charge ordering state in a dimer-chain system Ba5AlIr2O11. This newly synthesized single-crystal iridate features both tetravalent Ir4+ and pentavalent Ir5+ ions in each of dimers that are only linked via AlO4-tetrahedra along the b-axis. Despite the evident one-dimensional characteristic, the dimer-chains undergo an unexpected long-rang order at TM = 4.5 K with a large magnetic anisotropy. The magnetic transition is unusually resilient to magnetic field up to 14 T but more susceptible to even modest hydrostatic pressure up to 10 kbar. Furthermore, a subtle structural change discerned at TS = 200 K marks a charge ordering that accompanies a huge enhancement in the dielectric constant and changes in the electrical resistivity. It is evident that the strong SOC imposes a j =1/2 (Ir4+) and singlet j =0 (Ir5+) states in each dimer, which critically hinges on the orbital and lattice degrees of freedom. This work was supported by NSF via Grant DMR 1265162.

  10. Crystal structure and luminescence properties of a novel red-emitting phosphor BaAlBO{sub 3}F{sub 2}:Eu{sup 3+}

    SciTech Connect

    Chen, Wanping Zhou, Ahong; Liu, Yan; Dai, Xiaoyan; Yang, Xin

    2014-12-15

    A series of novel red-emitting phosphors BaAlBO{sub 3}F{sub 2}:xEu{sup 3+} (0.001≤x≤0.08) were first synthesized via a high temperature solid-state reaction. X-ray diffraction and photoluminescence spectroscopy were used to characterize the crystal structure and photoluminescence properties of the phosphor, respectively. The phosphor can be effectively excited with a 395 nm light, and shows a dominant {sup 5}D{sub 0}−{sup 7}F{sub 2} emission with chromatic coordination of 0.628 and 0.372. The optimal doping concentration is about 0.04. Rietveld refinement results and the luminescence behavior of Eu{sup 3+} indicate that the Eu{sup 3+} ion occupies a C{sub 3} symmetry site, and the host BaAlBO{sub 3}F{sub 2} has a hexagonal structure with P-6 space group. In addition, the phosphor could be a potential candidate as red-emitting phosphor for application in white light-emitting diode. - Graphical abstract: The luminescence behavior and Rietveld refinement of BaAlBO{sub 3}F{sub 2}:Eu{sup 3+} indicate that the red-emitting phosphor has potential application in white LED and the host has a hexagonal structure with P-6 space group. - Highlights: • A novel red-emitting phosphor BaAlBO{sub 3}F{sub 2}:Eu{sup 3+} is first synthesized. • The crystal structure of BaAlBO{sub 3}F{sub 2} is confirmed. • The phosphor shows potential application in white LED.

  11. Alkaline Earth Metal Zirconate Perovskites MZrO3 (M=Ba(2+), Sr(2+), Ca(2+)) Derived from Molecular Precursors and Doped with Eu(3+) Ions.

    PubMed

    Drąg-Jarząbek, Anna; John, Łukasz; Petrus, Rafał; Kosińska-Klähn, Magdalena; Sobota, Piotr

    2016-03-24

    The effect of alkaline earth metal alkoxides on the protonation of zirconocene dichloride was investigated. This approach enabled the design of compounds with preset molecular structures for generating high-purity binary metal oxide perovskites MZrO3 (M=Ba(2+), Sr(2+), Ca(2+)). Single-source molecular precursors [Ba4 Zr2 (μ6 -O)(μ3 ,η(2)-OR)8 (OR)2(η(2) -HOR)2 (HOR)2 Cl4], [Sr4 Zr2 (μ6 -O)(μ3 ,η(2)-OR)8 (OR)2 (HOR)4 Cl4], [Ca4 Zr2 (μ6-O)(μ3 ,η(2)-OR)8 (OR)2 Cl4], and [Ca6 Zr2 (μ2 ,η(2)-OR)12 (μ-Cl)2 (η(2) -HOR)4 Cl6 ]⋅8 CH2 Cl2 were prepared via elimination of the cyclopentadienyl ring from Cp2 ZrCl2 as CpH in the presence of M(OR)2 and alcohol ROH (ROH=CH3OCH2 CH2OH) as a source of protons. The resulting complexes were characterized by elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray diffraction. The compounds were then thermally decomposed to MCl2 /MZrO3 mixtures. Leaching of MCl2 from the raw powder with deionized water produced highly pure perovskite-like oxide particles of 40-80 nm in size. Luminescence studies on Eu(3+)-doped MZrO3 revealed that the perovskites are attractive host lattices for potential applications in display technology. PMID:26891039

  12. Temperature driven nano-domain evolution in lead-free Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}-50(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} piezoceramics

    SciTech Connect

    Lu, Shengbo Xu, Zhengkui; Su, Shi; Zuo, Ruzhong

    2014-07-21

    Hierarchical micro- and nanoscale domain structures in Pb-free Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}-50(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} piezoceramics were investigated by transmission electron microscopy. In situ heating and cooling studies of domain structure evolution reveal an irreversible domain transformation from a wedge-shaped rhombohedral nanodomain structure to a lamellar tetragonal domain structure, which could be associated with strong piezoelectricity in Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}-50(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} piezoceramics.

  13. Major soil element (Ca, Mg, K, Na, Al, Fe) distribution along the Qinghai-Tibet Railway

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Zhang, Y.; Zhang, H.; Ding, M.; Lin, X.

    2011-12-01

    The Tibetan Plateau (TP), which has been called the third polar region, is the highest plateau in the world. There are a series of special soils present in the TP, which are extremely important in soil sciences for their particularities. Soil chemical composition is one of the necessary indices of soil characteristics. The major element content of the soil, such as Ca, Mg, K, Na, not only can affect the soil pH value and soil fertility but also are the main drivers of soil geochemical processes. It is helpful to understand the TP environmental characteristics, to study the major soil element content.The Qinghai-Tibet Railway (QTR) is the highest-elevation and the longest highland railway on earth. There are nearly all types of TP soil along the QTR. Most of the areas along the QTR are in fairly pristine condition. This offers a good platform to study the natural environmental characteristics of the soil. This study selected 240 soil samples from 28 sample areas along the Qinghai-Tibet Railway, and the aluminum, iron, calcium, sodium, potassium and magnesium content in the soil were measured with ICP-AES. The results indicated: (1) Compared with the national soil background values, the Ca content in soil was higher along the QTR and Al was lower; but the Fe, Mg, K and Na contents were similar. (2) Along the whole QTR, the soil Al, Fe and Mg content showed a decreasing trend from Xining to Lhasa, the changes in K and Na values were relatively complex, and the distribution of Ca could be divided three sections. (3) The soil element contents varied with different soil types and parent materials. Most of the six elements content was minimum in soil, which derived from debris materials for ice and water, and the elements content was maximum in soil, which evolved from debris for flood, and the content of soil Ca developed from debris for lake was maximum. The amount of each element present in the Hapli-Cryic Aridosols and Calci-Cryic Aridosols was relatively higher than

  14. Refinement of Eutectic Si in High Purity Al-5Si Alloys with Combined Ca and P Additions

    NASA Astrophysics Data System (ADS)

    Ludwig, Thomas Hartmut; Li, Jiehua; Schaffer, Paul Louis; Schumacher, Peter; Arnberg, Lars

    2015-01-01

    The effects of combined additions of Ca and P on the eutectic Si in a series of high purity Al-5 wt pct Si alloys have been investigated with the entrained droplet technique and complementary sets of conventional castings. Differential scanning calorimetry (DSC) and thermal analysis were used to investigate the eutectic droplet undercooling and the recalescence undercooling, respectively. Optical microscopy, SEM, EPMA, and TEM were employed to characterize the resultant microstructures. It was found that 250 ppm Ca addition to Al-5Si wt pct alloys with higher P contents leads to a significant increase of the eutectic droplet undercooling. For low or moderate cooling rates, the TEM results underline that Ca additions do not promote Si twinning. Thus, a higher twin density cannot be expected in Ca containing Al-Si alloys after, e.g., sand casting. Consequently, a refinement of the eutectic Si from coarse flake-like to fine plate-like structure, rather than a modification of the eutectic Si to a fibrous morphology, was achieved. This strongly indicates that the main purpose of Ca additions is to counteract the coarsening effect of the eutectic Si imposed by higher P concentrations. Significant multiple Si twinning was observed in melt-spun condition; however, this can be attributed to the higher cooling rate. After DSC heating (slow cooling), most of Si twins disappeared. Thus, the well-accepted impurity-induced twinning mechanism may be not valid in the case of Ca addition. The possible refinement mechanisms were discussed in terms of nucleation and growth of eutectic Si. We propose that the pre-eutectic Al2Si2Ca phase and preferential formation of Ca3P2 deactivate impurity particles, most likely AlP, poisoning the nucleation sites for eutectic Si.

  15. A simple method for the normal pressure synthesis of Cu 1- xTl xBa 2Ca 3Cu 4O 12- δ superconductor

    NASA Astrophysics Data System (ADS)

    Khan, Nawazish A.; Khurram, A. A.; Javed, Asim

    2005-05-01

    A very simple method for the direct synthesis of Cu 1- xTl xBa 2Ca 3Cu 4O 12- δ (Cu 1- xTl x-1234) superconductor is reported. A predominant single phase Cu 1- xTl x-1234 is achieved by the solid state reaction of Ba(NO 3) 2, CaCO 3 and Cu(CN) at first stage and with appropriate amount of Tl 2O 3 at the second stage. These materials were fired twice for 24 h at 880 °C followed by intermediate grinding. Thoroughly ground and fired material was mixed with Tl 2O 3 in appropriate amount and pellets were made by applying a pressure of 5 tons. Pellets were wrapped in an aluminum foil and sintered at 880 °C for 3-30 min. A predominantly single phase of Cu 1- xTl xBa 2Ca 3Cu 4O 12- δ was achieved with an inclusion of unknown impurity. The resistivity measurements established the onset temperature of superconductivity [ Tc (onset)] at 120 K and zero resistivity critical temperature [ Tc( R = 0)] at 106 K. Bulk superconductivity was also confirmed by ac-magnetic susceptibility measurements. The surface of the samples was analyzed by electron microscopy and their composition by energy dispersive X-ray spectroscopy (EDX) measurements. For optimizing the carriers in the final compound, post-annealing experiments were carried out in the flowing nitrogen atmosphere. For the study of the doping mechanisms, in the post-annealed samples, the phonon modes of Cu 1- xTl x-1234 were investigated by infrared absorption measurements. The absorption mode of O δ [O3] atoms decreased in intensity after the post-annealing and the apical oxygen modes were softened to lower wave numbers. The softening of these phonon modes suggested the reduction of thallium from Tl 3+ to Tl 1+; which resulted in an increase of [ Tc( R = 0)] of the material.

  16. Structural, Thermal and Electrical Study of Multiferroic BiFeO3 Ceramic with Al3+ and Ba2+ Co-substitution

    NASA Astrophysics Data System (ADS)

    Wang, GeMing; Kothari, Deepti; Reddy, V. Raghavendra; Gupta, Ajay

    BiFe1-xAlxO3(x=0.05, 0.1) and BixBa1-xFe0.95Al0.05O3 (x=0.05, 0.07) ceramics were synthesized and their crystal structure, thermal and ferroelectric properties were investigated. X-ray diffraction and Raman data of the ceramics showed all the samples were rhombohedral with small crystal structure distortion. DSC results revealed the evolution of Neel Temperature (TN) by Al and Ba co-doping. The substitution of Al3+ at Fe site changes the TN significantly. Doping effects in terms of crystal structure, electrical property variation are discussed in this paper.

  17. Enhanced photoluminescence of Ca2Al2SiO7:Eu3+ by charge compensation method

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Wang, J.; Zhang, M.; Ding, W.; Su, Q.

    2007-09-01

    The effect of compensator on optical properties of Ca2Al2SiO7:Eu3+ is systematically investigated by the X-ray powder diffraction, photo-luminescence (PL) properties and lifetime. It is obviously observed that the PL intensity of Eu3+ under 394 nm excitation increases in the order of Ca1.86Eu0.14Al2SiO7 (CAS), Ca1.72Na0.14Eu0.14Al2SiO7 (CASNa) and Ca1.86Eu0.14Al2.14Si0.86O7 (CASAl), the intensity of Eu3+ are 100%, 134%, 184%, and the lifetime of Eu3+ are 0.75 ms, 1.28 ms and 1.39 ms, respectively. A charge compensation model is proposed to explain the changes in the emission intensity and lifetime of Eu3+ in Ca2Al2SiO7 with different compensation methods.

  18. Synthesis, structural characterization and properties of SrAl{sub 4−x}Ge{sub x}, BaAl{sub 4−x}Ge{sub x}, and EuAl{sub 4−x}Ge{sub x} (x≈0.3–0.4)—Rare examples of electron-rich phases with the BaAl{sub 4} structure type

    SciTech Connect

    Zhang, Jiliang; Bobev, Svilen

    2013-09-15

    Three solid solutions with the general formula AEAl{sub 4−x}Ge{sub x} (AE=Eu, Sr, Ba; 0.32(1)≤x≤0.41(1)) have been synthesized via the aluminum self-flux method, and their crystal structures have been established from powder and single-crystal X-ray diffraction. They are isotypic and crystallize with the well-known BaAl{sub 4} structure type, adopted by the three AEAl{sub 4} end members. In all structures, Ge substitutes Al only at the 4e Wyckoff site. Results from X-rays photoelectron spectroscopy on EuAl{sub 4−x}Ge{sub x} and EuAl{sub 4} indicate that the interactions between the Eu{sup 2+} cations and the polyanionic framework are enhanced in the Ge-doped structure, despite the slightly elevated Fermi level. Magnetic susceptibility measurements confirm the local moment magnetism, expected for the [Xe]4f{sup 7} electronic configuration of Eu{sup 2+} and suggest strong ferromagnetic interactions at cryogenic temperatures. Resistivity data from single-crystalline samples show differences between the title compounds, implying different bonding characteristics despite the close Debye temperatures. A brief discussion on the observed electron count and homogeneity ranges for AEAl{sub 4−x}Ge{sub x} (AE=Eu, Sr, Ba) is also presented. - Graphical abstract: AEAl{sub 4−x}Ge{sub x} (AE=Eu, Sr, Ba; 0.32(1)≤x≤0.41(1)), three “electron-rich” phases with BaAl{sub 4} structure type have been synthesized and characterized. Display Omitted - Highlights: • Three BaAl{sub 4}-type ternary aluminum germanides have been synthesized with Eu, Sr and Ba. • Eu, Sr and Ba cations have no apparent influence on the solubility of Ge. • The Ge atoms substitute Al on one of two framework sites, thereby strengthening the interactions between the cations and the polyanionic framework.

  19. Hole-doping effect on the Verwey-type transition and magnetoresistivity of Ba(Sm,Ca)Fe 2O 5+ δ

    NASA Astrophysics Data System (ADS)

    Nakamura, J.; Lindén, J.; Yamauchi, H.; Karppinen, M.

    2002-02-01

    Two series of samples of the oxygen-deficient double-perovskite phase, Ba(Sm,Ca)Fe 2O 5+ δ were synthesized employing a sample encapsulation technique that utilizes Fe metal as an oxygen getter. The hole-doping level on the FeO 2 plane was controlled by varying the amount of excess oxygen or the Ca concentration at the Sm site. Earlier it had been found that at room temperature five-coordinated Fe 2+ and Fe 3+ species form pairs by sharing a d electron, leading to the formation of a Fe 2.5+ fluctuating valence state [Phys. Rev. B 60 (1999) 15,251]. At TV, a Verwey-type transition occurred, signifying the charge separation of the Fe 2.5+ fluctuating valence state into high-spin Fe 2+ and Fe 3+. Moreover, related to the Verwey-type transition a negative magnetoresistance peak with a magnitude of a few percent was observed [Appl. Phys. Lett. 77 (2000) 1683]. The position of the peak was found to correspond to the jumps seen in the susceptibility and resistivity vs. temperature curves. For the present samples, it is found that the value of TV is severely decreased upon increasing the Ca concentration, as seen by susceptibility and magnetoresistivity measurements. Introduction of excess oxygen leads to a less severe decrease of the transition temperature. The observed behavior of TV was reproduced by a simple model based on combinatorial-entropy calculations.

  20. Photoluminescence and thermoluminescence studies of CaAl2O4:Dy(3+) phosphor.

    PubMed

    Ziyauddin, Mohammad; Tigga, Shalinta; Brahme, Nameeta; Bisen, D P

    2016-02-01

    Calcium aluminate phosphors activated by Dy(3+) have been prepared by a combustion method at a temperature of 600°C. Photoluminescence (PL) and thermoluminescence (TL) properties of gamma-irradiated Dy-doped calcium aluminate were investigated. The PL spectrum shows a broad peak around 488 nm and 573 nm, under 347 nm excitation. Thermoluminescence studies were performed for different concentrations of Dy. Optimum intensity of photoluminescence was found for 0.02 mol% concentration of Dy. It was found that initially the peak TL intensity increases with increasing concentration of Dy in the CaAl2O4 host, attains a maximum value for 0.05 mol% concentration and decreases with further increase in the doping concentration due to concentration quenching. PMID:25920456

  1. Evolution of Ca-Al-rich bodies in the earliest solar system Growth by incorporation

    NASA Technical Reports Server (NTRS)

    Wark, D. A.; Lovering, J. F.

    1982-01-01

    Thirty different Allende Ca-Al-rich inclusions (CAIs), 11 of type A and 19 of type B, were examined for spinel palisades and framboids, and the possible origins of these structures are discussed. Possible mechanisms for in situ formation of palisades are assessed, all of them either being rejected outright or considered highly implausible. The evidence for external formation and incorporation of palisade bodies is then assessed, and possible mechanisms are considered. It is proposed that type B CAIs are residues from the heating and incomplete evaporation of interstellar dust during the accretion of the protosolar nebula, and that type A CAIs are later condensates from completely evaporated dust whose exotic O-16-rich component became more diluted in the gas phase.

  2. Properties and performance of the LiCaAlF6:Cr3+ laser material

    NASA Astrophysics Data System (ADS)

    Payne, Stephen A.; Chase, Lloyd L.; Atherton, L. Jeffrey; Caird, John A.; Kway, Wayne L.; Shinn, Michelle D.; Hughes, Robert S.; Smith, Larry K.

    1990-04-01

    The laser properties of the LiCaAlF6:Cr3+ (Cr:LiCAF) material are reviewed. The impact of the absorption and emission spectra on the laser performance is discussed. Laser-pumping and flashlamp-pumping experiments have shown that Cr:LiCAF has potential for high efficiency, although the presence of scattering losses remains a significant problem. The "gradient freeze" growth technique has been found to generate lower-loss material compared to Czochralski growth. The thermal lensing of Cr:LiCAF has been measured to be small and is in rough agreement with the magnitude expected on the basis of the intrinsic thermo-optical properties.

  3. Growth and spectral characters of Nd:CaGdAlO4 crystal

    NASA Astrophysics Data System (ADS)

    Di, Juqing; Sun, Xiaohui; Xu, Xiaodong; Xia, Changtai; Sai, Qinglin; Yu, Haohai; Wang, Yicheng; Zhu, Liu; Gao, Yuan; Guo, Xueyi

    2016-04-01

    In this paper, crystal growth and polarized spectra of Nd:CaGdAlO4 (Nd:CALGO) crystal were reported. The maximal absorption cross-sections are 6.8 and 7.5 × 10-20 cm2 for π-polarization and σ-polarization, and the emission cross-sections are 12.5 × 10-20 cm2 with full width at half maximum (FWHM) of 18 and 11 nm, respectively. The Judd-Ofelt (JO) theory was used to calculate the spectral parameters and the effective intensity parameters Ω2, Ω4 and Ω6 were 0.8 × 10-20 cm2, 7.5 × 10-20 cm2 and 5.8 × 10-20 cm2, respectively. The lifetime was 123 μs. The results show that Nd:CALGO crystal is a promising medium for laser output.

  4. Hydrogen reduction of wustite single crystals doped with Mg, Mn, Ca, Al, and Si

    NASA Astrophysics Data System (ADS)

    Moukassi, M.; Gougeon, M.; Steinmetz, P.; Dupre, B.; Gleitzer, C.

    1984-06-01

    In order to investigate the reduction mechanism of wustite in the presence of impurities usually met in the ironmaking industry, single crystals have been prepared with Mg, Mn, Ca, Al, and Si as dopants. The amounts of dopant in the lattice is around 4,4,2.5,0.5, and 0.01 mol pct, respectively, at 800 ‡C. For reduction with pure hydrogen, from 600 to 950 ‡C, Ca is the most efficient for accelerating the process at high degrees of reduction (75 pct) Mg and Mn are also active in this respect. Al has only a slowing down effect. Si also slows down the reaction at temperatures between 600 < T < 850 ‡C, but it becomes accelerating at T > 850 ‡C. In the presence of 20 torrs of water vapor in the gas, Mg and Mn are less efficient and unable to prevent the same slowing down of reaction observed with pure wustite at around 850 ‡C and classically called the ‡rate minimum‡. Our interpretation of these results is mainly based upon the observations of microstructures of partly reduced crystals which show a change in the texture of the iron produced which can be correlated with the reduction rate. These observations lead to a possible explanation in terms of the role of inclusions of impurity oxides on the sintering process of the metal, correlated with their ability to dissolve into the wustite lattice. However, this suggestion cannot apply in the case of Si at low temperatures, and this element is therefore supposed to play a role in the stages of reaction associated with the surface of the crystals.

  5. Effects of Al2O3 and CaO/SiO2 Ratio on Phase Equilbria in the ZnO-"FeO"-Al2O3-CaO-SiO2 System in Equilibrium with Metallic Iron

    NASA Astrophysics Data System (ADS)

    Zhao, Baojun; Hayes, Peter C.; Jak, Evgueni

    2011-02-01

    The phase equilibria and liquidus temperatures in the ZnO-"FeO"-Al2O3-CaO-SiO2 system in equilibrium with metallic iron have been determined experimentally in the temperature range 1383 K to 1573 K (1150 °C to 1300 °C). The experimental conditions were selected to characterize lead blast furnace and imperial smelting furnace slags. The results are presented in a form of pseudoternary sections ZnO-"FeO"-(Al2O3 + CaO + SiO2) with fixed CaO/SiO2 and (CaO + SiO2)/Al2O3 ratios. It was found that wustite and spinel are the major primary phases in the composition range investigated. Effects of Al2O3 concentration as well as the CaO/SiO2 ratio on the primary phase field, the liquidus temperature, and the partitioning of ZnO between liquid and solid phases have been discussed for zinc-containing slags.

  6. Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

    DOE PAGESBeta

    Tarantini, C.; Kametani, F.; Lee, S.; Jiang, J.; Weiss, J. D.; Jaroszynski, J.; Hellstrom, E. E.; Eom, C. B.; Larbalestier, D. C.

    2014-12-03

    Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature,Tc, of the material. In this study we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density (Fp=Jc xmore » μ₀H) by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m3 at 22.5 T and 4.2 K, the highest value ever reported in any 122 phase.« less

  7. Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2.

    PubMed

    Tarantini, C; Kametani, F; Lee, S; Jiang, J; Weiss, J D; Jaroszynski, J; Hellstrom, E E; Eom, C B; Larbalestier, D C

    2014-01-01

    Ba(Fe(1-x)Co(x))(2)As(2) is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, J(c). Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, T(c), of the material. In this paper we demonstrate that strain induced by the substrate can further improve J(c) of both single and multilayer films by more than that expected simply due to the increase in T(c). The multilayer deposition of Ba(Fe(1-x)Co(x))(2)As(2) on CaF2 increases the pinning force density (F(p) = J(c) × µ0H) by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m(3) at 22.5 T and 4.2 K, the highest value ever reported in any 122 phase. PMID:25467177

  8. Interplay between spin-orbit coupling and strong correlation effects: Comparison of the three osmate double perovskites Ba2A OsO6 (A =Na , Ca, Y)

    NASA Astrophysics Data System (ADS)

    Gangopadhyay, Shruba; Pickett, Warren E.

    2016-04-01

    High formal valence Os-based double perovskites are a focus of current interest because they display strong interplay of large spin-orbit coupling and strong electronic correlation. Here we present the electronic and magnetic characteristics of a sequence of three cubic Os based double perovskites Ba2A OsO6 (A =Na , Ca, Y), with formal valences of Os +7(d1) ,Os +6(d2) , and Os +5(d3) . For these first principles based calculations we apply an "exact exchange for correlated electrons" functional, with exact exchange applied in a hybrid fashion solely to the Os (5 d ) states. While Ba2NaOsO6 is a reported ferromagnetic Dirac-Mott insulator studied previously, the other two show antiferromagnetic ordering while all retain the undistorted cubic structure. For comparison purposes we have investigated only the ferromagnetic ordered phase. A metal-insulator transition is predicted to occur upon rotating the direction of magnetization in all three materials, reflecting the central role of spin-orbit coupling in these small gap osmates. Surprises arising from comparing formal charge states with the radial charge densities are discussed. Chemical shielding factors and orbital susceptibilities are provided for comparison with future nuclear magnetic resonance data.

  9. Oxygen vacancies and peroxo groups on regular and low-coordinated sites of MgO, CaO, SrO, and BaO surfaces

    NASA Astrophysics Data System (ADS)

    Di Valentin, Cristiana; Ferullo, Ricardo; Binda, Riccardo; Pacchioni, Gianfranco

    2006-03-01

    The formation of an oxygen vacancy and the simultaneous re-adsorption of an oxygen atom on regular and low-coordinated (LC) sites (edges and corners) of the surface of alkaline-earth oxides with cubic rock salt structure, MgO, CaO, SrO, and BaO, has been investigated using DFT cluster model calculations. The process corresponds to the formation of a surface Frenkel defect when the vacancy formation energy is partially compensated by the energy gained in the formation of a peroxo group. The structural and electronic properties of vacancies and peroxo groups along the series of alkaline-earth oxides have been analyzed. We found that the role of low-coordinated sites on the surface chemistry of alkaline-earth oxides is of crucial importance for MgO, but decreases for the heavier members. For instance, on BaO the formation of a peroxo group is practically site-insensitive. This is not the case of the vacancy formation, which is always favored on the low-coordinated sites.

  10. Average and local structure of the Pb-free ferroelectric perovskites (Sr,Sn)TiO3 and (Ba,Ca,Sn)TiO3

    DOE PAGESBeta

    Laurita, Geneva; Page, Katharine; Suzuki, Shoichiro; Seshadri, Ram

    2015-12-16

    The characteristic structural off -centering of Pb2+ in oxides, associated with its 6s2 lone pair, allows it to play a dominant role in polar materials, and makes it a somewhat ubiquitous component of ferroelectrics. In this work, we examine the compounds Sr0.9Sn0.1TiO3 and Ba0.79Ca0.16Sn0.05TiO3 using neutron total scattering techniques with data acquired at di erent temperatures. In these compounds, previously reported as ferroelectrics, Sn2+ appears to display some of the characteristics of Pb2+. We compare the local and long-range structures of the Sn2+-substituted compositions to the unsubstituted parent compounds SrTiO3 and BaTiO3. Lastly, we find that even at these smallmore » substitution levels, the Sn2+ lone pairs drive the local ordering behavior, with the local structure of both compounds more similar to the structure of PbTiO3 rather than the parent compounds.« less

  11. Crystal Growth and Electronic Raman Scattering Study of Model High-Tc Cuprate HgBa2 CaCu2 O6 +Ä

    NASA Astrophysics Data System (ADS)

    Wang, Lichen; Li, Yuan; Luo, Xiangpeng; Li, Jiarui; Yuan Li's group in ICQM Team

    In this talk, I will report our recent progress on crystal growth of HgBa2CaCu2O6 +x (Hg1212), which possesses a simple tetragonal crystal structure and the highest ambient-pressure Tc (128 K) among all cuprate superconductors with two CuO2 sheets in the primitive cell. Improvement in single-crystal synthesis was made possible by using self-designed high-pressure furnaces and a two-layer encapsulation method, and we demonstrate that the hole concentration can be homogeneously tuned in the underdoped region by post-growth annealing. Our electronic Raman scattering experiments reveal that the maximum of the d-wave superconducting gap increases from single-layer HgBa2CuO4 +x to double-layer Hg1212. In the same spectra, it is found that the characteristic energy of spin excitations, as manifested by the energy of the two-magnon signal, also increases in a nearly proportional fashion. This result is consistent with the idea that magnetic interactions are closely related to the Cooper pairing mechanism.

  12. Density and symmetry of unoccupied electronic states of Tl sub 2 Ba sub 2 CaCu sub 2 O sub 8

    SciTech Connect

    Romberg, H.; Nuecker, N.; Alexander, M.; Fink, J. ); Hahn, D.; Zetterer, T.; Otto, H.H.; Renk, K.F. )

    1990-02-01

    The local density and symmetry of unoccupied electronic states at the O and Cu sites in Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} single crystals has been investigated by measuring O 1{ital s} and Cu 2{ital p} absorption edges. High-energy electron-energy-loss spectroscopy in transmission has been used. There are O 2{ital p}{sub {ital x},{ital y}} states at the Fermi level from the CuO{sub 2} planes and O 2{ital p}{sub {ital z}} states from the BaO and TlO layers. The empty Cu 3{ital d} states have predominantly 3{ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} symmetry. There is an admixture of about 10% probably with 3{ital d}{sub 3{ital z}{sup 2}{minus}{ital r}{sup 2}} character.

  13. Isovalent Ca and Ba substitutions in thermoelectric layer-structured oxyselenide Sr2CoO2Cu2Se2

    NASA Astrophysics Data System (ADS)

    Chou, T. L.; Mustonen, O.; Tripathi, T. S.; Karppinen, M.

    2016-01-01

    Multilayered compounds typically present exotic functionalities, and some of them have been suggested as potential materials for thermoelectric conversion owing to their unique capability to decouple electronic and heat transport. Here we report new [CoO2] and [Cu2Se2] layered A 2CoO2Cu2Se2 compounds in which Sr at the intervening alkaline-earth A site is partially replaced with Ca or Ba. The parent Sr2CoO2Cu2Se2 phase is a direct gap p-type semiconductor, and density functional theory (DFT) calculations indicate its topmost valence band consists of Cu 3d-Se 4p states. Upon the isovalent cation substitution the lattice modification in the ab plane is constrained by the stiff [CoO2] layer such that the lattice shrinkage/expansion mainly happens along the c axis. Substitution of Sr with the heavier and larger Ba significantly enhances the thermopower but more hole states would be required to optimize the thermoelectric performance. Thermal stability is related to the inter-oxide-selenide-layer interaction, and our thermogravimetric measurement data reveal that the A 2CoO2Cu2Se2 materials could operate in the intermediate temperature region.

  14. Isovalent Ca and Ba substitutions in thermoelectric layer-structured oxyselenide Sr2CoO2Cu2Se2.

    PubMed

    Chou, T L; Mustonen, O; Tripathi, T S; Karppinen, M

    2016-01-27

    Multilayered compounds typically present exotic functionalities, and some of them have been suggested as potential materials for thermoelectric conversion owing to their unique capability to decouple electronic and heat transport. Here we report new [CoO2] and [Cu2Se2] layered A2CoO2Cu2Se2 compounds in which Sr at the intervening alkaline-earth A site is partially replaced with Ca or Ba. The parent Sr2CoO2Cu2Se2 phase is a direct gap p-type semiconductor, and density functional theory (DFT) calculations indicate its topmost valence band consists of Cu 3d-Se 4p states. Upon the isovalent cation substitution the lattice modification in the ab plane is constrained by the stiff [CoO2] layer such that the lattice shrinkage/expansion mainly happens along the c axis. Substitution of Sr with the heavier and larger Ba significantly enhances the thermopower but more hole states would be required to optimize the thermoelectric performance. Thermal stability is related to the inter-oxide-selenide-layer interaction, and our thermogravimetric measurement data reveal that the A2CoO2Cu2Se2 materials could operate in the intermediate temperature region. PMID:26702873

  15. Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

    PubMed Central

    Tarantini, C.; Kametani, F.; Lee, S.; Jiang, J.; Weiss, J. D.; Jaroszynski, J.; Hellstrom, E. E.; Eom, C. B.; Larbalestier, D. C.

    2014-01-01

    Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, Tc, of the material. In this paper we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density (Fp = Jc × µ0H) by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m3 at 22.5 T and 4.2 K, the highest value ever reported in any 122 phase. PMID:25467177

  16. Flux Pinning by Cr Nanoparticles in Cu_{0.5} Tl_{0.5} Ba2 Ca2 Cu3 O_{10-δ } Superconductor

    NASA Astrophysics Data System (ADS)

    Waqee-ur-Rehman, M.; Mumtaz, M.; Qasim, Irfan; Nadeem, K.

    2016-04-01

    Increase in flux pinning strength of Cu_{0.5} Tl_{0.5} Ba2 Ca2 Cu3 O_{10-δ } (CuTl-1223) superconductor has been observed after addition of Cr nanoparticles. We have thoroughly investigated the infield response of Cr nanoparticles-added CuTl-1223 superconductor in an external applied magnetic field in the range of 0-7 T. Solid-state reaction technique has been employed to synthesize (Cr)x -CuTl-1223; x = 0-1.00 wt% nanoparticle-superconductor composites. The flux pinning mechanism has been analyzed on the basis of thermally activated flux flow model in the presence of a small current (10 μ A). The increase in activation energy and decrease in transition width of CuTl-1223 superconducting phase show the enhancement in its flux pinning strength upon the addition of Cr nanoparticles.

  17. Unconventional High-Energy-State Contribution to the Cooper Pairing in the Underdoped Copper-Oxide Superconductor HgBa2 Ca2 Cu3 O8 +δ

    NASA Astrophysics Data System (ADS)

    Loret, B.; Sakai, S.; Gallais, Y.; Cazayous, M.; Méasson, M.-A.; Forget, A.; Colson, D.; Civelli, M.; Sacuto, A.

    2016-05-01

    We study the temperature-dependent electronic B1 g Raman response of a slightly underdoped single crystal HgBa2 Ca2 Cu3 O8 +δ with a superconducting critical temperature Tc=122 K . Our main finding is that the superconducting pair-breaking peak is associated with a dip on its higher-energy side, disappearing together at Tc. This result reveals a key aspect of the unconventional pairing mechanism: spectral weight lost in the dip is transferred to the pair-breaking peak at lower energies. This conclusion is supported by cellular dynamical mean-field theory on the Hubbard model, which is able to reproduce all the main features of the B1 g Raman response and explain the peak-dip behavior in terms of a nontrivial relationship between the superconducting gap and the pseudogap.

  18. (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics Synthesized by a Gel-Casting Method

    NASA Astrophysics Data System (ADS)

    Xiong, Wei

    2016-05-01

    (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) powder was synthesized by a solid-state reaction method, then the ceramics were fabricated by gel-casting and die-pressing routes, respectively. Piezoelectric coefficient (d 33 ) was measured by the d 33 m; Planar mode electromechanical coupling coefficient (k p ), dielectric loss (tanδ) and relative permittivity (ɛ r ) were measured by the impedance analyzer. Results of measurements showed that in the range of tested sintering temperature (1300-1500°C), gel-casting samples showed better piezoelectric and electromechanical coupling coefficients (d 33 = 395 pC/N, k p = 0.44) compared with die-pressing samples, and comparable dielectric properties were also observed. (tanδ = 0.037, ɛ r = 3267).

  19. μSR study on multi-layered HgBa 2Ca 4Cu 5O y (Hg-1245) superconductor

    NASA Astrophysics Data System (ADS)

    Tokiwa, K.; Ito, S.; Okumoto, H.; Higemoto, W.; Nishiyama, K.; Iyo, A.; Tanaka, Y.; Watanabe, T.

    2003-05-01

    We have carried out zero-field muon spin relaxation (ZF-μSR) measurements in multi-layered HgBa2Ca4Cu5Oy (Hg-1245) superconductor with Tc of 108 K. The variation of ZF-μSR time spectra from Gaussian-type to exponential-type behavior was observed with decreasing temperature below 60 K and the muon precessions were also observed below 45 K. These results indicate the appearance of a static magnetic order of Cu moments at muon sites below Tc. Compared with the results of NMR measurements, they suggest that this magnetic order is caused in three under-doped inner planes of five CuO2 planes in Hg-1245.

  20. Crystal Structures of the Trifluoromethyl Sulfonates M(SO3CF3)2 (M = Mg, Ca, Ba, Zn, Cu) from Synchrotron X-ray Powder Diffraction Data

    SciTech Connect

    Dinnebier,R.; Sofina, N.; Hildebrandt, L.; Jansen, M.

    2006-01-01

    The crystal structures of divalent metal salts of trifluoromethyl sulfonic acid ('trifluoromethyl sulfonates') M(SO{sub 3}CF{sub 3}){sub 2} (M = Mg, Ca, Ba, Zn, Cu) were determined from high-resolution X-ray powder diffraction data. Magnesium, calcium and zinc trifluoromethyl sulfonate crystallize in the rhombohedral space group R{bar 3}. Barium trifluoromethyl sulfonate crystallizes in the monoclinic space group I2/a(C2/c) and copper trifluoromethyl sulfonate crystallizes in the triclinic group P{bar 1}. Within the crystal structures the trifluoromethyl sulfonate anions are arranged in double layers with the apolar CF{sub 3} groups pointing towards each other. The cations are located next to the SO{sub 3} groups. The symmetry relations between the different crystal structures have been analyzed.

  1. Effect of local A-site strain on dipole stability in A6GaNb9O30 (A = Ba, Sr, Ca) tetragonal tungsten bronze relaxor dielectrics.

    PubMed

    Miller, Andrew J; Rotaru, Andrei; Arnold, Donna C; Morrison, Finlay D

    2015-06-21

    A series of isovalently A-site substituted relaxor dielectric tetragonal tungsten bronzes of general formula Ba(6-x-y)Sr(x)Ca(y)GaNb(9)O(30) were investigated. The long-range (average) crystal structure as determined by conventional diffraction techniques varies monotonically according to Vegard's law. The dielectric properties, however, do not display a similar, simple "average size" dependence and instead show a dependence on the statistical size variance, i.e. size mismatch, of the A-cation. The difficulties in Vogel-Fulcher analysis of relative permittivity and the complementary approach of using dielectric loss data fitted to Jonscher's empirical universal dielectric relaxation model is discussed. PMID:25687218

  2. Closely related magnetic and dielectric transitions in the “114” magnetoelectric Zn-doped CaBaCo{sub 4}O{sub 7}

    SciTech Connect

    Seikh, Md. Motin; Caignaert, V. Preethi Meher, K. R. S.; Maignan, A.; Raveau, B.; Suard, E.

    2014-12-28

    We report on the impact of zinc doping upon the magneto-electric properties of CaBaCo{sub 4}O{sub 7}.We show that the presence of less than 1% Zn at the Co sites decreases T{sub C} from 64 K to 48 K and generates two magnetic transitions, concomitant with changes of slope of dielectric permittivity, at 54 K and 77 K, respectively. Powder neutron diffraction and magnetic data show the existence of an incommensurate magnetic phase and a spin-flop transition in this temperature range. The crossover of the magnetodielectric effect of this oxide, from positive below 50 K to negative above this temperature emphasizes the primordial role of the incommensurate magnetic phase in the evolution of these properties.

  3. Low field AC susceptibility study of intergranular critical current density in Mg-substituted CuBa2Ca3Cu4O12-y high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Agarwal, S. K.; Kumaraswamy, B. V.

    2005-05-01

    Measurements of the a.c.susceptibility (χ=χ‧+iχ″) have been made on the Mg substituted high TC superconducting system, CuBa2(MgxCa1-x)3Cu4O12-y (Cu-1234) with x=0, 0.10 & 0.20, at different values of the a.c.field amplitude. Estimates of the intergranular critical current density(JC) made from the field dependent χ″-T curves show an improvement in the Mg-substituted Cu-1234 system. Results have been analysed in the light of the crystal structure and the superconducting anisotropy factor (γ=ξab/ξc) of the Cu-1234 system. Lower superconducting anisotropy emanating from Mg substitution has been found to be significant, resulting in better superconducting properties.

  4. High-pressure effect on Tc of HgBa2Ca3Cu4O10+δ up to 30 GPa

    NASA Astrophysics Data System (ADS)

    Taku, S.; Shimizu, K.; Eisaki, H.; Iyo, A.; Uchida, S.

    2008-07-01

    In order to investigate the pressure dependence of Tc of the Hg-based cuprates, we performed the electrical resistance measurements of high purity HgBa2Ca2Cu3O10+δ (Hg-1234) synthesized under pressure. We used a diamond-anvil cell to generate high pressure up to 30 GPa. In this work, two Hg-1234 samples with different hole concentration (Tc = 125 K for optimaldoped sample and Tc = 124 K for underdoped one at ambient pressure) were measured. With applying pressure Tc of underdoped sample increased (dT/dP = +0.6 K/GPa) and passed through a peak with 143 K at ~30 GPa and decreased drastically at higher pressure. This behavior was different from previous works for Hg-1234 and Hg-1223, in which the Tc saturates above the pressure giving the maximum Tc.

  5. Synthesis and magnetic susceptibility of M /SUB x/ V/sub 2/O/sub 3//sup +/y solid solutions (M = Ca, Sr, Ba)

    SciTech Connect

    Volkov, V.L.; Milova, G.D.; Perelyaev, V.A.

    1985-12-01

    The authors synthesize and study the magnetic susceptibility of solid solutions of alkaline-earth metal oxides in V/sub 2/O/sub 3/. As the initial substances ultrapure V/sub 2/O/sub 5/, CaCo/sub 3/, BaCO/sub 3/, and SrCO/sub 3/ and chemically pure metavanadates and orthovanadates of alkaline-earth metals were used. The x-ray analysis was carried out on a DRON-2.5 diffractometer with ionization detection of Cu Ka radiation. The magnetic susceptibility was measured by the Faraday method. The authors establish the existence of solid solutions of composition MxV/sub 2/O/sub 3//sup +/y, determine their crystallographic parameters, and study the magnetic susceptibility. The transition temperature of the specimens decreases as the radius of the M/sup 2 +/ ions and the unit-cell parameter c of the crystal decrease.

  6. Multiple caloric effects in (Ba0.865Ca0.135Zr0.1089Ti0.8811Fe0.01)O3 ferroelectric ceramic

    NASA Astrophysics Data System (ADS)

    Patel, Satyanarayan; Chauhan, Aditya; Vaish, Rahul

    2015-07-01

    Multiple caloric effects have been investigated for Fe-doped bulk (Ba0.865Ca0.135Zr0.1089Ti0.8811Fe0.01)O3 (BCZTO-Fe) ferroelectric ceramic. Indirect predictions were made using Maxwell's relations in conjunction with data from experimental observations. It was revealed that bulk BCZTO-Fe has huge untapped potential for solid-state refrigeration. A peak electrocaloric effect of 0.45 K (347 K) was predicted for 0-3 kV.mm-1 electric field, significantly higher than other BCZTO based materials. A maximum elastocaloric cooling of 1.4 K (298 K) was achieved for applied stress of 0-200 MPa. Finally, an unforeseen component of electric field driven caloric effect has been reported as inverse piezocaloric effect, with a maximum temperature change of 0.28 K (298 K).

  7. Unconventional High-Energy-State Contribution to the Cooper Pairing in the Underdoped Copper-Oxide Superconductor HgBa_{2}Ca_{2}Cu_{3}O_{8+δ}.

    PubMed

    Loret, B; Sakai, S; Gallais, Y; Cazayous, M; Méasson, M-A; Forget, A; Colson, D; Civelli, M; Sacuto, A

    2016-05-13

    We study the temperature-dependent electronic B_{1g} Raman response of a slightly underdoped single crystal HgBa_{2}Ca_{2}Cu_{3}O_{8+δ} with a superconducting critical temperature T_{c}=122  K. Our main finding is that the superconducting pair-breaking peak is associated with a dip on its higher-energy side, disappearing together at T_{c}. This result reveals a key aspect of the unconventional pairing mechanism: spectral weight lost in the dip is transferred to the pair-breaking peak at lower energies. This conclusion is supported by cellular dynamical mean-field theory on the Hubbard model, which is able to reproduce all the main features of the B_{1g} Raman response and explain the peak-dip behavior in terms of a nontrivial relationship between the superconducting gap and the pseudogap. PMID:27232035

  8. Flux Pinning by Cr Nanoparticles in Cu_{0.5}Tl_{0.5}Ba2Ca2Cu3O_{10-δ } Superconductor

    NASA Astrophysics Data System (ADS)

    Waqee-ur-Rehman, M.; Mumtaz, M.; Qasim, Irfan; Nadeem, K.

    2016-09-01

    Increase in flux pinning strength of Cu_{0.5}Tl_{0.5}Ba2Ca2Cu3O_{10-δ }(CuTl-1223) superconductor has been observed after addition of Cr nanoparticles. We have thoroughly investigated the infield response of Cr nanoparticles-added CuTl-1223 superconductor in an external applied magnetic field in the range of 0-7 T. Solid-state reaction technique has been employed to synthesize (Cr)x-CuTl-1223; x = 0-1.00 wt% nanoparticle-superconductor composites. The flux pinning mechanism has been analyzed on the basis of thermally activated flux flow model in the presence of a small current (10 μ A). The increase in activation energy and decrease in transition width of CuTl-1223 superconducting phase show the enhancement in its flux pinning strength upon the addition of Cr nanoparticles.

  9. (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics Synthesized by a Gel-Casting Method

    NASA Astrophysics Data System (ADS)

    Xiong, Wei

    2016-08-01

    (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) powder was synthesized by a solid-state reaction method, then the ceramics were fabricated by gel-casting and die-pressing routes, respectively. Piezoelectric coefficient ( d 33 ) was measured by the d 33 m; Planar mode electromechanical coupling coefficient ( k p ), dielectric loss ( tanδ) and relative permittivity ( ɛ r ) were measured by the impedance analyzer. Results of measurements showed that in the range of tested sintering temperature (1300-1500°C), gel-casting samples showed better piezoelectric and electromechanical coupling coefficients ( d 33 = 395 pC/N, k p = 0.44) compared with die-pressing samples, and comparable dielectric properties were also observed. ( tanδ = 0.037, ɛ r = 3267).

  10. Effect of diamagnetic Ca, Sr, Pb, and Ba substitution on the crystal structure and multiferroic properties of the BiFeO3 perovskite

    NASA Astrophysics Data System (ADS)

    Khomchenko, V. A.; Kiselev, D. A.; Vieira, J. M.; Jian, Li; Kholkin, A. L.; Lopes, A. M. L.; Pogorelov, Y. G.; Araujo, J. P.; Maglione, M.

    2008-01-01

    In this work, we studied the effect of heterovalent Ca, Sr, Pb, and Ba substitution on the crystal structure, dielectric, local ferroelectric, and magnetic properties of the BiFeO3 multiferroic perovskite. Ceramic solid solutions with the general formula Bi0.7A0.3FeO3 (A is a doping element) were prepared and characterized by x-ray diffraction, dielectric, piezoresponse force microscopy (PFM), and magnetic measurements. It is shown that the crystal structure of the compounds is described within the space group R3c, permitting the spontaneous polarization, whose existence was confirmed by the PFM data. Magnetic properties of the solid solutions are determined by the ionic radius of the substituting element. Experimental results suggest that the increase in the radius of the A-site ion leads to the effective suppression of the spiral spin structure of BiFeO3, resulting in the appearance of net magnetization.

  11. Millimeter wave inducing subharmonic steps in the Tl2Ba2CaCu2O8 thin film bicrystal Josephson junction

    NASA Astrophysics Data System (ADS)

    Liu, X.; Hu, L.; Xie, W.; Wang, P.; Ma, L. J.; Zhao, X. J.; He, M.; Zhang, X.; Ji, L.

    2015-04-01

    The bicrystal Josephson junction (BJJ) was fabricated by patterning microbridge into Tl2Ba2CaCu2O8 (Tl-2212) thin film grown epitaxially on the bicrystal SrTiO3 (STO) substrate. The millimeter wave responses of BJJ were researched by experiment and numerical simulation. Shapiro steps and subharmonic steps were both observed in the current-voltage (I-V) curve at the liquid nitrogen temperature. In the resistive-capacitive-inductive shunted junction (RCLSJ) model, both of the Shapiro steps and subharmonic steps were reproduced with varying capacitances and inductances. The result of simulation has a good agreement with the experiment. The relative large capacitance and inductance correspond to distinct subharmonic steps.

  12. Diminishing sign anomaly and scaling behavior of the mixed-state Hall resistivity in Tl2Ba2Ca2Cu3O10 films containing columnar defects

    NASA Technical Reports Server (NTRS)

    Budhani, R. C.; Liou, S. H.; Cai, Z. X.

    1993-01-01

    The issues of sign reversal of the Hall voltage and scaling between longitudinal (rho(xx)) and Hall (rho(xy)) resistivities are studied in Tl2Ba2Ca2Cu3O10 films in which the vortex dynamics is drastically changed by flux pinning at heavy-ion-irradiation-induced linear defects. While the sign anomaly diminishes with increasing defect concentration, the power law rho(xy) is approximately equal to rho(xx) exp beta, beta = 1.85 +/- 0.1, holds even after irradiation. This result shows that the scaling is a universal feature of the mixed state in this system. The sign anomaly, on the other hand, is not consistent with a model that invokes pinning-induced backflow in the vortex core as the mechanism for this effect.

  13. Optical waveguide properties of Ca0.4Ba0.6Nb2O6 crystal formed by oxygen ion irradiation

    NASA Astrophysics Data System (ADS)

    Wang, Tie-Jun; Zhou, Yu-Fan; Yu, Xiao-Fei; Liu, Tao; Zhang, Lian; Song, Hong-Lian; Qiao, Mei; Wang, Xue-Lin

    2015-07-01

    We report the fabrication of a planar optical waveguide in a Ca0.4Ba0.6Nb2O6 crystal by irradiation with 6.0 MeV oxygen ions. We measured the guiding mode by the prism-coupling method at 633 nm and 1539 nm. The near-field intensity distributions were measured by the end-face coupling setup at a wavelength of 633 nm. The reflectivity calculation method (RCM) was used for reconstructing refractive index profiles. SRIM was used to simulate the electronic and nuclear stopping power caused by oxygen ion irradiation, and the finite-difference beam propagation method (FD-BPM) was used to simulate the near-field intensity distributions. Micro-Raman spectra were measured at room temperature in air to study the differences between the substrate and waveguide region.

  14. The features of structural transformations in lanthanum manganites La{sub 1−x}A{sub x}MnO{sub 3+δ} (A = Ca, Sr, Ba)

    SciTech Connect

    Sedykh, Vera D.

    2014-10-27

    In this work, the effect of the ionic radius and concentration of a doping element on the features of the structural transformations in polycrystalline lanthanum manganites, La{sub 1−x}A{sub x}MnO{sub 3+δ} (A = Ca, Sr, Ba), has been studied by Mössbauer spectroscopy and X-ray diffraction analysis. For Mössbauer investigations, a small amount of {sup 57}Fe (2 at%) Mössbauer isotope was introduced into the samples. It follows from the analysis of the obtained data that both common features of the structural transformations and differences between them exist in lanthanum manganites depending on ionic radius and concentration of a doping element.

  15. Ultrasonically-enhanced mechanochemical synthesis of CaAl-layered double hydroxides intercalated by a variety of inorganic anions.

    PubMed

    Szabados, Márton; Mészáros, Rebeka; Erdei, Szabolcs; Kónya, Zoltán; Kukovecz, Ákos; Sipos, Pál; Pálinkó, István

    2016-07-01

    CaAl-layered double hydroxides (CaAl-LDHs) were synthesised with various interlayer anions (CO3(2-), F(-), Cl(-), Br(-) and I(-)) by mechanochemical pre-treatment followed by ultrasonic irradiation in aqueous media. The parameters of the syntheses (duration of pre-milling and sonication, quality of the aqueous media, temperature) were altered in order to optimise the procedure and to understand the formation of LDH and other secondary products. The products were characterised by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The optimisation resulted in close-to-phase-pure CaAl-LDHs, not only with carbonate and chloride interlayer anions, but the hard-to-intercalate bromide and iodide as well. PMID:26964966

  16. Para-conductivity and critical regime of (Tl1-xCx)Ba2Ca3Cu4O12-δ superconductors

    NASA Astrophysics Data System (ADS)

    Khan, Nawazish A.; Ahmad, Shakil

    2012-08-01

    We have synthesized (Tl1-yCy)Ba2Ca3Cu4O12-δ (Tl1-yCy-1234) (y = 0, 0.25, 0.5, and 0.75) samples at normal pressure and studied the role of carbon doping on the intrinsic superconductivity parameters via excess conductivity analysis (FIC) of resistivity data. The FIC analysis in the transition region is carried out by using Ginzburg-Landau equations, whereas beyond the critical regimes, we have employed Lawrence and Doniach (LD) and Maki-Thompson models. Through such analyses, it is observed that the values of Bc(0), Bc1(0), and Jc(0) are marginally decreased whereas vF, τφ, ξc(0), J (interlayer-coupling parameter), and width of three dimensional regimes are increased with carbon doping in (Tl1-yCy)Ba2Ca3Cu4O12-δ (Tl1-yCy-1234) (y = 0, 0.25, 0.5, and 0.75) samples. Since the absolute values of vF, τφ, and ξc(0) crucially depend on the coherence length of the carriers, which in turn depends on the density of the carriers. Increase in the values of these parameters strongly suggests that the numbers of the carriers get homogenized in the inner and outer CuO2 planes, which suppress the pseudo-gap in the final compound. The suppression in the pseudo-gap can be witnessed in the form of an increase in the width of 3D LD regime with the doping of carbon in the final compound.

  17. Inelastic neutron scattering studies of phonon spectra, and simulations of pressure-induced amorphization in tungstates A W O4 (A =Ba ,Sr ,Ca , and Pb )

    NASA Astrophysics Data System (ADS)

    Goel, Prabhatasree; Gupta, M. K.; Mittal, R.; Rols, S.; Achary, S. N.; Tyagi, A. K.; Chaplot, S. L.

    2015-03-01

    Lattice dynamics and high-pressure phase transitions in A W O4 (A =Ba ,Sr ,Ca , and Pb ) have been investigated using inelastic neutron scattering experiments, ab initio density functional theory calculations, and extensive molecular dynamics simulations. The vibrational modes that are internal to W O4 tetrahedra occur at the highest energies consistent with the relative stability of W O4 tetrahedra. The neutron data and the ab initio calculations are found to be in excellent agreement. The neutron and structural data are used to develop and validate an interatomic potential model. The model is used for classical molecular dynamics simulations to study their response to high pressure. We have calculated the enthalpies of the scheelite and fergusonite phases as a function of pressure, which confirms that the scheelite to fergusonite transition is second order in nature. With increase in pressure, there is a gradual change in the A O8 polyhedra, while there is no apparent change in the W O4 tetrahedra. We found that all the four tungstates amorphize at high pressure. This is in good agreement with available experimental observations which show amorphization at around 45 GPa in BaW O4 and 40 GPa in CaW O4 . Further molecular dynamics simulations at high pressure and high temperature indicate that application of pressure at higher temperature hastens the process of amorphization. On amorphization, there is an abrupt increase in the coordination of the W atom while the bisdisphenoids around the A atom are considerably distorted. The pair-correlation functions of the various atom pairs corroborate these observations. Our observations aid in predicting the pressure of amorphization in SrW O4 and PbW O4 .

  18. Shrinking of anionic polyacrylate coils induced by Ca2+, Sr2+ and Ba2+: A combined light scattering and ASAXS study

    NASA Astrophysics Data System (ADS)

    Schweins, R.; Goerigk, G.; Huber, K.

    2006-10-01

    Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly, precipitation thresholds were established for three different alkaline earth cations Ca2+, Sr2+ and Ba2+. Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl2]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations Ca2+, Sr2+ and Ba2+. Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr counterions around the polyacrylate chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful separation of the pure-resonant terms, which solely stem from the counterions. The Sr2+ scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of [SrCl2]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains. Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly smaller than the respective overall size of the NaPA particles.

  19. Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III; Bansal, Narottam P.

    1990-01-01

    Glass of stoichiometric celsian composition, BaO-Al2O3-SiO2, has a density of 3.39 g/cu cm, a thermal expansion coefficient of 6.6 x 10 to the -6th/C, a glass-transition temperature of 910 C, and a dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot-pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass have been studied. CIP'd samples, after appropriate heat treatments, always crystallized out as celsian, whereas presence of 5-10 wt pct of an additive was necessary for formation of celsian in sintered as well as hot-pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot-pressing resulted in fully dense samples.

  20. Morphology control and luminescence properties of BaMgAl 10O 17:Eu 2+ phosphors prepared by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Zhou, Yonghui; Lin, Jun

    2005-02-01

    Starting from the aqueous solutions of metal nitrates with citric acid and polyethylene glycol (PEG) as additives, BaMgAl 10O 17:Eu 2+ (BAM:Eu 2+) phosphors were prepared by a two-step spray pyrolysis (SP) method. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectra were used to characterize the resulted BAM:Eu 2+ phosphors. The obtained BAM:Eu 2+ phosphor particles have spherical shape, submicron size (0.5-3 μm). The effects of process conditions of the spray pyrolysis, such as molecular weight and concentration of PEG, on the morphology and luminescence properties of phosphor particles were investigated. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.03 g/ml in the precursor solution. Moreover, the emission intensity of the phosphors increased with increasing of metal ion concentration in the solution. Compared with the BAM:Eu 2+ phosphor prepared by citrate-gel method, spherical BAM:Eu 2+ phosphor particles showed a higher emission intensity.

  1. Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III; Bansal, Narottam P.

    1990-01-01

    Glass of stoichiometric celsian composition, BaO-Al2O3-2SiO2, is a potential glass-ceramic matrix for high-temperature composites. The glass has a density of 3.39 g/cu cm, thermal expansion coefficient of 6.6 x 10(exp -6)/deg C glass transition temperature of 910 C, and dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass were studied. CIP'ed samples, after appropriate heat treatments, always crystallized out as celsian whereas the presence of 5 to 10 weight percent of an additive was necessary for formation of celsian in sintered as well as hot pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot pressing resulted in fully dense samples.

  2. Time-Dependent Negative Capacitance Effects in Al2O3/BaTiO3 Bilayers.

    PubMed

    Kim, Yu Jin; Yamada, Hiroyuki; Moon, Taehwan; Kwon, Young Jae; An, Cheol Hyun; Kim, Han Joon; Kim, Keum Do; Lee, Young Hwan; Hyun, Seung Dam; Park, Min Hyuk; Hwang, Cheol Seong

    2016-07-13

    The negative capacitance (NC) effects in ferroelectric materials have emerged as the possible solution to low-power transistor devices and high-charge-density capacitors. Although the steep switching characteristic (subthreshold swing < sub-60 mV/dec) has been demonstrated in various devices combining the conventional transistors with ferroelectric gates, the actual applications of the NC effects are still some way off owing to the inherent hysteresis problem. This work reinterpreted the hysteretic properties of the NC effects within the time domain and demonstrated that capacitance (charge) boosting could be achieved without the hysteresis from the Al2O3/BaTiO3 bilayer capacitors through short-pulse charging. This work revealed that the hysteresis phenomenon in NC devices originated from the dielectric leakage of the dielectric layer. The suppression of charge injection via the dielectric leakage, which usually takes time, inhibits complete ferroelectric polarization switching during a short pulse time. It was demonstrated that a nonhysteretic NC effect can be achieved only within certain limited time and voltage ranges, but that these are sufficient for critical device applications. PMID:27231754

  3. [Photoluminescence properties of nanocrystalline A3(VO4)2:Eu(A = Mg, Ca, Sr and Ba)].

    PubMed

    Fu, Xiao-yan; Niu, Shu-yun; Zhang, Hong-wu; Xin, Qin

    2006-01-01

    A series of europium doped alkali earth orthovanadates were prepared by Pechini-type sol-gel. The powders were characterized by transmission electron microscopy (TEM), infrared spectrum (IR) and photoluminescence (PL). The results of TEM show that high-quality nanopowders with controlled particle size about 50 nm were prepared. The relation between alkali earth ions and luminescence properties was observed from the results of luminescence spectra. Due to the similar ion radius of Ca2+ ions and Eu3+ ions, Ca3 (VO4 )2:Eu powders exhibit the strongest emission intensity among the four kind of phosphors. PMID:16827335

  4. Two competing soft modes and an unusual phase transition in the stuffed tridymite-type oxide BaAl2O4

    NASA Astrophysics Data System (ADS)

    Ishii, Y.; Mori, S.; Nakahira, Y.; Moriyoshi, C.; Park, J.; Kim, B. G.; Moriwake, H.; Taniguchi, H.; Kuroiwa, Y.

    2016-04-01

    We investigated the structural phase transition of BaAl2O4 , which has a network structure with corner-sharing AlO4 tetrahedra, via synchrotron x-ray thermal diffuse scattering measurements and first-principles calculations. BaAl2O4 shows the structural phase transition at TC=451.4 K from the P 6322 parent crystal structure to the low-temperature superstructure with a cell volume of 2 a ×2 b ×c . This phase transition is unusual, in which two energetically competing phonon modes at M and K points soften simultaneously. When approaching TC from above, the K -point mode appears first. However, this K -point mode is overcome by the later-developed M -point mode. The thermal diffuse scattering intensities from both modes increase sharply at TC; therefore, both modes soften simultaneously. The first-principles calculations demonstrate that the M -point mode is electrostatically more preferable than the K -point mode and determines the eventual low-temperature structure, although these two modes are competing energetically. This competition is characteristic of BaAl2O4 , which is ascribed to the structurally flexible network structure of this compound.

  5. Effect of Sr 2+-doping on structure and luminescence properties of BaAl 2Si 2O 8:Eu 2+ phosphors

    NASA Astrophysics Data System (ADS)

    Ma, Mingxing; Zhu, Dachuan; Zhao, Cong; Han, Tao; Cao, Shixiu; Tu, Mingjing

    2012-03-01

    Sr 2+ doped BaAl 2Si 2O 8:Eu 2+ phosphor was synthesized by chemical co-precipitation method. With the increase of Sr 2+ concentration, the phase structure of (Ba 0.965 - x Sr xEu 0.035)Al 2Si 2O 8 changes from hexagonal phase to monoclinic phase owing to large activation energy in SrAl 2Si 2O 8 system. (Ba 0.965 - x Sr xEu 0.035)Al 2Si 2O 8 phosphor exhibits a broad blue band peaking at 425 nm due to the 4f 65d-4f 7( 8S 7/2) transition of Eu 2+ ions. The emission intensity increases, accompanied by the blue shift of emission maximum from 459 to 417 nm with the Sr 2+ doping concentration increasing. The optimal concentration of Sr 2+ ion is 40%, and the phosphor shows high color stability in CIE chromaticity diagram. The result indicates that Sr 2+ doped phosphor not only can enhance the relative intensity but also can adjust the chromaticity coordinate.

  6. Luminescent and aging characteristics of blue emitting (Ca 1- x,Mg x)Al 2Si 2O 8:Eu 2+ phosphor for PDPs application

    NASA Astrophysics Data System (ADS)

    Im, Won Bin; Kim, Yong-Il; Kang, Jong Hyuk; Jeon, Duk Young

    2005-06-01

    We have evaluated thermal stability and aging property of a blue color-emitting phosphor, CaAl 2Si 2O 8:Eu 2+ (CAS:Eu 2+), synthesized by conventional solid-state reaction method. When both CAS:Eu 2+ and BaMgAl 10O 19:Eu 2+ (BAM) were baked in air at 500 °C for 20 min, the decrease of photoluminescence (PL) intensity of CAS:Eu 2+ was lower than that of BAM. The aging property of CAS:Eu 2+ was also better than that of BAM. Due to its rigid structure and unlimited framework of silicon-oxygen and aluminum-oxygen around Eu 2+ ions, Eu 2+ ions were protected from outer oxidizing atmosphere and plasma discharge. After analysis of aging property and thermal stability, the differences of these thermal stability and aging property of CAS:Eu 2+ from those of BAM were ascribed to its crystal structure which plays a role of a shield for Eu 2+ ions against oxidation atmosphere and Xe ion bombardment.

  7. Free-electron-like Hall effect and deviations from free-electron behavior in Ca-Al amorphous alloys

    NASA Astrophysics Data System (ADS)

    Mayeya, F. M.; Hickey, B. J.; Howson, M. A.

    1995-06-01

    The Hall coefficients of Ca-Al amorphous alloys have been measured at 4.2 K over a wide range of compositions. It is shown that the magnitude of the Hall coefficients are close to the nearly-free-electron (NFE) prediction for low Ca concentrations but deviate significantly from the NFE values for Ca concentration greater than 45 at. %. The deviations from the free-electron values have previously been attributed to the effects of s-d hybridization, while a reduction in magnitude by Au doping has been argued to result from the side-jump effect.

  8. Water-induced morphology changes in BaO/γ-Al2O3 NOx storage materials: an FTIR, TPD, and time-resolved synchrotron XRD study

    SciTech Connect

    Szanyi, Janos; Kwak, Ja Hun; Kim, Do Heui; Wang, Xianqin; Chimentao, Ricardo J.; Hanson, Jonathan; Epling, William S.; Peden, Charles HF

    2007-03-29

    The effect of water on the morphology of BaO/Al2O3-based NOx storage materials was investigated using Fourier transform infrared spectroscopy, temperature programmed desorption, and time-resolved synchrotron X-ray diffraction techniques. The results of this multi-spectroscopy study reveal that, in the presence of water, surface Ba-nitrates convert to bulk nitrates, and water facilitates the formation of large Ba(NO3)2 particles. This process is completely reversible, i.e. after the removal of water from the storage material a significant fraction of the bulk nitrates re-convert to surface nitrates. NO2 exposure of a H2O-containing (wet) BaO/Al2O3 sample results in the formation of nitrites and bulk nitrates exclusively, i.e. no surface nitrates form. After further exposure to NO2, the nitrites completely convert to bulk nitrates. The amount of NOx taken up by the storage material is, however, essentially unaffected by the presence of water, regardless of whether the water was dosed prior to or after NO2 exposure. Based on the results of this study we are now able to explain most of the observations reported in the literature on the effect of water on NOx uptake on similar storage materials.

  9. Microwave dielectric properties of CaCu3Ti4O12-Al2O3 composite

    NASA Astrophysics Data System (ADS)

    Rahman, Mohd Fariz Ab; Abu, Mohamad Johari; Karim, Saniah Ab; Zaman, Rosyaini Afindi; Ain, Mohd Fadzil; Ahmad, Zainal Arifin; Mohamed, Julie Juliewatty

    2016-07-01

    (1-x)CaCu3Ti4O12 + (x)Al2O3 composite (0 ≤ x ≤0.25) was prepared via conventional solid-state reaction method. The fabrication of sample was started with synthesizing stoichiometric CCTO from CaCO3, CuO and TiO2 powders, then wet-mixed in deionized water for 24 h. The process was continued with calcined CCTO powder at 900 °C for 12 h before sintered at 1040 °C for 10 h. Next, the calcined CCTO powder with different amount of Al2O3 were mixed for 24 h, then palletized and sintered at 1040 °C for 10. X-ray diffraction analysis on the sintered samples showed that CCTO powder was in a single phase, meanwhile the trace of secondary peaks which belong to CaAl2O4 and Corundum (Al2O3) could be observed in the other samples Scanning electron microscopy analysis showed that the grain size of the sample is firstly increased with addition of Al2O3 (x = 0.01), then become smaller with the x > 0.01. Microwave dielectric properties showed that the addition of Al2O3 (x = 0.01) was remarkably reduced the dielectric loss while slightly increased the dielectric permittivity. However, further addition of Al2O3 was reduced both dielectric loss and permittivity at least for an order of magnitude.

  10. Thermally and optically stimulated radiative processes in Eu and Y co-doped LiCaAlF6 crystal

    NASA Astrophysics Data System (ADS)

    Fukuda, Kentaro; Yanagida, Takayuki; Fujimoto, Yutaka

    2015-06-01

    Yttrium co-doping was attempted to enhance dosimeter performance of Eu doped LiCaAlF6 crystal. Eu doped and Eu, Y co-doped LiCaAlF6 were prepared by the micro-pulling-down technique, and their dosimeter characteristics such as optically stimulated luminescence (OSL) and thermally stimulated luminescence (TSL) were investigated. By yttrium co-doping, emission intensities of OSL and TSL were enhanced by some orders of magnitude. In contrast, scintillation characteristics of yttrium co-doped crystal such as intensity of prompt luminescence induced by X-ray and light yield under neutron irradiation were degraded.

  11. Binary, ternary and quaternary silicates of CaO, BaO and ZnO in high thermal expansion seals for solid oxide fuel cells studied by high-temperature X-ray diffraction (HT-XRD)

    SciTech Connect

    Kerstan, Marita; Mueller, Matthias; Ruessel, Christian

    2011-12-15

    Highlights: Black-Right-Pointing-Pointer We examined the thermal expansion of various silicates of CaO, BaO and ZnO. Black-Right-Pointing-Pointer Thermal expansions were determined by dilatometry and high-temperature X-ray diffraction. Black-Right-Pointing-Pointer High-temperature X-ray diffraction enabled to determine anisotropic thermal expansion. Black-Right-Pointing-Pointer CaSiO{sub 3}, Ca{sub 3}Si{sub 2}O{sub 7} and BaCa{sub 2}Si{sub 3}O{sub 9} exhibit the highest thermal expansion. Black-Right-Pointing-Pointer CaSiO{sub 3}, Ca{sub 3}Si{sub 2}O{sub 7} and BaCa{sub 2}Si{sub 3}O{sub 9} are suitable as components in high temperature seals. -- Abstract: Gas-tight seals based on glasses suitable for joining of materials with high thermal expansion coefficients are for example required for solid-oxide fuel cells. If these seals are to be used at high temperatures, they can only be fabricated from glasses which enable the crystallization of phases with high thermal expansion coefficients. This paper reports on some components from systems suitable for high thermal expansion seals: binary calcium silicates, CaSiO{sub 3}, Ca{sub 3}Si{sub 2}O{sub 7} and Ca{sub 2}SiO{sub 4} zinc silicates, Zn{sub 2}SiO{sub 4}, ternary silicates of BaO, CaO and ZnO, BaCa{sub 2}Si{sub 3}O{sub 9}, Ca{sub 2}ZnSi{sub 2}O{sub 7}, and one quaternary silicate, Ba{sub 2}CaZn{sub 2}Si{sub 6}O{sub 17,} studied by high-temperature X-ray diffraction. Only CaSiO{sub 3}, Ca{sub 3}Si{sub 2}O{sub 7} and BaCa{sub 2}Si{sub 3}O{sub 9} exhibit thermal expansion coefficients in the range suitable for high thermal expansion seals of 11.2-11.8 Multiplication-Sign 10{sup -6} K{sup -1} (100-800 Degree-Sign C). The thermal expansions strongly depend on the respective crystallographic axis. The coefficient of thermal expansion of a sealing glass is not only affected by the thermal expansions of the crystalline phases, but also by that of the residual glassy phase as well as by the elastic properties. The phase

  12. Kasatkinite, Ba2Ca8B5Si8O32(OH)3 · 6H2O6, a new mineral from the Bazhenovskoe deposit, the Central Urals, Russia

    NASA Astrophysics Data System (ADS)

    Pekov, I. V.; Chukanov, N. V.; Filinchuk, Ya. E.; Zadov, A. E.; Kononkova, N. N.; Epanchintsev, S. G.; Kaden, P.; Kutzer, A.; Göttlicher, J.

    2013-12-01

    A new mineral, kasatkinite, Ba2Ca8B5Si8O32(OH)3 · 6H2O, has been found at the Bazhenovskoe chrysotile asbestos deposit, the Central Urals, Russia in the cavities in rhodingite as a member of two assemblages: (l) on prehnite, with pectolite, calcite, and clinochlore; and (2) on grossular, with diopside and pectolite. Kasatkinite occurs as spherulites or bunches up to 3 mm in size, occasionally combined into crusts. Its individuals are acicular to hair-like, typically split, with a polygonal cross section, up to 0.5 mm (rarely, to 6 mm) in length and to 20 μm in thickness. They consist of numerous misoriented needle-shaped subindividuals up to several dozen μm long and no more than 1 μm thick. Kasatkinite individuals are transparent and colorless; its aggregates are snow white. The luster is vitreous or silky. No cleavage was observed; the fracture is uneven or splintery for aggregates. Individuals are flexible and elastic. The Mohs' hardness is 4-4.5. D meas = 2.95(5), D calc = 2.89 g/cm3. Kasatkinite is optically biaxial (+), α = 1.600(5), β = 1.603(2), γ = 1.626(2), 2 V meas = 30(20)°, 2 V calc = 40°. The IR spectrum is given. The 11B MAS NMR spectrum shows the presence of BO4 in the absence of BO3 groups. The chemical composition of kasatkinite (wt %; electron microprobe, H2O by gas chromatography) is as follows: 0.23 Na2O, 0.57 K2O, 28.94 CaO, 16.79 BaO, 11.57 B2O3, 0.28 Al2O3, 31.63 SiO2, 0.05 F, 9.05 H2O, -0.02 -O=F2; the total is 99.09. The empirical formula (calculated on the basis of O + F = 41 apfu, taking into account the TGA data) is: Na0.11K0.18Ba1.66Ca7.84B5.05Al0.08Si8.00O31.80(OH)3.06F0.04 · 6.10H2O. Kasatkinite is monoclinic, space group P21/ c, P2/ c, or Pc; the unit-cell dimensions are a = 5.745(3), b = 7.238(2), c = 20.79 (1) Å, β = 90.82(5)°, V = 864(1) Å3, Z = 1. The strongest reflections ( d Å- I[ hkl]) in the X-ray powder diffractions pattern are: 5.89-24[012], 3.48-2.1[006], 3.36-24[114]; 3.009-100[, 121, ], 2

  13. Phase separation enhanced magneto-electric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films

    PubMed Central

    Alberca, A.; Munuera, C.; Azpeitia, J.; Kirby, B.; Nemes, N. M.; Perez-Muñoz, A. M.; Tornos, J.; Mompean, F. J.; Leon, C.; Santamaria, J.; Garcia-Hernandez, M.

    2015-01-01

    We study the origin of the magnetoelectric coupling in manganite films on ferroelectric substrates. We find large magnetoelectric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films in experiments based on the converse magnetoelectric effect. The magnetization changes by around 30–40% upon applying electric fields on the order of 1 kV/cm to the BaTiO3 substrate, corresponding to magnetoelectric coupling constants on the order of α = (2–5)·10−7 s/m. Magnetic anisotropy is also affected by the electric field induced strain, resulting in a considerable reduction of coercive fields. We compare the magnetoelectric effect in pre-poled and unpoled BaTiO3 substrates. Polarized neutron reflectometry reveals a two-layer behavior with a depressed magnetic layer of around 30 Å at the interface. Magnetic force microscopy (MFM) shows a granular magnetic structure of the La0.7Ca0.3MnO3. The magnetic granularity of the La0.7Ca0.3MnO3 film and the robust magnetoelastic coupling at the La0.7Ca0.3MnO3/BaTiO3 interface are at the origin of the large magnetoelectric coupling, which is enhanced by phase separation in the manganite. PMID:26648002

  14. Dynamic coupling-decoupling crossover in the current-driven vortex-state in Tl[sub 2]Ba[sub 2]CaCu[sub 2]O[sub 8]studied using terahertz time-domain spectroscopy

    SciTech Connect

    Thorsmølle, V. K.; Averitt, R. D.; Aranson, I. S.; Maley, M. P.; Bulaevskiĭ, L. N.; Taylor, Antoinette J.,

    2004-01-01

    Employing terahertz time-domain spectroscopy in transmission, they have measured the Josephson plasma resonance in Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} high-T{sub c} thin films, and studied the current-driven coupling-decoupling crossover in the driven vortex lattice.

  15. Phase separation enhanced magneto-electric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films.

    PubMed

    Alberca, A; Munuera, C; Azpeitia, J; Kirby, B; Nemes, N M; Perez-Muñoz, A M; Tornos, J; Mompean, F J; Leon, C; Santamaria, J; Garcia-Hernandez, M

    2015-01-01

    We study the origin of the magnetoelectric coupling in manganite films on ferroelectric substrates. We find large magnetoelectric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films in experiments based on the converse magnetoelectric effect. The magnetization changes by around 30-40% upon applying electric fields on the order of 1 kV/cm to the BaTiO3 substrate, corresponding to magnetoelectric coupling constants on the order of α = (2-5) · 10(-7) s/m. Magnetic anisotropy is also affected by the electric field induced strain, resulting in a considerable reduction of coercive fields. We compare the magnetoelectric effect in pre-poled and unpoled BaTiO3 substrates. Polarized neutron reflectometry reveals a two-layer behavior with a depressed magnetic layer of around 30 Å at the interface. Magnetic force microscopy (MFM) shows a granular magnetic structure of the La0.7Ca0.3MnO3. The magnetic granularity of the La0.7Ca0.3MnO3 film and the robust magnetoelastic coupling at the La0.7Ca0.3MnO3/BaTiO3 interface are at the origin of the large magnetoelectric coupling, which is enhanced by phase separation in the manganite. PMID:26648002

  16. Evaluating controlling factors to Al(i)/(Ca + Mg) molar ratio in acidic soil water, southern and southwestern China: multivariate approach.

    PubMed

    Guo, Jing-Heng; Zhang, Xiao-Shan; Vogt, Rolf D; Xiao, Jin-Song; Zhao, Da-Wei; Xiang, Ren-Jun; Luo, Jia-Hai

    2007-06-01

    Al(i)/(Ca + Mg) molar ratio in soil water has been used as an indicator to the effects of acid deposition on terrestrial ecosystems. However, the main factors controlling this ratio have not been well documented in southern and southwestern China. In this study, we presented the variation in inorganic aluminum (Al(i)) and Al(i)/(Ca + Mg) molar ratio in different sites and soil horizons based on two to three years monitoring data, and evaluated the main factors controlling Al(i)/(Ca + Mg) molar ratio using principle component analysis (PCA) and partial least square (PLS) regression. Monitoring data showed although Al(i)/(Ca + Mg) molar ratios in most soil water were lower than assumed critical 1.0, higher molar ratios were found in some soil water at TSP and LXH site. Besides acid loading, both soil properties and soil water chemistry affected the value of Al(i)/(Ca + Mg) molar ratio in soil water. Partial least square (PLS) indicated that they had different relative importance in different soil horizons. In A-horizon, soil aluminum saturation (AlS) had higher influence on Al(i)/(Ca + Mg) molar ratio than soil water chemistry did; higher soil aluminum saturation (AlS) led to higher Al(i)/(Ca + Mg) molar ratio in soil water. In the deeper horizons (i.e., B(1)-, B(2)- and BC-horizon), inorganic aluminum (Al(i)) in soil water had more and more important role in regulating Al(i)/(Ca + Mg) molar ratio. On regional scale, soil aluminum saturation (AlS) as well as cation exchange capacity (CEC) was the dominant factor controlling Al(i)/(Ca + Mg) molar ratio. This should be paid enough attention on when making regional acid rain control policy in China. PMID:17057971

  17. Biotic and geochemical (δ18O, δ13C, Mg/Ca, Ba/Ca) responses of Globigerinoides ruber morphotypes to upper water column variations during the last deglaciation, Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Antonarakou, A.; Kontakiotis, G.; Mortyn, P. G.; Drinia, H.; Sprovieri, M.; Besiou, E.; Tripsanas, E.

    2015-12-01

    Within the Gulf of Mexico (GOM), the Bryant Canyon is exceptional in that rapid sedimentation sustained by high rates of terrigenous sediment delivery and surface marine productivity make this basin an excellent recorder of paleoenvironmental and paleoclimatic conditions. We present a new 21-kyr record of sea surface temperature (SST) and local salinity changes from the NW GOM (core JPC-26) approximated from combined Globigerinoides ruber morphotype-specific δ18O and Mg/Ca, as well as Ba/Ca, which reflect the subtropical GOM hydrographic dynamics and their relationship to both Mississippi River discharges and climate evolution during the last deglaciation. Overall, the reconstructed SST and SSS-related patterns reveal notable variations in amplitude between the analyzed morphotypes, adding valuable insights to previously published G. ruber (w, mixed) GOM records. Especially during the deglaciation, Bryant Canyon meltwater flooding events (BCDFs) and associated sea surface freshening seem to be more pronounced than the SST reduction. Our Mg/Ca-derived SST records of both morphotypes (G. ruber sensu stricto (s.s.) and G. ruber sensu lato (s.l.)) show comparable general trends, but with important SST differences (ΔT). We interpret down-core ΔT as a record of changing upper water column hydrography, with particular influence from the deglacial meltwater (BCDFs) or Holocene (BCHFs) flooding events. During the warm intervals, the deeper, thicker and probably more seasonally persistent mixed layer led to more uniform thermal conditions for both G. ruber morphotypes and therefore to a minimum ΔT. On the contrary, during the cold and low salinity periods, the shallower mixed layer favored more habitat divergence, and caused a maximum thermal gradient in the well-stratified upper water column. Overall, this supports the notion that G. ruber s.s. is consistently calcifying in warmer waters than G. ruber s.l., either due to a shallower depth habitat or to a more summer

  18. Photocatalytic properties of CoOx-loaded nano-crystalline perovskite oxynitrides ABO2N (A = Ca, Sr, Ba, La; B = Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Oehler, Florian; Ebbinghaus, Stefan G.

    2016-04-01

    Highly crystalline niobium- and tantalum-based oxynitride perovskite nanoparticles were obtained from hydrothermally synthesized oxide precursors by thermal ammonolysis at different temperatures. The samples were studied with respect to their morphological, optical and thermal properties as well as their photocatalytic activity in the decomposition of methyl orange. Phase pure oxynitrides were obtained at rather low ammonolysis temperatures between 740 °C (CaNbO2N) and 1000 °C (BaTaO2N). Particle sizes were found to be in the range 27 nm-146 nm and large specific surface areas up to 37 m2 g-1 were observed. High photocatalytic activities were found for CaNbO2N and SrNbO2N prepared at low ammonolysis temperatures. CoOx as co-catalyst was loaded on the oxynitride particles resulting in a strong increase of the photocatalytic activities up to 30% methyl orange degradation within 3 h for SrNbO2N:CoOx.

  19. Tululite, Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36: a new Ca zincate-aluminate from combustion metamorphic marbles, central Jordan

    NASA Astrophysics Data System (ADS)

    Khoury, Hani N.; Sokol, Ella V.; Kokh, Svetlana N.; Seryotkin, Yurii V.; Nigmatulina, Elena N.; Goryainov, Sergei V.; Belogub, Elena V.; Clark, Ian D.

    2016-02-01

    Tululite (Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36 (the hypothetical end-member formula Ca14{Fe3+O6}[SiO4][Zn5Al9]O26) (IMA2014-065) is a new natural Ca zincate-aluminate, identified in medium-temperature (800-850 °C) combustion metamorphic (CM) spurrite-fluorellestadite marbles from central Jordan. The type locality (Tulul Al Hammam area) is situated in the northern part of the Siwaqa complex, the largest area of the "Mottled Zone" Formation in the Dead Sea region. The marbles originated from bitumen-rich chalky marine sediments of the Maastrichtian-Paleogene Muwaqqar Chalk Marl Formation, which have low clay content (and, consequently, low Al) and high Zn, Cd, and U enrichments. The bulk CM rocks derived from the low-Al protolith have unusually high (Zn + Cd)/Al ratios ( 0.2) and, as a result, a mineralogy with negligibly small percentages of Ca aluminates having low Ca:Al molar ratios (minerals of mayenite supergroup, Ca:Al = 6:7) common to most of calcareous CM rocks in the Mottled Zone. Instead, the mineral assemblage of the Zn-rich marbles contains tululite, with high Ca:Al = 2.55 molar ratios and Zn substituting for a large portion of Al (Zn:Al = 1.1). Tululite occurs in thin clusters as irregular grains with indented outlines (20-100 μm in size), having typical open-work textures associated with rock-forming calcite, fluorellestadite, spurrite, and accessory Zn-rich periclase, lime-monteponite solid solutions, calcium uranates, and zincite. Marbles also bear brownmillerite, dorrite, fluormayenite, high-fluorine Ca aluminate, and lakargiite. Secondary phases are brucite, gel-like calcium silicate hydrates and calcium silicate aluminate hydrates, including Zn- and U-bearing and Cd-rich compounds, Si-bearing hydrated compounds after calcium uranates, and basic Cd chlorides. The empirical formula of the holotype tululite (a mean of 32 analyses) is (Ca13.29Cd0.75)Σ14.04(Al5.46Zn5.20Fe3+ 2.23Si0.95Mn3+ 1.01Mg0.78P0.41)Σ16.04O36. Tululite is cubic, space

  20. Eu2+ and Mn2+ Co-doped BaMgAl10O17 Blue- and Green-Emitting Phosphor: A Luminescence and EPR Study

    NASA Astrophysics Data System (ADS)

    Singh, Vijay; Sivaramaiah, G.; Rao, J. L.; Singh, N.; Srivastava, Anoop K.; Jirimali, H. D.; Li, J.; Gao, H.; Kumaran, R. Senthil; Singh, Pramod K.; Dhoble, S. J.

    2016-06-01

    Eu2+ and Mn2+ co-doped BaMgAl10O17 phosphor has been prepared by a solution combustion method. The structural, morphological and compositional analysis of the BaMgAl10O17:Eu2+ and Mn2+ powders have been studied by x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. The electron paramagnetic resonance (EPR) spectrum exhibited resonance signals with the effective g values of g ≈ 4.88 and g ≈ 1.98. The resonance signal with the effective g value of g ≈ 4.88 is characteristic of Eu2+ ions whereas g ≈ 1.98 is due to Mn2+ ions. The number of spins participating in resonance, Gibbs free energy, magnetic susceptibility, Curie constant, effective magnetic moment, zero-field splitting parameter and hyperfine splitting constant have been evaluated. From optical and EPR correlation, it is inferred that Eu2+ and Mn2+ are present in the BaMgAl10O17 matrix.

  1. High mobility field effect transistor based on BaSnO{sub 3} with Al{sub 2}O{sub 3} gate oxide

    SciTech Connect

    Park, Chulkwon; Kim, Useong; Ju, Chan Jong; Park, Ji Sung; Kim, Young Mo; Char, Kookrin

    2014-11-17

    We fabricated an n-type accumulation-mode field effect transistor based on BaSnO{sub 3} transparent perovskite semiconductor, taking advantage of its high mobility and oxygen stability. We used the conventional metal-insulator-semiconductor structures: (In,Sn){sub 2}O{sub 3} as the source, drain, and gate electrodes, Al{sub 2}O{sub 3} as the gate insulator, and La-doped BaSnO{sub 3} as the semiconducting channel. The Al{sub 2}O{sub 3} gate oxide was deposited by atomic layer deposition technique. At room temperature, we achieved the field effect mobility value of 17.8 cm{sup 2}/Vs and the I{sub on}/I{sub off} ratio value higher than 10{sup 5} for V{sub DS} = 1 V. These values are higher than those previously reported on other perovskite oxides, in spite of the large density of threading dislocations in the BaSnO{sub 3} on SrTiO{sub 3} substrates. However, a relatively large subthreshold swing value was found, which we attribute to the large density of charge traps in the Al{sub 2}O{sub 3} as well as the threading dislocations.

  2. Glass structure and NIR emission of Er3+ at 1.5 μm in oxyfluoride BaF2-Al2O3-B2O3 glasses

    NASA Astrophysics Data System (ADS)

    Shinozaki, Kenji; Pisarski, Wojciech; Affatigato, Mario; Honma, Tsuyoshi; Komatsu, Takayuki

    2015-12-01

    The glass structure, photoluminescence properties of Eu3+, Judd-Ofelt analysis, and near infrared emissions of Er3+ at 1.5 μm in the oxyfluoride glasses and glass-ceramics of 1Eu2O3- or 1Er2O3-doped 50BaF2-xAl2O3-(50 - x)B2O3 (x = 0-25 mol%) were investigated. It was clarified on the ground of Raman scattering spectroscopy and F1s and O1s XPS measurements that the glass with no Al2O3 (1Er2O3-50BaF2-50B2O3) is composed of BO3, BO2F and BO3F units with F-Ba bonds. The glasses with 25Al2O3 (1Er2O3-50BaF2-25Al2O3-25B2O3) is mainly composed of BO3- and Al(O,F)x units. Existence of non-bridging oxygen was not detected by O1s-XPS spectra. It was proposed that these structures are largely affected on crystallization behavior, e.g., the glass with no Al2O3 forms BaF2 and β-BaB2O4 due to Ba-F bonds and the glass with 25Al2O3 forms BaAlBO3F2 because the glass structure composed of BO3 and Al(O,F) units is similar to the BaAlBO3F2 crystal structure. Judd-Ofelt parameters of Er3+ and Eu3+ in the glasses showed almost the same values in Ω4 and Ω6 for each glass, on the other hand Ω2 decreased with addition of Al2O3. The emission spectra of Er3+ at 1.5 μm in the glasses and glass-ceramics with BaAlBO3F2 crystals showed broad peaks. It is proposed that oxyfluoride glasses and glass-ceramics based on the BaF2-Al2O3-B2O3 system have a high potential for optical device applications such as broadband optical amplifiers.

  3. High Permittivity (1 - x)Ba(Zr(0.2)Ti(0.8))O3 - x(Ba(0.7)Ca(0.3))TiO3 (x = 0.45) Epitaxial Thin Films with Nanoscale Phase Fluctuations.

    PubMed

    Scarisoreanu, Nicu D; Craciun, Floriana; Moldovan, Antoniu; Ion, Valentin; Birjega, Ruxandra; Ghica, Corneliu; Negrea, Raluca F; Dinescu, Maria

    2015-11-01

    Epitaxial (1 - x)Ba(Ti0.8Zr0.2)TiO3 - x(Ba0.7Ca0.3)TiO3, x = 0.45 (BCZT 45), thin films have been deposited on (001) SrTiO3 (STO) and (001/100) SrLaAlO4 (SLAO) substrates by pulsed laser deposition. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) confirmed the epitaxial growth of the films. A high structural quality has been evidenced for the BCZT/STO films. Geometric phase analysis (GPA) associated with the HRTEM enabled us to obtain microstrain analysis and the in-plane and out-of-plane lattice parameter variation on different areas. Tetragonality ratio fluctuations at nanoscale level which are relevant for the existence of nanodomains have been evidenced on the BCZT/STO films. The in-plane dielectric constant has been measured on interdigital electrodes deposited by lift-off technique on the top of the films. High values of dielectric permittivity (>3000) combined with low dielectric loss (<0.01) are obtained for BCZT 45 film deposited on STO substrate, showing nearly constant values between 1 kHz and 10 MHz. The high dielectric permittivity of BCZT thin films was attributed to their high structural quality and to the loss of rotation stability of the polarization associated with the presence of nanodomains. This results into a divergence of fluctuations of polarization direction and a peak of dielectric susceptibility. The enhanced switching of such nanodomain configuration was probed by piezoforce microscopy, by writing and reading domains during topography scanning. PMID:26488203

  4. Accelerator mass spectrometry with fully stripped 26Al, 63Cl, 41Ca and (su59)Ni ions

    NASA Astrophysics Data System (ADS)

    Faestermann, H.; Kato, K.; Korschinek, G.; Krauthan, P.; Nolte, E.; Rühm, W.; Zerle, L.

    1990-04-01

    The detection system of accelerator mass spectrometry (AMS) with completely stripped ions of 26Al, 36Cl, 41Ca and 59Ni at the Munich accelerator laboratory and measurements with these ions are presented. Detection limits are given. The presented applications are: dating of groundwater of the Milk River aquifer and deduction of the neutron fluence and spectrum of the Hiroshima A-bomb.

  5. Progress in the material development of LiCaAlF sub 6 :Cr sup 3+ laser crystals

    SciTech Connect

    Michelle D. Shinn.; Chase, L.L.; Caird, J.A.; Payne, S.A.; Atherton, L.J.; Kway, W.L.

    1990-03-01

    High Cr{sup 3+} doping levels, up to 8 mole percent, and low losses have been obtained with the tunable solid-state laser material LiCaAlF{sub 6}:Cr{sup 3+} (Cr:LiCAF). Measurements and calculations show that high pumping and extraction efficiencies are possible with the improved material. 13 refs., 4 figs., 1 tab.

  6. Photoelectron velocity-map imaging and theoretical studies of heteronuclear metal carbonyls MNi(CO)3 (-) (M = Mg, Ca, Al).

    PubMed

    Xie, Hua; Zou, Jinghan; Yuan, Qinqin; Fan, Hongjun; Tang, Zichao; Jiang, Ling

    2016-03-28

    The heteronuclear metal carbonyl anions MNi(CO)3 (-) (M = Mg, Ca, Al) have been investigated using photoelectron velocity-map imaging spectroscopy. Electron affinities of neutral MNi(CO)3 (M = Mg, Ca, Al) are measured from the photoelectron spectra to be 1.064 ± 0.063, 1.050 ± 0.064, and 1.541 ± 0.040 eV, respectively. The C-O stretching mode in these three clusters is observed and the vibrational frequency is determined to be 2049, 2000, and 2041 cm(-1) for MgNi(CO)3, CaNi(CO)3, and AlNi(CO)3, respectively. Density functional theory calculations are carried out to elucidate the geometric and electronic structures and to aid the experimental assignments. It has been found that three terminal carbonyls are preferentially bonded to the nickel atom in these heterobinuclear nickel carbonyls MNi(CO)3 (-1/0), resulting in the formation of the Ni(CO)3 motif. Ni remains the 18-electron configuration for MgNi(CO)3 and CaNi(CO)3 neutrals, but not for AlNi(CO)3. This is different from the homobinuclear nickel carbonyl Ni-Ni(CO)3 with the involvement of three bridging ligands. Present findings would be helpful for understanding CO adsorption on alloy surfaces. PMID:27036444

  7. Photoelectron velocity-map imaging and theoretical studies of heteronuclear metal carbonyls MNi(CO)3- (M = Mg, Ca, Al)

    NASA Astrophysics Data System (ADS)

    Xie, Hua; Zou, Jinghan; Yuan, Qinqin; Fan, Hongjun; Tang, Zichao; Jiang, Ling

    2016-03-01

    The heteronuclear metal carbonyl anions MNi(CO)3- (M = Mg, Ca, Al) have been investigated using photoelectron velocity-map imaging spectroscopy. Electron affinities of neutral MNi(CO)3 (M = Mg, Ca, Al) are measured from the photoelectron spectra to be 1.064 ± 0.063, 1.050 ± 0.064, and 1.541 ± 0.040 eV, respectively. The C-O stretching mode in these three clusters is observed and the vibrational frequency is determined to be 2049, 2000, and 2041 cm-1 for MgNi(CO)3, CaNi(CO)3, and AlNi(CO)3, respectively. Density functional theory calculations are carried out to elucidate the geometric and electronic structures and to aid the experimental assignments. It has been found that three terminal carbonyls are preferentially bonded to the nickel atom in these heterobinuclear nickel carbonyls MNi(CO)3-1/0, resulting in the formation of the Ni(CO)3 motif. Ni remains the 18-electron configuration for MgNi(CO)3 and CaNi(CO)3 neutrals, but not for AlNi(CO)3. This is different from the homobinuclear nickel carbonyl Ni-Ni(CO)3 with the involvement of three bridging ligands. Present findings would be helpful for understanding CO adsorption on alloy surfaces.

  8. Stabilization of moisture-reactive raw materials for improved synthesis of Ca-α-SiAlON:Eu2+ phosphor

    NASA Astrophysics Data System (ADS)

    Kim, Jin-Myung; Kim, Mi-Ju; Lee, Jae-Wook; Park, Young-Jo

    2014-09-01

    The raw materials needed to make the Ca-α-SiAlON:Eu2+ phosphor contain highly moisture-reactive Ca3N2. Exposing them to a preheating process prior to high-temperature synthesis stabilized the raw materials against oxidation. Preheating above 1200 °C in a tube furnace directly connected to a glove box, resulted in the formation of intermediate phases such as CaAlSiN3, which provided higher moisture resistance to the raw materials. We found that even after exposure to a humid environment, the preheated samples maintained PL characteristics similar to the conventional unexposed samples, while the PL intensity and particle homogeneity of the un-preheated samples were severely deteriorated.

  9. The effect of grain size on the fluctuation-induced conductivity of Cu1-xTlxBa2Ca3Cu4O12-δ superconductor thin films

    NASA Astrophysics Data System (ADS)

    Khurram, A. A.; Mumtaz, M.; Khan, Nawazish A.; Ahadian, M. M.; Iraji-zad, Azam

    2007-08-01

    The high temperature superconductor thin films Cu1-xTlxBa2Ca3Cu4O12-δ (Cu1-xTlx- 1234) are post-annealed in a nitrogen atmosphere. The zero-resistivity critical temperature (Tc(R = 0)) of these thin films is increased from 92.3 to 104 K. The grain size is enhanced and their morphology is improved with the post-annealing. The enlargement of grain size is linked to fluctuation-induced conductivity (FIC) in the light of Aslamazov-Larkin (AL) theory. The FIC measurements have shown that the cross-over of three-dimensional (3D) to two-dimensional (2D) behaviour of fluctuations is shifted to higher temperature values with an increase of post-annealing temperature. These results have shown that the removal of oxygen and the increased grain size are the most likely sources of the increase in the cross-over temperature, T* to higher values.

  10. Czochralski growth of single-crystal gehlenite (Ca 2Al 2SiO 7)

    NASA Astrophysics Data System (ADS)

    Finch, C. B.; Ball, F. L.; Bates, J. B.

    1981-09-01

    Single-crystal boules of gehlenite (Ca 2Al 2SiO 7) were grown from even- and off-stoichiometry melts under differing conditions of oxygen fugacity (ƒ O2). Growth was accomplished by the Czochralski method at 1600°C and 10 5 Pa (1 atm) total pressure, using inductively heated Ir or Pt-20%Rh crucibles. The supra melt gas ambients included air ( ƒ O2 = 0.2 × 10 4Pa), Ar (10 Pa), Ar-50%CO 2-2%H 2 (10 -2 Pa), and Ar-4%H 2-1.5%H 2O (10 -4 Pa). Colorless, transparent material up to 8 mm diam. by 15 mm long was obtained from the evenly stoichiometric melt composition under Ar at growth rates of 1.5 mm/h or less. Growth at rates exceeding 2 mm/h or growth at a high ƒ O2 (e.g., air), led to the formation of bubbles and elongated voids or inclusions, predominantly in the core regions of boules. Optical, X-ray diffraction, and electron-induced X-ray flourescence data are included.

  11. Experimentally Produced Spinel Rims on Ca-Al-Rich Inclusion Bulk Compositions

    NASA Technical Reports Server (NTRS)

    Paque, Julie M.; Le, L.; Lofgren, G. E.

    1998-01-01

    Most Ca-Al-rich inclusions (CAls) from Allende are surrounded by a series of mineralogically distinct rim layers. Proposed modes of formation for these layers include flash heating, evaporation, and condensation. The innermost of these rim layers is generally spinel (SP), in some cases intergrown with perovskite (PV), and commonly containing varying amounts of secondary iron increasing towards the edge of the CAI. The SP or SP+PV rim is not always contiguous with the other rim layers, indicating that it is probably the result of a separate event. We have produced continuous SP rims on synthetic analogs representing Type A/B1, average Type B, and Type B2 bulk compositions by reheating a solid glass experimental charge to subliquidus crystallization temperatures. This experimental result is consistent with the formation of chondrules; and CAIs by more than one sequence of heating and cooling. Previous work indicated that prior crystallization events produced observable effects in the texture and chemistry of the final run product. Information on the nature of the heating/cooling cycles experienced by CAls and chondrules is important in modeling the environment of their formation. Additional information is contained in the original extended abstract.

  12. Luminescence properties of a solid solution typed (Ba,Ca)3MgSi2O8: Eu2+, Mn2+ phosphor with a 660 nmfeatured photosynthetic action spectrum

    NASA Astrophysics Data System (ADS)

    Song, Jun; Sun, Liang; Li, Jian; Ma, Jian; Wang, Da-jian

    2014-09-01

    A solid-solution-phase Ba1.75Ca1.25MgSi2O8: Eu2+, Mn2+ phosphor in the photosynthetic action spectrum with dual band emissions at 438 nm and 660 nm is fabricated. X-ray diffraction (XRD) confirms the presence of the solid-solution phase. With the supporting information from the diffuse reflection spectrum, a feasible way to obtain higher energy-transfer (ET) efficiency is attained, and the ET efficiency of Eu2+-Mn2+ is enhanced to 76%. The mechanism of this enhancement is owing to variation of the solid solution composition of Ca3MgSi2O8 and Ba3MgSi2O8, which contributes to the extension of the critical distance. Temperature-dependent results show an enhancement which is attributed to Ca. These enhancements show great promise for improving eco-lighting devices.

  13. Discharge properties of Mg-Al-Mn-Ca and Mg-Al-Mn alloys as anode materials for primary magnesium-air batteries

    NASA Astrophysics Data System (ADS)

    Yuasa, Motohiro; Huang, Xinsheng; Suzuki, Kazutaka; Mabuchi, Mamoru; Chino, Yasumasa

    2015-11-01

    The discharge behaviors of rolled Mg-6 mass%Al-0.3 mass%Mn-2 mass%Ca (AMX602) and Mg-6 mass%Al-0.3 mass%Mn (AM60) alloys used as anodes for Magnesium-air batteries were investigated. The AMX602 alloy exhibited superior discharge properties compared to the AM60 alloy, especially at low current density. The discharge products of the AMX602 alloy were dense and thin, and many cracks were observed at all current densities. In addition, the discharge products were detached at some sites. These sites often corresponded to the positions of Al2Ca particles. The comparison of the discharge and corrosion tests indicated that the dense and thin discharge products of AMX602 were easily cracked by dissolution of the Mg matrix around Al2Ca particles, and the cracks promoted the penetration of the electrolyte into the discharge products, retaining the discharge activity. In contrast, concerning the AM60 alloy, thick discharge products were formed on the surface during discharge, and cracking of the discharge products hardly occurred, degrading the discharge properties. Localized and deeply corroded pits that could result from the detachment of metal pieces from the anode during discharge were partly observed in the AM60 alloy. It is suggested that these detached metal pieces are another reason for the low discharge properties of the AM60 alloy.

  14. Nucleosynthetic W isotope anomalies and the Hf-W chronometry of Ca-Al-rich inclusions

    NASA Astrophysics Data System (ADS)

    Kruijer, Thomas S.; Kleine, Thorsten; Fischer-Gödde, Mario; Burkhardt, Christoph; Wieler, Rainer

    2014-10-01

    Ca-Al-rich inclusions (CAI) are the oldest dated objects formed in the solar system and are pivotal reference points in early solar system chronology. Knowledge of their initial 182Hf/180Hf and 182W/184W is essential, not only for obtaining precise Hf-W ages relative to the start of the solar system, but also to assess the distribution of short-lived radionuclides in the early solar nebula. However, the interpretation of Hf-W data for CAI is complicated by nucleosynthetic W isotope variations. To explore their extent and nature, and to better quantify the initial Hf and W isotope compositions of the solar system, we obtained Hf-W data for several fine- and coarse-grained CAI from three CV3 chondrites. The fine-grained CAI exhibit large and variable anomalies in ε183W (εiW equals 0.01% deviation from terrestrial values), extending to much larger anomalies than previously observed in CAI, and reflecting variable abundances of s- and r-process W isotopes. Conversely, the coarse-grained (mostly type B) inclusions show only small (if any) nucleosynthetic W isotope anomalies. The investigated CAI define a precise correlation between initial ε182W and ε183W, providing a direct empirical means to correct the ε182W of any CAI for nucleosynthetic isotope anomalies using their measured ε183W. After correction for nucleosynthetic W isotope variations, the CAI data define an initial 182Hf/180Hf of (1.018±0.043)×10-4 and an initial ε182W of -3.49±0.07. The Hf-W formation intervals of the angrites D'Orbigny and Sahara 99555 relative to this CAI initial is 4.8±0.6 Ma, in good agreement with Al-Mg ages of these two angrites. This renders a grossly heterogeneous distribution of 26Al in the inner solar system unlikely, at least in the region were CAI and angrites formed.

  15. Constraints on Titanite Acitvity in the System CaTiSiO4O-CaAlSiO4F: Implications for Thermobarometry in Metamorphic Rocks

    NASA Astrophysics Data System (ADS)

    Tropper, P.; Manning, C. E.; Essene, E. J.

    2006-12-01

    Titanite is a common accessory mineral that could be used reliably in phase equilibrium calculations, if activity-composition relations in Al-F titanites were known. Troitzsch and Ellis (2001, CMP, 142, 543) and Tropper et al. (2002, JPet., 43, 1787) gave non-ideal mixing models along the join CaTiSiO4O- CaAlSiO4F. Tropper et al. (2002) derived a negative interaction parameter W, whereas Troitzsch and Ellis (2001) derived a regular model with both positive and negative W, but favored positive values. These differences strongly influence calculated CaTiSiO4O activity (attn). Although more experiments are needed, our result that γttn<1 at high T indicates a large degree of non-ideal behavior, even at >900°C, which in turn will affect thermobarometry. Comparing available activity models shows that at these T, attn is substantially underestimated by the fully ionic model used by Manning and Bohlen (1991, CMP, 109, 1), in which attn = XCaXTiXSi(XO)5. This model assumes independent mixing of Al for Ti and random mixing of F and O on all O sites. However, F substitutes only in one O site (O1; Oberti et al., 1991, EJM, 3, 777). A fully ionic model should therefore be recast as attn = XCaXTiXSiXO, where XO indicates the mole fraction of O on the (O1) site. The substitution of F on the O1 site is coupled with Al, so it is called the ideal coupled model. Unlike the regular model, the prefered ionic model departs strongly from ideality at ≤600°C, consistent with independent constraints. However, experimentally determined attn is approximated by an ideal molecular model (XTi) at ≥900°C, so this model is recommended for thermobarometry in high- T metamorphic rocks until more data are available. Recalculation of the P recorded by the three eclogites from Manning and Bohlen (1991) using the different activity models discussed here yields differences that may be as high as 2.0 GPa.

  16. Microstructure and Fatigue Behavior of Friction Stir-welded Noncombustive Mg-9Al-Zn-Ca Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Zhou, L.; Li, Z. Y.; Nakata, K.; Feng, J. C.; Huang, Y. X.; Liao, J. S.

    2016-06-01

    Microstructure and fatigue behavior of friction stir-welded noncombustive Mg-9Al-Zn-Ca magnesium alloy were investigated. The as-received hot-extruded material consisted of equiaxed α-Mg grains with β-Mg17Al12 and Al2Ca compounds distributed along the grain boundaries. Friction stir welding produced much refined α-Mg grains accompanied by the dissolution of the eutectic β-Mg17Al12 phase, while Al2Ca phase was dispersed homogenously into the Mg matrix. Friction stir welding produced slightly increased hardness and tensile strength in the defect-free welds compared with the base material due to microstructural refinement and uniform distribution of intermetallic compounds. The load-controlled uniaxial tensile high-cycle fatigue tests indicated that fatigue strength of 90 MPa was obtained for the friction stir-welded joint with fatigue crack initiated basically near the specimen's surface and at the retreating side of the joint. Crack propagation was characterized by cleavage and fatigue striations.

  17. Antiferromagnetism in CaAl2Si2-type CaMn2As2 and SrMn2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; Johnston, D. C.

    Magnetic susceptibility versus temperature χ (T) measurements of CaMn2As2 and SrMn2As2 crystals show clear antiferromagnetic (AFM) transitions at TN ~ 65 K and 120 K,1 respectively. The anisotropic behaviors in χ (T <=TN) suggest that both compounds are noncollinear antiferromagnets which may result either from an intrinsic noncollinear structure or from multiple collinear AFM domains that are not aligned collinearly.2 The χ (T) data at T >TN reveal that both compounds exhibit strong short-range AFM ordering, evidently associated with quasi-two-dimensional spin lattices. The electrical resistivities show insulating ground states with activation energies of ~ 63 meV in CaMn2As2 and 44 meV in SrMn2As2 . The experimental results thus reveal that both (Ca , Sr) Mn2As2 materials are AFM insulators at low temperatures and in analogy with the high Tc cuprates, may be potential parent compounds for CaAl2Si2-type superconductors. Work was supported by the USDOE under Contract No. DE-AC02-07CH11358.

  18. Core-shell-shell heterostructures of α-NaLuF4:Yb/Er@NaLuF4:Yb@MF2 (M = Ca, Sr, Ba) with remarkably enhanced upconversion luminescence.

    PubMed

    Su, Yue; Liu, Xiuling; Lei, Pengpeng; Xu, Xia; Dong, Lile; Guo, Xianmin; Yan, Xingxu; Wang, Peng; Song, Shuyan; Feng, Jing; Zhang, Hongjie

    2016-07-01

    Core-shell-shell heterostructures of α-NaLuF4:Yb/Er@NaLuF4:Yb@MF2 (M = Ca, Sr, Ba) have been successfully fabricated via the thermal decomposition method. Upconversion nanoparticles (UCNPs) were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), upconversion luminescence (UCL) spectroscopy, etc. Under 980 nm excitation, the emission intensities of the UCNPs are remarkably enhanced after coating the MF2 (M = Ca, Sr, and Ba) shell. Among these samples, CaF2 coated UCNPs show the strongest overall emission, while BaF2 coated UCNPs exhibit the longest lifetime. These results demonstrate that alkaline earth metal fluorides are ideal materials to improve the UCL properties. Meanwhile, although the lattice mismatch between the ternary NaREF4 core and the binary MF2 (M = Sr and Ba) shell is relatively large, the successfully synthesized NaLuF4:Yb/Er@NaLuF4:Yb@MF2 indicates a new outlook on the fabrication of heterostructural core-shell UCNPs. PMID:27327414

  19. Phase equilibrium and structural properties in the Ca-Al-Si-O system up to the P,T conditions of the Earth's lowermost transition zone.

    NASA Astrophysics Data System (ADS)

    Gréaux, S.; Nishiyama, N.; Kono, Y.; Shinmei, T.; Irifune, T.

    2008-12-01

    Ca- and Al-bearing silicates have been extensively investigated for their importance into the mantle processes. In the transition zone, majorite garnet and Ca-perovskite are reported to be the major hosts of Ca as well as deposits of Al [1]. At higher P, Ca gets completely exsolved from the majorite to the Ca-pv. It is observed that Al plays a significant role in the Ca-Si-O system by inducing new phase equilibriums [2,3,4], and influencing the physical properties of the Ca-pv [5]. It is then suggested that phase transitions and chemical reactions involving Ca- and Al-bearing silicates could conciliate mineralogical results and seismological observations in the region of the transition zone [3,6]. We studied the phase equilibrium at HP-HT in the grossular and anorthite systems using a Kawai-type multi- anvil apparatus up to 25 GPa and 2000 K. Grossular garnet is reported to decompose into a mix of corundum and Ca-pv [3] or to transform into a perovskite of grossular composition [7]. Our study shows that grossular mainly decomposes into a mix of Al-Ca-pv and CAS phase in the same P range and higher T. Anorthite is also found to mainly decompose into a mix of Al-Ca-pv and CAS phase. Despite some Al-content in the Ca-pv, the CAS phase is the major host of Al, which suggests according to previous studies [3,5], a lower solubility of Al into the perovskite structure at high T. The Al-content of the Ca-pv as well as the presence of another Al-rich Ca-bearing silicate in zone of variable temperatures and composition as subducting slabs are discussed for their possible implication into the transition zone processes. [1] T. Irifune, 1994. Nature 370, 131-133 [2] L. Gautron et al., 1996. Phys. Earth Planet. Int. 94, 71-81 [3] N. Takafuji et al., 2002. Phys. Chem. Mineral 29, 532-537 [4] S. Zhai and E. Ito, 2008. Phys. Earth Planet. Int. In press [5] T. Kurashina et al., 2004. Phys. Earth Planet. Int. 145, 67-7 [6] L. Stixrude et al., 1996. Am. Mineral. 81, 1293-1296 [7] H

  20. Structural and dielectric properties of A(Fe{sub 1/2}Ta{sub 1/2})O{sub 3} [A = Ba, Sr, Ca

    SciTech Connect

    Dutta, Alo

    2011-04-15

    Graphical abstract: FTIR spectra of BFT, SFT and CFT at room temperature. Research highlights: {yields} The structural and dielectric properties of BaFe{sub 1/2}Ta{sub 1/2}O{sub 3}, SrFe{sub 1/2}Ta{sub 1/2}O{sub 3} and CaFe{sub 1/2}Ta{sub 1/2}O{sub 3}. {yields} Fourier transform infrared spectra show two primary phonon modes of the samples at around 450 cm{sup -1} and 620 cm{sup -1}. {yields} The compounds show significant frequency dispersion in its dielectric properties. {yields} The relaxation mechanism of the samples is modelled by Cole-Cole equation. -- Abstract: The complex perovskite oxide barium iron tantalate (BFT), BaFe{sub 1/2}Ta{sub 1/2}O{sub 3}, strontium iron tantalate (SFT), SrFe{sub 1/2}Ta{sub 1/2}O{sub 3} and calcium iron tantalate (CFT), CaFe{sub 1/2}Ta{sub 1/2}O{sub 3} are synthesized by a solid-state reaction technique. Rietveld refinement of the X-ray diffraction data of the samples shows that BFT and SFT crystallize in cubic structure, with lattice parameter a = 4.06 A for BFT and 3.959 A for SFT, whereas CFT crystallizes in orthorhombic structure having lattice parameters a = 5.443 A, b = 5.542 A and c = 7.757 A. Fourier transform infrared spectra show two primary phonon modes of the samples at around 450 cm{sup -1} and 620 cm{sup -1}. The compounds show significant frequency dispersion in its dielectric properties. The complex impedance plane plots of the samples show that the relaxation (conduction) mechanism in these materials is purely a bulk effect arising from the semiconductive grains. The relaxation mechanism of the samples is modelled by Cole-Cole equation. The frequency dependent conductivity spectra are found to follow the power law.

  1. Nanocrystalline Ba{sub 0.97}Ca{sub 0.03}SO{sub 4}:Eu for ion beams dosimetry

    SciTech Connect

    Lochab, S. P.; Kanjilal, D.; Salah, Numan; Habib, Sami S.; Lochab, Jyoti; Ranjan, Ranju; Aleynikov, V. E.; Rupasov, A. A.; Pandey, A.

    2008-08-01

    Nanoparticles of Ba{sub 0.97}Ca{sub 0.03}SO{sub 4}:Eu have been irradiated by 48 MeV Li{sup 3+}, 75 MeV C{sup 6+}, and 90 MeV O{sup 7+} ion beams with a fluence range of 1x10{sup 9}-1x10{sup 13} ion/cm{sup 2}. The thermoluminescence (TL) glow curves along with the response curves of this nanophosphor have been investigated and compared with those of the corresponding microcrystalline samples. TL glow curve of the nanophosphor exposed to {gamma}-rays has also been included in the letter with the aim of reporting some of the comparative measurements. The glow curves of the ion-beam irradiated nanomaterials are similar in their shapes to those induced by gamma rays, with a shift in the peak positions to the higher temperature side by around 30 K. The TL intensity of the ion-beam irradiated nanomaterials is found to decrease, while going from low to high atomic number (Z) ions (i.e., Li{sup 3+}{yields}O{sup 7+}). Similar trend was also observed in the linearity of the TL response curves. The response curve of Li ion irradiated nanomaterials is sublinear in the whole range of studied fluences. C ion has also a more or less similar response, while the O ion has a sublinear response over a shorter range of 1x10{sup 9}-1x10{sup 12} ion/cm{sup 2}, and above this range the response saturates. These results for the nanomaterials are much better than that of the corresponding microcrystalline sample irradiated by Li{sup 3+} ions. The curve was sublinear up to the fluence 1x10{sup 10} ion/cm{sup 2} and then saturates at higher fluences. The wider sublinear TL response of the nanocrystalline Ba{sub 0.97}Ca{sub 0.03}SO{sub 4}:Eu makes it superior to its corresponding microform and thus makes it a suitable candidate as a dosimeter to be used for detecting the doses of ions, especially the Li and C ions for their application in cancer radiotherapy and radiation biology.

  2. Effect of SiO2 on the Crystallization Behaviors and In-Mold Performance of CaF2-CaO-Al2O3 Slags for Drawing-Ingot-Type Electroslag Remelting

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-Bin; Li, Jing; Cho, Jung-Wook; Jiang, Fang; Jung, In-Ho

    2015-10-01

    The crystallization characteristics of CaF2-CaO-Al2O3 slags with varying amounts of SiO2 were experimentally studied. The effects of slag crystallization behaviors on the horizontal heat transfer and lubrication performance in drawing-ingot-type electroslag remelting (ESR) were also evaluated in terms of as-cast ingots surface quality and drawing-ingot operation. The results show that increasing SiO2 addition from 0 to 6.8 mass pct strongly suppresses the crystallization of ESR type CaF2-CaO-Al2O3 slags. The crystallization temperature of the studied slags decreases with the increase in SiO2 addition. The liquidus temperatures of the slags also show a decreasing trend with increasing SiO2 content. In CaF2-CaO-Al2O3-(SiO2) slags, faceted 11CaO·7Al2O3·CaF2 crystals precipitate first during continuous cooling of the slag melts, followed by the formation of CaF2 at lower temperatures. 11CaO·7Al2O3·CaF2 was confirmed to be the dominant crystalline phase in the studied slags. CaF2-CaO-Al2O3 slags with a small amount of SiO2 addition are favorable for providing sound lubrication and horizontal heat transfer in mold for drawing-ingot-type ESR, which consequently bring the improvement in the surface quality of ESR ingot and drawing-ingot operating practice as demonstrated by plant trials.

  3. Thermoluminescence and synchrotron radiation studies on the persistent luminescence of BaAl{sub 2}O{sub 4}:Eu{sup 2+},Dy{sup 3+}

    SciTech Connect

    Rodrigues, L.C.V.; Stefani, R.; Brito, H.F.; Felinto, M.C.F.C.; Hoelsae, J.; Lastusaari, M.; Laamanen, T.; Malkamaeki, M.

    2010-10-15

    The persistent luminescence materials, barium aluminates doped with Eu{sup 2+} and Dy{sup 3+} (BaAl{sub 2}O{sub 4}:Eu{sup 2+},Dy{sup 3+}), were prepared with the combustion synthesis at temperatures between 400 and 600 {sup o}C as well as with the solid state reaction at 1500 {sup o}C. The concentrations of Eu{sup 2+}/Dy{sup 3+} (in mol% of the Ba amount) ranged from 0.1/0.1 to 1.0/3.0. The electronic and defect energy level structures were studied with thermoluminescence (TL) and synchrotron radiation (SR) spectroscopies: UV-VUV excitation and emission, as well as with X-ray absorption near-edge structure (XANES) methods. Theoretical calculations using the density functional theory (DFT) were carried out in order to compare with the experimental data. - Graphical abstract: BaAl{sub 2}O{sub 4}:Eu{sup 2+},Dy{sup 3+} phosphors: Thermoluminescence glow curve and synchrotron radiation spectra. Persistent luminescence photographs obtained after ceased UV irradiation.

  4. Phase equilibria and elements partitioning in zirconolite-rich region of Ca-Zr-Ti-Al-Gd-Si-O system

    SciTech Connect

    Knyazev, O.A.; Stefanovsky, S.V.; Ioudintsev, S.V.; Nikonov, B.S.; Omelianenko, B.I.; Mokhov, A.V.; Yakushev, A.I.

    1997-12-31

    Zirconolite-rich ceramics were produced by the cold crucible melting technique in an air atmosphere, at 1550 {+-} 50 C and 1 atm. Four samples with overall composition (in wt.%): 4.9-14.3 CaO; 19.0-41.3 ZrO{sub 2}; 24.1-42.6 TiO{sub 2}; 1.3-11.3 Al{sub 2}O{sub 3}; 6.8-30.0 Gd{sub 2}O{sub 3}; and 1.1-8.5 SiO{sub 2} have been studied. Total phases in the ceramics consist of major zirconolite and minor rutile, perovskite, zirconia, aluminium titanate, and glass. The Gd{sub 2}O{sub 3} content in zirconolite reaches up to 31.4 wt.% corresponding to the formula: (Ca{sub 0.4},Gd{sub 0.7})Zr{sub 1.0}(Ti{sub 1.4},Al{sub 0.5})O{sub 7.0}. The data on the phase composition agree well with coupled Gd incorporation into the mineral structure: Ca(II) + Ti(IV) = Gd(III) + Al(III), and 2Gd(III) = Ca(II) + Zr(IV). The highest Gd contents observed in the other phases are 25.4% for zirconia, 12.6% in glass, 8.8% in perovskite, and 1.4% for rutile. The rest of the elements` distribution in the samples are analyzed.

  5. Teaching the Modes of Ca[superscript 2+] Transport between the Plasma Membrane and Endoplasmic Reticulum Using a Classic Paper by Kwan et al.

    ERIC Educational Resources Information Center

    Liang, Willmann

    2009-01-01

    This teaching article uses the report by Kwan et al., "Effects of methacholine, thapsigargin, and La[superscript 3+] on plasmalemmal and intracellular Ca[superscript 2+] transport in lacrimal acinar cells," where the effects of Ca[superscript 2+]-mobilizing agents in regulating Ca[superscript 2+] fluxes were examined under various conditions.…

  6. Characterization of ZrO2 buffer layers for sequentially evaporated Y-Ba-CuO on Si and Al2O3 substrates

    NASA Technical Reports Server (NTRS)

    Valco, George J.; Rohrer, Norman J.; Pouch, John J.; Warner, Joseph D.; Bhasin, Kul B.

    1988-01-01

    Thin film high temperature superconductors have the potential to change the microwave technology for space communications systems. For such applications it is desirable that the films be formed on substrates such as Al2O3 which have good microwave properties. The use of ZrO2 buffer layers between Y-Ba-Cu-O and the substrate has been investigated. These superconducting films have been formed by multilayer sequential electron beam evaporation of Cu, BaF2 and Y with subsequent annealing. The three layer sequence of Y/BaF2/Cu is repeated four times for a total of twelve layers. Such a multilayer film, approximately 1 micron thick, deposited directly on SrTiO3 and annealed at 900 C for 45 min produces a film with a superconducting onset of 93 K and critical temperature of 85 K. Auger electron spectroscopy in conjunction with argon ion sputtering was used to obtain the distribution of each element as a function of depth for an unannealed film, the annealed film on SrTiO3 and annealed films on ZrO2 buffer layers. The individual layers were apparent. After annealing, the bulk of the film on SrTiO3 is observed to be fairly uniform while films on the substrates with buffer layers are less uniform. The Y-Ba-Cu-O/ZrO2 interface is broad with a long Ba tail into the ZrO2, suggesting interaction between the film and the buffer layer. The underlying ZrO2/Si interface is sharper. The detailed Auger results are presented and compared with samples annealed at different temperatures and durations.

  7. Crustal structure of and boundary between the AlCaPa and Tisza terrains in the Pannonian basin

    NASA Astrophysics Data System (ADS)

    Hetényi, György; Ren, Yong; Dando, Ben; Stuart, Graham W.; Houseman, Gregory A.

    2014-05-01

    The evolution of the Pannonian Basin is strongly linked to that of the surrounding Alpine, Carpathian and Dinaric orogens. The eastward extrusion of Alpine-type basement that accompanied lithospheric thinning must have been accompanied by mantle downwelling and/or subduction along the Carpathians but the motive forces for these movements are debated. The internal structure of the crust within the basin is mostly covered by relatively recent sedimentary infill whose variable thickness further complicates seismic imaging. Palaeomagnetic and geological data have, however, shown that two tectonic terrains of distinct origin: AlCaPa and Tisza, occupy the basin's NW and SE part respectively. The two units have undergone different amounts of extension during opposite orientation rotations (counter-clockwise and clockwise, respectively). The boundary between these two units, known as the Mid-Hungarian Zone, is recognized as a major sinistral shear zone, geophysically clearly marked across the basin by a trough in Bouguer gravity. The Carpathian Basins Project deployed 49 broadband seismological stations perpendicular to the boundary between the AlCaPa and Tisza units. A NW-SE oriented swath of three lines covers a 450 km long and 75 km wide area. We use these and 4 permanent stations to image the crustal structure of and the boundary between AlCaPa and Tisza using the receiver function technique. The measured Moho depths show no significant change in crustal thickness between the two terrains, but the Moho is not or very weakly imaged along a ca. 40 km wide strip centred on the MHZ. Our Moho depths elsewhere in the basin agree with earlier controlled-source seismic results and recent shear-wave velocity models deduced from ambient noise analysis. The lack of a sharp Moho image beneath the MHZ implies that the crust-mantle boundary between AlCaPa and Tisza is not a sharp transition but rather a gradual increase in velocity with depth. The distinct low in gravity anomalies

  8. Thermal expansion behaviour in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Competing effects of water and oxygen ordering

    SciTech Connect

    Zhou Qingdi; Kennedy, Brendan J.; Avdeev, Maxim

    2011-09-15

    Neutron diffractions studies reveal the presence of oxygen disorder in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Synchrotron X-ray studies demonstrate that these oxides have a double perovskite-type structure with the cell size increasing as the size of the B cation increases from 8.2114(2) A for B=Ca to 8.4408(1) A for B=Ba. It is postulated that a combination of local clustering of the anions and vacancies together with water-water and water-host hydrogen bonds plays a role in defining the volume of the encapsulated water clusters and that changes in the local structure upon heating result in anomalous thermal expansion observed in variable temperature diffraction measurements. - Graphical abstract: The oxides Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba) have unusual anion disorder. There is a lag in the contraction in the cell size of Sr{sub 2}CaSbO{sub 5.5}nH{sub 2}O established from X-ray diffraction measurements following the loss of water suggesting changes on the local structure are important. Highlights: > The average structures of the defect perovskites Sr{sub 2}MSbO{sub 5.5} established. > Anion and cation disorder quantified by neutron and synchrotron X-ray diffraction. > Anomalous thermal expansion due to local clustering of anions and vacancies observed.

  9. Crystal structure and X-ray photoemission spectroscopic study of A{sub 2}LaMO{sub 6} [A=Ba, Ca; M=Nb, Ta

    SciTech Connect

    Dutta, Alo; Saha, Sujoy; Sinha, T.P.

    2015-09-15

    The X-ray photoemission spectroscopic (XPS) study of the double perovskite oxides A{sub 2}LaMO{sub 6} [A=Ba, Ca; M=Nb, Ta] synthesized by the solid-state reaction technique has been carried out to investigate the nature of the chemical state of the constituent ions and the bonding between them. The Rietveld refinement of the X-ray diffraction patterns suggests the monoclinic crystal structure of all the materials at room temperature. The negative and positive chemical shifts of the core level XPS spectrum of O-1s and Nb-3d{sub 3/2}/Ta-4f{sub 5/2} respectively suggest the covalent bonding between Nb/Ta cations and O ion. The change of the bonding strength between the anion and the cations from one material to another has been analyzed. The vibrational property of the materials is investigated using the room temperature Raman spectra. A large covalency of Ta-based compound than Nb compound is confirmed from the relative shifting of the Raman modes of the materials. - Graphical abstract: Crystal structure of two perovskite oxides CLN and CLT is investigated. XPS study confirms the two different co-ordination environments of Ca and covalent bonding between B-site cations and O-ion. - Highlights: • Ordered perovskite structure obtained by Rietveld refinement of XRD patterns. • Study of nature of chemical bonding by X-ray photoemission spectroscopy. • Opposite chemical shift of d-states of Nb/Ta with respect to O. • Covalent bonding between d-states of Nb/Ta and O. • Relative Raman shifts of CLN and CLT substantiate the more covalent character of Ta than Nb.

  10. Preparation of Ca-Si Films on (001) Al2O3 Substrates by an RF Magnetron Sputtering Method and Their Electrical Properties

    NASA Astrophysics Data System (ADS)

    Uehara, Mutsuo; Akiyama, Kensuke; Shimizu, Takao; Matsushima, Masaaki; Uchida, Hiroshi; Kimura, Yoshisato; Funakubo, Hiroshi

    2016-06-01

    The constituent phases, electrical conductivity, and Seebeck coefficient of Ca-Si films deposited on (001) Al2O3 substrates by a radio frequency magnetron sputtering method using a Mg disk target with Ca and Si chips are investigated. X-ray diffraction analysis indicates that the films consist of a single phase of CaSi2, CaSi or Ca5Si3 that are deposited together with the films consisting of a mixture of CaSi2 and CaSi. Films with a CaSi2 or CaSi single phase exhibit a metallic behavior. In contrast, films with a Ca5Si3 single phase show p-type conduction and their Seebeck coefficient reaches 90 μV/K at 400°C.

  11. Large pyroelectric figure of merits for Sr-modified Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics

    NASA Astrophysics Data System (ADS)

    Patel, Satyanarayan; Chauhan, Aditya; Vaish, Rahul

    2016-02-01

    In the present work ferroelectric, dielectric and pyroelectric properties of Sr-modified Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics were investigated. A significant increase in polarization has been observed, from 16 μC/cm2 to 25 μC/cm2 for 15% Sr added BCZT compositions. Correspondingly an improvement in dielectric constant, from 2743 to 4040, was observed at room temperature (1 MHz). It was found that Curie-Weiss temperature (TCW) decreases from 357 K to 308 K for 15% Sr containing BCZT ceramics. Simultaneously, it also enhances the order-disorder to displacing phase transition as γ varies from 1.91 to 1.31. Pyroelectric coefficient was found to be 25 μC/cm2K at 308 K. Finally, pyroelectric figures of merit (FOMs) for voltage responsivity (Fv), current responsivity (Fi), detectivity (Fd), energy harvesting (Fe) and new energy harvesting (Fe∗) are calculated. A large improvement in pyroelectric FOMs indicates that it might be a potential material for pyroelectric applications.

  12. Luminescence properties of a novel green emitting Ba2CaZn2Si6O17:Eu2+ phosphor for white light - Emitting diodes applications

    NASA Astrophysics Data System (ADS)

    Annadurai, G.; Kennedy, S. Masilla Moses; Sivakumar, V.

    2016-05-01

    A novel green emitting Ba2CaZn2Si6O17:Eu2+ (BCZSO:Eu2+) phosphor was synthesized using conventional high temperature solid state reaction method. Powder X-ray diffraction was carried out to confirm the phase formation of the synthesized phosphors. Photoluminescence emission spectrum was recorded under excitation at 340 nm. The BCZSO:Eu2+ phosphor exhibited an intense asymmetric green emission band around 502 nm which originated from the 4f65d1 → 4f7 transition of Eu2+ ion. The optimum doping concentration of Eu2+ was found to be 0.06 mol. The energy transfer mechanism among Eu2+ in BCZSO phosphor was found to be a dipole-dipole interaction, and the critical distance (RC) for the Eu2+ ions calculated by the concentration quenching and spectral overlap methods were 23.2 Å and 13.7 Å, respectively. The decay curve of BCZSO:Eu2+ phosphors were discussed. The CIE chromaticity coordinate values (x = 0.259, y = 0.463) of BCZSO:Eu2+ phosphor were located in green region and the correlated color temperature was 7571 K. All these properties gave an indication that BCZSO:Eu2+ phosphor could be a potential green-emitting phosphor for UV based white light emitting diodes.

  13. Electrocaloric effect in Ba0.2Ca0.8Ti0.95Ge0.05O3 determined by a new pyroelectric method

    NASA Astrophysics Data System (ADS)

    Asbani, B.; Dellis, J.-L.; Gagou, Y.; Kaddoussi, H.; Lahmar, A.; Amjoud, M.; Mezzane, D.; Kutnjak, Z.; El Marssi, M.

    2015-09-01

    The present letter explores the electrocaloric effect (ECE) in the lead-free oxide Ba0.8Ca0.2Ti0.95Ge0.05O3 ceramics (BCTG). The electrocaloric responsivity ξ =(\\frac{\\text{d}T}{\\text{d}E}) was determined by two different methods using the Maxwell relationship ξ\\propto≤ft(\\frac{\\partial P}{\\partial T}\\right)E . In a first well-known indirect method, P\\text-E hysteresis loops were measured in a wide temperature range from which the pyroelectric coefficient pE=≤ft(\\frac{\\partial P}{\\partial T}\\right)E and thus ξ were determined by derivation of P(T,~E) data. In the second novel method the pyroelectric coefficient p E and consequently the electrocaloric responsivity ξ were determined by direct measurements of the pyroelectric currents under different applied electric fields. Within the experimental error, good agreement was obtained between two methods with ξ = 0.18 +/- 0.05 \\cdot 10-6 \\text{K}\\cdot \\text{m}\\cdot \\text{V}-1 at about 410 K.

  14. Observation of superconductivity at 30~46 K in A(x)Fe₂Se₂(A = Li, Na, Ba, Sr, Ca, Yb, and Eu).

    PubMed

    Ying, T P; Chen, X L; Wang, G; Jin, S F; Zhou, T T; Lai, X F; Zhang, H; Wang, W Y

    2012-01-01

    New iron selenide superconductors by intercalating smaller-sized alkali metals (Li, Na) and alkaline earths using high-temperature routes have been pursued ever since the discovery of superconductivity at about 30 K in KFe₂Se₂, but all have failed so far. Here we demonstrate that a series of superconductors with enhanced T(c) = 30∼46 K can be obtained by intercalating metals, Li, Na, Ba, Sr, Ca, Yb, and Eu in between FeSe layers by the ammonothermal method at room temperature. Analysis on their powder X-ray diffraction patterns reveals that all the main phases can be indexed based on body-centered tetragonal lattices with a∼3.755-3.831 Å while c∼15.99-20.54 Å. Resistivities show the corresponding sharp transitions at 45 K and 39 K for NaFe₂Se₂ and Ba₀.₈Fe₂Se₂, respectively, confirming their bulk superconductivity. These findings provide a new starting point for studying the properties of these superconductors and an effective synthetic route for the exploration of new superconductors as well. PMID:22645642

  15. Synthesis, structural, electrical and magnetic studies of La0.5Ca0.45-xSrxBa0.05MnO3

    NASA Astrophysics Data System (ADS)

    Munirathinam, B.; Krishnaiah, M.; Devarajan, U.; Esakki Muthu, S.; Arumugam, S.

    2012-07-01

    Half doped mixed valence manganite system La0.5Ca0.45-xSrxBa0.05MnO3 (with x=0.1, 0.2, and 0.3) synthesized through a low temperature nitrate route is systematically investigated in this paper. The electronic transport and magnetic properties are analyzed and compared apart from the study of unit cell structure and composition. The system is found to crystallize only in orthorhombic structure (Pnma) and the electronic phase transitions are observed to be of second order. The charge and orbital ordering have been observed to coexist with ferromagnetism in x=0.1 compound. Application of small polaron and variable range hopping models to resistivity data of the system corresponding to high temperature range shows increasing mobility of eg electrons with x, with the later model describing the electronic transport very closely than the former. The temperature dependent magnetization of the compounds shows monotonic increase of paramagnetic to ferromagnetic transition (TC) with x. Ferromagnetism is exhibited for the complete temperature range down from respective TC in contrast to antiferromagnetism usually exhibited by half-doped compounds in the low temperature range. The plots of magnetization versus magnetic field reveal a transition from soft to hard magnetic character for all the compounds as the temperature is lowered.

  16. Legitional behavior of 5,5-diethylbarbituric acid sodium salt (HL) towards Mg, Ca, Sr, Ba(II), spectral, thermal and biological studies

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; El-Metwaly, Nashwa M.

    2011-03-01

    A new series of sodium barbital complexes with Alkaline earth metals (Mg2+, Ca2+, Sr2+ and Ba2+ ions) was prepared. The molecular formulas for the isolated complexes were suggested basically on the elemental analysis data. The binuclear central were proposed for all investigated complexes. The geometry suggested based on knowing the coordination sits for each complex was built on concerning with the shift observed in IR spectra surround the coordinating groups. The shifts in charge transfer bands appeared in the electronic spectra of the complexes supports the coordination process. The presence of solvent molecules coordinately attached with central metal atoms as well as the conjugated anions was supported based on thermogravimetric analysis. The kinetic parameters were calculated for each complex. The theoretical calculations for the molecular modeling structures reflect an insight about their stability in comparing with the free ligand. The XRD studies were performed and concluding the nanocrystalline feature for all complexes. The biochemical effect of all investigated compounds was performed towards Gram-negative and Gram-positive bacteria as well as their degradation effect on calf Thymus DNA. The biological performance is the major goal in this study especially with such essential metal ions.

  17. Growth of Cu 0.5Tl 0.5Ba 2Ca 3Cu 4-yZn yO 12-δ superconductor with optimum carriers

    NASA Astrophysics Data System (ADS)

    Mumtaz, M.; Khan, Nawazish A.; Khan, E. U.

    2010-05-01

    We have tried to vary the carriers concentration in Cu 0.5Tl 0.5Ba 2Ca 3Cu 4-yZn yO 12-δ ( y = 0, 1, 1.5, 2, 2.5) superconductor with the help of post-annealing experiments carried out in nitrogen, oxygen and air and to investigate its effects on the superconductivity parameters. The zero resistivity critical temperature [ T c( R = 0)], the magnitude of diamagnetism and critical current [ I c( H = 0)] are found to increase in Zn free samples after post-annealing in oxygen and air, while these superconducting properties have been suppressed after post-annealing in nitrogen at 550 °C for 6 h. The post-annealing of Zn-doped samples in air has marginally increased the superconducting properties, while these properties have been suppressed after post-annealing in nitrogen and oxygen. These studies have led us to the definite conclusion that the Zn-doped material has grown with optimum carriers concentration.

  18. Effects of Cr2O3 doping on the microstructure and electrical properties of (Ba,Ca)(Zr,Ti)O3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Xia, Xiang; Jiang, Xiangping; Chen, Chao; Jiang, Xingan; Tu, Na; Chen, Yunjing

    2016-04-01

    Lead-free ceramics (Ba0.85Ca0.15)(Zr0.9Ti0.1)O3-x wt.%Cr2O3 (BCZT-xCr) were prepared via the conventional solid-state reaction method. The microstructure and electrical properties of BCZT-xCr samples were systematically studied. XRD and Raman results showed that all samples possessed a single phased perovskite structure and were close to the morphotropic phase boundary (MPB). With the increase of the Cr content, the rhombohedral-tetragonal phase transition temperature (T R-T) increases slightly, and the Curie temperature (T C) shifts towards the low temperature side. XPS analysis reveals that Cr3+ and Cr5+ ions co-existed in Cr-doped BCZT ceramics, indicating the different impact on the electrical properties from Cr ions as "acceptor" or "donor". For the x = 0.1 sample, relative high piezoelectric constants d 33 (~316 pC/N) as well as high Q m (~554) and low tanδ (~0.8%) were obtained. In addition, the AC conductivity was also investigated. Hopping charge was considered as the main conduction mechanism at low temperature. As the temperature increases, small polarons and oxygen vacancies conduction played important roles.

  19. AuBa 2(Y 1- x, Ca x)Cu 2O 7: a new superconducting gold cuprate with Tc above 80 K

    NASA Astrophysics Data System (ADS)

    Bordet, P.; LeFloch, S.; Chaillout, C.; Duc, F.; Gorius, M. F.; Perroux, M.; Capponi, J. J.; Toulemonde, P.; Tholence, J. L.

    1997-02-01

    We have synthesised by the high pressure-high temperature technique a new layered gold cuprate of chemical formula AuBa 2(Y 1- x,Ca x)Cu 2O 7 (0 ≤ × ≤ 0.4) (hereafter denoted as Au-1212). The structural properties of this compound are investigated by means of electron microscopy and powder X-ray diffraction. The average structure (orthorhombic Pmmm, a = 3.8298(5) Å, b = 3.8420(5) Å, c = 12.111(1) Å for nominal composition x = 0.4) is very similar to that of YBa 2Cu 3O 7, with Au 3+ cations in square planar coordination sharing corners to form chains running along the b axis. Electron microscopy reveals the presence of a superstructure with double b parameter, which is attributed to a long range ordered zig-zag conformation of the square chains. For x = 0, the formal copper valence is 2 + and the compound is insulating. Doping of the conducting CuO 2 planes is achieved by the partial substitution of yttrium by calcium, up to x ≈ 0.4. Upon substitution, the compound becomes superconducting with a maximum Tc at ∼ 82 K for x ≈ 0.4.

  20. Oxygen ordering in the high-Tc superconductor HgBa2CaCu2O6+δ as revealed by perturbed angular correlation

    NASA Astrophysics Data System (ADS)

    Mendonça, T. M.; Correia, J. G.; Haas, H.; Odier, P.; Tavares, P. B.; da Silva, M. R.; Lopes, A. M. L.; Pereira, A. M.; Gonçalves, J. N.; Amaral, J. S.; Darie, C.; Araujo, J. P.

    2011-09-01

    Lattice sites and collective ordering of oxygen atoms in HgBa2CaCu2O6+δ were studied using the perturbed angular correlation (PAC) technique at ISOLDE/CERN. The electric field gradients (EFG) at 199mHg nuclei have been measured as functions of oxygen doping on the Hg planes, above and below Tc. In comparison with the results obtained for oxygen and fluorine doping in Hg-1201, the analysis shows a different oxygen ordering exhibited by Hg-1212. Moreover, for all studied cases, the experimental results show that at a local scale there is non uniform oxygen distribution. A series of ab initio EFG calculations allowed to infer that at low concentrations, regions without oxygen coexist with regions where O2δ dumbbell molecules are located at the center of the Hg mesh. On the other side, at high concentrations, O2δ dumbbell molecules coexist with single Oδ atoms occupying the center of the Hg mesh. The present results suggest that oxygen sits on the Hg planes in the form of a molecule and not as a single atom.

  1. Effects of Cr2O3 doping on the microstructure and electrical properties of (Ba,Ca)(Zr,Ti)O3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Xia, Xiang; Jiang, Xiangping; Chen, Chao; Jiang, Xingan; Tu, Na; Chen, Yunjing

    2016-06-01

    Lead-free ceramics (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3- x wt.%Cr2O3 (BCZT- xCr) were prepared via the conventional solid-state reaction method. The microstructure and electrical properties of BCZT- xCr samples were systematically studied. XRD and Raman results showed that all samples possessed a single phased perovskite structure and were close to the morphotropic phase boundary (MPB). With the increase of the Cr content, the rhombohedral-tetragonal phase transition temperature ( T R-T) increases slightly, and the Curie temperature ( T C) shifts towards the low temperature side. XPS analysis reveals that Cr3+ and Cr5 + ions co-existed in Cr-doped BCZT ceramics, indicating the different impact on the electrical properties from Cr ions as "acceptor" or "donor". For the x = 0.1 sample, relative high piezoelectric constants d 33 (˜316 pC/N) as well as high Q m (˜554) and low tanδ (˜0.8%) were obtained. In addition, the AC conductivity was also investigated. Hopping charge was considered as the main conduction mechanism at low temperature. As the temperature increases, small polarons and oxygen vacancies conduction played important roles.

  2. Direct imaging of the structural domains in the iron pnictides AFe[subscript 2]As[subscript 2] (A=Ca, Sr, Ba)

    SciTech Connect

    Tanatar, M.A.; Kreyssig, A.; Nandi, S.; Ni, N.; Bud'ko, S.L.; Canfield, P.C.; Goldman, A.I.; Prozorov, R.

    2009-06-29

    The parent compounds of recently discovered iron-arsenide superconductors, AFe{sub 2}As{sub 2} with alkaline earth A=Ca,Sr,Ba, undergo simultaneous structural and magnetic phase transitions at a temperature T{sub SM}. Using a combination of polarized light microscopy and spatially resolved high-energy synchrotron x-ray diffraction we show that the orthorhombic distortion leads to the formation of 45{sup o}-type structural domains in all parent compounds. Domains penetrate through the sample thickness in the c direction and are not affected by crystal imperfections such as growth terraces. The domains form regular stripe patterns in the plane with a characteristic dimension of 10--50 {mu}m. The direction of the stripes is fixed with respect to the tetragonal (100) and (010) directions but can change by 90{sup o} on thermal cycling through the transition. This domain pattern may have profound implications for intrinsic disorder and anisotropy of iron arsenides.

  3. Investigation about relationships between the symmetries of ferroelectric crystal Ca0.28Ba0.72Nb2O6 and second-harmonic patterns

    NASA Astrophysics Data System (ADS)

    Xu, Tianxiang; Yu, Haohai; Zhang, Huaijin; Wang, Jiyang

    2015-08-01

    The broadband quasi-phase matching (QPM) process in a uniaxial ferroelectric crystal Ca0.28Ba0.72Nb2O6 (CBN-28) was demonstrated with the second-harmonic wavelength range from 450 nm to 650 nm, and the relationship between the symmetries of CBN-28 and the second-harmonic patterns was experimentally and theoretically investigated based on the random anti-parallel domains in the crystal and QPM conditions. The dependences of frequency-doubled patterns on the wavelength and anisotropy of the nonlinear crystal were also studied, and the frequency-doubled photons were found to be trapped on circles. By analyzing the light-matter interacting Hamiltonians, the trapping force for second-harmonic photons was found to be centripetal and tunable by the fundamental lasers, and the variation tendencies of the rotational velocity of second-harmonic generation photons could also be predicated. The results indicate that the CBN-28 ferroelectric crystal is a promising nonlinear optical material for the generation of broadband frequency-doubled waves, and the analysis on centripetal force based on the interaction Hamiltonians may provide a novel recognition for the investigation of QPM process to be further studied.

  4. Massive production of A2SiO4:Eu3+ and A2SiO4:Eu2+ (A = Ca, Sr, Ba) microspheres and luminescent properties

    NASA Astrophysics Data System (ADS)

    Wei, Fengjun; Jia, Qiuli

    2015-06-01

    A2SiO4:Eu3+ and A2SiO4:Eu2+ (A = Ca, Sr, Ba) microspheres with dense structure were synthesized by the modified spray-drying process. The obtained samples were characterized by XRD, SEM, and spectrophotometer. The XRD results reveal that all samples are isostructure. The SEM results show that the obtained samples are microspheres with size in the range of 0.6-2.2 μm. Dextrin plays an important role in the formation of spherical morphology. The excitation and emission spectra of the samples indicate that Eu3+ (or Eu2+) ions doped into different alkaline earth silicates will give different emission bands in different color regions and with different emission intensities. A2SiO4:Eu3+ samples show characteristic emission bands originating from 5D0 → 7Fj transitions of Eu3+ ions. A2SiO4:Eu2+ samples show different emission bands. The two emission bands for Sr2SiO4:Eu2+ relate to the two Eu2+ activator sites locating at two Sr2+ sites in Sr2SiO4 host. The difference of luminescent properties relates to the different sites of Eu3+ (or Eu2+) ions in the A2SiO4 hosts.

  5. Effect of Mg(2+), Ca(2+), Sr(2+) and Ba(2+) metal ions on the antifungal activity of ZnO nanoparticles tested against Candida albicans.

    PubMed

    Haja Hameed, Abdulrahman Syedahamed; Karthikeyan, Chandrasekaran; Senthil Kumar, Venugopal; Kumaresan, Subramanian; Sasikumar, Seemaisamy

    2015-01-01

    The antifungal ability of pure and alkaline metal ion (Mg(2+), Ca(2+), Sr(2+) and Ba(2+)) doped ZnO nanoparticles (NPs) prepared by the co-precipitation method was tested against the pathogenic yeast, Candida albicans (C. albicans), and the results showed that the Mg-doped ZnO NPs possessed greater effect than the other alkaline metal ion doped ZnO NPs. The impact of the concentration of Mg doped ZnO sample on the growth of C. albicans was also studied. The Minimal Fungicidal Concentration (MFC) of the Mg doped ZnO NPs was found to be 2000 μg/ml for which the growth of C. albicans was completely inhibited. The ZnO:Mg sample (1.5mg/ml) with various concentrations of histidine reduced the fungicidal effect of the nanoparticles against C. albicans, which was deliberately explained by the role of ROS. The ZnO:Mg sample added with 5mM of histidine scavenged the ample amount of generated ROS effectively. The binding of the NPs with fungi was observed by their FESEM images and their electrostatic attraction is confirmed by the zeta potential measurement. PMID:25953555

  6. Phase transition in ABi4Ti4O15 (A=Ca,Sr,Ba) Aurivillius oxides prepared through a soft chemical route

    NASA Astrophysics Data System (ADS)

    Rout, S. K.; Sinha, E.; Hussian, A.; Lee, J. S.; Ahn, C. W.; Kim, I. W.; Woo, S. I.

    2009-01-01

    A series of compounds, CaBi4Ti4O15 (CBT), SrBi4Ti4O15 (SBT), and BaBi4Ti4O15 (BBT), belonging to the Aurivillus-type structure (four layers) has been prepared by a modified chemical route. Different oxalates were precipitated from their respective nitrate solution onto the surface of TiO2 powders. The room temperature x-ray diffraction study reveled that the compounds were having orthorhombic symmetry. Considering the tolerance factor, a significant deformation of the perovskite block is observed and that decreases with increase in ionic radius of A site atom. Temperature dependent dielectric study showed normal ferroelectric to paraelectric transition well above the room temperature except for BBT. The BBT ceramic showed a relaxorlike behavior near phase transition. The quantitative characterization and comparison of relaxor behavior were based on empirical parameters γ and ΔTres. The dielectric relaxation rate follows the Vogel-Fulcher relation with activation energy=0.02 eV and freezing temperature=362 °C. All these measurements confirmed its relaxorlike phase transition.

  7. Millimeter wave characteristics of intrinsic Josephson junctions with planar equiangular spiral antenna in misaligned Tl2Ba2CaCu2O8 thin film

    NASA Astrophysics Data System (ADS)

    Liu, X.; Wang, P.; Xie, W.; Ma, L. J.; Zhao, X. J.; He, M.; Ji, L.; Zhang, X.

    2015-12-01

    An intrinsic Josephson junctions (IJJs) microbridge with planar equiangular spiral antenna (PESA) is proposed and studied by simulation and experiment. This IJJs circuit is simulated firstly to obtain the minimum of reflection coefficient and pattern. Secondly, IJJs with PESA are fabricated on misaligned Tl2Ba2CaCu2O8 superconducting film. The millimeter wave characteristics are investigated by a Febry-Pérot resonator, which consists of a spherical mirror antenna and a plane mirror. At 37.4 GHz, the IJJs and the millimeter wave show an optimum coupling, which deviate from the simulation for only 0.004 GHz. In addition, the extent of the coupling between IJJs and the resonator is discussed at different angle for the polarization direction of the spherical mirror antenna with the microbridge. The result shows that the strongest coupling is obtained at 0-30° angle. Good conformance of measurements and simulations illustrate the effectiveness of our design in strong coupling between sample and resonator.

  8. Spin dynamics, short range order and spin freezing in Y0.5Ca0.5BaCo4O7

    SciTech Connect

    Stewart, John Ross; Ehlers, Georg; Fouquet, Peter; Mutka, Hannu; Payen, Christophe; Lortz, Rolf

    2011-01-01

    Y0.5Ca0.5BaCo4O7 was recently introduced as a possible candidate for capturing some of the predicted classical spin kagome ground-state features. Stimulated by this conjecture, we have taken up a more complete study of the spin correlations in this compound with neutron scattering methods on a powder sample characterized with high-resolution neutron diffraction and the temperature dependence of magnetic susceptibility and specific heat. We have found that the frustrated near-neighbor magnetic correlations involve not only the kagome planes but concern the full Co sublattice, as evidenced by the analysis of the wave-vector dependence of the short-range order. We conclude from our results that the magnetic moments are located on the Co sublattice as a whole and that correlations extend beyond the two-dimensional kagome planes. We identify intriguing dynamical properties, observing high-frequency fluctuations with a Lorentzian linewidth G?20 meV at ambient temperature. On cooling a low-frequency ({approx}1 meV) dynamical component develops alongside the high-frequency fluctuations, which eventually becomes static at temperatures below T {approx} 50 K. The high-frequency response with an overall linewidth of {approx}10 meV prevails at T?2 K, coincident with a fully elastic short-range-ordered contribution.

  9. Hillesheimite, (K,Ca,□)2(Mg,Fe,Ca,□)2[(Si,Al)13O23(OH)6](OH) · 8H2O, a new phyllosilicate mineral of the Günterblassite group

    NASA Astrophysics Data System (ADS)

    Chukanov, N. V.; Zubkova, N. V.; Pekov, I. V.; Belakovskiy, D. I.; Schüller, W.; Ternes, B.; Blass, G.; Pushcharovsky, D. Yu.

    2013-12-01

    A new mineral, hillesheimite, has been found in the Graulai basaltic quarry, near the town of Hillesheim, the Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany. It occurs in the late assemblage comprising nepheline, augite, fluorapatite, magnetite, perovskite, priderite, götzenite, lamprophyllite-group minerals, and åkermanite. Colorless flattened crystals of hillesheimite reaching 0.2 × 1 × 1.5 mm in size and aggregates of the crystals occur in miarolitic cavities in alkali basalt. The mineral is brittle, with Mohs' hard-ness 4. Cleavage is perfect parallel to (010) and distinct on (100) and (001). D calc = 2.174 g/cm3, D meas = 2.16(1) g/cm3. IR spectrum is given. Hillesheimite is biaxial (-), α = 1.496(2), β = 1.498(2), γ = 1.499(2), 2 V meas = 80°. The chemical composition (electron microprobe, mean of 4 point analyses, H2O determined from structural data, wt %) is as follows: 0.24 Na2O, 4.15 K2O, 2.14 MgO, 2.90 CaO, 2.20 BaO, 2.41 FeO, 15.54 Al2O3, 52.94 SiO2, 19.14 H2O, total is 101.65. The empirical formula is: K0.96Na0.08Ba0.16Ca0.56Mg0.58Fe{0.37/2+}[Si9.62Al3.32O23(OH)6][(OH)0.82(H2O)0.18] · 8H2O. The crystal structure has been determined from X-ray single-crystal diffraction data, R = 0.1735. Hillesheimite is orthorhombic, space group Pmmn, the unit-cell dimensions are: a = 6.979(11), b = 37.1815(18), c = 6.5296(15) Å; V=1694(3) Å3, Z = 2. The crystal structure is based on the block [(Si,Al)13O25(OH)4] consisting of three single tetrahedral layers linked via common vertices and is topologically identical to the triple layers in günterblassite and umbrianite. The strong reflections [ d Å ( I %)] in the X-ray powder diffraction pattern are: 6.857(58), 6.545(100), 6.284(53), 4.787(96), 4.499(59), 3.065(86), 2.958(62), 2.767(62). The mineral was named after its type locality. Type specimens are deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, registration number 4174/1.

  10. Dielectric and magnetic properties of xCoFe{sub 2}O{sub 4}–(1 − x)[0.5Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}–0.5(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3}] composites

    SciTech Connect

    Rani, Jyoti; Yadav, K.L.; Prakash, Satya

    2014-12-15

    Highlights: • Spinel–perovskite xCoFe{sub 2}O{sub 4}–(1 − x)(0.5Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}–0.5(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3}) composites have been synthesized by solid state reaction method. • Two anomalies in dielectric constant have been identified, and the composites show relaxor behaviour. • The magnetic properties of the composites improve with increasing concentration of CoFe{sub 2}O{sub 4}. • Enhanced magnetodielectric effect is found, and magnetoelectric coupling has been confirmed by Δϵ ∼ γM{sup 2} relation. • Optical band gap energy of these composites has been reported for the first time. - Abstract: xCoFe{sub 2}O{sub 4}–(1 − x)(0.5Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}–0.5(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3}) composites with x = 0.1, 0.2, 0.3 and 0.4 have been synthesized by solid state reaction method. X-ray diffraction analysis and field emission secondary electron microscopy have been used for structural and morphological analysis, respectively. The spinel CoFe{sub 2}O{sub 4} and perovskite 0.5Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}–0.5(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} phase could be identified in the composites. Two anomalies in dielectric constant have been identified: first one is close to ferroelectric to paraelectric phase transition of 0.5Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}–0.5(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} ceramic and the other lies near the magnetic transition temperature of CoFe{sub 2}O{sub 4}. There is an increase in magnetocapacitance and saturation magnetization of the composites at room temperature with increase in CoFe{sub 2}O{sub 4} content. The magnetoelectric coupling coefficient (γ) was approximated by Δϵ ∼ γM{sup 2} relation. The optical band gap energy of the composites decreases with increase in CoFe{sub 2}O{sub 4} content.

  11. Synthesis and hydration behavior of calcium zirconium aluminate (Ca{sub 7}ZrAl{sub 6}O{sub 18}) cement

    SciTech Connect

    Kang, Eun-Hee; Yoo, Jun-Sang; Kim, Bo-Hye; Choi, Sung-Woo; Hong, Seong-Hyeon

    2014-02-15

    Calcium zirconium aluminate (Ca{sub 7}ZrAl{sub 6}O{sub 18}) cements were prepared by solid state reaction and polymeric precursor methods, and their phase evolution, morphology, and hydration behavior were investigated. In polymeric precursor method, a nearly single phase Ca{sub 7}ZrAl{sub 6}O{sub 18} was obtained at relatively lower temperature (1200 °C) whereas in solid state reaction, a small amount of CaZrO{sub 3} coexisted with Ca{sub 7}ZrAl{sub 6}O{sub 18} even at higher temperature (1400 °C). Unexpectedly, Ca{sub 7}ZrAl{sub 6}O{sub 18} synthesized by polymeric precursor process was the large-sized and rough-shaped powder. The planetary ball milling was employed to control the particle size and shape. The hydration behavior of Ca{sub 7}ZrAl{sub 6}O{sub 18} was similar to that of Ca{sub 3}Al{sub 2}O{sub 6} (C3A), but the hydration products were Ca{sub 3}Al{sub 2}O{sub 6}·6H{sub 2}O (C3AH6) and several intermediate products. Thus, Zr (or ZrO{sub 2}) stabilized the intermediate hydration products of C3A.

  12. A Density Model Based on the Modified Quasichemical Model and Applied to the NaF-AlF3-CaF2-Al2O3 Electrolyte

    NASA Astrophysics Data System (ADS)

    Robelin, Christian; Chartrand, Patrice

    2007-12-01

    A theoretical model for the density of multicomponent inorganic liquids based on the modified quasichemical model has been presented in a previous article. In the present article, this model is applied to the NaF-AlF3-CaF2-Al2O3 electrolyte. By introducing in the Gibbs energy of the liquid phase, temperature-dependent molar volume expressions for the pure fluorides and oxides, and pressure-dependent excess parameters for the binary (and sometimes higher-order) interactions, it is possible to reproduce, and eventually predict, the molar volume and the density of the multicomponent liquid phase using standard interpolation methods. All available density data for the NaF-AlF3-CaF2-Al2O3 liquid were collected and critically evaluated, and optimized pressure-dependent model parameters have been found. This new volumetric model can be used with Gibbs energy minimization software, to calculate the molar volume and the density of cryolite-based melts used for the electroreduction of alumina in Hall-Héroult cells.

  13. In vitro controlled release of vitamin C from Ca/Al layered double hydroxide drug delivery system.

    PubMed

    Gao, Xiaorui; Chen, Le; Xie, Juan; Yin, Yaobing; Chang, Tao; Duan, Yancong; Jiang, Nan

    2014-06-01

    A new drug delivery system for vitamin C (VC), Ca/Al layered double hydroxide (LDH), is demonstrated in this work. VC anions were intercalated successfully in the Ca/Al LDH gallery by a coprecipitation method. The interlayer space of 9.8Å suggests that VC anions are vertical to the LDH layers in the form of interdigitated bilayer. The loading of VC in LDH is 36.4wt.%. The thermal stability of VC is significantly enhanced after intercalation. In vitro VC release results show that the release time of VC in a phosphate buffer at pH7.4 was significantly extended, and the maximal percentage of VC released is 80% of the total. The Avrami-Erofe'ev equation most satisfactorily explains the release kinetics of VC, which is that the release of VC is mainly dominated by the ion-exchange reaction. PMID:24863197

  14. CN-mayenite Ca12Al14O32(CN)2: Replacing mobile oxygen ions by cyanide ions

    NASA Astrophysics Data System (ADS)

    Schmidt, Alexander; Lerch, Martin; Eufinger, Jens-Peter; Janek, Jürgen; Dolle, Raimund; Wiemhöfer, Hans-Dieter; Tranca, Ionut; Islam, Mazharul M.; Bredow, Thomas; Boysen, Hans; Hoelzel, Markus

    2014-12-01

    CN-mayenite (Ca12Al14O32(CN)2) is a promising candidate for high-temperature CN- conductivity in a solid due to its special structural features. It was prepared by a solid-gas reaction. The transport processes were investigated by means of in situ high-temperature neutron diffraction, impedance spectroscopy and additional Hebb-Wagner measurements. Diffusion pathways and activation energies were determined additionally by quantum-chemical calculations. Ca12Al14O32(CN)2 shows a surprisingly high ionic conductivity of σ = 1.4•10-3 S/cm at 1173 K (Ea = 4.3 eV) and can be considered as first example of a new kind of solid anion conductor with a mobile molecular anion.

  15. On the photo-luminescence properties of sol–gel derived undoped and Dy{sup 3+} ion doped nanocrystalline Scheelite type AMoO{sub 4} (A = Ca, Sr and Ba)

    SciTech Connect

    Jena, Paramananda; Gupta, Santosh K.; Natarajan, V.; Padmaraj, O.; Satyanarayana, N.; Venkateswarlu, M.

    2015-04-15

    Nanocrystalline Scheelite type Dy doped AMoO{sub 4} [where A = Ba, Sr and Ca] samples were prepared by acrylamide assisted sol–gel process and characterized by XRD, FT-Raman, FTIR, SEM and photoluminescence (PL). PL of undoped sample shows blue/green emission in CaMoO{sub 4} and SrMoO{sub 4} but multicolour visible emission leading to near white light in BaMoO{sub 4} nanoparticles; the origin of which is explained. It was observed that on doping 0.5 mol% of Dy{sup 3+} in molybdate samples complete energy transfer takes place in case of SrMoO{sub 4} and BaMoO{sub 4}, but host contributed substantially in Dy doped BaMoO{sub 4} sample, resulting in biexponential decay. It was also observed that symmetry around Dy{sup 3+} decreases as the size of alkaline earth ion increases. Due to combined blue, yellow and red colour emission in dysprosium doped sample; all samples showed near white light emission under UV and near UV excitation.

  16. Crystal structure of Na 2MMgP 2O 8 ( M: Ba, Sr, Ca) orthophosphates and their luminescence properties activated by Eu 2+; analogous structural behaviors of glaserite-type phosphates and silicates

    NASA Astrophysics Data System (ADS)

    Yonesaki, Yoshinori; Matsuda, Chihiro

    2011-12-01

    Rietveld refinements of X-ray powder diffraction data and vibrational spectroscopy have confirmed the crystal structure of Na 2MMgP 2O 8 ( M: Ba, Sr, Ca) prepared by a standard solid state reaction. They have glaserite-type layered structure. Na 2MMgP 2O 8 has a trigonal P3¯ form for M=Ba, and monoclinic P2 1/ c forms for M=Sr and Ca. The observed structural transition is analogous to the corresponding layered orthosilicate M3MgSi 2O 8. Eu 2+-doped Na 2MMgP 2O 8 exhibits an intense blue to violet emission under ultraviolet excitation, based on 5 d-4 f electron transition of Eu 2+ ions. The emission character is very sensitive to the structural transition induced by M2+ and the subsequent site symmetry changes.

  17. A new series of oxycarbonate superconductors (Cu(0.5)C(0.5))(m)Ba(m+1)Ca(n-1)Cu(n)O2(m+n)+1

    NASA Technical Reports Server (NTRS)

    Takayama-Muromachi, E.; Kawashima, T.; Matsui, Y.

    1995-01-01

    We found a new series of oxycarbonate superconductors in the Ba-CaCu-C-O system under high pressure of 5 GPa. Their ideal formula is (Cu(0.5)C(0.5)(m)Ba(m+1)Ca(n-1)Cu(n)O2)((m+n)+1) ((Cu,C)-m(m+1)(n-1)n). Thus far, n = 3, 4 members of the m = 1 series, (Cu,C)-1223 and (Cu,C)-1234, have been prepared in bulk while n = 4, 5 members, (Cu,C)-2334 and (Cu,C)-2345, have been prepared for the m = 2 series. (Cu,C)-1223 shows superconductivity below 67 K while T(sub c)'s of other compounds are above 110 K. In particular, (Cu,C)-1234 has the highest T(sub c) of 117 K.

  18. LARGE PIEZOELECTRIC EFFECT IN LOW-TEMPERATURE-SINTERED LEAD-FREE (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 THICK FILMS

    NASA Astrophysics Data System (ADS)

    Feng, Zuyong; Shi, Dongqi; Dou, Shixue; Hu, Yihua; Tang, Xingui

    2012-09-01

    High-quality piezoelectric (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 thick films with dense and homogenous microstructures were fabricated at a low sintering temperature (900°C) using a CuBi2O4 sintering aid. The 10 μm thick film exhibited a high longitudinal piezoelectric constant d33,eff of 210 pC/N with estimated unconstrained d33 value of 560 pC/N very close to that in the corresponding bulks. Such excellent piezoelectric effect in the low-temperature sintered (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 thick films is comparable to the case of lead-based PZT thick films, and may be a promising application in lead-free microdevices such as piezoelectric microelectromechanical systems (MEMS).

  19. Critical magnetic fields of superconducting aluminum-substituted Ba{sub 8}Si{sub 42}Al{sub 4} clathrate

    SciTech Connect

    Li, Yang Garcia, Jose; Lu, Kejie; Shafiq, Basir; Franco, Giovanni; Lu, Junqiang; Rong, Bo; Chen, Ning; Liu, Yang; Liu, Lihua; Song, Bensheng; Wei, Yuping; Johnson, Shardai S.; Luo, Zhiping; Feng, Zhaosheng

    2015-06-07

    In recent years, efforts have been made to explore the superconductivity of clathrates containing crystalline frameworks of group-IV elements. The superconducting silicon clathrate is unusual in that the structure is dominated by strong sp{sup 3} covalent bonds between silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. This paper reports on critical magnetic fields of superconducting Al-substituted silicon clathrates, which were investigated by transport, ac susceptibility, and dc magnetization measurements in magnetic fields up to 90 kOe. For the sample Ba{sub 8}Si{sub 42}Al{sub 4}, the critical magnetic fields were measured to be H{sub C1} = 40.2 Oe and H{sub C2} = 66.4 kOe. The London penetration depth of 4360 Å and the coherence length 70 Å were obtained, whereas the estimated Ginzburg–Landau parameter of κ = 62 revealed that Ba{sub 8}Si{sub 42}Al{sub 4} is a strong type-II superconductor.

  20. Photoluminescence properties of Si-N-doped BaAl{sub 12}O{sub 19}:Mn{sup 2+} phosphors for three-dimensional plasma display panels

    SciTech Connect

    Liu, Bitao; Han, Boyu; Zhang, Feng; Wen, Yan; Zhu, Ge; Zhang, Jia; Wang, Yuhua

    2012-01-15

    Highlights: Black-Right-Pointing-Pointer The brightness of Si-N-doped BHA phosphor is 119.9% of the un-doped BHA. Black-Right-Pointing-Pointer The decay time of Si-N-doped BHA phosphor is shorter than the un-doped sample. Black-Right-Pointing-Pointer The Si-N doping BHA is expected to be potentially applicable to 3D PDPs. -- Abstract: Si-N-doped BaAl{sub 12}O{sub 19}:Mn{sup 2+} phosphors were synthesized by a conventional solid-state reaction. It reveals that an efficiently host absorption in the vacuum ultraviolet region, which could be ascribed to the restricted Reidinger defects and oxygen vacancies by the Si-N doping. A fortified energy transfer from host to the activators was observed because of the newly formed defect energy levels which generated from the un-equivalence substitution of Si-N for Al-O. The shorter decay time of 4.05 ms was obtained which due to the increased defect concentration. This result indicates that Si-N doping BaAl{sub 12}O{sub 19}:Mn{sup 2+} phosphors would meet the requirements of 3D PDPs.