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Sample records for creates homogenous batio3

  1. Mn-Doped BaTiO3 Thin Film Sintered Using Nanocrystals and Its Dielectric Properties

    NASA Astrophysics Data System (ADS)

    Takezawa, Yoko; Kobayashi, Keisuke; Nakasone, Fumi; Suzuki, Toshimasa; Mizuno, Youichi; Imai, Hiroaki

    2009-11-01

    BaTiO3 thin films homogeneously doped with Mn were prepared by a novel powder-sintering thin-film process. Mn-doped BaTiO3 nanocrystals 5-7 nm in diameter were synthesized by a sol-gel method and sintered to form a highly densified microstructure containing columnar grains epitaxially grown on a (111)-oriented Pt/TiO2/Al2O3 substrate at a low temperature of 800 °C. On the basis of the results of various structural analyses, Mn was suggested to act as an acceptor in the perovskite structure of BaTiO3, which was also supported by the experimental finding indicating that the leakage current density was significantly improved compared with that of a nondoped BaTiO3 thin film. Moreover, the dielectric constant of the Mn-doped BaTiO3 thin film, 728 at 10 kHz with a loss tangent of 1.3%, was higher than that of the nondoped BaTiO3 thin film, probably owing to the electrostrictive effect induced by in-plane tensile stress. These results clearly indicate the feasibility of using doped BaTiO3 nanocrystals in the powder-sintering thin-film process for improving dielectric properties.

  2. Oxygen nonstoichiometry and dielectric evolution of BaTiO3. Part I—improvement of insulation resistance with reoxidation

    NASA Astrophysics Data System (ADS)

    Yang, G. Y.; Dickey, E. C.; Randall, C. A.; Barber, D. E.; Pinceloup, P.; Henderson, M. A.; Hill, R. A.; Beeson, J. J.; Skamser, D. J.

    2004-12-01

    Impedance spectroscopy, transmission electron microscopy, and electron energy-loss spectroscopy are used to correlate local electrical properties with the microstructure and microchemistry of BaTiO3 in Ni-electrode multilayer ceramic capacitors. High densities of linear defects and some grains with structural modulations are observed in BaTiO3 grains in the as-cofired capacitors. The modulated structure is formed on {111} planes of the BaTiO3. Both types of structural defects are associated with high concentrations of oxygen vacancies. In particular, the oxygen content in the BaTiO3 grains that are in direct contact with the internal Ni electrodes is less uniform with a systematic decrease in oxygen content towards the electrode. In the capacitors that are reoxidized in a higher oxygen partial pressure at lower temperature, the BaTiO3 grains are almost free of linear defects and structural modulations and the oxygen content is homogeneous throughout the BaTiO3 active layers. A concomitant improvement in the total insulation resistance is observed.

  3. Magnetoelectric coupling in multiferroic BaTiO3-CoFe2O4 composite nanofibers via electrospinning

    NASA Astrophysics Data System (ADS)

    Fu, Bi; Lu, Ruie; Gao, Kun; Yang, Yaodong; Wang, Yaping

    2015-07-01

    Magnetoelectric (ME) coupling in Pb-based multiferroic composites has been widely investigated due to the excellent piezoelectric property of lead zirconate titanate (PZT). In this letter, we report a strategy to create a hybrid Pb-free ferroelectric and ferromagnetic material and detect its ME coupling at the nanoscale. Hybrid Pb-free multiferroic BaTiO3-CoFe2O4 (BTO-CFO) composite nanofibers (NFs) were generated by sol-gel electrospinning. The perovskite structure of BTO and the spinel structure of CFO nanograins were homogenously distributed in the composite NFs and verified by bright-field transmission electron microscopy observations along the perovskite [111] zone axis. Multiferroicity was confirmed by amplitude-voltage butterfly curves and magnetic hysteresis loops. ME coupling was observed in terms of a singularity on a dM/dT curve at the ferroelectric Curie temperature (TC) of BaTiO3. The lateral ME coefficient was investigated by the evolution of the piezoresponse under an external magnetic field of 1000 Oe and was estimated to be α31 =0.78× 104 \\text{mV cm}-1 \\text{Oe}-1 . These findings could enable the creation of nanoscale Pb-free multiferroic composite devices.

  4. Ferroelectricity in (BaTiO3)n/(SrTiO3)m Superlattices Containing as Few as one BaTiO3 Layer (n=1)

    NASA Astrophysics Data System (ADS)

    Schlom, Darrell

    2007-03-01

    The question of how thin a ferroelectric can be and still be ferroelectric has been the source of an intensive research effort over the past decade. Several studies, both theoretical and experimental, have concluded that with appropriate boundary conditions ferroelectricity can exist in superlattices containing BaTiO3 or PbTiO3 layers as thin as one unit cell. In this talk I will show the results of experiment and theory for BaTiO3/SrTiO3 superlattices grown by reactive molecular-beam epitaxy (MBE) on three different substrates: TiO2-terminated (001) SrTiO3, (110) DyScO3, and (110) GdScO3. With the aid of reflection high-energy electron diffraction (RHEED), precise single-monolayer doses of BaO, SrO, and TiO2 were deposited sequentially to create commensurate BaTiO3/SrTiO3 superlattices with a variety of periodicities. The superlattices consist of an n unit-cell-thick slab of BaTiO3 followed by an m unit-cell-thick slab of SrTiO3, which are designated [(BaTiO3)n/(SrTiO3)m]q, where q is the number of times the bilayer is repeated. X-ray diffraction (XRD) measurements exhibit clear superlattice peaks and the narrowest rocking curves ever reported for oxide superlattices. High-resolution transmission electron microscopy reveals nearly atomically abrupt interfaces. UV Raman results show that the BaTiO3 in these [(BaTiO3)n/(SrTiO3)m]q superlattices is tetragonal and the SrTiO3 is polar due to strain. Temperature-dependent UV Raman and XRD reveal the paraelectric-to-ferroelectric transition temperature (TC). Our results* demonstrate (1) that [(BaTiO3)n/(SrTiO3)m]q superlattices containing as few as one strained BaTiO3 layer (n=1) are ferroelectric and (2) the sensitivity of TC to the boundary conditions. Comparisons to ab initio and phase-field modeling of the properties of these [(BaTiO3)n/(SrTiO3)m]q ferroelectric superlattices will be made and the importance of strain demonstrated. In addition to probing finite size effects and the importance of mechanical boundary

  5. Magnetic properties of mixed spinel BaTiO3-NiFe2O4 composites

    NASA Astrophysics Data System (ADS)

    Sarkar, Babusona; Dalal, Biswajit; Dev Ashok, Vishal; Chakrabarti, Kaushik; Mitra, Amitava; De, S. K.

    2014-03-01

    Solid solution of nickel ferrite (NiFe2O4) and barium titanate (BaTiO3), (100-x)BaTiO3-(x) NiFe2O4 has been prepared by solid state reaction. Compressive strain is developed in NiFe2O4 due to mutual structural interaction across the interface of NiFe2O4 and BaTiO3 phases. Quantitative analysis of X-ray diffraction and X-ray photo electron spectrum suggest mixed spinel structure of NiFe2O4. A systematic study of composition dependence of composite indicates BaTiO3 causes a random distribution of Fe and Ni cations among octahedral and tetrahedral sites during non-equilibrium growth of NiFe2O4. The degree of inversion decreases monotonically from 0.97 to 0.75 with increase of BaTiO3 content. Temperature dependence of magnetization has been analyzed by four sublattice model to describe complex magnetic exchange interactions in mixed spinel phase. Curie temperature and saturation magnetization decrease with increase of BaTiO3 concentration. Enhancement of strain and larger occupancy of Ni2+ at tetrahedral site increase coercivity up to 200 Oe. Magnetostructual coupling induced by BaTiO3 improves coercivity in NiFe2O4. An increase in the demagnetization and homogeneity in magnetization process in NiFe2O4 is observed due to the interaction with diamagnetic BaTiO3.

  6. Influence of nanogold additives on phase formation, microstructure and dielectric properties of perovskite BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Nonkumwong, Jeeranan; Ananta, Supon; Srisombat, Laongnuan

    2015-06-01

    The formation of perovskite phase, microstructure and dielectric properties of nanogold-modified barium titanate (BaTiO3) ceramics was examined as a function of gold nanoparticle contents by employing a combination of X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, Archimedes principle and dielectric measurement techniques. These ceramics were fabricated from a simple mixed-oxide method. The amount of gold nanoparticles was found to be one of the key factors controlling densification, grain growth and dielectric response in BaTiO3 ceramics. It was found that under suitable amount of nanogold addition (4 mol%), highly dense perovskite BaTiO3 ceramics with homogeneous microstructures of refined grains (~0.5-3.1 μm) and excellence dielectric properties can be produced.

  7. Electrical Properties of BaTiO3-Based Multilayer Ceramic Capacitors Sintered with Plasma-Treated Glass Powder

    NASA Astrophysics Data System (ADS)

    Jeong, Dae-Yong; Lee, Soon-il; Lee, Heun-Young; Kim, Min-Kee; Yoon, Jung-Rag

    2013-10-01

    The influence of glass power morphology on the electrical and microstructural properties of BaTiO3-based multilayer ceramic capacitors (MLCCs) was investigated to enhance the reliability of MLCCs. For a sintering additive, glass particles of different sizes and shapes were prepared by jet-milling and RF plasma treatment. Plasma treatment decreased the glass particle size and transformed the irregular shape of glass particles into homogeneous spherical shapes. It was found that MLCCs sintered with plasma-treated glass powder have a more homogeneous microstructure, a clear core-shell structure, a more stable capacitance against voltage and temperature changes, and a higher degradation resistance. It is inferred that nanosized spherical glass powder prepared by plasma treatment helps so-called magic dopants such as rare-earth elements to be distributed homogeneously around the BaTiO3 particles.

  8. Preparation of BaTiO3/Cu2O and BaTiO3/Cu2O/Au Complexes: Their Photocatalytic and Antipathogenic Effect.

    PubMed

    Cho, Sung-Woo; Nam, Dae-Hyun; Kim, Lee-Han; Jung, Dongwoon

    2016-05-01

    BaTiO3/Cu2O and BaTiO3/Cu2O/Au complexes were prepared from CuCl2, HAuCl4 solution, and BaTiO3 by the solution method. BaTiO3 particles were dispersed in a CuCl2 solution, and the BaTiO3/CuO complex was produced through crystallization of CuO onto the BaTiO3 surface by hydrolysis of CuCl2 in the first stage. After the reaction, CuO was reduced to Cu2O by treatment with glucose, thereby yielding the BaTiO3/Cu2O complex. The BaTiO3/Cu2O/Au complex was prepared by treating the BaTiO3/Cu2O particles with HAuCl4. Under visible light, the obtained BaTiO3/Cu2O0/Au complex showed higher photocatalytic activity than the Degussa P-25sample. In addition, the BaTiO3/Cu2O complex showed excellent antipathogenic effect. PMID:27483887

  9. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.; Potember, Richard S.

    1991-01-01

    The principle objectives of this ongoing research involve the preparation and characterization of polycrystalline single-domain thin films of BaTiO3 for photorefractive applications. These films must be continuous, free of cracks, and of high optical quality. The two methods proposed are sputtering and sol-gel related processing.

  10. Ferroelectric-like metallic state in electron doped BaTiO3

    PubMed Central

    Fujioka, J.; Doi, A.; Okuyama, D.; Morikawa, D.; Arima, T.; Okada, K. N.; Kaneko, Y.; Fukuda, T.; Uchiyama, H.; Ishikawa, D.; Baron, A. Q. R.; Kato, K.; Takata, M.; Tokura, Y.

    2015-01-01

    We report that a ferroelectric-like metallic state with reduced anisotropy of polarization is created by the doping of conduction electrons into BaTiO3, on the bases of x-ray/electron diffraction and infrared spectroscopic experiments. The crystal structure is heterogeneous in nanometer-scale, as enabled by the reduced polarization anisotropy. The enhanced infrared intensity of soft phonon along with the resistivity reduction suggests the presence of unusual electron-phonon coupling, which may be responsible for the emergent ferroelectric structure compatible with metallic state. PMID:26289749

  11. Growth of BaTiO3-PVDF composite thick films by using aerosol deposition

    NASA Astrophysics Data System (ADS)

    Cho, Sung Hwan; Yoon, Young Joon

    2016-01-01

    Barium titanate (BaTiO3)-polyvinylidene fluoride (PVDF) composite thick films were grown by using aerosol deposition at room temperature with BaTiO3 and PVDF powders. To produce a uniform composition in ceramic and polymer composite films, which show a substantial difference in specific gravity, we used PVDF-coated BaTiO3 powders as the starting materials. An examination of the microstructure confirmed that the BaTiO3 were well distributed in the PVDF matrix in the form of a 0 - 3 compound. The crystallite size in the BaTiO3-PVDF composite thick films was 5 ˜ 50 times higher than that in pure BaTiO3 thick films. PVDF plays a role in suppressing the fragmentation of BaTiO3 powder during the aerosol deposition process and in controlling the relative permittivity.

  12. Conformal BaTiO3 Films with High Piezoelectric Coupling through an Optimized Hydrothermal Synthesis.

    PubMed

    Zhou, Zhi; Bowland, Christopher C; Patterson, Brendan A; Malakooti, Mohammad H; Sodano, Henry A

    2016-08-24

    Two-dimensional (2D) ferroelectric films have vast applications due to their dielectric, ferroelectric, and piezoelectric properties that meet the requirements of sensors, nonvolatile ferroelectric random access memory (NVFeRAM) devices, and micro-electromechanical systems (MEMS). However, the small surface area of these 2D ferroelectric films has limited their ability to achieve higher memory storage density in NVFeRAM devices and more sensitive sensors and transducer. Thus, conformally deposited ferroelectric films have been actively studied for these applications in order to create three-dimensional (3D) structures, which lead to a larger surface area. Most of the current methods developed for the conformal deposition of ferroelectric films, such as metal-organic chemical vapor deposition (MOCVD) and plasma-enhanced vapor deposition (PECVD), are limited by high temperatures and unstable and toxic organic precursors. In this paper, an innovative fabrication method for barium titanate (BaTiO3) textured films with 3D architectures is introduced to alleviate these issues. This fabrication method is based on converting conformally grown rutile TiO2 nanowire arrays into BaTiO3 textured films using a simple two-step hydrothermal process which allows for thickness-controlled growth of conformal films on patterned silicon wafers coated with fluorine-doped tin oxide (FTO). Moreover, the processing parameters have been optimized to achieve a high piezoelectric coupling coefficient of 100 pm/V. This high piezoelectric response along with high relative dielectric constant (εr = 1600) of the conformally grown textured BaTiO3 films demonstrates their potential application in sensors, NVFeRAM, and MEMS. PMID:27487556

  13. Formation of BaTiO 3 from Citrate Precursor

    NASA Astrophysics Data System (ADS)

    Rajendran, M.; Rao, M. Subba

    1994-12-01

    On thermal decomposition barium bis(citrato)oxotitanate (IV) citrate heptahydrate produces stoichiometric BaTiO3 fine powders at about 650°C. Thermal decomposition of the precursor proceeds through three major stages, viz. (i) dehydration, (ii) decomposition of the citrate to form an oxycarbonate intermediate Ba2Ti2O5CO3, and (iii) decomposition of the intermediate carbonate to form BaTiO3. Spectroscopic and thermoanalytical techniques are presently employed to characterize the precursor and the intermediates isolated at various stages. As-prepared BaTiO3 is a mixture of cubic and tetragonal phases. The primary particle size of the powder is on the order of 100 nm, as revealed by the TEM technique. Calcining the powders above 800°C results in the formation of complete tetragonal phase with improved crystallinity. The resultant powders are sinter active to give dense monophasic ceramic compacts having densities in the range 95-99% of the theoretical value. Depending on the processing conditions, the dielectric constant (εr) varies from 1600 to 3000 at 1 kHz, while the dielectric loss, tan δ, ranges from 0.003 to 0.009 at 300 K.

  14. Submerged arc discharge technique to explore novel non-carbon nanotubes: Syntheses of nanotubes from ZnO and BaTiO3

    NASA Astrophysics Data System (ADS)

    Sano, Noriaki; Tamon, Hajime

    2014-04-01

    A unique reaction field using arc discharge in water can create novel nanostructures, where an extreme temperature drop is observed in bubbles around a hot arc plasma zone. Here, a Mo anode had a hole at its tip, into which ZnO or BaTiO3 powder was stuffed. The cathode received film products on its surface. It was revealed that BaTiO3 nanotubes were firstly synthesized as novel nanotubes when BaTiO3 powder was stuffed in the anode hole. When ZnO powder was stuffed in the anode hole, narrow ZnO nanotubes were synthesized. The diameter of the ZnO nanotubes synthesized was the smallest ever reported.

  15. BaTiO3 supercages: unusual oriented nanoparticle aggregation and continuous ordering transition in morphology.

    PubMed

    Li, Juan; Hietala, Sami; Tian, Xuelin

    2015-01-27

    Here we report the organic-free mesocrystalline superstructured cages of BaTiO3, i.e., the BaTiO3 supercages, which are synthesized by a one-step templateless and additive-free route using molten hydrated salt as the reaction medium. An unusual three-dimensional oriented aggregation of primary BaTiO3 nanoparticles in the medium of high ionic strength, which normally favors random aggregation, is identified to take place at the early stage of the synthesis. The spherical BaTiO3 aggregates further experience a remarkable continuous ordering transition in morphology, consisting of nanoparticle faceting and nanosheet formation steps. This ordering transition in conjunction with Ostwald ripening-induced solid evacuation leads to the formation of unique supercage structure of BaTiO3. Benefiting from their structure, the BaTiO3 supercages exhibit improved microwave absorption property. PMID:25514033

  16. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.

    1993-01-01

    During the period covered by this report, October 11, 1991 through October 10, 1992, the research has progressed in a number of different areas. The sol-gel technique was initially studied and experimentally evaluated for depositing films of BaTiO3. The difficulties with the precursors and the poor quality of the films deposited lead to the investigation of pulsed laser deposition as an alternative approach. The development of the pulsed laser deposition technique has resulted in continuous improvements to the quality of deposited films of BaTiO3. The initial depositions of BaTiO3 resulted in amorphous films, however, as the pulsed laser deposition technique continued to evolve, films were deposited in the polycrystalline state, then the textured polycrystalline state, and most recently heteroepitaxial films have also been successfully deposited on cubic (100) oriented SrTiO3 substrates. A technique for poling samples at room temperature and in air is also undergoing development with some very preliminary but positive results. The analytical techniques, which include x-ray diffraction, ferroelectric analysis, UV-Vis spectrophotometry, scanning electron microscopy with x-ray compositional analysis, optical and polarized light microscopy, and surface profilometry have been enhanced to allow for more detailed evaluation of the samples. In the area of optical characterization, a pulsed Nd:YAG laser has been incorporated into the experimental configuration. Now data can also be acquired within various temporal domains resulting in more detailed information on the optical response of the samples and on their photorefractive sensitivity. The recent establishment of collaborative efforts with two departments at Johns Hopkins University and the Army Research Lab at Fort Belvoir has also produced preliminary results using the metallo-organic decomposition technique as an alternative method for thin film processing of BaTiO3. RF and DC sputtering is another film deposition approach that should be initiated in the near future. Other techniques for optical characterization, which may even allow for intragrannular (within single grains) investigations, are also being considered.

  17. Electro-optic and dielectric properties of photorefractive BaTiO3 and KNbO3

    NASA Astrophysics Data System (ADS)

    Zgonik, Marko; Nakagawa, Kiyoshi; Günter, Peter

    1995-08-01

    Recently determined complete sets of materials parameters describing the dielectric, elastic, piezoelectric, elasto-optic, and electro-optic properties of BaTiO3 and KNbO3 crystals at room temperature are used to calculate the effective electro-optic coefficients and dielectric constants required for describing photorefractive phenomena. We show a substantial deviation of the new values from the electro-optic coefficients for homogeneously applied electric fields that were used previously in describing the photorefractive effects. We derive angular dependences of the effective electro-optic coefficients and the effective dielectric constants relevant for grating recording in both crystals and verify them experimentally.

  18. Characterization of LiF/CuO-Codoped BaTiO3 for Embedded Capacitors

    NASA Astrophysics Data System (ADS)

    Lee, Kyoungho

    2015-03-01

    Sintering additives for BaTiO3 were studied in order to facilitate the use of BaTiO3 as a material for embedded decoupling capacitors in high-density multilayered low-temperature cofired ceramic (LTCC) modules for mobile communication systems and three-dimensional (3D) printing modules. Among the studied additives, the CuO/LiF mixture was the most promising sintering additive for cofiring BaTiO3 with a commercial low-permittivity ( ɛ r) LTCC sheet (MLS-22, NEG Co.). The temperature dependence of the dielectric properties of BaTiO3 was successfully controlled by adjusting the CuO/LiF amount and ratio and the sintering temperature. BaTiO3 codoped with 10 wt.% LiF/CuO (1:1 ratio) and sintered at 860°C for 30 min showed 95% sintering density. The room-temperature permittivity ( ɛ r) of LiF/CuO-codoped BaTiO3 was 1620 at 1 MHz, and the temperature coefficient of capacitance satisfied the X5R specification. After cofiring this LiF/CuO-codoped BaTiO3 ceramic with an MLS-22 sheet at 860°C, there was no crack formation at the layer boundary. Also a chemical compatibility test revealed that there were no severe reactions between the LiF/CuO-codoped BaTiO3 and an Ag electrode.

  19. Theoretical Analysis of Oxygen Vacancy Formation in Zr-Doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Umeda, Yuji; Takano, Kosuke; Kojima, Takashi; Kuwabara, Akihide; Moriwake, Hiroki

    2012-09-01

    One of the most serious problems for the development of multilayer ceramic capacitors (MLCCs) is that their electrical resistance decreases under long-term DC voltage. Oxygen vacancy migration in BaTiO3 is thought to be one cause of this deterioration. In this study, to understand this mechanism, quantitative analysis of the oxygen vacancy formation energy [Ef(VO)] in Zr-doped and undoped BaTiO3 was performed. The Ef(VO) of Zr-doped BaTiO3 was higher than that of undoped BaTiO3 because the valence of Ti in undoped BaTiO3 easily changed from +4 to +3 owing to oxygen vacancy formation, compared with that in Zr-doped BaTiO3. We also prepared undoped (BaTiO3) and Zr-doped (BaZr0.05Ti0.95O3) ceramic samples sintered under reducing atmosphere (T = 1573 K pO2 = 10-13 MPa). BaZr0.05Ti0.95O3 remained an insulator, but BaTiO3 showed semiconducting behavior. This experimental result corresponds well to theoretical results of first-principles calculations.

  20. Nanostructural evolution of one-dimensional BaTiO3 structures by hydrothermal conversion of vertically aligned TiO2 nanotubes

    NASA Astrophysics Data System (ADS)

    Muñoz-Tabares, J. A.; Bejtka, K.; Lamberti, A.; Garino, N.; Bianco, S.; Quaglio, M.; Pirri, C. F.; Chiodoni, A.

    2016-03-01

    The use of TiO2 nanotube (NT) arrays as templates for hydrothermal conversion of one-dimensional barium titanate (BaTiO3) structures is considered a promising synthesis approach, even though the formation mechanisms are not yet fully understood. Herein we report a nanostructural study by means of XRD and (HR)TEM of high aspect ratio TiO2-NTs hydrothermally converted into BaTiO3. The nanostructure shows two different and well-defined regions: at the top the conversion involves complete dissolution of NTs and subsequent precipitation of BaTiO3 crystals by homogeneous nucleation, followed by the growth of dendritic structures by aggregation and oriented attachment mechanisms. Instead, at the bottom, the low liquid/solid ratio, due to the limited amount of Ba solution that infiltrates the NTs, leads to the rapid crystallization of such a solution into BaTiO3, thus allowing the NTs to act as a template for the formation of highly oriented one-dimensional nanostructures. The in-depth analysis of the structural transformations that take place during the formation of the rod-like arrays of BaTiO3 could help elucidate the conversion mechanism, thus paving the way for the optimization of the synthesis process in view of new applications in energy harvesting devices, where easy and low temperature processing, controlled composition, morphology and functional properties are required.The use of TiO2 nanotube (NT) arrays as templates for hydrothermal conversion of one-dimensional barium titanate (BaTiO3) structures is considered a promising synthesis approach, even though the formation mechanisms are not yet fully understood. Herein we report a nanostructural study by means of XRD and (HR)TEM of high aspect ratio TiO2-NTs hydrothermally converted into BaTiO3. The nanostructure shows two different and well-defined regions: at the top the conversion involves complete dissolution of NTs and subsequent precipitation of BaTiO3 crystals by homogeneous nucleation, followed by the

  1. Dielectric response of polystyrene - BaTiO3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Korotkova, Tatyana N.; Sysoev, Oleg I.; Belov, Pavel A.; Emelianov, Nikita A.; Velyaev, Yury O.; Mandalawi, Wissam M. Al; Korotkov, Leonid N.

    2016-07-01

    The series of composite materials based on polystyrene and non-ferroelectric BaTiO3 nanoparticles ((1-x)PS-xBT, where the volume concentration x = 0-1.0) was prepared. Their dielectric properties were studied within the temperature range 20-160 °C at the frequency of 100 kHz. It is found that an increase in the barium titanate concentration leads to increase of the both dielectric permittivity (ɛ) and dielectric losses (tgδ). The concentration dependence of ɛ can be described by the modified Kerner model. It was found that the glass transition in polystyrene matrix is diffused and its temperature is increased with concentration x.

  2. Multiferroic properties of nanocrystalline BaTiO 3

    NASA Astrophysics Data System (ADS)

    Mangalam, R. V. K.; Ray, Nirat; Waghmare, Umesh V.; Sundaresan, A.; Rao, C. N. R.

    2009-01-01

    Some of the Multiferroics [H. Schmid, Ferroelectrics 162 (1994) 317] form a rare class of materials that exhibit magneto-electric coupling arising from the coexistence of ferromagnetism and ferroelectricity, with potential for many technological applications [J.F. Scott, Nat. Mater. 6 (2007) 256; N.A. Spaldin, M. Fiebig, Science 309 (2005) 391]. Over the last decade, an active research on multiferroics has resulted in the identification of a few routes that lead to multiferroicity in bulk materials [C. Ederer, N.A. Spaldin, Nat. Mater. 3 (2004) 849; D.V. Efremov, J. van den Brink, D.I. Khomskii, Nat. Mater. 3 (2004) 853; N. Hur, S. Park, P.A. Sharma, J.S. Ahn, S. Guha, S.W. Cheong, Nature 429 (2004) 392]. While ferroelectricity in a classic ferroelectric such as BaTiO 3 is expected to diminish with the reducing particle size, [C.H. Ahn, K.M. Rabe, J.M. Triscone, Science 303 (2004) 488; J. Junquera, P. Ghosez, Nature 422 (2003) 506] ferromagnetism cannot occur in its bulk form [N.A. Hill, J. Phys. Chem. B 104 (2000) 6694]. Here, we use a combination of experiment and first-principles simulations to demonstrate that multiferroic nature emerges in intermediate size nanocrystalline BaTiO 3, ferromagnetism arising from the oxygen vacancies at the surface and ferroelectricity from the core. A strong coupling between a surface polar phonon and spin is shown to result in a magnetocapacitance effect observed at room temperature, which can open up possibilities of new electro-magneto-mechanical devices at the nano-scale.

  3. Facile synthesis of BaTiO3 nanotubes and their microwave absorption properties.

    PubMed

    Zhu, Yao-Feng; Zhang, Li; Natsuki, Toshiaki; Fu, Ya-Qin; Ni, Qing-Qing

    2012-04-01

    Uniform BaTiO(3) nanotubes were synthesized via a simple wet chemical route at low temperature (50 °C). The as-synthesized BaTiO(3) nanotubes were characterized using powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results show that the BaTiO(3) nanotubes formed a cubic phase with an average diameter of ~10 nm and wall thickness of 3 nm at room temperature. The composition of the mixed solvent (ethanol and deionized water) was a key factor in the formation of these nanotubes; we discuss possible synthetic mechanisms. The microwave absorption properties of the BaTiO(3) nanotubes were studied at microwave frequencies between 0.5 and 15 GHz. The minimum reflection loss of the BaTiO(3) nanotubes/paraffin wax composite (BaTiO(3) nanotubes weight fraction = 70%) reached 21.8 dB (~99.99% absorption) at 15 GHz, and the frequency bandwidth less than -10 dB is from 13.3 to 15 GHz. The excellent absorption property of BaTiO(3) nanotubes at high frequency indicates that these nanotubes could be promising microwave-absorbing materials. PMID:22409350

  4. Characterization of hollow BaTiO3 nanofibers and intense visible photoluminescence

    NASA Astrophysics Data System (ADS)

    Woong Lee, Kui; Siva Kumar, Koppala; Heo, Gaeun; Seong, Maeng-Je; Yoon, Jong-Won

    2013-10-01

    BaTiO3 hollow nanofibers were fabricated by electrospinning and then subsequent calcination of as-spun nanofibers with a heating rate of 2.5 °C/min. Scanning electron microscope and transmission electron microscope (TEM) results indicated that the heating rate had a significant effect on the morphology of the BaTiO3 hollow nanofibers. The X-ray diffraction, Raman spectroscopy, and TEM results indicate the prepared BaTiO3 hollow nanofibers have tetragonal phases. From the results of the X-ray photoelectron spectroscopy analysis, in the amorphous BaTiO3 nanofiber, peaks at 457.2 eV for Ti 2p3/2 were also found, which corresponded to the Ti3+ ions. However, in the crystalline BaTiO3 nanofibers, peaks of Ti 2p3/2 showed the Ti4+ ions. Intense visible photoluminescence was observed in the amorphous BaTiO3 nanofiber, which is calcined below a temperature of 500 °C. The observed intense photoluminescence was ascribed to a multiphonon process with localized states within the band gap of the highly disordered states. In the crystalline BaTiO3 hollow fiber, low intensity of photoluminescence showed at the visible region, which is originated from an intrinsic Ba defect.

  5. Preparation and characterization of highly crystallized BaTiO3 layer on Ni nanoparticles

    NASA Astrophysics Data System (ADS)

    Hao, Yanan; Wang, Xiaohui; Zhang, Hui; Li, Longtu

    2015-01-01

    A uniform polycrystalline BaTiO3 layer is coated on Ni nanoparticles by an economic and effective one-step sol-precipitation method for future applications in next-generation multilayer ceramic capacitors. Using NaOH to provide strong alkaline conditions, a highly crystallized BaTiO3 layer is obtained with high efficiency. The influence of the BaTiO3 coating amount on the properties of Ni powders is examined. Transmission electron microscopy and energy-dispersive spectroscopy show that the BaTiO3 layer is continuous and uniform. X-ray photoelectron spectra of the Ba, O states show that a strong bonding was formed between the coating layer and the Ni surfaces. Through this bonding, BaTiO3 can heterogeneously nucleate and crystallize on the Ni surfaces. This polycrystalline BaTiO3 layer is very effective in protecting Ni from oxidation as well as increasing the shrinkage onset temperature of Ni nanoparticles. Moreover, these properties can be further improved by increasing the BaTiO3 coating amount.

  6. Absence of low-temperature phase transitions in epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Tenne, D. A.; Xi, X. X.; Li, Y. L.; Chen, L. Q.; Soukiassian, A.; Zhu, M. H.; James, A. R.; Lettieri, J.; Schlom, D. G.; Tian, W.; Pan, X. Q.

    2004-05-01

    We have studied phase transitions in epitaxial BaTiO3 thin films by Raman spectroscopy. The films are found to remain in a single ferroelectric phase over the temperature range from 5 to 325 K. The low-temperature phase transitions characteristic of bulk BaTiO3 (tetragonal-orthorhombic-rhombohedral) are absent in the films. X-ray diffraction shows that the BaTiO3 films are under tensile strain due to the thermal expansion mismatch with the buffer layer. A phase-field calculation of the phase diagram and domain structures in BaTiO3 thin films predicts, without any priori assumption, that an orthorhombic phase with in-plane polarization is the thermodynamically stable phase for such values of tensile strain and temperature, consistent with the experimental Raman results.

  7. In situ growth BaTiO3 nanocubes and their superlattice from an aqueous process

    NASA Astrophysics Data System (ADS)

    Dang, Feng; Mimura, Kenichi; Kato, Kazumi; Imai, Hiroaki; Wada, Satoshi; Haneda, Hajime; Kuwabara, Makoto

    2012-02-01

    Ordered aggregated BaTiO3 nanocubes with a narrow size distribution were obtained in an aqueous process by using bis(ammonium lactate) titanium dihydroxide (TALH) as Ti source in the presence of oleic acid and tert-butylamine. Kinetics of the formation of BaTiO3 nanocubes indicated that an in situ growth mechanism was dominant and the superlattice of nanocubes formed in situ through the growth of BaTiO3 nanoparticles in Ti-based hydrous gel. The size and morphology of nanocubes were controlled by tuning the concentration and molar ratio of surfactants. A novel growth model dependant on the structure of Ti precursor for the formation and morphology control of BaTiO3 nanocubes and their superlattice was demonstrated.Ordered aggregated BaTiO3 nanocubes with a narrow size distribution were obtained in an aqueous process by using bis(ammonium lactate) titanium dihydroxide (TALH) as Ti source in the presence of oleic acid and tert-butylamine. Kinetics of the formation of BaTiO3 nanocubes indicated that an in situ growth mechanism was dominant and the superlattice of nanocubes formed in situ through the growth of BaTiO3 nanoparticles in Ti-based hydrous gel. The size and morphology of nanocubes were controlled by tuning the concentration and molar ratio of surfactants. A novel growth model dependant on the structure of Ti precursor for the formation and morphology control of BaTiO3 nanocubes and their superlattice was demonstrated. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr11594h

  8. Probing the Metal-Insulator Transition in BaTiO3 by Electrostatic Doping

    NASA Astrophysics Data System (ADS)

    Raghavan, Santosh; Zhang, Jack Y.; Shoron, Omor F.; Stemmer, Susanne

    2016-07-01

    The metal-to-insulator transition in BaTiO3 is investigated using electrostatic doping, which avoids effects from disorder and strain that would accompany chemical doping. SmTiO3/BaTiO3/SrTiO3 heterostructures are doped with a constant sheet carrier density of 3 ×1014 cm-2 that is introduced via the polar SmTiO3/BaTiO3 interface. Below a critical BaTiO3 thickness, the structures exhibit metallic behavior with high carrier mobilities at low temperatures, similar to SmTiO3/SrTiO3 interfaces. Above this thickness, data indicate that the BaTiO3 layer becomes ferroelectric. The BaTiO3 lattice parameters increase to a value consistent with a strained, tetragonal unit cell, the structures are insulating below ˜125 K , and the mobility drops by more than an order of magnitude, indicating self-trapping of carriers. The results shed light on the interplay between charge carriers and ferroelectricity.

  9. Properties of polycarbonate containing BaTiO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Lomax, J. F.; Fontanella, J. J.; Edmondson, C. A.; Wintersgill, M. C.; Wolak, M. A.; Westgate, M. A.; Lomax, E. A.; Lomax, P. Q.; Bogle, X.; Rúa, A.; Greenbaum, S. G.

    2014-03-01

    The real part of the relative permittivity, ɛ', and dielectric loss, tan δ, have been determined at audio frequencies at temperatures from about 5 K to 350 K for nano-composites composed of BaTiO3 nanoparticles and polycarbonate. The room temperature breakdown strength was also measured and thermal analysis, nuclear magnetic resonance and scanning electron microscopy studies were carried out. For some films the nanoparticles were surface-treated (STNP) while for others they were not (UNP). For concentrations of UNP greater than about 3.4 vol. %, ɛ' is much larger than expected on the basis of laws of mixing. On the other hand, ɛ' for materials made using STNP is well-behaved. Correspondingly, increased loss (ɛ″ or tan δ) in the vicinity of room temperature is observed for the materials made from UNP. The anomalously large values of relative permittivity and increased loss are attributed to the presence of large aggregates in the materials made using the UNP. For both UNP-and STNP-based materials, the breakdown strength is found to decrease as nanoparticle concentration increases. The breakdown strength for the materials made using STNP is found to be larger for all concentrations than for those containing UNP despite the presence of large aggregates in some of the STNP-based materials. This shows that breakdown is strongly affected by the nanoparticle surfaces and/or the interface layer. It is also found that the breakdown strength for materials made using UNP increases as particle size increases. Finally, variable temperature and pressure proton nuclear magnetic resonance relaxation measurements were made to assess the effect of nanoparticle inclusion on polymer motion, and the effects were found to be very minor.

  10. Electric in-plane polarization in multiferroic CoFe2O4/BaTiO3 nanocomposite tuned by magnetic fields

    NASA Astrophysics Data System (ADS)

    Schmitz-Antoniak, Carolin; Schmitz, Detlef; Borisov, Pavel; de Groot, Frank M. F.; Stienen, Sven; Warland, Anne; Krumme, Bernhard; Feyerherm, Ralf; Dudzik, Esther; Kleemann, Wolfgang; Wende, Heiko

    2013-06-01

    Ferrimagnetic CoFe2O4 nanopillars embedded in a ferroelectric BaTiO3 matrix are an example for a two-phase magnetoelectrically coupled system. They operate at room temperature and are free of any resource-critical rare-earth element, which makes them interesting for potential applications. Prior studies succeeded in showing strain-mediated coupling between the two subsystems. In particular, the electric properties can be tuned by magnetic fields and the magnetic properties by electric fields. Here we take the analysis of the coupling to a new level utilizing soft X-ray absorption spectroscopy and its associated linear dichroism. We demonstrate that an in-plane magnetic field breaks the tetragonal symmetry of the (1,3)-type CoFe2O4/BaTiO3 structures and discuss it in terms of off-diagonal magnetostrictive-piezoelectric coupling. This coupling creates staggered in-plane components of the electric polarization, which are stable even at magnetic remanence due to hysteretic behaviour of structural changes in the BaTiO3 matrix. The competing mechanisms of clamping and relaxation effects are discussed in detail.

  11. Synthesis and Microwave Absorption Properties of BaTiO3-polypyrrole Composite

    NASA Astrophysics Data System (ADS)

    Li, Qiao-ling; Zhang, Cun-rui; Li, Jian-qiang

    2010-10-01

    BaTiO3 powders are prepared by sol-gel method by cotton template. Polypyrrole is prepared by chemical oxidation route in the emulsion polymerization system. Then BaTiO3-polypyrrole composites with different mixture ratios are prepared by as-prepared material. The structure, morphology, and properties of the composites are characterized with Infrared spectrum, X-ray diffraction, scanning electron microscope, and net-wok analyzer. The complex permittivity and reflection loss of the composites are measured at different microwave frequencies in S-band and C-band (0.03-6 GHz) employing vector network analyzer model PNA 3629D vector. The effect of the mass ratio of BaTiO3 to polypyrrole on the microwave loss properties of the composites is investigated. A possible microwave absorbing mechanism of BaTiO3-polypyrrole composite is proposed. The BaTiO3-polypyrrole composite can find applications in suppression of electromagnetic interference and reduction of radar signature.

  12. Influencing Factor Investigation on Dynamic Hydrothermal Growth of Gapped Hollow BaTiO3 Nanospheres

    NASA Astrophysics Data System (ADS)

    Gao, Jiabing; Shi, Haiyue; Yang, Jing; Li, Tao; Zhang, Rui; Chen, Deliang

    2015-08-01

    Gapped hollow BaTiO3 nanospheres with an apparent diameter of 93 ± 19 nm (shell thickness of 10-20 nm) were synthesized via a dynamic hydrothermal process using TiO2 sols and Ba2+ ions as the Ti and Ba sources in alkaline aqueous solutions. The phases and morphologies of the BaTiO3 samples were characterized by X-ray diffraction (XRD), SEM, TEM, and Raman spectra. The effects of the hydrothermal temperatures and durations, NaOH concentrations, and Ba/Ti ratios on the formation of gapped hollow BaTiO3 nanospheres were systematically investigated. The optimum conditions for forming gapped hollow BaTiO3 nanospheres are hydrothermal treatment at 180 °C for 10-20 h under a continuous magnetic stirring with NaOH concentrations of about 1 mol/L and molar Ba/Ti ratios of 1.2-1.5. The formation mechanism of the gapped hollow BaTiO3 nanospheres is understood as the combination of the orientated attachment and reversed crystal growth.

  13. Sintering and Microstructure of BaTiO3 Nano Particles Synthesized by Molten Salt Method.

    PubMed

    Lee, Chang-Hyun; Shin, Hyo-Soon; Yeo, Dong-Hun; Ha, Gook-Hyun; Nahm, Sahn

    2016-05-01

    In order to establish thinner dielectric layers in thick film electronic components such as MLCC (Multilayer ceramic capacitor), BaTiO3 nanoparticles have been utilized. However, studies on the synthesis of nanoparticles smaller than 20 nm, the characteristics of the BaTiO3 powder, and the powder's sintering are lacking. Therefore, this paper aims to synthesize BaTiO3 particles smaller than 20 nm by using the molten salt method and evaluate the microstructure and dielectric properties by varying the sintering temperature from 750 degrees C to 1200 degrees C. Through the molten salt method and by using KOH-KCl mixed salt, 20 nm BaTiO3 powder was synthesized at a low temperature of 150 degrees C. Sintering the pellets formed from the synthesized 20 nm BaTiO3 nano powder led to the observation of an unusual phenomenon where the particles grew to approximate sizes below 850 degrees C where densification progressed. At sintering temperatures above 950 degrees C, particles that expanded into rod shapes were observed and these particles were identified to be unreacted TiO2 based on the results of the EDX (Energy Dispersive X-ray Spectroscopy) analysis and phase analysis results. PMID:27483905

  14. BaTiO3 and polypropylene nanocomposites for capacitor applications

    NASA Astrophysics Data System (ADS)

    Dong, Daxuan; Tang, Longxiang; Zhu, Lei; Lee, Je; Case Western Reserve University Collaboration; Agiltron, Inc Collaboration

    2013-03-01

    A novel strategy to uniformly disperse 70-nm BaTiO3 ferroelectric nanoparticles in a dielectric polypropylene (PP) matrix is developed in order to achieve high dielectric constant and high energy density for capacitor applications. By modifying BaTiO3 surface with a bis-phosphonic acid-terminated polyhedral oligomeric selsisquioxane (POSS), a nanocomposite with BaTiO3@POSS uniformly dispersed in PP matrix was achieved. The nanocomposite film containing a high nanoparticle content of 30 vol.% exhibited a high dielectric constant of 32 and a breakdown voltage of 220 MV/m, but with a high energy loss. Improvement of this nanocomposite by understanding the interfacial polarization is carried out in this work. The dielectric constant difference between BaTiO3 and PP can generate interfacial polarization and subsequent internal conduction in BaTiO3 particles upon bipolar polarization. Reduction of this internal conduction mechanism will significantly reduce the hysteresis loss in polymer nanodielectrics.

  15. Reduced energy loss in poly(vinylidene fluoride) nanocomposites by filling with a small loading of core-shell structured BaTiO3/SiO2 nanofibers

    NASA Astrophysics Data System (ADS)

    Liu, Shaohui; Xue, Shuangxi; Shen, Bo; Zhai, Jiwei

    2015-07-01

    Homogeneous ceramic-polymer nanocomposites consisting of core-shell structured BaTiO3/SiO2 nanofibers and a p oly(vinylidene fluoride) (PVDF) polymer matrix have been prepared. The correlation between the energy discharged density and interfacial polarization is studied in PVDF nanocomposites by the measurements of the discharge performance and impedance spectroscopy. According to the results of dielectric constant, breakdown strength, and complex impedance analysis, coating SiO2 layers on the surface of BaTiO3 nanofibers can block the movement of charge carriers through the nanocomposites by playing a shielding role on the charge-rich inter layer, which resulted in weak Maxwell-Wagner-Sillars interfacial polarization and thus reduces the energy loss and improved the energy discharged density of the nanocomposites. The energy discharged density in the nanocomposite with 2.5 vol. % BaTiO3/SiO2 core-shell nanofibers is 6.28 J/cm3 at 3.3 MV/cm, which is over 11.94% higher than that of nanocomposite with BaTiO3 nanofibers at the same electric field.

  16. Photovoltaic properties of ferroelectric BaTiO3 thin films RF sputter deposited on silicon

    NASA Technical Reports Server (NTRS)

    Dharmadhikari, V. S.; Grannemann, W. W.

    1982-01-01

    Ferroelectric thin films of BaTiO3 have been successfully deposited on n-type silicon substrates at temperatures above 500 C by RF sputtering in an O2/Ar atmosphere. Analysis by X-ray diffraction patterns show that films deposited at room temperature are amorphous. At temperatures above 500 C, crystalline BaTiO3 films with a tetragonal structure are obtained. The polarization-electric field (P-E) hysteresis loops and a broad peak in the dielectric constant versus temperature curve at Curie point indicate that the RF sputtered BaTiO3 films are ferroelectric. An anomalous photovoltaic effect is observed in these thin films which is related to the remanent polarization of the material. The results on open-circuit and short-circuit measurements provide an important basis for a better understanding of the role of photovoltaic field, photovoltaic current, and the pyroelectric properties in photoferroelectric domain switching.

  17. Interfacial reactions and microstructure of BaTiO 3 films prepared using fluoride precursor method

    NASA Astrophysics Data System (ADS)

    Fujihara, Shinobu; Schneller, Theodor; Waser, Rainer

    2004-01-01

    Interfacial reactions of BaF 2 and TiO 2 were investigated in preparing BaTiO 3 thin films using a fluoride precursor method. Trifluoroacetate solutions were prepared from barium acetate, titanium tetraisopropoxide (TTIP), and trifluoroacetic acid (TFA, CF 3COOH) with additives such as water and acetylacetone. The solutions were deposited on platinized Si wafers by spin-coating, were pyrolysed at 400 °C in air and were finally heated typically at 700 °C in a water vapor atmosphere. The perovskite BaTiO 3 phase was obtained although a small portion of BaF 2 remained unreacted. Thus, the films were characterized as the mixture of BaTiO 3, BaF 2, and amorphous TiO 2. Influence of the solution chemistry on the phase evolution and microstructure was examined in order to discuss the reaction pathway of the perovskite phase.

  18. Experimental and first principle studies on electronic structure of BaTiO3

    NASA Astrophysics Data System (ADS)

    Sagdeo, Archna; Ghosh, Haranath; Chakrabarti, Aparna; Kamal, C.; Ganguli, Tapas; Phase, D. M.; Deb, S. K.

    2014-04-01

    We have carried out photoemission experiments to obtain valence band spectra of various crystallographic symmetries of BaTiO3 system which arise as a function of temperature. We also present results of a detailed first principle study of these symmetries of BaTiO3 using generalized gradient approximation for the exchange-correlation potential. Here we present theoretical results of density of states obtained from DFT based simulations to compare with the experimental valence band spectra. Further, we also perform calculations using post density functional approaches like GGA + U method as well as non-local hybrid exchange-correlation potentials like PBE0, B3LYP, HSE in order to understand the extent of effect of correlation on band gaps of different available crystallographic symmetries (5 in number) of BaTiO3.

  19. Defect mechanisms in high resistivity BaTiO3-Bi(Zn1/2Ti1/2)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Raengthon, Natthaphon; DeRose, Victoria J.; Brennecka, Geoffrey L.; Cann, David P.

    2012-09-01

    The defect mechanisms that underpin the high energy density dielectric 0.8BaTiO3-0.2Bi(Zn1/2Ti1/2)O3 were investigated. Characterization of the nominally stoichiometric composition revealed the presence of a Ti3+-related defect center, which is correlated with lower resistivities and an electrically heterogeneous microstructure. In compositions with 2 mol. % Ba-deficiency, a barium vacancy-oxygen vacancy pair (VBa-VO), acted as an electron-trapping site. This defect was responsible for a significant change in the transport behavior with a high resistivity and an electrically homogeneous microstructure.

  20. Dielectric response of BaZrO3/BaTiO3 superlattice

    NASA Astrophysics Data System (ADS)

    Wang, D.; Jiang, Z.

    2016-06-01

    We use the first-principles-based molecular dynamic approach to simulate dipolar dynamics of BaZrO3/BaTiO3 superlattice, and obtain its dielectric response. The dielectric response is decomposed into its compositional, as well as the in-plane and out-of-plane parts, which are then discussed in the context of chemical ordering of Zr/Ti ions. We reveal that, while the in-plane dielectric response of BaZrO3/BaTiO3 superlattice also shows dispersion over probing frequency, it shall not be categorized as relaxor.

  1. Effect of surface moisture on dielectric behavior of ultrafine BaTiO3 particulates.

    NASA Technical Reports Server (NTRS)

    Mountvala, A. J.

    1971-01-01

    The effects of adsorbed H2O on the dielectric properties of ultrafine BaTiO3 particulates of varying particle size and environmental history were determined. The dielectric behavior depends strongly on surface hydration. No particle size dependence of dielectric constant was found for dehydroxylated surfaces in ultrafine particulate (unsintered) BaTiO3 materials. For equivalent particle sizes, the ac conductivity is sensitive to surface morphology. Reactions with H2O vapor appear to account for the variations in dielectric properties. Surface dehydration was effectively accomplished by washing as-received powders in isopropanol.

  2. Structural properties of composites of polyvinylidene fluoride and mechanically activated BaTiO3 particles

    NASA Astrophysics Data System (ADS)

    Pavlović, V. P.; Pavlović, V. B.; Vlahović, B.; Božanić, D. K.; Pajović, J. D.; Dojčilović, R.; Djoković, V.

    2013-11-01

    Nanocomposites of electroactive ceramics and ferroelectric polymers exploit favorable features of the matrix polymer and the nanostructured filler to produce new functional materials for pressure and IR sensors. In this study, the influence of mechanical activation of barium titanate (BaTiO3) particles on the structural properties of BaTiO3/polyvinylidene fluoride (PVDF) nanocomposites was investigated. Nanocomposite films were prepared by the solution casting method and characterized by scanning electron microscopy, x-ray diffraction and Raman spectroscopy. It was found that mechanically activated fillers promote the formation of a ferroelectric β-phase during crystallization of PVDF.

  3. Reflectance Profile of BaTiO3 on Multilayer Antireflection Coating Systems

    NASA Astrophysics Data System (ADS)

    Karaomerlioglu, Filiz

    2011-05-01

    Antireflection (AR) coating systems are very important technology for optoelectronic devices. The optical characteristics of the system can be regulated by external electric or thermal field, and designed broadband ultra low reflection coating systems. It is investigated optical properties of multilayer AR coatings based on different ferroelectric materials to reduce reflectance in other studies. In this study, reflectance profile of BaTiO3 on multilayer AR coating systems has been developed in the visible region. It has been used ZnSe and ZrO2 as multilayer AR coatings, and BaTiO3 as the substrate. Fortran program has been simulated on Fresnell equations base.

  4. Nanoscale BaTiO3 MOSCAP formation for ferroelectric field effect transistor application

    NASA Astrophysics Data System (ADS)

    Ponath, Patrick; Posadas, Agham; Schmidt, Michael; Hurley, Paul; Duffy, Ray; Demkov, Alex

    Titanates are an important class of materials with many interesting functional properties and applications for non-volatile memory, i.e. BaTiO3, which is a promising candidate for the realization of a ferroelectric field-effect transistor. However, the difficulty of chemically etching titanates has hindered their commercial use in device manufacturing so far. Here, we report a technique to circumvent this problem. Using molecular beam epitaxy, we grew compressively strained ferroelectric BaTiO3, within photolithographically defined openings of a sacrificial SiO2 layer on germanium (001) with Pt as a top electrode. Etching away the sacrificial SiO2 can reveal isolated nanoscale gate stacks circumventing the need to etch the titanate thin film. Using X-ray diffraction we find that the BaTiO3 film is tetragonal with the longer c-axis being out of plane, which is a requirement for the ferroelectric field effect transistor. The crystal quality of the BaTiO3 films grown in the openings is confirmed using RHEED and cross-sectional transmission electron microscopy. Focused ion beam etching of the Pt layer is then used to electrically isolate a Pt/BaTiO3/SrTiO3/Ge stack to perform electrical measurements.

  5. Densification mechanism of BaTiO3 films on Cu substrates fabricated by aerosol deposition

    NASA Astrophysics Data System (ADS)

    Kim, Hong-Ki; Lee, Seung-Hwan; Lee, Sung-Gap; Lee, Young-Hie

    2015-05-01

    In order to achieve the aerosol deposition (AD) process as a thin film deposition process, the densification mechanism of the AD process was investigated. BaTiO3 films with thicknesses of 0.2, 0.5, and 2 μm on Cu substrates were fabricated using the AD process at room temperature in order to investigate the densification mechanism according to the increased the film thickness; we also investigated the resulting properties, including the microstructure, the electrical properties, and the hardness. As a result, we confirmed that the enhanced hammering effect (which is a densification procedure that works by continuous impaction of ceramic particles onto pre-impacted particles), formed dense BaTiO3 films with greater hardness and decreased leakage current characteristics. Furthermore, we concluded that the BaTiO3 particles, which were sufficiently fractured due to the hammering effect, were important in fabricating the dense BaTiO3 thin films. Therefore, we suggested the two-step deposition method (deposition and etching).[Figure not available: see fulltext.

  6. Lead-free BaTiO3 nanowires-based flexible nanocomposite generator

    NASA Astrophysics Data System (ADS)

    Park, Kwi-Il; Bae, Soo Bin; Yang, Seong Ho; Lee, Hyung Ik; Lee, Kisu; Lee, Seung Jun

    2014-07-01

    We have synthesized BaTiO3 nanowires (NWs) via a simple hydrothermal method at low temperature and developed a lead-free, flexible nanocomposite generator (NCG) device by a simple, low-cost, and scalable spin-coating method. The hydrothermally grown BaTiO3 NWs are mixed in a polymer matrix without a toxic dispersion enhancer to produce a piezoelectric nanocomposite (p-NC). During periodical and regular bending and unbending motions, the NCG device fabricated by utilizing a BaTiO3 NWs-polydimethylsiloxane (PDMS) composite successfully harvests the output voltage of ~7.0 V and current signals of ~360 nA, which are utilized to drive a liquid crystal display (LCD). We also characterized the instantaneous power (~1.2 μW) of the NCG device by calculating the load voltage and current through the connected external resistance.We have synthesized BaTiO3 nanowires (NWs) via a simple hydrothermal method at low temperature and developed a lead-free, flexible nanocomposite generator (NCG) device by a simple, low-cost, and scalable spin-coating method. The hydrothermally grown BaTiO3 NWs are mixed in a polymer matrix without a toxic dispersion enhancer to produce a piezoelectric nanocomposite (p-NC). During periodical and regular bending and unbending motions, the NCG device fabricated by utilizing a BaTiO3 NWs-polydimethylsiloxane (PDMS) composite successfully harvests the output voltage of ~7.0 V and current signals of ~360 nA, which are utilized to drive a liquid crystal display (LCD). We also characterized the instantaneous power (~1.2 μW) of the NCG device by calculating the load voltage and current through the connected external resistance. Electronic supplementary information (ESI) available: PDF materials involve the linear superposition test results (Fig. S1) and the durability test results (Fig. S2) of BaTiO3 NWs-based NCG device. A video file (Video S1) shows the power up of an LCD screen by the NCG device without any external energy source. See DOI: 10.1039/c4nr02246g

  7. 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

  8. Microstructure evolution and electrical characterization of Lanthanum doped Barium Titanate (BaTiO3) ceramics

    NASA Astrophysics Data System (ADS)

    Billah, Masum; Ahmed, A.; Rahman, Md. Miftaur; Mahbub, Rubbayat; Gafur, M. A.; Bashar, M. Shahriar

    2016-07-01

    In the current work, we investigated the structural and dielectric properties of Lanthanum oxide (La2O3) doped Barium Titanate (BaTiO3) ceramics and established a correlation between them. Solid state sintering method was used to dope BaTiO3 with 0.3, 0.5 and 0.7 mole% La2O3 under different sintering parameters. The raw materials used were La2O3 nano powder of ~80nm grain size and 99.995% purity and BaTiO3 nano powder of 100nm grain size and 99.99% purity. Grain size distribution and morphology of fracture surface of sintered pellets were examined by Field Emission Scanning Electron Microscope and X-Ray Diffraction analysis was conducted to confirm the formation of desired crystal structure. The research result reveal that grain size and electrical properties of BaTiO3 ceramic significantly enhanced for small amount of doping (up to 0.5 mole% La2O3) and then decreased with increasing doping concentration. Desired grain growth (0.80-1.3 µm) and high densification (<90% theoretical density) were found by proper combination of temperature, sintering parameters and doping concentration. We found the resultant stable value of dielectric constant was 10000-12000 at 100-300 Hz in the temperature range of 30°-50° C for 0.5 mole% La2O3 with corresponding shift of curie temperature around 30° C. So overall this research showed that proper La3+ concentration can control the grain size, increase density, lower curie temperature and hence significantly improve the electrical properties of BaTiO3 ceramics.

  9. 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

  10. Chemical synthesis of nanocrystalline BaTiO3 and Ba1-xSrxTi1-yZryO3 [(i) x = 0.03, y = 0 (ii) x = 0, y = 0.03 ] ceramics

    NASA Astrophysics Data System (ADS)

    Das, R. N.; Pramanik, P.

    2004-03-01

    Nanocrystalline BaTiO3 powders were prepared via a chemical process. This process involved the addition of aqueous barium nitrate, titanyl nitrate, triethanolamine (TEA) and sucrose to produce a homogeneous complex solution. After the complete evaporation of homogenous solution, the Ba-Ti-TEA-sucrose complex decomposed and produced black, fluffy precursor materials. The precursor materials on calcinations to 700 °C for 2 h produced nanocrystalline BaTiO3 with the corresponding average x-ray and TEM particle size {\\sim } 20 nm. BaTiO3 powders modified with SrTiO3 [Ba1-xSrxTi1-yZryO3 (x = 0.03, y = 0)] and BaZrO3 [Ba1-xSrxTi1-yZryO3 (x = 0, y = 0.03)] were also prepared using this route and investigated through x-ray diffraction and energy dispersive x-ray analysis.

  11. Polarization sensitive surface band structure of doped BaTiO3(001).

    PubMed

    Rault, J E; Dionot, J; Mathieu, C; Feyer, V; Schneider, C M; Geneste, G; Barrett, N

    2013-09-20

    We present a spatial and wave-vector resolved study of the electronic structure of micron sized ferroelectric domains at the surface of a BaTiO(3)(001) single crystal. The n-type doping of the BaTiO(3) is controlled by in situ vacuum and oxygen annealing, providing experimental evidence of a surface paraelectric-ferroelectric transition below a critical doping level. Real space imaging of photoemission threshold, core level and valence band spectra show contrast due to domain polarization. Reciprocal space imaging of the electronic structure using linearly polarized light provides unambiguous evidence for the presence of both in- and out-of-plane polarization with two- and fourfold symmetry, respectively. The results agree well with first principles calculations. PMID:24093301

  12. Friction imprint effect in mechanically cleaved BaTiO3 (001)

    NASA Astrophysics Data System (ADS)

    Long, Christian J.; Ebeling, Daniel; Solares, Santiago D.; Cannara, Rachel J.

    2014-09-01

    Adsorption, chemisorption, and reconstruction at the surfaces of ferroelectric materials can all contribute toward the pinning of ferroelectric polarization, which is called the electrical imprint effect. Here, we show that the opposite is also true: freshly cleaved, atomically flat surfaces of (001) oriented BaTiO3 exhibit a persistent change in surface chemistry that is driven by ferroelectric polarization. This surface modification is explored using lateral force microscopy (LFM), while the ferroelectric polarization is probed using piezoresponse force microscopy. We find that immediately after cleaving BaTiO3, LFM reveals friction contrast between ferroelectric domains. We also find that this surface modification remains after the ferroelectric domain distribution is modified, resulting in an imprint of the original ferroelectric domain distribution on the sample surface. This friction imprint effect has implications for surface patterning as well as ferroelectric device operation and failure.

  13. Effect of BaTiO3 Nanopowder Concentration on Rheological Behaviour of Ceramic Inkjet Inks

    NASA Astrophysics Data System (ADS)

    Kyrpal, R.; Dulina, I.; Ragulya, A.

    2015-04-01

    The relationship between rheological properties of ceramic inkjet inks based on BaTiO3 nanopowder and solid phase concentration has been investigated. In the ink volume takes place the formation periodic colloidal structures (PCS). The determining factor of structure formation is powder-dispersant ratio. Structural constitution of in the system with the low pigment concentration represented as PCS2, that contains solid particles in deflocculated that stabilized by the presence of adsorption-solvate layers. Dilatant structure formation for such inks explained by constrained conditions of the interaction. Samples with high BaTiO3 concentration have been classified as PKS1. Dilatant properties of the PKS1 resulted in particles rearrangement under the influence of the flow. In the region of some values powder-dispersant ratio take place conversation PKS2 to PKS1 and ink structure transformation from monodisperse to aggregate state.

  14. XMCD studies of thin Co films on BaTiO3

    NASA Astrophysics Data System (ADS)

    Welke, M.; Gräfe, J.; Govind, R. K.; Babu, V. H.; Trautmann, M.; Schindler, K.-M.; Denecke, R.

    2015-08-01

    Different layer thicknesses of cobalt ranging from 2.6 Å (1.5 ML) up to 55 Å (30.5 ML) deposited on ferroelectric BaTiO3 have been studied regarding their magnetic behavior. The layers have been characterized using XMCD spectroscopy at remanent magnetization. After careful data analysis the magnetic moments of the cobalt could be determined using the sum rule formalism. There is a sudden and abrupt onset in magnetism starting at thicknesses of 9 Å (5 ML) of cobalt for measurements at 120 K and of 10 Å (5.5 ML) if measured at room temperature. Initial island growth and subsequent coalescence of Co on BaTiO3 is suggested to explain the sudden onset. In that context, no magnetically dead layers are observed.

  15. Thickness dependent charge transport in ferroelectric BaTiO3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Singh, Pooja; Rout, P. K.; Singh, Manju; Rakshit, R. K.; Dogra, Anjana

    2015-09-01

    We have investigated the effect of ferroelectric barium titanate (BaTiO3) film thickness on the charge transport mechanism in pulsed laser deposited epitaxial metal-ferroelectric semiconductor junctions. The current (I)-voltage (V) measurements across the junctions comprising of 20-500 nm thick BaTiO3 and conducting bottom electrode (Nb: SrTiO3 substrate or La2/3Ca1/3MnO3 buffer layer) demonstrate the space charge limited conduction. Further analysis indicates a reduction in the ratio of free to trapped carriers with increasing thickness in spite of decreasing trap density. Such behaviour arises the deepening of the shallow trap levels (<0.65 eV) below conduction band with increasing thickness. Moreover, the observed hysteresis in I-V curves implies a bipolar resistive switching behaviour, which can be explained in terms of charge trapping and de-trapping process.

  16. Stress effect on Raman spectra of Ce-doped BaTiO3 films

    NASA Astrophysics Data System (ADS)

    Chen, M. S.; Shen, Z. X.; Tang, S. H.; Shi, W. S.; Cui, D. F.; Chen, Z. H.

    2000-08-01

    Ce-doped BaTiO3 (BTO:Ce) thin films prepared on MgO (100) substrates by pulsed laser deposition (PLD) at oxygen pressure of 1.2×10-3 and 17 Pa have been studied by micro-Raman spectroscopy, x-ray diffraction (XRD) and atomic force microscopy (AFM). The film deposited at lower oxygen pressure has a larger lattice parameter in the direction normal to the substrate surface, and the film has smaller grains and a smoother surface. The polarized Raman peaks of both as-deposited films show blue shifts and linewidth broadening in comparison to those of the BaTiO3 single crystal. The blue shifts are attributed to tensile stresses in the films. Our results indicate that the grain size increases and the tensile stress relaxes with annealing. We have shown that quantum confinement and oxygen vacancies are not the dominant factors for the observed Raman spectral changes.

  17. Effect of oxygen partial pressure and anneal temperature on BaTiO3 thin film crystal structure

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Sun, De-gui; Fu, Xiuhua; Liu, Dong-mei; Pan, Yong-gang; Yang, Fei

    2015-08-01

    BaTiO3 film is deposited on single crystal MgO substrate with pulsed laser deposition, and its crystal structure and surface roughness are characterized by X-ray diffraction instrument and atomic force microscope. BaTiO3 film crystal quality is analyzed under three different oxygen partial pressure and three different annealing temperatures. The result shows that when the oxygen partial pressure is 15Pa, crystal surface (001) and (002) diffraction peak of BaTiO3 thin films have higher intensity. It indicated that the film has a good c-axis orientation. When the annealing temperature is 800°C, the intensity of diffraction peak is the maximum, and peak shape is sharper. BaTiO3 crystal film is obtained with highly preferred orientation, and film density is improved. Thus the film has less surface roughness and good crystalline state.

  18. Grain Growth Kinetics of BaTiO3 Nanocrystals During Calcining Process

    NASA Astrophysics Data System (ADS)

    Song, Xiao-lan; He, Xi; Yang, Hai-ping; Qu, Yi-xin; Qiu, Guan-zhou

    2008-06-01

    BaTiO3 nanocrystals were synthesized by sol-gel method using barium acetate (Ba(CH3COO)2) and tetra-butyl titanate (Ti(OC4H9)4) as raw materials. Xerogel precursors and products were characterized by means of thermogravimetric/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD) and transmission electron microscope (TEM). The influence of the calcination temperature and duration on the lattice constant, the lattice distortion, and the grain size of BaTiO3 nanocrystals was discussed based on the XRD results. The grain growth kinetics of BaTiO3 nanocrystals during the calcination process were simulated with a conventional grain growth model which only takes into account diffusion, and an isothermal model proposed by Qu and Song, which takes into account both diffusion and surface reactions. Using these models, the pre-exponential factor and the activation energy of the rate constant were estimated. The simulation results indicate that the isothermal model is superior to the conventional one in describing the grain growth process, implying that both diffusion and surface reactions play important roles in the grain growth process.

  19. Comprehensive examination of dopants and defects in BaTiO3 from first principles

    NASA Astrophysics Data System (ADS)

    Sharma, V.; Pilania, G.; Rossetti, G. A., Jr.; Slenes, K.; Ramprasad, R.

    2013-04-01

    An extensive assessment of the physicochemical factors that control the behavior of dopant-related defects in BaTiO3 has been performed using high-throughput first-principles computations. Dopants spanning the Periodic Table—44 in total—including K-As, Rb-Sb, and Cs-Bi were considered, and have allowed us to reveal previously unknown correlations, chemical trends, and the interplay between stability, chemistry, and electrical activity. We quantitatively show that the most important factor that determines dopant stability in BaTiO3 is the dopant ionic size (followed by its oxidation state). Moreover, we are also able to identify definitively dopants that are O vacancy formers and suppressors, and those that would lead to p-type versus n-type conduction. Our results are in agreement with available experimental data (with no violations thus far), and point to an attractive computational route to dopant selection in BaTiO3 as well as in other materials.

  20. Excimer laser assisted re-oxidation of BaTiO3 thin films on Ni metal foils

    NASA Astrophysics Data System (ADS)

    Bharadwaja, S. S. N.; Rajashekhar, A.; Ko, S. W.; Qu, W.; Motyka, M.; Podraza, N.; Clark, T.; Randall, C. A.; Trolier-McKinstry, S.

    2016-01-01

    Excimer laser assisted re-oxidation for reduced, crystallized BaTiO3 thin films on Ni-foils was investigated. It was found that the BaTiO3 can be re-oxidized at an oxygen partial pressure of ˜50 mTorr and substrate temperature of 350 °C without forming a NiOx interface layer between the film and base metal foil. The dielectric permittivity of re-oxidized films was >1000 with loss tangent values <2% at 100 Hz, 30 mVrms excitation signal. Electron Energy Loss Spectroscopy indicated that BaTiO3 thin films can be re-oxidized to an oxygen stoichiometry close to ˜3 (e.g., stoichiometric). High resolution cross sectional transmission electron microscopy showed no evidence of NiOx formation between the BaTiO3 and the Ni foil upon excimer laser re-oxidation. Spectroscopic ellipsometry studies on laser re-oxidized [001]C and [111]C BaTiO3 single crystals indicate that the re-oxidation of BaTiO3 single crystals is augmented by photo-excitation of the ozone, as well as laser pulse induced temperature and local stress gradients.

  1. Relating Electronic and Geometric Structure of Atomic Layer Deposited BaTiO3 to its Electrical Properties

    PubMed Central

    2016-01-01

    Atomic layer deposition allows the fabrication of BaTiO3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO’s bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Ti content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate–film interfaces reveal BTO’s homogeneous growth on RuO2 and its distorted growth on SiO2. This work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices. PMID:27009677

  2. Relating Electronic and Geometric Structure of Atomic Layer Deposited BaTiO3 to its Electrical Properties.

    PubMed

    Torgersen, Jan; Acharya, Shinjita; Dadlani, Anup Lal; Petousis, Ioannis; Kim, Yongmin; Trejo, Orlando; Nordlund, Dennis; Prinz, Fritz B

    2016-04-21

    Atomic layer deposition allows the fabrication of BaTiO3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO's bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Ti content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate-film interfaces reveal BTO's homogeneous growth on RuO2 and its distorted growth on SiO2. This work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices. PMID:27009677

  3. Relating electronic and geometric structure of atomic layer deposited BaTiO3 to its electrical properties

    DOE PAGESBeta

    Torgersen, Jan; Acharya, Shinjita; Dadlani, Anup Lal; Petousis, Ioannis; Kim, Yongmin; Trejo, Orlando; Nordlund, Dennis; Prinz, Fritz B.

    2016-03-24

    Atomic layer deposition allows the fabrication of BaTiO3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO’s bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Timore » content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate–film interfaces reveal BTO’s homogeneous growth on RuO2 and its distorted growth on SiO2. As a result, this work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices.« less

  4. Solid-state synthesis of Bi2O3/BaTiO3 heterostructure: preparation and photocatalytic degradation of methyl orange

    NASA Astrophysics Data System (ADS)

    Ren, Pengrong; Fan, Huiqing; Wang, Xin

    2013-06-01

    In this work, Bi2O3/BaTiO3 heterostructure were prepared through a solid milling and annealing process. It was found that Bi3+ dissolved in the BaTiO3 lattice and the chemical bond was constructed between the interface of Bi2O3 and BaTiO3 after annealing process. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-visible absorption spectra were used to characterize the Bi2O3/BaTiO3 heterostructure. Furthermore, UV-induced catalytic activities of the Bi2O3/BaTiO3 heterostructure was studied by a degradation reaction of methyl orange (MO) dye. The band gap of the Bi2O3/BaTiO3 heterostructure was estimated to be 3.0 eV. Compared with pure Bi2O3 powders, the Bi2O3/BaTiO3 heterostructure had a much higher catalytic activity. An excellent performance of the photocatalytic property of the Bi2O3/BaTiO3 heterostructure is ascribed to high mobility of species and effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the Bi2O3/BaTiO3 junction interface, demonstrating that the Bi2O3/BaTiO3 heterostructure is a promising candidate as a photocatalyst.

  5. Tuning polarization states and interface properties of BaTiO3/SrTiO3 heterostructure by metal capping layers

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Yang, Ming; Shen, Lei; Wu, Qing Yun; Xu, Lei; Feng, Yuan Ping; Rusydi, Andrivo

    2016-04-01

    How to tune two-dimensional electron gas at interface of heterostructures is becoming an important question for both fundamental physics and electronic applications. Here, using density functional theory calculations, we find that the polarization state of BaTiO3 in metal capped BaTiO3/SrTiO3 heterostructures changes dramatically, depending on the termination of BaTiO3 and the different metal layers (M =Al , Fe, Pt Au). Most interestingly, for Pt on the BaO-terminated BaTiO3/SrTiO3, interface conductivity can be tuned. With a paraelectric state in BaTiO3, Pt_BaTiO 3 /SrTiO3 remains insulating at interface, while when BaTiO3 is ferroelectric, a hole- or electron-conducting BaTiO3/SrTiO3 interface can be realized, depending on its polarization direction in BaTiO3. This conducting interface and the top Pt layer screen the depolarization field, and thus stabilize the ferroelectricity in BaTiO3. Our result provides important clues for the reversibly tunable conductivity at oxide interfaces.

  6. Origins of enhanced electromechanical coupling in ferroelectric BaTiO3

    NASA Astrophysics Data System (ADS)

    Pramanick, Abhijit; Diallo, Souleymane; Delaire, Olivier; Calder, Stuart; Christianson, Andrew; Wang, Xun-Li; Fernandez-Baca, Jaime

    2014-03-01

    The origins of enhanced piezoelectric coupling along non-polar crystallographic directions in ferroelectric BaTiO3 are investigated using in situ neutron spectroscopy. It is observed that an electric field applied away from the equilibrium polarization direction causes a stiffening of the transverse acoustic (TA) phonon branch and consequently increases interaction between the TA and the transverse optic (TO) soft mode for a range of wave vectors extending from the Brillouin zone center. This provides a direct lattice dynamics mechanism for enhanced electromechanical coupling, and could act as a guide for designing improved piezoelectric materials.

  7. Giant bulk photovoltaic effect in thin ferroelectric BaTiO3 films

    NASA Astrophysics Data System (ADS)

    Zenkevich, A.; Matveyev, Yu.; Maksimova, K.; Gaynutdinov, R.; Tolstikhina, A.; Fridkin, V.

    2014-10-01

    The voltage generated in a noncentrosymmetric crystal due to the bulk photovoltaic effect (BPE) can greatly exceed the energy gap, however, the light energy conversion efficiency is extremely low. Here we show that the BPE is remarkably enhanced in the case of thin films. The measurements of the BPE in heteroepitaxial single domain ferroelectric BaTiO3 thin films reveal the enhancement of both photoinduced electric field and conversion efficiencies of the BPE by more than 4 orders of magnitude. Besides the fundamental aspect, our results indicate the potential for the use of the BPE in photovoltaic applications.

  8. Phase composition identification and microstructure of BaTiO3-containing sodium-aluminoborosilicate glass-ceramics

    NASA Astrophysics Data System (ADS)

    Harizanova, Ruzha; Abrashev, Miroslav; Avramova, Ivalina; Vladislavova, Liliya; Bocker, Christian; Tsutsumanova, Gichka; Avdeev, Georgi; Rüssel, Christian

    2016-02-01

    Bulk glasses with a composition 20.1Na2O/23.1BaO/23.0TiO2/7.6B2O3/17.4SiO2/3Al2O3/5.8Fe2O3 containing less than 30 mol% glass-forming oxides are synthesized. Information on the valency of the glass constituents is obtained by x-ray photoelectron spectroscopy and it is concluded that all species are predominantly present in their oxidized state. Glassy samples are annealed above the glass transition temperature which leads to the crystallization of BaTiO3 for all time-temperature applied schedules. The phase composition of the glass-ceramics is studied by x-ray diffraction and the formation of cubic BaTiO3 is suggested. Temperature-dependent Raman spectroscopy confirms the presence of solely cubic BaTiO3. The microstructures of all annealed samples are similar and consist of globular interconnected particles in which nanosized BaTiO3 crystals grow randomly. The mean size of the spherical formations increases with the increasing annealing time from 200 to 600 nm. Electron microscopy suggests that during the annealing process first phase separation and then crystallization of BaTiO3 occurs.

  9. The Effect of Polarization on Local Electronic Structure in Ferroelectric Nano-Domains in BaTiO3

    NASA Astrophysics Data System (ADS)

    Morales, Erie; Perez, Carlos; Bonnell, Dawn; MSE Team

    Novel ferroelectric BaTiO3 applications ranging from sensors to nanogenerators require a detailed understanding of atomic interactions at surfaces. Single crystals provide a platform that allows the exploitation of surface physical and chemical properties that can be readily transferred to other ABO3 perovskites. The processes that result in the atomic and electronic structures of surfaces in tandem with polarization of domains are necessary steps towards understanding BaTiO3. Here we treat BaTiO3 surface using sputtering-annealing cycles that yield the (6x1) reconstruction. We demonstrate that it is possible to pole a thin BaTiO3 single crystal in ultra high vacuum using scanning tunneling microscopy (STM). We determine that we can prepare BaTiO3 using in-situ annealing that allows us to control the size of poled region to 40nm. We pole in constant-current mode in STM by applying a bias of less than 10 V between tip and sample for 100ms. STM and scanning tunneling spectroscopy characterization allow us to map topography and local density of states, respectively. For a given unique pulse, the poled domains show a fluctuating electronic occupation of conduction bands and shifting of valence band. We will also discuss the effect of polarization on molecular adsorption.

  10. Preferentially oriented BaTiO3 thin films deposited on silicon with thin intermediate buffer layers

    PubMed Central

    2013-01-01

    Barium titanate (BaTiO3) thin films are prepared by conventional 2-methoxy ethanol-based chemical solution deposition. We report highly c-axis-oriented BaTiO3 thin films grown on silicon substrates, coated with a lanthanum oxynitrate buffer layer of 8.9 nm. The influence of the intermediate buffer layer on the crystallization of BaTiO3 film is investigated. The annealing temperature and buffer layer sintering conditions are optimized to obtain good crystal growth. X-ray diffraction measurements show the growth of highly oriented BaTiO3 thin films having a single perovskite phase with tetragonal geometry. The scanning electron microscopy and atomic force microscopy studies indicate the presence of smooth, crack-free, uniform layers, with densely packed crystal grains on the silicon surface. A BaTiO3 film of 150-nm thickness, deposited on a buffer layer of 7.2 nm, shows a dielectric constant of 270, remnant polarization (2Pr) of 5 μC/cm2, and coercive field (Ec) of 60 kV/cm. PMID:23391429

  11. The structural properties of BaTiO3: TiO2: PMMA composite films at room temperature

    NASA Astrophysics Data System (ADS)

    Dey, Subhrangsu; Singh, S.; Singh, S. M.; Rajput, Nikhil; Kumar, Neeraj

    2016-05-01

    Present works based on the performance of the composite films of Barium Titanate (BaTiO3) with Titanium Dioxide (TiO2) and Poly (methyl methacrylate) (PMMA) prepared by simple solution casting technique. Different wt. % compositions of BaTiO3 have been selected to find out the best optimized condition for further investigations. The structural properties have been carried out at room temperature using X-ray crystallography (XRD). The average crystallite size of the BaTiO3 particles in the composite films has been found to be lies in between ˜ 20 -70 nm. It has been found that the peak intensities increase with increasing the wt. % of BaTiO3 in the composite films at room temperature (RT). The XRD analysis revealed that the addition of TiO2 has played a crucial role to enhance the crystalline nature of the composite films at room temperature. Efforts have been made to correlate the results with investigated XRD results of pure BaTiO3 and its composites as observed by other workers at room temperature.

  12. The Structure of BaTiO3 and BaTiO3-YBa2Cu3O7-δ Thin Films Studied by X-Ray Triple-Axis Diffraction

    NASA Astrophysics Data System (ADS)

    Yu, W. X.; Cui, S. F.; Wu, L. S.; Mai, Z. H.; Li, C. L.; Cui, D. F.; Chen, Z. H.

    The structures of BaTiO3 thin films and BaTiO3/YBa2Cu3O7-δ bilayer films grown on SrTiO3 and LaAlO3 substrates, respectively by pulsed laser deposition, have been investigated by X-ray triple-axis diffraction. The orientation, the interface mismatch and strain status, and the in-plane and perpendicular lattice constants of the epilayers have been determined by reciprocal space map analysis. The results show that both the lattice constants and the structural imperfections of the BaTiO3 layers are relevant to the oxygen partial pressure. The a⊥/a‖ increases while the full width at half maximum (FWHM) of the rocking curves decreases with the decrease in the partial oxygen pressure.

  13. Emergence of Long-Range Order in BaTiO_{3} from Local Symmetry-Breaking Distortions.

    PubMed

    Senn, M S; Keen, D A; Lucas, T C A; Hriljac, J A; Goodwin, A L

    2016-05-20

    By using a symmetry motivated basis to evaluate local distortions against pair distribution function data, we show without prior bias, that the off-center Ti displacements in the archetypal ferroelectric BaTiO_{3} are zone centered and rhombohedral-like across its known ferroelectric and paraelectric phases. We construct a simple Monte Carlo model that captures our main experimental findings and demonstrate how the rich crystallographic phase diagram of BaTiO_{3} emerges from correlations of local symmetry-breaking distortions alone. Our results strongly support the order-disorder picture for these phase transitions, but can also be reconciled with the soft-mode theory of BaTiO_{3} that is supported by some spectroscopic techniques. PMID:27258883

  14. Emergence of Long-Range Order in BaTiO3 from Local Symmetry-Breaking Distortions

    NASA Astrophysics Data System (ADS)

    Senn, M. S.; Keen, D. A.; Lucas, T. C. A.; Hriljac, J. A.; Goodwin, A. L.

    2016-05-01

    By using a symmetry motivated basis to evaluate local distortions against pair distribution function data, we show without prior bias, that the off-center Ti displacements in the archetypal ferroelectric BaTiO3 are zone centered and rhombohedral-like across its known ferroelectric and paraelectric phases. We construct a simple Monte Carlo model that captures our main experimental findings and demonstrate how the rich crystallographic phase diagram of BaTiO3 emerges from correlations of local symmetry-breaking distortions alone. Our results strongly support the order-disorder picture for these phase transitions, but can also be reconciled with the soft-mode theory of BaTiO3 that is supported by some spectroscopic techniques.

  15. Engineered unique elastic modes at a BaTiO3/2x1-Ge(001) interface

    DOE PAGESBeta

    Kumah, D. P.; Dogan, M.; Ngai, J. H.; Qiu, D.; Zhang, Z.; Su, D.; Specht, E. D.; Ismail-Beigi, S.; Ahn, C. H.; Walker, F. J.

    2016-03-07

    Here, the strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO3. While the complex crystal structure is predicted using first-principles theory, it is further shown that the details ofmore » the structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO3 induced by the symmetry of forces exerted by the germanium substrate.« less

  16. Engineered Unique Elastic Modes at a BaTiO3/(2 ×1 )-Ge (001 ) Interface

    NASA Astrophysics Data System (ADS)

    Kumah, D. P.; Dogan, M.; Ngai, J. H.; Qiu, D.; Zhang, Z.; Su, D.; Specht, E. D.; Ismail-Beigi, S.; Ahn, C. H.; Walker, F. J.

    2016-03-01

    The strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2 ×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO3 . While the complex crystal structure is predicted using first-principles theory, it is further shown that the details of the structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO3 induced by the symmetry of forces exerted by the germanium substrate.

  17. Ferroelectric BaTiO3 phase of orthorhombic crystal structure contained in nanoparticles

    NASA Astrophysics Data System (ADS)

    Ram, S.; Jana, A.; Kundu, T. K.

    2007-09-01

    Ferroelectric BaTiO3 phase of a Pnma orthorhombic crystal structure is synthesized from a chemical method using a polymer complex of Ba2+ and Ti4+ with polyvinyl alcohol (PVA). After burning out the polymer at temperature as high as 550 °C in air for 2 h results in an average 15 nm crystallite BaTiO3 size, with lattice parameters a =0.6435 nm, b =0.5306 nm, c =0.8854 nm, and density 5.124 g/cm3. The relationship between dielectric constant ɛr and temperature showed a single Curie transition temperature TC=131 °C, with as large a ɛr value as 263 at TC. A low value of dissipation factor tan δ, as small as 0.033 at room temperature (frequency f =1 kHz), with good insulating properties made the sample promising for use in uncooled infrared detectors and thermal imaging applications. The ɛr value is nearly independent of f value up to 100 kHz. A spectrum of sharp EPR signals of g values 2.21 to 1.88 characterizes three major kinds of VBa-, VTi3-, and Ti3+-Vo2+ paramagnetic species present in the imperfections.

  18. Microwave dielectric characterisation of 3D-printed BaTiO3/ABS polymer composites

    PubMed Central

    Castles, F.; Isakov, D.; Lui, A.; Lei, Q.; Dancer, C. E. J.; Wang, Y.; Janurudin, J. M.; Speller, S. C.; Grovenor, C. R. M.; Grant, P. S.

    2016-01-01

    3D printing is used extensively in product prototyping and continues to emerge as a viable option for the direct manufacture of final parts. It is known that dielectric materials with relatively high real permittivity—which are required in important technology sectors such as electronics and communications—may be 3D printed using a variety of techniques. Among these, the fused deposition of polymer composites is particularly straightforward but the range of dielectric permittivities available through commercial feedstock materials is limited. Here we report on the fabrication of a series of composites composed of various loadings of BaTiO3 microparticles in the polymer acrylonitrile butadiene styrene (ABS), which may be used with a commercial desktop 3D printer to produce printed parts containing user-defined regions with high permittivity. The microwave dielectric properties of printed parts with BaTiO3 loadings up to 70 wt% were characterised using a 15 GHz split post dielectric resonator and had real relative permittivities in the range 2.6–8.7 and loss tangents in the range 0.005–0.027. Permittivities were reproducible over the entire process, and matched those of bulk unprinted materials, to within ~1%, suggesting that the technique may be employed as a viable manufacturing process for dielectric composites. PMID:26940381

  19. Memristive behavior in BaTiO 3 thin films integrated with semiconductors

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Prater, John; Narayan, Jay

    BaTiO3 has been studied for emerging non-volatile memory applications. However, most of the previous work has focused on this material when it was deposited on insulting oxide substrates such as SrTiO3. Unfortunately, this substrate is not suitable for CMOS-based microelectronics applications. This motivated us to carry out the present work. We have studied the resistive switching behavior in BaTiO3/La0.7Sr0.3MnO3 (BTO/LSMO) heterostructures integrated with Si (100) using pulsed laser deposition1,2. I-V measurements were conducted on BTO (500nm)/LSMO (25nm) devices at 200K, with the compliance current of 10mA. Here, Pt was used as a top electrode and LSMO served as bottom electrode. A few important observations are noted: (a) broad hysteresis in forward and reverse voltage sweeps -ideal for memory applications, (b) the ratio of high resistance to low resistance state is ~600 -important for switching devices, (c) the device is stable at least up to 50 cycles. However, we found that hysteretic behavior was collapsed after 36 cycles upon oxygen annealing of the device at 1 atmospheric pressure, 200o C for 1 hour, inferring the important role of oxygen vacancies in the resistive switching behavior of BTO/LSMO device. The comprehensive experimental data will be presented and discussed.1,2.

  20. 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.

  1. 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.

  2. Microwave dielectric characterisation of 3D-printed BaTiO3/ABS polymer composites

    NASA Astrophysics Data System (ADS)

    Castles, F.; Isakov, D.; Lui, A.; Lei, Q.; Dancer, C. E. J.; Wang, Y.; Janurudin, J. M.; Speller, S. C.; Grovenor, C. R. M.; Grant, P. S.

    2016-03-01

    3D printing is used extensively in product prototyping and continues to emerge as a viable option for the direct manufacture of final parts. It is known that dielectric materials with relatively high real permittivity—which are required in important technology sectors such as electronics and communications—may be 3D printed using a variety of techniques. Among these, the fused deposition of polymer composites is particularly straightforward but the range of dielectric permittivities available through commercial feedstock materials is limited. Here we report on the fabrication of a series of composites composed of various loadings of BaTiO3 microparticles in the polymer acrylonitrile butadiene styrene (ABS), which may be used with a commercial desktop 3D printer to produce printed parts containing user-defined regions with high permittivity. The microwave dielectric properties of printed parts with BaTiO3 loadings up to 70 wt% were characterised using a 15 GHz split post dielectric resonator and had real relative permittivities in the range 2.6–8.7 and loss tangents in the range 0.005–0.027. Permittivities were reproducible over the entire process, and matched those of bulk unprinted materials, to within ~1%, suggesting that the technique may be employed as a viable manufacturing process for dielectric composites.

  3. Microwave dielectric characterisation of 3D-printed BaTiO3/ABS polymer composites.

    PubMed

    Castles, F; Isakov, D; Lui, A; Lei, Q; Dancer, C E J; Wang, Y; Janurudin, J M; Speller, S C; Grovenor, C R M; Grant, P S

    2016-01-01

    3D printing is used extensively in product prototyping and continues to emerge as a viable option for the direct manufacture of final parts. It is known that dielectric materials with relatively high real permittivity-which are required in important technology sectors such as electronics and communications-may be 3D printed using a variety of techniques. Among these, the fused deposition of polymer composites is particularly straightforward but the range of dielectric permittivities available through commercial feedstock materials is limited. Here we report on the fabrication of a series of composites composed of various loadings of BaTiO3 microparticles in the polymer acrylonitrile butadiene styrene (ABS), which may be used with a commercial desktop 3D printer to produce printed parts containing user-defined regions with high permittivity. The microwave dielectric properties of printed parts with BaTiO3 loadings up to 70 wt% were characterised using a 15 GHz split post dielectric resonator and had real relative permittivities in the range 2.6-8.7 and loss tangents in the range 0.005-0.027. Permittivities were reproducible over the entire process, and matched those of bulk unprinted materials, to within ~1%, suggesting that the technique may be employed as a viable manufacturing process for dielectric composites. PMID:26940381

  4. Mesoscale flux-closure domain formation in single-crystal BaTiO3.

    PubMed

    McQuaid, R G P; McGilly, L J; Sharma, P; Gruverman, A; Gregg, J M

    2011-01-01

    Over 60 years ago, Charles Kittel predicted that quadrant domains should spontaneously form in small ferromagnetic platelets. He expected that the direction of magnetization within each quadrant should lie parallel to the platelet surface, minimizing demagnetizing fields,and that magnetic moments should be configured into an overall closed loop, or flux-closure arrangement. Although now a ubiquitous observation in ferromagnets, obvious flux-closure patterns have been somewhat elusive in ferroelectric materials. This is despite the analogous behaviour between these two ferroic subgroups and the recent prediction of dipole closure states by atomistic simulations research. Here we show Piezoresponse Force Microscopy images of mesoscopic dipole closure patterns in free-standing, single-crystal lamellae of BaTiO(3). Formation of these patterns is a dynamical process resulting from system relaxation after the BaTiO(3) has been poled with a uniform electric field. The flux-closure states are composed of shape conserving 90° stripe domains which minimize disclination stresses. PMID:21792183

  5. Effects of oxygen vacancies and grain sizes on the dielectric response of BaTiO3

    NASA Astrophysics Data System (ADS)

    Choi, Youn-Kyu; Hoshina, Takuya; Takeda, Hiroaki; Teranishi, Takeshi; Tsurumi, Takaaki

    2010-11-01

    The effects of grain size and oxygen vacancies on the dielectric responses of BaTiO3 ceramics were investigated using wideband dielectric spectroscopy. Both dipole and ionic polarizations were enhanced by the reduction in grain size down to 2.5 μm. The annealing in low oxygen partial pressure markedly suppressed the dipole polarization possibly due to the domain-wall clamping by oxygen vacancies. To explain the dielectric response of BaTiO3 ceramics, a complex structure including gradient lattice strain layers (GLSL) were proposed as a model of 90° domain structure.

  6. Formation of secondary phase at grain boundary of flash-sintered BaTiO3.

    PubMed

    Uehashi, Akinori; Sasaki, Katsuhiro; Tokunaga, Tomoharu; Yoshida, Hidehiro; Yamamoto, Takahisa

    2014-11-01

    Recently, Raj et.al. have developed a very unique sintering technique, called flash-sintering [1]. According to their report, fully densified ZrO2-3mol%Y2O3 ceramic bulks were successfully obtained only at 800°C for 5sec. Considering the conventional sintering condition around 1500°C for a few hours necessary to obtain ZrO2-3mol%Y2O3 ceramic bulks, their sintering technique is very attracting from a viewpoint of sintering temperature, soaking time and further the physical phenomena. The flash-sintering is a technique that green compacts were heating under application of high electric field. When furnace temperature reaches at a critical temperature, the electric current abruptly increases and the compact sinters near full density with a very high shrinkage rate. So far, a few studies about flash-sintering were reported for Y2O3 [2], SrTiO3, MgO-Al2O3. To understand the detail mechanism of flash-sintering, more case studies must be necessary. In this study, we focused BaTiO3 widely used for electro-ceramics, which has not been investigated from a viewpoint of flash-sintering.Green compacts were prepared from BaTiO3 raw powders (0.1-m, 99.9%, SAKAI chemical industry Co. Ltd., Lot. No.1308607) after uniaxially pressed at 100MPa into a rectangular shape with 2x10x30mm(3). The green compacts were suspended into a box type furnace by Pt-wires with Pt-based paste. Then, the furnace temperature was raised at 300°C/h under application of electric field ranged from 25V/cm to 350V/cm with monitoring the specimen current. After sintering, the shrinkages, microstructure of the sintered compacts were investigated.Sintering rates at all electric fields were found to be accelerated by applying electric field in BaTiO3. The appearance of abrupt current increment was confirmed over the application of 75V/cm. For example, a density of green compact reached about 90% relative density of BaTiO3 only at 1020°C for 1min at 100V/cm. However, the final shrinkages were revealed to decrease with an increase in electric fields, which is very different from the case of ZrO2-3mol%Y2O3 and Y2O3 ceramics. This fact means that application of high electric fields does not effectively operate for enhancement of shrinkage rates in the case of BaTiO3. In contrast, only gradual current increment was observed at 25V/cm, which is categorized in field-assisted sintering (FAST) process. The density of the green compact at 25V/cm was more than 95%.To investigate the mechanism of the decrease in a total shrinkage with electric fields, the microstructure of flash-sintered compact was observed. As a result, it was found that discharge occurs during flash-sintering process, indicating that the input power due to high electric fields does not work effectively. A typical example of the microstructure near the discharge area is shown in Fig. 1. Fig. 1 is a TEM bright field image taken from BaTiO3 flash-sintered at 100V/cm. As seen in the image, the formation of a secondary phase along the grain boundary can be clearly seen. Diffractometric and EDS analysis have revealed that the secondary phase is BaTi4O9, one of compounds between BaO and TiO2 system. By discharging, grain boundaries partially melt and a part of Ba vaporizes to form BaTi4O9 with cooling. To investigate flash-sintering behaviors, it was concluded that FAST process play an important role to enhance the shrinklage rate in the case of BaTiO3.jmicro;63/suppl_1/i19/DFU048F1F1DFU048F1Fig. 1.TEM bright field image of a secondary phase and the electron diffraction pattern taken from the secondary phase. PMID:25359812

  7. Magnetic and nonlinear optical properties of BaTiO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ramakanth, S.; Hamad, Syed; Venugopal Rao, S.; James Raju, K. C.

    2015-05-01

    In our earlier studies the BaTiO3 samples were processed at higher temperatures like 1000oC and explained the observed magnetism in it. It is found that the charge transfer effects are playing crucial role in explaining the observed ferromagnetism in it. In the present work the samples were processed at lower temperatures like 650oC-800oC. The carrier densities in these particles were estimated to be ˜ 1019-1020/cm3 range. The band gap is in the range of 2.53eV to 3.2eV. It is observed that magnetization increased with band gap narrowing. The higher band gap narrowed particles exhibited increased magnetization with a higher carrier density of 1.23×1020/cm3 near to the Mott critical density. This hint the exchange interactions between the carriers play a dominant role in deciding the magnetic properties of these particles. The increase in charge carrier density in this undoped BaTiO3 is because of oxygen defects only. The oxygen vacancy will introduce electrons in the system and hence more charge carriers means more oxygen defects in the system and increases the exchange interactions between Ti3+, Ti4+, hence high magnetic moment. The coercivity is increased from 23 nm to 31 nm and then decreased again for higher particle size of 54 nm. These particles do not show photoluminescence property and hence it hints the absence of uniformly distributed distorted [TiO5]-[TiO6] clusters formation and charge transfer between them. Whereas these charge transfer effects are vital in explaining the observed magnetism in high temperature processed samples. Thus the variation of magnetic properties like magnetization, coercivity with band gap narrowing, particle size and charge carrier density reveals the super paramagnetic nature of BaTiO3 nanoparticles. The nonlinear optical coefficients extracted from Z-scan studies suggest that these are potential candidates for optical imaging and signal processing applications.

  8. Enhancement of ferroelectric Curie temperature in BaTiO3 films via strain-induced defect dipole alignment.

    PubMed

    Damodaran, Anoop R; Breckenfeld, Eric; Chen, Zuhuang; Lee, Sungki; Martin, Lane W

    2014-09-01

    The combination of epitaxial strain and defect engineering facilitates the tuning of the transition temperature of BaTiO3 to >800 °C. Advances in thin-film deposition enable the utilization of both the electric and elastic dipoles of defects to extend the epitaxial strain to new levels, inducing unprecedented functionality and temperature stability in ferroelectrics. PMID:25099557

  9. Rapid-Thermal-Processed BaTiO3 Thin Films Deposited by Liquid-Source Misted Chemical Deposition

    NASA Astrophysics Data System (ADS)

    Horng, Ray-Hua; Wuu, Dong-Sing; Chan, Shih-Hsiung; Chiang, Ming-Chung; Huang, Tiao-Yuan; Sze, Simon

    1998-03-01

    BaTiO3 thin films deposited on the RuO2(250 nm)/Ru(20 nm)/TiN(200 nm)/Ti(20 nm)/(100)Si substrates by liquid-source misted chemical deposition are reported. The rapid thermal processing (RTP) technique was used for post deposition annealing. It was found that the strain was released and grain size increased for BaTiO3 films treated at high RTP temperature or for long RTP time. The interface between BaTiO3 and the bottom electrode was still sharp for the RTP-treated sample at 950°C. The leakage current density decreases as the RTP temperature increases. It can be decreased to 2.09 nA/cm2 under a supply voltage of 1.5 V. The dielectric constant can be increased up to 250 measured at 100 kHz for the sample treated by RTP at 950°C. The improvements in the BaTiO3 characteristics are due to the fact that RTP can enhance the crystallinity, relax the strain, alleviate the impurities in the films and does not result in significant interdiffusion of the materials.

  10. Structural study and ferroelectricity of epitaxial BaTiO3 films on silicon grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Mazet, L.; Bachelet, R.; Louahadj, L.; Albertini, D.; Gautier, B.; Cours, R.; Schamm-Chardon, S.; Saint-Girons, G.; Dubourdieu, C.

    2014-12-01

    Integration of epitaxial complex ferroelectric oxides such as BaTiO3 on semiconductor substrates depends on the ability to finely control their structure and properties, which are strongly correlated. The epitaxial growth of thin BaTiO3 films with high interfacial quality still remains scarcely investigated on semiconductors; a systematic investigation of processing conditions is missing although they determine the cationic composition, the oxygen content, and the microstructure, which, in turn, play a major role on the ferroelectric properties. We report here the study of various relevant deposition parameters in molecular beam epitaxy for the growth of epitaxial tetragonal BaTiO3 thin films on silicon substrates. The films were grown using a 4 nm-thick epitaxial SrTiO3 buffer layer. We show that the tetragonality of the BaTiO3 films, the crystalline domain orientations, and SiO2 interfacial layer regrowth strongly depend on the oxygen partial pressure and temperature during the growth and on the post-deposition anneal. The ferroelectricity of the films, probed using piezoresponse force microscopy, is obtained in controlled temperature and oxygen pressure conditions with a polarization perpendicular to the surface.

  11. Phase evolution in sonochemically synthesized Fe(3+) doped BaTiO3 nanocrystallites: structural, magnetic and ferroelectric characterisation.

    PubMed

    Dutta, Dimple P; Roy, Mainak; Maiti, Nandita; Tyagi, Avesh K

    2016-04-14

    The properties of nanomaterials are highly dependent on their size, morphology, crystal phase, etc., which in turn depend on the method of synthesis. We report here the electrical and magnetic characterisation of sonochemically synthesized Fe(3+) doped nano BaTiO3 samples. The dopant ion concentration has been optimized and the coexistence of ferromagnetism and ferroelectricity has been observed in the sample. With increase in Fe(3+) doping from 0 to 20 mol%, a gradual phase change from tetragonal to hexagonal occurred in these sonochemically synthesized BaTiO3 nanomaterials. Below 15 mol% Fe concentration the material displays ferroelectric behaviour with the absence of any magnetic ordering, while at an Fe concentration of ∼15 mol% the material exhibits both room temperature ferromagnetism and ferroelectricity. Ferromagnetism as well as relaxor type behaviour has been observed in the BaTiO3:Fe(3+)(20%) sample. We have studied the ferromagnetic and ferroelectric ordering in these sonochemically synthesized Fe(3+) doped BaTiO3 nanomaterials and have tried to correlate the results with their crystal structure and morphology. The origin of ferromagnetism in these materials has been attributed to both intrinsic as well as extrinsic factors. PMID:27003320

  12. Molecular-dynamics simulation of threshold displacement energies in BaTiO3

    NASA Astrophysics Data System (ADS)

    Gonzalez, E.; Abreu, Y.; Cruz, C. M.; Piñera, I.; Leyva, A.

    2015-09-01

    Molecular-dynamics simulations were used to calculate threshold displacement energies for each atom type in BaTiO3 perovskite. A primary knock-on atom with an energy range between 10 and 300 eV in principal crystallographic directions at 300 K was introduced. A statistical approach has been applied calculating displacement probability curves along main crystallographic directions. For each sublattice, the simulation was repeated from different initial conditions to estimate the uncertainty in the threshold displacement energy calculated values. The threshold displacement energies vary considerably with crystallographic direction and sublattice. The weighted average threshold displacement energies are 40 eV for oxygen, 64 eV for barium and 97 eV for titanium atoms. These values are comparable to ab initio calculated and experimentally derived values in perovskites. These results are proposed as threshold displacement energies, ideal for simulation programs that use atomic displacement calculation algorithms.

  13. Stress-induced phase transition in ferroelectric domain walls of BaTiO3

    NASA Astrophysics Data System (ADS)

    Stepkova, V.; Marton, P.; Hlinka, J.

    2012-05-01

    The seminal paper by Zhirnov (1958 Zh. Eksp. Teor. Fiz. 35 1175-80) explained why the structure of domain walls in ferroelectrics and ferromagnets is drastically different. Here we show that the antiparallel ferroelectric walls in rhombohedral ferroelectric BaTiO3 can be switched between the Ising-like state (typical for ferroelectrics) and a Bloch-like state (unusual for ferroelectric walls but typical for magnetic ones). Phase-field simulations using a Ginzburg-Landau-Devonshire model suggest that this symmetry-breaking transition can be induced by a compressive epitaxial stress. The strain-tunable chiral properties of these domain walls promise a range of novel phenomena in epitaxial ferroelectric thin films.

  14. Electric dipole sheets in BaTiO3/BaZrO3 superlattices

    NASA Astrophysics Data System (ADS)

    Jiang, Zhijun; Xu, Bin; Li, Fei; Wang, Dawei; Jia, C.-L.

    2015-01-01

    We investigate two-dimensional electric dipole sheets in the superlattice made of BaTiO3 and BaZrO3 using first-principles-based Monte Carlo simulations and density functional calculations. Electric dipole domains and complex patterns are observed and complex dipole structures with various symmetries (e.g., P m a 2 ,C m c m , and P m c 21 ) are further confirmed by density functional calculations, which are found to be almost degenerate in energy with the ferroelectric ground state of the A m m 2 symmetry, therefore strongly resembling magnetic sheets. More complex dipole patterns, including vortices and antivortices, are also observed, which may constitute the intermediate states that overcome the high-energy barrier of different polarization orientations previously predicted by A. I. Lebedev [Phys. Solid State 55, 1198 (2013), 10.1134/S1063783413060218]. We also show that such system possesses large electrostrictive effects that may be technologically important.

  15. Local structural investigation of Eu3+-doped BaTiO3 nanocrystals

    NASA Astrophysics Data System (ADS)

    Rabuffetti, Federico A.; Culver, Sean P.; Lee, John S.; Brutchey, Richard L.

    2014-02-01

    A structural investigation of sub-15 nm xEu:BaTiO3 nanocrystals (x = 0-5 mol%) was conducted to determine the distribution of the Eu3+ ion in the BaTiO3 lattice. Pair distribution function analysis of X-ray total scattering data (PDF), steady-state photoluminescence, and X-ray absorption spectroscopy (XANES/EXAFS) were employed to interrogate the crystal structure of the nanocrystals and the local atomic environment of the Eu3+ ion. The solubility limit of the Eu3+ ion in the nanocrystalline BaTiO3 host synthesized via the vapor diffusion sol-gel method was estimated to be ~4 mol%. A contraction of the perovskite unit cell volume was observed upon incorporation of 1 mol% of europium, while an expansion was observed for nominal concentrations between 1 and 3 mol%. The average Eu-O distance and europium coordination number decreased from 2.46 Å and 9.9 to 2.42 Å and 8.6 for europium concentrations of 1 and 5 mol%, respectively. Structural trends were found to be consistent with the substitution of Eu3+ for Ba2+via creation of a Ti4+ vacancy at low europium concentrations (<1 mol%), and with the substitution of Eu3+ for both Ba2+ and Ti4+ at high europium concentrations (1-3 mol%). The significance of accounting for local structural distortions to rationalize the distribution of lanthanide ions in the perovskite host is highlighted.A structural investigation of sub-15 nm xEu:BaTiO3 nanocrystals (x = 0-5 mol%) was conducted to determine the distribution of the Eu3+ ion in the BaTiO3 lattice. Pair distribution function analysis of X-ray total scattering data (PDF), steady-state photoluminescence, and X-ray absorption spectroscopy (XANES/EXAFS) were employed to interrogate the crystal structure of the nanocrystals and the local atomic environment of the Eu3+ ion. The solubility limit of the Eu3+ ion in the nanocrystalline BaTiO3 host synthesized via the vapor diffusion sol-gel method was estimated to be ~4 mol%. A contraction of the perovskite unit cell volume was observed upon incorporation of 1 mol% of europium, while an expansion was observed for nominal concentrations between 1 and 3 mol%. The average Eu-O distance and europium coordination number decreased from 2.46 Å and 9.9 to 2.42 Å and 8.6 for europium concentrations of 1 and 5 mol%, respectively. Structural trends were found to be consistent with the substitution of Eu3+ for Ba2+via creation of a Ti4+ vacancy at low europium concentrations (<1 mol%), and with the substitution of Eu3+ for both Ba2+ and Ti4+ at high europium concentrations (1-3 mol%). The significance of accounting for local structural distortions to rationalize the distribution of lanthanide ions in the perovskite host is highlighted. Electronic supplementary information (ESI) available: (1) Detailed experimental procedures; (2) structural parameters derived from Rietveld analysis of XRD data; (3) additional TEM images and particle size distribution histograms; (4) structure functions Q[S(Q) - 1]; (5) time-resolved spectra of the 5D0 --> 7F2 decay; and (6) k2-weighted and normalized χ(k) EXAFS spectra. See DOI: 10.1039/c3nr06610j

  16. Voltage generation from individual BaTiO(3) nanowires under periodic tensile mechanical load.

    PubMed

    Wang, Zhaoyu; Hu, Jie; Suryavanshi, Abhijit P; Yum, Kyungsuk; Yu, Min-Feng

    2007-10-01

    Direct tensile mechanical loading of an individual single-crystal BaTiO(3) nanowire was realized to reveal the direct piezoelectric effect in the nanowire. Periodic voltage generation from the nanowire was produced by a periodically varying tensile mechanical strain applied with a precision mechanical testing stage. The measured voltage generation from the nanowire was found to be directly proportional to the applied strain rate and was successfully modeled through the consideration of an equivalent circuit for a piezoelectric nanowire under low-frequency operation. The study, besides demonstrating a controlled experimental method for the study of direct piezoelectric effect in nanostructures, implies also the use of such perovskite piezoelectric nanowires for efficient energy-harvesting applications. PMID:17894515

  17. Fe modified BaTiO3: Influence of doping on ferroelectric property

    NASA Astrophysics Data System (ADS)

    Mishra, Ashutosh; Bisen, Supriya; Jarabana, Kanaka Mahalakshmi; Mishra, Niyati

    2015-06-01

    We have investigate the ferroelectric property of Fe modified Barium Titanate (BaTiO3) with possible tetragonal structure via solid state route was prepared. Modified sample of BaTi1-xFexO3 (x=0.01, 0.02) were structural characterized by X-ray Diffraction (XRD) using a Bruker D8 Advance XRD instruments, the value of 2θ is in between 20° to 80°. Fourier transform infrared spectroscopy (FTIR) using a Bruker, vertex instruments has been performs to obtain Ti-O bonding in the modified sample; the region of wavenumber is from 4000 cm-1 to 400 cm-1. P-E hysteresis loop measurements have been traced for different applied voltage- 100V, 300V and 500V.

  18. Dielectric response of Cu/amorphous BaTiO3/Cu capacitors

    NASA Astrophysics Data System (ADS)

    Gonon, P.; El Kamel, F.

    2007-04-01

    Cu/amorphous BaTiO3/Cu capacitors were tested for their dielectric properties in the 0.1Hz -100kHz range, from room temperature to 350°C. The amorphous barium titanate dielectric layer was deposited by rf sputtering on water-cooled copper electrodes. The room-temperature dielectric constant is around 18 and the dissipation factor is 3×10-3 at 100kHz. When increasing temperature the dielectric response displays an important frequency dispersion with the appearance of a marked loss peak at low frequencies. This dispersion is ascribed to electrode polarization effects, as evidenced by measurements performed on various film thicknesses and by using different electrodes. The electrode polarization phenomenon is discussed using a simple space charge model and is shown to be related to mobile oxygen vacancies.

  19. Magnetic and ferroelectric properties of Zn and Mn co-doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Keshari Das, Sangram; Kumar Roul, Binod

    2015-06-01

    This paper reports an approach to obtaining multiferroic properties in co-doped (Zn:Mn) BaTiO3 near room temperature. Interestingly, an unusual magnetic hysteresis loop is observed in the co-doped compositions in which the central portion of the loop is squeezed. However, in the composition Ba0.9Zn0.1Ti0.9Mn0.1O3, a broad magnetic hysteresis loop is observed. Such a magnetic effect is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. The observation of the above type of magnetic properties is likely to be due to the presence of exchange interactions between Mn ions. A lossy-type of ferroelectric hysteresis loop is also observed in co-doped ceramic compositions near room temperature. Author S. K. Das supported financially by CSIR, New Delhi (Grant No. 09/750 (0005)/2009-EMR-I).

  20. 90-degree polarization switching in BaTiO3 crystals without domain wall motion

    NASA Astrophysics Data System (ADS)

    Li, Y. W.; Scott, J. F.; Fang, D. N.; Li, F. X.

    2013-12-01

    We report 90° polarization switching in a BaTiO3 crystal without domain wall (DW) motion by prefabricating samples with interlocking domains via compression. During electric re-poling of the depoled and aged crystals, 90° domain nucleation still exists, but 90° DW motion is inhibited by the strong constraints from surrounding domains, leading to DW-free 90° polarization switching. The measured coercive field of 500 V/mm for the DW-free 90° switching is close to the intrinsic values and much larger than that of 80 V/mm via 90° DW motion. Compared to the rather difficult domain-free 180° polarization switching in ultrathin films, 90° DW-free switching is easier.

  1. Negative Capacitance in BaTiO3/BiFeO3 Bilayer Capacitors.

    PubMed

    Hou, Ya-Fei; Li, Wei-Li; Zhang, Tian-Dong; Yu, Yang; Han, Ren-Lu; Fei, Wei-Dong

    2016-08-31

    Negative capacitances provide an approach to reduce heat generations in field-effect transistors during the switch processes, which contributes to further miniaturization of the conventional integrated circuits. Although there are many studies about negative capacitances using ferroelectric materials, the direct observation of stable ferroelectric negative capacitances has rarely been reported. Here, we put forward a dc bias assistant model in bilayer capacitors, where one ferroelectric layer with large dielectric constant and the other ferroelectric layer with small dielectric constant are needed. Negative capacitances can be obtained when external dc bias electric fields are larger than a critical value. Based on the model, BaTiO3/BiFeO3 bilayer capacitors are chosen as study objects, and negative capacitances are observed directly. Additionally, the upward self-polarization effect in the ferroelectric layer reduces the critical electric field, which may provide a method for realizing zero and/or small dc bias assistant negative capacitances. PMID:27502999

  2. Influence of defects on ferroelectric and electrocaloric properties of BaTiO3

    NASA Astrophysics Data System (ADS)

    Grünebohm, Anna; Nishimatsu, Takeshi

    2016-04-01

    We report modifications of the ferroelectric and electrocaloric properties of BaTiO3 by defects. For this purpose, we have combined ab initio based molecular dynamics simulations with a simple model for defects. We find that different kinds of defects modify the ferroelectric transition temperatures and polarization, reduce the thermal hysteresis of the transition, and are no obstacle for a large caloric response. For a locally reduced polarization, the ferroelectric transition temperature and the adiabatic response are slightly reduced. For polar defects, an intriguing picture emerges. The transition temperature is increased by polar defects and the temperature range of the large caloric response is broadened. Even more remarkable, we find an inverse caloric effect in a broad temperature range.

  3. Impedance spectroscopy of V2O5-Bi2O3-BaTiO3 glass-ceramics

    NASA Astrophysics Data System (ADS)

    Al-syadi, Aref M.; Yousef, El Sayed; El-Desoky, M. M.; Al-Assiri, M. S.

    2013-12-01

    The glasses within composition as: (80 - x)V2O5/20Bi2O3/xBaTiO3 with x = 2.5, 5, 7.5 and 10 mol% have been prepared. The glass transition (Tg) increases with increasing BaTiO3 content. Synthesized glasses ceramic containing BaTi4O9, Ba3TiV4O15 nanoparticles of the order of 25-35 nm and 30-46 nm, respectively were estimated using XRD. The dielectric properties over wide ranges of frequencies and temperatures were investigated as a function of BaTiO3 content by impedance spectroscopy measurements. The hopping frequency, ωh, dielectric constant, ɛ', activation energies for the DC conduction, Eσ, the relaxation process, Ec, and stretched exponential parameter β of the glasses samples have been estimated. The, ωh,β, decrease from 51.63 to 0.31 × 106 (s-1), 0.84 to 0.79 with increasing BaTiO3 respectively. Otherwise, the Eσ, increase from 0.279 to 0.306 eV with increasing BaTiO3. The value of dielectric constant equal 9.5·103 for the 2.5BaTiO3/77.5V2O5/20Bi2O3 glasses-ceramic at 330 K for 1 KHz which is ten times larger than that of same glasses composition. Finally the relaxation properties of the investigated glasses are presented in the electric modulus formalism, where the relaxation time and the respective activation energy were determined.

  4. High Performance Flexible Piezoelectric Nanogenerators based on BaTiO3 Nanofibers in Different Alignment Modes.

    PubMed

    Yan, Jing; Jeong, Young Gyu

    2016-06-22

    Piezoelectric nanogenerators, harvesting energy from mechanical stimuli in our living environments, hold great promise to power sustainable self-sufficient micro/nanosystems and mobile/portable electronics. BaTiO3 as a lead-free material with high piezoelectric coefficient and dielectric constant has been widely examined to realize nanogenerators, capacitors, sensors, etc. In this study, polydimethylsiloxane (PDMS)-based flexible composites including BaTiO3 nanofibers with different alignment modes were manufactured and their piezoelectric performance was examined. For the study, BaTiO3 nanofibers were prepared by an electrospinning technique utilizing a sol-gel precursor and following calcination process, and they were then aligned vertically or horizontally or randomly in PDMS matrix-based nanogenerators. The morphological structures of BaTiO3 nanofibers and their nanogenerators were analyzed by using SEM images. The crystal structures of the nanogenerators before and after poling were characterized by X-ray diffraction. The dielectric and piezoelectric properties of the nanogenerators were investigated as a function of the nanofiber alignment mode. The nanogenerator with BaTiO3 nanofibers aligned vertically in the PDMS matrix sheet achieved high piezoelectric performance of an output power of 0.1841 μW with maximum voltage of 2.67 V and current of 261.40 nA under a low mechanical stress of 0.002 MPa, in addition to a high dielectric constant of 40.23 at 100 Hz. The harvested energy could thus power a commercial LED directly or be stored into capacitors after rectification. PMID:27237223

  5. Functional properties of BaTiO3-Ni0.5Zn0.5Fe2O4 magnetoelectric ceramics prepared from powders with core-shell structure

    NASA Astrophysics Data System (ADS)

    Curecheriu, L. P.; Buscaglia, M. T.; Buscaglia, V.; Mitoseriu, L.; Postolache, P.; Ianculescu, A.; Nanni, P.

    2010-05-01

    In the present work, diphasic ceramic composites with core-shell nanostructures formed by Ni0.50Zn0.50Fe2O4 core and BaTiO3 shell were investigated. Their properties were compared with those of composites prepared by coprecipitation. The core-shell structure was confirmed by microstructural powder analysis. Homogeneous microstructures with a good phase mixing and percolated dielectric phase by the magnetic one were obtained from coprecipitated powders. Less homogeneous microstructures resulted in ceramics produced from the powder prepared by core-shell method, with isolated small ferrite grains besides large ferrite aggregates embedded into the BaTiO3 matrix. Both the ferroelectric and magnetic phases preserve their basic properties in bulk composite form. However, important differences in the dielectric relaxation and conduction mechanisms were found as result of the microstructural difference. Extrinsic contributions play important roles in modifying the electric properties in both ceramics, causing space charge effect, Maxwell-Wagner relaxations and hopping conductivity, mainly due to the ferrite low resistivity phase. The conductivity and dielectric modulus spectra analysis allowed to identify different polaron contributions associated with the microstructural differences. It results that by using the core-shell method, improved dielectric properties and limited hopping contributions can be realized.

  6. Processing and Characterization of Carbonate-Free BaTiO3 Nanoscale Particles Obtained by a Rapid Ultrasound-Assisted Wet Chemical Approach

    NASA Astrophysics Data System (ADS)

    Ashiri, Rouholah; Moghtada, Abdolmajid; Shahrouzianfar, Ali

    2015-08-01

    This work highlights an innovative one-step synthesis pathway for obtaining tailor-made carbonate-free BaTiO3 nanocrystals at low temperature. The work also tries to characterize the processing of the nanocrystals. Well-defined and stoichiometric BaTiO3 nanocrystals were prepared sonochemically at 323 K (50 °C) in only 45 minutes, which were rather easy to manipulate. The particle size distribution was rather narrow. The results indicated that the size of BaTiO3 nanocrystals can be tailored by changing the reactants concentration. The kinetic of BaTiO3 formation was more rapid for the precursor solutions with higher BaCl2 concentration. The particle size was also very sensitive to the Ba/Ti ratio of the precursor solution and ultrasonication conditions. The as-dried precipitates were generally composed of loose agglomerates resulting from the assembly of several BaTiO3 nanocrystals during drying stage of the preparation. This agglomeration can be potentially used for self-assembling of the obtained BaTiO3 nanocrystals in miniaturization of multilayer ceramic capacitors and for the development of other nano-devices organized by BaTiO3 nanocrystals.

  7. Lattice dynamics of crystals with tetragonal BaTiO3 structure

    NASA Astrophysics Data System (ADS)

    Freire, J. D.; Katiyar, R. S.

    1988-02-01

    A lattice-dynamical formalism using the rigid-ion model due to Born and Huang is applied to the ferroelectric crystals PbTiO3 and BaTiO3, in the tetragonal phase. The model includes short-range interactions of axially symmetric type between various ions in the primitive cell and long-range Coulomb interactions. The stability conditions are worked out in the manner described by Katiyar and are used to determine several first-order derivative potential constants for the crystals. The number of potential constants was further reduced by considering the variation of radial force constants with the ion-ion distance, as given by the exponential formalism of Born and Mayer. Zone-center phonons and a few of the low-frequency zone-boundary phonons were used for the nonlinear least-squares fitting. In general, we obtained excellent agreement between the calculated and observed frequencies. The resulting parameters showed that the short-range interaction between the nearest titanium and oxygen is approximately 1 order of magnitude stronger than the interactions between the lead and oxygen or between the oxygens. The calculations showed that the lowest transverse-optic mode of E symmetry in PbTiO3 has eigenvectors similar to those predicted by Last, whereas in BaTiO3 the ionic movement in the lowest optic E mode can be approximated by the description of Slater. The phonon dispersion curves for various directions of the wave vector q were computed. These results are in good agreement with the inelastic neutron measurements by Shirane et al. A calculation of the oblique phonons near the zone center is presented and compared with the available experimental data. These calculations show that the long-range Coulomb forces dominate the anisotropic forces in these crystals. A theoretical approach for computing the elastic, dielectric, and piezoelectric properties is presented and the proposed model applied for calculating these constants. The results are compared with the experimental data where existed. Finally, a least-squares analysis of the observed phonons in PbTiO3 near the tetragonal-cubic phase-transition temperature was carried out to understand the influence of anharmonic forces and the mechanism of the phase transition in this crystal. In general, the variation in the parameters obtained is very small. This shows that the small anharmonic forces may be sufficient to explain the variation of frequencies with temperature.

  8. Some Aspects of the Failure Mechanisms in BaTiO3-Based Multilayer Ceramic Capacitors

    NASA Technical Reports Server (NTRS)

    Liu, David Donhang; Sampson, Michael J.

    2012-01-01

    The objective of this presentation is to gain insight into possible failure mechanisms in BaTiO3-based ceramic capacitors that may be associated with the reliability degradation that accompanies a reduction in dielectric thickness, as reported by Intel Corporation in 2010. The volumetric efficiency (microF/cm3) of a multilayer ceramic capacitor (MLCC) has been shown to not increase limitlessly due to the grain size effect on the dielectric constant of ferroelectric ceramic BaTiO3 material. The reliability of an MLCC has been discussed with respect to its structure. The MLCCs with higher numbers of dielectric layers will pose more challenges for the reliability of dielectric material, which is the case for most base-metal-electrode (BME) capacitors. A number of MLCCs manufactured using both precious-metal-electrode (PME) and BME technology, with 25 V rating and various chip sizes and capacitances, were tested at accelerated stress levels. Most of these MLCCs had a failure behavior with two mixed failure modes: the well-known rapid dielectric wearout, and so-called 'early failures." The two failure modes can be distinguished when the testing data were presented and normalized at use-level using a 2-parameter Weibull plot. The early failures had a slope parameter of Beta >1, indicating that the early failures are not infant mortalities. Early failures are triggered due to external electrical overstress and become dominant as dielectric layer thickness decreases, accompanied by a dramatic reduction in reliability. This indicates that early failures are the main cause of the reliability degradation in MLCCs as dielectric layer thickness decreases. All of the early failures are characterized by an avalanche-like breakdown leakage current. The failures have been attributed to the extrinsic minor construction defects introduced during fabrication of the capacitors. A reliability model including dielectric thickness and extrinsic defect feature size is proposed in this presentation. The model can be used to explain the Intel-reported reliability degradation in MLCCs with respect to the reduction of dielectric thickness. It can also be used to estimate the reliability of a MLCC based on its construction and microstructure parameters such as dielectric thickness, average grain size, and number of dielectric layers. Measures for preventing early failures are also discussed in this document.

  9. Acoustic Imaging of Ferroelectric Domains in BaTiO3 Single Crystals Using Atomic Force Microscope

    NASA Astrophysics Data System (ADS)

    Zeng, Huarong; Shimamura, Kiyoshi; Kannan, Chinna Venkadasamy; Villora, Encarnacion G.; Takekawa, Shunji; Kitamura, Kenji; Yin, Qingrui

    2007-01-01

    An “alternating-force-modulated” atomic force microscope (AFM) operating in the acoustic mode, generated by launching acoustic waves on the piezoelectric transducer that is attached to the cantilever, was used to visualize the ferroelectric domains in barium titanate (BaTiO3) single crystals by detecting acoustic vibrations generated by the tip and transmitted through the sample placed beneath it to the transducer. The acoustic signal was found to reflect locally elastic microstructures at low frequencies, while high-frequency acoustic images revealed strip like domain configurations of internal substructures in BaTiO3 single crystals. The underlying acoustic imaging mechanism using the AFM was discussed in terms of the interaction between the excited acoustic wave and ferroelectric domains.

  10. Single-crystalline BaTiO3 films grown by gas-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Matsubara, Yuya; Takahashi, Kei S.; Tokura, Yoshinori; Kawasaki, Masashi

    2014-12-01

    Thin BaTiO3 films were grown on GdScO3 (110) substrates by metalorganic gas-source molecular beam epitaxy. Titanium tetra-isopropoxide (TTIP) was used as a volatile precursor that provides a wide growth window of the supplied TTIP/Ba ratio for automatic adjustment of the film composition. Within the growth window, compressively strained films can be grown with excellent crystalline quality, whereas films grown outside of the growth window are relaxed with inferior crystallinity. This growth method will provide a way to study the intrinsic properties of ferroelectric BaTiO3 films and their heterostructures by precise control of the stoichiometry, structure, and purity.

  11. Nanoparticle-Sintered BaTiO3 Thin Films and Its Orientation Control by Solid Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Nakasone, Fumi; Kobayashi, Keisuke; Suzuki, Toshimasa; Mizuno, Youichi; Chazono, Hirokazu; Imai, Hiroaki

    2008-11-01

    A novel powder-sintering thin-film process using nanocrystals of sol-gel-derived BaTiO3 without sintering additives yields a highly densified microstructure containing columnar grains at low temperatures of 800 °C. The BaTiO3 thin film fabricated on a (111)-oriented Pt/TiO2/Al2O3 substrate shows high crystallinity and a relatively high dielectric constant of 635 at 10 kHz with a low loss tangent of 0.007. Furthermore, the controllability of the crystallographic orientations of thin films by solid phase epitaxy is demonstrated on the basis of the optimization of surface nucleation and the subsequent grain growth on epitaxially grown platinum electrodes and single-crystal SrTiO3 substrates.

  12. Structural evidence for enhanced polarization in a commensurate short-period BaTiO3/SrTiO3 superlattice

    NASA Astrophysics Data System (ADS)

    Tian, W.; Jiang, J. C.; Pan, X. Q.; Haeni, J. H.; Li, Y. L.; Chen, L. Q.; Schlom, D. G.; Neaton, J. B.; Rabe, K. M.; Jia, Q. X.

    2006-08-01

    A short-period (BaTiO3)6/(SrTiO3)5 superlattice was characterized by x-ray diffraction and transmission electron microscopy. The superlattice is epitaxially oriented with the c axes of BaTiO3 and SrTiO3 normal to the (001) surface of the SrTiO3 substrate. Despite the large in-plane lattice mismatch between BaTiO3 and SrTiO3 (˜2.2%), the superlattice interfaces were found to be nearly commensurate. The crystallographic c /a ratio of the superlattice was measured and the results agree quantitatively with first-principles calculations and phase-field modeling. The agreement supports the validity of the enhanced spontaneous polarization predicted for short-period BaTiO3/SrTiO3 superlattices.

  13. Strong flux pinning enhancement in YBa2Cu3O7-x films by embedded BaZrO3 and BaTiO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ding, Fa-Zhu; Gu, Hong-Wei; Zhang, Teng; Wang, Hong-Yan; Qu, Fei; Qiu, Qing-Quan; Dai, Shao-Tao; Peng, Xing-Yu

    2013-07-01

    YBa2Cu3O7-x (YBCO) films with embedded BaZrO3 and BaTiO3 nanoparticles were fabricated by metalorganic deposition using trifluoroacetates (TFA-MOD). Both X-ray diffraction and transmission electron microscopy revealed that these BaZrO3 and BaTiO3 nanoparticles had random orientations and were distributed stochastically in the YBCO matrix. The unique combined microstructure enhances the critical current density (Jc) of the BaZrO3/BaTiO3 doped-YBCO films, while keeping the critical transition temperature (Tc) close to that in the pure YBCO films. These results indicate that BaZrO3 and BaTiO3 nanoparticles provide strong flux pinning in YBCO films.

  14. Both High Reliability and Giant Electrocaloric Strength in BaTiO3 Ceramics

    PubMed Central

    Bai, Yang; Han, Xi; Zheng, Xiu-Cheng; Qiao, Lijie

    2013-01-01

    BaTiO3 has a giant electrocaloric strength, |ΔT|/|ΔE|, because of a large latent heat and a sharp phase transition. The electrocaloric strength of a new single crystal, as giant as 0.48 K·cm/kV, is twice larger than the previous best result, but it remarkably decreased to 0.18 K·cm/kV after several times of thermal cycles accompanied by alternating electric fields, because the field-induced phase transition and domain switching resulted in numerous defects such as microcracks. The ceramics prepared from nano-sized powders showed a high electrocaloric strength of 0.14 K·cm/kV, comparable to the single crystals experienced electrocaloric cycles, because of its unique microstructure after proper sintering process. Moreover, its properties did not change under the combined effects of thermal cycles and alternating electric fields, i.e. it has both large electrocaloric effect and good reliability, which are desirable for practical applications. PMID:24100662

  15. Symmetry, strain, defects, and the nonlinear optical response of crystalline BaTiO3/silicon

    NASA Astrophysics Data System (ADS)

    Kormondy, Kristy; Abel, Stefan; Popoff, Youri; Sousa, Marilyne; Caimi, Daniele; Siegwart, Heinz; Marchiori, Chiara; Rossell, Marta; Demkov, Alex; Fompeyrine, Jean

    Recent progress has been made towards exploiting the linear electro-optic or Pockels effect in ferroelectric BaTiO3 (BTO) for novel integrated silicon photonics devices. In such structures, the crystalline symmetry and domain structure of BTO determine which electro-optic tensor elements are accessible under application of an external electric field. For epitaxial thin films of BTO on Si (001), the role of defects in strain relaxation can lead to very different crystalline symmetry even for films of identical thickness. Indeed, through geometric phase analysis of high-resolution scanning transmission electron microscopy images, we map changes of the in-plane and out-of-plane lattice parameters across two 80-nm-thick BTO films. A corresponding 20% difference in the effective electro-optic response was measured by analyzing induced rotation of the polarization of a laser beam (λ = 1550 nm) transmitted through lithographically defined electrodes. Understanding, controlling, and modelling the role of BTO symmetry in nonlinear optics is of fundamental importance for the development of a hybrid BTO/Si photonics platform.. Work supported by the NSF (IRES-1358111), AFOSR (FA9550-12-10494), and European Commission (FP7-ICT-2013-11-619456-SITOGA).

  16. Improved ferroelectric, piezoelectric and electrostrictive properties of dense BaTiO3 ceramic

    NASA Astrophysics Data System (ADS)

    Baraskar, Bharat G.; Kakade, S. G.; James, A. R.; Kambale, R. C.; Kolekar, Y. D.

    2016-05-01

    The ferroelectric, piezoelectric and electrostrictive properties of BaTiO3 (BT) dense ceramic synthesized by solid-state reaction were investigated. X-ray diffraction study confirmed tetragonal crystal structure having c/a ~1.0144. The dense microstructure was evidenced from morphological studies with an average grain size ~7.8 µm. Temperature dependent dielectric measurement showed the maximum values of dielectric constant, ɛr = 5617 at Curie temperature, Tc = 125 °C. The saturation and remnant polarization, Psat. = 24.13 µC/cm2 and Pr =10.42 µC/cm2 achieved respectively for the first time with lower coercive field of Ec=2.047 kV/cm. The polarization current density-electric field measurement exhibits the peaking characteristics, confirms the saturation state of polarization for BT. The strain-electric field measurements revealed the "sprout" shape nature instead of typical "butterfly loop". This shows the excellent converse piezoelectric response with remnant strain ~ 0.212% and converse piezoelectric constant d*33 ~376.35 pm/V. The intrinsic electrostrictive coefficient was deduced from the variation of strain with polarization with electrostrictive coefficient Q33~ 0.03493m4/C2.

  17. Virus-directed design of a flexible BaTiO3 nanogenerator.

    PubMed

    Jeong, Chang Kyu; Kim, Insu; Park, Kwi-Il; Oh, Mi Hwa; Paik, Haemin; Hwang, Geon-Tae; No, Kwangsoo; Nam, Yoon Sung; Lee, Keon Jae

    2013-12-23

    Biotemplated synthesis of functional nanomaterials has received increasing attention for applications in energy, catalysis, bioimaging, and other technologies. This approach is justified by the unique abilities of biological systems to guide sophisticated assembly and organization of molecules and materials into distinctive nanoscale morphologies that exhibit physicochemical properties highly desirable for specific purposes. Here, we present a high-performance, flexible nanogenerator using anisotropic BaTiO3 (BTO) nanocrystals synthesized on an M13 viral template through the genetically programmed self-assembly of metal ion precursors. The filamentous viral template realizes the formation of a highly entangled, well-dispersed network of anisotropic BTO nanostructures with high crystallinity and piezoelectricity. Even without the use of additional structural stabilizers, our virus-enabled flexible nanogenerator exhibits a high electrical output up to ∼300 nA and ∼6 V, indicating the importance of nanoscale structures for device performances. This study shows the biotemplating approach as a facile method to design and fabricate nanoscale materials particularly suitable for flexible energy harvesting applications. PMID:24229091

  18. Performance analysis of resistive switching devices based on BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Samardzic, Natasa; Kojic, Tijana; Vukmirovic, Jelena; Tripkovic, Djordjije; Bajac, Branimir; Srdic, Vladimir; Stojanovic, Goran

    2016-03-01

    Resitive switching devices, memristors, have recenty attracted much attention due to promising performances and potential applications in the field of logic and memory devices. Here, we present thin film BaTiO3 based memristor fabricated using ink-jet printing technique. Active material is a single layer barium titanate film with thickness of ̴100 nm, sandwitched between metal electodes. Printing parameters were optimized aiming to achieve stable drop flow and uniform printed layer. Current-voltage characteristics show typical memristive behavior with pinched hysteresis loop crossed at the origin, with marked differences between High Resistive State (HRS) and Low Resistive State (LRS). Obtained resistive states are stable during numerous switching processes. The device also shows unipolar switching effect for negative voltage impulses. Variable voltage impulse amplitudes leads to the shifting of the energy levels of electode contacts resulting in changing of the overall current through the device. Structural charcterization have been performed using XRD analysis and SEM micrography. High-temperature current-voltage measurements combined with transport parameter analysis using Hall efect measurement system (HMS 3000) and Impedance Analyzer AC measurements allows deeper insigth into conduction mechanism of ferroelectric memristors.

  19. BaTiO3/PVDF Nanocomposite Film with High Energy Storage Density

    NASA Astrophysics Data System (ADS)

    Wang, Xiaohui

    2016-03-01

    A gradated multilayer BaTiO3/poly(vinylidenefluoride) thin film structure is presented to achieve both a higher breakdown strength and a superior energy-storage capability. Key to the process is the sequential deposition of uniform dispersions of the single component source, which generate a blended PVDF-BTO-PVDF structure prior to full evaporation of solvent, and thermal treatment of the dielectric. The result is like sandwich structure with partial 0-3 character. The central layer designed to provide the high electric displacement, is composed of high volume fraction 6-10 nm BTO nanocrystals produced by a TEG-sol method. The outer layers of the structure are predominantly PVDF, with a significantly lower volume fraction of BTO, taking advantage of the higher dielectric strength for pure PVDF at the electrode-nanocomposite interface. The film is mechanically flexible, and can be removed from the substrate, with total thicknesses in the range 1.2 - 1.5 μm. Parallel plate capacitance devices improved dielectric performances, compared to reported values for BTO-PVDF 0-3 nanocomposites, with a maximal discharged energy density of 19.4J/cm3 and dielectric breakdown strengths of up to 495 kV/mm.

  20. A New Synthesis Strategy For High-Quality Fe / BaTiO3 Multiferroics

    NASA Astrophysics Data System (ADS)

    Chen, X.; Kim, J.; Kim, J. S.; Rojas, G.; Skomski, R.; Bode, M.; Bhattacharya, A.; Santos, T.; Guisinger, N.; Gruverman, A.; Lu, H.; Enders, A.

    2010-03-01

    Ultrathin film BaTiO3/Nb-SrTiO3 (BTO/STO) and Fe/BTO nanostructures were investigated with variable temperature scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) under ultrahigh vacuum. BTO films of 8 -- 13 unit cells thickness were grown by ozone-assisted molecular beam epitaxy on STO, and transferred through air into the STM chamber. Atomically flat, clean and unreconstructed films were recovered after annealing them in 1x10-4 mBar oxygen at 970K. Fe nanoclusters were deposited on the BTO by noble gas buffer layer assisted growth, and further studied by LEED and STM. The sharp 1x1 LEED images after cluster deposition show that the clusters are crystalline, suggesting that the interface oxidation is minimal. This synthesis route has thus the potential to fabricate ordered, atomically flat interfaces by suppressing interface mixing and Fe oxidation, which is a significant advantage over MBE deposition of Fe on BTO. The samples obtained are currently used as model system for the study of interface contributions to the magnetoelectric effect in multiferroics.

  1. Non-linear second harmonic generation (SHG) studies of BaTiO3/SrTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Vlahos, Eftihia; Lee, Che-Hui; Wu, Pingping; Wung Bark, Chung; Jang, Ho Won; Folkman, Chad; Hyub Baek, Seung; Park, J. W.; Biegalski, Mike; Tenne, Dmitri; Schlom, Darrell; Chen, Long-Qing; Eom, Chang-Beom; Gopalan, Venkatraman

    2010-03-01

    Theoretical phase-field simulations predict that certain types of superlattices consisting of alternating (BaTiO3)n/(SrTiO3)n layers have novel vortex domain wall configurations which give rise to exceptionally high polarization tunability combined with negligible polarization hysteresis. Optical second harmonic generation (SHG) was used to probe the phase and transition temperatures of multilayer (BaTiO3)m/(SrTiO3)n superlattices, as a function of epitaxial strain. In addition, in-plane electro-optic measurements were carried out. The experimental results are in excellent agreement both with theoretical predictions, as well as the temperature-strain phase diagram obtained experimentally from UV Raman studies. The ferroelectric, in-plane SHG signal, from the tensile strained SrTiO3 layers reveals an mm2 point group symmetry, whereas the point group symmetry of the compressively strained BaTiO3 layers, was determined to be 4mm.

  2. Polarization and lattice strains in epitaxial BaTiO3 films grown by high-pressure sputtering

    NASA Astrophysics Data System (ADS)

    Petraru, A.; Pertsev, N. A.; Kohlstedt, H.; Poppe, U.; Waser, R.; Solbach, A.; Klemradt, U.

    2007-06-01

    High-quality BaTiO3 films with thicknesses ranging from 2.9to175nm were grown epitaxially on SrRuO3-covered (001)-oriented SrTiO3 substrates by high-pressure sputtering. The crystal structure of these films was studied by conventional and synchrotron x-ray diffraction. The in-plane and out-of-plane lattice parameters were determined as a function of film thickness by x-ray reciprocal space mapping around the asymmetric (1¯03) Bragg reflection. BaTiO3 films were found to be fully strained by the SrTiO3 substrate up to a thickness of about 30nm. Ferroelectric capacitors were then fabricated by depositing SrRuO3 top electrodes, and the polarization-voltage hysteresis loops were recorded at the frequencies 1-30kHz. The observed thickness effect on the lattice parameters and polarization in BaTiO3 films was analyzed in the light of strain and depolarizing-field effects using the nonlinear thermodynamics theory. The theoretical predictions are in reasonable agreement with the measured thickness dependences, although the maximum experimental values of the spontaneous polarization and the out-of-plane lattice parameter exceed the theoretical estimates (43μC /cm2 vs 35μC/cm2 and 4.166Å vs 4.143Å). Possible origins of the revealed discrepancy between theory and experiment are discussed.

  3. Chemical and microstructural characterization of rf-sputtered BaTiO3 nano-capacitors with Ni electrodes

    NASA Astrophysics Data System (ADS)

    Reck, James N.; Cortez, Rebecca; Xie, S.; Zhang, Ming; O'Keefe, Matthew; Dogan, Fatih

    2012-05-01

    Chemical and microstructural evaluation techniques have been used to characterize sputter deposited 100-150 nm thick BaTiO3 nano-capacitors with 30 nm thick Ni electrodes fabricated on Si/SiO2 wafers. More than 99% of devices had resistance > 20 MΩ. Electrodes were found to have a roughness, Ra, of about 0.66 ± 0.04 nm, and the BaTiO3 had a Ra value of 1.3 ± 0.12 nm. Characterization of the BaTiO3 film chemistry with X-ray Photoelectron Spectroscopy (XPS) showed the films had excess oxygen and Ba:Ti ratios ranging from 0.78 to 1.1, depending on sputtering conditions. X-ray diffraction showed a broad peak between approximately 20° and 35° 2θ, indicating the films were either amorphous or contained grain sizes less than 5 nm. Focused ion beam images confirmed the presence of smooth, conformal films, with no visible signs of macro-defects such as pin-holes, cracks, or pores. High resolution transmission electron microscopy (TEM) and electron diffraction patterns confirmed the presence of a nearly amorphous film with limited short range order. No correlation was found between the chemical and microstructural studies with the dielectric permittivity (280-1000), loss (0.02-0.09), and/or resistivity (8.7 × 1010-1.5 × 1012 Ω cm) values.

  4. Metastable monoclinic and orthorhombic phases and electric field induced irreversible phase transformation at room temperature in the lead-free classical ferroelectric BaTiO3

    NASA Astrophysics Data System (ADS)

    Kalyani, Ajay Kumar; Khatua, Dipak Kumar; Loukya, B.; Datta, Ranjan; Fitch, Andy N.; Senyshyn, Anatoliy; Ranjan, Rajeev

    2015-03-01

    For decades it has been a well-known fact that among the few ferroelectric compounds in the perovskite family, namely, BaTiO3, KNbO3, PbTiO3, and Na1 /2Bi1 /2TiO3 , the dielectric and piezoelectric properties of BaTiO3 are considerably higher than the others in polycrystalline form at room temperature. Further, similar to ferroelectric alloys exhibiting morphotropic phase boundary, single crystals of BaTiO3 exhibit anomalously large piezoelectric response when poled away from the direction of spontaneous polarization at room temperature. These anomalous features in BaTiO3 remained unexplained so far from the structural standpoint. In this work, we have used high-resolution synchrotron x-ray powder diffraction, atomic resolution aberration-corrected transmission electron microscopy, in conjunction with a powder poling technique, to reveal that at 300 K (i) the equilibrium state of BaTiO3 is characterized by coexistence of metastable monoclinic Pm and orthorhombic (Amm2) phases along with the tetragonal phase, and (ii) strong electric field switches the polarization direction from the [001] direction towards the [101] direction. These results suggest that BaTiO3 at room temperature is within an instability regime, and that this instability is the fundamental factor responsible for the anomalous dielectric and piezoelectric properties of BaTiO3 as compared to the other homologous ferroelectric perovskite compounds at room temperature. Pure BaTiO3 at room temperature is therefore more akin to lead-based ferroelectric alloys close to the morphotropic phase boundary where polarization rotation and field induced ferroelectric-ferroelectric phase transformations play a fundamental role in influencing the dielectric and piezoelectric behavior.

  5. Large piezoelectric response of BiFeO3/BaTiO3 polycrystalline films induced by the low-symmetry phase.

    PubMed

    Hou, Y F; Li, W L; Zhang, T D; Wang, W; Cao, W P; Liu, X L; Fei, W D

    2015-05-01

    BaTiO3, BiFeO3 and BiFeO3/BaTiO3 polycrystalline films were prepared by the radio frequency magnetron sputtering on the Pt/Ti/SiO2/Si substrate. The phase structure, converse piezoelectric coefficient and domain structure of BaTiO3, BiFeO3 and BiFeO3/BaTiO3 thin films are characterized by XRD and PFM, respectively. The converse piezoelectric coefficient d33 of BiFeO3/BaTiO3 thin films is 119.5 pm V(-1), which is comparable to that of lead-based piezoelectric films. The large piezoelectric response of BiFeO3/BaTiO3 thin films is ascribed to the low-symmetry T-like phase BiFeO3, because the spontaneous polarization vector of T-like phase (with monoclinic symmetry) BiFeO3 can rotate easily under external field. In addition, the reduced leakage current and major domains with upward polarization are also attributed to the large piezoelectricity. PMID:25866266

  6. Spin-Coating and Characterization of Multiferroic MFe2O4 (M=Co, Ni) / BaTiO3 Bilayers

    NASA Astrophysics Data System (ADS)

    Quandt, Norman; Roth, Robert; Syrowatka, Frank; Steimecke, Matthias; Ebbinghaus, Stefan G.

    2016-01-01

    Bilayer films of MFe2O4 (M=Co, Ni) and BaTiO3 were prepared by spin coating of N,N-dimethylformamide/acetic acid solutions on platinum coated silicon wafers. Five coating steps were applied to get the desired thickness of 150 nm for both the ferrite and perovskite layer. XRD, IR and Raman spectroscopy revealed the formation of phase-pure ferrite spinels and BaTiO3. Smooth surfaces with roughnesses in the order of 3 to 5 nm were found in AFM investigations. Saturation magnetization of 347 emu cm-3 for the CoFe2O4/BaTiO3 and 188 emu cm-3 for the NiFe2O4/BaTiO3 bilayer, respectively were found. For the CoFe2O4/BaTiO3 bilayer a strong magnetic anisotropy was observed with coercivity fields of 5.1 kOe and 3.3 kOe (applied magnetic field perpendicular and parallel to film surface), while for the NiFe2O4/BaTiO3 bilayer this effect is less pronounced. Saturated polarization hysteresis loops prove the presence of ferroelectricity in both systems.

  7. Improved Dielectric Properties and Energy Storage Density of Poly(vinylidene fluoride-co-hexafluoropropylene) Nanocomposite with Hydantoin Epoxy Resin Coated BaTiO3.

    PubMed

    Luo, Hang; Zhang, Dou; Jiang, Chao; Yuan, Xi; Chen, Chao; Zhou, Kechao

    2015-04-22

    Energy storage materials are urgently demanded in modern electric power supply and renewable energy systems. The introduction of inorganic fillers to polymer matrix represents a promising avenue for the development of high energy density storage materials, which combines the high dielectric constant of inorganic fillers with supernal dielectric strength of polymer matrix. However, agglomeration and phase separation of inorganic fillers in the polymer matrix remain the key barriers to promoting the practical applications of the composites for energy storage. Here, we developed a low-cost and environmentally friendly route to modifying BaTiO3 (BT) nanoparticles by a kind of water-soluble hydantoin epoxy resin. The modified BT nanoparticles exhibited homogeneous dispersion in the ferroelectric polymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix and strong interfacial adhesion with the polymer matrix. The dielectric constants of the nanocomposites increased significantly with the increase of the coated BT loading, while the dielectric loss of the nanocomposites was still as low as that of the pure P(VDF-HFP). The energy storage density of the nanocomposites was largely enhanced with the coated BT loading at the same electric field. The nanocomposite with 20 vol % BT exhibited an estimated maximum energy density of 8.13 J cm(-3), which was much higher than that of pure P(VDF-HFP) and other dielectric polymers. The findings of this research could provide a feasible approach to produce high energy density materials for practical application in energy storage. PMID:25822911

  8. Temperature- and Frequency-Dependent Dielectric Properties of Sol-Gel-Derived BaTiO3-NaNbO3 Solid Solutions

    NASA Astrophysics Data System (ADS)

    Kwon, Do-Kyun; Goh, Yumin; Son, Dongsu; Kim, Baek-Hyun; Bae, Hyunjeong; Perini, Steve; Lanagan, Michael

    2016-01-01

    A sol-gel-derived powder synthesis method has been used to prepare BaTiO3-NaNbO3 (BT-NN) solid-solution ceramic samples with various compositions. Fine and homogeneous complex perovskite ceramics were obtained at lower processing temperatures than used in conventional solid-state processing. The ferroelectric and relaxor ferroelectric properties of the sol-gel-synthesized (1 - x)BaTiO3- xNaNbO3 [(1 - x)BT- xNN] ceramics in the wide composition range of 0 < x ≤ 0.7 were extensively studied. Structural and dielectric characterization results revealed that a low level of NN addition ( x = 0.04) to BT is sufficient to cause a continuous relaxor-to-ferroelectric transition, and the relaxor behavior was consistently observed at compositions with high NN content up to x = 0.7. A number of relaxor parameters including the Curie temperature, Burns temperature, freezing temperature, γ, diffuseness parameter ( δ), and activation energy were determined from the temperature and frequency dependency of the real part of the dielectric permittivity for various BT-NN compositions using the Curie-Weiss law and Vögel-Fulcher relationship. The systematic changes of these parameters with respect to composition indicate that a continuous crossover between BT-based relaxor and NN-based relaxor occurs at a composition near x = 0.4.

  9. Creating Only Isotropic Homogeneous Turbulence in Liquid Helium near Absolute Zero

    NASA Astrophysics Data System (ADS)

    Ihas, G. G.; Thompson, K. J.; Labbe, G.; McClintock, P. V. E.

    2012-02-01

    Flow through a grid is a standard method to produce isotropic, homogeneous turbulence for laboratory study. This technique has been used to generate quantum turbulence (QT) above 1 K in superfluid heliumootnotetextS. R. Stalp, L. Skrbek, and R. J. Donnelly, Phys. Rev. Lett. 82, 4831 (1999). where QT seems to mimic classical turbulence. Efforts have been made recentlyootnotetextG. G. Ihas, G. Labbe, S-c. Liu, and K. J. Thompson, J. Low Temp. Phys. 150, 384 (2008). to make similar measurements near absolute zero, where there is an almost total absence of normal fluid and hence classical viscosity. This presents the difficulty that most motive force devices produce heat which overwhelms the phenomena being investigated. The process of designing and implimenting a ``dissipation-free'' motor for pulling a grid through superfluid helium at millikelvin temperatures has resulted in the development of new techniques which have broad application in low temperature research. Some of these, such as Meissner-affect magnetic drives, capacitive and inductive position sensors, and magnetic centering devices will be described. Heating results for devices which can move in a controlled fashion from very low speed up to 10 cm/s will be presented. Acknowledgement: We thank W.F. Vinen for many useful discussions.

  10. Shrinkage Behavior and Diffusion in Ni-based Internal Electrodes with Additional Amount and Particle Size of BaTiO3 Additive

    NASA Astrophysics Data System (ADS)

    Kang, Ji-Hun; Joo, Dongwon; Jung, Yeon-Gil; Paik, Ungyu

    2008-02-01

    The effect of additional amount and particle size of BaTiO3 additive on shrinkage behavior and inter-diffusion in Ni-based internal electrodes has been investigated, in order to reduce the large shrinkage mismatch between the internal electrode and the dielectric layer and to control the thermal and/or residual stresses in multilayer ceramic capacitors (MLCCs). Ni powder of 100-500 nm and two kinds of BaTiO3 powders of 100 and 200 nm were used as matrix and additive, respectively. The Ni and BaTiO3 powders were mixed with volume ratios of 95:5, 90:10, 85:15, respectively, and then cold-isostatic pressed. The shrinkage of starting materials and each composite was measured in a range of 700-1300 °C with 150 °C interval in H2/Ar atmosphere, using ASTM standard method. Diffusion phenomena at interface of Ni/BaTiO3 composites with 85:15 and 90:10 volume ratios were investigated using SEM, EDX, and TEM. The particle size affects the shrinkage behavior in relatively low temperatures below 1000 °C, showing a turning point at that temperature. The final shrinkage of composites is matched with that of bulk BaTiO3 of smaller particle size, independent of additional amount of BaTiO3 additive. A reaction layer of about 1000 nm wide is observed at the interface between the Ni and BaTiO3 powders in the composite of 85:15 volume ratio. The quantitative amount of elemental Ni diffused into the BaTiO3 is about 9.7 mass% in the composite of 90:10 volume ratio, without another phase seen in the Ni.

  11. Effect of BaTiO3 impurity on the NaNO2 structure in (0.9)NaNO2 + (0.1)BaTiO3 composite

    NASA Astrophysics Data System (ADS)

    Naberezhnov, A. A.; Alekseeva, O. A.; Stukova, E. V.; Borisov, S. A.; Simkin, V. G.

    2015-12-01

    The temperature evolution of the crystalline structure of the composite based on the ferroelectric mixture 0.9NaNO2 + 0.1BaTiO3 is analyzed using the neutron diffraction method. It is shown that the values of the order parameter of NaNO2 in the composite in the temperature range 360-430 K is smaller as compared to the bulk substance, which may indicate the coexistence of the ferroelectric and incommensurate phases of sodium nitrite in this interval.

  12. Modified structural and frequency dependent impedance formalism of nanoscale BaTiO3 due to Tb inclusion

    NASA Astrophysics Data System (ADS)

    Borah, Manjit; Mohanta, Dambarudhar

    2016-05-01

    We report the effect of Tb-doping on the structural and high frequency impedance response of the nanoscale BaTiO3 (BT) systems. While exhibiting a mixed phase crystal structure, the nano-BT systems are found to evolve with edges, and facets. The interplanar spacing of crystal lattice fringes is ~0.25 nm. The Cole-Cole plots, in the impedance formalism, have demonstrated semicircles which are the characteristic feature of grain boundary resistance of several MΩ. A lowering of ac conductivity with doping was believed to be due to the manifestation of oxygen vacancies and vacancy ordering.

  13. Space charge limited transient currents and oxygen vacancy mobility in amorphous BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    El Kamel, F.; Gonon, P.; Ortega, L.; Jomni, F.; Yangui, B.

    2006-05-01

    Time-dependent transient currents were studied at elevated temperatures (200-220 °C) in amorphous barium titanate thin film capacitors. Current transients display a peak whose time position varies with applied voltage and temperature. The response is analyzed through space charge limited current transient theories. Extracted drift mobilities are in the 10-11-10-12 cm2 V-1 s-1 range and show an activation energy of 1 eV. The phenomena are associated with oxygen vacancies migration in BaTiO3.

  14. Effect of oxygen vacancy on the dielectric relaxation of BaTiO3 thin films in a quenched state

    NASA Astrophysics Data System (ADS)

    Yao, Sheng-Hong; Yuan, Jin-Kai; Gonon, Patrice; Bai, Jinbo; Pairis, Sébastien; Sylvestre, Alain

    2012-05-01

    A thermal treatment below the crystallization temperature followed by rapid cooling down was adopted onto as-deposited BaTiO3 (BTO) amorphous films to freeze the microstructure activated at annealed temperature. A large increase of dielectric constant from 19 to 329 was observed at 0.1 Hz for the BTO film annealed at 600 °C for 60 min. Subsequently, three separated dielectric relaxations were exploited as a function of the frequency and temperature. Such dielectric responses were analyzed in terms of the activation energy. The evolution of oxygen vacancy with temperature can be invoked as being responsible for the observed dielectric relaxations.

  15. High-density capacitors based on amorphous BaTiO3 layers grown under hydrogen containing atmosphere

    NASA Astrophysics Data System (ADS)

    Gonon, P.; El Kamel, F.

    2007-06-01

    Addition of hydrogen (H2) during the sputter deposition of BaTiO3 amorphous thin films drastically modifies their dielectric properties. Films grown under hydrogen containing atmospheres display large capacitances (several μF /cm2 for 1μm thick films), that are hundred times higher than capacitances measured for films grown without hydrogen. This is explained by the formation of a double-layer capacitor which arises from mobile protons (protonic conduction with an activation energy around 0.3eV). These films could find applications for the elaboration of integrated supercapacitors.

  16. Origins of large enhancement in electromechanical coupling for nonpolar directions in ferroelectric BaTiO3

    NASA Astrophysics Data System (ADS)

    Pramanick, A.; Diallo, S. O.; Delaire, O.; Calder, S.; Christianson, A. D.; Wang, X.-L.; Fernandez-Baca, J. A.

    2013-11-01

    The origins of enhanced piezoelectric coupling along nonpolar crystallographic directions in ferroelectric BaTiO3 are investigated using in situ neutron spectroscopy. It is observed that an electric field applied away from the equilibrium polarization direction causes a stiffening of the transverse acoustic (TA) phonon branch and consequently increases interaction between the TA and the transverse optic soft mode for a range of wave vectors extending from the Brillouin zone center. This provides a direct lattice dynamics mechanism for enhanced electromechanical coupling, and could act as a guide for designing improved piezoelectric materials.

  17. Band gap narrowing in BaTiO3 nanoparticles facilitated by multiple mechanisms

    NASA Astrophysics Data System (ADS)

    Ramakanth, S.; James Raju, K. C.

    2014-05-01

    In the present work, BaTiO3 nanoparticles of four different size ranges were prepared by sol-gel method. The optical band gap of these particles at some size ranges has come down to 2.53 eV from 3.2 eV, resulting in substantial increase in optical absorption by these ferroelectric nanoparticles making them potential candidates for light energy harvesting. XRD results show the presence of higher compressive strain in 23 nm and 54 nm size particles, they exhibit a higher band gap narrowing, whereas tensile strain is observed in 31 nm and 34 nm particles, and they do not show the marginal band gap narrowing. The 23 nm and 54 nm particles also show a coupling of free carriers to phonons by increasing the intensity of LO phonon mode at 715 cm-1. The higher surface charge density is expected in case of enhanced surface optical Raman modes (638 cm-1) contained in 31 and 34 nm size particles. In addition to this, the red shift in an LO mode Raman spectral line at 305 cm-1 with decrease in particle size depicts the presence of phonon confinement in it. The enhanced optical absorption in 23 nm and 54 nm size particles with a narrowed band gap of 3 eV and 2.53 eV is due to exchange correlation interactions between the carriers present in these particles. In 31 nm and 34 nm range particles, the absorption got bleached exhibiting increased band gaps of 3.08 eV and 3.2 eV, respectively. It is due to filling up of conduction band resulting from weakening of exchange correlation interactions between the charge carriers. Hence, it is concluded that the band gap narrowing in the nanoparticles of average size 23 nm/54 nm is a consequence of multiple effects like strain, electron-phonon interaction, and exchange correlation interactions between the carriers which is subdued in some other size ranges like 31 nm/34 nm.

  18. Strain-induced magnetic domain wall control by voltage in hybrid piezoelectric BaTiO3 ferrimagnetic TbFe structures

    PubMed Central

    Rousseau, Olivier; Weil, Raphael; Rohart, Stanislas; Mougin, Alexandra

    2016-01-01

    This paper reports on the voltage dependence of the magnetization reversal of a thin amorphous ferromagnetic TbFe film grown on a ferroelectric and piezoelectric BaTiO3 single crystal. Magneto-optical measurements, at macroscopic scale or in a microscope, demonstrate how the ferroelectric BaTiO3 polarisation history influences the properties of the perpendicularly magnetized TbFe film. Unpolarised and twinned regions are obtained when the sample is zero voltage cooled whereas flat and saturated regions are obtained when the sample is voltage cooled through the ferroelectric ordering temperature of the BaTiO3 crystal, as supported by atomic force microscopy experiments. The two steps involved in the TbFe magnetization reversal, namely nucleation and propagation of magnetic domain walls, depend on the polarisation history. Nucleation is associated to coupling through strains with the piezoelectric BaTiO3 crystal and propagation to pinning with the ferroelastic surface patterns visible in the BaTiO3 topography. PMID:26987937

  19. 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.

  20. Strain-induced magnetic domain wall control by voltage in hybrid piezoelectric BaTiO3 ferrimagnetic TbFe structures.

    PubMed

    Rousseau, Olivier; Weil, Raphael; Rohart, Stanislas; Mougin, Alexandra

    2016-01-01

    This paper reports on the voltage dependence of the magnetization reversal of a thin amorphous ferromagnetic TbFe film grown on a ferroelectric and piezoelectric BaTiO3 single crystal. Magneto-optical measurements, at macroscopic scale or in a microscope, demonstrate how the ferroelectric BaTiO3 polarisation history influences the properties of the perpendicularly magnetized TbFe film. Unpolarised and twinned regions are obtained when the sample is zero voltage cooled whereas flat and saturated regions are obtained when the sample is voltage cooled through the ferroelectric ordering temperature of the BaTiO3 crystal, as supported by atomic force microscopy experiments. The two steps involved in the TbFe magnetization reversal, namely nucleation and propagation of magnetic domain walls, depend on the polarisation history. Nucleation is associated to coupling through strains with the piezoelectric BaTiO3 crystal and propagation to pinning with the ferroelastic surface patterns visible in the BaTiO3 topography. PMID:26987937

  1. Strain-induced magnetic domain wall control by voltage in hybrid piezoelectric BaTiO3 ferrimagnetic TbFe structures

    NASA Astrophysics Data System (ADS)

    Rousseau, Olivier; Weil, Raphael; Rohart, Stanislas; Mougin, Alexandra

    2016-03-01

    This paper reports on the voltage dependence of the magnetization reversal of a thin amorphous ferromagnetic TbFe film grown on a ferroelectric and piezoelectric BaTiO3 single crystal. Magneto-optical measurements, at macroscopic scale or in a microscope, demonstrate how the ferroelectric BaTiO3 polarisation history influences the properties of the perpendicularly magnetized TbFe film. Unpolarised and twinned regions are obtained when the sample is zero voltage cooled whereas flat and saturated regions are obtained when the sample is voltage cooled through the ferroelectric ordering temperature of the BaTiO3 crystal, as supported by atomic force microscopy experiments. The two steps involved in the TbFe magnetization reversal, namely nucleation and propagation of magnetic domain walls, depend on the polarisation history. Nucleation is associated to coupling through strains with the piezoelectric BaTiO3 crystal and propagation to pinning with the ferroelastic surface patterns visible in the BaTiO3 topography.

  2. Enhanced hydrogen storage properties of the 2LiBH4-MgH2 composite with BaTiO3 as an additive.

    PubMed

    Wang, Jiasheng; Han, Shumin; Wang, Zhibin; Ke, Dandan; Liu, Jingjing; Ma, Mingzhen

    2016-04-19

    The 2LiBH4-MgH2 + 20 wt% BaTiO3 composite was prepared by ball-milling LiBH4, MgH2 and BaTiO3, and the effect of BaTiO3 on the hydrogen storage properties of the composite was investigated. TG-DSC results show that the onset dehydrogenation temperature of the composite is 299 °C, which is 124 °C lower than that of 2LiBH4-MgH2, and the dehydrogenation amount of the composite increases from 6.86 wt% to 7.48 wt% at 500 °C. Kinetic tests show that the dehydrogenation amount of 2LiBH4-MgH2 + 20 wt% BaTiO3 reaches 1.5 wt% within 400 seconds, almost 10 times that of 2LiBH4-MgH2. BaTiO3 reacts with LiBH4 during the dehydrogenation of the composite and generates BaB6 and TiO2. BaB6 is beneficial to lower the stability of LiBH4, while TiO2 has a catalytic effect in improving the hydrogenation/dehydrogenation kinetics of the reaction between Mg and LiBH4. PMID:26990634

  3. Controlled Confinement of Half-metallic 2D Electron Gas in BaTiO3/Ba2FeReO6/BaTiO3 Heterostructures: A First-principles Study

    NASA Astrophysics Data System (ADS)

    Saha-Dasgupta, Tanusri; Baidya, Santu; Waghmare, Umesh; Paramekanti, Arun

    Using density functional theory calculations, we establish that the half-metallicity of bulk Ba2FeReO6 survives down i to 1 nm thickness in BaTiO3/Ba2FeReO6/BaTiO3 heterostructures grown along the (001) and (111) directions. The confinement of the two-dimensional (2D) electron gas in this quantum well structure arises from the suppressed hybridization between Re/Fe d states and unoccupied Ti d states, and it is further strengthened by polar fields for the (111) direction. This mechanism, distinct from the polar catastrophe, leads to an order of magnitude stronger confinement of the 2D electron gas than that at the LaAlO3/SrTiO3 interface. We further show low-energy bands of (111) heterostructure display nontrivial topological character. Our work opens up the possibility of realizing ultra-thin spintronic devices. Journal Ref: Phys. Rev. B 92, 161106(R) (2015) S.B. and T.S.D thank Department of Science and Technology, India for the support through Thematic Unit of Excellence. AP was supported by NSERC (Canada).

  4. AES study on the chemical composition of ferroelectric BaTiO3 thin films RF sputter-deposited on silicon

    NASA Technical Reports Server (NTRS)

    Dharmadhikari, V. S.; Grannemann, W. W.

    1983-01-01

    AES depth profiling data are presented for thin films of BaTiO3 deposited on silicon by RF sputtering. By profiling the sputtered BaTiO3/silicon structures, it was possible to study the chemical composition and the interface characteristics of thin films deposited on silicon at different substrate temperatures. All the films showed that external surface layers were present, up to a few tens of angstroms thick, the chemical composition of which differed from that of the main layer. The main layer had stable composition, whereas the intermediate film-substrate interface consisted of reduced TiO(2-x) oxides. The thickness of this intermediate layer was a function of substrate temperature. All the films showed an excess of barium at the interface. These results are important in the context of ferroelectric phenomena observed in BaTiO3 thin films.

  5. Surface reaction characteristics at low temperature synthesis BaTiO 3 particles by barium hydroxide aqueous solution and titanium tetraisopropoxide

    NASA Astrophysics Data System (ADS)

    Zeng, Min

    2011-05-01

    Well-crystallized cubic phase BaTiO 3 particles were prepared by heating the mixture of barium hydroxide aqueous solution and titania derived from the hydrolysis of titanium isopropoxide (TTIP) at 328 K, 348 K or 368 K for 24 h. The morphology and size of obtained particles depended on the reaction temperature and the Ba(OH) 2/TTIP molar ratio. By the direct hydrolytic reaction of titanium tetraisopropoxide, the high surface area titania (TiO 2) was obtained. The surface adsorption characteristics of the titania particles had been studied with different electric charges OH - ions or H + ions. The formation mechanism and kinetics of BaTiO 3 were examined by measuring the concentration of [Ba 2+] ions in the solution during the heating process. The experimental results showed that the heterogeneous nucleation of BaTiO 3 occurred on the titania surface, according to the Avrami's equation.

  6. Structural evolution across the insulator-metal transition in oxygen-deficient BaTiO3-δ studied using neutron total scattering and Rietveld analysis

    DOE PAGESBeta

    Jeong, I.-K.; Lee, Seunghun; Jeong, Se-Young; Won, C. J.; Hur, N.; Llobet, A.

    2011-08-29

    Oxygen-deficient BaTiO3-δ exhibits an insulator-metal transition with increasing δ. We performed neutron total scattering measurements to study structural evolution across an insulator-metal transition in BaTiO3-δ. Despite its significant impact on resistivity, slight oxygen reduction (δ=0.09) caused only a small disturbance on the local doublet splitting of Ti-O bond. This finding implies that local polarization is well preserved under marginal electric conduction. In the highly oxygen-deficient metallic state (δ=0.25), however, doublet splitting of the Ti-O bond became smeared. The smearing of the local Ti-O doublet is complemented with long-range structural analysis and demonstrates that the metallic conduction in the highly oxygen-reducedmore » BaTiO3-δ is due to the appearance of nonferroelectric cubic lattice.« less

  7. Electrical and reliability characteristics of Mn-doped nano BaTiO3-based ceramics for ultrathin multilayer ceramic capacitor application

    NASA Astrophysics Data System (ADS)

    Gong, Huiling; Wang, Xiaohui; Zhang, Shaopeng; Tian, Zhibin; Li, Longtu

    2012-12-01

    Nano BaTiO3-based dielectric ceramics were prepared by chemical coating approach, which are promising for ultrathin multilayer ceramic capacitor (MLCC) applications. The doping effects of Mn element on the microstructures and dielectric properties of the ceramics were investigated. The degradation test and impedance spectroscopy were employed to study the resistance degradation and the conduction mechanism of Mn-doped nano-BaTiO3 ceramic samples. It has been found that the reliability characteristics greatly depended on the Mn-doped content. Moreover, the BaTiO3 ceramic with grain size in nanoscale is more sensitive to the Mn-doped content than that in sub-micron scale. The addition of 0.3 mol. % Mn is beneficial for improving the reliability of the nano BaTiO3-based ceramics, which is an important parameter for MLCC applications. However, further increasing the addition amount will deteriorate the performance of the ceramic samples.

  8. Resistive switching properties of epitaxial BaTiO(3-δ) thin films tuned by after-growth oxygen cooling pressure.

    PubMed

    Heo, Yooun; Kan, Daisuke; Shimakawa, Yuichi; Seidel, Jan

    2016-01-01

    BaTiO3-δ, i.e. oxygen-deficient barium titanate (BaTiO3), thin films grown on GdScO3(110) substrates with SrRuO3 conductive electrodes by pulsed laser deposition are studied by X-ray diffraction and conductive AFM to characterize their structure and nanoscale electronic properties. Bias- and time-dependent resistive switching measurements reveal a strong dependence on the oxygen vacancy concentration, which can be tuned by after-growth oxygen cooling conditions of thin films. The results indicate that the resistive switching properties of BaTiO3-δ can be enhanced by controlling oxygen deficiency and provide new insight for potential non-volatile resistive random-access memory (RRAM) applications. PMID:26603263

  9. Controlled extrinsic magnetoelectric coupling in BaTiO3/Ni nanocomposites: Effect of compaction pressure on interfacial anisotropy

    NASA Astrophysics Data System (ADS)

    Brosseau, C.; Castel, V.; Potel, M.

    2010-07-01

    The dynamical control of the dielectric response in magnetoelectric (ME) nanocomposites (NCs) renders an entire additional degree of freedom to the functionality of miniaturized magnetoelectronics and spintronics devices. In composite materials, the ME effect is realized by using the concept of product properties. Through the investigation of the microwave properties of a series of BaTiO3/Ni NCs fabricated by compaction of nanopowders, we present experimental evidence that the compaction (uniaxial) pressure in the range 33-230 MPa affects significantly the ME features. The Ni loading was varied from zero (BaTiO3 only) to 63 vol %. Our findings revealed that the ME coupling coefficient exhibits a large enhancement for specific values of the Ni volume fraction and compaction pressure. The coupling effects in the NCs were studied by looking at the relationships among the crystallite orientation and the magnetic properties. The magnetization curves for different directions of the applied magnetic field cannot be superimposed. We suggest that the average magnetization measurements on these NCs under compressive stress are dominated by strain anisotropy rather than magnetocrystalline anisotropy. Overall, these observations are considered to be evidence of stress-induced microstructural changes under pressure which strongly affect the elastic interaction between the magnetostrictive and piezoelectric phases in these NCs. These results have a potential technological impact for designing precise tunable ME NCs for microwave devices such as tunable phase shifters, resonators, and delay lines.

  10. Enhanced piezoelectricity in plastically deformed nearly amorphous Bi12TiO20-BaTiO3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Yu, Dan; Zhao, Minglei; Wang, Chunlei; Wang, Lihai; Su, Wenbin; Gai, Zhigang; Wang, Chunming; Li, Jichao; Zhang, Jialiang

    2016-07-01

    Bulk Bi12TiO20-BaTiO3 (BTO-BT) nanocomposites are fabricated through the high-temperature interfacial reaction between nanometer-sized BaTiO3 particles and melting Bi12TiO20. Although the obtained BTO-BT nanocomposites are nearly amorphous and display very weak ferroelectricity, they exhibit relatively strong piezoelectricity without undergoing the electrical poling process. The volume fraction of crystalline Bi12TiO20 is reduced to less than 10%, and the piezoelectric constant d33 is enhanced to 13 pC/N. Only the presence of the macroscopic polar amorphous phases can explain this unusual thermal stable piezoelectricity. Combining the results from X-ray diffraction, Raman spectroscopy, and thermal annealing, it can be confirmed that the formation of macroscopic polar amorphous phases is closely related to the inhomogeneous plastic deformation of the amorphous Bi12TiO20 during the sintering process. These results highlight the key role of plastically deformed amorphous Bi12TiO20 in the Bi12TiO20-based polar composites, and the temperature gradient driven coupling between the plastic strain gradient and polarization in amorphous phases is the main poling mechanism for this special type of bulk polar material.

  11. Ultrafast magneto-optical spectroscopy of BiFeO3-BaTiO3 based structures

    NASA Astrophysics Data System (ADS)

    Magill, Brenden A.; Bishop, Michael; McGill, Stephen A.; Zhou, Yuon; Chopra, Anuj; Maurya, Deepam; Song, Hyun-Cheol; Priya, Shashank; Khodaparast, Giti A.

    2015-09-01

    Ultrafast optical spectroscopy can provide insight into fundamental microscopic interactions, dynamics and the coupling of several degrees of freedom. Pump/ probe studies can reveal the answer to questions like "What are the achievable switching speeds in multiferroics?", "What is the influence of the crystallographic orientation and domain states on the available switching states?", and "What is the effect of the hetrostructure on promoting the coupling between the varying field excitations?". In this presentation, we report on two color (400/800nm) ultrafast pump-probe differential reflectance spectroscopy of BiFeO3-BaTiO3 structures to probe the coupling between optical and acoustic phonons to spin waves. The data presented here is a combination of different transient reflectivity measurements to probe both the carrier and spin dynamics. The (001)-BiFeO3-BaTiO3 thin films were prepared using pulsed laser deposition on vicinal SrTiO3 substrates using La0.70 Sr0.30MnO3 bottom electrodes. Crystal orientation and topography were analyzed by x-ray diffraction and atomic force microscopy. . Our results are important to developing devices on the basis of this material system. This work was supported by the AFOSR through grant FA9550-14-1-0376,NSF-Career Award DMR-0846834, and the Virginia Tech Institute for Critical Technology and Applied Science.

  12. Facile synthesis of submicron BaTiO 3 crystallites by a liquid-solid reaction method

    NASA Astrophysics Data System (ADS)

    Zhang, Yong Cai; Wang, Gen Lin; Li, Kun Wei; Zhang, Ming; Hu, Xiao Ya; Wang, Hao

    2006-05-01

    Uniform, submicron BaTiO 3 crystallites in tetragonal structure were synthesized by a novel low-temperature liquid-solid reaction method mainly via two simple steps: firstly, BaO 2·H 2O 2 submicron particles of about 130-450 nm were precipitated from the reaction of BaCl 2 and H 2O 2 in a slightly alkaline (pH 8) aqueous solution under the ambient condition; secondly, tetragonal phase BaTiO 3 submicrocrystals with the size in the range of 180 to 400 nm could be produced by subjecting the as-prepared BaO 2·H 2O 2 and commercial TiO 2 submicron particles to thermal treatment in air at 700 °C for 10 h. The as-obtained products were characterized by X-ray powder diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma-atomic emission spectroscopy, and scanning electron microscopy.

  13. Structural and morphological transformations of BaTiO3 nanocrystals in thin layers of borate oxide glasses

    NASA Astrophysics Data System (ADS)

    Kedrov, V. V.; Shmyt'ko, I. M.

    2015-02-01

    The influence of thin layers (2-15 μm) of some oxide glass melts on BaTiO3 nanocrystallites has been investigated using X-ray diffractometry and scanning electron microscopy. It has been shown that lead borate and sodium borate glass melts bring about the dissolution of BaTiO3 nanocrystallites and the subsequent crystallization in glasses of lead titanate PbTiO3 and sodium titanate Na2TiO3, respectively. It has been found that thin layers of melts of these glasses have a strong orientation effect on crystallites of the PbTiO3 and Na2TiO3 compounds newly synthesized from barium titanate. The orientation effect exerted by these glass layers results in the formation of a pronounced texture of the perovskite crystallites with the texture axes oriented along the [100] and [001] directions parallel to the surface normal of the substrate for lead titanate and the orientation of the planes of the film surface for the sodium titanium oxide.

  14. cc domains with intrinsic screening and absence of closure domains in atomically ordered BaTiO3 in UHV

    NASA Astrophysics Data System (ADS)

    Watanabe, Y.; Kaku, S.; Nakamura, K.

    2010-03-01

    cc domains have been observed in ordinary environments, where extraneous screening hampers rigorous comparison with theories. Indeed, recent theories predict closure domains in the absence of extraneous screening. Therefore, we performed simultaneous topographic, electrostatic and piezoelectric imaging of atomically clean, free surface of BaTiO3 single crystal by AFM operated in ultra high vacuum (UHV).footnotetextS. Kaku et al., J.Kor.Phys.Soc.55,799(2009) BaTiO3 surface retains stoichiometry in UHV because of the absence of volatile elements (Pb, Bi, Li) and low TC The surface cleanness is confirmed by the detection of chemical bonding. Three imaging methods verified the assignment of ac and cc domains, which is consistent with conventional theory and experiments. These ac and cc domains change reversibly by weak electric field of 2kV/cm at RT. In addition, the temperature dependence of the domains agrees with convention theories. These observations prove the absence of dominating control of defects and impurities on the observed domains. The sole deviation is the reduction of the potential difference to 1/30 of the conventional theories. The described intrinsic nature of the domains indicates an intrinsic screening in cc domains, which is consistent with the intrinsic surface carrier layer on ferroelectrics.footnotetextWatanabe et al. PRL86332(2001), PRB57,789(1998)

  15. Strain-induced insulator–metal transition in ferroelectric BaTiO3 (001) surface: First-principles study

    NASA Astrophysics Data System (ADS)

    Lin, Yang; Chang-An, Wang; Cong, Liu; Ming-Hui, Qin; Xu-Bing, Lu; Xing-Sen, Gao; Min, Zeng; Jun-Ming, Liu

    2016-07-01

    The electronic properties of TiO2-terminated BaTiO3 (001) surface subjected to biaxial strain have been studied using first-principles calculations based on density functional theory. The Ti ions are always inward shifted either at compressive or tension strains, while the inward shift of the Ba ions occurs only for high compressive strain, implying an enhanced electric dipole moment in the case of high compressive strain. In particular, an insulator–metal transition is predicted at a compressive biaxial strain of 0.0475. These changes present a very interesting possibility for engineering the electronic properties of ferroelectric BaTiO3 (001) surface. Project supported by the National Natural Science Foundation of China (Grant Nos. 1574091, 51272078, and 51431006), the Natural Science Foundation of Guangdong Province of China (Grant No. 2015A030313375), the Science and Technology Planning Project of Guangdong Province of China (Grant No. 2015B090927006), and the Program for International Innovation Cooperation Platform of Guangzhou City, China (Grant No. 2014J4500016).

  16. In situ observation of reversible domain switching in aged Mn-doped BaTiO3 single crystals

    NASA Astrophysics Data System (ADS)

    Zhang, L. X.; Ren, X.

    2005-05-01

    Very recently, a giant recoverable electrostrain effect has been found in aged Fe-doped BaTiO3 single crystals; this effect is based on a defect-mediated reversible domain-switching mechanism. However, the reversible domain-switching process itself is yet to be directly verified. In the present study, we performed in situ domain observation during electric field cycling for an aged Mn-doped BaTiO3 single crystal and simultaneously measured its polarization (P) -field (E) hysteresis loop. In addition, the electrostrain behavior of the sample was also characterized. Such experimentation made it possible to correlate the mesoscopic domain-switching behavior with the macroscopic properties. It was found that the aged sample shows a remarkable reversible domain switching during electric field cycling; it corresponds very well to a “double” hysteresis loop and a giant recoverable electrostrain effect (with a maximum strain of 0.4%). This provides direct mesoscopic evidence for our reversible domain-switching mechanism. By contrast, an unaged sample shows irreversible domain-switching behavior during electric field cycling; it corresponds to a normal hysteresis loop and a butterfly-type irrecoverable electrostrain behavior. This indicates that the reversible domain switching in the aged sample is related to point-defect migration during aging. We further found that the large recoverable strain is available over a wide frequency range. This is important for the application of this electrostrain effect.

  17. Yellow-orange upconversion emission in Eu3+-Yb3+ codoped BaTiO3 phosphor

    NASA Astrophysics Data System (ADS)

    Kumari, Astha; Rai, Vineet Kumar; Kumar, Kaushal

    2014-06-01

    The Eu3+-Yb3+ codoped BaTiO3 phosphor is prepared via co-precipitation method and its upconversion emission is studied by 980 nm diode laser excitation. The X-ray diffraction pattern of the prepared sample showed the tetragonal BaTiO3 phase. The co-doped phosphor showed sharp upconversion emission bands peaking at ∼592, ∼614, ∼ 654, ∼704 and ∼796 nm due to the 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, 5D0 → 7F4 and 5D0 → 7F6 transitions, respectively of Eu3+ ions. The sharp band at 489 nm is assigned to the 2F5/2 → 2F7/2 transition of Yb3+ ion while the broad band around 505 nm is assigned to the defect states present in the sample. Based on the available experimental data, the process involved in the UC emissions has been explored and elaborated.

  18. Relation between electrical properties of aerosol-deposited BaTiO3 thin films and their mechanical hardness measured by nano-indentation

    PubMed Central

    2012-01-01

    To achieve a high capacitance density for embedded decoupling capacitor applications, the aerosol deposition (AD) process was applied as a thin film deposition process. BaTiO3 films were fabricated on Cu substrates by the AD process at room temperature, and the film thickness was reduced to confirm the limit of the critical minimum thickness for dielectric properties. As a result, the BaTiO3 thin films that were less than 1-μm thick showed unstable electric properties owing to their high leakage currents. Therefore, to overcome this problem, the causes of the high leakage currents were investigated. In this study, it was confirmed that by comparing BaTiO3 thin films on Cu substrates with those on stainless steels (SUS) substrates, macroscopic defects and rough interfaces between films and substrates influence the leakage currents. Moreover, based on the deposition mechanism of the AD process, it was considered that the BaTiO3 thin films on Cu substrates with thicknesses of less than 1 μm are formed with chinks and weak particle-to-particle bonding, giving rise to leakage currents. In order to confirm the relation between the above-mentioned surface morphologies and the dielectric behavior, the hardness of BaTiO3 films on Cu and SUS substrates was investigated by nano-indentation. Consequently, we proposed that the chinks and weak particle-to-particle bonding in the BaTiO3 thin films with thicknesses of less than 0.5 μm on Cu substrates could be the main cause of the high leakage currents. PMID:22616759

  19. Vortices of polarization in BaTiO3 core-shell nanoceramics: Calculations based on ab initio derived Hamiltonian versus Landau theory

    NASA Astrophysics Data System (ADS)

    Anoufa, M.; Kiat, J. M.; Kornev, I.; Bogicevic, C.

    2013-10-01

    In this paper, we want to emphasize the fact that many experimental properties of ceramics can be explained by the existence of a core-shell structure of the grains, particularly at small sizes. In this framework, we have studied BaTiO3 (BT) ceramics constituted of core-shell nanoparticles, nanowires, or nanoplanes by using ab initio derived effective Hamiltonian calculations whose application range is for large values of shell thickness and low values of shell permittivity. Many differences and new features compared to the situation of nanodots are induced by the core-shell structure. For instance, phase sequences are different; there is also a coexistence of vortices found by Naumov, Bellaiche, and Fu [I. I. Naumov, L. Bellaiche, and H. Fu, Nature (London)10.1038/nature03107 432, 737 (2004)] in the case of isolated dots with a homogeneous polarization, a transition from cubic paraelectric phase towards nonpolar rhombohedral phase, anomalies in dielectric permittivity associated with the onset of toroidal moments, etc. Afterwards, we compare these results with those obtained by the Landau theory of core-shell ceramics we have recently published. However, the ab initio calculations fail to capture the physics at small shell thickness and/or high shell permittivity, whereas the Landau theory fails to predict the peculiar properties of the phases in which vortices exist. Therefore, in a tentative way to build a global theory, we have constructed a Landau potential using both the polarization and the toroidal moment as competing order parameters, which allows us to propose a phase diagram, whatever the thickness and permittivity of the shell are.

  20. Effects of A-site nonstoichiometry on oxide ion conduction in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Prasertpalichat, Sasiporn; Schmidt, Whitney; Cann, David P.

    2016-06-01

    Lead free 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping (through Bi-excess) and acceptor-doping (through Na-excess). Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry. A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions. Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms. Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by ˜3-4 orders of magnitude and an associated activation energy of 1.57eV which was close to half of the optical bandgap. In contrast, an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions. In addition, the Na-excess compositions exhibited low resistivities (ρ˜103Ω-cm) with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in (Bi0.5Na0.5)TiO3. Long term annealing studies were also conducted at 800∘C to identify changes in crystal structure and electrical properties. The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 ceramics are very sensitive to Bi/Na stoichiometry.

  1. Mode sequence, frequency change of nonsoft phonons, and LO-TO splitting in strained tetragonal BaTiO3

    NASA Astrophysics Data System (ADS)

    Raeliarijaona, Aldo; Fu, Huaxiang

    2015-09-01

    Ultraviolet Raman spectroscopy revealed the existence of an unusual large-frequency shift occurring to a nonsoft mode of E (TO4 ) when BaTiO3 is strained to a SrTiO3 substrate [D. Tenne et al., Science 313, 1614 (2006), 10.1126/science.1130306]. It raised two interesting questions: (i) whether there are other nonsoft modes that possess similar or even larger strain-induced frequency shifts and (ii) how the mode sequence is altered by these shifts in frequency. Note that mode sequence is also pivotal in correctly indexing and assigning the spectroscopy peaks observed in all Raman experiments. By mapping out the evolutions of individual phonon modes as a function of strain using first-principles density functional perturbation calculations, we determine the mode sequence and strain-induced phonon frequency shifts in prototypical BaTiO3. Our study reveals that the mode sequence is drastically different when BaTiO3 is strained to SrTiO3 compared to that in the unstrained structure, caused by multiple mode crossings. Furthermore, we predict that three other nonsoft modes, A1(TO2), E (LO4 ), and A1(TO3), display even larger strain-induced frequency shifts than E (TO4 ). The strain responses of individual modes are found to be highly mode specific, and a mechanism that regulates the magnitude of the frequency shift is provided. As another key outcome of this study, we tackle a long-standing problem of LO-TO splitting in ferroelectrics. A rigorous definition for the LO-TO splitting is formulated, which allows this critical quantity to be calculated quantitatively. The definition immediately reveals a new finding; that is, a large LO-TO splitting not only exists for E (LO4 ), which is previously known and originates from a soft mode, it also occurs for a nonsoft A1(LO3) mode. The LO-TO splitting is shown to decrease drastically with compressive strain, and this decrease cannot be explained by the Born effective charges and high-frequency dielectric constants.

  2. Self-scanning of a dye laser due to feedback from a BaTiO(3) phase-conjugate reflector.

    PubMed

    Whitten, W B; Ramsey, J M

    1984-02-01

    Feedback from a self-pumped BaTiO(3) phase-conjugate reflector into an untuned cw dye laser produces substantial line narrowing (4-6 GHz) and generates a recurrent wavelength sweep from the rhodamine 6G peak at 618 nm to as far as 644 nm. PMID:19718230

  3. Polarisation dependence of Schottky barrier heights at ferroelectric BaTiO3 / RuO2 interfaces: influence of substrate orientation and quality

    NASA Astrophysics Data System (ADS)

    Hubmann, Andreas H.; Li, Shunyi; Zhukov, Sergey; von Seggern, Heinz; Klein, Andreas

    2016-07-01

    In situ x-ray photoelectron spectroscopy was employed to examine the change in Schottky barrier height Δ {Φ\\text{B}} at BaTiO3/RuO2 interfaces upon polarisation reversal for [1 0 0], [1 1 0] and [1 1 1] oriented BaTiO3 single crystals. Compared to previous measurements on BaTiO3/RuO2 interfaces (Chen and Klein 2012 Phys. Rev. B 86 094105), the crystals exhibit a significantly reduced dependence of barrier height on polarisation direction. This is connected to a much higher polarisation of the present cystals, which is comparable to the accepted bulk polarisation of BaTiO3 of 26~μ \\text{C}~\\text{c}{{\\text{m}}-2} and which exhibit the expected dependence on crystal orientation. This indicates a much higher crystal quality in the present experiments, which is also confirmed by a Kolmogorov–Avrami–Ishibashi like polarisation switching dynamics. It is observed that Δ {Φ\\text{B}} is reduced for the [1 1 0] and [1 1 1] orientation and scales with polarisation as long as crystals from the same batch are used. The fact, that a poor polarisation hysteresis behaviour relates to a high polarisation dependence of Schottky barrier height, indicates that the electrode’s ability to screen ferroelectric polarisation charges depends sensitively on crystal and/or interface quality.

  4. Structural and dielectric properties of laser ablated BaTiO3 films deposited over electrophoretically dispersed CoFe2O4 grains

    NASA Astrophysics Data System (ADS)

    Barbosa, J. G.; Gomes, I. T.; Pereira, M. R.; Moura, C.; Mendes, J. A.; Almeida, B. G.

    2014-10-01

    Thin film nanocomposites with mixed connectivity, composed by CoFe2O4 grains, deposited by electrophoresis on Si|Pt substrates, and subsequently covered by a laser ablation deposited BaTiO3 layer were prepared with different cobalt ferrite concentrations. Their structure presented a combination of BaTiO3, with its tetragonal and the orthorhombic phases coexisting at room temperature, and CoFe2O4 with the cubic spinel structure. The cobalt ferrite nanograins were under in-plane tensile stress, while the BaTiO3 phase was under in-plane compressive stress. The dielectric measurements showed that as the barium titanate grain size decreased, its ferroelectric Curie temperature shifted to lower temperatures relative to the bulk. This grain size dependent TC shift was associated and modeled by a core-shell structure of BaTiO3 grains in the films, with a tetragonal core and cubic shell. Additionally, a diffuse tetragonal-orthorhombic phase transition was observed and, in agreement with Raman spectroscopy results, associated to the coexistence of barium titanate orthorhombic and tetragonal phases in the room temperature region. This led to the formation of polar nanoclusters with random polarization orientations, which induced a frustrated phase transition between the tetragonal and orthorhombic phases of barium titanate in the films.

  5. 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

  6. Structural and ferroelectric properties of BaTiO 3/YBa 2Cu 3O 7 heterostructures prepared by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, H. S.; Liu, Y. W.; Ma, K.; Peng, Z. Q.; Cui, D. F.; Lu, H. B.; Zhou, Y. L.; Chen, Z. H.; Li, L.; Yang, G. Z.

    1997-08-01

    Heteroepitaxial BaTiO 3(BTO)/YBa 2Cu 3O 7(YBCO) thin films were grown on (100) SrTiO 3(STO) substrates by ozone assistant laser molecular beam epitaxy (L sbnd MBE). The results show that by using this technique, high quality ferroelectric/superconductor heterostructures with high crystalline quality and desirable device performance can be obtained.

  7. BaTiO3-SrTiO3 multilayer thin film electro-optic waveguide modulator

    NASA Astrophysics Data System (ADS)

    Hiltunen, Jussi; Seneviratne, Dilan; Sun, Rong; Stolfi, Michael; Tuller, Harry L.; Lappalainen, Jyrki; Lantto, Vilho

    2006-12-01

    Mach-Zehnder electro-optic waveguide modulators were fabricated based on BaTiO3 (BTO )-SrTiO3 (STO) multilayer thin film stacks grown on single crystal MgO substrates by pulsed laser deposition. X-ray diffraction measurements confirmed the formation of a BTO-STO superlattice with periodicity of 11unit cells. Strip-loaded waveguides were formed by patterning a SixNy film deposited onto the BTO-STO stack while Al electrodes of 3mm length and 13μm separation were fabricated in the vicinity of the active waveguide arm of the Mach-Zehnder modulator. An effective electro-optic coefficient of 73pm/V at 1550nm wavelength was determined for the deposited BTO-STO superlattice by measuring the output intensity as a function of applied electric field.

  8. Morphogenesis mechanisms in the solvothermal synthesis of BaTiO3 from titanate nanorods and nanotubes.

    PubMed

    Bogicevic, Christine; Thorner, Gentien; Karolak, Fabienne; Haghi-Ashtiani, Paul; Kiat, Jean-Michel

    2015-02-28

    A rich variety of single crystalline BaTiO3 (BT) nanostructures have been synthesized by two different routes using titanate nanorods and nanotubes as precursors. Free standing, mixed or agglomerated nanotori, solid or hollow nanospheres and nanocubes were obtained. A careful analysis of the shape evolution of the resulting BT nano-objects obtained with both types of precursors and different parameters (precursor composition and shape, temperature, Ba/Ti molar ratio) allowed an improved understanding of the nanostructure formation. The morphogenesis models at play such as Ostwald ripening and the Kirkendall effect have been identified. Other mechanisms hereafter called the self and merging rebuilding processes and a tentative Turing-reaction-diffusion-model are proposed to explain the formation of these obtained nanoparticles. PMID:25630867

  9. Experimental study and theoretical prediction of dielectric permittivity in BaTiO3/polyimide nanocomposite films

    NASA Astrophysics Data System (ADS)

    Fan, Ben-Hui; Zha, Jun-Wei; Wang, Dong-Rui; Zhao, Jun; Dang, Zhi-Min

    2012-02-01

    Theoretical models were used to predict dielectric permittivities of the thermosetting polyimide (PI) matrix nanocomposite films loading with BaTiO3 (BT) nanoparticles prepared by the alkoxide route. The observed dielectric permittivities are in good agreement with calculated values using Jayasundere equation and effective medium theory when the interactions of nanoparticle-nanoparticle and nanoparticle-polymer are considered. Additionally, temperature dependence of dielectric permittivity of the BT/PI nanocomposite films at 103 Hz was also studied for both heating from -50 to 150 °C and cooling from 150 to -50 °C. The transformation in crystal phase of BT and changes of free volume in PI were considered to be the main factors influencing the dielectric permittivities of the BT/PI nanocomposite films.

  10. Influence of temperature on the dielectric nonlinearity of BaTiO3-based multi-layer ceramic capacitors

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Kim, Mi-Yang

    2016-06-01

    Temperature dependence of the dielectric nonlinearity was investigated for the BaTiO3 multilayer ceramic capacitor. The decrease in temperature caused a significant increase in the degree of dielectric nonlinearity. The Preisach analysis shows that such effect corresponds to a decrease in reversible and a significant increase in irreversible domain wall contribution to polarization. The magnitude of spontaneous polarization (PS) was increased with decreasing temperature. It can be associated with phase transition from pseudo-cubic to monoclinic and its resultant change in the polar direction, which was observed through transmission electron microscopy. These results demonstrate that the increase in PS with the decrease in temperature inhibits domain wall motion in low driving field as it is anticipated to increase the degree of intergranular constraints during domain wall motion. But it results in a more steep increase in the dielectric constants beyond the threshold field where domain wall motion can occur.

  11. Multiferroic properties of microwave sintered BaTiO3-SrFe12O19 composites

    NASA Astrophysics Data System (ADS)

    Katlakunta, Sadhana; Raju, Pantagani; Meena, Sher Singh; Srinath, Sanyadanam; Sandhya, Reddigari; Kuruva, Praveena; Murthy, Sarabu Ramana

    2014-09-01

    The composites of xSrFe12O19-(1-x) BaTiO3 where x=0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1were prepared by Sol-gel method and consequently densified at 1100 °C/90 min using microwave sintering method. The phase formation and diphase microstructure of the composite samples was examined by X-ray diffraction and field emission electron microscope (FESEM), respectively. The effects of constituent phase variation on the ferroelectric, dielectric and magnetic properties were examined. It was observed that with a decrease of x, the Curie temperature shifted towards low temperature side.

  12. Chemistry and structure of BaTiO3 ultra-thin films grown by different O2 plasma power

    NASA Astrophysics Data System (ADS)

    Wang, J. L.; Leroy, J.; Niu, G.; Saint-Girons, G.; Gautier, B.; Vilquin, B.; Barrett, N.

    2014-01-01

    We present a study of the chemical and atomic properties of 5 nm TiO2-terminated BaTiO3 (0 0 1) epitaxial films on Nb-doped SrTiO3, as a function of the atomic oxygen plasma power for film growth. Lower plasma power produces non-stoichiometric films with oxygen vacancies and Ti3+ ions. The larger Ti3+ ion radius and the in-plane clamping gives rise to an increase in the out-of-plane lattice parameter. XPS measures the Ti3+ concentration and the concomitant increase in dissociative water uptake in the film, giving rise to on-top OH- adsorption on surface Ti, proton adsorption on surface oxygen, and a near surface Ba-OH environment.

  13. Influence of interfacial coherency on ferroelectric switching of superlattice BaTiO3/SrTiO3

    SciTech Connect

    Wu, Pingping; Ma, Xingqiao; Li, Yulan; Eom, C.B.; Schlom, Darrell G.; Gopalan, Venkatraman; Chen, Long-Qing

    2015-04-11

    Switching behavior of (BaTiO3)8/ (SrTiO3)4 heterostructure superlattice grown on SrTiO3 substrate was studied by employing the phase field method. To investigate the constraint effect of the substrate on switching, three types of superlattice/substrate interface mechanical relaxation conditions were considered, i.e. the fully ommensurate, partially relaxed and fully relaxed. Our simulation results demonstrated that the hysteresis loops under the three types of constraints were very different. The interfacial coherency affects dramatically the coercivity and remanence of the superlattice films. The mechanism of the hysteresis loop varying with interfacial coherency was analyzed by the ferroelectric domain configuration and its evolution during the switching process. The hysteresis loop of fully relaxed superlattice shows application potential on ferroelectric energy storage materials.

  14. Effects of MgO Doping on DC Bias Aging Behavior of Mn-Doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Hahn, Dong Woo; Hong, Jeong Oh; Han, Young Ho

    2008-07-01

    The capacitance aging of multilayer ceramic capacitors (MLCCs) based on BaTiO3 dielectrics under DC electric fields has been studied. At a DC field of 1 V/µm, the capacitance of MLCC specimens decreased immediately in a very short period (<10 s, the first stage) and then decreased continuously with time (the second stage). Substitution of Mn ions markedly increased the slope of aging curves in the second stage. MgO doping significantly decreased the second stage aging rate of Mn-doped specimens. This aging rate decreased in the second stage with increasing MgO content. This may be due to the existence of a stable defect complex (MgTi''-VO••) inhibiting domain wall motion. MgO-doped specimens showed a small decrease in capacitance in the first stage, which may be due to small grain size and low dielectric permittivity.

  15. Effect of Vanadium Addition on Reliability and Microstructure of BaTiO3-Based Multilayer Ceramic Capacitors

    NASA Astrophysics Data System (ADS)

    Natsui, Hidesada; Shibahara, Takeshi; Yonezawa, Yu; Kido, Osamu

    2012-09-01

    The vanadium distribution in multilayer ceramic capacitors (MLCCs), sintered under a reducing atmosphere, was investigated using scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS), and insulation resistance degradation was analyzed using impedance spectroscopy in highly accelerated lifetime tests to clarify the effects of vanadium on both the electrical properties and microstructure of MLCCs. Vanadium mitigated insulation resistance degradation and increased the reliability of MLCCs. Moreover, vanadium content increased and insulation resistance at the ceramic/electrode interface decreased slowly. This change in dynamics directly resulted in an improved lifetime of MLCCs. The results of STEM-EELS analysis showed that vanadium distributed along the grain boundary and grain boundary junction, but substituted into BaTiO3 at the ceramic/electrode interface. Therefore, it is considered that vanadium substitution at the ceramic/electrode interface improves the reliability of MLCCs.

  16. Dielectric Properties of Rare-Earth-Oxide-Doped BaTiO3 Ceramics Fired in Reducing Atmosphere

    NASA Astrophysics Data System (ADS)

    Okino, Yoshikazu; Shizuno, Hisamitsu; Kusumi, Shinya; Kishi, Hiroshi

    1994-09-01

    In order to gain an understanding of highly reliable electrical characteristics for the Ho-doped multilayer ceramic capacitors with Ni electrodes, dielectric properties of various rare-earth-oxide-doped BaTiO3 ceramics were studied. The smaller ionic radius rare-earth-oxide (Dy, Ho, Er)-doped samples showed lower resistivity in reducing atmosphere, but higher resistivity in oxidizing atmosphere at the cooling stage, compared with the larger-ion (La, Sm, Gd)-doped samples. Multilayer ceramic capacitors with Ni electrodes using the smaller-ion-doped materials showed smaller aging rate and longer lifetime. We developed Ni-electrode MLCs with X7R specification as 1 µ F in the 2125 type.

  17. Microstructure defects mediated charge transport in Nb-doped epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Zhou, Jian; Jing, Xiaosai; Alexe, Marin; Dai, Jiyan; Qin, Minghui; Wu, Sujuan; Zeng, Min; Gao, Jinwei; Lu, Xubing; Liu, J.-M.

    2016-05-01

    Nb-doped BaTiO3 (BNTO) films were deposited on MgO substrates at different substrate temperatures by pulsed laser deposition. The temperature dependence of their resistivity, carrier mobility and carrier concentration were systematically investigated. It reveals that the BNTO films deposited at lower temperature show higher resistivity and lower carrier mobility, and only show semiconductor characteristics at measurement temperatures ranging from 10 to 400 K. There is a metal-semiconductor transition at about 20 K for the films grown at relatively higher temperature. The intrinsic mechanism responsible for the different charge transport behavior was revealed by microstructure studies. Low crystal quality and high density of microstructure defects, observed for BNTO films grown at low temperatures, are, in particular, massively affecting the charge transport behavior of the BNTO films. The mediated charge transport of the microstructure defects is dominated by the thermal excitation process.

  18. Ferroelectric polarization and resistive switching characteristics of ion beam assisted sputter deposited BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Silva, J. P. B.; Kamakshi, Koppole; Sekhar, K. C.; Moreira, J. Agostinho; Almeida, A.; Pereira, M.; Gomes, M. J. M.

    2016-05-01

    In this work, 150 nm thick polycrystalline BaTiO3 (BTO) films were deposited on Pt/TiO2/SiO2/Si substrate by ion beam assisted sputter deposition technique. The bias voltage dependent resistive switching (RS) and ferroelectric polarization characteristics of Au/BTO/Pt devices are investigated. The devices display the stable bipolar RS characteristics without an initial electroforming process. Fittings to current-voltage (I-V) curves suggest that low and high resistance states are governed, respectively, by filamentary model and trap controlled space charge limited conduction mechanism, where the oxygen vacancies act as traps. Presence of oxygen vacancies is evidenced from the photoluminescence spectrum. The devices also display P-V loops with remnant polarization (Pr) of 5.7 μC/cm2 and a coercive electric field (Ec) of 173.0 kV/cm. The coupling between the ferroelectric polarization and RS effect in BTO films is demonstrated.

  19. Composites of hybrids BaTiO3/carbon nanotubes/polyvinylidene fluoride with high dielectric properties

    NASA Astrophysics Data System (ADS)

    Fan, Benhui; Bai, Jinbo

    2015-11-01

    High dielectric composites were prepared based on polyvinylidene fluoride (PVDF) and hybrids BaTiO3-carbon nanotubes (H-BT-CNTs) with a special structure. The hybrids that BT was a core and CNTs grew outside were fabricated by chemical vapor deposition. Due to the special structure, composite’s dielectric permittivity reached 1777 at 100 Hz and 80 at 1 MHz, while loss tangent maintained as 6 at 100 Hz and 0.56 at 1 MHz, respectively. Moreover, dielectric permittivity and ac conductivity of composite were further enhanced after annealing process at moderate temperature. These improved properties were originated from the reformation of conductive network and BT-CNTs structure inside PVDF matrix.

  20. Pseudo Jahn-Teller origin of ferroelectric instability in BaTiO3 type perovskites: The Green's function approach and beyond

    NASA Astrophysics Data System (ADS)

    Polinger, V.; Garcia-Fernandez, P.; Bersuker, I. B.

    2015-01-01

    The local origin of dipolar distortions in ABO3 perovskite crystals is reexamined by means of a novel approach, the Green's function method augmented by DFT computations. The ferroelectric distortions are shown to be induced by the pseudo Jahn-Teller effect (PJTE). The latter involves vibronic hybridization (admixture) of the ground state to same-spin opposite-parity excited electronic bands. Similar to numerous molecular calculations, the PJT approach provides a deeper insight into the nature of chemical bonding in the octahedral cluster [BO6] and, in particular, reveals the local origin of its polar instability. This allows predicting directly which transition ions can create ferroelectricity. In particular, the necessary conditions are established when an ABO3 perovskite crystal with an electronic dn configuration of the complex ion [BO6] can possess both proper ferroelectric and magnetic properties. Distinguished from the variety of cluster approaches to local properties, the Green's function method includes the influence of the local vibronic-coupling perturbation on the whole crystal via the inter-cell interaction responsible for creation of electronic and vibrational bands. Calculated Green's functions combined with the corresponding numeric estimates for the nine electronic bands, their density of states, and the local adiabatic potential energy surface (APES) confirm the eight-minimum form of this surface and feasibility of the PJT origin of the polar instability in BaTiO3. We show also that multicenter long-range dipole-dipole interactions critically depend on the PJTE largely determining the magnitude of the local dipoles. DFT calculations for the bulk crystal and its clusters confirm that the dipolar distortions are of local origin, but become possible only when their influence on (relaxation of) the whole lattice is taken into account. The results are shown to be in full qualitative and semiquantitative agreement with the experimental data for this

  1. Morphogenesis mechanisms in the solvothermal synthesis of BaTiO3 from titanate nanorods and nanotubes

    NASA Astrophysics Data System (ADS)

    Bogicevic, Christine; Thorner, Gentien; Karolak, Fabienne; Haghi-Ashtiani, Paul; Kiat, Jean-Michel

    2015-02-01

    A rich variety of single crystalline BaTiO3 (BT) nanostructures have been synthesized by two different routes using titanate nanorods and nanotubes as precursors. Free standing, mixed or agglomerated nanotori, solid or hollow nanospheres and nanocubes were obtained. A careful analysis of the shape evolution of the resulting BT nano-objects obtained with both types of precursors and different parameters (precursor composition and shape, temperature, Ba/Ti molar ratio) allowed an improved understanding of the nanostructure formation. The morphogenesis models at play such as Ostwald ripening and the Kirkendall effect have been identified. Other mechanisms hereafter called the self and merging rebuilding processes and a tentative Turing-reaction-diffusion-model are proposed to explain the formation of these obtained nanoparticles.A rich variety of single crystalline BaTiO3 (BT) nanostructures have been synthesized by two different routes using titanate nanorods and nanotubes as precursors. Free standing, mixed or agglomerated nanotori, solid or hollow nanospheres and nanocubes were obtained. A careful analysis of the shape evolution of the resulting BT nano-objects obtained with both types of precursors and different parameters (precursor composition and shape, temperature, Ba/Ti molar ratio) allowed an improved understanding of the nanostructure formation. The morphogenesis models at play such as Ostwald ripening and the Kirkendall effect have been identified. Other mechanisms hereafter called the self and merging rebuilding processes and a tentative Turing-reaction-diffusion-model are proposed to explain the formation of these obtained nanoparticles. Electronic supplementary information (ESI) available: Derivation of the reaction-diffusion-model coefficients. See DOI: 10.1039/c4nr06266c

  2. Mechanism of high dielectric performance of polymer composites induced by BaTiO3-supporting Ag hybrid fillers

    NASA Astrophysics Data System (ADS)

    Fang, Fang; Yang, Wenhu; Yu, Shuhui; Luo, Suibin; Sun, Rong

    2014-03-01

    BaTiO3-supporting Ag hybrid particles (BT-Ag) with varied fraction of Ag were synthesized by reducing silver nitrate in the glycol solution containing BaTiO3 (BT) suspensions. The Ag nano particles with a size of about 20 nm were discretely grown on the surface of the BT. The dielectric performance of the composites containing the BT-Ag as fillers in the matrix of polyvinylidene fluoride (PVDF) was investigated. The relative permittivity (ɛr) of the BT-Ag/PVDF composites increased prominently with the increase of BT-Ag loading amount, and the typical conductive path of the conductor/polymer system was not observed even with a high loading of BT-Ag. The ɛr at 100 Hz for the three BT-(0.31, 0.49, 0.61)Ag/PVDF composites at room temperature were 283, 350, and 783, respectively. The ɛr of the composites was enhanced by more than 3 times compared with that of the composite containing untreated BT nanoparticles at frequencies over 1 kHz and the loss tangent (tan δ) was less than 0.1 which should be attributed to the low conductivity of the composites. Theoretical calculations based on the effective medium percolation theory model and series-parallel model suggested that the enhanced permittivity of BT-Ag/PVDF composites should arise from the ultrahigh permittivity of BT-Ag fillers, which was over 104 and associated with the content of Ag deposited on the surface of BT.

  3. Weak ferromagnetism in the ferroelectric BiFeO3-ReFeO3-BaTiO3 solid solutions (Re=Dy,La)

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Seog; Cheon, Chae Il; Lee, Chang Hee; Jang, Pyung Woo

    2004-07-01

    The binary and ternary solid solutions, BiFeO3-BaTiO3, BiFeO3-ReFeO3-BaTiO3 (Re=Dy,Pr,La), and BiFeO3-BaFeO2.5-BaTiO3 have been explored for attaining ferromagnetic ferroelectrics in bulk ceramics and understanding the effect of rare earth orthoferrites ReFeO3 on the spontaneous magnetization. The coexistence of ferromagnetism and ferroelectricity has been observed over the composition range of 0.2⩽x⩽0.4 in the (1-x)BiFeO3-xBaTiO3 at room temperature. The introduction of DyFeO3 and LaFeO3 expands the composition range of the coexistence. The most superior ferromagnetic ferroelectrics obtained in this study are the 0.65BiFeO3-0.025DyFeO3-0.325BaTiO3 (Pr=5 μC/cm2,Mr=0.1 emu/g), 0.4875BiFeO3-0.025DyFeO3-0.4875BaTiO3 (Pr=7 μC/cm2,Mr=0.06 emu/g), and 0.475BiFeO3-0.05LaFeO3-0.475BaTiO3 (Pr=3.2 μC/cm2,Mr=0.2 emu/g). The spontaneous magnetization strongly depends on both the type and amount of the substitution components, DyFeO3, LaFeO3, PrFeO3, and BaFeO2.5 rather than the degree of G-type antiferromagnetic ordering. The origin of the spontaneous magnetization has been discussed in terms of antiferromagnetic ordering and charge carrier mediation.

  4. Electron-Phonon Couplings of the Interfacial Mode in FeSe Thin Films on SrTiO3 and BaTiO3

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Berlijn, Tom; Rademaker, Louk; Johnston, Steve

    Monolayers FeSe on SrTiO3 or BaTiO3 substrates possess highest superconducting transition temperatures in Fe-based superconductors with Tc ~ 70 K measured by angle-resolved photoemission spectroscopy (ARPES) and other experiments. Furthermore, the high Tc's concur with exact replica bands in ARPES spectra. A forward scattering mechanism with small momentum transfer through the electron-phonon interaction has been proposed to explain the high Tc's and the replica bands. We apply ab initio techniques to study such coupling in monolayer and bilayer FeSe thin films on SrTiO3, BaTiO3, and oxygen-vacant SrTiO3 substrates. Our results confirm the forward scattering nature of electron-phonon coupling of the oxygen polar mode whose energy coincides with the off-set energy of the replica bands.

  5. Oxygen-induced surface reconstruction of SrRuO3 and its effect on the BaTiO3 interface.

    PubMed

    Shin, Junsoo; Borisevich, Albina Y; Meunier, Vincent; Zhou, Jing; Plummer, E Ward; Kalinin, Sergei V; Baddorf, Arthur P

    2010-07-27

    Atomically engineered oxide multilayers and superlattices display unique properties responsive to the electronic and atomic structures of the interfaces. We have followed the growth of ferroelectric BaTiO3 on SrRuO3 electrode with in situ atomic scale analysis of the surface structure at each stage. An oxygen-induced surface reconstruction of SrRuO3 leads to formation of SrO rows spaced at twice the bulk periodicity. This reconstruction modifies the structure of the first BaTiO3 layers grown subsequently, including intermixing observed with cross-section spectroscopy. These observations reveal that this common oxide interface is much more interesting than previously reported and provide a paradigm for oxygen engineering of oxide structure at an interface. PMID:20575506

  6. Effect of rhodium doping on the growth and characteristics of BaTiO 3 single crystals grown by step-cooling method

    NASA Astrophysics Data System (ADS)

    Madeswaran, S.; Giridharan, N. V.; Varatharajan, R.; Ravi, G.; Jayavel, R.

    2004-06-01

    Single crystals of Rh-doped BaTiO 3 have been grown by high-temperature solution growth technique. The dopant has significant effect on the growth parameters and crystal properties. Bulk single crystals of dimensions 5×5×4 mm 3 have been grown with optimized growth conditions. Layer growth and vein-like structure patterns, indicative of 2D-nucleation mechanism, have been observed on the grown crystals. The dopant level in the grown crystals was estimated by EDX analysis. The crystals possess tetragonal structure and the tetragonality decreases for higher dopant concentration. Rh doping in BaTiO 3 leads to decrease in dielectric constant and Curie temperature ( Tc) values.

  7. Structure and magnetic properties of the composite of Co1.75Fe1.25O4 and BaTiO3

    NASA Astrophysics Data System (ADS)

    Kazhugasalamoorthy, S.; Bhowmik, R. N.

    2015-06-01

    We report the structure and magnetic properties of a composite consisting of magnetic Co1.75Fe1.25O4 and ferroelectric BaTiO3. The composite material was prepared by heating the mixture at 1000 °C. XRD pattern of the composite confirms the presence of cubic (CoFe2O4) and tetragonal (BaTiO3) phases and a minor impurity phase of BaCO3. Line scan in the energy dispersive analysis of X-ray spectrum indicated the separation of the ferrite particles about 15-23 µm in the composite. The composite material became magnetically soft in comparison to the Co-ferrite and shows scope for tailoring ferromagnetic parameters at room temperature.

  8. Rietveld refined structural and room temperature vibrational properties of BaTiO3 doped La0.67Ba0.33MnO3 composites

    NASA Astrophysics Data System (ADS)

    Dar, M. A.; Sheikh, M. W.; Malla, M. S.; Varshney, Dinesh

    2016-05-01

    The composites of (1-x) La0.67Ba0.33MnO3 (LBMO) + xBaTiO3 (BTO) (x = 0, 0.25 and 1.0) were synthesized by conventional solid-state reaction method. Rietveld refinement was employed to characterize the structural information of the prepared ceramics. The result of the Rietveld refinement of X-ray powder diffraction of La0.67Ba0.33MnO3 and BaTiO3 shows that these compounds crystallize in rhombohedral (R3c) and tetragonal (P4mm), respectively. The structural parameters and the reliability factors for the LBMO-BTO composite ceramics were successfully determined by the Rietveld refinement. At room temperature, Raman active phonon modes predicted by the group theory were observed only in BaTiO3 and composite sample. Pure LBMO does not show any Raman active Phonon mode at room temperature.

  9. Fabrication of BaTiO3-Based Dielectrics for Ultrathin-Layer Multilayer Ceramic Capacitor Application by a Modified Coating Approach

    NASA Astrophysics Data System (ADS)

    Tian, Zhibin; Wang, Xiaohui; Zhang, Yichi; Song, Tae-Ho; Hur, Kang Heon; Li, Longtu

    2011-02-01

    The development of multilayer ceramic capacitor (MLCC) with base metal electrode (BME) requires precise controlling of the microstructure in a very thin dielectric layer (<1 µm). In this paper, a modified coating approach for high coverage of BaTiO3 powder for further MLCC application has been developed. The well dispersed and coated BaTiO3 powders are prepared and the relative mechanism has been discussed. Furthermore, the ultrafine grained X7R dielectric ceramics were produced by both conventional mixing and modified coating methods. Compared with the conventional mixing method, the ceramics prepared by the coating approach exhibited better TCC (the temperature coefficient of capacitance) performance, with dielectric constant over 2000 and grain size below 150 nm. In addition, it is found through the coating method the content of additives can be reduced to a relatively smaller amount than that required in conventional mixing method.

  10. Misfit strain-misfit strain diagram of epitaxial BaTiO3 thin films: Thermodynamic calculations and phase-field simulations

    NASA Astrophysics Data System (ADS)

    Sheng, G.; Zhang, J. X.; Li, Y. L.; Choudhury, S.; Jia, Q. X.; Liu, Z. K.; Chen, L. Q.

    2008-12-01

    The effect of anisotropic strains on the phase transitions and domains structures of BaTiO3 thin films was studied using both thermodynamic calculations and phase-field simulations. The misfit strain-misfit strain domain stability diagrams were predicted. The similarity and significant differences between the diagrams from thermodynamic calculations assuming single domains and from phase-field simulations were analyzed. Typical domain structures as a result of anisotropic misfit strains are presented.

  11. NIR to blue light upconversion in Tm3+/Yb3+ codoped BaTiO3 tellurite glass

    NASA Astrophysics Data System (ADS)

    Kumari, Astha; Rai, Vineet Kumar

    2015-05-01

    Upconversion is an interesting optical property, generally shown by rare-earth doped materials. This unusual optical behavior shown by these rare-earths doped materials are due to their peculiar atomic configuration and electronic transitions. Here, the Tm3+-Yb3+ codoped BaTiO3 glass with TeO2 as former has been prepared by conventional melt and quench technique and the upconversion property has been investigated with the help of near infrared (NIR) to Visible UC study. The generation of the visible UC bands around ˜ 476 nm, ˜ 653 nm, ˜ 702 nm and one NIR UC band at ˜795 nm are assigned due to the 1G4→ 3H6, 1G4→ 3F4, 3F2→ 3H6 and 3H4→ 3H6 transitions respectively. The generations of these upconversion bands have been discussed in detail with the help of energy level diagram. The colour coordinates corresponding to the prepared material have been shown with the help of CIE chromaticity diagram. These glasses can be very appropriately used in the fabrication of solid state laser and as NIR to blue light upconverter.

  12. Hybrid chitosan-Pluronic F-127 films with BaTiO3:Co nanoparticles: Synthesis and properties

    NASA Astrophysics Data System (ADS)

    Fuentes, S.; Dubo, J.; Barraza, N.; González, R.; Veloso, E.

    2015-03-01

    In this study, magnetic BaTiO3:Co (BT:Co) nanoparticles prepared using a combined sol-gel-hydrothermal technique were dispersed in a chitosan/Pluronic F-127 solution (QO/Pl) to obtain a nanocomposite hybrid films. Nanoparticles and hybrid films were characterized by X-ray powder diffraction, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and alternating gradient magnetometry (AGM). Experimental results indicated that the BT:Co nanoparticles were encapsulated in the QO/Pl hybrid films and that the magnetic properties of the QO/Pl/BT:Co nanocomposites are similar to the naked BT:Co nanoparticles. Results indicate that Co doping produces an enhancement in the ferromagnetic behavior of the BT nanoparticle. The coating restricts this enhancement only to low-fields, leaving the diamagnetic behavior of BT at high-fields. Magnetically stable sizes (PSD) were obtained at 3% Co doping for both naked nanoparticles and hybrid films. These show an increased magnetic memory capacity and a softer magnetic hardness with respect to non-doped BT nanoparticles.

  13. Composite-hydroxide-mediated approach an effective synthesis route for BaTiO3 functional nanomaterials

    NASA Astrophysics Data System (ADS)

    Khan, Taj Muhammad; Zakria, M.; Shakoor, Rana. I.; Hussain, Shabbir

    2016-04-01

    This paper describes synthesis of the functional BaTiO3 (BT) nanostructures by composite-hydroxide-mediated (CHM) approach. The effect of processing temperature on the nucleation and the optical, structural properties is investigated. The nanostructures prepared at various temperatures (180, 220 and 250 °C) are thermally stable and nucleate in different morphologies, which shows a temperature-dependent mechanism of the CHM approach. The nanostructures are cubic in nature with an average particle size in the range of 97-250 nm. The local crystal structure investigated by Raman spectroscopy reveals a certain degree of tetragonality on atomic scale in the local phase structure. The micrographs of scanning electron microscopy (SEM) indicate formation of the nanocuboids at 180 and 220 °C with larger particle size. At 250 °C, the product shows ball-like spherical morphology. Energy-dispersive X-ray (EDX) confirms the existence of Ba, Ti and O elements in the product, which indicates a chemically pure product. Further signature on the formation, purity and chemical bonding is obtained from FT-IR spectroscopy. Based on these experimental results, size, morphology manipulation and possible growth mechanisms are proposed with CHM at low temperature and without surfactant.

  14. Optical Second Harmonic Generation in the BaTiO3 phase of magnetically aligned multiferroic nanofibers

    NASA Astrophysics Data System (ADS)

    Gasperi, Katia

    Multiferroic materials enable the exploration of electrical control of magnetic properties and vice versa. Their increasing interest is especially due to their potential applications in the industry of information storage. Thanks to recent progress in nanotechnology, they have also been found to have many other applications such as transducers and sensors, and they already occupy a unique place in the biomedical field. The objective of this project is to study multiferroic nanofibers made of cobalt ferrite CoFe2O 4 (CFO) and barium titanate BaTiO3 (BTO) with a specific focus in the characterization of the ferroelectric phase. We researched the state of knowledge concerning the size effects on phase transition for nanoparticles and polycrystals BTO. The ferroelectric phase transition of BTO occurs when it changes from a tetragonal (anisotropic) crystal structure to a cubic (isotropic) structure. This change suggests that optical second harmonic generation (SHG) is a good measurement technique for monitoring the phase transition of the BTO half of the nanofibers. We designed and prepared a temperature dependent SHG experiment on magnetically aligned fibers in transmission with the possibility to investigate the polarization dependence of the signal. We also prepared interdigital electrodes on glass for the future study of the fibers in an external electric field.

  15. Temperature-dependent high energy-resolution EELS of ferroelectric and paraelectric BaTiO3 phases

    NASA Astrophysics Data System (ADS)

    Bugnet, Matthieu; Radtke, Guillaume; Woo, Steffi Y.; Zhu, Guo-zhen; Botton, Gianluigi A.

    2016-01-01

    Probing the ferroelectricity at the nanometer scale is of particular interest for a wide range of applications. In this Rapid Communication, the structural distortion of BaTiO3 (BTO) is studied in its ferroelectric (rhombohedral and tetragonal), and paraelectric phases from the O K near edge structures in electron energy loss spectroscopy. Modifications of the electronic structure are detected in the lowest energy fine structure (FS) of the O K edge in the ferroelectric phases, and are interpreted by core-hole valence-electron screening geometry. For the paraelectric phase, the lowest energy FS of the O K edge is comparable to the one obtained at room temperature, which is inconsistent with an expected cubic structure. The variations observed in the O K near edge structures, such as a broader and more asymmetric lowest energy FS at low temperature, suggest that the magnitude of the Ti+4 off-centering along <111 > increases in lower-temperature phases. These findings demonstrate the sensitivity of the O K near edge structures to the structural distortions of BTO polymorphs, and form a basis for further investigations on defective or strained BTO at the nanoscale.

  16. Grain-growth effect on dielectric nonlinearity of BaTiO3-based multi-layer ceramic capacitors

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Kim, Mi-Yang; Nam, Chan-Hee; Seo, Jung-Wook; Wi, Sung-Kwon; Hur, Kang-Heon

    2015-08-01

    A significant difference in dielectric nonlinearity was contrasted between fine- and coarse-grained BaTiO3-based multilayer ceramic capacitors. Grain growth resulted in a decrease in dielectric constant in low field but a steep increase with increase in alternating current field, which can be associated with a decrease in reversible and a significant increase in irreversible domain wall contribution from Preisach analysis. Fine-grained specimens showed almost cubic structure despite ferroelectric domain contrasts, which is anticipated to significantly reduce strain incompatibility during domain wall motion, and clean domain boundaries with no lattice defects. However, coarse-grained specimens with high aspect ratio of the tetragonal lattice should accompany lattice distortion with increased intergranular constraints during domain wall motion, and many lattice defects were observed near domain boundaries. These results demonstrate experimentally the presence of weak pinning centers in coarse-grained specimens, which inhibit domain wall motion in low alternating current fields. Long-range motion occurs beyond the threshold field and results in an abrupt increase in dielectric constant.

  17. Field-induced domain switching in BaTiO3-based multilayer ceramic capacitors observed by polarized Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Gao, Haigen; Yue, Zhenxing; Xi, Xiaoqing; Li, Longtu

    2012-11-01

    Polarized Raman spectroscopy was employed to observe field-induced domain switching in BaTiO3-based multilayer ceramic capacitors (MLCCs). Un-polarized Raman intensities of vibration modes A1(TO2,TO3) are decreased with increasing the external field from 0 MV/m to 5 MV/m, which is caused by the decrease of c-domain volumes. This phenomenon can be visualized from the simulated image gained from the mapping results in cross polarization. It shows that the c-domains are switched to the direction of electric field (3.75 MV/m). We also found that the load to imprint Vickers indentation on the polished MLCCs surface can drive the domains out of the plane parallel to internal electrodes into in-plane textures. Meanwhile, the in-plane domains in the investigated area are switched to form a uniform orientation by the local introduced compressive stress. Due to the existence of cracks, the domains near cracks will re-orient and align with the direction of the relative tensile stress, resulting in a different orientation.

  18. Junction size dependence of ferroelectric properties in e-beam patterned BaTiO3 ferroelectric tunnel junctions

    NASA Astrophysics Data System (ADS)

    Singh, A. V.; Althammer, M.; Rott, K.; Reiss, G.; Gupta, A.

    2015-09-01

    We investigate the switching characteristics in BaTiO3-based ferroelectric tunnel junctions patterned in a capacitive geometry with circular Ru top electrode with diameters ranging from ˜430 to 2300 nm. Two different patterning schemes, viz., lift-off and ion-milling, have been employed to examine the variations in the ferroelectric polarization, switching, and tunnel electro-resistance resulting from differences in the pattering processes. The values of polarization switching field are measured and compared for junctions of different diameter in the samples fabricated using both patterning schemes. We do not find any specific dependence of polarization switching bias on the size of junctions in both sample stacks. The junctions in the ion-milled sample show up to three orders of resistance change by polarization switching and the polarization retention is found to improve with increasing junction diameter. However, similar switching is absent in the lift-off sample, highlighting the effect of patterning scheme on the polarization retention.

  19. 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

  20. Atomic Displacements at a Σ3(111) Grain Boundary in BaTiO_3: A First-principles Determination

    NASA Astrophysics Data System (ADS)

    Zhao, Y. J.; Geng, W. T.; Kim, Miyoung; Freeman, A. J.; Delley, B.

    2000-03-01

    BaTiO3 based ceramics are extensively used in the production of many electroceramic components such as capacitors and positive temperature coefficient thermistors. The electrical properties are known to be grain boundary(GB) phenomena and related to their atomic structure near the grain boundary(K. Hayashi, et al., J. Am. Ceram. Soc., 79), 1669(1996). Jia and Thust(C.L. Jia and A. Thust, Phys. Rev. Lett. 82), 5052 (1999) observed an expansion of the Ti-Ti spacing across the Σ3(111) GB in cubic BaTiO3 by use of high-resolution transmission electron microscopy along with an exit plane wave analysis. We employed the first-principles band structure DMol3 total energy/atomic force method( B. Delley, J. Chem. Phys. 92), 508(1990) within LDA to investigate the atomic and electronic structures at a Σ3(111) GB in cubic BaTiO_3. Full relaxation of the atomic structure was determined according to the calculated atomic forces. Our first-principles calculations indicate an expansion of the nearest Ti-Ti spacing across the GB plane and a contraction of the nearest BaO-BaO spacing, in good agreement with experiment. The origin of the atomic displacements were then explained with an electronic structure analysis.

  1. Local manifestations of a static magnetoelectric effect in nanostructured BaTiO3-BaFe12O9 composite multiferroics

    NASA Astrophysics Data System (ADS)

    Trivedi, Harsh; Shvartsman, Vladimir V.; Lupascu, Doru C.; Medeiros, Marco S. A.; Pullar, Robert C.; Kholkin, Andrei L.; Zelenovskiy, Pavel; Sosnovskikh, Andrey; Shur, Vladimir Ya.

    2015-02-01

    A study on magnetoelectric phenomena in the barium titanate-barium hexaferrite (BaTiO3-BaFe12O19) composite system, using high resolution techniques including switching spectroscopy piezoresponse force microscopy (SSPFM) and spatially resolved confocal Raman microscopy (CRM), is presented. It is found that both the local piezoelectric coefficient and polarization switching parameters change on the application of an external magnetic field. The latter effect is rationalized by the influence of magnetostrictive stress on the domain dynamics. Processing of the Raman spectral data using principal component analysis (PCA) and self-modelling curve resolution (SMCR) allowed us to achieve high resolution phase distribution maps along with separation of average and localized spectral components. A significant effect of the magnetic field on the Raman spectra of the BaTiO3 phase has been revealed. The observed changes are comparable with the classical pressure dependent studies on BaTiO3, confirming the strain mediated character of the magnetoelectric coupling in the studied composites.

  2. Phase diagram in strained epitaxial BaTiO3/SrTiO3 superlattices studied by ultraviolet Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Tenne, Dmitri; Schmidt, J. D.; Turner, P.; Soukiassian, A.; Schlom, D. G.; Nakhmanson, S.; Xi, X. X.; Li, Y. L.; Chen, L. Q.; Bernhagen, M.; Reiche, P.; Uecker, R.; Katiyar, R.

    2009-03-01

    Strain effect on phase transitions in nanoscale BaTiO3/SrTiO3 ferroelectric superlattices (SLs) has been studied by ultraviolet (UV) Raman scattering. A series of coherently strained (BaTiO3)8/(SrTiO3)4 SLs have been grown by molecular beam epitaxiy on rare earth scandate (GdScO3, DyScO3, SmScO3, NdScO3) and SrTiO3 substrates. This allowed a systematic strain variation in the SLs. UV Raman data allowed the determination of the ferroelectric phase transition temperature (Tc) and indicated the presence of different ferroelectric phases with out-of-plane and in-plane components of polarization in SLs, depending on strain and temperature. Experimental Raman results are supported by first-principles calculations of structural instabilities in BaTiO3/SrTiO3 SLs and thermodynamic phase-field modeling of phase diagrams and ferroelectric polarization as a function of temperature and strain.

  3. Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO3-buffered ferroelectric BaTiO3 film on GaAs

    DOE PAGESBeta

    Qiao, Q.; Zhang, Y.; Contreras-Guerrero, Rocio; Droopad, Ravi; Pantelides, S. T.; Pennycook, Stephen J.; Ogut, Serdar; Klie, Robert F.

    2015-11-16

    The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO3 thin filmsgrown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO3 grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. We also use a combination of aberration-corrected scanning transmission electron microscopy and first-principles densitymore » functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectricpolarization of a BaTiO3 thin filmgrown on GaAs. Moreover, we demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO3), and propose that the presence of surface charge screening allows the formation of switchable domains.« less

  4. On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films.

    PubMed

    Tileli, Vasiliki; Duchamp, Martial; Axelsson, Anna-Karin; Valant, Matjaz; Dunin-Borkowski, Rafal E; Alford, Neil McN

    2015-01-01

    The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces. PMID:25406863

  5. Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO3-buffered ferroelectric BaTiO3 film on GaAs

    NASA Astrophysics Data System (ADS)

    Qiao, Qiao; Zhang, Yuyang; Contreras-Guerrero, Rocio; Droopad, Ravi; Pantelides, Sokrates T.; Pennycook, Stephen J.; Ogut, Serdar; Klie, Robert F.

    2015-11-01

    The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO3 thin films grown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO3 grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. Here, we use a combination of aberration-corrected scanning transmission electron microscopy and first-principles density functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectric polarization of a BaTiO3 thin film grown on GaAs. We demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO3), and propose that the presence of surface charge screening allows the formation of switchable domains.

  6. Vertical Interface Induced Dielectric Relaxation in Nanocomposite (BaTiO3)1-x:(Sm2O3)x Thin Films

    PubMed Central

    Li, Weiwei; Zhang, Wei; Wang, Le; Gu, Junxing; Chen, Aiping; Zhao, Run; Liang, Yan; Guo, Haizhong; Tang, Rujun; Wang, Chunchang; Jin, Kuijuan; Wang, Haiyan; Yang, Hao

    2015-01-01

    Vertical interfaces in vertically aligned nanocomposite thin films have been approved to be an effective method to manipulate functionalities. However, several challenges with regard to the understanding on the physical process underlying the manipulation still remain. In this work, because of the ordered interfaces and large interfacial area, heteroepitaxial (BaTiO3)1-x:(Sm2O3)x thin films have been fabricated and used as a model system to investigate the relationship between vertical interfaces and dielectric properties. Due to a relatively large strain generated at the interfaces, vertical interfaces between BaTiO3 and Sm2O3 are revealed to become the sinks to attract oxygen vacancies. The movement of oxygen vacancies is confined at the interfaces and hampered by the misfit dislocations, which contributed to a relaxation behavior in (BaTiO3)1-x:(Sm2O3)x thin films. This work represents an approach to further understand that how interfaces influence on dielectric properties in oxide thin films. PMID:26061829

  7. In situ stress measurements during pulsed laser deposition of BaTiO3 and SrTiO3 atomic layers on Pt(0 0 1)

    NASA Astrophysics Data System (ADS)

    Premper, J.; Sander, D.; Kirschner, J.

    2015-04-01

    We apply the cantilever deflection technique to measure stress in nm thin BaTiO3 and SrTiO3 films during pulsed laser deposition on a Pt(0 0 1) single crystal cantilever substrate. We find a compressive film stress of -4.2 GPa for BaTiO3 on Pt(0 0 1) (misfit = -2.3%), whereas the deposition of SrTiO3 (misfit = +0.4%) induces a tensile stress of +1.5 GPa. The stress measurements are augmented by in situ low energy electron diffraction experiments which indicate an epitaxial order of the films. We apply continuum elasticity to calculate film stress. We conclude that sign and magnitude of the measured stress are due to the epitaxial misfit between film and substrate, which is -2.3% and +0.4% for BaTiO3 and SrTiO3, respectively. We identify that in addition to misfit also the oxygen partial pressure during PLD film growth influences film stress. PLD growth in an oxygen-free environment leads to factor of two increased tensile stress in SrTiO3 on Pt(0 0 1) as compared to growth at pO2 =10-4 mbar. The role of film stoichiometry for film stress is discussed.

  8. Vertical Interface Induced Dielectric Relaxation in Nanocomposite (BaTiO3)1-x:(Sm2O3)x Thin Films.

    PubMed

    Li, Weiwei; Zhang, Wei; Wang, Le; Gu, Junxing; Chen, Aiping; Zhao, Run; Liang, Yan; Guo, Haizhong; Tang, Rujun; Wang, Chunchang; Jin, Kuijuan; Wang, Haiyan; Yang, Hao

    2015-01-01

    Vertical interfaces in vertically aligned nanocomposite thin films have been approved to be an effective method to manipulate functionalities. However, several challenges with regard to the understanding on the physical process underlying the manipulation still remain. In this work, because of the ordered interfaces and large interfacial area, heteroepitaxial (BaTiO3)1-x:(Sm2O3)x thin films have been fabricated and used as a model system to investigate the relationship between vertical interfaces and dielectric properties. Due to a relatively large strain generated at the interfaces, vertical interfaces between BaTiO3 and Sm2O3 are revealed to become the sinks to attract oxygen vacancies. The movement of oxygen vacancies is confined at the interfaces and hampered by the misfit dislocations, which contributed to a relaxation behavior in (BaTiO3)1-x:(Sm2O3)x thin films. This work represents an approach to further understand that how interfaces influence on dielectric properties in oxide thin films. PMID:26061829

  9. Local manifestations of a static magnetoelectric effect in nanostructured BaTiO3-BaFe12O9 composite multiferroics.

    PubMed

    Trivedi, Harsh; Shvartsman, Vladimir V; Lupascu, Doru C; Medeiros, Marco S A; Pullar, Robert C; Kholkin, Andrei L; Zelenovskiy, Pavel; Sosnovskikh, Andrey; Shur, Vladimir Ya

    2015-03-14

    A study on magnetoelectric phenomena in the barium titanate-barium hexaferrite (BaTiO3-BaFe12O19) composite system, using high resolution techniques including switching spectroscopy piezoresponse force microscopy (SSPFM) and spatially resolved confocal Raman microscopy (CRM), is presented. It is found that both the local piezoelectric coefficient and polarization switching parameters change on the application of an external magnetic field. The latter effect is rationalized by the influence of magnetostrictive stress on the domain dynamics. Processing of the Raman spectral data using principal component analysis (PCA) and self-modelling curve resolution (SMCR) allowed us to achieve high resolution phase distribution maps along with separation of average and localized spectral components. A significant effect of the magnetic field on the Raman spectra of the BaTiO3 phase has been revealed. The observed changes are comparable with the classical pressure dependent studies on BaTiO3, confirming the strain mediated character of the magnetoelectric coupling in the studied composites. PMID:25683862

  10. Vertical Interface Induced Dielectric Relaxation in Nanocomposite (BaTiO3)1-x:(Sm2O3)x Thin Films

    NASA Astrophysics Data System (ADS)

    Li, Weiwei; Zhang, Wei; Wang, Le; Gu, Junxing; Chen, Aiping; Zhao, Run; Liang, Yan; Guo, Haizhong; Tang, Rujun; Wang, Chunchang; Jin, Kuijuan; Wang, Haiyan; Yang, Hao

    2015-06-01

    Vertical interfaces in vertically aligned nanocomposite thin films have been approved to be an effective method to manipulate functionalities. However, several challenges with regard to the understanding on the physical process underlying the manipulation still remain. In this work, because of the ordered interfaces and large interfacial area, heteroepitaxial (BaTiO3)1-x:(Sm2O3)x thin films have been fabricated and used as a model system to investigate the relationship between vertical interfaces and dielectric properties. Due to a relatively large strain generated at the interfaces, vertical interfaces between BaTiO3 and Sm2O3 are revealed to become the sinks to attract oxygen vacancies. The movement of oxygen vacancies is confined at the interfaces and hampered by the misfit dislocations, which contributed to a relaxation behavior in (BaTiO3)1-x:(Sm2O3)x thin films. This work represents an approach to further understand that how interfaces influence on dielectric properties in oxide thin films.

  11. Effect of oxygen content on the dielectric and ferroelectric properties of laser-deposited BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Li, C. L.; Chen, Z. H.; Zhou, Y. L.; Cui, D. F.

    2001-06-01

    BaTiO3 thin films were epitaxially grown on SrTiO3 (001) and LaNiO3/SrTiO3 substrates by pulsed laser deposition under different oxygen pressures. The oxygen content in the BaTiO3 films was determined using modified Rutherford backscattering. The structural characteristics of the films were analysed by x-ray diffraction θ/2θ scan, ϕ scan, and symmetric and asymmetric ω scans. The dielectric and ferroelectric properties of the films were measured by an impedance analyser and by a Sawyer-Tower circuit, respectively. It was found that the atomic ratio of O/Ba and Ti/Ba in the BaTiO3 films increases with oxygen pressure. The films fabricated in the intermediate oxygen pressure range of 2 to 10 Pa show the c-axis oriented tetragonal structure with a stoichiometry close to the ideal value. These films exhibit a relatively large dielectric constant, small dielectric loss and good ferroelectricity with a symmetric hysteresis loop. For growth at low oxygen pressure i.e. 0.1 Pa, the film with tetragonal c-axis orientation shows significant degradation in its dielectric properties. For a higher deposition oxygen pressure of 20 Pa, the film has tetragonal a-axis orientation and shows no ferroelectricity but has the largest dielectric constant.

  12. On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Tileli, Vasiliki; Duchamp, Martial; Axelsson, Anna-Karin; Valant, Matjaz; Dunin-Borkowski, Rafal E.; Alford, Neil Mcn.

    2014-11-01

    The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces.The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces. Electronic supplementary information (ESI) available: Magnetic moment data of the structure, linear decomposition graph of the interface layer in its constituent components of CoFe2O4 and BaTiO3, reference Fe L3,2 EEL data used for MLLS analysis of the Fe oxidation and coordination variation, and a table detailing the partial ionization cross-sections used for quantitative MLLS analysis. See DOI: 10.1039/c4nr04339a

  13. Multiferroic approach for Cr,Mn,Fe,Co,Ni,Cu substituted BaTiO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Verma, Kuldeep Chand; Kotnala, R. K.

    2016-05-01

    Multiferroic magnetoelectric (ME) at room temperature is significant for new design nano-scale spintronic devices. We have given a comparative study to report multiferroicity in BaTM0.01Ti0.99O3 [TM = Cr,Mn,Fe,Co,Ni,Cu (1 mol% each) substituted BaTiO3 (BTO)] nanoparticles. The TM ions influenced both nano-size and lattice distortion of Ti–O6 octahedra to the BTO. X ray diffraction study indicates that the dopant TM could influence lattice constants, distortion, tetragonal splitting of diffraction peaks (002/200) as well as peak shifting of diffraction angle in the BTO lattice. This can induce lattice strain which responsible to oxygen defects formation to mediate ferromagnetism. Also, the lattice strain effect could responsible to reduce the depolarization field of ferroelectricity and provide piezoelectric and magnetostrictive strains to enhance ME coupling. The size of BTO nanoparticles is varied in 13–51 nm with TM doping. The room temperature magnetic measurement indicates antiferromagnetic exchange interactions in BTO lattice with TM ions. The zero-field cooling and field cooling magnetic measurement at 500 Oe indicates antiferromagnetic to ferromagnetic transition. It also confirms that the substitution of Cr, Fe and Co into BTO could induce strong antiferromagnetic behavior. However, the substitutions of Mn, Ni and Cu have weak antiferromagnetic character. The temperature dependent dielectric measurements indicates polarization enhancement that influenced with both nano-size as well TM ions and exhibits ferroelectric phase transition with relaxor-like characteristics. Dynamic ME coupling is investigated, and the longitudinal ME voltage coefficient, α ME is equivalent to linear ME coupling coefficient, α (={\\varepsilon }{{o}}{\\varepsilon }{{r}}{α }{{ME}}) is also calculated.

  14. Comprehensive dielectric performance of bismuth acceptor doped BaTiO3 based nanocrystal thin film capacitors

    SciTech Connect

    Liu, SY; Zhang, HN; Sviridov, L; Huang, LM; Liu, XH; Samson, J; Akins, D; Li, J; O'Brien, S

    2012-11-07

    We present a novel approach to preparing bismuth acceptor doped barium titanate nanocrystal formulations that can be deposited in conjunction with polymers in order to prepare a thin film nanocomposite dielectric that exhibits desirable capacitor characteristics. Exploring the limits of dielectric function in nanocomposites is an important avenue of materials research, while paying strict attention to the overall device quality, namely permittivity, loss and equivalent series resistance (ESR). Pushing capacitor function to higher frequencies, a desirable goal from an electrical engineering point of view, presents a new set of challenges in terms of minimizing interfacial, space charge and polarization effects within the dielectric. We show the ability to synthesize BaTi0.96Bi0.04O3 or BaTi0.97Bi0.03O3 depending on nominal molar concentrations of bismuth at the onset. The low temperature solvothermal route allows for substitution at the titanium site (strongly supported by Rietveld and Raman analysis). Characterization is performed by XRD with Rietveld refinement, Raman Spectroscopy, SEM and HRTEM. A mechanism is proposed for bismuth acceptor substitution, based on the chemical reaction of the alkoxy-metal precursors involving nucleophilic addition. Dielectric analysis of the nanocrystal thin films is performed by preparing nanocrystal/PVP 2-2 nanocomposites (no annealing) and comparing BaTi0.96Bi0.04O3 and BaTi0.97Bi0.03O3 with undoped BaTiO3. Improvements of up to 25% in capacitance (permittivity) are observed, with lower loss and dramatically improved ESR, all to very high frequency ranges (>10 MHz).

  15. Surface modified BaTiO3 nanoparticles as the matrix for phospholipids and as extracting probes for LLME of hydrophobic proteins in Escherichia coli by MALDI-MS.

    PubMed

    Kailasa, Suresh Kumar; Wu, Hui-Fen

    2013-09-30

    In this paper, we report the dual function of 12-hydroxy octadecanoic acid (HOA)-modified barium titanate nanoparticles (BaTiO3 NPs) as the matrix for phospholipids (PLs) and as hydrophobic affinity probes for liquid-liquid microextraction (LLME) of hydrophobic proteins in Escherichia coli prior to their identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS). FT-IR, SEM and TEM were used for the characterization of the HOA-modified BaTiO3 NPs. The surface modified BaTiO3 NPs acted as multifunctional probes (as extracting probes and as the matrix) for the analysis of PLs by MALDI-MS. Compared to 2,5-dihydroxybenzoic acid (2,5-DHB), the HOA-modified BaTiO3 NPs provided good PLs mass spectra with similar or improved signal-to-noise (S/N) ratio, which demonstrated the potentiality of HOA-modified BaTiO3 NPs as a PLs purpose matrix. This method was found to be linear in concentration ranges of 1.0-5.0 μM and 1.0-10.0 μM for L-A-phosphatidyl-l-serine (PS) and L-A-phsophatidic acid sodium (PA) with correlation coefficient (R(2)) values from 0.9905 to 0.9987. The detection limits were 0.20-0.35 μM and 0.25-0.40 μM for PS and PA, respectively. We also demonstrated the HOA-modified BaTiO3 NPs as extracting and as preconcentrating probes for the LLME of hydrophobic proteins in E. coli prior to their identification by MALDI-MS. Thus, the surface modified BaTiO3 NPs-assisted LLME coupled with MALDI-MS provides a simple methodology for the efficient extraction and determination of hydrophobic molecules in biological samples. PMID:23953472

  16. Magnetic properties of BaTiO3 and BaTi1-xMxO3 (M=Co, Fe) nanocrystals by hydrothermal method

    NASA Astrophysics Data System (ADS)

    Yang, Lihong; Qiu, Hongmei; Pan, Liqing; Guo, Zhengang; Xu, Mei; Yin, Jinhua; Zhao, Xuedan

    2014-01-01

    BaTiO3 and BaTi1-xMxO3 (M=Co, Fe) nanocrystals were prepared by hydrothermal method. X-ray diffraction analysis indicated that all of the samples were of single-phase with tetragonal perovskite structure. The BaTiO3 prepared exhibited weak ferromagnetism rather than diamagnetism, probably due to the oxygen vacancies at the surface. Paramagnetism was observed for all BaTi1-xCoxO3 samples with 0.05≤x≤0.25. The Curie-Weiss fit revealed the paramagnetic moment per Co ion were 4.09 μB, 4.12 μB, and 4.36 μB for x=0.15, 0.20, and 0.25 respectively. Room temperature hysteresis loops of the Fe-doped BaTiO3 samples were observed at the doping level x between 0.2 and 0.5. The saturation magnetization firstly increased with increasing Fe content, but gradually decreased. The divergence was observed in the temperature dependence of the field cooling (FC) and zero-FC (ZFC) magnetization curves, indicating a spin-glass behavior arising from micromagnetic state, i.e. the mixing of ferromagnetic, and antiferromagnetic phases. The observed ferromagnetism may originate from the coupling between the secondary-nearest Fe ions and the antiferromagnetism may be due to the coupling between the nearest Fe ions. The ferromagnetic coupling competes with the antiferromagnetic coupling. Therefore, the ferromagnetic properties are predominant when the Fe doping level are at a certain range.

  17. Influence of excess Ba concentration on the dielectric nonlinearity in Mn and V-doped BaTiO3 multi layer ceramic capacitors

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Kim, Sun-Jung; Kim, Sang-Hyuk; Kim, Doo-Young

    2013-12-01

    The effect of excess Ba concentration on the dielectric nonlinearity was investigated in Mn and V-doped BaTiO3 multi layer ceramic capacitors (MLCC) under the same grain size condition, which was described by the Preisach model utilizing the first order reversal curve (FORC) distribution. The high-field dielectric constant and its ac field dependence dramatically changed increasing to a maximum and then decreasing with the increase of Ba concentration. The saturation polarization which scales to the magnitude of spontaneous polarization also showed similar behavior. These results indicate that the dependence of the dielectric constant on the Ba concentration is associated with the variation of both domain wall contribution and the magnitude of the spontaneous polarization, which could be correlated with the same dependence on the Ba concentration of the reversible FORC distribution at zero bias and the irreversible FORC distribution near origin. In the corresponding bulk specimens of the dielectrics of MLCC, almost the same amount of the Ba2TiSi2O8 second phases were detected irrespective of Ba concentration, which shows that the excess Ba incorporate into BaTiO3. Thus, low and high Ba concentration corresponds to Ba-deficient and Ba-rich or Ti-deficient BaTiO3, respectively, which results in a small spontaneous polarization and low domain wall density. The intermediate Ba concentration for the maximum dielectric constant is supposed to be near stoichiometric condition in the ABO3 structure corresponding to large spontaneous polarization and high domain wall density. The excess Ba concentration and its resultant A/B stoichiometry is a crucial factor controlling dielectric properties.

  18. Structure and Catalytic Activity of Cr-Doped BaTiO3 Nanocatalysts Synthesized by Conventional Oxalate and Microwave Assisted Hydrothermal Methods.

    PubMed

    Srilakshmi, Chilukoti; Saraf, Rohit; Prashanth, V; Rao, G Mohan; Shivakumara, C

    2016-05-16

    In the present study synthesis of BaTi1-xCrxO3 nanocatalysts (x = 0.0 ≤ x ≤ 0.05) by conventional oxalate and microwave assisted hydrothermal synthesis methods was carried out to investigate the effect of synthesis methods on the physicochemical and catalytic properties of nanocatalysts. These catalysts were thoroughly characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 physisortion, and total acidity by pyridine adsorption method. Their catalytic performance was evaluated for the reduction of nitrobenzene using hydrazine hydrate as the hydrogen source. Structural parameters refined by Rietveld analysis using XRD powder data indicate that BaTi1-xCrxO3 conventional catalysts were crystallized in the tetragonal BaTiO3 structure with space group P4mm, and microwave catalysts crystallized in pure cubic BaTiO3 structure with space group Pm3̅m. TEM analysis of the catalysts reveal spherical morphology of the particles, and these are uniformly dispersed in microwave catalysts whereas agglomeration of the particles was observed in conventional catalysts. Particle size of the microwave catalysts is found to be 20-35 nm compared to conventional catalysts (30-48 nm). XPS studies reveal that Cr is present in the 3+ and 6+ mixed valence state in all the catalysts. Microwave synthesized catalysts showed a 4-10-fold increase in surface area and pore volume compared to conventional catalysts. Acidity of the BaTiO3 catalysts improved with Cr dopant in the catalysts, and this could be due to an increase in the number of Lewis acid sites with an increase in Cr content of all the catalysts. Catalytic reduction of nitrobenzene to aniline studies reveals that BaTiO3 synthesized by microwave is very active and showed 99.3% nitrobenzene conversion with 98.2% aniline yield. The presence of Cr in the catalysts facilitates a faster reduction reaction in all the catalysts, and its effect is particularly notable in conventional synthesized catalysts. PMID:27145140

  19. Dipole spring ferroelectrics in superlattice SrTiO3/BaTiO3 thin films exhibiting constricted hysteresis loops

    SciTech Connect

    Wu, Pingping; Ma, Xingqiao; Li, Yulan; Gopalan, Venkatraman; Chen , L.Q.

    2012-03-01

    Ferroelectric superlattice heterostructures have recently been explored for potential applications in electronic devices. In this letter we employed the phase-field approach to simulate the domain structure and switching of a (BaTiO3)8/(SrTiO3)3 superlattice film constrained by a GdScO3 substrate. A constricted ferroelectric hysteresis loop was observed with a high saturation polarization but a small coercive field. The shape of the hysteresis loop is understood by analyzing the ferroelectric polarization distributions during switching. It is demonstrated that the constricted loop show a similar mechanism to the exchange coupling effect in magnetic multilayers.

  20. Monolithic integration of room-temperature multifunctional BaTiO3-CoFe2O4 epitaxial heterostructures on Si(001).

    PubMed

    Scigaj, Mateusz; Dix, Nico; Gázquez, Jaume; Varela, María; Fina, Ignasi; Domingo, Neus; Herranz, Gervasi; Skumryev, Vassil; Fontcuberta, Josep; Sánchez, Florencio

    2016-01-01

    The multifunctional (ferromagnetic and ferroelectric) response at room temperature that is elusive in single phase multiferroic materials can be achieved in a proper combination of ferroelectric perovskites and ferrimagnetic spinel oxides in horizontal heterostructures. In this work, lead-free CoFe2O4/BaTiO3 bilayers are integrated with Si(001) using LaNiO3/CeO2/YSZ as a tri-layer buffer. They present structural and functional properties close to those achieved on perovskite substrates: the bilayers are fully epitaxial with extremely flat surface, and exhibit robust ferromagnetism and ferroelectricity at room temperature. PMID:27550543

  1. Monolithic integration of room-temperature multifunctional BaTiO3-CoFe2O4 epitaxial heterostructures on Si(001)

    PubMed Central

    Scigaj, Mateusz; Dix, Nico; Gázquez, Jaume; Varela, María; Fina, Ignasi; Domingo, Neus; Herranz, Gervasi; Skumryev, Vassil; Fontcuberta, Josep; Sánchez, Florencio

    2016-01-01

    The multifunctional (ferromagnetic and ferroelectric) response at room temperature that is elusive in single phase multiferroic materials can be achieved in a proper combination of ferroelectric perovskites and ferrimagnetic spinel oxides in horizontal heterostructures. In this work, lead-free CoFe2O4/BaTiO3 bilayers are integrated with Si(001) using LaNiO3/CeO2/YSZ as a tri-layer buffer. They present structural and functional properties close to those achieved on perovskite substrates: the bilayers are fully epitaxial with extremely flat surface, and exhibit robust ferromagnetism and ferroelectricity at room temperature. PMID:27550543

  2. Microstructure, Growth Mechanism, Magnetoelectricity, and Raman Scattering of Featherlike CoFe2O4-BaTiO3 Nanostructures

    NASA Astrophysics Data System (ADS)

    Deng, Yu; Zhou, Jianxin; Wu, Di; Yu, Huiqiang; Du, Youwei

    2012-11-01

    Featherlike (CoFe2O4)0.3-(BaTiO3)0.7 (CFO-BTO) nanostructures were synthesized by a hydrothermal reaction and polymer-assisted deposition. With CFO nanopillars embedded in the BTO matrix, the nanostructures show an average diameter of 250 nm and lengths of up to 5 µm. The microstructure and growth mechanism of the nanostructures were investigated. A large magnetoelectric (ME) coefficient of 51.8 mV cm-1 Oe-1 at room temperature and a strong phonon abnormality between 110 and 140 °C are discussed.

  3. Synthesis of flower-like BaTiO3/Fe3O4 hierarchically structured particles and their electrorheological and magnetic properties.

    PubMed

    Wang, Baoxiang; Yin, Yichao; Liu, Chenjie; Yu, Shoushan; Chen, Kezheng

    2013-07-21

    Flower-like BaTiO3/Fe3O4 hierarchically structured particles composed of nano-scale structures on micro-scale materials were synthesized by a simple solvothermal approach and characterized by the means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), magnetic testing and rotary viscometer. The influences on the morphology and structure of solvothermal times, type and amount of surfactant, EG : H2O ratio, etc. were studied. Magnetic testing results show that the samples have strong magnetism and they exhibit superparamagnetic behavior, as evidenced by no coercivity and the remanence at room temperature, due to their very small sizes, observed on the M-H loop. The saturation magnetization (M(s)) value can achieve 18.3 emu g(-1). The electrorheological (ER) effect was investigated using a suspension of the flower-like BaTiO3/Fe3O4 hierarchically structured particles dispersed in silicone oil. We can observe a slight shear-thinning behavior of shear viscosity at a low shear rate region even at zero applied electric field and a Newtonian fluid behavior at high shear rate regions. PMID:23714846

  4. Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO3/SrTiO3 Composite Barriers.

    PubMed

    Wang, Lingfei; Cho, Myung Rae; Shin, Yeong Jae; Kim, Jeong Rae; Das, Saikat; Yoon, Jong-Gul; Chung, Jin-Seok; Noh, Tae Won

    2016-06-01

    Ferroelectric tunnel junctions (FTJs) have attracted increasing research interest as a promising candidate for nonvolatile memories. Recently, significant enhancements of tunneling electroresistance (TER) have been realized through modifications of electrode materials. However, direct control of the FTJ performance through modifying the tunneling barrier has not been adequately explored. Here, adding a new direction to FTJ research, we fabricated FTJs with BaTiO3 single barriers (SB-FTJs) and BaTiO3/SrTiO3 composite barriers (CB-FTJs) and reported a systematic study of FTJ performances by varying the barrier thicknesses and compositions. For the SB-FTJs, the TER is limited by pronounced leakage current for ultrathin barriers and extremely small tunneling current for thick barriers. For the CB-FTJs, the extra SrTiO3 barrier provides an additional degree of freedom to modulate the barrier potential and tunneling behavior. The resultant high tunability can be utilized to overcome the barrier thickness limits and enhance the overall CB-FTJ performances beyond those of SB-FTJ. Our results reveal a new paradigm to manipulate the FTJs through designing multilayer tunneling barriers with hybrid functionalities. PMID:27195918

  5. Ultrafast Anisotropic Optical Response and Coherent Acoustic Phonon Generation in Polycrystalline BaTiO3 -BiFeO3

    NASA Astrophysics Data System (ADS)

    Magill, B. A.; Khodaparast, G. A.; Gyu Kang, M.; Zhou, Y.; Song, H.-C.; Priya, S.

    Ultrafast optical spectroscopy can provide insight into fundamental microscopic interactions, dynamics and the coupling of several degrees of freedom. Pump/ probe studies can reveal the answer to questions like ``What are the achievable switching speeds in multiferroics?'', ``What is the influence of the crystallographic orientation and domain states on the available switching states?'', and ``What is the effect of the hetrostructure on promoting the coupling between the varying field excitations?''. In this presentation, we report on two color (400/800nm) ultrafast pump-probe differential reflectance spectroscopy of BiFeO3 - BaTiO3 structures. The (001) - BiFeO 3 - BaTiO 3 thin films were prepared using pulsed laser deposition on vicinal SrTiO3 substrates using LSMO bottom electrodes. Crystal orientation and topography were analyzed by x-ray diffraction and atomic force microscopy. The films were found to exhibit perovskite phase and in our study, we introduce the first observation of photoexcited strain waves, with the frequencies in the GHz range. Supported by the AFOSR through Grant FA9550-14-1-0376.

  6. Sheets of Vertically Aligned BaTiO3 Nanotubes Reduce Cell Proliferation but Not Viability of NIH-3T3 Cells

    PubMed Central

    Giannini, Marianna; Giannaccini, Martina; Sibillano, Teresa; Giannini, Cinzia; Liu, Dun; Wang, Zhigang; Baù, Andrea; Dente, Luciana; Cuschieri, Alfred; Raffa, Vittoria

    2014-01-01

    All biomaterials initiate a tissue response when implanted in living tissues. Ultimately this reaction causes fibrous encapsulation and hence isolation of the material, leading to failure of the intended therapeutic effect of the implant. There has been extensive bioengineering research aimed at overcoming or delaying the onset of encapsulation. Nanotechnology has the potential to address this problem by virtue of the ability of some nanomaterials to modulate interactions with cells, thereby inducing specific biological responses to implanted foreign materials. To this effect in the present study, we have characterised the growth of fibroblasts on nano-structured sheets constituted by BaTiO3, a material extensively used in biomedical applications. We found that sheets of vertically aligned BaTiO3 nanotubes inhibit cell cycle progression - without impairing cell viability - of NIH-3T3 fibroblast cells. We postulate that the 3D organization of the material surface acts by increasing the availability of adhesion sites, promoting cell attachment and inhibition of cell proliferation. This finding could be of relevance for biomedical applications designed to prevent or minimize fibrous encasement by uncontrolled proliferation of fibroblastic cells with loss of material-tissue interface underpinning long-term function of implants. PMID:25506693

  7. Magnetic and electrical properties on possible room temperature hybrid multiferroic BaTiO3/La2/3Sr1/3MnO3

    NASA Astrophysics Data System (ADS)

    Ordoñez, John Edward; Gómez, María Elena; Lopera Muñoz, Wilson; Prieto, Pedro Antonio; Thin Film Group Team; Center of Excellence on Novel Materials-CENM, Cali, Colombia Team

    2015-03-01

    We addressed to deposit the ferromagnetic phase of the La1-xSrxMnO3 and the ferroelectric BaTiO3 for possible hybrid multiferroic heterostructure. We have optimized the growth parameters for depositing BaTiO3(BTO) / La2/3Ca1/3MnO3(LCMO) / (001) SrTiO3 by sputtering RF and DC, respectively, in pure oxygen atmosphere and a substrate temperature of 830°C. Keeping fixed the magnetic layer thickness (tLSMO = 40 nm) and varying the thickness of the ferroelectric layer (tBTO = 20, 40, 80, 100 nm). We want to point out the influence of the thicknesses ratio (tBTO/tLSMO) on electrical and magnetic properties. From x-ray diffraction (XRD) analysis, we found the bragg peaks for LSMO maintain its position but BTO peak shift to lower Bragg angle indicating a strained BTO film. Magnetization and polarization measurements indicate a possible multiferroic behavior in the bilayers. Hysteresis loop measurements of bilayers show ferromagnetic behavior. Authors thank Instituto de Nanociencia de Aragón, Zaragoza, Spain. Work partially supported by COLCIENCIAS-UNIVALLE Project 110656933104 Contract No. 2013-0002, CI 7917 and CI 7978.

  8. Effects of Microstructure on the Curie Temperature in BaTiO3-Ho2O3-MgO-SiO2 System

    NASA Astrophysics Data System (ADS)

    Nishikawa, Jun; Hagiwara, Tomoya; Kobayashi, Keisuke; Mizuno, Youichi; Kishi, Hiroshi

    2007-10-01

    In response to the demand for multilayer ceramic capacitors (MLCCs) with stable capacitance in a wide temperature range, a material with high Curie temperature (Tc) has recently been being developed. In this study, we investigated the effects of microstructure on the Tc for the BaTiO3-Ho2O3-MgO-SiO2 system with various Ho and Si contents. As the Ho/Si ratio increased, the secondary phase (Pyrochlore) increased; further, the tetragonality of the BaTiO3 phase at 125 °C increased, and the Tc shifted toward higher temperatures. A transmission electron microscope equipped with energy dispersive X-ray spectrometer (TEM-EDS) analysis revealed that the core-shell structure is the key to understand this Tc shift: a thin shell with a high concentration of Ho was the most promising microstructure for a high-Tc material in this composition system. We discussed the mechanism of the Tc shift from the viewpoints of both microstructure and crystal structure.

  9. Incorporation of Zn(2+) ions into BaTiO3:Er(3+)/Yb(3+) nanophosphor: an effective way to enhance upconversion, defect luminescence and temperature sensing.

    PubMed

    Mahata, Manoj Kumar; Koppe, Tristan; Mondal, Tanusree; Brüsewitz, Christoph; Kumar, Kaushal; Kumar Rai, Vineet; Hofsäss, Hans; Vetter, Ulrich

    2015-08-28

    Ferroelectric BaTiO3 became a multifunctional material via doping of lanthanide ions (0.3 mol% Er(3+)/3.0 mol% Yb(3+)) and subsequently upconversion luminescence was enhanced by incorporation of Zn(2+) ions. Upconversion luminescence of BaTiO3:Er(3+)/Yb(3+) perovskite nanophosphor has been studied using 800 and 980 nm laser excitations. The emission dynamics is studied with respect to its dependence on input power and external temperature including lifetime. Based on time-resolved spectroscopy, it is inferred that two types of Er(3+) sites are present in the barium titanate lattice. The first one is a short lived component (minor species) present at 6-coordinated Ti-sites of low symmetry while the second one is a long lived component (major species), present at 12-coordinated Ba-sites with high symmetry. The influence of the introduction of Zn(2+) ions on the lifetime of (4)S3/2 and (4)F9/2 levels of Er(3+) ions is also investigated. Enhanced temperature sensing performance (120 K to 505 K) of the material is observed using the fluorescence intensity ratio technique, employing the emission from the thermally coupled, (2)H11/2 and (4)S3/2 energy levels of Er(3+) ions. The defect luminescence of the material is also found to increase upon Zn-doping. PMID:26206553

  10. Large electrostrain and high optical temperature sensitivity in BaTiO3-(Na0.5Ho0.5)TiO3 multifunctional ferroelectric ceramics.

    PubMed

    Li, Jun; Chai, Xiaona; Wang, Xusheng; Xu, Chao-Nan; Gu, Yihao; Zhao, Haifeng; Yao, Xi

    2016-08-01

    Ferroelectric (1 -x)BaTiO3-x(Na0.5Ho0.5)TiO3 ceramics with ferroelectric and up-conversion luminescent multifunctions were designed and fabricated by a solid state reaction process. Their structure, ferroelectric, piezoelectric, up-conversion photoluminescence and relative optical temperature sensing properties were investigated systematically. Crystal structure analysis and Rietveld refinements based on the powder X-ray diffraction data show that the ceramics crystallized in the tetragonal perovskite space group P4mm at room temperature. Enhanced electrical properties and strong green up-conversion luminescence with thermally coupled green emission bands centered at 523 and 553 nm were observed. For a typical sample x equals 0.05, a large electrostrain of 0.279% was obtained under a 70 kV cm(-1) electric field that is comparable to that of the PZT4. Meanwhile, the excellent optical temperature sensitivity (0.0063 K(-1) at 480 K) is higher than that of Er-doped BaTiO3 nanocrystal materials. The results suggest that the BaTiO3-(Na0.5Ho0.5)TiO3 material should be an attractive material for piezoelectric actuator and temperature sensing device applications. PMID:27244098

  11. 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

  12. Comparative ab initio calculations of SrTiO3/BaTiO3 and SrZrO3/PbZrO3 (0 0 1) heterostructures

    NASA Astrophysics Data System (ADS)

    Piskunov, Sergei; Eglitis, Roberts I.

    2016-05-01

    Using a B3PW hybrid exchange-correlation functional within the density functional theory (DFT) we calculated from the first principles the electronic structure of BaTiO3/SrTiO3 and PbZrO3/SrZrO3 (0 0 1) interfaces. The optical band gap of both BaTiO3/SrTiO3 and PbZrO3/SrZrO3 (0 0 1) interfaces depends mostly from BaO or TiO2 and SrO or ZrO2 termination of the upper layer, respectively. Based on the results of our calculations we predict increase of the Ti-O and Zr-O chemical bond covalency near the SrTiO3/BaTiO3 and SrZrO3/PbZrO3 (0 0 1) interfaces as compared to the BaTiO3 and PbZrO3 bulk.

  13. 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

  14. Enhanced dielectric properties of three-phase-percolative composites based on thermoplastic-ceramic matrix (BaTiO3 + PVDF) and ZnO radial nanostructures.

    PubMed

    Wang, Guangsheng

    2010-05-01

    Three-phase-percolative composites with ZnO radial nanoclusters (R-ZnO) and BaTiO(3) (BT) nanoparticles embedded into polyvinylidene fluoride (PVDF) were prepared by using a simple blending and hot-molding technique. The BT + PVDF composite with a volume fraction of 30 vol % BT particles were employed as a thermoplastic-ceramic matrix. Compared with the two-phase-percolative composites of R-ZnO/PVDF, the three-phase-percolative (R-ZnO/(BT + PVDF)) composites showed enhanced dielectric constant and decreased dielectric loss. The percolation theory was used to explain the experimental results. The increased percolation threshold was studied in detail, and the thermal stability was also investigated. PMID:20415481

  15. High-rate performance of ferroelectric BaTiO3-coated LiCoO2 for Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Teranishi, Takashi; Yoshikawa, Yumi; Sakuma, Ryo; Hashimoto, Hideki; Hayashi, Hidetaka; Kishimoto, Akira; Fujii, Tatsuo

    2014-10-01

    The high charge-discharge rate characteristics of composite cathodes consisting of ferroelectric BaTiO3 (BT)-coated LiCoO2 (LC), synthesized via a simple sol-gel route, were evaluated, and the rate showed stepwise increases to as high as 5C. The LC-BT composite cathode annealed at 600 °C, LC-BT-600, notably retained high capacities, i.e., 122 mAh/g at 30 cycles, 5C and 99 mAh/g at 60 cycles, 5C. These capacities corresponded to 83% and 67% of the initial values and were as high as 158% and 245% of the capacities of bare LC over the same cycles, respectively. The ferroelectricity of the coated BT contributed to the improvement in high-rate performance.

  16. One — dimensional laser beam steering using frequency detuning in two — wave mixing with a BaTiO 3 crystal

    NASA Astrophysics Data System (ADS)

    Dharmsaktu, K. S.; Joseph, Joby; Singh, Kehar

    2000-06-01

    We demonstrate a method of one-dimensional laser beam deflection using frequency detuning in two-wave mixing. Energy exchange between the interfering beams in a photo-refractive BaTiO 3 crystal has been used for deflection of a pump beam into predetermined probe beam directions. A one-dimensional array of several beams is generated from a single probe beam, employing a piezo-mirror and beam splitter combination. Probe beams so produced are detuned by exciting the piezo-mirror with a periodic near-saw-tooth voltage so as to produce running fringes. However, stable holographic gratings are recorded by matching the frequency of the probe beam with that of a pump beam reflected from another vibrating piezo-mirror, thereby controlling the direction of beam deflection.

  17. Induced Ti magnetization at La0.7Sr0.3MnO3 and BaTiO3 interfaces

    DOE PAGESBeta

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; Freeland, J. W.; Zhou, H.; Steadman, P.; Bencok, P.; Leon, C.; Santamaria, J.

    2016-04-01

    In artificial multiferroics hybrids consisting of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric BaTiO3 epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. Moreover, the Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. But, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures.

  18. Critical interparticle distance for the remarkably enhanced dielectric constant of BaTiO3-Ag hybrids filled polyvinylidene fluoride composites

    NASA Astrophysics Data System (ADS)

    Luo, Suibin; Yu, Shuhui; Fang, Fang; Lai, Maobai; Sun, Rong; Wong, Ching-Ping

    2014-06-01

    Discrete nano Ag-deposited BaTiO3 (BT-Ag) hybrids with varied Ag content were synthesized, and the hybrids filled polyvinylidene fluoride (PVDF) composites were prepared. The effect of Ag content on the dielectric properties of the composites were analyzed based on the diffused electrical double layer theory. Results showed that with a higher Ag content in BT-Ag hybrids, the dielectric constant of BT-Ag/PVDF composites increases fast with the filler loading, while the dielectric loss and conductivity showed a suppressed and moderate increase. The dielectric constant of BT-0.61Ag/PVDF (61 wt. % of Ag in BT-Ag hybrid) composites reached 613, with the dielectric loss of 0.29 at 1 kHz. It was deduced that remarkably enhanced dielectric constant appeared when the interparticle distance decreased to a critical value of about 20 nm.

  19. Dipole spring ferroelectrics in superlattice SrTiO3/BaTiO3 thin films exhibiting constricted hysteresis loops

    SciTech Connect

    Wu, Pingping; Ma, Xingqiao; Li, Yulan; Gopalan, Venkatraman; Chen , L.Q.

    2012-03-01

    Ferroelectric superlattice heterostructures have recently been explored for potential applications in electronic devices. In this letter we employed the phase-field approach to simulate the domain structure and switching of a (BaTiO3)8/(SrTiO3)3 superlattice film constrained by a GdScO3 substrate. A constricted ferroelectric hysteresis loop was observed with a high saturation polarization but a small coercive field. The shape of the hysteresis loop is understood by analyzing the ferroelectric polarization distributions during switching. It is demonstrated that the multilayers stack behave as dipole spring ferroelectric, named in analogy to exchange spring magnets in magnetic multilayers that show similar loops.

  20. Inhomogeneity issues in the growth of Na 1/2Bi 1/2TiO 3-BaTiO 3 single crystals

    NASA Astrophysics Data System (ADS)

    Bubesh Babu, J.; Madeswaran, G.; He, Ming; Zhang, D. F.; Chen, X. L.; Dhanasekaran, R.

    2008-01-01

    Lead-free piezoelectric single crystals of Na 1/2Bi 1/2TiO 3-BaTiO 3 (NBT-BT) have been grown by flux and zone melting techniques. Growth was carried out by employing two flux systems: (a) Bi 2O 3 and (b) Bi 2O 3 and Na 2CO 3 fluxes. In order to avoid the serious problem of composition variations suffered in flux growth technique, metal strip heated zone melting (MSHZM) technique was employed for the growth of NBT-BT crystals. Inductively coupled plasma (ICP) analysis was carried out for the grown crystals and the composition variations in the crystals obtained from flux and MSHZM techniques were analyzed. Results reveal that the composition variations suffered in the flux-grown crystals have been avoided by adopting the zone melting technique.

  1. Thermally stimulated depolarization current analysis for the dielectric aging of Mn and V-codoped BaTiO3 multi layer ceramic capacitor

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Park, Jae-Sung; Kim, Sang-Hyuk; Kim, Doo-Young

    2013-07-01

    Dielectric aging of Mn and V-codoped BaTiO3 was investigated. The increase of V concentration had little influence on aging, whereas that of Mn increased it. Thermally stimulated depolarization current (TSDC) of low Mn concentration specimen showed one peak, whereas Mn-increased specimen showed two peaks. The first and second peak is supposed to be caused by the phase transition of the undoped core region and the defect dipole of Mn such as MnTi″-VO•• or MnTi'-VO••, respectively. High TSDC associated with the defect dipole of Mn and significant aging rate experimentally demonstrates that the dielectric aging is controlled by the defect dipole.

  2. Induced Ti magnetization at La0.7Sr0.3MnO3 and BaTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; Freeland, J. W.; Zhou, H.; Steadman, P.; Bencok, P.; Leon, C.; Santamaria, J.

    2016-04-01

    In artificial multiferroics hybrids consisting of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric BaTiO3 epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. The Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. However, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures.

  3. Effect of solution combusted TiO2 nanopowder within commercial BaTiO3 dielectric layer on the photoelectric properties for AC powder electroluminescence devices.

    PubMed

    Park, Sung; Choi, Gil Rak; Kim, Youn Cheol; Lee, Jae Chun; Lee, Ju Hyeon

    2013-05-01

    A unique synthesis method was developed, which is called solution combustion method (SCM). TiO2 nanopowder was synthesized by this method. This SCM TiO2 nanopowder (-35 nm) was added to the dielectric layer of AC powder electroluminescence (EL) device. The dielectric layer was made of commercial BaTiO3 powder (-1.2 microm) and binding polymer. 0, 5, 10 and 15 wt% of SCM TiO2 nanopowder was added to the dielectric layer during fabrication of AC powder EL device respectively. Dielectric constant of these four kinds of dielectric layers was measured. The brightness and current density of AC powder EL device were also measured. When 10 wt% of SCM TiO2 nanopowder was added, dielectric constant and brightness were increased by 30% and 101% respectively. Furthermore, the current density was decreased by 71%. This means that the brightness was double and the power consumption was one third. PMID:23858874

  4. Effects of sintering temperature on the electric properties of Mn-modified BiFeO3-BaTiO3 bulk ceramics

    NASA Astrophysics Data System (ADS)

    Kim, D. J.; Lee, M. H.; Park, J. S.; Kim, M.-H.; Song, T. K.; Kim, W.-J.; Jang, K. W.; Kim, S. S.; Do, D.

    2015-04-01

    Mn-modified 0.67Bi1.05FeO3-0.33BaTiO3 ceramics were prepared via a solid-state reaction process by using a quenching method after a sintering process at various temperatures. We obtained ceramics with improved electric properties within a narrow sintering temperature range. At the optimized sintering temperature of 990 °C, improved ferroelectric and piezoelectric properties were observed in the 1-mol% Mn-modified ceramic. The small-field and the large-field piezoelectric constants ( d 33 and d 33*) were 135 pC/N and 250 pm/V, respectively, and the leakage current density was about 2.4 × 10-7 A/cm2. The remnant polarization ( P r ) and the coercive field ( E c ) were 29 μC/cm2 and 28 kV/cm, respectively.

  5. Layer by layer growth of BaTiO 3 thin films with extremely smooth surfaces by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, H. S.; Ma, K.; Cui, D. F.; Peng, Z. Q.; Zhou, Y. L.; Lu, H. B.; Chen, Z. H.; Li, L.; Yang, G. Z.

    1997-05-01

    Using pure ozone-assisted laser molecular beam epitaxy, we have grown c-axis-oriented single crystal BaTiO 3 thin films on SrTiO 3 substrates at temperatures ( Ts) of 400-750°C and under ambient gas pressures of 5 × 10 -5 to 1 × 10 -1 Pa, respectively. Stripy reflection high-energy electron diffraction (RHEED) patterns and regular RHEED intensity oscillations reveal the smooth surface and layer-by-layer epitaxial growth of the films. Scanning electron microscopy analysis shows that the films are free of pinholes, grain boundaries and outgrowths on the surface. In addition, we found a strong dependence of the film lattice constant c on Ts, which might be related to the strain in the film.

  6. Elastic excitations in BaTiO3 single crystals and ceramics: Mobile domain boundaries and polar nanoregions observed by resonant ultrasonic spectroscopy

    NASA Astrophysics Data System (ADS)

    Salje, Ekhard K. H.; Carpenter, Michael A.; Nataf, Guillaume F.; Picht, Gunnar; Webber, Kyle; Weerasinghe, Jeevaka; Lisenkov, S.; Bellaiche, L.

    2013-01-01

    The dynamic properties of elastic domain walls in BaTiO3 were investigated using resonance ultrasonic spectroscopy (RUS). The sequence of phase transitions is characterized by minima in the temperature dependence of RUS resonance frequencies and changes in Q factors (resonance damping). Damping is related to the friction of mobile twin boundaries (90° ferroelectric walls) and distorted polar nanoregions (PNRs) in the cubic phase. Damping is largest in the tetragonal phase of ceramic materials but very low in single crystals. Damping is also small in the low-temperature phases of the ceramic sample and slightly increases with decreasing temperature in the single crystal. The phase angle between the real and imaginary part of the dynamic response function changes drastically in the cubic and tetragonal phases and remains constant in the orthorhombic phase. Other phases show a moderate dependence of the phase angle on temperature showing systematic changes of twin microstructures. Mobile twin boundaries (or sections of twin boundaries such as kinks inside twin walls) contribute strongly to the energy dissipation of the forced oscillation while the reduction in effective modulus due to relaxing twin domains is weak. Single crystals and ceramics show strong precursor softening in the cubic phase related to polar nanoregions (PNRs). The effective modulus decreases when the transition point of the cubic-tetragonal transformation is approached from above. The precursor softening follows temperature dependence very similar to recent results from Brillouin scattering. Between the Burns temperature (≈586 K) and Tc at 405 K, we found a good fit of the squared RUS frequency [˜Δ (C11-C12)] to a Vogel-Fulcher process with an activation energy of ˜0.2 eV. Finally, some first-principles-based effective Hamiltonian computations were carried out in BaTiO3 single domains to explain some of these observations in terms of the dynamics of the soft mode and central mode.

  7. Interplay between size, composition, and phase transition of nanocrystalline Cr(3+)-doped BaTiO3 as a path to multiferroism in perovskite-type oxides.

    PubMed

    Ju, Ling; Sabergharesou, Tahereh; Stamplecoskie, Kevin G; Hegde, Manu; Wang, Ting; Combe, Nicole A; Wu, Hongyu; Radovanovic, Pavle V

    2012-01-18

    Multiferroics, materials that exhibit coupling between spontaneous magnetic and electric dipole ordering, have significant potential for high-density memory storage and the design of complex multistate memory elements. In this work, we have demonstrated the solvent-controlled synthesis of Cr(3+)-doped BaTiO(3) nanocrystals and investigated the effects of size and doping concentration on their structure and phase transformation using X-ray diffraction and Raman spectroscopy. The magnetic properties of these nanocrystals were studied by magnetic susceptibility, magnetic circular dichroism (MCD), and X-ray magnetic circular dichroism (XMCD) measurements. We observed that a decrease in nanocrystal size and an increase in doping concentration favor the stabilization of the paraelectric cubic phase, although the ferroelectric tetragonal phase is partly retained even in ca. 7 nm nanocrystals having the doping concentration of ca. 5%. The chromium(III) doping was determined to be a dominant factor for destabilization of the tetragonal phase. A combination of magnetic and magneto-optical measurements revealed that nanocrystalline films prepared from as-synthesized paramagnetic Cr(3+)-doped BaTiO(3) nanocrystals exhibit robust ferromagnetic ordering (up to ca. 2 μ(B)/Cr(3+)), similarly to magnetically doped transparent conducting oxides. The observed ferromagnetism increases with decreasing constituent nanocrystal size because of an enhancement in the interfacial defect concentration with increasing surface-to-volume ratio. Element-specific XMCD spectra measured by scanning transmission X-ray microscopy (STXM) confirmed with high spatial resolution that magnetic ordering arises from Cr(3+) dopant exchange interactions. The results of this work suggest an approach to the design and preparation of multiferroic perovskite materials that retain the ferroelectric phase and exhibit long-range magnetic ordering by using doped colloidal nanocrystals with optimized composition and size as functional building blocks. PMID:22239686

  8. Structure-Curie temperature relationships in BaTiO3-based ferroelectric perovskites: Anomalous behavior of (Ba ,Cd )TiO3 from DFT, statistical inference, and experiments

    NASA Astrophysics Data System (ADS)

    Balachandran, Prasanna V.; Xue, Dezhen; Lookman, Turab

    2016-04-01

    One of the key impediments to the development of BaTiO3-based materials as candidates to replace toxic-Pb-based solid solutions is their relatively low ferroelectric Curie temperature (TC). Among many potential routes that are available to modify TC, ionic substitutions at the Ba and Ti sites remain the most common approach. Here, we perform density functional theory (DFT) calculations on a series of A TiO3 and Ba B O3 perovskites, where A =Ba , Ca, Sr, Pb, Cd, Sn, and Mg and B =Ti , Zr, Hf, and Sn. Our objective is to study the relative role of A and B cations in impacting the TC of the tetragonal (P 4 m m ) and rhombohedral (R 3 m ) ferroelectric phases in BaTiO3-based solid solutions, respectively. Using symmetry-mode analysis, we obtain a quantitative description of the relative contributions of various divalent (A ) and tetravalent (B ) cations to the ferroelectric distortions. Our results show that Ca, Pb, Cd, Sn, and Mg have large mode amplitudes for ferroelectric distortion in the tetragonal phase relative to Ba, whereas Sr suppresses the distortions. On the other hand, Zr, Hf, and Sn tetravalent cations severely suppress the ferroelectric distortion in the rhombohedral phase relative to Ti. In addition to symmetry modes, our calculated unit-cell volume also agrees with the experimental trends. We subsequently utilize the symmetry modes and unit-cell volumes as features within a machine learning approach to learn TC via an inference model and uncover trends that provide insights into the design of new high-TCBaTiO3 -based ferroelectrics. The inference model predicts CdTiO3-BaTiO3 solid solutions to have a higher TC and, therefore, we experimentally synthesized these solid solutions and measured their TC. Although the calculated mode strength for CdTiO3 in the tetragonal phase is even larger than that for PbTiO3, the TC of CdTiO3-BaTiO3 solid solutions in the tetragonal phase does not show any appreciable enhancement. Thus, CdTiO3-BaTiO3 does not follow the inference model, which is based on established data and trends for A TiO3 . Rather, our experimental phase diagram for CdTiO3-BaTiO3 suggests that it behaves markedly differently from any other BaTiO3-based systems studied so far.

  9. FAST TRACK COMMUNICATION: Re-entrant-like relaxor behaviour in the new 0.99BaTiO3 0.01AgNbO3 solid solution

    NASA Astrophysics Data System (ADS)

    Lei, Chao; Ye, Zuo-Guang

    2008-06-01

    A new solid solution of 0.99BaTiO3-0.01AgNbO3 was prepared by a solid state reaction. Its structural, dielectric and ferroelectric properties were investigated. Besides the three phase transitions associated with pure BaTiO3, the dielectric permittivity shows an additional peak around 100 °C. This peak exhibits a dielectric relaxation satisfying the Vogel-Fulcher law, indicating typical relaxor behaviour. The relaxor state occurs after the paraelectric to ferroelectric phase transition upon cooling, i.e., inside the ferroelectric phase, indicating a re-entrant-like phenomenon. This unusual phase transition sequence has never been reported in canonical lead-based ferroelectrics. Moreover, the relaxor state arises from a tetragonal phase rather than from a cubic phase as observed in conventional complex perovskite relaxors.

  10. Piezoelectric properties of (K0.5Na0.5)NbO3-BaTiO3 lead-free ceramics prepared by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Men, Tian-Lu; Yao, Fang-Zhou; Zhu, Zhi-Xiang; Wang, Ke; Li, Jing-Feng

    2016-07-01

    (K,Na)NbO3 (KNN)-based lead-free piezoceramics have been the spotlight in search for practically viable candidates to replace the hazardous but dominating lead-containing counterparts. In this work, BaTiO3 (BT) modified KNN ceramics were fabricated by spark plasma sintering (SPS) and the influence of BT content as well as sintering temperature on the phase structure, microstructure, and electrical properties were investigated. It was found that the 0.96(Na0.5K0.5)NbO3-0.04BaTiO3 (BT4) ceramics sintered at 1000∘C have the optimal performance. Additionally, in-depth analysis of the electrical hysteresis revealed that the internal bias field originating from accumulation of space charges at grain boundaries is responsible for the asymmetry in the hysteresis loops.

  11. Magnetic properties of BaTiO3/La0.7Sr0.3MnO3 thin films integrated on Si(100)

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Fan, Wu; Prater, J. T.; Narayan, J.

    2014-12-01

    Two-phase multiferroic heterostructures composed of room-temperature ferroelectric BaTiO3 (BTO) and ferromagnetic La0.7Sr0.3MnO3 (LSMO) epitaxial thin films were grown on technologically important substrate Si (100). Bilayers of BTO/LSMO thin films display ferromagnetic Curie transition temperatures of ˜350 K, close to the bulk value, which are independent of BTO films thickness in the range of 25-100 nm. Discontinuous magnetization jumps associated with BTO structural transitions were suppressed in M(T) curves, probably due to substrate clamping effect. Interestingly, at cryogenic temperatures, the BTO/LSMO structure with BTO layer thickness of 100 nm shows almost 2-fold higher magnetic coercive field, 3-fold reduction in saturation magnetization, and improved squareness compared to the sample without BTO. We believe that the strong in-plane spin pinning of the ferromagnetic layer induced by BTO layer at BTO/LSMO interface could cause such changes in magnetic properties. This work forms a significant step forward in the integration of two-phase multiferroic heterostructures for CMOS applications.

  12. Visible light absorption in La, Cr co-doped SrTiO3 and BaTiO3 for ferroelectric photovoltaics

    NASA Astrophysics Data System (ADS)

    Comes, Ryan; McBriarty, Martin; Ong, Phuong-Vu; Heald, Steve; Carroll, Gerard; Gamelin, Daniel; Freedy, Keren; Smolin, Sergey; Baxter, Jason; Kaspar, Tiffany; Bowden, Mark; Sushko, Peter; Chambers, Scott

    Ferroelectric materials offer intriguing possibilities as photovoltaic materials, as their built-in electric field is ideal for separation of optically-excited electron-hole pairs without the need for a p-n junction. However, the majority of ferroelectrics suffer from a wide optical band gap outside the visible range. By co-doping La and Cr into epitaxial SrTiO3 and BaTiO3 (SLTCO/BLTCO) thin films, we show that absorption in the visible light regime can be achieved with a band gap of ~2.3 eV while preserving ideal stoichiometry. Through x-ray photoelectron spectroscopy, spectroscopic ellipsometry, photoconductivity and ultrafast pump-probe transient reflectance measurements, we show that visible light excitation of Cr 3d valence electrons into the Ti 3d conduction band produces optical carriers. Using piezoresponse force microscopy and polarized x-ray absorption fine structure measurements, we measure the ferroelectric polarization of the doped BLTCO films. These results are compared to density functional theory models to understand the optical and structural properties of the materials.

  13. Multiferroic Ni0.6Zn0.4Fe2O4-BaTiO3 nanostructures: Magnetoelectric coupling, dielectric, and fluorescence

    NASA Astrophysics Data System (ADS)

    Verma, Kuldeep Chand; Singh, Sukhdeep; Tripathi, S. K.; Kotnala, R. K.

    2014-09-01

    Multiferroic nanostructures of Ni0.6Zn0.4Fe2O4-BaTiO3 (NZF/BT) have been prepared by two synthesis routes, i.e., chemical combustion (CNZF/BT) and hydrothermal (HNZF/BT). The synthesis of CNZF/BT results in nanoparticles of average size 4 nm at 500 °C annealing. However, the synthesis of HNZF/BT with hydrolysis temperature 180 °C/48 h shows nanowires of diameter 3 nm and length >150 nm. A growth mechanism in the fabrication of nanoparticles and wires is given. X-ray diffraction is used to identify the crystalline phase. The transmission electron microscopy shows the dimensions of NZF/BT nanostructures. The ferromagnetism, ferroelectricity, and magnetoelectric coupling show more enhancements in HNZF/BT nanowires than CNZF/BT nanoparticles. The observed polarization depends upon shape of nanostructures, tetragonal phase, and epitaxial strain. The tension induced by the surface curvature of nanowire counteracts the near-surface depolarizing effect and meanwhile leads to unusual enhancement of polarization. The ferromagnetism depends upon superficial spin canting, spin pinning of nanocomposite, and oxygen vacancy clusters. The magnetoelectric coefficient as the function of applied dc magnetizing field under ac magnetic field 5 Oe and frequency 1093 Hz is measured. The nanodimensions of NZF/BT are observed dielectric constant up to 120 MHz. The optical activity of NZF/BT nanostructures is shown by Fluorescence spectra.

  14. Electric Field and Structural Phase Transition Induced Magnetization Effects in BaTiO3 -FeRh Heterostructures Probed using Polarized Neutron Reflectometry

    NASA Astrophysics Data System (ADS)

    Bennett, Steven; Ward, Thomas; Biegalski, Michael; Wong, Tony; Liu, Zhiqi; Ambaye, Haile; Glavic, Artur

    2015-03-01

    The ability to change the magnetic state of a material with an electric field opens up a plethora of possible devices in spintronics and memory applications. A strong candidate material for such a control is FeRh, whose magneto-structural phase transition from antiferromagnetic (AFM) to ferromagnetic (FM) at T ~350K, has shown to be controllably changed by an electric field when grown on ferroelectric BaTiO3 (BTO). It has been suggested that this shift is largely due to the -0.47% in plane compressive strain induced by the piezoelectric BTO. Here we show a sharp repeatable change in magnetization as the system is heated/cooled through the tetragonal to orthorhombic (280-290K) and orthorhombic to rhombohedral (180-205K) crystalline phase transitions of BTO. To further characterize the effect polarized neutron reflectometry (PNR) was used to evolve the depth profile of magnetization in FeRh within the temperature vicinity of these transitions with and without the application of electric field. This work was carried out at the Center for Nanophase Materials Sciences (CNMS) and the Spallation Neutron Source (SNS) supported by the Scientific User Facilities Divisions, Office of Basic Energy Sciences, DOE.

  15. Phase Structure, Piezoelectric and Multiferroic Properties of SmCoO3-Modified BiFeO3-BaTiO3 Lead-Free Ceramics

    NASA Astrophysics Data System (ADS)

    Jiang, Na; Tian, Mijie; Luo, Lingling; Zheng, Qiaoji; Shi, Dongliang; Lam, Kwok Ho; Xu, Chenggang; Lin, Dunmin

    2016-01-01

    (0.75- x)BiFeO3-0.25BaTiO3- xSmCoO3 + 1 mol.% MnO2 lead-free multiferroic ceramics were synthesized by a conventional ceramic fabrication technique. The effects of SmCoO3 on phase structure, piezoelectricity and multiferroicity of the ceramics were studied. All the ceramics can be well sintered at a low sintering temperature of 960°C. The crystalline structure of the ceramics is transformed from rhombohedral to tetragonal symmetry with increasing the amount of SmCoO3. A morphotropic phase boundary of rhombohedral and tetragonal phases is formed at x = 0.01-0.04. A small amount of SmCoO3 is shown to improve the ferroelectric, piezoelectric and magnetoelectric properties of the ceramics. For the ceramics with x = 0.01-0.03, enhanced resistivity ( R ˜ 1.2 × 109 Ω cm to 2.1 × 109 Ω cm), piezoelectricity ( d 33 ˜ 65 pC/N to 106 pC/N) and ferroelectricity ( P r ˜ 6.38 μC/cm2 to 22.89 μC/cm2) are obtained. The ferromagnetism of the materials is greatly enhanced by the doping of SmCoO3 such that a very high magnetoelectric coefficient of ˜742 mV/(cm Oe) is obtained at x = 0.01, suggesting a promising potential in multiferroic devices.

  16. In situ impedance analysis on BaTiO3-LiCoO2 composite cathodes for lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Teranishi, Takashi; Yoshikawa, Yumi; Sakuma, Ryo; Okamura, Hirokazu; Hayashi, Hidetaka; Kishimoto, Akira; Takeda, Yasuo

    2015-10-01

    In situ electrochemical impedance spectroscopy (EIS) was undertaken to investigate the contribution of a ferroelectric artificial solid electrolyte interface (SEI) to the enhancement of the rate capability of lithium ion batteries. Resistance elements, consisting of the cell reactions, the resistance of the electrolyte, Rsol, that of the Li metal anode reaction, RLi, and the charge transfer resistance, Rct, were measured. A small ferroelectric BaTiO3 (BT) load, ˜1 mol %, notably reduced Rct and Rsol compared with bare LiCoO2 (LC), indicating that loaded ferroelectric BT SEIs effectively promote Li inter/deintercalation into and from the active material, LC, and restrict cobalt ion dissolution into the electrolyte liquid. Lower Rct and Rsol resulted in a significantly higher capacity retention ratio at a 10 C rate compared with the initial cycle for small BT load, ˜1 mol %. The capacity retention dropped rapidly, accompanied by a slight increase in Rct for larger BT loads, 5 and 15 mol %, which may be attributed to the thicker BT layer and the existence of the impurity phase, BaCO3. These results imply that the ferroelectric SEI affected the kinetics of mobile Li ions at the cathode-electrolyte interface, significantly enhancing the rate capability.

  17. Non-isothermal crystallization kinetics of the BaTiO3-KNbO3-SiO2 glass

    NASA Astrophysics Data System (ADS)

    Yang, H. Y.; Yang, Y. S.; Choi, H. W.

    2015-04-01

    We have investigated the non-isothermal formation kinetics of nanocrystals from the BaTiO3-KNbO3-SiO2 (BKSO) glass at temperatures from room temperature to 800 °C. The thermal characteristics and the structural transformations of the BKSO glass have been studied by means of a differential thermal analysis and X-ray diffraction. The crystallization of BKSO glass is found to accompany a single-step occurrence of a tetragonal Ba3TiNb4O15 nanocrystal structure. During the crystallization, a nanocrystals with a size of ˜40 nm at the initial stage grow with increasing temperature and reach a size of ˜120 nm by the time the crystallization finishes. We use the non-isothermal model of Johnson-Mehl-Avrami-Kolmogorov to characterize the kinetics of the crystallization process for the BKSO glass. The Avrami exponent of 3.5 indicates that the crystallization mechanisms is an increasing nucleation rate with diffusion-controlled growth. In the view of applications, providing information on how to control the size of nanograins systematically by simply controlling the annealing temperature of the glass state, as described in this study, should be useful.

  18. Effects of starting powder and thermal treatment on the aerosol deposited BaTiO3 thin films toward less leakage currents

    PubMed Central

    2014-01-01

    To prepare high-density integrated capacitors with low leakage currents, 0.2-μm-thick BaTiO3 thin films were successfully deposited on integrated semiconductor substrates at room temperature by the aerosol deposition (AD) method. In this study, the effects of starting powder size were considered in an effort to remove macroscopic defects. A surface morphology of 25.3 nm and an interface roughness of less than 50 nm were obtained using BT-03B starting powder. The nano-crystalline thin films achieved after deposition were annealed at various temperatures to promote crystallization and densification. Moreover, the influence of rapid thermal annealing process on the surface morphology and crystal growth was evaluated. As the annealing temperature increased from room temperature to 650°C, the root mean square (RMS) roughness decreased from 25.3 to 14.3 nm. However, the surface was transformed into rough performance at 750°C, which agreed well with the surface microstructure trend. Moreover, the crystal growth also reveals the changes in surface morphology via surface energy analysis. PMID:25246860

  19. Metastable antiparallel polarization configurations in BaTiO3/PbZr0.2Ti0.8O3 epitaxial bilayer

    NASA Astrophysics Data System (ADS)

    Salev, Pavel; Grigoriev, Alexei

    A combination of LGD and semiconductor theories predicts the electrostatic screening of a large polarization mismatch between BaTiO3 (BTO) and Pb(Zr,Ti)O3 (PZT) ferroelectric layers. The source of this screening is in an increased concentration of interfacial free charge carriers due to the strong bending of electronic bands inside the layers. The enhanced concentration of free charges at the interface can allow for independent polarization reversal in each ferroelectric layer suggesting possible antiparallel polarization configurations in BTO/PZT bilayer. We confirmed these theoretical predictions of layer-by-layer switching by demonstrating double polarization switching in epitaxial BTO/PZT thin films. The layer-by-layer switching leads to formation of head-to-head (H-H) and tail-to-tail (T-T) polarization configurations, which have an enhanced dielectric permittivity when compared to parallel polarization domain configurations. While both H-H and T-T states are unstable at a zero electric field, we found that antiparallel polarization configurations can be stabilized by applying a small bias. Our findings provide a pathway to engineer new multilayer systems with switchable multistate polarizations and dielectric responses.

  20. Effect of combined external uniaxial stress and dc bias on the dielectric property of BaTiO3-based dielectrics in multilayer ceramic capacitor: thermodynamics and experiments

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Yue, Zhenxing; Sun, Tieyu; Gou, Huanlin; Li, Longtu

    2008-02-01

    The dielectric properties of (Nb, Y)-doped BaTiO3 in a multilayer ceramic capacitor (MLCC) under combined external uniaxial compressive stress and dc bias field were investigated at room temperature by using a modified Ginsburg-Landau-Devonshire thermodynamic theory and the dielectric measurement. It is found that although dc bias decreases the dielectric properties dominantly, the influence of the external uniaixial compressive stress should not be neglected. When applied along a direction perpendicular to the internal electrode layer in the MLCC, the external uniaixal compressive stress will strengthen the negative effect of dc bias. In contrast, the external uniaxial compressive stress along a direction parallel to the internal electrode layer in the MLCC will increase the dielectric permittivity under dc bias field, i.e. improve the ɛ-V response of the MLCC. Furthermore, although there is a difference between the calculated permittivity and the measured permittivity, the effects of the combined external uniaxial compressive stress and dc bias field on the dielectric permittivity described through two approaches are in good agreement.

  1. Difference between compositional and grain size effect on the dielectric nonlinearity of Mn and V-doped BaTiO3 multilayer ceramic capacitors

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    The difference between compositional and grain size effect on the dielectric nonlinearity was contrasted in Mn and V-doped BaTiO3 multilayer ceramic capacitors utilizing the first order reversal curve (FORC) distribution based on the Preisach model. The high field dielectric constants can be increased either by the adjustment of additive composition, that is, Ba concentration maintaining the same grain size, or by increasing its size. The former compositional effect caused an enhanced dielectric constant in both low and high field region, which can be associated with the increase in the saturation polarization, the reversible and the irreversible FORC distributions near zero bias. The latter grain growth effect, on the other hand, resulted in a decrease of the dielectric constants in the low field but a steep ac field dependence of them, which can be correlated with a decrease of the reversible FORC distribution and a significant increase of the irreversible FORC distribution near origin. These results show that the compositional effect is caused by the increase of the magnitude of the spontaneous polarization and the domain wall density, whereas the grain size effect is caused by the increase in the size of the domain and its wall, which increases the probability of domain pinning by weakly pinning centers but enables its long range motion beyond the threshold field.

  2. Substrate clamping effect onto magnetoelectric coupling in multiferroic BaTiO3-CoFe2O4 core-shell nanofibers via coaxial electrospinning

    NASA Astrophysics Data System (ADS)

    Fu, Bi; Lu, Ruie; Gao, Kun; Yang, Yaodong; Wang, Yaping

    2015-10-01

    We report large lateral magnetoelectric (ME) coupling coefficients α 31 of 1.2×104 \\text{mV} \\text{cm}-1 \\text{Oe}-1 and 3.5× 104 \\text{mV} \\text{cm}-1 \\text{Oe}-1 in substrate bonded and free-standing multiferroic BaTiO3-CoFe2O4 (BTO-CFO) core-shell nanofibers (NFs) with and without substrate clamping effect, respectively. The BTO-CFO core-shell NFs were synthesised by a sol-gel coaxial electrospinning technique, and their ME coupling was directly observed by demonstrating the evolution of piezoelectric coefficient (d 33), ferroelectric domain, and phase contrast induced by an external magnetic field. These impressed α 31 coefficients originated from the nanoconfinement of the interphase elastic interaction between the ferromagnetic core fiber and the ferroelectric shell interlayer, as well as the strain transformation at the one-dimensional (1D) fiber boundary. This means that the decreasing substrate clamping effect results in an enhanced ME coupling in multiferroic NFs, which is similar to that of thin films. These findings make people understand the substrate clamping effect and enable nanoscale ME device applications.

  3. Enhancement of the Electrical Properties in BaTiO3/PbZr0.52Ti0.48O3 Ferroelectric Superlattices.

    PubMed

    He, Bin; Wang, Zhanjie

    2016-03-01

    In this study, BaTiO3/Pb(Zr0.52Ti0.48)O3 (BTO/PZT) ferroelectric superlattices have been grown on the Nb-doped SrTiO3 (NSTO) single-crystal substrate by pulsed laser deposition, and their electrical properties were investigated in detail. The leakage current was reduced significantly in the BTO/PZT superlattices, and the conduction mechanism could be interpreted as the bulk-limited mechanism. In addition, a more symmetric hysteresis loop was observed in the BTO/PZT superlattices compared with the pure PZT and BTO films. The BTO/PZT superlattices with the modulation thickness of 9.8 nm showed remarkably improved dielectric properties with dielectric constant and loss of 684 and 0.02, respectively, measured at the frequency of 10 kHz. Based on these experimental results, it can be considered that the BTO/PZT interfaces play a very important role for the enhanced electrical properties of the BTO/PZT superlattices. PMID:26913563

  4. Novel magnetoelectric ceramic composites by control of the interface reactions in Fe2O3@BaTiO3 core-shell structures

    NASA Astrophysics Data System (ADS)

    Curecheriu, Lavinia; Postolache, Petronel; Buscaglia, Maria Teresa; Buscaglia, Vincenzo; Ianculescu, Adelina; Mitoseriu, Liliana

    2014-08-01

    In the present work, composite ceramics of ferroelectric BaTiO3 (BT) with magnetic αFe2O3 were prepared from powders synthesized by two different methods: (a) core-shell powders of Fe2O3@BT and (b) Fe2O3-BT composites from mixed powders with the same composition. The M(H) loops at room temperature show a "wasp-waisted" character, with multiple components, determined as result of the formation of magnetic phases with contrasting coercivities (hard BaFe12O19 and soft Ba12Ti28Fe15O84 phases) in different ratios, as indicated by the magnetic first-order-reversal curves analysis. The core-shell composite ceramics generally showed slightly improved dielectric properties and smaller conductivity. The high field properties of composite ceramics show a strong nonlinearity in both cases, together with a reduction of zero field permittivity, making from these composites possible tunable materials interesting for applications. Their multifunctional character is enhanced by the presence of a complex magnetic character with soft/hard components.

  5. Correlation between I (current)-V (voltage) characteristics and thermally stimulated depolarization current of Mn-doped BaTiO3 multilayer ceramic capacitor

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Kim, Sang-Hyuk; Kim, Doo-Young

    2013-08-01

    I (Current)-V (voltage) characteristics of Mn-doped BaTiO3 multilayer ceramic capacitor were investigated. The increase of Mn concentration reduced the slope of current increase with increasing dc field and enhanced the dc field to the abrupt increase of current and thereby breakdown. Ohmic, Schottky, and Poole-Frenkel type conduction was successively observed with the increase of dc field in all specimens. The region of Child's law did not appear before breakdown, which suggests space charge limited (SCL) conduction with field enhanced trap barrier lowering. A peak of thermally stimulated depolarization current (TSDC) beyond 300 °C associated with trapped space charges appeared, which increased by the increase of Mn concentration. In addition, the peak intensity increased to a maximum value and then decreased again with increasing polarization dc field in TSDC measurement. Its activation energies were around 1.9 eV for all specimens, which is very close to the energy level for the ionization of Mn3+/Mn2+. These results experimentally demonstrate the role of the variable valence acceptor Mn as trapping center for injected charges, and the occurrence of field enhanced trap charge release, and therefore, the conduction mechanism can be described by the SCL model incorporating the Poole-Frenkel effect.

  6. First-principles-based calculation of the electrocaloric effect in BaTiO3: A comparison of direct and indirect methods

    NASA Astrophysics Data System (ADS)

    Marathe, Madhura; Grünebohm, Anna; Nishimatsu, Takeshi; Entel, Peter; Ederer, Claude

    2016-02-01

    We use molecular dynamics simulations for a first-principles-based effective Hamiltonian to calculate two important quantities characterizing the electrocaloric effect in BaTiO3, the adiabatic temperature change Δ T and the isothermal entropy change Δ S , for different electric field strengths. We compare direct and indirect methods to obtain Δ T and Δ S , and we confirm that both methods indeed lead to an identical result provided that the system does not actually undergo a first order phase transition. We also show that a large electrocaloric response is obtained for electric fields beyond the critical field strength for the first order phase transition. Furthermore, our work fills several gaps regarding the application of the first-principles-based effective Hamiltonian approach, which represents a very attractive and powerful method for the quantitative prediction of electrocaloric properties. In particular, we consider the full temperature and field dependence of the calculated specific heat for the indirect calculation of Δ T , and we discuss the importance of maintaining thermal equilibrium during the field ramping when calculating Δ T using the direct method within a molecular dynamics approach.

  7. Study on Occupation Behavior of Y2O3 in X8R Nonreducible BaTiO3-Based Dielectric Ceramics

    NASA Astrophysics Data System (ADS)

    Yao, Guofeng; Wang, Xiaohui; Li, Longtu

    2011-12-01

    The effects of Y2O3 on BaTiO3-MgO-MnO2-CaZrO3 nonreducible ceramics were investigated. Specimens with Y2O3 contents ranging from 1.0 to 2.5 mol % were prepared via the solid state method. The Curie temperature (Tc) and the electrical properties were closely related to the occupation behavior of yttrium, which is known as an amphoteric element. Tc increased almost linearly as a function of Y2O3 content when the doping content was low. Transmission electron microscopy (TEM) indicated a typical “core-shell” structure. The lattice parameters corresponding to the grain cores and the shells were determined by X-ray diffractometry (XRD) separately. The relief of the internal stresses arising from the lattice mismatch was responsible for the Tc shift. The specimens doped by a high level of Y2O3 can fulfill the EIA X8R specification with a high dielectric constant (ɛRT > 2400) and a low dielectric loss (tan δ< 1.1%). A high insulation resistivity and a slow degradation rate were obtained when a sufficient amount of Y2O3 was incorporated, which were attributed to the substitution of Ti4+ and the formation of a donor-acceptor complex.

  8. Influence of Ga-concentration on the electrical and magnetic properties of magnetoelectric CoGaxFe2–xO4/BaTiO3 composite

    DOE PAGESBeta

    Ni, Yan; Zhang, Zhen; Nlebedim, Cajetan I.; Jiles, David C.

    2015-03-20

    Multiferroic materials exhibit magnetoelectric (ME) coupling and promise new device applications including magnetic sensors, generators, and filters. An effective method for developing ME materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, the electrical and magnetic properties of Ga doped magnetoelectric CoGaxFe2–xO4/BaTiO3 composite are studied systematically. It is found that Ga doping improves the sensitivity of magnetoelastic response and stabilizes the magnetic phase of the composites. More importantly, Ga doping reduces the electrical conductivity of composite, as well as the dielectric loss. An enhancement of the electrostrainmore » with doping Ga is also observed. Quantitative estimation indicates that magnetoelectric coupling is enhanced for Ga-doped CoGaxFe2–xO4/BaTiO3 composites. As a result, the present work is beneficial to the practical application of composite CoFe2O4/BaTiO3-based multiferroic materials.« less

  9. Signal processing in photoacoustic detection of phase transitions by means of the autospectra correlation-based method: Evaluation with ceramic BaTiO3

    NASA Astrophysics Data System (ADS)

    Mejía-Uriarte, E. V.; Navarrete, M.; Villagrán-Muniz, M.

    2004-09-01

    This work describes a simple numerical procedure which, when applied to digitally recorded photoacoustic (PA) signals, allows the construction of thermal profiles (rS,drS/dT) to determine: the transition order, the phase transition temperature (Tc), and the phase transformation temperature range (ΔT), on samples, which undergo low-high transitions. During continuous heating of the sample, the ultrasonic signal was generated using a pulsed laser beam incident on a surface and detected on the opposite surface of the sample using a long quartz bar attached to a piezoelectric sensor. The thermal profile, rS, is built from a sequence of the ordinary correlation coefficients ri associated with an interval of temperature. The ri coefficients are calculated from amplitude spectra pairs. The amplitude spectra are obtained via fast Fourier transforms from original PA records. This procedure is applied on samples of bulk ceramic BaTiO3 to obtain their thermal behavior. The PA signal and temperature sample were registered every 0.2°. The samples were heated from room temperature to 137 °C at a rate of 0.1 °C min-1. The thermal profile rS shows the entire thermal history including the structural phase transition from tetragonal to cubic (T-C), which appears as a jump on the graph within an uncertainty of 2%. The drS/dT profile shows that the T-C phase transformation occurs over a range of temperatures. The results are in agreement with those reported in the literature.

  10. The influence of Mn on the grain-boundary potential barrier characteristics of donor-doped BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Illingsworth, J.; Al-Allak, H. M.; Brinkman, A. W.; Woods, J.

    1990-02-01

    Two compositions of BaTiO3 positive temperature coefficient of resistance ceramics, prepared identically except for the fact that a small addition of Mn (0.04 at. %) was made to one of them, were studied. The samples were sintered simultaneously in air at 1400 °C for 1 h and then annealed at 1200 ° for 5 h, using a muffle furnace. Room-temperature dielectric measurements in the audio- and radio-frequency ranges confirmed that Mn has a negligible effect on the bulk resistance. Arrhenius plots of resistivity vs 1/[Tɛ'm(T)] were found to give straight lines for Tc

  11. Electric field induced lattice strain in pseudocubic Bi(Mg1/2Ti1/2)O3-modified BaTiO3-BiFeO3 piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Fujii, Ichiro; Iizuka, Ryo; Nakahira, Yuki; Sunada, Yuya; Ueno, Shintaro; Nakashima, Kouichi; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Wada, Satoshi

    2016-04-01

    Contributions to the piezoelectric response in pseudocubic 0.3BaTiO3-0.1Bi(Mg1/2Ti1/2)O3-0.6BiFeO3 ceramics were investigated by synchrotron X-ray diffraction under electric fields. All of the lattice strain determined from the 110, 111, and 200 pseudocubic diffraction peaks showed similar lattice strain hysteresis that was comparable to the bulk butterfly-like strain curve. It was suggested that the hysteresis of the lattice strain and the lack of anisotropy were related to the complex domain structure and the phase boundary composition.

  12. Development of Triple Scale Finite Element Analyses Based on Crystallographic Homogenization Methods

    NASA Astrophysics Data System (ADS)

    Nakamachi, Eiji

    2004-06-01

    Crystallographic homogenization procedure is implemented in the piezoelectric and elastic-crystalline plastic finite element (FE) code to assess its macro-continuum properties of piezoelectric ceramics and BCC and FCC sheet metals. Triple scale hierarchical structure consists of an atom cluster, a crystal aggregation and a macro- continuum. In this paper, we focus to discuss a triple scale numerical analysis for piezoelectric material, and apply to assess a macro-continuum material property. At first, we calculate material properties of Perovskite crystal of piezoelectric material, XYO3 (such as BaTiO3 and PbTiO3) by employing ab-initio molecular analysis code CASTEP. Next, measured results of SEM and EBSD observations of crystal orientation distributions, shapes and boundaries of a real material (BaTiO3) are employed to define an inhomogeneity of crystal aggregation, which corresponds to a unit cell of micro-structure, and satisfies the periodicity condition. This procedure is featured as a first scaling up from the molecular to the crystal aggregation. Finally, the conventional homogenization procedure is implemented in FE code to evaluate a macro-continuum property. This final procedure is featured as a second scaling up from the crystal aggregation (unit cell) to macro-continuum. This triple scale analysis is applied to design piezoelectric ceramic and finds an optimum crystal orientation distribution, in which a macroscopic piezoelectric constant d33 has a maximum value.

  13. Structural, dielectric and ferroelectric studies of (x) Mg0.25Cu0.25Zn0.5Fe2O4 + (1-x) BaTiO3 magnetoelectric nano-composites

    NASA Astrophysics Data System (ADS)

    Khader, S. Abdul; Muneeswaran, M.; Giridharan, N. V.; Sankarappa, T.

    2016-05-01

    The Particulate nano-composites of ferrite and ferroelectric phases having the general formula (x) Mg0.25Cu0.25Zn0.5Fe2O4 + (1-x) BaTiO3 (x=15%, 30% and 45%) were synthesized by sintering mixtures of highly ferroelectric BaTiO3 (BT) and highly magneto-strictive magnetic component Mg0.25Cu0.25Zn0.5Fe2O4(MCZF). The presence of constituent phases of ferrite, ferroelectric and their composites were probed and confirmed by X-ray diffraction (XRD) studies. Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM). The variation of dielectric constant and dissipation factor as a function of frequency from 100 Hz to 1 MHz at room temperature were carried out using a Hioki LCR Hi-Tester. The dielectric constant and dielectric loss were found to decrease rapidly in the low frequency region and became almost constant in the high frequency region. The electrical conductivity deduced from the measured dielectric data has been thoroughly analyzed and found that the conduction mechanism in these composites is in conformity with small polaron hopping model. The ferroelectric properties of synthesized magneto-electric nano-composites were measured using P-E loop tracer.

  14. Octonary resistance states in La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junctions

    DOE PAGESBeta

    Yue -Wei Yin; Tao, Jing; Huang, Wei -Chuan; Liu, Yu -Kuai; Yang, Sheng -Wei; Dong, Si -Ning; Zhu, Yi -Mei; Li, Qi; Li, Xiao -Guang

    2015-10-06

    General drawbacks of current electronic/spintronic devices are high power consumption and low density storage. A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents four resistance states in a single device and therefore provides an alternative way to achieve high density memories. Here, an MFTJ device with eight nonvolatile resistance states by further integrating the design of noncollinear magnetization alignments between the ferromagnetic layers is demonstrated. Through the angle-resolved tunneling magnetoresistance investigations on La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 junctions, it is found that, besides collinear parallel/antiparallel magnetic configurations, the MFTJ shows at least two other stable noncollinear (45°more » and 90°) magnetic configurations. As a result, combining the tunneling electroresistance effect caused by the ferroelectricity reversal of the BaTiO3 barrier, an octonary memory device is obtained, representing potential applications in high density nonvolatile storage in the future.« less

  15. Magnetoelectric coupling and phase transition in BiFeO3 and (BiFeO3)0.95(BaTiO3)0.05 ceramics

    NASA Astrophysics Data System (ADS)

    Wang, T.-H.; Tu, C.-S.; Chen, H.-Y.; Ding, Y.; Lin, T. C.; Yao, Y.-D.; Schmidt, V. H.; Wu, K.-T.

    2011-02-01

    In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO-5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic-paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)-orthorhombic (O)-cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO-5%BT exhibits a R-C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO-5%BT remains less than 0.04 below 150 °C.

  16. Structural and dielectric properties of BaTiO3-Bi(Mg1/2Ti1/2)O3 thin films fabricated by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Moki, Shota; Kimura, Junichi; Kaneko, Noriyuki; Funakubo, Hiroshi; Uchida, Hiroshi

    2014-09-01

    Thin films of the BaTiO3-Bi(Mg1/2Ti1/2)O3 (BT-BMT) solid-solution system were fabricated with the aim of achieving a stable temperature coefficient of capacitance (TCC) favorable for high-temperature electronics. A single perovskite phase with pseudocubic symmetry was obtained for the films fabricated by chemical solution deposition on (111)Pt/TiO2/(100)Si substrates in the composition range of x = 0-0.80 for (1 - x)BT-xBMT. BMT added to the BaTiO3-based films enhanced the crystallinity of the perovskite phase and resulted in saturated P-E hysteresis behavior with remanent polarization of up to 13 µC/cm2. BMT addition led to gradual dielectric relaxation, which also resulted in stable TCC behavior with a relative dielectric constant of approximately 400 in the temperature range of RT - 400 °C, especially for the BT-BMT films with x = 0.20-0.40.

  17. Structural, dielectric and magnetic studies of (x) Ni0.7Co0.1Cu0.2Fe2O4 + (1-x) BaTiO3 magnetoelectric composites

    NASA Astrophysics Data System (ADS)

    Khader, S. Abdul; Parveez, Asiya; Giridharan, N. V.; Sankarappa, T.

    2016-05-01

    The Magneto-electric composites (x) Ni0.7Co0.1Cu0.2Fe2O4 + (1-x) BaTiO3 (x=10%, 20% and 30%) were synthesized by sintering mixtures of highly ferroelectric BaTiO3 (BT) and highly magneto-strictive component Ni0.7Co0.1Cu0.2Fe2O4 (NCCF). The presences of constituent phases in magneto-electric composites were probed by X-ray diffraction (XRD) studies. The peaks observed in the XRD spectrum indicated spinel cubic structure for NCCF ferrite phase and tetragonal perovskite structure for BT and, both spinel and pervoskite structures for synthesized ME composites. Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM). Frequency and composition dependent dielectric properties of synthesized composites were measured from 100 Hz to 1 MHz at room temperature using Hioki LCR Hi-TESTER. The dielectric dispersion is observed at lower frequencies for the synthesized ME composites. The hysteresis behavior was studied to understand the magnetic ordering in the synthesized composites using a Vibrating Sample Magnetometer (VSM). It is observed that the values of saturation magnetization increases along with the ferrite content.

  18. The Effects of Strain and Vacancies on the Electric and Vibrational Properties of Ferroelectric BaTiO3 from First-principles

    NASA Astrophysics Data System (ADS)

    Raeliarijaona, Aldo

    The studies of ferroelectricity (FE) are of technological significance because of the multitude of applicable properties that ferroelectric materials exhibit. The mastery, and control of these properties necessitate the knowledge of the fundamental physics governing these insulating materials. In this dissertation I present the results of first-principles investigations of the behavior of the fundamental ferroelectric properties under strain, and in the presence of vacancies. In the first part I introduce the important FE properties, their common behavior, and their numerous valuable applications. Following this background on FEs, a review of theoretical methods is presented with topics such as: Density Functional Theory (DFT), Pseudopotential method, Berry Phase Calculation and Density Functional Perturbation Theory (DFPT). Further, new theoretical approaches are introduced in this dissertation to enable the study of polarization for charged system. In this work I report behaviors of polarization in rhombohedral (R3m) BaTiO3 (BTO) that do not conform with intuition, or the current state of known behavior of epitaxially strained BTO. These studies reveal a polarization that increases with tensile strain, instead of compressive strain, and a polarization that is anticorrelated with an elongation of the out-of-plane axis. Additionally, the studies indicate strain-driven phase transitions to R3c and Cm upon application of moderate epitaxial compressive (eta=-1.75%) and small tensile strain (eta=+0.375%), respectively. A simple physical explanation, which can be extended to FE materials of the same symmetry, is also provided for this unusual FE behavior. I also report the studies on the evolution of phonon modes of vibration under strain in tetragonal (P4mm) BTO, revealing that careful analyses are necessary in the assignment of vibration modes in strained system due to different mode ordering between unstrained and strained systems. The splitting between Longitudinal Optical and Transverse Optical vibration mode is rigorously defined in this work, and shown to depend on mode mixing. The evolution of important quantities such as dielectric constant is also presented in this work. Finally, the results of investigations on the influence of vacancies on ferroelectric and ferromagnetic properties will be presented in this dissertation. First, the studies of vacancy formation energy are highlighted, which shows the type and charge character of the vacancy that are most likely to occur under any given growth conditions. Afterward, I present the effect of vacancies on polarization and polarization switching in tetragonal BTO, demonstrating the relevance of polarization change in charged polar system, and proposing a method of calculating the polarization and an new polarization-switching pathway in FE BTO in the presence of charged vacancies. Then, I reveal the possibility of vacancy-induced ferromagnetism in BTO, and the microscopic origin of this ferromagnetism.

  19. Homogeneity Pursuit

    PubMed Central

    Ke, Tracy; Fan, Jianqing; Wu, Yichao

    2014-01-01

    This paper explores the homogeneity of coefficients in high-dimensional regression, which extends the sparsity concept and is more general and suitable for many applications. Homogeneity arises when regression coefficients corresponding to neighboring geographical regions or a similar cluster of covariates are expected to be approximately the same. Sparsity corresponds to a special case of homogeneity with a large cluster of known atom zero. In this article, we propose a new method called clustering algorithm in regression via data-driven segmentation (CARDS) to explore homogeneity. New mathematics are provided on the gain that can be achieved by exploring homogeneity. Statistical properties of two versions of CARDS are analyzed. In particular, the asymptotic normality of our proposed CARDS estimator is established, which reveals better estimation accuracy for homogeneous parameters than that without homogeneity exploration. When our methods are combined with sparsity exploration, further efficiency can be achieved beyond the exploration of sparsity alone. This provides additional insights into the power of exploring low-dimensional structures in high-dimensional regression: homogeneity and sparsity. Our results also shed lights on the properties of the fussed Lasso. The newly developed method is further illustrated by simulation studies and applications to real data. Supplementary materials for this article are available online. PMID:26085701

  20. The electrocaloric effect and thermal stability of 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 modified by WO3

    NASA Astrophysics Data System (ADS)

    Wang, Ju; Li, Qiang; Ma, Yuan; Liu, Guocai; Zhao, Yuwei; Fan, Huiqing

    2016-05-01

    The solid-state reaction method is used to prepare the 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 modified by WO3 lead-free ceramic. The unpoled (Bi0.5Na0.5)0.94Ba0.06Ti1-(3/2) x W x O3 with pseudo-cubic structure undergoes transition from ferroelectric to relaxor ferroelectric that happens in the T d. The maximum reversible temperature change |Δ T| = 0.8 K occurs at the room temperature due to the decline of temperature. In addition, |Δ T| = 0.15 K at the (Bi0.5Na0.5)0.94Ba0.06Ti1-(3/2) x W x O3 with x = 0.75 mol% exhibits good thermal stability at the temperature range of 303-413 K.

  1. Quenching-induced circumvention of integrated aging effect of relaxor lead lanthanum zirconate titanate and (Bi1/2Na1/2)TiO3-BaTiO3

    NASA Astrophysics Data System (ADS)

    Zang, Jiadong; Jo, Wook; Rödel, Jürgen

    2013-01-01

    The effect of quenching on the dielectric properties of ceramic Pb0.92La0.08(Zr0.65Ti0.35)0.98O3 (PLZT 8/65/35) and (Bi1/2Na1/2)TiO3-6 mol. %BaTiO3 (BNT-6BT) was investigated after annealing at a wide range of temperatures. The dielectric permittivity showed that the magnitude and shape profile of the permittivity were significantly affected by the quenching process in comparison to furnace-cooled specimens. We propose that the changes originate from a circumvention of integrated aging that takes place during cooling process. A comparison between PLZT 8/65/35 and BNT-6BT allowed us to conclude that two different types of polar nanoregions exist in BNT-6BT and the transition between them peaks at around 300 °C.

  2. Direct observation of the symmetry breaking of the nanometer-scale local structure in the paraelectric cubic phase of BaTiO3 using convergent-beam electron diffraction

    NASA Astrophysics Data System (ADS)

    Tsuda, Kenji; Tanaka, Michiyoshi

    2016-07-01

    Nanometer-scale local structures of the cubic phase of barium titanate (BaTiO3) are investigated by convergent-beam electron diffraction (CBED) using a nanometer-size electron probe. Breaking of the cubic symmetry has been discovered in the nanometer-scale areas of the cubic phase. This indicates the existence of local polarization clusters as a precursor of the phase transition. Symmetry-breaking index maps for the fourfold rotation symmetry are given at different temperatures with the combined use of scanning transmission electron microscopy and CBED methods (STEM-CBED). A spatially hierarchical structure of the cubic phase is proposed, which may explain different local symmetries reported using different experimental probes.

  3. Nanoscale phase quantification in lead-free (Bi1 /2Na1 /2) TiO3-BaTiO3 relaxor ferroelectrics by means of 23Na NMR

    NASA Astrophysics Data System (ADS)

    Groszewicz, Pedro B.; Breitzke, Hergen; Dittmer, Robert; Sapper, Eva; Jo, Wook; Buntkowsky, Gerd; Rödel, Jürgen

    2014-12-01

    We address the unsolved question on the structure of relaxor ferroelectrics at the atomic level by characterizing lead-free piezoceramic solid solutions (100 -x ) (Bi1 /2Na1 /2) TiO3-x BaTiO3 (BNT -x BT ) (for x =1 ,4 ,6 , and 15). Based on the relative intensity between spectral components in quadrupolar perturbed 23Na nuclear magnetic resonance, we present direct evidence of the coexistence of cubic and polar local symmetries in these relaxor ferroelectrics. In addition, we demonstrate how the cubic phase vanishes whenever a ferroelectric state is induced, either by field cooling or changing the dopant amount, supporting the relation between this cubic phase and the relaxor state.

  4. Influence of tetragonal platelets on the dielectric permittivity of 0.964 Na1 /2Bi1 /2TiO3-0.036 BaTiO3

    NASA Astrophysics Data System (ADS)

    Pforr, Florian; Major, Márton; Donner, Wolfgang; Stuhr, Uwe; Roessli, Bertrand

    2016-07-01

    We study the temperature-dependent evolution of the octahedral tilt order in a lead-free relaxor ferroelectric and its impact on the ferroelectric properties. Using diffuse neutron scattering on a 0.964 Na1 /2Bi1 /2TiO3-0.036 BaTiO3 single crystal, we suggest a model for the temperature-dependent nanostructure of this perovskite that features chemically pinned tetragonal platelets embedded in the rhombohedral matrix, often separated by a cubic intermediate phase. Our results show a clear correlation between the squared thickness of the tetragonal platelets and the dielectric permittivity. This is interpreted as a sign for increased polarizability of the strained and distorted lattice at the center of the tetragonal platelets.

  5. Enhanced ferroelectric and piezoelectric response in Mn-doped Bi0.5Na0.5TiO3-BaTiO3 lead-free film by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Jin, Chengchao; Wang, Feifei; Leung, Chung Ming; Yao, Qirong; Tang, Yanxue; Wang, Tao; Shi, Wangzhou

    2013-10-01

    Mn-doped Bi0.5Na0.5TiO3-BaTiO3 thin film with the composition around the morphotropic phase boundary was grown on Pt-electrodized Si substrate by pulsed laser deposition. Highly (1 0 0)-oriented film with pure perovskite structure was obtained through carefully controlling the growth conditions. Well-defined ferroelectric P-E loop was obtained with the average remnant polarization Pr and coercive field Ec of ∼11.3 μC/cm2 and ∼6.5 kV/mm, respectively. Polycrystalline structures and multidomain states were revealed by piezoresponse force microscopy and large local strain response was obtained with the normalized strain Smax/Emax up to 92 pm/V. The excellent global electrical properties make it quite promising in environmental-friendly ferroelectric and piezoelectric devices.

  6. Growth and electric properties of (100)-oriented Mn-doped (Bi0.5Na0.5)TiO3-BaTiO3 thin film by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Jin, Chengchao; Wang, Feifei; Leung, Chung Ming; Tang, Yanxue; Wang, Tao; Yao, Qirong; Shi, Wangzhou

    2014-06-01

    Mn-doped (Bi0.5Na0.5)TiO3-BaTiO3 (BNBMT) thin film with the composition near the morphotropic phase boundary was grown on (La0.6Sr0.4)CoO3-electroded SrTiO3 single-crystal substrate by using pulsed laser deposition method. Ascribed to the crystal structure and lattice similarity, (100)-oriented BNBMT film with pure single-phase perovskite structure was obtained through carefully controlling the growth conditions. Enhanced ferroelectric and dielectric properties were obtained with large remanent polarization P r of ˜21 μC/cm2, coercive field E c of ˜7.4 kV/mm and dielectric constant of ˜750 at 1 kHz. The excellent global electrical properties of the BNBMT film are promising for environmentally friendly ferroelectric devices.

  7. Microstructural influence on the broadband dielectric properties of BaTiO3-Ni0.5Zn0.5Fe2O4 core-shell composites: Experiment and modeling

    NASA Astrophysics Data System (ADS)

    Sakanas, A.; Grigalaitis, R.; Banys, J.; Curecheriu, L.; Mitoseriu, L.; Buscaglia, V.

    2015-11-01

    Dielectric measurements of core-shell BaTiO3-Ni0.5Zn0.5Fe2O4 ferroelectric-ferrimagnetic composites, sintered at two temperatures (1050 °C and 1150 °C), were performed in a broadband frequency range of 10 Hz-1 THz at various temperatures of 100-500 K. The comparison of temperature dependences reveals a drastic change of permittivity as a function of sintering temperature, as a result of modifications induced on the microstructural parameters as grain size and density. Effective medium approach was used in order to better describe processes associated with the constituent composite phases. Complex specific resistivity coupled with Maxwell-Wagner-Hashin-Shtrikman model allowed to associate lower frequency processes with grain boundary effects. We concluded that the main factor influencing the electrical properties of core-shell composites is the structure and interfaces, instead of the constituent materials themselves.

  8. Enhanced piezoelectric properties of BaZrO3-substituted 0.67BiFeO3-0.33BaTiO3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Park, J. S.; Lee, M. H.; Kim, D. J.; Kim, M.-H.; Song, T. K.; Kim, S. W.; Kim, W.-J.; Kumar, S.

    2015-04-01

    Lead-free ceramics with compositions of (1- x)[0.67Bi1.05FeO3-0.33BaTiO3]- xBaZrO3 ( x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) [BF-BT-BZ x] have been prepared through a conventional solid-state reaction method. The effects of BZ substitution on the crystal structural, microstructural, piezoelectric, and electrical properties of the ceramics were investigated. The X-ray diffraction patterns revealed that all ceramics were formed with a mixed structure of rhombohedral and tetragonal perovskite phases. For x = 0.03, good ferroelectric and piezoelectric properties were observed: 2 P r = 43 μC/cm2 and 2 E c = 61 kV/cm. The static- and dynamic-piezoelectric constants were observed to be 52 pC/N and 330 pm/V, respectively.

  9. Three-dimensional phases-connectivity and strong magnetoelectric response of self-assembled feather-like CoFe 2O 4-BaTiO 3 nanostructures

    NASA Astrophysics Data System (ADS)

    Deng, Yu; Zhou, Jianxin; Wu, Di; Du, Yulei; Zhang, Mingsheng; Wang, Dunhui; Yu, Huiqiang; Tang, Shaolong; Du, Youwei

    2010-08-01

    Magnetoelectric (ME) (CoFe 2O 4) 0.3-(BaTiO 3) 0.7 (CFO-BTO) nanostructures have been synthesized by a combinative using of hydrothermal reaction and polymer-assisted deposition. The feather-like nanostructures have an average diameter of 250 nm and lengths up to 5 μm, with the single-crystal CFO nanopillars embedded in the BTO matrix. The CFO-BTO nanostructures exhibit good ferromagnetic and ferroelectric properties, as well as a large ME coefficient of 51.8 mV/cm Oe. A model has been proposed to explain the three-dimensional phases-connectivity of the nanostructures. And it is suggested that the novel type of phases-connectivity greatly promote the ME response.

  10. Unification of the negative electrocaloric effect in Bi1/2Na1/2TiO3-BaTiO3 solid solutions by Ba1/2Sr1/2TiO3 doping

    NASA Astrophysics Data System (ADS)

    Uddin, Sarir; Zheng, Guang-Ping; Iqbal, Yaseen; Ubic, Rick; Yang, Junhe

    2013-12-01

    The microscopic mechanisms of the negative electrocaloric effect (ECE) of the single-phase (1-x)(0.94Bi1/2Na1/2TiO3-0.06BaTiO3)-xBa1/2Sr1/2TiO3 (BNT-BT-BST) perovskite solid solutions fabricated via the sol-gel technique are explored in this study. Dielectric and mechanical relaxation analyses are employed to investigate the ferroelectric and structural transitions of the samples. The electrocaloric properties of the samples were measured by thermodynamics Maxwell relations. The difference between the depolarization temperature (Td) and the maximum dielectric constant temperature (Tm) was found to decrease with increasing BST content. Doping with BST stabilized the ferroelectric phase along with unifying the EC temperature changes (ΔT) to only negative values. The origin of the uniform negative ECE of BNT-BT-BST is discussed.

  11. Effects of site substitutions and concentration on the structural, optical and visible photoluminescence properties of Er doped BaTiO3 thin films prepared by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Maneeshya, L. V.; Thomas, P. V.; Joy, K.

    2015-08-01

    The structural, optical and visible photoluminescence of the Erbium (Er) doped BaTiO3 (BT:Er) thin films were studied in terms of Er3+ substitutions for Ba and Ti sites with different Er3+ doping concentrations (0, 1, 3 and 5 wt%). X-ray diffraction pattern of BT:Er films with different Er3+ concentration showed tetragonal phase with preferred orientation along (1 0 1) plane. The lattice constant of BT:Er film of 1 wt% Er3+ shrank and then expanded for higher concentration. This indicates that Er3+ ions are completely incorporated into the host lattice by substituting for Ba2+ sites for 1 wt% Er3+ and then Ti4+ sites for higher Er3+ concentration in the BaTiO3 host. The crystallite size decreased for 1 wt% and then increased for higher Er (3 and 5 wt%) concentrations. The Scanning electron microscopy images revealed well patterned arrangement of larger spherical grains with neck formation. X-ray photoelectron spectroscopy analysis confirmed the presence of barium, titanium, erbium and oxygen in BT:Er films. An average transmittance >80% in visible region were observed for all the films. Optical band gap energy of BT:Er films were found to vary with increase in Er3+ concentration. The high refractive index >2 of these films can be used in optical application and anti-reflection coatings. Photoluminescence spectra of the films exhibited an increase in the emission intensity up to 3 wt% of Er3+ and then a decrease, due to self quenching. The improved optical properties of BT:Er films makes suitable for optical applications.

  12. Ceramic synthesis of 0.08BiGaO3–0.90BaTiO3–0.02LiNbO3 under high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Hui, Jin; Yong, Li; Mou-Sheng, Song; Lin, Chen; Xiao-Peng, Jia; Hong-An, Ma

    2016-07-01

    In this paper, the preparation of 0.08BiGaO3-0.90BaTiO3-0.02LiNbO3 is investigated at pressure 3.8 GPa and temperature 1100–1200 °C. Experimental results indicate that not only is the sintered rate more effective, but also the sintered temperature is lower under high pressure and high temperature than those of under normal pressure. It is thought that the adscititious pressure plays the key role in this process, which is discussed in detail. The composition and the structure of the as-prepared samples are recorded by XRD patterns. The result shows that the phases of BaTiO3, BaBiO2.77, and Ba2Bi4Ti5O18 with piezoelectric ceramic performance generate in the sintered samples. Furthermore, the surface morphology characteristics of the typical samples are also investigated using a scanning electron microscope. It indicates that the grain size and surface structure of the samples are closely related to the sintering temperature and sintering time. It is hoped that this study can provide a new train of thought for the preparation of lead-free piezoelectric ceramics with excellent performance. Project supported by the National Natural Science Foundation of China (Grant No. 51172089), the Natural Science Foundation of Education Department of Guizhou Province, China (Grant Nos. KY [2013]183 and LH [2015]7232), and the Research Fund for the Doctoral Program of Tongren University, China (Grant No. DS1302).

  13. Synthesis and piezoelectric properties of BaTiO3-doped lead-free Li0.12Na0.88NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Mitra, Supratim; Rathore, Deepshikha

    2016-05-01

    New lead-free (1-x)Li0.12Na0.88NbO3-xBaTiO3 [(1-x)LNN-xBT] (x = 0.0, 0.1, 0.2, 0.3, 0.4) piezoelectric ceramics have been synthesized using conventional ceramics processing route. The phase analysis revealed that material undergoes two phase transition: orthorhombic to tetragonal around x = 0.2 and tetragonal to cubic for x ≥ 0.3. The microstructural analysis confirms a homogeneous solid solution, well developed grains and a high sintered density. Ferroelectric and piezoelectric properties were investigated and the material is found suitable for memory, piezoelectric vibrators and low power transducers applications.

  14. Crystallization and electrical characteristics of 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 thin films under different annealing temperature and atmosphere.

    PubMed

    Diao, Chien-Chen; Yang, Cheng-Fu; Lin, Jing-Jenn

    2011-12-01

    0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 +1 wt% Bi2O3 (NBT-BT3) ceramic is used as target to deposit the NBT-BT3 thin films. The excess 1wt% Bi2O3 is used to compensate the vaporization of Bi2O3 during the sintering and annealing processes. NBT-BT3 thin films are successfully deposited using radio frequency (RF) magnetron sputter method and crystallized subsequently using a conventional furnace annealing (CFA) process. The annealed process is conducted in air and in oxygen atmosphere at temperatures ranging from 600-800 degrees C for 60 min. As compared with the as-deposited NBT-BT3 thin films, the CFA-treated process has improved the grain growth and crystallization. We will show that the annealing atmosphere is the more important parameter to influence the grain growth and crystallization of NBT-BT3 thin films than the annealing temperature. The influences of CFA-treated temperature and atmosphere on the electrical characteristics of NBT-BT3 thin films, including the polarization characteristics (Pr, Ps, and Ec values), the capacitance-voltage (C-V) curves, and the leakage current density-electric field (J-E) curves, are also investigated in this study. PMID:22408948

  15. Dramatic influence of Dy3+ doping on strain and domain structure in lead-free piezoelectric 0.935(Na1/2Bi1/2)TiO3-0.065BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Li, C. Q.; Yao, Q. R.; Zhang, J. Z.; Hu, Z. G.; Wang, F. F.; Liu, A. Y.; Shi, W. Z.; Chu, J. H.

    2015-12-01

    An electric-field induced giant strain response and doping level dependent domain structural variations have been studied in the dysprosium (Dy3+)-modified 0.935(Na1/2Bi1/2)TiO3-0.065BaTiO3(xDy : NBBT) ceramics with the doping levels of 0%, 0.5%, 1%, and 2%. X-ray diffraction and Raman spectroscopy analyses not only demonstrates the change in ionic configurations induced by Dy3+ doping, but also shows the local crystal symmetry for x ≥ 0.5% doping levels to deviate from the idealized cubic structure. Piezoresponse force microscopy measurement exhibits the presence of an intermediate phase with orthorhombic symmetry at the critical Dy3+ doping level of 2%. Moreover, at this doping level, a giant recoverable nonlinear strain of ˜0.44% can be observed with high normalized strain (Smax/Emax) of 728 pm/V. At the same applied field, the strain exhibits a 175% increase than that of NBBT ceramic. Such a large strain stems from the varying coherence lengths of polar nanoregions (PNRs) and an unusual reversible 90° domain switching caused by the symmetry conforming property of point defects, where the restoring force is provided by unswitchable defects. The mechanism reveals a new possibility to achieve large electric-field strain effect for a wide range of ferroelectric systems, which can lead to applications in novel "on-off" actuators.

  16. Effect of grain boundary layer strain on the magnetic and transport properties of (100- x) La 0.7Ca 0.3MnO 3/( x) BaTiO 3 composites showing enhanced magnetoresistance

    NASA Astrophysics Data System (ADS)

    Bose, Esa; Taran, S.; Karmakar, S.; Chaudhuri, B. K.; Pal, S.; Sun, C. P.; Yang, H. D.

    2007-07-01

    A ferromagnetic/ferroelectric composite system, viz. (100- x)La 0.7Ca 0.3 MnO 3 [LCMO]/( x) BaTiO 3 [BTO] (with x=0.0%, 1.0%, 5.0%, 7.5%, 10.0% and 15.0%, in wt%) has been synthesized and the temperature-dependent DC magnetization M( T), resistivity ρ( T), magnetoresistance (MR), and thermoelectric power S( T) have been studied. Both metal-insulator transition temperature ( TMI) and the corresponding Curie temperature ( TC) decrease whereas peak resistivity at TMI increases as x is enhanced from 0.0% to 10.0%. For x>10.0%, this trend of variation is reversed. A maximum three-fold increase of magnetoresistance (MR) is observed (for sample with x=10.0%) due to the addition of ferroelectric (non-magnetic) perovskite BTO (compared to the mother compound LCMO). Interestingly, thermoelectric power S( T) shows a pronounced depression (dip) near the magnetic transition region for the composite samples. The above results have been analyzed considering strain induced by the LCMO/BTO grain boundary layer (BL).

  17. Dielectric and impedance spectroscopic studies of 0.8BaTiO3-0.2Bi0.5K0.5TiO3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Ramesh, M. N. V.; Ramesh, K. V.

    2015-06-01

    0.8BaTiO3-0.2Bi0.5K0.5TiO3 (BT-BKT20) lead-free ceramics were prepared by conventional solid state reaction method followed by high energy ball milling. The formation of a single phase tetragonal structure in the material was confirmed by X-ray diffraction. Frequency and temperature-dependent dielectric studies show relaxor behavior in the BT-BKT20 which was found to obey modified Curie-Weiss law with degree of diffuseness 1.573. Complex impedance and electric modulus spectroscopy studies reveal temperature-dependent relaxation process in the material. The Cole-Cole plots were measured at high temperatures at which grain effect was observed. Impedance and electric modulus spectroscopy studies show non-Debye kind of conductivity relaxation process in the present material. Activation energies were calculated from impedance and electric modulus spectroscopy and the values of activation energy indicated that the conduction is ionic in nature. AC and DC conductivity have been measured and studied at different temperatures.

  18. Effect of Cooling Rate on the Microstructure and Mechanical Properties of Sn-1.0Ag-0.5Cu-0.2BaTiO3 Composite Solder

    NASA Astrophysics Data System (ADS)

    Yang, Li; Ge, Jinguo; Liu, Haixiang; Xu, Liufeng; Bo, Anbing

    2015-11-01

    The microstructure, interfacial intermetallic compound (IMC) layer, microhardness, tensile properties, and fracture surfaces of Sn-1.0Ag-0.5Cu-0.2BaTiO3 composite solder were explored under three different cooling conditions (water-, air-, and furnace-cooled) during solidification. The average grain size was refined and the volume fraction of primary β-Sn dendrites increased with increasing cooling rate. The thickness of the IMC layer increased as the cooling rate was decreased, and the morphology also transformed from scallop shaped, for a rapid cooling rate, to irregular shaped for slower cooling; a Cu3Sn IMC layer was detected between the Cu6Sn5 IMC and copper substrate under the furnace-cooled condition, but not in water- or air-cooled specimens. The mechanical properties, including the microhardness and tensile properties, improved with rapid solidification due to the combined effects of grain refinement and a secondary strengthening mechanism. Fracture surfaces after tensile tests showed that the amount of dimples decreased and a cleavage-like pattern increased as the cooling rate was decreased from the water-cooled to furnace-cooled condition, so the fracture process transformed from ductile to mixed-mode fracture. A refined microstructure and excellent mechanical properties were obtained for the rapidly cooled sample.

  19. Thermal, dielectric and ferroelectric properties of 0.925BaTiO3-0.075Pb(Zn1/3Nb2/3)O3 ceramic

    NASA Astrophysics Data System (ADS)

    Suchanicz, J.; Nogas-Ćwikiel, E.; Sitko, D.; Handke, B.; Jelen, P.; Klimczyk, P.

    2015-08-01

    New low-lead content 0.925BaTiO3-0.075PbZn1/3Nb2/3O3 (0.925BT-0.075PZN) ceramic was fabricated by the spark-plasma-sintering method. X-ray diffraction measurements showed that the obtained specimen possesses a pure perovskite structure. The microstructure investigation indicated a dense ceramic structure with 95% relative density determined by the Archimedes method. Composition undergoes a sequence of phase transitions as pure barium titanate (BT). Dielectric study revealed that the electric permittivity decreases at its maximum and the phase transition shifts to a higher temperature after lead zinc niobate doping of BT. Besides, the dielectric dispersion and polarization increases and decreases, respectively. Obtained results were discussed in term of the difference between ionic size and its mass and local elastic and electric fields. The results show that investigated ceramic is one of the promising low-lead materials for electronic applications.

  20. Multilayer ceramic capacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 for temperature stable and high energy density capacitor applications

    NASA Astrophysics Data System (ADS)

    Kumar, Nitish; Ionin, Aleksey; Ansell, Troy; Kwon, Seongtae; Hackenberger, Wesley; Cann, David

    2015-06-01

    The need for miniaturization without compromising cost and performance continues to motivate research in advanced capacitor devices. In this report, multilayer ceramic capacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 (BT-BZT) were fabricated and characterized. In bulk ceramic embodiments, BT-BZT has been shown to exhibit relative permittivities greater than 1000, high resistivities (ρ > 1 GΩ-cm at 300 °C), and negligible saturation up to fields as high as 150 kV/cm. Multilayer capacitor embodiments were fabricated and found to exhibit similar dielectric and resistivity properties. The energy density for the multilayer ceramics reached values of ˜2.8 J/cm3 at room temperature at an applied electric field of ˜330 kV/cm. This represents a significant improvement compared to commercially available multilayer capacitors. The dielectric properties were also found to be stable over a wide range of temperatures with a temperature coefficient of approximately -2000 ppm/K measured from 50 to 350 °C, an important criteria for high temperature applications. Finally, the compatibility of inexpensive Ag-Pd electrodes with these ceramics was also demonstrated, which can have implications on minimizing the device cost.

  1. Phase diagram and electrostrictive properties of Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Shan-Tao; Yan, Feng; Yang, Bin; Cao, Wenwu

    2010-09-01

    Phase diagram of Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3 ternary system has been analyzed and (0.94-x)BNT-0.06BT-xKNN (0.15≤x≤0.30) ceramics have been prepared and investigated. Pseudocubic structures were confirmed by x-ray diffractions and its preliminary Rietveld refinements. P-E, S-E, and S-P2 profiles (where P, E, and S denote polarization, electric field, and strain, respectively) indicate electrostrictive behavior of all ceramics. The compositions with x =0.20 and 0.25 show pure electrostrictive characteristics. The dissipation energy, electrostrictive strain, and electrostrictive coefficient have been determined and compared with other lead-free and lead-containing electrostrictors. The electrostrictive coefficient can reach as high as 0.026 m4/C2, about 1.5 times of the value of traditional Pb-based electrostrictors.

  2. Enhanced electrostricitive properties and thermal endurance of textured (Bi0.5Na0.5)TiO3-BaTiO3-(K0.5Na0.5)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Hao, Jigong; Ye, Chenggen; Shen, Bo; Zhai, Jiwei

    2013-08-01

    Textured 0.92(Bi0.5Na0.5)TiO3-0.06BaTiO3-0.02(K0.5Na0.5)NbO3 (BNT-BT-KNN) ceramics have been produced by tape casting with pure-phase (Bi0.5Na0.5)TiO3 templates. Through the approach of texture construction, enhanced electrostrictive response was obtained with an electrostrictive coefficient Q33 (˜0.024 m4/C2 at 60 kV/cm) and good thermostability comparable with that of traditional Pb-based electrostrictors. Even at an electric-field as low as 35 kV/cm or at a temperature as high as 180 °C, samples still possess a large electrostrictive response with Q33 > 0.022 m4/C2, suggesting it is very promising for practical applications as a lead-free electrostrictive material owning to its wide usage range. Moreover, reducing the applied electric-filed or increasing temperature can both induce the predominant to pure electrostriction transition due to the little contributions of electrostriction strain from ferroelectric domain switching. Our work may provide a new recipe for designing high-performance BNT-based lead-free electrostrictive materials by means of texture construction.

  3. Effect of misfit strain on multiferroic and magnetoelectric properties of epitaxial La0.7Sr0.3MnO3/BaTiO3 bilayer

    NASA Astrophysics Data System (ADS)

    Li, T. X.; Zhang, M.; Yu, F. J.; Hu, Z.; Li, K. S.; Yu, D. B.; Yan, H.

    2012-02-01

    La0.7Sr0.3MnO3/BaTiO3 (LSMO/BTO) bilayer films were grown on (0 0 1) oriented SrTiO3 (STO), LaAlO3 (LAO) and (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates by pulsed laser deposition. The bilayer deposited on the LSAT substrate presented the best ferromagnetic properties due to the smallest lattice mismatch between LSAT and LSMO. However, the best ferroelectric properties and strongest magnetoelectric (ME) effect existed in the bilayer on the STO substrate due to the minimal compressive strain in the BTO film. All these showed similar frequency-dependent ME behaviour from 0.1 to 100 kHz, and the largest value of ME voltage coefficient (αE) was obtained on the STO substrate. The values of αE were around 263 mV cm-1 Oe-1, 202 mV cm-1 Oe-1 and 169 mV cm-1 Oe-1 at 1 kHz on STO, LSAT and LAO substrates, respectively, which were at least one order of magnitude higher than previously reported values for similar composites and were ascribed mainly to the rather low dielectric constant of the BTO film.

  4. Large enhancement of magnetic anisotropy and laser induced resistive switching effect in La0.7Sr0.3MnO3 films due to strain from BaTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Kalappattil, V.; Das, R.; Srikanth, H.; Phan, M. H.; Moya, X.

    Multifunctional oxide materials are interesting for their fundamental physical properties and technological applications. Epitaxial films of La0.7Sr0.3MnO3 (LSMO) on BaTiO3 (BTO) show intriguing properties such as a giant magnetoelectric effect due to strain from BTO substrate. The LSMO film shows sharp jumps in magnetization M(T) and resistance R(T) at first-order structural phase transitions of BTO (TR-O 200K and TO-T 270 K) due to strain coupling from BTO. A temperature evolution of effective in-plane anisotropy field (HK) measured using the radio-frequency transverse susceptibility (TS) shows a sharp increase in HK around TR-O, which vanishes around TO-T.The in-plane magnetic anisotropy plays an important role in changing the magnetic and resistive states around TO-T. A switchable laser-induced resistive change of up to 300 %, which is about 10 times greater than those of conventional oxide systems, has been achieved in LSMO films using a 0.5 W violet laser just below the TO-T.The repeatability and stability of the laser-induced resistive switching effect reveal potential applications of LSMO/BTO heterostructures in developing new type of temperature sensors and memory devices. Work at USF supported by ARO Grant No. W911NF-15-1-0626.

  5. Visible Light-Induced Photocatalytic and Antibacterial Activity of Li-Doped Bi0.5Na0.45K0.5TiO3-BaTiO3 Ferroelectric Ceramics

    NASA Astrophysics Data System (ADS)

    Kushwaha, H. S.; Halder, Aditi; Jain, D.; Vaish, Rahul

    2015-11-01

    The visible light-active ferroelectric photocatalyst Bi0.5Na0.45Li0.05K0.5TiO3-BaTiO3 (BNKLBT) was synthesized by a solid-state method and its photocatalytic, photoelectrochemical, and antibacterial properties were investigated. In a chronoamperometric study the current density under visible light was 30 μA/cm2, which is three times more than that observed under dark conditions. The compound's visible light photocatalytic activity was investigated for degradation of an organic dye (methyl orange) and an estrogenic pollutant (estriol).The kinetic rate constants calculated for photocatalytic degradation of methyl orange and estriol were 0.007 and 0.056 min-1, respectively. High photocatalytic and photoelectrochemical activity was a result of effective separation of photo-generated charge carriers, because of the ferroelectric nature of the catalyst. The effect of different charge-trapping agents on photocatalytic degradation was studied to investigate the effect of active species and the degradation pathway. Antimicrobial activity was investigated for Escherichia coli and Aspergillus flavus. The anti-bacterial action of BNKLBT was compared with that of the commercial antibiotic kanamycin (k30).

  6. Temperature dependence of Zr and Ti K-edge XANES spectra for para- and ferro-electric perovskite-type PbZrO3, PbTiO3 and BaTiO3

    NASA Astrophysics Data System (ADS)

    Yoshiasa, A.; Nakatani, T.; Hiratoko, T.; Tobase, T.; Nakatsuka, A.; Okube, M.; Arima, H.; Sugiyama, K.

    2016-05-01

    Zr and Ti K-edge XANES spectra of PbZrO3, PbTiO3 and BaTiO3 perovskite-type compounds were measured in the temperature range from 10K to 850K. Quantitative comparisons for the near-edge spectra were performed in a wide temperature range using the absorption intensity invariant point (AIIP) standardization. Clear temperature dependence for pre-edge shoulder is identified by the calculating the temperature difference of the XANES spectrum intensity. Decrease of pre-edge shoulder and peak intensity is observed only in the para- and ferro-electric phases and draw curves, not straight lines. The gradients for shoulder and pre-edge peak intensity are rich in a variety. The decrease in absorption of pre-edge peak and shoulder is speculated due to the shift from the off-centre position of the Zr atom with respect to the oxygen octahedron to center position. The Zr ion in the PbZrO3 para-electric phase has same temperature behaviors of Ti ions in the ferroelectric perovskite.

  7. Tuning of dielectric, pyroelectric and ferroelectric properties of 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 ceramic by internal clamping

    NASA Astrophysics Data System (ADS)

    Patel, Satyanarayan; Chauhan, Aditya; Kundu, Swarup; Madhar, Niyaz Ahamad; Ilahi, Bouraoui; Vaish, Rahul; Varma, K. B. R.

    2015-08-01

    This study systematically investigates the phenomenon of internal clamping in ferroelectric materials through the formation of glass-ceramic composites. Lead-free 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 (BNT-BT-ST) bulk ferroelectric ceramic was selected for the course of investigation. 3BaO - 3TiO2 - B2O3 (BTBO) glass was then incorporated systematically to create sintered samples containing 0%, 2%, 4% and 6% glass (by weight). Upon glass induction features like remnant polarization, saturation polarization, hysteresis losses and coercive field could be varied as a function of glass content. Such effects were observed to benefit derived applications like enhanced energy storage density ˜174 kJ/m3 to ˜203 kJ/m3 and pyroelectric coefficient 5.7x10-4 Cm-2K-1 to 6.8x10-4 Cm-2K-1 by incorporation of 4% glass. Additionally, BNT-BT-ST depolarization temperature decreased from 457K to 431K by addition of 4% glass content. Glass incorporation could systematically increases diffuse phase transition and relaxor behavior temperature range from 70 K to 81K and 20K to 34 K, respectively when 6% and 4% glass content is added which indicates addition of glass provides better temperature stability. The most promising feature was observed to be that of dielectric response tuning. It can be also used to control (to an extent) the dielectric behavior of the host ceramic. Dielectric permittivity and losses decreased from 1278 to 705 and 0.109 to 0.107 for 6% glass, at room temperature. However this reduction in dielectric constant and loss increases pyroelectric figures of merit (FOMs) for high voltage responsivity (Fv) high detectivity (Fd) and energy harvesting (Fe) from 0.018 to 0.037 m2C-1, 5.89 to 8.85 μPa-1/2 and 28.71 to 61.55 Jm-3K-2, respectively for 4% added ceramic-glass at room temperature. Such findings can have huge implications in the field of tailoring ferroelectric response for application specific requirements.

  8. Orthogonality Measurement for Homogenous Projects-Bases

    ERIC Educational Resources Information Center

    Ivan, Ion; Sandu, Andrei; Popa, Marius

    2009-01-01

    The homogenous projects-base concept is defined. Next, the necessary steps to create a homogenous projects-base are presented. A metric system is built, which then will be used for analyzing projects. The indicators which are meaningful for analyzing a homogenous projects-base are selected. The given hypothesis is experimentally verified. The…

  9. 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).

  10. Strongly enhanced flux pinning in the YBa2Cu3O7 -x films with the co-doping of BaTiO3 nanorod and Y2O3 nanoparticles at 65 K

    NASA Astrophysics Data System (ADS)

    Wang, Hong-Yan; Ding, Fa-Zhu; Gu, Hong-Wei; Zhang, Teng

    2015-09-01

    YBa2Cu3O7 - x (YBCO) films with co-doping BaTiO3 (BTO) and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates (TFA-MOD). The properties of the BTO/Y2O3 co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM). The optimized content of yttrium excess in the BTO/Y2O3 co-doped YBCO films is 10 mol.%, and the critical current density is as high as ˜17 mA/cm2 (self-field, 65 K) by the magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density (JC) not only at the self-magnetic field, but also in the applied magnetic field. Project supported by the National Natural Science Foundation of China (Grant No. 51272250), the National Basic Research Program of China (Grant No. 2011CBA00105), the National High Technology Research and Development Program of China (Grant No. 2014AA032702), and the Natural Science Foundation of Beijing, China (Grant No. 2152035).

  11. Liquid phase sintering of 20Bi(Zn0.5Ti0.5)O 3-80BaTiO3 dielectrics with bismuth-zinc-borate and bismuth borosilicate glasses

    NASA Astrophysics Data System (ADS)

    Shahin, David I.

    Dielectrics in the Bi(Zn0.5Ti0.5)O3-BaTiO 3 system (specifically 20BZT-80BT, in mol%) are promising candidates for high energy density capacitor applications due to broad temperature-dependent dielectric constant maxima and a relatively field-independent permittivity. Bulk samples require sintering temperatures of greater than 1180°C to reach useful densities. Due to incompatibility of Bi with low-pO2 processing, BZT-BT-based multilayer capacitors must utilize noble metal electrodes that resist oxidation during sintering. Sintering temperatures must be reduced to allow use of less expensive electrode materials (Cu, etc.). This work studies the reduced temperature sintering behavior and dielectric properties of BZT-BT sintered with 30Bi2O3-30ZnO-40B 2O3 and 50Bi2O3-25B2O 3-25SiO2 (mol%) liquid phase formers. Dielectrics sintered with 1v% borate additions and 5v% additions of either the borate or borosilicate achieved relative densities greater than 95% after sintering at 1000°C for four hours. All compositions retained the relaxor behavior exhibited by pure 20BZT-80BT. Increased borate additions led to greater dielectric constant reductions, while increased borosilicate additions yielded no clear trend in the dielectric constant reduction. Energy densities were estimated between 0.3-0.5 J/cm3; smaller glass additions typically led to larger energy densities. Dielectrics sintered with 1v% borate additions are of interest due to their high relative densities (approx. 96%) and energy densities of approximately 0.5 J/cm3 under 100kV/cm electric fields. Studies of BZT-BT/glass interfaces revealed the formation of crystalline interfacial layers less than 10 microns thick. The borate formed a bismuth titanate phase (likely Bi4Ti3O12) during heating to 700°C, whereas the borosilicate formed a barium silicate phase (likely BaSiO3) during processing to 800°C. Similar phases are expected to be present in the liquid phase sintered dielectrics and likely affect the BZT-BT sintering and dielectric behavior.

  12. High Piezoelectric Response in (Li0.5Sm0.5)2+-Modified 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 Near the Nonergodic-Ergodic Relaxor Transition

    NASA Astrophysics Data System (ADS)

    Xu, Jiwen; Li, Qinglin; Zhou, Changrong; Zeng, Weidong; Xiao, Jianrong; Ma, Jiafeng; Yuan, Changlai; Chen, Guohua; Rao, Guanghui; Li, Xuqiong

    2016-06-01

    The (Bi0.5Na0.5)TiO3-BaTiO3 system is a promising Pb-free piezoelectric material to substitute for environmentally undesirable Pb-based ferroelectrics. However, understanding the origin of its high piezoelectric response is a fundamental issue that has remained unclear for decades. Here, complex ions (Li0.5Sm0.5)2+ were introduced to dictate the stability of the electrically-induced ferroelectric state in 0.93(Bi0.5Na0.5)1- x (Li0.5Sm0.5) x TiO3-0.07BaTiO3 relaxor ceramics. The applied electric field induces a phase transition from a non-ergodic state to a ferroelectric state as well as the realignment of ferroelectric domains. The non-ergodic relaxor state with x = 0-0.02 is accompanied by relatively high piezoelectric activity and the strongest piezoelectricity is observed near the crossover from the nonergodic to the ergodic state. The stable␣ferroelectric state cannot survive after the removal of the application electric field for the high doping level due to the enhancement of the random field, which is responsible for the rapid decrease of piezoelectric properties for x > 0.02 compositions.

  13. Interfacial Ion Intermixing Effect on Four-Resistance States in La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 Multiferroic Tunnel Junctions.

    PubMed

    Huang, Weichuan; Lin, Yue; Yin, Yuewei; Feng, Lei; Zhang, Dalong; Zhao, Wenbo; Li, Qi; Li, Xiaoguang

    2016-04-27

    A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents at least four resistance states in a single memory cell and therefore opens an avenue for the development of the next generation of high-density nonvolatile memory devices. Here, using the all-perovskite-oxide La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 as a model MFTJ system, we demonstrate asymmetrical Mn-Ti sublattice intermixing at the La0.7Sr0.3MnO3/BaTiO3 interfaces by direct local measurements of the structure and valence, which reveals the relationship between ferroelectric polarization directions and four-resistance states, and the low temperature anomalous tunneling behavior in the MFTJ. These findings emphasize the crucial role of the interfaces in MFTJs and are quite important for understanding the electric transport of MFTJs as well as designing high-density multistates storage devices. PMID:27055530

  14. Structure and electrical properties of 0.80 Na0.5 Bi0.5 TiO3-0.16 K0.5 Bi0.5 TiO3-0.04 BaTiO3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Aravinth, K.; Muneeswaran, M.; Babu, G. Anandha; Giridharan, N. V.; Ramasamy, P.

    2016-05-01

    Lead free pervoskite 0.80 Na0.5 Bi0.5 TiO3-0.16 K0.5 Bi0.5 TiO3-0.04 BaTiO3 (NKBBT) ceramics were fabricated via conventional solid state processing technique sintered at 1200 °C and their crystal structures and electrical properties were systematically studied. Structure of the prepared NKBBT ceramics was confirmed by Powder X-ray diffraction analysis. The dependence of dielectric constant on temperature for various frequencies (100 Hz-100 KHz) has been determined. The diffuse transition is observed in the variation of dielectric constant and it provides evidence for the relaxor characteristics. The ferroelectric response of the NKBBT ceramics with different frequency was studied. Polarisation electric field hysteresis loops revealed that the remnant polarization is 6.88 µC/cm2 and coercive electric field is 66.42 kV/cm.

  15. Giant strain with ultra-low hysteresis and high temperature stability in grain oriented lead-free K0.5Bi0.5TiO3-BaTiO3-Na0.5Bi0.5TiO3 piezoelectric materials

    PubMed Central

    Maurya, Deepam; Zhou, Yuan; Wang, Yaojin; Yan, Yongke; Li, Jiefang; Viehland, Dwight; Priya, Shashank

    2015-01-01

    We synthesized grain-oriented lead-free piezoelectric materials in (K0.5Bi0.5TiO3-BaTiO3-xNa0.5Bi0.5TiO3 (KBT-BT-NBT) system with high degree of texturing along the [001]c (c-cubic) crystallographic orientation. We demonstrate giant field induced strain (~0.48%) with an ultra-low hysteresis along with enhanced piezoelectric response (d33 ~ 190pC/N) and high temperature stability (~160°C). Transmission electron microscopy (TEM) and piezoresponse force microscopy (PFM) results demonstrate smaller size highly ordered domain structure in grain-oriented specimen relative to the conventional polycrystalline ceramics. The grain oriented specimens exhibited a high degree of non-180° domain switching, in comparison to the randomly axed ones. These results indicate the effective solution to the lead-free piezoelectric materials. PMID:25716551

  16. Mechanical homogenization increases bacterial homogeneity in sputum.

    PubMed

    Stokell, Joshua R; Khan, Ammad; Steck, Todd R

    2014-07-01

    Sputum obtained from patients with cystic fibrosis (CF) is highly viscous and often heterogeneous in bacterial distribution. Adding dithiothreitol (DTT) is the standard method for liquefaction prior to processing sputum for molecular detection assays. To determine if DTT treatment homogenizes the bacterial distribution within sputum, we measured the difference in mean total bacterial abundance and abundance of Burkholderia multivorans between aliquots of DTT-treated sputum samples with and without a mechanical homogenization (MH) step using a high-speed dispersing element. Additionally, we measured the effect of MH on bacterial abundance. We found a significant difference between the mean bacterial abundances in aliquots that were subjected to only DTT treatment and those of the aliquots which included an MH step (all bacteria, P = 0.04; B. multivorans, P = 0.05). There was no significant effect of MH on bacterial abundance in sputum. Although our results are from a single CF patient, they indicate that mechanical homogenization increases the homogeneity of bacteria in sputum. PMID:24759710

  17. Is the Universe homogeneous?

    PubMed

    Maartens, Roy

    2011-12-28

    The standard model of cosmology is based on the existence of homogeneous surfaces as the background arena for structure formation. Homogeneity underpins both general relativistic and modified gravity models and is central to the way in which we interpret observations of the cosmic microwave background (CMB) and the galaxy distribution. However, homogeneity cannot be directly observed in the galaxy distribution or CMB, even with perfect observations, since we observe on the past light cone and not on spatial surfaces. We can directly observe and test for isotropy, but to link this to homogeneity we need to assume the Copernican principle (CP). First, we discuss the link between isotropic observations on the past light cone and isotropic space-time geometry: what observations do we need to be isotropic in order to deduce space-time isotropy? Second, we discuss what we can say with the Copernican assumption. The most powerful result is based on the CMB: the vanishing of the dipole, quadrupole and octupole of the CMB is sufficient to impose homogeneity. Real observations lead to near-isotropy on large scales--does this lead to near-homogeneity? There are important partial results, and we discuss why this remains a difficult open question. Thus, we are currently unable to prove homogeneity of the Universe on large scales, even with the CP. However, we can use observations of the cosmic microwave background, galaxies and clusters to test homogeneity itself. PMID:22084298

  18. Creating Poetry.

    ERIC Educational Resources Information Center

    Drury, John

    Encouraging exploration and practice, this book offers hundreds of exercises and numerous tips covering every step involved in creating poetry. Each chapter is a self-contained unit offering an overview of material in the chapter, a definition of terms, and poetry examples from well-known authors designed to supplement the numerous exercises.…

  19. Nonstationary homogeneous nucleation

    NASA Technical Reports Server (NTRS)

    Harstad, K. G.

    1974-01-01

    The theory of homogeneous condensation is reviewed and equations describing this process are presented. Numerical computer solutions to transient problems in nucleation (relaxation to steady state) are presented and compared to a prior computation.

  20. Creating Community

    PubMed Central

    Budin, Wendy C.

    2009-01-01

    In this column, the editor of The Journal of Perinatal Education describes ways that Lamaze International is helping to create a community for those who share a common interest in promoting, supporting, and protecting natural, safe, and healthy childbirth. The editor also describes the contents of this issue, which offer a broad range of resources, research, and inspiration for childbirth educators in their efforts to promote normal birth. PMID:19936112

  1. Creating bulk nanocrystalline metal.

    SciTech Connect

    Fredenburg, D. Anthony; Saldana, Christopher J.; Gill, David D.; Hall, Aaron Christopher; Roemer, Timothy John; Vogler, Tracy John; Yang, Pin

    2008-10-01

    Nanocrystalline and nanostructured materials offer unique microstructure-dependent properties that are superior to coarse-grained materials. These materials have been shown to have very high hardness, strength, and wear resistance. However, most current methods of producing nanostructured materials in weapons-relevant materials create powdered metal that must be consolidated into bulk form to be useful. Conventional consolidation methods are not appropriate due to the need to maintain the nanocrystalline structure. This research investigated new ways of creating nanocrystalline material, new methods of consolidating nanocrystalline material, and an analysis of these different methods of creation and consolidation to evaluate their applicability to mesoscale weapons applications where part features are often under 100 {micro}m wide and the material's microstructure must be very small to give homogeneous properties across the feature.

  2. Inverse focusing inside turbid media by creating an opposite virtual objective.

    PubMed

    Yu, Yeh-Wei; Chen, Szu-Yu; Lin, Che-Chu; Sun, Ching-Cherng

    2016-01-01

    Limited by the penetration depth, imaging of thick bio-tissues can be achieved only by epi-detection geometry. Applications based on forward-emitted signals or bidirectional illumination are restricted by lack of an opposite objective. A method for creating an opposite virtual objective inside thick media through phase conjugation was first proposed. Under forward illumination, the backward scattering light from the media was collected to generate a phase conjugate wave, which was sent back to the media and formed an inverse focusing light. Samples combined with a diffuser or a mouse skin were used as specimens. Inverse focusing was successfully demonstrated by applying holography-based optical phase conjugation with a BaTiO3. This result indicates the capability to create an opposite virtual objective inside live tissues. The proposed method is compatible with current coherent imaging and super-resolution imaging technologies. It creates a possible way for forward-emitted signals collection and bidirectional illumination in thick specimens. PMID:27404383

  3. Inverse focusing inside turbid media by creating an opposite virtual objective

    PubMed Central

    Yu, Yeh-Wei; Chen, Szu-Yu; Lin, Che-Chu; Sun, Ching-Cherng

    2016-01-01

    Limited by the penetration depth, imaging of thick bio-tissues can be achieved only by epi-detection geometry. Applications based on forward-emitted signals or bidirectional illumination are restricted by lack of an opposite objective. A method for creating an opposite virtual objective inside thick media through phase conjugation was first proposed. Under forward illumination, the backward scattering light from the media was collected to generate a phase conjugate wave, which was sent back to the media and formed an inverse focusing light. Samples combined with a diffuser or a mouse skin were used as specimens. Inverse focusing was successfully demonstrated by applying holography-based optical phase conjugation with a BaTiO3. This result indicates the capability to create an opposite virtual objective inside live tissues. The proposed method is compatible with current coherent imaging and super-resolution imaging technologies. It creates a possible way for forward-emitted signals collection and bidirectional illumination in thick specimens. PMID:27404383

  4. Inverse focusing inside turbid media by creating an opposite virtual objective

    NASA Astrophysics Data System (ADS)

    Yu, Yeh-Wei; Chen, Szu-Yu; Lin, Che-Chu; Sun, Ching-Cherng

    2016-07-01

    Limited by the penetration depth, imaging of thick bio-tissues can be achieved only by epi-detection geometry. Applications based on forward-emitted signals or bidirectional illumination are restricted by lack of an opposite objective. A method for creating an opposite virtual objective inside thick media through phase conjugation was first proposed. Under forward illumination, the backward scattering light from the media was collected to generate a phase conjugate wave, which was sent back to the media and formed an inverse focusing light. Samples combined with a diffuser or a mouse skin were used as specimens. Inverse focusing was successfully demonstrated by applying holography-based optical phase conjugation with a BaTiO3. This result indicates the capability to create an opposite virtual objective inside live tissues. The proposed method is compatible with current coherent imaging and super-resolution imaging technologies. It creates a possible way for forward-emitted signals collection and bidirectional illumination in thick specimens.

  5. Homogeneity and Entropy

    NASA Astrophysics Data System (ADS)

    Tignanelli, H. L.; Vazquez, R. A.; Mostaccio, C.; Gordillo, S.; Plastino, A.

    1990-11-01

    RESUMEN. Presentamos una metodologia de analisis de la homogeneidad a partir de la Teoria de la Informaci6n, aplicable a muestras de datos observacionales. ABSTRACT:Standard concepts that underlie Information Theory are employed in order design a methodology that enables one to analyze the homogeneity of a given data sample. Key : DATA ANALYSIS

  6. Effect of the Yb3+ Concentration in Up-Conversion and Electrical Properties of Ho3+/Yb3+ Co-doped (0.94Na0.5Bi0.5TiO3-0.06BaTiO3) Ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Qian; Li, Yanxia; Li, Jun; Chai, Xiaona; Zhao, Haifeng; Wang, Xusheng; Yao, Xi

    2016-07-01

    Ho3+/Yb3+ co-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-BT:Ho3+/Yb3+) ceramics were synthesized by solid-state reaction and characterized by x-ray diffraction (XRD), luminescent, dielectric, ferroelectric and piezoelectric measurements. The XRD diffraction data showed that all the ceramics were single phase with a perovskite structure. Bright green up-conversion (UC) emission bands (545 nm) and weak red UC emission bands (660 nm) corresponded to the transitions from (5F4, 5S2) → 5I8 and 4I5 → 5I8, respectively. Furthermore, optimized UC emission intensity was observed in the NBT-BT:0.005Ho3+/0.03Yb3+ samples. The thermal behavior of UC emission in the ceramics was also investigated and the maximum sensitivity based on fluorescence intensity ratio (FIR) technology was approximately 0.0042 K-1 at 100 K. Moreover, relatively good dielectric properties ( ɛ = 4475) and ferroelectric properties ( P r = 32 μ/cm2 and E c = 37 kV) were obtained in NBT-BT:0.005Ho3+/0.005Yb3+. As a multi-functional material, NBT-BT:Ho3+/Yb3+ ceramics may be useful in electro-optical devices.

  7. Ferroelectric control of spin injection in La0.7 Sr0.3 MnO3 /BaTiO3 /La0.5 Ca0.5 MnO3 /La0.7 Sr0.3 MnO3 multiferroic tunnel junctions with a bilayer barrier

    NASA Astrophysics Data System (ADS)

    Yin, Yuewei; Miao, L. D.; Du, R. Z.; Li, Q.

    2015-03-01

    Using a ferroelectric (FE) barrier with ferromagnetic electrodes has become a promising method for controlling spin injection by purely electrical means, which is an important challenge in spintronics. Recently, we have designed a La0.7Sr0.3MnO3(LSMO) /BaTiO3(BTO) /La0.5Ca0.5MnO3(LCMO) /LSMO tunnel junctions in which the reversal of FE polarization of BTO will magnetoelectrically lead to a FM metallic - antiferromagnetic insulating phase transition in LCMO and result in an enhanced tunneling electroresistance (TER). Using the bilayer barrier, we observed that the spin injection can be controlled by barrier polarization reversal as shown in the change of tunneling magnetoresistance (TMR). The temperature evolution of tunnel electromagnetoresistance (TEMR) (percentage ratio between the TMR values for the two polarization states), which is directly proportional to the change of tunnel-current spin polarization, was studied and larger TEMR was obtained with increasing temperature. Meanwhile, TEMR increases with TER effect for samples with different LCMO insertion thicknesses, suggesting a controllable strong electric control of tunnel-current spin polarization using a designed structure with proper interfaces.

  8. Lead- and alkali-metal-free BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 solid-solution thin films with high dielectric constant prepared on Si substrates by solution-based method

    NASA Astrophysics Data System (ADS)

    Kimura, Junichi; Mohamed-Tahar, Chentir; Shimizu, Takao; Uchida, Hiroshi; Funakubo, Hiroshi

    2014-09-01

    Lead- and alkali-metal-free BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 solid-solution thin films were prepared on (111)cSrRuO3/(111)Pt/TiO2/SiO2/(100)Si substrates by chemical solution deposition (CSD) and their crystal structure and dielectric properties were investigated. The lattice spacing as a function of z/(x + z) in xBaTiO3-0.1Bi(Mg0.5Ti0.5)O3-zBiFeO3 indicated the existence of phase boundaries (pseudocubic/rhombohedral) in the range of z/(x + z) = 0.33-0.56, where the relatively high relative dielectric constant, ɛr, of above 800 was obtained. On the other hand, dielectric loss, tan δ, of below 0.2 was confirmed in the range z/(x + z) = 0-0.87, which rapidly increased toward z/(x + z) = 1.0. The relatively high ɛr values of these films deposited on Si substrates by a solution-based process suggest that they can be used as alternative to Pb(Zr,Ti)O3, KNbO3, and (Bi1/2Na1/2)TiO3-based films.

  9. Properties of (Bi0.5Na0.5)TiO3-BaTiO3-(Bi0.5Na0.5)(Mn1/3Nb2/3)O3 Lead-Free Piezoelectric Ceramics and Its Application to Ultrasonic Cleaner

    NASA Astrophysics Data System (ADS)

    Tou, Tonshaku; Hamaguti, Yuki; Maida, Yuichi; Yamamori, Haruo; Takahashi, Kazutoshi; Terashima, Yoshimitsu

    2009-07-01

    The lead-free piezoelectric ceramics 0.82(Bi0.5Na0.5)TiO3-0.15BaTiO3-0.03(Bi0.5Na0.5)(Mn1/3Nb2/3)O3 (abbreviated as BNT-BT-BNMN) was prepared by a conventional process of ceramic engineering. The X-ray diffractometer (XRD) analysis showed that all compositions could form a single perovskite phase. The ceramics showed excellent piezoelectric properties with a coupling factor kt=41%, a mechanical quality factor Qm=500, a piezoelectric constant d33=110 pC/N, a relative permittivity ɛ33T/ɛ0=520, a dissipation factor tan δ=0.66%, a Curie point Tc=260 °C, and a density ρ=5.5 g/cm3. The physical properties of the ceramics were superior to those of hard Pb(Zr,Ti)O3 (PZT). The high-power characteristics of the ceramics were superior to those of hard PZT. A cylinder sample of lead-free ceramics was used to fabricate a bolt-clamped Langevin transducer (BLT) for application in the ultrasonic cleaner. The vibration velocity of BLT using the ceramics was higher than that of hard PZT under the same input power. The cleaning effect of an ultrasonic cleaner using the BLTs was very high and sufficiently good for commercial application.

  10. Effect of Nb-donor and Fe-acceptor dopants in (Bi1/2Na1/2)TiO3-BaTiO3-(K0.5Na0.5)NbO3 lead-free piezoceramics

    NASA Astrophysics Data System (ADS)

    Jo, Wook; Erdem, Emre; Eichel, Rüdiger-A.; Glaum, Julia; Granzow, Torsten; Damjanovic, Dragan; Rödel, Jürgen

    2010-07-01

    The role of Fe as an acceptor and Nb as a donor in [0.94-x](Bi1/2Na1/2)TiO3-0.06BaTiO3-x (K0.5Na0.5)NbO3 (100xKNN) (x=0.02 and 0.03) lead-free piezoceramics was investigated. X-ray diffraction analyses show that all the profiles are best-fitted with a cubic symmetry where Fe doping tends to induce a lattice expansion, while Nb doping does the opposite. The strain and polarization characteristics are enhanced and suppressed by the acceptor and donor dopants, respectively. The improvement in the electrical properties with acceptor doping is accompanied by the stabilization of a ferroelectric order. Electron paramagnetic resonance spectroscopic analysis suggests that the stabilization of the ferroelectric order by the Fe dopant originates from the formation of (FeTi'-VO••)• defect dipoles.

  11. Effect of the Yb3+ Concentration in Up-Conversion and Electrical Properties of Ho3+/Yb3+ Co-doped (0.94Na0.5Bi0.5TiO3-0.06BaTiO3) Ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Qian; Li, Yanxia; Li, Jun; Chai, Xiaona; Zhao, Haifeng; Wang, Xusheng; Yao, Xi

    2016-04-01

    Ho3+/Yb3+ co-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-BT:Ho3+/Yb3+) ceramics were synthesized by solid-state reaction and characterized by x-ray diffraction (XRD), luminescent, dielectric, ferroelectric and piezoelectric measurements. The XRD diffraction data showed that all the ceramics were single phase with a perovskite structure. Bright green up-conversion (UC) emission bands (545 nm) and weak red UC emission bands (660 nm) corresponded to the transitions from (5F4, 5S2) → 5I8 and 4I5 → 5I8, respectively. Furthermore, optimized UC emission intensity was observed in the NBT-BT:0.005Ho3+/0.03Yb3+ samples. The thermal behavior of UC emission in the ceramics was also investigated and the maximum sensitivity based on fluorescence intensity ratio (FIR) technology was approximately 0.0042 K-1 at 100 K. Moreover, relatively good dielectric properties (ɛ = 4475) and ferroelectric properties (P r = 32 μ/cm2 and E c = 37 kV) were obtained in NBT-BT:0.005Ho3+/0.005Yb3+. As a multi-functional material, NBT-BT:Ho3+/Yb3+ ceramics may be useful in electro-optical devices.

  12. Strictly homogeneous laterally complete modules

    NASA Astrophysics Data System (ADS)

    Chilin, V. I.; Karimov, J. A.

    2016-03-01

    Let A be a laterally complete commutative regular algebra and X be a laterally complete A-module. In this paper we introduce a notion of homogeneous and strictly homogeneous A-modules. It is proved that any homogeneous A-module is strictly homogeneous A-module, if the Boolean algebra of all idempotents in A is multi-σ-finite.

  13. SP CREATE. Creating Sample Plans

    SciTech Connect

    Spears, J.H.; Seebode, L.

    1998-11-10

    The program has been designed to increase the accuracy and reduce the preparation time for completing sampling plans. It consists of our files 1. Analyte/Combination (AnalCombo) A list of analytes and combinations of analytes that can be requested of the onsite and offsite labs. Whenever a specific combination of analytes or suite names appear on the same line as the code number, this indicates that one sample can be placed in one bottle to be analyzed for these paremeters. A code number is assigned for each analyte and combination of analytes. 2. Sampling Plans Database (SPDb) A database that contains all of the analytes and combinations of analytes along with the basic information required for preparing a sample plan. That basic information includes the following fields; matrix, hold time, preservation, sample volume, container size, if the bottle caps are taped, acceptable choices. 3. Sampling plans create (SPcreate) a file that will lookup information from the Sampling Plans Database and the Job Log File (JLF98) A major database used by Sample Managemnet Services for recording more than 100 fields of information.

  14. Homogeneous and inhomogeneous eddies

    SciTech Connect

    Pavia, E.G.

    1994-12-31

    This work deals with mesoscale warm oceanic eddies; i.e., self-contained bodies of water which transport heat, among other things, for several months and for several hundreds of kilometers. This heat transport is believed to play an important role in the atmospheric and oceanic conditions of the region where it is being transported. Here the author examines the difference in evolution between eddies modeled as blobs of homogeneous water and eddies in which density varies in the horizontal. Preliminary results suggest that instability is enhanced by inhomogeneities, which would imply that traditional modeling studies, based on homogeneous vortices have underestimated the rate of heat-release from oceanic eddies to the surroundings. The approach is modeling in the simplest form; i.e., one single active layer. Although previous studies have shown the drastic effect on stability brought by two or more dynamically-relevant homogeneous layers, the author believes the single-layer eddy-model has not been investigated thoroughly.

  15. HOMOGENEOUS NUCLEAR POWER REACTOR

    DOEpatents

    King, L.D.P.

    1959-09-01

    A homogeneous nuclear power reactor utilizing forced circulation of the liquid fuel is described. The reactor does not require fuel handling outside of the reactor vessel during any normal operation including complete shutdown to room temperature, the reactor being selfregulating under extreme operating conditions and controlled by the thermal expansion of the liquid fuel. The liquid fuel utilized is a uranium, phosphoric acid, and water solution which requires no gus exhaust system or independent gas recombining system, thereby eliminating the handling of radioiytic gas.

  16. Homogeneous quantum electrodynamic turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    1992-01-01

    The electromagnetic field equations and Dirac equations for oppositely charged wave functions are numerically time-integrated using a spatial Fourier method. The numerical approach used, a spectral transform technique, is based on a continuum representation of physical space. The coupled classical field equations contain a dimensionless parameter which sets the strength of the nonlinear interaction (as the parameter increases, interaction volume decreases). For a parameter value of unity, highly nonlinear behavior in the time-evolution of an individual wave function, analogous to ideal fluid turbulence, is observed. In the truncated Fourier representation which is numerically implemented here, the quantum turbulence is homogeneous but anisotropic and manifests itself in the nonlinear evolution of equilibrium modal spatial spectra for the probability density of each particle and also for the electromagnetic energy density. The results show that nonlinearly interacting fermionic wave functions quickly approach a multi-mode, dynamic equilibrium state, and that this state can be determined by numerical means.

  17. HOMOGENEOUS NUCLEAR REACTOR

    DOEpatents

    Hammond, R.P.; Busey, H.M.

    1959-02-17

    Nuclear reactors of the homogeneous liquid fuel type are discussed. The reactor is comprised of an elongated closed vessel, vertically oriented, having a critical region at the bottom, a lower chimney structure extending from the critical region vertically upwardly and surrounded by heat exchanger coils, to a baffle region above which is located an upper chimney structure containing a catalyst functioning to recombine radiolyticallydissociated moderator gages. In operation the liquid fuel circulates solely by convection from the critical region upwardly through the lower chimney and then downwardly through the heat exchanger to return to the critical region. The gases formed by radiolytic- dissociation of the moderator are carried upwardly with the circulating liquid fuel and past the baffle into the region of the upper chimney where they are recombined by the catalyst and condensed, thence returning through the heat exchanger to the critical region.

  18. Homogeneous quantum electrodynamic turbulence

    SciTech Connect

    Shebalin, J.V.

    1992-10-01

    The electromagnetic field equations and Dirac equations for oppositely charged wave functions are numerically time-integrated using a spatial Fourier method. The numerical approach used, a spectral transform technique, is based on a continuum representation of physical space. The coupled classical field equations contain a dimensionless parameter which sets the strength of the nonlinear interaction (as the parameter increases, interaction volume decreases). For a parameter value of unity, highly nonlinear behavior in the time-evolution of an individual wave function, analogous to ideal fluid turbulence, is observed. In the truncated Fourier representation which is numerically implemented here, the quantum turbulence is homogeneous but anisotropic and manifests itself in the nonlinear evolution of equilibrium modal spatial spectra for the probability density of each particle and also for the electromagnetic energy density. The results show that nonlinearly interacting fermionic wave functions quickly approach a multi-mode, dynamic equilibrium state, and that this state can be determined by numerical means.

  19. Homogeneous spaces of Dirac groupoids

    NASA Astrophysics Data System (ADS)

    Jotz Lean, Madeleine

    2016-06-01

    A Poisson structure on a homogeneous space of a Poisson groupoid is homogeneous if the action of the Lie groupoid on the homogeneous space is compatible with the Poisson structures. According to a result of Liu, Weinstein and Xu, Poisson homogeneous spaces of a Poisson groupoid are in correspondence with suitable Dirac structures in the Courant algebroid defined by the Lie bialgebroid of the Poisson groupoid. We show that this correspondence result fits into a more natural context: the one of Dirac groupoids, which are objects generalizing Poisson groupoids and multiplicative closed 2-forms on groupoids.

  20. STEAM STIRRED HOMOGENEOUS NUCLEAR REACTOR

    DOEpatents

    Busey, H.M.

    1958-06-01

    A homogeneous nuclear reactor utilizing a selfcirculating liquid fuel is described. The reactor vessel is in the form of a vertically disposed tubular member having the lower end closed by the tube walls and the upper end closed by a removal fianged assembly. A spherical reaction shell is located in the lower end of the vessel and spaced from the inside walls. The reaction shell is perforated on its lower surface and is provided with a bundle of small-diameter tubes extending vertically upward from its top central portion. The reactor vessel is surrounded in the region of the reaction shell by a neutron reflector. The liquid fuel, which may be a solution of enriched uranyl sulfate in ordinary or heavy water, is mainiained at a level within the reactor vessel of approximately the top of the tubes. The heat of the reaction which is created in the critical region within the spherical reaction shell forms steam bubbles which more upwardly through the tubes. The upward movement of these bubbles results in the forcing of the liquid fuel out of the top of these tubes, from where the fuel passes downwardly in the space between the tubes and the vessel wall where it is cooled by heat exchangers. The fuel then re-enters the critical region in the reaction shell through the perforations in the bottom. The upper portion of the reactor vessel is provided with baffles to prevent the liquid fuel from splashing into this region which is also provided with a recombiner apparatus for recombining the radiolytically dissociated moderator vapor and a control means.

  1. Strongly Interacting Homogeneous Fermi Gases

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Patel, Parth; Yan, Zhenjie; Struck, Julian; Zwierlein, Martin

    2016-05-01

    We present a homogeneous box potential for strongly interacting Fermi gases. The local density approximation (LDA) allows measurements on traditional inhomogeneous traps to observe a continuous distribution of Fermi gases in a single shot, but also suffer from a broadened response due to line-of-sight averaging over varying densities. We trap ultracold Fermionic (6 Li) in an optical homogeneous potential and characterize its flatness through in-situ tomography. A hybrid approach combining a cylindrical optical potential with a harmonic magnetic trap allows us to exploit the LDA and measure local RF spectra without requiring significant image reconstruction. We extract various quantities from the RF spectra such as the Tan's contact, and discuss further measurements of homogeneous Fermi systems under spin imbalance and finite temperature.

  2. Homogenizing Developmental Studies and ESL.

    ERIC Educational Resources Information Center

    Weaver, Margaret E.

    A discussion of pragmatic issues in both developmental studies (DS) and English-as-a-second-language (ESL) instruction at the college level argues that because the two fields have common problems, challenges, and objectives, they have become homogenized as one in many institutions. Because full-time college faculty avoid teaching developmental…

  3. High frequency homogenization for structural mechanics

    NASA Astrophysics Data System (ADS)

    Nolde, E.; Craster, R. V.; Kaplunov, J.

    2011-03-01

    We consider a net created from elastic strings as a model structure to investigate the propagation of waves through semi-discrete media. We are particularly interested in the development of continuum models, valid at high frequencies, when the wavelength and each cell of the net are of similar order. Net structures are chosen as these form a general two-dimensional example, encapsulating the essential physics involved in the two-dimensional excitation of a lattice structure whilst retaining the simplicity of dealing with elastic strings. Homogenization techniques are developed here for wavelengths commensurate with the cellular scale. Unlike previous theories, these techniques are not limited to low frequency or static regimes, and lead to effective continuum equations valid on a macroscale with the details of the cellular structure encapsulated only through integrated quantities. The asymptotic procedure is based upon a two-scale approach and the physical observation that there are frequencies that give standing waves, periodic with the period or double-period of the cell. A specific example of a net created by a lattice of elastic strings is constructed, the theory is general and not reliant upon the net being infinite, none the less the infinite net is a useful special case for which Bloch theory can be applied. This special case is explored in detail allowing for verification of the theory, and highlights the importance of degenerate cases; the specific example of a square net is treated in detail. An additional illustration of the versatility of the method is the response to point forcing which provides a stringent test of the homogenized equations; an exact Green's function for the net is deduced and compared to the asymptotics.

  4. Homogeneous Pt-bimetallic Electrocatalysts

    SciTech Connect

    Wang, Chao; Chi, Miaofang; More, Karren Leslie; Markovic, Nenad; Stamenkovic, Vojislav

    2011-01-01

    Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt{sub 3}M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2-3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt{sub 3}M nanocatalysts validated the volcano curve established on extended surfaces, with Pt{sub 3}Co being the most active alloy.

  5. Homogeneous enzyme immunoassay for netilmicin.

    PubMed Central

    Wenk, M; Hemmann, R; Follath, F

    1982-01-01

    A newly developed homogeneous enzyme immunoassay for the determination of netilmicin in serum was evaluated and compared with a radioenzymatic assay. A total of 102 serum samples from patients treated with netilmicin were measured by both methods. This comparison showed an excellent correlation (r = 0.993). The enzyme immunoassay has proved to be precise, accurate, and specific. Because of its rapidity and the ease of performance, this method is a useful alternative to current assays for monitoring serum netilmicin concentrations. PMID:6760807

  6. Variable valve timing in a homogenous charge compression ignition engine

    DOEpatents

    Lawrence, Keith E.; Faletti, James J.; Funke, Steven J.; Maloney, Ronald P.

    2004-08-03

    The present invention relates generally to the field of homogenous charge compression ignition engines, in which fuel is injected when the cylinder piston is relatively close to the bottom dead center position for its compression stroke. The fuel mixes with air in the cylinder during the compression stroke to create a relatively lean homogeneous mixture that preferably ignites when the piston is relatively close to the top dead center position. However, if the ignition event occurs either earlier or later than desired, lowered performance, engine misfire, or even engine damage, can result. The present invention utilizes internal exhaust gas recirculation and/or compression ratio control to control the timing of ignition events and combustion duration in homogeneous charge compression ignition engines. Thus, at least one electro-hydraulic assist actuator is provided that is capable of mechanically engaging at least one cam actuated intake and/or exhaust valve.

  7. ISOTOPE METHODS IN HOMOGENEOUS CATALYSIS.

    SciTech Connect

    BULLOCK,R.M.; BENDER,B.R.

    2000-12-01

    The use of isotope labels has had a fundamentally important role in the determination of mechanisms of homogeneously catalyzed reactions. Mechanistic data is valuable since it can assist in the design and rational improvement of homogeneous catalysts. There are several ways to use isotopes in mechanistic chemistry. Isotopes can be introduced into controlled experiments and followed where they go or don't go; in this way, Libby, Calvin, Taube and others used isotopes to elucidate mechanistic pathways for very different, yet important chemistries. Another important isotope method is the study of kinetic isotope effects (KIEs) and equilibrium isotope effect (EIEs). Here the mere observation of where a label winds up is no longer enough - what matters is how much slower (or faster) a labeled molecule reacts than the unlabeled material. The most careti studies essentially involve the measurement of isotope fractionation between a reference ground state and the transition state. Thus kinetic isotope effects provide unique data unavailable from other methods, since information about the transition state of a reaction is obtained. Because getting an experimental glimpse of transition states is really tantamount to understanding catalysis, kinetic isotope effects are very powerful.

  8. Heterogeneous nucleation or homogeneous nucleation?

    NASA Astrophysics Data System (ADS)

    Liu, X. Y.

    2000-06-01

    The generic heterogeneous effect of foreign particles on three dimensional nucleation was examined both theoretically and experimentally. It shows that the nucleation observed under normal conditions includes a sequence of progressive heterogeneous processes, characterized by different interfacial correlation function f(m,x)s. At low supersaturations, nucleation will be controlled by the process with a small interfacial correlation function f(m,x), which results from a strong interaction and good structural match between the foreign bodies and the crystallizing phase. At high supersaturations, nucleation on foreign particles having a weak interaction and poor structural match with the crystallizing phase (f(m,x)→1) will govern the kinetics. This frequently leads to the false identification of homogeneous nucleation. Genuine homogeneous nucleation, which is the up-limit of heterogeneous nucleation, may not be easily achievable under gravity. In order to check these results, the prediction is confronted with nucleation experiments of some organic and inorganic crystals. The results are in excellent agreement with the theory.

  9. Create a Logo.

    ERIC Educational Resources Information Center

    Duchen, Gail

    2002-01-01

    Presents an art lesson that introduced students to graphic art as a career path. Explains that the students met a graphic artist and created a logo for a pretend client. Explains that the students researched logos. (CMK)

  10. Invariant distributions on compact homogeneous spaces

    SciTech Connect

    Gorbatsevich, V V

    2013-12-31

    In this paper, we study distributions on compact homogeneous spaces, including invariant distributions and also distributions admitting a sub-Riemannian structure. We first consider distributions of dimension 1 and 2 on compact homogeneous spaces. After this, we study the cases of compact homogeneous spaces of dimension 2, 3, and 4 in detail. Invariant distributions on simply connected compact homogeneous spaces are also treated. Bibliography: 18 titles.

  11. Numerical experiments in homogeneous turbulence

    NASA Technical Reports Server (NTRS)

    Rogallo, R. S.

    1981-01-01

    The direct simulation methods developed by Orszag and Patternson (1972) for isotropic turbulence were extended to homogeneous turbulence in an incompressible fluid subjected to uniform deformation or rotation. The results of simulations for irrotational strain (plane and axisymmetric), shear, rotation, and relaxation toward isotropy following axisymmetric strain are compared with linear theory and experimental data. Emphasis is placed on the shear flow because of its importance and because of the availability of accurate and detailed experimental data. The computed results are used to assess the accuracy of two popular models used in the closure of the Reynolds-stress equations. Data from a variety of the computed fields and the details of the numerical methods used in the simulation are also presented.

  12. Challenges of daily data homogenization

    NASA Astrophysics Data System (ADS)

    Gruber, C.; Auer, I.; Mestre, O.

    2009-04-01

    In recent years the growing demand of extreme value studies has led to the development of methods for the homogenisation of daily data. The behaviour of some of these methods has been investigated: Two methods (HOM: Della-Marta and Wanner, 2006 and SPLIDHOM: Mestre et al., submitted) which adjust the whole distribution of the climate element (especially minimum and maximum temperature) have been compared to the simpler Vincent's method (Vincent et al., 2002) which interpolates monthly adjustment factors onto daily data. The results indicate that the behaviour of the methods HOM and SPLIDHOM is very similar, although the complexity of these methods is different. They can improve the results compared to the Vincent's method when inhomogeneities in higher order moments occur. However, their applicability is limited since highly correlated neighbour series are required. More over, more data in the intervals before and after breaks is needed if the whole distribution shall be adjusted instead of the mean only. Due to these limitations a combination of distribution dependent adjustment methods and the Vincent method seems to be necessary for the homogenization of many time series. A dataset of Austrian daily maximum and minimum temperature data is used to illustrate the challenges of distribution dependent homogenization methods. Emphasis is placed on the estimation of the (sampling) uncertainty of these methods. Therefore a bootstrap approach is used. The accuracy of the calculated adjustments varies mainly between about 0.5°C for mean temperatures and more than one degree Celsius for the margins of the distribution. These uncertainty estimates can be valuable for extreme value studies.

  13. Polyurethane phantoms with homogeneous and nearly homogeneous optical properties

    NASA Astrophysics Data System (ADS)

    Keränen, Ville T.; Mäkynen, Anssi J.; Dayton, Amanda L.; Prahl, Scott A.

    2010-02-01

    Phantoms with controlled optical properties are often used for calibration and standardization. The phantoms are typically prepared by adding absorbers and scatterers to a clear host material. It is usually assumed that the scatterers and absorbers are uniformly dispersed within the medium. To explore the effects of this assumption, we prepared paired sets of polyurethane phantoms (both with identical masses of absorber, India ink and scatterer, titanium dioxide). Polyurethane phantoms were made by mixing two polyurethane parts (a and b) together and letting them cure in a polypropylene container. The mixture was degassed before curing to ensure a sample without bubbles. The optical properties were controlled by mixing titanium dioxide or India ink into polyurethane part (a or b) before blending the parts together. By changing the mixing sequence, we could change the aggregation of the scattering and absorbing particles. Each set had one sample with homogeneously dispersed scatterers and absorbers, and a second sample with slightly aggregated scatterers or absorbers. We found that the measured transmittance could easily vary by a factor of twenty. The estimated optical properties (using the inverse adding-doubling method) indicate that when aggregation is present, the optical properties are no longer proportional to the concentrations of absorbers or scatterers.

  14. Creating Pupils' Internet Magazine

    ERIC Educational Resources Information Center

    Bognar, Branko; Šimic, Vesna

    2014-01-01

    This article presents an action research, which aimed to improve pupils' literary creativity and enable them to use computers connected to the internet. The study was conducted in a small district village school in Croatia. Creating a pupils' internet magazine appeared to be an excellent way for achieving the educational aims of almost all…

  15. Creating an Interactive Globe.

    ERIC Educational Resources Information Center

    Martin, Kurt D.

    1989-01-01

    Describes a hands-on geography activity that is designed to teach longitude and latitude to fifth-grade students. Children create a scale model of the earth from a 300 gram weather balloon. This activity incorporates geography, mathematics, science, art, and homework. Provides information for obtaining materials. (KO)

  16. How Banks Create Money.

    ERIC Educational Resources Information Center

    Beale, Lyndi

    This teaching module explains how the U.S. banking system uses excess reserves to create money in the form of new deposits for borrowers. The module is part of a computer-animated series of four-to-five-minute modules illustrating standard concepts in high school economics. Although the module is designed to accompany the video program, it may be…

  17. Creating Quality Media Materials.

    ERIC Educational Resources Information Center

    Hortin, John A.; Bailey, Gerald D.

    1982-01-01

    Innovation, imagination, and student creativity are key ingredients in creating quality media materials for the small school. Student-produced media materials, slides without a camera, personalized slide programs and copy work, self-made task cards, self-made overhead transparencies, graphic materials, and utilization of the mass media are some of…

  18. Creating a Reference Toolbox.

    ERIC Educational Resources Information Center

    Scott, Jane

    1997-01-01

    To help students understand that references are tools used to locate specific information, one librarian has her third-grade students create their own reference toolboxes as she introduces dictionaries, atlases, encyclopedias, and thesauri. Presents a lesson plan to introduce print and nonprint thesauri to third and fourth graders and includes a…

  19. Creating Photo Illustrations.

    ERIC Educational Resources Information Center

    Wilson, Bradley

    2003-01-01

    Explains the uses of photo illustrations. Notes that the key to developing a successful photo illustration is collaborative planning. Outlines the following guidelines for photo illustrations: never set up a photograph to mimic reality; create only abstractions with photo illustrations; clearly label photo illustrations; and never play photo…

  20. Creating Happy Memories.

    ERIC Educational Resources Information Center

    Weeks, Denise Jarrett

    2001-01-01

    Some teachers are building and sharing their wisdom and know-how through lesson study, in the process creating memorable learning experiences for students and for each other. This paper describes how lesson study can transform teaching and how schools are implementing lesson study. A sidebar presents questions to consider in lesson study. (SM)

  1. Creating dedicated bioenergy crops

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Bioenergy is one of the current mechanisms of producing renewable energy to reduce our use of nonrenewable fossil fuels and to reduce carbon emissions into the atmosphere. Humans have been using bioenergy since we first learned to create and control fire - burning manure, peat, and wood to cook food...

  2. Create a Critter Collector.

    ERIC Educational Resources Information Center

    Hinchey, Elizabeth K.; Nestlerode, Janet A.

    2001-01-01

    Presents methods for creating appropriate ways of collecting live specimens to use for firsthand observation in the classroom. Suggests ecological questions for students to address using these devices. This project is ideal for schools that have access to piers or bridges on a coastal body of water. (NB)

  3. Creating a Market.

    ERIC Educational Resources Information Center

    Kazimirski, J.; And Others

    The second in a series of programmed books, "Creating a Market" is published by the International Labour Office as a manual for persons studying marketing. This manual was designed to meet the needs of the labor organization's technical cooperation programs and is primarily concerned with consumer goods industries. Using a fill-in-the-blanks and…

  4. Looking, Writing, Creating.

    ERIC Educational Resources Information Center

    Katzive, Bonnie

    1997-01-01

    Describes how a middle school language arts teacher makes analyzing and creating visual art a partner to reading and writing in her classroom. Describes a project on art and Vietnam which shows how background information can add to and influence interpretation. Describes a unit on Greek mythology and Greek vases which leads to a related visual…

  5. Creating an Interactive PDF

    ERIC Educational Resources Information Center

    Branzburg, Jeffrey

    2008-01-01

    There are many ways to begin a PDF document using Adobe Acrobat. The easiest and most popular way is to create the document in another application (such as Microsoft Word) and then use the Adobe Acrobat software to convert it to a PDF. In this article, the author describes how he used Acrobat's many tools in his project--an interactive…

  6. Creating a Classroom Makerspace

    ERIC Educational Resources Information Center

    Rivas, Luz

    2014-01-01

    What is a makerspace? Makerspaces are community-operated physical spaces where people (makers) create do-it-yourself projects together. These membership spaces serve as community labs where people learn together and collaborate on projects. Makerspaces often have tools and equipment like 3-D printers, laser cutters, and soldering irons.…

  7. Creating a Virtual Gymnasium

    ERIC Educational Resources Information Center

    Fiorentino, Leah H.; Castelli, Darla

    2005-01-01

    Physical educators struggle with the challenges of assessing student performance, providing feedback about motor skills, and creating opportunities for all students to engage in game-play on a daily basis. The integration of technology in the gymnasium can address some of these challenges by improving teacher efficiency and increasing student…

  8. Creating Special Events

    ERIC Educational Resources Information Center

    deLisle, Lee

    2009-01-01

    "Creating Special Events" is organized as a systematic approach to festivals and events for students who seek a career in event management. This book looks at the evolution and history of festivals and events and proceeds to the nuts and bolts of event management. The book presents event management as the means of planning, organizing, directing,…

  9. Creating Dialogue by Storytelling

    ERIC Educational Resources Information Center

    Passila, Anne; Oikarinen, Tuija; Kallio, Anne

    2013-01-01

    Purpose: The objective of this paper is to develop practice and theory from Augusto Boal's dialogue technique (Image Theatre) for organisational use. The paper aims to examine how the members in an organisation create dialogue together by using a dramaturgical storytelling framework where the dialogue emerges from storytelling facilitated by…

  10. Create Your State

    ERIC Educational Resources Information Center

    Dunham, Kris; Melvin, Samantha

    2011-01-01

    Students are often encouraged to work together with their classmates, sometimes with other classes, occasionally with kids at other schools, but rarely with kids across the country. In this article the authors describe the Create Your State project, a collaborative nationwide project inspired by the Texas Chair Project wherein the artist, Damien…

  11. Creating Quality Schools.

    ERIC Educational Resources Information Center

    American Association of School Administrators, Arlington, VA.

    This booklet presents information on how total quality management can be applied to school systems to create educational improvement. Total quality management offers education a systemic approach and a new set of assessment tools. Chapter 1 provides a definition and historical overview of total quality management. Chapter 2 views the school…

  12. Creating Geoscience Leaders

    NASA Astrophysics Data System (ADS)

    Buskop, J.; Buskop, W.

    2013-12-01

    The United Nations Educational, Scientific, and Cultural Organization recognizes 21 World Heritage in the United States, ten of which have astounding geological features: Wrangell St. Elias National Park, Olympic National Park, Mesa Verde National Park, Chaco Canyon, Glacier National Park, Carlsbad National Park, Mammoth Cave, Great Smokey Mountains National Park, Hawaii Volcanoes National Park, and Everglades National Park. Created by a student frustrated with fellow students addicted to smart phones with an extreme lack of interest in the geosciences, one student visited each World Heritage site in the United States and created one e-book chapter per park. Each chapter was created with original photographs, and a geological discovery hunt to encourage teen involvement in preserving remarkable geological sites. Each chapter describes at least one way young adults can get involved with the geosciences, such a cave geology, glaciology, hydrology, and volcanology. The e-book describes one park per chapter, each chapter providing a geological discovery hunt, information on how to get involved with conservation of the parks, geological maps of the parks, parallels between archaeological and geological sites, and how to talk to a ranger. The young author is approaching UNESCO to publish the work as a free e-book to encourage involvement in UNESCO sites and to prove that the geosciences are fun.

  13. AQUEOUS HOMOGENEOUS REACTORTECHNICAL PANEL REPORT

    SciTech Connect

    Diamond, D.J.; Bajorek, S.; Bakel, A.; Flanagan, G.; Mubayi, V.; Skarda, R.; Staudenmeier, J.; Taiwo, T.; Tonoike, K.; Tripp, C.; Wei, T.; Yarsky, P.

    2010-12-03

    Considerable interest has been expressed for developing a stable U.S. production capacity for medical isotopes and particularly for molybdenum- 99 (99Mo). This is motivated by recent re-ductions in production and supply worldwide. Consistent with U.S. nonproliferation objectives, any new production capability should not use highly enriched uranium fuel or targets. Conse-quently, Aqueous Homogeneous Reactors (AHRs) are under consideration for potential 99Mo production using low-enriched uranium. Although the Nuclear Regulatory Commission (NRC) has guidance to facilitate the licensing process for non-power reactors, that guidance is focused on reactors with fixed, solid fuel and hence, not applicable to an AHR. A panel was convened to study the technical issues associated with normal operation and potential transients and accidents of an AHR that might be designed for isotope production. The panel has produced the requisite AHR licensing guidance for three chapters that exist now for non-power reactor licensing: Reac-tor Description, Reactor Coolant Systems, and Accident Analysis. The guidance is in two parts for each chapter: 1) standard format and content a licensee would use and 2) the standard review plan the NRC staff would use. This guidance takes into account the unique features of an AHR such as the fuel being in solution; the fission product barriers being the vessel and attached systems; the production and release of radiolytic and fission product gases and their impact on operations and their control by a gas management system; and the movement of fuel into and out of the reactor vessel.

  14. Turbulence in homogeneous shear flows

    NASA Astrophysics Data System (ADS)

    Pumir, Alain

    1996-11-01

    Homogeneous shear flows with an imposed mean velocity U=Syx̂ are studied in a period box of size Lx×Ly×Lz, in the statistically stationary turbulent state. In contrast with unbounded shear flows, the finite size of the system constrains the large-scale dynamics. The Reynolds number, defined by Re≡SL2y/ν varies in the range 2600⩽Re⩽11300. The total kinetic energy and enstrophy in the volume of numerical integration have large peaks, resulting in fluctuations of kinetic energy of order 30%-50%. The mechanism leading to these fluctuations is very reminiscent of the ``streaks'' responsible for the violent bursts observed in turbulent boundary layers. The large scale anisotropy of the flow, characterized by the two-point correlation tensor depends on the aspect ratio of the system. The probability distribution functions (PDF) of the components of the velocity are found to be close to Gaussian. The physics of the Reynolds stress tensor, uv, is very similar to what is found experimentally in wall bounded shear flows. The study of the two-point correlation tensor of the vorticity <ωiωj> suggests that the small scales become isotropic when the Reynolds number increases, as observed in high Reynolds number turbulent boundary layers. However, the skewness of the z component of vorticity is independent of the Reynolds number in this range, suggesting that some small scale anisotropy remains even at very high Reynolds numbers. An analogy is drawn with the problem of turbulent mixing, where a similar anisotropy is observed.

  15. Homogeneous catalysts in hypersonic combustion

    SciTech Connect

    Harradine, D.M.; Lyman, J.L.; Oldenborg, R.C.; Pack, R.T.; Schott, G.L.

    1989-01-01

    Density and residence time both become unfavorably small for efficient combustion of hydrogen fuel in ramjet propulsion in air at high altitude and hypersonic speed. Raising the density and increasing the transit time of the air through the engine necessitates stronger contraction of the air flow area. This enhances the kinetic and thermodynamic tendency of H/sub 2/O to form completely, accompanied only by N/sub 2/ and any excess H/sub 2/(or O/sub 2/). The by-products to be avoided are the energetically expensive fragment species H and/or O atoms and OH radicals, and residual (2H/sub 2/ plus O/sub 2/). However, excessive area contraction raises air temperature and consequent combustion-product temperature by adiabatic compression. This counteracts and ultimately overwhelms the thermodynamic benefit by which higher density favors the triatomic product, H/sub 2/O, over its monatomic and diatomic alternatives. For static pressures in the neighborhood of 1 atm, static temperature must be kept or brought below ca. 2400 K for acceptable stability of H/sub 2/O. Another measure, whose requisite chemistry we address here, is to extract propulsive work from the combustion products early in the expansion. The objective is to lower the static temperature of the combustion stream enough for H/sub 2/O to become adequately stable before the exhaust flow is massively expanded and its composition ''frozen.'' We proceed to address this mechanism and its kinetics, and then examine prospects for enhancing its rate by homogeneous catalysts. 9 refs.

  16. Design and testing of a refractive laser beam homogenizer

    NASA Astrophysics Data System (ADS)

    Fernelius, N. C.; Bradley, K. R.; Hoekstra, B. L.

    1984-09-01

    A survey is made of various techniques to create a homogeneous or flat top laser beam profile. A refractive homogenizer was designed for use with a ND:YAG laser with output at its fundamental (1.06 micrometer) and frequency doubled (532 nm) modes. The system consists of a 2X beam expander and two faceted cylindrical lenses with differing focal lengths. Each cylindrical lens focusses its input into a strip the width of a facet. By orienting their axes at a 90 degree angle and focussing them on the same plane, the beam is concentrated into a square focus. Formulae for calculating the facet angles are derived and a FORTRAN computer square focus. Formulae for calculating the facet angles are derived and a FORTRAN computer program was written to calculate them with a precision greater than one is able to fabricate them.

  17. Creating new growth platforms.

    PubMed

    Laurie, Donald L; Doz, Yves L; Sheer, Claude P

    2006-05-01

    Sooner or later, most companies can't attain the growth rates expected by their boards and CEOs and demanded by investors. To some extent, such businesses are victims of their own successes. Many were able to sustain high growth rates for a long time because they were in high-growth industries. But once those industries slowed down, the businesses could no longer deliver the performance that investors had come to take for granted. Often, companies have resorted to acquisition, though this strategy has a discouraging track record. Over time, 65% of acquisitions destroy more value than they create. So where does real growth come from? For the past 12 years, the authors have been researching and advising companies on this issue. With the support of researchers at Harvard Business School and Insead, they instituted a project titled "The CEO Agenda and Growth". They identified and approached 24 companies that had achieved significant organic growth and interviewed their CEOs, chief strategists, heads of R&D, CFOs, and top-line managers. They asked, "Where does your growth come from?" and found a consistent pattern in the answers. All the businesses grew by creating new growth platforms (NGPs) on which they could build families of products and services and extend their capabilities into multiple new domains. Identifying NGP opportunities calls for executives to challenge conventional wisdom. In all the companies studied, top management believed that NGP innovation differed significantly from traditional product or service innovation. They had independent, senior-level units with a standing responsibility to create NGPs, and their CEOs spent as much as 50% of their time working with these units. The payoff has been spectacular and lasting. For example, from 1985 to 2004, the medical devices company Medtronic grew revenues at 18% per year, earnings at 20%, and market capitalization at 30%. PMID:16649700

  18. Creating healthy camp experiences.

    PubMed

    Walton, Edward A; Tothy, Alison S

    2011-04-01

    The American Academy of Pediatrics has created recommendations for health appraisal and preparation of young people before participation in day or resident camps and to guide health and safety practices for children at camp. These recommendations are intended for parents, primary health care providers, and camp administration and health center staff. Although camps have diverse environments, there are general guidelines that apply to all situations and specific recommendations that are appropriate under special conditions. This policy statement has been reviewed and is supported by the American Camp Association. PMID:21444589

  19. Creating corporate advantage.

    PubMed

    Collis, D J; Montgomery, C A

    1998-01-01

    What differentiates truly great corporate strategies from the merely adequate? How can executives at the corporate level create tangible advantage for their businesses that makes the whole more than the sum of the parts? This article presents a comprehensive framework for value creation in the multibusiness company. It addresses the most fundamental questions of corporate strategy: What businesses should a company be in? How should it coordinate activities across businesses? What role should the corporate office play? How should the corporation measure and control performance? Through detailed case studies of Tyco International, Sharp, the Newell Company, and Saatchi and Saatchi, the authors demonstrate that the answers to all those questions are driven largely by the nature of a company's special resources--its assets, skills, and capabilities. These range along a continuum from the highly specialized at one end to the very general at the other. A corporation's location on the continuum constrains the set of businesses it should compete in and limits its choices about the design of its organization. Applying the framework, the authors point out the common mistakes that result from misaligned corporate strategies. Companies mistakenly enter businesses based on similarities in products rather than the resources that contribute to competitive advantage in each business. Instead of tailoring organizational structures and systems to the needs of a particular strategy, they create plain-vanilla corporate offices and infrastructures. The company examples demonstrate that one size does not fit all. One can find great corporate strategies all along the continuum. PMID:10179655

  20. Creating sustainable performance.

    PubMed

    Spreitzer, Gretchen; Porath, Christine

    2012-01-01

    What makes for sustainable individual and organizational performance? Employees who are thriving-not just satisfied and productive but also engaged in creating the future. The authors found that people who fit this description demonstrated 16% better overall performance, 125% less burnout, 32% more commitment to the organization, and 46% more job satisfaction than their peers. Thriving has two components: vitality, or the sense of being alive and excited, and learning, or the growth that comes from gaining knowledge and skills. Some people naturally build vitality and learning into their jobs, but most employees are influenced by their environment. Four mechanisms, none of which requires heroic effort or major resources, create the conditions for thriving: providing decision-making discretion, sharing information about the organization and its strategy, minimizing incivility, and offering performance feedback. Organizations such as Alaska Airlines, Zingerman's, Quicken Loans, and Caiman Consulting have found that helping people grow and remain energized at work is valiant on its own merits-but it can also boost performance in a sustainable way. PMID:22299508

  1. Entanglement Created by Dissipation

    SciTech Connect

    Alharbi, Abdullah F.; Ficek, Zbigniew

    2011-10-27

    A technique for entangling closely separated atoms by the process of dissipative spontaneous emission is presented. The system considered is composed of two non-identical two-level atoms separated at the quarter wavelength of a driven standing wave laser field. At this atomic distance, only one of the atoms can be addressed by the laser field. In addition, we arrange the atomic dipole moments to be oriented relative to the inter-atomic axis such that the dipole-dipole interaction between the atoms is zero at this specific distance. It is shown that an entanglement can be created between the atoms on demand by tuning the Rabi frequency of the driving field to the difference between the atomic transition frequencies. The amount of the entanglement created depends on the ratio between the damping rates of the atoms, but is independent of the frequency difference between the atoms. We also find that the transient buildup of an entanglement between the atoms may differ dramatically for different initial atomic conditions.

  2. Ecological and evolutionary consequences of biotic homogenization.

    PubMed

    Olden, Julian D; Leroy Poff, N; Douglas, Marlis R; Douglas, Michael E; Fausch, Kurt D

    2004-01-01

    Biotic homogenization, the gradual replacement of native biotas by locally expanding non-natives, is a global process that diminishes floral and faunal distinctions among regions. Although patterns of homogenization have been well studied, their specific ecological and evolutionary consequences remain unexplored. We argue that our current perspective on biotic homogenization should be expanded beyond a simple recognition of species diversity loss, towards a synthesis of higher order effects. Here, we explore three distinct forms of homogenization (genetic, taxonomic and functional), and discuss their immediate and future impacts on ecological and evolutionary processes. Our goal is to initiate future research that investigates the broader conservation implications of homogenization and to promote a proactive style of adaptive management that engages the human component of the anthropogenic blender that is currently mixing the biota on Earth. PMID:16701221

  3. Creating innovative departments.

    PubMed

    von Segesser, Ludwig K

    2004-12-01

    'Creating an innovative department' as an objective implies further improvements in organization, function, and progression of a surgical unit active in patient care, research, and education. It is of prime importance to stress here the mutual benefits of patient care, research (the basis for future patient care) and education (the channel for training health care professionals in future patient care). Neither innovation (from latin innovare: to renew, revive) nor creation (from latin creare: to make, produce) is something that will fall from heaven without effort any time soon. Hence, a pro-active attitude towards progress is indicated. This requires searching for new ideas, allocation of resources, finding allies, getting focussed, and being persistent. One word says it all: WORK! PMID:15776856

  4. Creating With Carbon

    NASA Technical Reports Server (NTRS)

    2003-01-01

    A subsidiary of SI Diamond Technology, Inc., Applied Nanotech, of Austin, Texas, is creating a buzz among various technology firms and venture capital groups interested in the company s progressive research on carbon-related field emission devices, including carbon nanotubes, filaments of pure carbon less than one ten-thousandth the width of human hair. Since their discovery in 1991, carbon nanotubes have gained considerable attention due to their unique physical properties. For example, a single perfect carbon nanotube can range from 10 to 100 times stronger than steel, per unit weight. Recent studies also indicate that the nanotubes may be the best heat-conducting material in existence. These properties, combined with the ease of growing thin films or nanotubes by a variety of deposition techniques, make the carbon-based material one of the most desirable for cold field emission cathodes.

  5. Creating the living brand.

    PubMed

    Bendapudi, Neeli; Bendapudi, Venkat

    2005-05-01

    It's easy to conclude from the literature and the lore that top-notch customer service is the province of a few luxury companies and that any retailer outside that rarefied atmosphere is condemned to offer mediocre service at best. But even companies that position themselves for the mass market can provide outstanding customer-employee interactions and profit from them, if they train employees to reflect the brand's core values. The authors studied the convenience store industry in depth and focused on two that have developed a devoted following: QuikTrip (QT) and Wawa. Turnover rates at QT and Wawa are 14% and 22% respectively, much lower than the typical rate in retail. The authors found six principles that both firms embrace to create a strong culture of customer service. Know what you're looking for: A focus on candidates' intrinsic traits allows the companies to hire people who will naturally bring the right qualities to the job. Make the most of talent: In mass-market retail, talent is generally viewed as a commodity, but that outlook becomes a self-fulfilling prophesy. Create pride in the brand: Service quality depends directly on employees' attachment to the brand. Build community: Wawa and QT have made concerted efforts to build customer loyalty through a sense of community. Share the business context: Employees need a clear understanding of how their company operates and how it defines success. Satisfy the soul: To win an employee's passionate engagement, a company must meet his or her needs for security, esteem, and justice. PMID:15929408

  6. Creating Griffith Observatory

    NASA Astrophysics Data System (ADS)

    Cook, Anthony

    2013-01-01

    Griffith Observatory has been the iconic symbol of the sky for southern California since it began its public mission on May 15, 1935. While the Observatory is widely known as being the gift of Col. Griffith J. Griffith (1850-1919), the story of how Griffith’s gift became reality involves many of the people better known for other contributions that made Los Angeles area an important center of astrophysics in the 20th century. Griffith began drawing up his plans for an observatory and science museum for the people of Los Angeles after looking at Saturn through the newly completed 60-inch reflector on Mt. Wilson. He realized the social impact that viewing the heavens could have if made freely available, and discussing the idea of a public observatory with Mt. Wilson Observatory’s founder, George Ellery Hale, and Director, Walter Adams. This resulted, in 1916, in a will specifying many of the features of Griffith Observatory, and establishing a committee managed trust fund to build it. Astronomy popularizer Mars Baumgardt convinced the committee at the Zeiss Planetarium projector would be appropriate for Griffith’s project after the planetarium was introduced in Germany in 1923. In 1930, the trust committee judged funds to be sufficient to start work on creating Griffith Observatory, and letters from the Committee requesting help in realizing the project were sent to Hale, Adams, Robert Millikan, and other area experts then engaged in creating the 200-inch telescope eventually destined for Palomar Mountain. A Scientific Advisory Committee, headed by Millikan, recommended that Caltech Physicist Edward Kurth be put in charge of building and exhibit design. Kurth, in turn, sought help from artist Russell Porter. The architecture firm of John C. Austin and Fredrick Ashley was selected to design the project, and they adopted the designs of Porter and Kurth. Philip Fox of the Adler Planetarium was enlisted to manage the completion of the Observatory and become its

  7. Homogenization of precipitation time series with ACMANT

    NASA Astrophysics Data System (ADS)

    Domonkos, Peter

    2015-10-01

    New method for the time series homogenization of observed precipitation (PP) totals is presented; this method is a unit of the ACMANT software package. ACMANT is a relative homogenization method; minimum four time series with adequate spatial correlations are necessary for its use. The detection of inhomogeneities (IHs) is performed with fitting optimal step function, while the calculation of adjustment terms is based on the minimization of the residual variance in homogenized datasets. Together with the presentation of PP homogenization with ACMANT, some peculiarities of PP homogenization as, for instance, the frequency and seasonal variation of IHs in observed PP data and their relation to the performance of homogenization methods are discussed. In climatic regions of snowy winters, ACMANT distinguishes two seasons, namely, rainy season and snowy season, and the seasonal IHs are searched with bivariate detection. ACMANT is a fully automatic method, is freely downloadable from internet and treats either daily or monthly input. Series of observed data in the input dataset may cover different periods, and the occurrence of data gaps is allowed. False zero values instead of missing data code or physical outliers should be corrected before running ACMANT. Efficiency tests indicate that ACMANT belongs to the best performing methods, although further comparative tests of automatic homogenization methods are needed to confirm or reject this finding.

  8. String pair production in non homogeneous backgrounds

    NASA Astrophysics Data System (ADS)

    Bolognesi, S.; Rabinovici, E.; Tallarita, G.

    2016-04-01

    We consider string pair production in non homogeneous electric backgrounds. We study several particular configurations which can be addressed with the Euclidean world-sheet instanton technique, the analogue of the world-line instanton for particles. In the first case the string is suspended between two D-branes in flat space-time, in the second case the string lives in AdS and terminates on one D-brane (this realizes the holographic Schwinger effect). In some regions of parameter space the result is well approximated by the known analytical formulas, either the particle pair production in non-homogeneous background or the string pair production in homogeneous background. In other cases we see effects which are intrinsically stringy and related to the non-homogeneity of the background. The pair production is enhanced already for particles in time dependent electric field backgrounds. The string nature enhances this even further. For spacial varying electrical background fields the string pair production is less suppressed than the rate of particle pair production. We discuss in some detail how the critical field is affected by the non-homogeneity, for both time and space dependent electric field backgrouds. We also comment on what could be an interesting new prediction for the small field limit. The third case we consider is pair production in holographic confining backgrounds with homogeneous and non-homogeneous fields.

  9. Deforestation homogenizes tropical parasitoid-host networks.

    PubMed

    Laliberté, Etienne; Tylianakis, Jason M

    2010-06-01

    Human activities drive biotic homogenization (loss of regional diversity) of many taxa. However, whether species interaction networks (e.g., food webs) can also become homogenized remains largely unexplored. Using 48 quantitative parasitoid-host networks replicated through space and time across five tropical habitats, we show that deforestation greatly homogenized network structure at a regional level, such that interaction composition became more similar across rice and pasture sites compared with forested habitats. This was not simply caused by altered consumer and resource community composition, but was associated with altered consumer foraging success, such that parasitoids were more likely to locate their hosts in deforested habitats. Furthermore, deforestation indirectly homogenized networks in time through altered mean consumer and prey body size, which decreased in deforested habitats. Similar patterns were obtained with binary networks, suggesting that interaction (link) presence-absence data may be sufficient to detect network homogenization effects. Our results show that tropical agroforestry systems can support regionally diverse parasitoid-host networks, but that removal of canopy cover greatly homogenizes the structure of these networks in space, and to a lesser degree in time. Spatiotemporal homogenization of interaction networks may alter coevolutionary outcomes and reduce ecological resilience at regional scales, but may not necessarily be predictable from community changes observed within individual trophic levels. PMID:20583715

  10. Homogenization method based on the inverse problem

    SciTech Connect

    Tota, A.; Makai, M.

    2013-07-01

    We present a method for deriving homogeneous multi-group cross sections to replace a heterogeneous region's multi-group cross sections; providing that the fluxes and the currents on the external boundary, and the region averaged fluxes are preserved. The method is developed using diffusion approximation to the neutron transport equation in a symmetrical slab geometry. Assuming that the boundary fluxes are given, two response matrices (RMs) can be defined. The first derives the boundary current from the boundary flux, the second derives the flux integral over the region from the boundary flux. Assuming that these RMs are known, we present a formula which reconstructs the multi-group cross-section matrix and the diffusion coefficients from the RMs of a homogeneous slab. Applying this formula to the RMs of a slab with multiple homogeneous regions yields a homogenization method; which produce such homogenized multi-group cross sections and homogenized diffusion coefficients, that the fluxes and the currents on the external boundary, and the region averaged fluxes are preserved. The method is based on the determination of the eigenvalues and the eigenvectors of the RMs. We reproduce the four-group cross section matrix and the diffusion constants from the RMs in numerical examples. We give conditions for replacing a heterogeneous region by a homogeneous one so that the boundary current and the region-averaged flux are preserved for a given boundary flux. (authors)

  11. Higher Order Macro Coefficients in Periodic Homogenization

    NASA Astrophysics Data System (ADS)

    Conca, Carlos; San Martin, Jorge; Smaranda, Loredana; Vanninathan, Muthusamy

    2011-09-01

    A first set of macro coefficients known as the homogenized coefficients appear in the homogenization of PDE on periodic structures. If energy is increased or scale is decreased, these coefficients do not provide adequate approximation. Using Bloch decomposition, it is first realized that the above coefficients correspond to the lowest energy and the largest scale. This naturally paves the way to introduce other sets of macro coefficients corresponding to higher energies and lower scales which yield better approximation. The next task is to compare their properties with those of the homogenized coefficients. This article reviews these developments along with some new results yet to be published.

  12. Creating new market space.

    PubMed

    Kim, W C; Mauborgne, R

    1999-01-01

    Most companies focus on matching and beating their rivals. As a result, their strategies tend to take on similar dimensions. What ensues is head-to-head competition based largely on incremental improvements in cost, quality, or both. The authors have studied how innovative companies break free from the competitive pack by staking out fundamentally new market space--that is, by creating products or services for which there are no direct competitors. This path to value innovation requires a different competitive mind-set and a systematic way of looking for opportunities. Instead of looking within the conventional boundaries that define how an industry competes, managers can look methodically across them. By so doing, they can find unoccupied territory that represents real value innovation. Rather than looking at competitors within their own industry, for example, managers can ask why customers make the trade-off between substitute products or services. Home Depot, for example, looked across the substitutes serving home improvement needs. Intuit looked across the substitutes available to individuals managing their personal finances. In both cases, powerful insights were derived from looking at familiar data from a new perspective. Similar insights can be gleaned by looking across strategic groups within an industry; across buyer groups; across complementary product and service offerings; across the functional-emotional orientation of an industry; and even across time. To help readers explore new market space systematically, the authors developed a tool, the value curve, that can be used to represent visually a range of value propositions. PMID:10345394

  13. Creating alternatives in science

    PubMed Central

    2009-01-01

    Traditional scientist training at the PhD level does not prepare students to be competitive in biotechnology or other non-academic science careers. Some universities have developed biotechnology-relevant doctoral programmes, but most have not. Forming a life science career club makes a statement to university administrators that it is time to rework the curriculum to include biotechnology-relevant training. A career club can supplement traditional PhD training by introducing students to available career choices, help them develop a personal network and teach the business skills that they will need to be competitive in science outside of academia. This paper is an instructional guide designed to help students create a science career club at their own university. These suggestions are based on the experience gained in establishing such a club for the Graduate School at the University of Colorado Denver. We describe the activities that can be offered, the job descriptions for the offices required and potential challenges. With determination, a creative spirit, and the guidance of this paper, students should be able to greatly increase awareness of science career options, and begin building the skills necessary to become competitive in non-academic science. PMID:20161069

  14. Creating Sample Plans

    SciTech Connect

    Spears, Joseph H.; Seebode, Linda C.

    1999-03-24

    The program has been designed to increase the accuracy and reduce the preparation time for completing sampling plans. It consists of our files 1. Analyte/Combination (AnalCombo) A list of analytes and combinations of analytes that can be requested of the onsite and offsite labs. Whenever a specific combination of analytes or suite names appear on the same line as the code number, this indicates that one sample can be placed in one bottle to be analyzed for these paremeters. A code number is assigned for each analyte and combination of analytes. 2. Sampling Plans Database (SPDb) A database that contains all of the analytes and combinations of analytes along with the basic information required for preparing a sample plan. That basic information includes the following fields; matrix, hold time, preservation, sample volume, container size, if the bottle caps are taped, acceptable choices. 3. Sampling plans create (SPcreate) a file that will lookup information from the Sampling Plans Database and the Job Log File (JLF98) A major database used by Sample Managemnet Services for recording more than 100 fields of information.

  15. Creating Sample Plans

    Energy Science and Technology Software Center (ESTSC)

    1999-03-24

    The program has been designed to increase the accuracy and reduce the preparation time for completing sampling plans. It consists of our files 1. Analyte/Combination (AnalCombo) A list of analytes and combinations of analytes that can be requested of the onsite and offsite labs. Whenever a specific combination of analytes or suite names appear on the same line as the code number, this indicates that one sample can be placed in one bottle to bemore » analyzed for these paremeters. A code number is assigned for each analyte and combination of analytes. 2. Sampling Plans Database (SPDb) A database that contains all of the analytes and combinations of analytes along with the basic information required for preparing a sample plan. That basic information includes the following fields; matrix, hold time, preservation, sample volume, container size, if the bottle caps are taped, acceptable choices. 3. Sampling plans create (SPcreate) a file that will lookup information from the Sampling Plans Database and the Job Log File (JLF98) A major database used by Sample Managemnet Services for recording more than 100 fields of information.« less

  16. Self Creating Universe

    NASA Astrophysics Data System (ADS)

    Terry, Bruce

    2001-04-01

    Cosmology has deduced that our existence began 15 billion years ago but that does not constitute a true story. When compared against infinity, the true question one must as is, ‘why did creation begin now (a mere 15 billion give or take years ago) and not at some infinite point before? What could keep the one common original source static for an infinity, and then spring forth into existence?’ Also, accelerators are actually creating atmospheres much like that within quasars, black holes and stars. This destructive/creative environment is not that of original creation, it is of that which occurs in a later stage of cosmic evolution. Knowing that it is only a matter of movement or change, understanding what is moving is the key. Regardless of how much power is used to alter the character of a particle’s matter, it does not make its essence go away, nor does it make the understanding of original essence clearer. To find the true answer of what occurred, one must look back in time and think carefully over the process of elimination to find the original creation of matter, albeit different than that of the later processes. Matter and the physical laws formed themselves in an absolute infinity of blackness prior to light and no Big Bang scenario was necessary.

  17. Spatial homogenization methods for pin-by-pin neutron transport calculations

    NASA Astrophysics Data System (ADS)

    Kozlowski, Tomasz

    For practical reactor core applications low-order transport approximations such as SP3 have been shown to provide sufficient accuracy for both static and transient calculations with considerably less computational expense than the discrete ordinate or the full spherical harmonics methods. These methods have been applied in several core simulators where homogenization was performed at the level of the pin cell. One of the principal problems has been to recover the error introduced by pin-cell homogenization. Two basic approaches to treat pin-cell homogenization error have been proposed: Superhomogenization (SPH) factors and Pin-Cell Discontinuity Factors (PDF). These methods are based on well established Equivalence Theory and Generalized Equivalence Theory to generate appropriate group constants. These methods are able to treat all sources of error together, allowing even few-group diffusion with one mesh per cell to reproduce the reference solution. A detailed investigation and consistent comparison of both homogenization techniques showed potential of PDF approach to improve accuracy of core calculation, but also reveal its limitation. In principle, the method is applicable only for the boundary conditions at which it was created, i.e. for boundary conditions considered during the homogenization process---normally zero current. Therefore, there exists a need to improve this method, making it more general and environment independent. The goal of proposed general homogenization technique is to create a function that is able to correctly predict the appropriate correction factor with only homogeneous information available, i.e. a function based on heterogeneous solution that could approximate PDFs using homogeneous solution. It has been shown that the PDF can be well approximated by least-square polynomial fit of non-dimensional heterogeneous solution and later used for PDF prediction using homogeneous solution. This shows a promise for PDF prediction for off

  18. Non-Homogeneous Fractal Hierarchical Weighted Networks

    PubMed Central

    Dong, Yujuan; Dai, Meifeng; Ye, Dandan

    2015-01-01

    A model of fractal hierarchical structures that share the property of non-homogeneous weighted networks is introduced. These networks can be completely and analytically characterized in terms of the involved parameters, i.e., the size of the original graph Nk and the non-homogeneous weight scaling factors r1, r2, · · · rM. We also study the average weighted shortest path (AWSP), the average degree and the average node strength, taking place on the non-homogeneous hierarchical weighted networks. Moreover the AWSP is scrupulously calculated. We show that the AWSP depends on the number of copies and the sum of all non-homogeneous weight scaling factors in the infinite network order limit. PMID:25849619

  19. Producing tritium in a homogenous reactor

    DOEpatents

    Cawley, William E.

    1985-01-01

    A method and apparatus are described for the joint production and separation of tritium. Tritium is produced in an aqueous homogenous reactor and heat from the nuclear reaction is used to distill tritium from the lower isotopes of hydrogen.

  20. On homogeneous Einstein (α , β) -metrics

    NASA Astrophysics Data System (ADS)

    Yan, Zaili; Deng, Shaoqiang

    2016-05-01

    In this paper, we study homogeneous Einstein (α , β) -metrics. First, we deduce a formula for Ricci curvature of a homogeneous (α , β) -metric. Based on this formula, we obtain a sufficient and necessary condition for a compact homogeneous (α , β) -metric to be Einstein and with vanishing S-curvature. Moreover, we prove that any homogeneous Ricci flat (α , β) space with vanishing S-curvature must be a Minkowski space. Finally, we consider left invariant Einstein (α , β) -metrics on Lie groups with negative Ricci constant. Under some appropriate conditions, we show that the underlying Lie groups must be two step solvable. We also present a more convenient sufficient and necessary condition for the metric to be Einstein in this special case.

  1. Homogeneous cosmological models in Yang's gravitation theory

    NASA Technical Reports Server (NTRS)

    Fennelly, A. J.; Pavelle, R.

    1979-01-01

    We present a dynamic, spatially homogeneous solution of Yang's pure space gravitational field equations which is non-Einsteinian. The predictions of this cosmological model seem to be at variance with observations.

  2. Layout optimization using the homogenization method

    NASA Technical Reports Server (NTRS)

    Suzuki, Katsuyuki; Kikuchi, Noboru

    1993-01-01

    A generalized layout problem involving sizing, shape, and topology optimization is solved by using the homogenization method for three-dimensional linearly elastic shell structures in order to seek a possibility of establishment of an integrated design system of automotive car bodies, as an extension of the previous work by Bendsoe and Kikuchi. A formulation of a three-dimensional homogenized shell, a solution algorithm, and several examples of computing the optimum layout are presented in this first part of the two articles.

  3. Layout optimization using the homogenization method

    NASA Astrophysics Data System (ADS)

    Suzuki, Katsuyuki; Kikuchi, Noboru

    A generalized layout problem involving sizing, shape, and topology optimization is solved by using the homogenization method for three-dimensional linearly elastic shell structures in order to seek a possibility of establishment of an integrated design system of automotive car bodies, as an extension of the previous work by Bendsoe and Kikuchi. A formulation of a three-dimensional homogenized shell, a solution algorithm, and several examples of computing the optimum layout are presented in this first part of the two articles.

  4. Noncommutative complex structures on quantum homogeneous spaces

    NASA Astrophysics Data System (ADS)

    Ó Buachalla, Réamonn

    2016-01-01

    A new framework for noncommutative complex geometry on quantum homogeneous spaces is introduced. The main ingredients used are covariant differential calculi and Takeuchi's categorical equivalence for quantum homogeneous spaces. A number of basic results are established, producing a simple set of necessary and sufficient conditions for noncommutative complex structures to exist. Throughout, the framework is applied to the quantum projective spaces endowed with the Heckenberger-Kolb calculus.

  5. Creating a Toilet Training Plan

    MedlinePlus

    ... Size Email Print Share Creating a Toilet Training Plan Page Content Article Body These are the tools ... will need to create your own toilet-training plan and implement it at the best time for ...

  6. Effect of non-homogenous thermal stress during sub-lethal photodynamic antimicrobial chemotherapy

    NASA Astrophysics Data System (ADS)

    Gadura, N.; Kokkinos, D.; Dehipawala, S.; Cheung, E.; Sullivan, R.; Subramaniam, R.; Schneider, P.; Tremberger, G., Jr.; Holden, T.; Lieberman, D.; Cheung, T.

    2012-03-01

    Pathogens could be inactivated via a light source coupled with a photosensitizing agent in photodynamic antimicrobial chemotherapy (PACT). This project studied the effect of non-homogenous substrate on cell colony. The non-homogeneity could be controlled by iron oxide nano-particles doping in porous glassy substrates such that each cell would experience tens of hot spots when illuminated with additional light source. The substrate non-homogeneity was characterized by Atomic Force Microscopy, Transmission Electron Microscopy and Extended X-Ray Absorption Fine Structure at Brookhaven Synchrotron Light Source. Microscopy images of cell motion were used to study the motility. Laboratory cell colonies on non-homogenous substrates exhibit reduced motility similar to those observed with sub-lethal PCAT treatment. Such motility reduction on non-homogenous substrate is interpreted as the presence of thermal stress. The studied pathogens included E. coli and Pseudomonas aeruginosa. Non-pathogenic microbes Bacillus subtilis was also studied for comparison. The results show that sub-lethal PACT could be effective with additional non-homogenous thermal stress. The use of non-uniform illumination on a homogeneous substrate to create thermal stress in sub-micron length scale is discussed via light correlation in propagation through random medium. Extension to sub-lethal PACT application complemented with thermal stress would be an appropriate application.

  7. Analysis of homogeneous/non-homogeneous nanofluid models accounting for nanofluid-surface interactions

    NASA Astrophysics Data System (ADS)

    Ahmad, R.

    2016-07-01

    This article reports an unbiased analysis for the water based rod shaped alumina nanoparticles by considering both the homogeneous and non-homogeneous nanofluid models over the coupled nanofluid-surface interface. The mechanics of the surface are found for both the homogeneous and non-homogeneous models, which were ignored in previous studies. The viscosity and thermal conductivity data are implemented from the international nanofluid property benchmark exercise. All the simulations are being done by using the experimentally verified results. By considering the homogeneous and non-homogeneous models, the precise movement of the alumina nanoparticles over the surface has been observed by solving the corresponding system of differential equations. For the non-homogeneous model, a uniform temperature and nanofluid volume fraction are assumed at the surface, and the flux of the alumina nanoparticle is taken as zero. The assumption of zero nanoparticle flux at the surface makes the non-homogeneous model physically more realistic. The differences of all profiles for both the homogeneous and nonhomogeneous models are insignificant, and this is due to small deviations in the values of the Brownian motion and thermophoresis parameters.

  8. Homogenization of Periodic Systems with Large Potentials

    NASA Astrophysics Data System (ADS)

    Allaire, Grégoire; Capdeboscq, Yves; Piatnitski, Andrey; Siess, Vincent; Vanninathan, M.

    2004-11-01

    We consider the homogenization of a system of second-order equations with a large potential in a periodic medium. Denoting by ɛ the period, the potential is scaled as ɛ-2. Under a generic assumption on the spectral properties of the associated cell problem, we prove that the solution can be approximately factorized as the product of a fast oscillating cell eigenfunction and of a slowly varying solution of a scalar second-order equation. This result applies to various types of equations such as parabolic, hyperbolic or eigenvalue problems, as well as fourth-order plate equation. We also prove that, for well-prepared initial data concentrating at the bottom of a Bloch band, the resulting homogenized tensor depends on the chosen Bloch band. Our method is based on a combination of classical homogenization techniques (two-scale convergence and suitable oscillating test functions) and of Bloch waves decomposition.

  9. Rapid biotic homogenization of marine fish assemblages.

    PubMed

    Magurran, Anne E; Dornelas, Maria; Moyes, Faye; Gotelli, Nicholas J; McGill, Brian

    2015-01-01

    The role human activities play in reshaping biodiversity is increasingly apparent in terrestrial ecosystems. However, the responses of entire marine assemblages are not well-understood, in part, because few monitoring programs incorporate both spatial and temporal replication. Here, we analyse an exceptionally comprehensive 29-year time series of North Atlantic groundfish assemblages monitored over 5° latitude to the west of Scotland. These fish assemblages show no systematic change in species richness through time, but steady change in species composition, leading to an increase in spatial homogenization: the species identity of colder northern localities increasingly resembles that of warmer southern localities. This biotic homogenization mirrors the spatial pattern of unevenly rising ocean temperatures over the same time period suggesting that climate change is primarily responsible for the spatial homogenization we observe. In this and other ecosystems, apparent constancy in species richness may mask major changes in species composition driven by anthropogenic change. PMID:26400102

  10. Method of Mapping Anomalies in Homogenous Material

    NASA Technical Reports Server (NTRS)

    Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor)

    2016-01-01

    An electrical conductor and antenna are positioned in a fixed relationship to one another. Relative lateral movement is generated between the electrical conductor and a homogenous material while maintaining the electrical conductor at a fixed distance from the homogenous material. The antenna supplies a time-varying magnetic field that causes the electrical conductor to resonate and generate harmonic electric and magnetic field responses. Disruptions in at least one of the electric and magnetic field responses during this lateral movement are indicative of a lateral location of a subsurface anomaly. Next, relative out-of-plane movement is generated between the electrical conductor and the homogenous material in the vicinity of the anomaly's lateral location. Disruptions in at least one of the electric and magnetic field responses during this out-of-plane movement are indicative of a depth location of the subsurface anomaly. A recording of the disruptions provides a mapping of the anomaly.

  11. Commensurability effects in holographic homogeneous lattices

    NASA Astrophysics Data System (ADS)

    Andrade, Tomas; Krikun, Alexander

    2016-05-01

    An interesting application of the gauge/gravity duality to condensed matter physics is the description of a lattice via breaking translational invariance on the gravity side. By making use of global symmetries, it is possible to do so without scarifying homogeneity of the pertinent bulk solutions, which we thus term as "homogeneous holographic lattices." Due to their technical simplicity, these configurations have received a great deal of attention in the last few years and have been shown to correctly describe momentum relaxation and hence (finite) DC conductivities.

  12. Homogeneous Catalysis by Transition Metal Compounds.

    ERIC Educational Resources Information Center

    Mawby, Roger

    1988-01-01

    Examines four processes involving homogeneous catalysis which highlight the contrast between the simplicity of the overall reaction and the complexity of the catalytic cycle. Describes how catalysts provide circuitous routes in which all energy barriers are relatively low rather than lowering the activation energy for a single step reaction.…

  13. General Theorems about Homogeneous Ellipsoidal Inclusions

    ERIC Educational Resources Information Center

    Korringa, J.; And Others

    1978-01-01

    Mathematical theorems about the properties of ellipsoids are developed. Included are Poisson's theorem concerning the magnetization of a homogeneous body of ellipsoidal shape, the polarization of a dielectric, the transport of heat or electricity through an ellipsoid, and other problems. (BB)

  14. Homogeneous Immunoassays: Historical Perspective and Future Promise

    NASA Astrophysics Data System (ADS)

    Ullman, Edwin F.

    1999-06-01

    The founding and growth of Syva Company is examined in the context of its leadership role in the development of homogeneous immunoassays. The simple mix and read protocols of these methods offer advantages in routine analytical and clinical applications. Early homogeneous methods were based on insensitive detection of immunoprecipitation during antigen/antibody binding. The advent of reporter groups in biology provided a means of quantitating immunochemical binding by labeling antibody or antigen and physically separating label incorporated into immune complexes from free label. Although high sensitivity was achieved, quantitative separations were experimentally demanding. Only when it became apparent that reporter groups could provide information, not only about the location of a molecule but also about its microscopic environment, was it possible to design practical non-separation methods. The evolution of early homogenous immunoassays was driven largely by the development of improved detection strategies. The first commercial spin immunoassays, developed by Syva for drug abuse testing during the Vietnam war, were followed by increasingly powerful methods such as immunochemical modulation of enzyme activity, fluorescence, and photo-induced chemiluminescence. Homogeneous methods that quantify analytes at femtomolar concentrations within a few minutes now offer important new opportunities in clinical diagnostics, nucleic acid detection and drug discovery.

  15. Extension theorems for homogenization on lattice structures

    NASA Technical Reports Server (NTRS)

    Miller, Robert E.

    1992-01-01

    When applying homogenization techniques to problems involving lattice structures, it is necessary to extend certain functions defined on a perforated domain to a simply connected domain. This paper provides general extension operators which preserve bounds on derivatives of order l. Only the special case of honeycomb structures is considered.

  16. RELIABLE COMPUTATION OF HOMOGENEOUS AZEOTROPES. (R824731)

    EPA Science Inventory

    Abstract

    It is important to determine the existence and composition of homogeneous azeotropes in the analysis of phase behavior and in the synthesis and design of separation systems, from both theoretical and practical standpoints. A new method for reliably locating an...

  17. Homogeneity analysis of precipitation series in Iran

    NASA Astrophysics Data System (ADS)

    Hosseinzadeh Talaee, P.; Kouchakzadeh, Mahdi; Shifteh Some'e, B.

    2014-10-01

    Assessment of the reliability and quality of historical precipitation data is required in the modeling of hydrology and water resource processes and for climate change studies. The homogeneity of the annual and monthly precipitation data sets throughout Iran was tested using the Bayesian, Cumulative Deviations, and von Neumann tests at a significance level of 0.05. The precipitation records from 41 meteorological stations covering the years between 1966 and 2005 were considered. The annual series of Iranian precipitation were found to be homogeneous by applying the Bayesian and Cumulative Deviations tests, while the von Neumann test detected inhomogeneities at seven stations. Almost all the monthly precipitation data sets are homogeneous and considered as "useful." The outputs of the statistical tests for the homogeneity analysis of the precipitation time series had discrepancies in some cases which are related to different sensitivities of the tests to break in the time series. It was found that the von Neumann test is more sensitive than the Bayesian and Cumulative Deviations tests in the determination of inhomogeneity in the precipitation series.

  18. Confocal detection of planar homogeneous and heterogeneous immunosorbent assays

    NASA Astrophysics Data System (ADS)

    Ghafari, Homanaz; Zhou, Yanzhou; Ali, Selman; Hanley, Quentin S.

    2009-11-01

    Optically sectioned detection of fluorescence immunoassays using a confocal microscope enables the creation of both homo- and heterogeneous planar format assays. We report a set assays requiring optically sectioned detection using a model system and analysis procedures for separating signals of a surface layer from an overlying solution. A model sandwich assay with human immunoglobulin G as the target antigen is created on a glass substrate. The prepared surfaces are exposed to antigen and a FITC-labeled secondary antibody. The resulting preparations are either read directly to provide a homogeneous assay or after wash steps, giving a heterogeneous assay. The simplicity of the object shapes arising from the planar format makes the decomposition of analyte signals from the thin film bound to the surface and overlayer straightforward. Measured response functions of the thin film and overlayer fit well to the Cauchy-Lorentz and cumulative Cauchy-Lorentz functions, respectively, enabling the film and overlayer to be separated. Under the conditions used, the detection limits for the homogeneous and heterogeneous forms of the assay are 2.2 and 5.5 ng/ml, respectively. Planar format, confocally read fluorescence assays enable wash-free detection of antigens and should be applicable to a wide range of assays involving surface-bound species.

  19. Are geological media homogeneous or heterogeneous for neutron investigations?

    PubMed

    Woźnicka, U; Drozdowicz, K; Gabańska, B; Krynicka, E; Igielski, A

    2003-01-01

    The thermal neutron absorption cross section of a heterogeneous material is lower than that of the corresponding homogeneous one which contains the same components. When rock materials are investigated the sample usually contains grains which create heterogeneity. The heterogeneity effect depends on the mass contribution of highly and low-absorbing centers, on the ratio of their absorption cross sections, and on their sizes. An influence of the granulation of silicon and diabase samples on the absorption cross section measured with Czubek's method has been experimentally investigated. A 20% underestimation of the absorption cross section has been observed for diabase grains of sizes from 6.3 to 12.8 mm. PMID:12485675

  20. The Leadership Assignment: Creating Change.

    ERIC Educational Resources Information Center

    Calabrese, Raymond L.

    This book provides change-motivated leaders with an understanding of the change process and the tools to drive change. Eight change principles guide change agents in creating and sustaining change: prepare to lead change; knowledge is power; create empowering mental models; overcome resistance to change; lead change; accelerate the change process;…

  1. Pd/C catalyzed Suzuki-Miyaura cross coupling reaction: Is it heterogeneous or homogeneous?

    NASA Astrophysics Data System (ADS)

    Hoang, Tony Phuc

    The Suzuki-Miyaura cross-coupling reaction is a popular industrial method of creating covalent bonds between two carbons. This reaction can be catalyzed by a myriad of palladium catalyst including heterogeneous and homogeneous. The objective of this research is to study whether the Suzuki cross coupling reaction catalyzed by solid supported palladium catalysts is truly heterogeneous in nature (i.e. does the reaction occurs on the surface of the catalyst or does palladium leach from the solid support and catalyze the reaction in a homogenous manner).

  2. Homogeneous magnitude system of the Eurasian continent: S and L waves

    NASA Astrophysics Data System (ADS)

    Christoskov, L.; Kondorskaya, N. V.; Vanek, J.

    1983-07-01

    A research project was started by the Commission of Academies of Socialist Countries on Planetary Geophysics (KAPG) to establish a system of seismic reference stations of the Eurasian continent for determining reliable earthquake magnitudes. This system was called the Homogeneous Magnitude System (HMS), and seismologist of 13 institutions from Bulgaria, Czechoslovakia, German Democratic Republic, Poland, and the U.S.S.R. participated. The project was sponsored by the Commission on Practice of the International Association of Seismology and Physics of the Earth's Interior, which created a special working group for homogeneous magnitude system within its Subcommission on Magnitude.

  3. Homogeneous crystal nucleation in binary metallic melts

    NASA Technical Reports Server (NTRS)

    Thompson, C. V.; Spaepen, F.

    1983-01-01

    A method for calculating the homogeneous crystal nucleation frequency in binary metallic melts is developed. The free energy of crystallization is derived from regular solution models for the liquid and solid and is used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency from the classical theory. The method can account for the composition dependence of the maximum undercooling observed in a number of experiments on small droplet dispersions. It can also be used to calculate the driving force for crystal growth and to obtain more precise estimates of the homogeneous crystal nucleation frequency in glass-forming alloys. This method, although approximate, is simple to apply, and requires only knowledge of the phase diagram and a few readily available thermodynamic quantities as input data.

  4. Beyond relationships between homogeneous and heterogeneous catalysis

    SciTech Connect

    Dixon, David A.; Katz, Alexander; Arslan, Ilke; Gates, Bruce C.

    2014-08-13

    Scientists who regard catalysis as a coherent field have been striving for decades to articulate the fundamental unifying principles. But because these principles seem to be broader than chemistry, chemical engineering, and materials science combined, catalytic scientists commonly interact within the sub-domains of homogeneous, heterogeneous, and bio-catalysis, and increasingly within even narrower domains such as organocatalysis, phase-transfer catalysis, acid-base catalysis, zeolite catalysis, etc. Attempts to unify catalysis have motivated researchers to find relationships between homogeneous and heterogeneous catalysis and to mimic enzymes. These themes have inspired vibrant international meetings and workshops, and we have benefited from the idea exchanges and have some thoughts about a path forward.

  5. Homogeneous Superpixels from Markov Random Walks

    NASA Astrophysics Data System (ADS)

    Perbet, Frank; Stenger, Björn; Maki, Atsuto

    This paper presents a novel algorithm to generate homogeneous superpixels from Markov random walks. We exploit Markov clustering (MCL) as the methodology, a generic graph clustering method based on stochastic flow circulation. In particular, we introduce a graph pruning strategy called compact pruning in order to capture intrinsic local image structure. The resulting superpixels are homogeneous, i.e. uniform in size and compact in shape. The original MCL algorithm does not scale well to a graph of an image due to the square computation of the Markov matrix which is necessary for circulating the flow. The proposed pruning scheme has the advantages of faster computation, smaller memory footprint, and straightforward parallel implementation. Through comparisons with other recent techniques, we show that the proposed algorithm achieves state-of-the-art performance.

  6. Detonation in shocked homogeneous high explosives

    SciTech Connect

    Yoo, C.S.; Holmes, N.C.; Souers, P.C.

    1995-11-01

    We have studied shock-induced changes in homogeneous high explosives including nitromethane, tetranitromethane, and single crystals of pentaerythritol tetranitrate (PETN) by using fast time-resolved emission and Raman spectroscopy at a two-stage light-gas gun. The results reveal three distinct steps during which the homogeneous explosives chemically evolve to final detonation products. These are (1) the initiation of shock compressed high explosives after an induction period, (2) thermal explosion of shock-compressed and/or reacting materials, and (3) a decay to a steady-state representing a transition to the detonation of uncompressed high explosives. Based on a gray-body approximation, we have obtained the CJ temperatures: 3800 K for nitromethane, 2950 K for tetranitromethane, and 4100 K for PETN. We compare the data with various thermochemical equilibrium calculations. In this paper we will also show a preliminary result of single-shot time-resolved Raman spectroscopy applied to shock-compressed nitromethane.

  7. Resonant ultrasound spectroscopy and homogeneity in polycrystals.

    PubMed

    Kaplan, Gunes; Darling, T W; McCall, K R

    2009-01-01

    Resonant ultrasound spectroscopy (RUS) is capable of determining the bulk elastic properties of a solid from its characteristic vibration frequencies, given the dimensions, density and shape of the sample. The model used for extracting values of the elastic constants assumes perfect homogeneity, which can be approximated by average-isotropic polycrystals. This approximation is excellent in the small grain regime assumed for most averaging procedures, but for real samples with indeterminate grain size distributions, it is not clear where the approximation breaks down. RUS measurements were made on pure copper samples where the grain size distribution was changed by progressive heat treatments in order to find a quantitative limit for the loss of homogeneity. It is found that when a measure of the largest grains is 15% of the sample's smallest dimension, the deviation in RUS fits indicates elastic inhomogeneity. PMID:18804831

  8. Broken Ergodicity in Ideal, Homogeneous, Incompressible Turbulence

    NASA Technical Reports Server (NTRS)

    Morin, Lee; Shebalin, John; Fu, Terry; Nguyen, Phu; Shum, Victor

    2010-01-01

    We discuss the statistical mechanics of numerical models of ideal homogeneous, incompressible turbulence and their relevance for dissipative fluids and magnetofluids. These numerical models are based on Fourier series and the relevant statistical theory predicts that Fourier coefficients of fluid velocity and magnetic fields (if present) are zero-mean random variables. However, numerical simulations clearly show that certain coefficients have a non-zero mean value that can be very large compared to the associated standard deviation. We explain this phenomena in terms of broken ergodicity', which is defined to occur when dynamical behavior does not match ensemble predictions on very long time-scales. We review the theoretical basis of broken ergodicity, apply it to 2-D and 3-D fluid and magnetohydrodynamic simulations of homogeneous turbulence, and show new results from simulations using GPU (graphical processing unit) computers.

  9. CUDA Simulation of Homogeneous, Incompressible Turbulence

    NASA Technical Reports Server (NTRS)

    Morin, Lee; Shebalin, John V.; Shum, Victor; Fu, Terry

    2011-01-01

    We discuss very fast Compute Unified Device Architecture (CUDA) simulations of ideal homogeneous incompressible turbulence based on Fourier models. These models have associated statistical theories that predict that Fourier coefficients of fluid velocity and magnetic fields (if present) are zero-mean random variables. Prior numerical simulations have shown that certain coefficients have a non-zero mean value that can be very large compared to the associated standard deviation. We review the theoretical basis of this "broken ergodicity" as applied to 2-D and 3-D fluid and magnetohydrodynamic simulations of homogeneous turbulence. Our new simulations examine the phenomenon of broken ergodicity through very long time and large grid size runs performed on a state-of-the-art CUDA platform. Results comparing various CUDA hardware configurations and grid sizes are discussed. NS and MHD results are compared.

  10. Homogeneous freezing nucleation of stratospheric solution droplets

    NASA Technical Reports Server (NTRS)

    Jensen, Eric J.; Toon, Owen B.; Hamill, Patrick

    1991-01-01

    The classical theory of homogeneous nucleation was used to calculate the freezing rate of sulfuric acid solution aerosols under stratospheric conditions. The freezing of stratospheric aerosols would be important for the nucleation of nitric acid trihydrate particles in the Arctic and Antarctic stratospheres. In addition, the rate of heterogeneous chemical reactions on stratospheric aerosols may be very sensitive to their state. The calculations indicate that homogeneous freezing nucleation of pure water ice in the stratospheric solution droplets would occur at temperatures below about 192 K. However, the physical properties of H2SO4 solution at such low temperatures are not well known, and it is possible that sulfuric acid aerosols will freeze out at temperatures ranging from about 180 to 195 K. It is also shown that the temperature at which the aerosols freeze is nearly independent of their size.

  11. Homogeneity of kappa statistics in multiple samples.

    PubMed

    Reed, J F

    2000-08-01

    The measurement of intra-observer agreement when the data are categorical has been the subject of several investigators since Cohen first proposed the kappa (kappa) as a chance-corrected coefficient of agreement for nominal scales. Subsequent procedures have been developed to assess the agreement of several raters using a dichotomous classification scheme, assess majority agreement among several raters using a polytomous classification scheme, and the use of kappa as an indicator of the quality of a measurement. Further developments include inference procedures for testing the homogeneity of k>/=2 independent kappa statistics. An executable FORTRAN code for testing the homogeneity of kappa statistics (kappa(h)) across multiple sites or studies is given. The FORTRAN program listing and/or executable programs are available from the author on request. PMID:10927153

  12. A homogenization model of the annulus fibrosus.

    PubMed

    Yin, Luzhong; Elliott, Dawn M

    2005-08-01

    The objective of this study was to use a homogenization model of the anisotropic mechanical behavior of annulus fibrosus (AF) to address some of the issues raised in structural finite element and fiber-reinforced strain energy models. Homogenization theory describes the effect of microstructure on macroscopic material properties by assuming the material is composed of repeating representative volume elements. We first developed the general homogenization model and then specifically prescribed the model to in-plane single lamella and multi-lamellae AF properties. We compared model predictions to experimentally measured AF properties and performed parametric studies. The predicted tensile moduli (E theta and E z) and their dependence on fiber volume fraction and fiber angle were consistent with measured values. However, the model prediction for shear modulus (G thetaz) was two orders of magnitude larger than directly measured values. The values of E theta and E z were strongly dependent on the model input for matrix modulus, much more so than the fiber modulus. These parametric analyses demonstrated the contribution of the matrix in AF load support, which may play a role when protoeglycans are decreased in disc degeneration, and will also be an important design factor in tissue engineering. We next compared the homogenization model to a 3-D structural finite element model and fiber-reinforced energy models. Similarities between the three model types provided confidence in the ability of these models to predict AF tissue mechanics. This study provides a direct comparison between the several types of AF models and will be useful for interpreting previous studies and elucidating AF structure-function relationships in disc degeneration and for functional tissue engineering. PMID:15958225

  13. The Architecture of a Homogeneous Vector Supercomputer

    NASA Astrophysics Data System (ADS)

    Gustafson, J. L.; Hawkinson, S.; Scott, K.

    A new homogeneous computer architecture combines two fundamental techniques for high-speed computing: parallelism based on the binary n-cube interconnect, and pipelined vector arithmetic. The design makes extensive use of VLSI technology, resulting in a processing node that can be economically replicated. The new system achieves a careful balance between high-speed communication and floating-point computation. This paper describes the new architecture in detail and explores some of the issues in developing effective software.

  14. Spherical cloaking with homogeneous isotropic multilayered structures.

    PubMed

    Qiu, Cheng-Wei; Hu, Li; Xu, Xiaofei; Feng, Yijun

    2009-04-01

    We propose a practical realization of electromagnetic spherical cloaking by layered structure of homogeneous isotropic materials. By mimicking the classic anisotropic cloak by many alternating thin layers of isotropic dielectrics, the permittivity and permeability in each isotropic layer can be properly determined by effective medium theory in order to achieve invisibility. The model greatly facilitates modeling by Mie theory and realization by multilayer coating of dielectrics. Eigenmode analysis is also presented to provide insights of the discretization in multilayers. PMID:19518392

  15. MULTIGRID HOMOGENIZATION OF HETEROGENEOUS POROUS MEDIA

    SciTech Connect

    Dendy, J.E.; Moulton, J.D.

    2000-10-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL); this report, however, reports on only two years research, since this project was terminated at the end of two years in response to the reduction in funding for the LDRD Program at LANL. The numerical simulation of flow through heterogeneous porous media has become a vital tool in forecasting reservoir performance, analyzing groundwater supply and predicting the subsurface flow of contaminants. Consequently, the computational efficiency and accuracy of these simulations is paramount. However, the parameters of the underlying mathematical models (e.g., permeability, conductivity) typically exhibit severe variations over a range of significantly different length scales. Thus the numerical treatment of these problems relies on a homogenization or upscaling procedure to define an approximate coarse-scale problem that adequately captures the influence of the fine-scale structure, with a resultant compromise between the competing objectives of computational efficiency and numerical accuracy. For homogenization in models of flow through heterogeneous porous media, We have developed new, efficient, numerical, multilevel methods, that offer a significant improvement in the compromise between accuracy and efficiency. We recently combined this approach with the work of Dvorak to compute bounded estimates of the homogenized permeability for such flows and demonstrated the effectiveness of this new algorithm with numerical examples.

  16. Homogeneous cooling state of frictionless rod particles

    NASA Astrophysics Data System (ADS)

    Rubio-Largo, S. M.; Alonso-Marroquin, F.; Weinhart, T.; Luding, S.; Hidalgo, R. C.

    2016-02-01

    In this work, we report some theoretical results on granular gases consisting of frictionless 3D rods with low energy dissipation. We performed simulations on the temporal evolution of soft spherocylinders, using a molecular dynamics algorithm implemented on GPU architecture. A homogeneous cooling state for rods, where the time dependence of the system's intensive variables occurs only through a global granular temperature, has been identified. We have found a homogeneous cooling process, which is in excellent agreement with Haff's law, when using an adequate rescaling time τ(ξ), the value of which depends on the particle elongation ξ and the restitution coefficient. It was further found that scaled particle velocity distributions remain approximately Gaussian regardless of the particle shape. Similarly to a system of ellipsoids, energy equipartition between rotational and translational degrees of freedom was better satisfied as one gets closer to the elastic limit. Taking advantage of scaling properties, we have numerically determined the general functionality of the magnitude Dc(ξ), which describes the efficiency of the energy interchange between rotational and translational degrees of freedom, as well as its dependence on particle shape. We have detected a range of particle elongations (1.5 < ξ < 4.0), where the average energy transfer between the rotational and translational degrees of freedom results greater for spherocylinders than for homogeneous ellipsoids with the same aspect ratio.

  17. Homogeneous Biosensing Based on Magnetic Particle Labels

    PubMed Central

    Schrittwieser, Stefan; Pelaz, Beatriz; Parak, Wolfgang J.; Lentijo-Mozo, Sergio; Soulantica, Katerina; Dieckhoff, Jan; Ludwig, Frank; Guenther, Annegret; Tschöpe, Andreas; Schotter, Joerg

    2016-01-01

    The growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuation. PMID:27275824

  18. TESTING HOMOGENEITY WITH GALAXY STAR FORMATION HISTORIES

    SciTech Connect

    Hoyle, Ben; Jimenez, Raul; Tojeiro, Rita; Maartens, Roy; Heavens, Alan; Clarkson, Chris

    2013-01-01

    Observationally confirming spatial homogeneity on sufficiently large cosmological scales is of importance to test one of the underpinning assumptions of cosmology, and is also imperative for correctly interpreting dark energy. A challenging aspect of this is that homogeneity must be probed inside our past light cone, while observations take place on the light cone. The star formation history (SFH) in the galaxy fossil record provides a novel way to do this. We calculate the SFH of stacked luminous red galaxy (LRG) spectra obtained from the Sloan Digital Sky Survey. We divide the LRG sample into 12 equal-area contiguous sky patches and 10 redshift slices (0.2 < z < 0.5), which correspond to 120 blocks of volume {approx}0.04 Gpc{sup 3}. Using the SFH in a time period that samples the history of the universe between look-back times 11.5 and 13.4 Gyr as a proxy for homogeneity, we calculate the posterior distribution for the excess large-scale variance due to inhomogeneity, and find that the most likely solution is no extra variance at all. At 95% credibility, there is no evidence of deviations larger than 5.8%.

  19. Homogeneous Biosensing Based on Magnetic Particle Labels.

    PubMed

    Schrittwieser, Stefan; Pelaz, Beatriz; Parak, Wolfgang J; Lentijo-Mozo, Sergio; Soulantica, Katerina; Dieckhoff, Jan; Ludwig, Frank; Guenther, Annegret; Tschöpe, Andreas; Schotter, Joerg

    2016-01-01

    The growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuation. PMID:27275824

  20. Creating and Exploring Simple Models

    ERIC Educational Resources Information Center

    Hubbard, Miles J.

    2007-01-01

    Students manipulate data algebraically, and statistically to create models applied to a falling ball. They also borrow tools from arithmetic progressions to examine the relationship between the velocity and the distance the ball falls. (Contains 2 tables and 5 figures.)

  1. Homogenous charge compression ignition engine having a cylinder including a high compression space

    DOEpatents

    Agama, Jorge R.; Fiveland, Scott B.; Maloney, Ronald P.; Faletti, James J.; Clarke, John M.

    2003-12-30

    The present invention relates generally to the field of homogeneous charge compression engines. In these engines, fuel is injected upstream or directly into the cylinder when the power piston is relatively close to its bottom dead center position. The fuel mixes with air in the cylinder as the power piston advances to create a relatively lean homogeneous mixture that preferably ignites when the power piston is relatively close to the top dead center position. However, if the ignition event occurs either earlier or later than desired, lowered performance, engine misfire, or even engine damage, can result. Thus, the present invention divides the homogeneous charge between a controlled volume higher compression space and a lower compression space to better control the start of ignition.

  2. Effect of homogenization techniques on reducing the size of microcapsules and the survival of probiotic bacteria therein.

    PubMed

    Ding, W K; Shah, N P

    2009-08-01

    This study investigated 2 different homogenization techniques for reducing the size of calcium alginate beads during the microencapsulation process of 8 probiotic bacteria strains, namely, Lactobacillus rhamnosus, L. salivarius, L. plantarum, L. acidophilus, L. paracasei, Bifidobacterium longum, B. lactis type Bi-04, and B. lactis type Bi-07. Two different homogenization techniques were used, namely, ultra-turrax benchtop homogenizer and Microfluidics microfluidizer. Various settings on the homogenization equipment were studied such as the number of passes, speed (rpm), duration (min), and pressure (psi). The traditional mixing method using a magnetic stirrer was used as a control. The size of microcapsules resulting from the homogenization technique, and the various settings were measured using a light microscope and a stage micrometer. The smallest capsules measuring (31.2 microm) were created with the microfluidizer using 26 passes at 1200 psi for 40 min. The greatest loss in viability of 3.21 log CFU/mL was observed when using the ultra-turrax benchtop homogenizer with a speed of 1300 rpm for 5 min. Overall, both homogenization techniques reduced capsule sizes; however, homogenization settings at high rpm also greatly reduced the viability of probiotic organisms. PMID:19723206

  3. The Chemical Homogeneity of Open Clusters

    NASA Astrophysics Data System (ADS)

    Bovy, Jo

    2016-01-01

    Determining the level of chemical homogeneity in open clusters is of fundamental importance in the study of the evolution of star-forming clouds and that of the Galactic disk. Yet limiting the initial abundance spread in clusters has been hampered by difficulties in obtaining consistent spectroscopic abundances for different stellar types. Without reference to any specific model of stellar photospheres, a model for a homogeneous cluster is that it forms a one-dimensional sequence, with any differences between members due to variations in stellar mass and observational uncertainties. I present a novel method for investigating the abundance spread in open clusters that tests this one-dimensional hypothesis at the level of observed stellar spectra, rather than constraining homogeneity using derived abundances as is traditionally done. Using high-resolution APOGEE spectra for 49 giants in M67, NGC 6819, and NGC 2420 I demonstrate that these spectra form one-dimensional sequences for each cluster. With detailed forward modeling of the spectra and Approximate Bayesian Computation, I derive strong limits on the initial abundance spread of 15 elements: <0.01 (0.02) {dex} for C and Fe, ≲0.015 (0.03) {dex} for N, O, Mg, Si, and Ni, ≲0.02 (0.03) {dex} for Al, Ca, and Mn, and ≲0.03 (0.05) {dex} for Na, S, K, Ti, and V (at 68% and 95% confidence, respectively). The strong limits on C and O imply that no pollution by massive core-collapse supernovae occurred during star formation in open clusters, which, thus, need to form within ≲6 {Myr}. Further development of this and related techniques will bring the power of differential abundances to stars other than solar twins in large spectroscopic surveys and will help unravel the history of star formation and chemical enrichment in the Milky Way through chemical tagging.

  4. Sulfur isotope homogeneity of lunar mare basalts

    NASA Astrophysics Data System (ADS)

    Wing, Boswell A.; Farquhar, James

    2015-12-01

    We present a new set of high precision measurements of relative 33S/32S, 34S/32S, and 36S/32S values in lunar mare basalts. The measurements are referenced to the Vienna-Canyon Diablo Troilite (V-CDT) scale, on which the international reference material, IAEA-S-1, is characterized by δ33S = -0.061‰, δ34S ≡ -0.3‰ and δ36S = -1.27‰. The present dataset confirms that lunar mare basalts are characterized by a remarkable degree of sulfur isotopic homogeneity, with most new and published SF6-based sulfur isotope measurements consistent with a single mass-dependent mean isotopic composition of δ34S = 0.58 ± 0.05‰, Δ33S = 0.008 ± 0.006‰, and Δ36S = 0.2 ± 0.2‰, relative to V-CDT, where the uncertainties are quoted as 99% confidence intervals on the mean. This homogeneity allows identification of a single sample (12022, 281) with an apparent 33S enrichment, possibly reflecting cosmic-ray-induced spallation reactions. It also reveals that some mare basalts have slightly lower δ34S values than the population mean, which is consistent with sulfur loss from a reduced basaltic melt prior to eruption at the lunar surface. Both the sulfur isotope homogeneity of the lunar mare basalts and the predicted sensitivity of sulfur isotopes to vaporization-driven fractionation suggest that less than ≈1-10% of lunar sulfur was lost after a potential moon-forming impact event.

  5. Creating improved ASTER DEMs over glacierized terrain

    NASA Astrophysics Data System (ADS)

    Raup, B. H.; Khalsa, S. S.; Armstrong, R.

    2006-12-01

    Digital elevation models (DEMs) produced from ASTER stereo imagery over glacierized terrain frequently contain data voids, which some software packages fill by interpolation. Even when interpolation is applied, the results are often not accurate enough for studies of glacier thickness changes. DEMs are created by automatic cross-correlation between the image pairs, and rely on spatial variability in the digital number (DN) values for this process. Voids occur in radiometrically homogeneous regions, such as glacier accumulation areas covered with uniform snow, due to lack of correlation. The same property that leads to lack of correlation makes possible the derivation of elevation information from photoclinometry, also known as shape-from-shading. We demonstrate a technique to produce improved DEMs from ASTER data by combining the results from conventional cross-correlation DEM-generation software with elevation information produced from shape-from-shading in the accumulation areas of glacierized terrain. The resulting DEMs incorporate more information from the imagery, and the filled voids more accurately represent the glacier surface. This will allow for more accurate determination of glacier hypsometry and thickness changes, leading to better predictions of response to climate change.

  6. Compressible homogeneous shear: Simulation and modeling

    NASA Technical Reports Server (NTRS)

    Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.

    1992-01-01

    Compressibility effects were studied on turbulence by direct numerical simulation of homogeneous shear flow. A primary observation is that the growth of the turbulent kinetic energy decreases with increasing turbulent Mach number. The sinks provided by compressible dissipation and the pressure dilatation, along with reduced Reynolds shear stress, are shown to contribute to the reduced growth of kinetic energy. Models are proposed for these dilatational terms and verified by direct comparison with the simulations. The differences between the incompressible and compressible fields are brought out by the examination of spectra, statistical moments, and structure of the rate of strain tensor.

  7. Multifractal spectra in homogeneous shear flow

    NASA Technical Reports Server (NTRS)

    Deane, A. E.; Keefe, L. R.

    1988-01-01

    Employing numerical simulations of 3-D homogeneous shear flow, the associated multifractal spectra of the energy dissipation, scalar dissipation and vorticity fields were calculated. The results for (128) cubed simulations of this flow, and those obtained in recent experiments that analyzed 1- and 2-D intersections of atmospheric and laboratory flows, are in some agreement. A two-scale Cantor set model of the energy cascade process which describes the experimental results from 1-D intersections quite well, describes the 3-D results only marginally.

  8. Einstein billiards and spatially homogeneous cosmological models

    NASA Astrophysics Data System (ADS)

    de Buyl, Sophie; Pinardi, Gaïa; Schomblond, Christiane

    2003-12-01

    In this paper, we analyse the Einstein and Einstein Maxwell billiards for all spatially homogeneous cosmological models corresponding to three- and four-dimensional real unimodular Lie algebras and provide a list of those models which are chaotic in the Belinskii, Khalatnikov and Lifschitz (BKL) limit. Through the billiard picture, we confirm that, in D = 5 spacetime dimensions, chaos is present if off-diagonal metric elements are kept: the finite volume billiards can be identified with the fundamental Weyl chambers of hyperbolic Kac Moody algebras. The most generic cases bring in the same algebras as in the inhomogeneous case, but other algebras appear through special initial conditions.

  9. Homogeneous system UTBLI for 1964 - 1986.

    NASA Astrophysics Data System (ADS)

    Jovanović, B.; Durović, L.; Jovanović, M.

    1993-09-01

    Homogeneous results of universal time determinations derived from the observations by the Transit Instrument of Belgrade Astronomical Observatory (BLI) for the interval 1964 - 1986 are presented. They were prepared in accordance with IERS standards and listed in a table. In addition, using the smoothed values of monthly averaged UT1BLI-UT1BIH, an analysis on the variation of the local system UT1BLI is carried out, and also, systematic deviations after the adopted BIH model are shown. Undoubtedly, there exists a significant 11 - 14 year periodic change of UT1BLI system.

  10. Isotropic homogeneous universe with viscous fluid

    SciTech Connect

    Santos, N.O.; Dias, R.S.; Banerjee, A.

    1985-04-01

    Exact solutions are obtained for the isotropic homogeneous cosmological model with viscous fluid. The fluid has only bulk viscosity and the viscosity coefficient is taken to be a power function of the mass density. The equation of state assumed obeys a linear relation between mass density and pressure. The models satisfying Hawking's energy conditions are discussed. Murphy's model is only a special case of this general set of solutions and it is shown that Murphy's conclusion that the introduciton of bulk viscosity can avoid the occurrence of space-time singularity at finite past is not, in general, valid.

  11. Mirror Symmetry for Quasi-Homogeneous Singularities

    NASA Astrophysics Data System (ADS)

    Rathnakumara, Himal; Jarvis, Tyler

    2008-10-01

    I will present an introduction to mirror symmetry in the context of string theory. Then I will describe an instance of mirror symmetry for singularties defined by quasi-homogeneous polynomials in weighted projective spaces. Milnor rings and the FJRW (Fan-Jarvis-Ruan-Witten) rings associated with these singularities and their relation to the Landua-Ginzburg A model and the Landua-Ginzburg B model will be explained. Results of the calculations for certain singularities for which the mirror symmetry conjecture has been verified will be presented.

  12. Heterogeneity versus homogeneity of multiple sclerosis

    PubMed Central

    Sato, Fumitaka; Martinez, Nicholas E; Omura, Seiichi; Tsunoda, Ikuo

    2011-01-01

    The 10th International Congress of Neuroimmunology, including the 10th European School of Neuroimmunology Course, was held by the International Society of Neuroimmunology in Sitges (Barcelona, Spain) on 26–30 October 2010. The conference covered a wide spectrum of issues and challenges in both basic science and clinical aspects of neuroimmunology. Data and ideas were shared through a variety of programs, including review talks and poster sessions. One of the topics of the congress was whether multiple sclerosis is a homogenous or heterogenous disease, clinically and pathologically, throughout its course. PMID:21426254

  13. Local structures of homogeneous Hall MHD turbulence

    NASA Astrophysics Data System (ADS)

    Miura, H.; Araki, K.

    2011-12-01

    Local structures of decaying homogeneous and isotropic Hall MHD turbulence are studied by means of direct numerical simulations. Regions of strong vorticity and strong current density in Hall MHD turbulence are compared to those of single-fluid MHD turbulence. An analysis by the use of a low-pass filter reveals that the introduction of the Hall term can modify not only small-scale structures of the current density but also structures of the vorticity field, especially at the scales smaller than the ion skin depth.

  14. Homogeneous and hypersurface-homogeneous shear-free perfect fluids ingeneral relativity.

    NASA Astrophysics Data System (ADS)

    Collins, C. B.

    1988-08-01

    Shear-free, general-relativistic perfect fluids are investigated in the case where they are either homogeneous or hypersurface-homogeneous (and, in particular, spatially homogeneous). It is assumed that the energy density μ and the presurep of the fluid are related by a barotropic equation of statep = p(μ), where μ +p ≠ 0. Under such circumstances, it follows that either the fluid's volume expansion rate θ or the fluid's vorticity (i.e., rotation) ω must vanish. In the homogeneous case, this leads to only two possibilities: either ω = θ = 0 (the Einstein static solution), or ω ≠ 0,θ = 0 (the Gödel solution). In the hypersurface-homogeneous case, the situation is more complicated: either ω = 0, θ≠ 0 (as exemplified,inter alia, by the Friedmann-Robertson-Walker models), or ω ≠ 0, θ = 0 (which pertains, for example, in general stationary cylindrically symmetric fluids with rigid rotation, or ω = θ = 0 (as occurs for static spherically symmetric solutions). Each possibility is further subdivided in an invariant way, and related to the studies of other authors, thereby unifying and extending these earlier works.

  15. Microfluidic Generation of Monodisperse, Structurally Homogeneous Alginate Microgels for Cell Encapsulation and 3D Cell Culture.

    PubMed

    Utech, Stefanie; Prodanovic, Radivoje; Mao, Angelo S; Ostafe, Raluca; Mooney, David J; Weitz, David A

    2015-08-01

    Monodisperse alginate microgels (10-50 μm) are created via droplet-based microfluidics by a novel crosslinking procedure. Ionic crosslinking of alginate is induced by release of chelated calcium ions. The process separates droplet formation and gelation reaction enabling excellent control over size and homogeneity under mild reaction conditions. Living mesenchymal stem cells are encapsulated and cultured in the generated 3D microenvironments. PMID:26039892

  16. Plasma And Beam Homogeneity Of The RF-Driven Negative Hydrogen Ion Source For ITER NBI

    SciTech Connect

    Fantz, U.; Franzen, P.; Kraus, W.; Wuenderlich, D.; Gutser, R.; Berger, M.

    2009-03-12

    The neutral beam injection (NBI) system of ITER is based on a large RF driven negative hydrogen ion source. For good beam transmission ITER requires a beam homogeneity of better than 10%. The plasma uniformity and the correlation with the beam homogeneity are being investigated at the prototype ion sources at IPP. Detailed studies are carried out at the long pulse test facility MANITU with a source of roughly 1/8 of the ITER source size. The plasma homogeneity close to plasma grid is measured by optical emission spectroscopy and by fixed Langmuir probes working in the ion saturation region. The beam homogeneity is measured with a spatially resolved H{sub {alpha}} Doppler-shifted beam spectroscopy system. The plasma top-to-bottom symmetry improves with increasing RF power and increasing bias voltage which is applied to suppress the co-extracted electron current. The symmetry is better in deuterium than in hydrogen. The boundary layer near the plasma grid determines the plasma symmetry. At high ion currents with a low amount of co-extracted electrons the plasma is symmetrical and the beam homogeneity is typically 5-10%(RMS). The size scaling and the influence of the magnetic field strength of the filter field created by a plasma grid current is studied at the test facility RADI (roughly a 1/2 size ITER source) at ITER relevant RF power levels. In volume operation in deuterium (non-cesiated source), the plasma illumination of the grid is satisfying.

  17. Bio-inspired homogeneous multi-scale place recognition.

    PubMed

    Chen, Zetao; Lowry, Stephanie; Jacobson, Adam; Hasselmo, Michael E; Milford, Michael

    2015-12-01

    Robotic mapping and localization systems typically operate at either one fixed spatial scale, or over two, combining a local metric map and a global topological map. In contrast, recent high profile discoveries in neuroscience have indicated that animals such as rodents navigate the world using multiple parallel maps, with each map encoding the world at a specific spatial scale. While a number of theoretical-only investigations have hypothesized several possible benefits of such a multi-scale mapping system, no one has comprehensively investigated the potential mapping and place recognition performance benefits for navigating robots in large real world environments, especially using more than two homogeneous map scales. In this paper we present a biologically-inspired multi-scale mapping system mimicking the rodent multi-scale map. Unlike hybrid metric-topological multi-scale robot mapping systems, this new system is homogeneous, distinguishable only by scale, like rodent neural maps. We present methods for training each network to learn and recognize places at a specific spatial scale, and techniques for combining the output from each of these parallel networks. This approach differs from traditional probabilistic robotic methods, where place recognition spatial specificity is passively driven by models of sensor uncertainty. Instead we intentionally create parallel learning systems that learn associations between sensory input and the environment at different spatial scales. We also conduct a systematic series of experiments and parameter studies that determine the effect on performance of using different neural map scaling ratios and different numbers of discrete map scales. The results demonstrate that a multi-scale approach universally improves place recognition performance and is capable of producing better than state of the art performance compared to existing robotic navigation algorithms. We analyze the results and discuss the implications with respect to

  18. A compact setup to study homogeneous nucleation and condensation.

    PubMed

    Karlsson, Mattias; Alxneit, Ivo; Rütten, Frederik; Wuillemin, Daniel; Tschudi, Hans Rudolf

    2007-03-01

    An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 10(6) Pa resulting from mass flow rates of up to 600 l(N) min(-1) and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD. PMID:17411197

  19. Materials Data on BaTiO3 (SG:160) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-07-09

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  20. Giant persistent photoconductivity in BaTiO3/TiO2 heterostructures

    NASA Astrophysics Data System (ADS)

    Plodinec, Milivoj; Šantić, Ana; Zavašnik, Janez; Čeh, Miran; Gajović, Andreja

    2014-10-01

    The persistent photoconductivity (PPC) effect in nanotube arrays of barium titanate and TiO2 (BTO/TiO2NT) was studied at room temperature under daylight illumination. The BTO/TiO2NT heterostructures exhibited a giant PPC effect that was six orders of magnitude higher than the dark conductivity, followed by a slow relaxation for 3 h. The PPC in this material was explained by the existence of defects at the surfaces and the interfaces of the investigated heterostructures. The sample was prepared using a two-step synthesis: the anodization of a Ti-foil and a subsequent hydrothermal synthesis. The structural and electrical characteristics were studied by micro-Raman spectroscopy, field-emission-gun scanning electron microscopy, and impedance spectroscopy.

  1. Phase conjugation in BaTiO3 at 830 nanometers

    SciTech Connect

    Bendall, I.; Gookin, D.M.

    1992-03-01

    We have demonstrated self-pumped phase conjugation of semiconductor lasers at 830 nanometers in barium titanate using a self-contained geometry. The reflectivities and response times of this geometry are compared to those reported for self-pumped ring passive phase conjugate mirrors.

  2. Microwave synthesis of noncentrosymmetric BaTiO3 truncated nanocubes for charge storage applications.

    PubMed

    Swaminathan, V; Pramana, Stevin S; White, T J; Chen, L; Chukka, Rami; Ramanujan, R V

    2010-11-01

    Truncated nanocubes of barium titanate (BT) were synthesized using a rapid, facile microwave-assisted hydrothermal route. Stoichiometric composition of pellets of nanocube BT powders was prepared by two-stage microwave process. Characterization by powder XRD, Rietveld refinement, SEM, TEM, and dielectric and polarization measurements was performed. X-ray diffraction revealed a polymorphic transformation from cubic Pm3̅m to tetragonal P4mm after 15 min of microwave irradiation, arising from titanium displacement along the c-axis. Secondary electron images were examined for nanocube BT synthesis and annealed at different timings. Transmission electron microscopy showed a narrow particle size distribution with an average size of 70 ± 9 nm. The remanence and saturation polarization were 15.5 ± 1.6 and 19.3 ± 1.2 μC/cm(2), respectively. A charge storage density of 925 ± 47 nF/cm(2) was obtained; Pt/BT/Pt multilayer ceramic capacitor stack had an average leakage current density of 5.78 ± 0.46 × 10(-8) A/cm(2) at ±2 V. The significance of this study shows an inexpensive and facile processing platform for synthesis of high-k dielectric for charge storage applications. PMID:20945870

  3. Materials Data on BaTiO3 (SG:99) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  4. Impact of BaTiO(3) nanoparticles on pretransitional effects in liquid crystalline dodecylcyanobiphenyl.

    PubMed

    Rzoska, S J; Starzonek, S; Drozd-Rzoska, A; Czupryński, K; Chmiel, K; Gaura, G; Michulec, A; Szczypek, B; Walas, W

    2016-02-01

    The pretransitional behavior of dodecylcyanobiphenyl (12CB) (isotropic-smectic-A-solid mesomorphism) with d=50nmBaTiO(3) nanoparticles (NPs) linked to the cubic phase was monitored via temperature studies of dielectric constant. Tests were carried out in the isotropic, liquid crystal mesomorphic, and solid phases. For each phase transition the same value of the critical exponent α∼0.5 was obtained, including nanocolloids. All phase transitions show the weakly discontinuous nature. The temperature metric of the discontinuity ΔT notably decreases when adding nanoparticles. The addition of nanoparticles first decreases the dielectric constant by approximately 50% in comparison with pure 12CB, but already for a concentration ∼x=0.4% NP an increase over 50% takes place. It is notable that for the latter concentration unique hallmarks of the pretransitional effect emerge also for the solid-mesophase transition. All these indicate the important impact of nanoparticles on multimolecular mesoscale fluctuations. PMID:26986276

  5. Growth and characterization of high-performance photorefractive BaTiO3 crystals

    NASA Technical Reports Server (NTRS)

    Warde, C.; Garrett, M. H.; Chang, J. Y.; Jenssen, H. P.; Tuller, H. L.

    1991-01-01

    Barium titanate has been used for many nonlinear optical applications primarily because it has high grain and high self-pumped phase conjugate reflectivities. However, barium titanate has had a relatively slow response time, and thus low sensitivity. Therefore, it has not been suited to real-time operations. In this report we will describe the modifications in crystal growth, doping, reduction, and poling that have produced barium titanate crystals with the fastest photorefractive response time reported to date, approximately 21 microseconds with a beam-coupling gain coefficient of 38.7 cm(exp -1) and the highest sensitivity reported to date of 3.44 cm(exp 3)/kJ. The sensitivity of these barium titanate crystals is comparable to or greater than other photorefractive oxides. We will show, for the first time, beam-coupling in barium titanate at video frame rates. We infer from response time measurements that barium titanate has a phonon limited mobility. Also, photorefractive response time measurements as a function of the crystallographic orientation and grating wave vector for our cobalt-doped oxygen reduced crystals indicate that their faster response time arise because of an increase in the free carrier lifetime.

  6. Ferromagnetism and ferroelectricity in Fe doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Deka, Bipul; Ravi, S.; Perumal, A.; Pamu, D.

    2014-09-01

    We report the investigation of crystal structure, magnetic and dielectric properties of BaTi1-xFexO3 samples for x=0.0-0.3. The parent compound is found to crystallize in tetragonal structure while Fe doped samples are found to crystallize in the mixture of tetragonal and hexagonal phases but they are free from any impurity phase. Room temperature ferromagnetism with the transition temperature (Tc) of 462 K was observed for x=0.3 sample. Fe doped samples exhibit ferroelectric transition with transition temperature (TcF) in the range of 390 K for x=0.0-312 K for x=0.2. The dielectric constant, ε‧ is found to decrease with the increase in doping concentrations.

  7. All-dielectric invisibility cloaks made of BaTiO3-loaded polyurethane foam

    NASA Astrophysics Data System (ADS)

    Bao, Di; Rajab, Khalid Z.; Hao, Yang; Kallos, Efthymios; Tang, Wenxuan; Argyropoulos, Christos; Piao, Yongzhe; Yang, Shoufeng

    2011-10-01

    Transformation optics has led the way in the development of electromagnetic invisibility cloaks from science fiction to engineering practice. Invisibility cloaks have been demonstrated over a wide range of the electromagnetic spectrum, and with a variety of different fabrication techniques. However, all previous schemes have relied on the use of metamaterials consisting of arrays of sub-wavelength inclusions. We report on the first cloaking structure made of a high-κ dielectric-loaded foam mixture. A polyurethane foam mixed with different ratios of barium titanate is used to produce the required range of permittivities, and the invisibility cloak is demonstrated to work for all incident angles over a wide range of microwave frequencies. This method will greatly facilitate the development and large-scale manufacture of a wide range of transformation optics-based structures.

  8. Temperature dependent electrical transport characteristics of BaTiO3 modified lithium borate glasses

    NASA Astrophysics Data System (ADS)

    Thakur, Vanita; Singh, Anupinder; Awasthi, A. M.; Singh, Lakhwant

    2015-08-01

    The glass samples with composition (70B2O3-29Li2O-1Dy2O3)-xBT; x = 0, 10 and 20 weight percent, have been prepared by conventional melt quench technique. The dielectric measurements as a function of temperature have been carried out on these samples in the frequency range 1 Hz-10 MHz. The dielectric relaxation characteristics of these samples have been studied by analyzing dielectric spectroscopy, dielectric loss, electric modulus formulation and electrical conductivity spectroscopy. It is found that the dielectric permittivity of the samples increases with an increase in the temperature and BT content. The frequency dependent ac conductivity has been analyzed using Jonscher's universal power law whereas non exponential KWW function has been invoked to fit the experimental data of the imaginary part of the electric modulus. The values of the activation energy determined from the electric modulus and that from dc conductivity have been found to be quite close to each other suggesting that the same type of charge barriers are involved in the relaxation and the conduction mechanisms. The stretched exponent (β) and the power exponent (n) have been found to be temperature and composition dependent. The decrease in n with an increase in temperature further suggested that the ac conduction mechanism of the studied samples follows the correlated barrier hopping (CBH) model.

  9. Structural Polymorphism of Mn-Doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Dang, N. T.; Kozlenko, D. P.; Phan, T. L.; Kichanov, S. E.; Dang, N. V.; Thanh, T. D.; Khiem, L. H.; Jabarov, S. H.; Tran, T. A.; Vo, D. B.; Savenko, B. N.

    2016-05-01

    The crystal structure of BaTi1- x Mn x O3 (0 ≤ x ≤ 0.5) has been determined by means of neutron powder diffraction. Upon Mn doping, the BaTi1- x Mn x O3 system undergoes structural transformations from a polar tetragonal structure with space group P4mm to a non-polar 6H-type hexagonal structure with space group P6 3 /mmc at x > 0.01, and then to a non-polar 12R-type rhombohedral structure with space group R- 3m at x > 0.12. For the ferroelectric tetragonal phase, Mn doping leads to a reduction of the spontaneous polarization and the Curie temperature. In the 6H structure, Ti atoms display a strong preference for the corner-sharing octahedral sites, whereas both Ti and Mn randomly occupy the octahedral sites in the face-sharing dimers. In the 12R-structure, Ti atoms also have a strong preference for the corner-sharing octahedral sites, whereas Mn atoms occupy the octahedral sites at the centers of the face-sharing octahedral trimers. Both Ti and Mn atoms are distributed over the octahedral sites at the borders of the trimers. The absence of long-range magnetic order in the 6H-type and 12R-type phases was observed, which is due to the presence of the non-magnetic Ti ions at the centers of the corner-sharing octahedra connecting the face-sharing dimers (6H-type) and trimers (12R-type), breaking the magnetic interaction between the dimers/trimers and isolating them from each other.

  10. Nanocrystalline BaTiO3 powder via ambient conditions sol process (Prop.2001-071)

    SciTech Connect

    Payzant, E Andrew; Wang, X.; Hu, Michael Z.; Blom, Douglas Allen

    2005-01-01

    Nanocrystalline BaTiO{sub 3} particles have been prepared by ambient condition sol (ACS) process starting from soluble precursors of barium and titanium yielding a mixed oxide/hydroxide gel. The gel was peptized and crystallized in water under a refluxing condition. Higher initial pH and Ba/Ti ratio led to smaller crystallite sizes of BaTiO{sub 3} powders. Organic mineralizer, tetramethylammonium hydroxide (TMAH), can adsorb on the BaTiO{sub 3} nuclei and inhibited further growth of the particles. Adding a polymer during BaTiO{sub 3} synthesis led to a smaller particle size and increased redispersibility of the particles in water.

  11. Materials Data on BaTiO3 (SG:123) by Materials Project

    DOE Data Explorer

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  12. Journaling: creating space for "I".

    PubMed

    Charles, Jennell P

    2010-01-01

    As nurses engaged in a caring profession, it is critical that we learn not only to care for others but also to care for ourselves. To care effectively for ourselves, we must create the space and time in which to do this. Journaling is one tool that scholars offer as a way to create this space. Although there is no clear consensus about the best techniques for journaling, there is evidence that journaling, as a reflective, meditative activity, can promote creativity, self-awareness, and personal development. PMID:21140872

  13. The Statistical Mechanics of Ideal Homogeneous Turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2002-01-01

    Plasmas, such as those found in the space environment or in plasma confinement devices, are often modeled as electrically conducting fluids. When fluids and plasmas are energetically stirred, regions of highly nonlinear, chaotic behavior known as turbulence arise. Understanding the fundamental nature of turbulence is a long-standing theoretical challenge. The present work describes a statistical theory concerning a certain class of nonlinear, finite dimensional, dynamical models of turbulence. These models arise when the partial differential equations describing incompressible, ideal (i.e., nondissipative) homogeneous fluid and magnetofluid (i.e., plasma) turbulence are Fourier transformed into a very large set of ordinary differential equations. These equations define a divergenceless flow in a high-dimensional phase space, which allows for the existence of a Liouville theorem, guaranteeing a distribution function based on constants of the motion (integral invariants). The novelty of these particular dynamical systems is that there are integral invariants other than the energy, and that some of these invariants behave like pseudoscalars under two of the discrete symmetry transformations of physics, parity, and charge conjugation. In this work the 'rugged invariants' of ideal homogeneous turbulence are shown to be the only significant scalar and pseudoscalar invariants. The discovery that pseudoscalar invariants cause symmetries of the original equations to be dynamically broken and induce a nonergodic structure on the associated phase space is the primary result presented here. Applicability of this result to dissipative turbulence is also discussed.

  14. Homogenization in micro-magneto-mechanics

    NASA Astrophysics Data System (ADS)

    Sridhar, A.; Keip, M.-A.; Miehe, C.

    2016-07-01

    Ferromagnetic materials are characterized by a heterogeneous micro-structure that can be altered by external magnetic and mechanical stimuli. The understanding and the description of the micro-structure evolution is of particular importance for the design and the analysis of smart materials with magneto-mechanical coupling. The macroscopic response of the material results from complex magneto-mechanical interactions occurring on smaller length scales, which are driven by magnetization reorientation and associated magnetic domain wall motions. The aim of this work is to directly base the description of the macroscopic magneto-mechanical material behavior on the micro-magnetic domain evolution. This will be realized by the incorporation of a ferromagnetic phase-field formulation into a macroscopic Boltzmann continuum by the use of computational homogenization. The transition conditions between the two scales are obtained via rigorous exploitation of rate-type and incremental variational principles, which incorporate an extended version of the classical Hill-Mandel macro-homogeneity condition covering the phase field on the micro-scale. An efficient two-scale computational scenario is developed based on an operator splitting scheme that includes a predictor for the magnetization on the micro-scale. Two- and three-dimensional numerical simulations demonstrate the performance of the method. They investigate micro-magnetic domain evolution driven by macroscopic fields as well as the associated overall hysteretic response of ferromagnetic solids.

  15. Emergence of Leadership within a Homogeneous Group

    PubMed Central

    Eskridge, Brent E.; Valle, Elizabeth; Schlupp, Ingo

    2015-01-01

    Large scale coordination without dominant, consistent leadership is frequent in nature. How individuals emerge from within the group as leaders, however transitory this position may be, has become an increasingly common question asked. This question is further complicated by the fact that in many of these aggregations, differences between individuals are minor and the group is largely considered to be homogeneous. In the simulations presented here, we investigate the emergence of leadership in the extreme situation in which all individuals are initially identical. Using a mathematical model developed using observations of natural systems, we show that the addition of a simple concept of leadership tendencies which is inspired by observations of natural systems and is affected by experience can produce distinct leaders and followers using a nonlinear feedback loop. Most importantly, our results show that small differences in experience can promote the rapid emergence of stable roles for leaders and followers. Our findings have implications for our understanding of adaptive behaviors in initially homogeneous groups, the role experience can play in shaping leadership tendencies, and the use of self-assessment in adapting behavior and, ultimately, self-role-assignment. PMID:26226381

  16. Emergence of Leadership within a Homogeneous Group.

    PubMed

    Eskridge, Brent E; Valle, Elizabeth; Schlupp, Ingo

    2015-01-01

    Large scale coordination without dominant, consistent leadership is frequent in nature. How individuals emerge from within the group as leaders, however transitory this position may be, has become an increasingly common question asked. This question is further complicated by the fact that in many of these aggregations, differences between individuals are minor and the group is largely considered to be homogeneous. In the simulations presented here, we investigate the emergence of leadership in the extreme situation in which all individuals are initially identical. Using a mathematical model developed using observations of natural systems, we show that the addition of a simple concept of leadership tendencies which is inspired by observations of natural systems and is affected by experience can produce distinct leaders and followers using a nonlinear feedback loop. Most importantly, our results show that small differences in experience can promote the rapid emergence of stable roles for leaders and followers. Our findings have implications for our understanding of adaptive behaviors in initially homogeneous groups, the role experience can play in shaping leadership tendencies, and the use of self-assessment in adapting behavior and, ultimately, self-role-assignment. PMID:26226381

  17. Si isotope homogeneity of the solar nebula

    SciTech Connect

    Pringle, Emily A.; Savage, Paul S.; Moynier, Frédéric; Jackson, Matthew G.; Barrat, Jean-Alix E-mail: savage@levee.wustl.edu E-mail: moynier@ipgp.fr E-mail: Jean-Alix.Barrat@univ-brest.fr

    2013-12-20

    The presence or absence of variations in the mass-independent abundances of Si isotopes in bulk meteorites provides important clues concerning the evolution of the early solar system. No Si isotopic anomalies have been found within the level of analytical precision of 15 ppm in {sup 29}Si/{sup 28}Si across a wide range of inner solar system materials, including terrestrial basalts, chondrites, and achondrites. A possible exception is the angrites, which may exhibit small excesses of {sup 29}Si. However, the general absence of anomalies suggests that primitive meteorites and differentiated planetesimals formed in a reservoir that was isotopically homogenous with respect to Si. Furthermore, the lack of resolvable anomalies in the calcium-aluminum-rich inclusion measured here suggests that any nucleosynthetic anomalies in Si isotopes were erased through mixing in the solar nebula prior to the formation of refractory solids. The homogeneity exhibited by Si isotopes may have implications for the distribution of Mg isotopes in the solar nebula. Based on supernova nucleosynthetic yield calculations, the expected magnitude of heavy-isotope overabundance is larger for Si than for Mg, suggesting that any potential Mg heterogeneity, if present, exists below the 15 ppm level.

  18. On shearing fluids with homogeneous densities

    NASA Astrophysics Data System (ADS)

    Srivastava, D. C.; Srivastava, V. C.; Kumar, Rajesh

    2016-06-01

    In this paper, we study shearing spherically symmetric homogeneous density fluids in comoving coordinates. It is found that the expansion of the four-velocity of a perfect fluid is homogeneous, whereas its shear is generated by an arbitrary function of time M( t), related to the mass function of the distribution. This function is found to bear a functional relationship with density. The field equations are reduced to two coupled first order ordinary differential equations for the metric coefficients g_{11} and g_{22}. We have explored a class of solutions assuming that M is a linear function of the density. This class embodies, as a subcase, the complete class of shear-free solutions. We have discussed the off quoted work of Kustaanheimo (Comment Phys Math XIII:12, 1, 1947) and have noted that it deals with shear-free fluids having anisotropic pressure. It is shown that the anisotropy of the fluid is characterized by an arbitrary function of time. We have discussed some issues of historical priorities and credentials related to shear-free solutions. Recent controversial claims by Mitra (Astrophys Space Sci 333:351, 2011 and Gravit Cosmol 18:17, 2012) have also been addressed. We found that the singularity and the shearing motion of the fluid are closely related. Hence, there is a need for fresh look to the solutions obtained earlier in comoving coordinates.

  19. Homogeneous cooling of mixtures of particle shapes

    NASA Astrophysics Data System (ADS)

    Hidalgo, R. C.; Serero, D.; Pöschel, T.

    2016-07-01

    In this work, we examine theoretically the cooling dynamics of binary mixtures of spheres and rods. To this end, we introduce a generalized mean field analytical theory, which describes the free cooling behavior of the mixture. The relevant characteristic time scale for the cooling process is derived, depending on the mixture composition and the aspect ratio of the rods. We simulate mixtures of spherocylinders and spheres using a molecular dynamics algorithm implemented on graphics processing unit (GPU) architecture. We systematically study mixtures composed of spheres and rods with several aspect ratios and varying the mixture composition. A homogeneous cooling state, where the time dependence of the system's intensive variables occurs only through a global granular temperature, is identified. We find cooling dynamics in excellent agreement with Haff's law, when using an adequate time scale. Using the scaling properties of the homogeneous cooling dynamics, we estimated numerically the efficiency of the energy interchange between rotational and translational degrees of freedom for collisions between spheres and rods.

  20. Creating a New Professional Association

    ERIC Educational Resources Information Center

    Journal of College Reading and Learning, 2009

    2009-01-01

    This position paper investigates the merits and potential benefits of creating a new, more comprehensive professional association for members of the learning assistance and developmental education profession. This was the task assigned to the College Reading and Learning Association/National Association for Developmental Education (CRLA/NADE)…

  1. Creating Three-Dimensional Scenes

    ERIC Educational Resources Information Center

    Krumpe, Norm

    2005-01-01

    Persistence of Vision Raytracer (POV-Ray), a free computer program for creating photo-realistic, three-dimensional scenes and a link for Mathematica users interested in generating POV-Ray files from within Mathematica, is discussed. POV-Ray has great potential in secondary mathematics classrooms and helps in strengthening students' visualization…

  2. Creating Frameworks for Reflective Teaching

    ERIC Educational Resources Information Center

    Carter, Margie

    2007-01-01

    The task of creating organizational policies and systems that promote and support reflective teaching is multifaceted and seldom enumerated in early childhood professional literature. One of the best overviews the author has found comes from Carol Brunson Phillips and Sue Bredekamp (1998). The author opines that if the early childhood profession…

  3. Creating an Innovative Learning Organization

    ERIC Educational Resources Information Center

    Salisbury, Mark

    2010-01-01

    This article describes how to create an innovative learning (iLearning) organization. It begins by discussing the life cycle of knowledge in an organization, followed by a description of the theoretical foundation for iLearning. Next, the article presents an example of iLearning, followed by a description of the distributed nature of work, the…

  4. Creating Presentations on ICT Classes

    ERIC Educational Resources Information Center

    Marchis, Iuliana

    2010-01-01

    The article focuses on the creation of presentations on ICT classes. The first part highlights the most important steps when creating a presentation. The main idea is, that the computer presentation shouldn't consist only from the technological part, i.e. the editing of the presentation in a computer program. There are many steps before and after…

  5. Creating Highlander Wherever You Are

    ERIC Educational Resources Information Center

    Williams, Susan; Mullett, Cathy

    2016-01-01

    Highlander Research and Education Center serves as a catalyst for grassroots organizing and movement building. This article focuses on an interview with education coordinator Susan Williams who has worked at Highlander for 26 years. We discuss how others can and do create powerful popular education experiences anywhere, whether they have a…

  6. Can Children Really Create Knowledge?

    ERIC Educational Resources Information Center

    Bereiter, Carl; Scardamalia, Marlene

    2010-01-01

    Can children genuinely create new knowledge, as opposed to merely carrying out activities that resemble those of mature scientists and innovators? The answer is yes, provided the comparison is not to works of genius but to standards that prevail in ordinary research communities. One important product of knowledge creation is concepts and tools…

  7. Creating Space for Children's Literature

    ERIC Educational Resources Information Center

    Serafini, Frank

    2011-01-01

    As teachers struggle to balance the needs of their students with the requirements of commercial reading materials, educators need to consider how teachers will create space for children's literature in today's classrooms. In this article, 10 practical recommendations for incorporating children's literature in the reading instructional framework…

  8. Creating Time for Equity Together

    ERIC Educational Resources Information Center

    Renée, Michelle

    2015-01-01

    Iin urban communities across the nation, a broad range of partners have committed to reinventing educational time together to ensure equitable access to rich learning opportunities for all young people. Across the nation, education partners are using their creativity, commitment, and unique resources to create new school and system designs that…

  9. Creating a Global Perspective Campus

    ERIC Educational Resources Information Center

    Braskamp, Larry A.

    2011-01-01

    The author has written this Guidebook to assist users interested in creating a campus that will be more global in its mission, programs, and people. His approach is to focus on the views and contributions of the people who are engaged in higher education. Thus it has a "person" emphasis rather than a structural or policy point of view. The author…

  10. Creating a Culture of Leadership.

    ERIC Educational Resources Information Center

    Lewis, Phyllis H.

    1994-01-01

    In financially troubled times, the college or university must develop a culture of leadership. Leadership development programming can strengthen the institution by fostering a team approach to solving institutional problems, by increasing the effectiveness and efficiency of human resources, and by creating a pool of qualified professionals for…

  11. Absorbing metasurface created by diffractionless disordered arrays of nanoantennas

    SciTech Connect

    Chevalier, Paul; Bouchon, Patrick Jaeck, Julien; Lauwick, Diane; Kattnig, Alain; Bardou, Nathalie; Pardo, Fabrice; Haïdar, Riad

    2015-12-21

    We study disordered arrays of metal-insulator-metal nanoantenna in order to create a diffractionless metasurface able to absorb light in the 3–5 μm spectral range. This study is conducted with angle-resolved reflectivity measurements obtained with a Fourier transform infrared spectrometer. A first design is based on a perturbation of a periodic arrangement, leading to a significant reduction of the radiative losses. Then, a random assembly of nanoantennas is built following a Poisson-disk distribution of given density, in order to obtain a nearly perfect cluttered assembly with optical properties of a homogeneous material.

  12. Absorbing metasurface created by diffractionless disordered arrays of nanoantennas

    NASA Astrophysics Data System (ADS)

    Chevalier, Paul; Bouchon, Patrick; Jaeck, Julien; Lauwick, Diane; Bardou, Nathalie; Kattnig, Alain; Pardo, Fabrice; Haïdar, Riad

    2015-12-01

    We study disordered arrays of metal-insulator-metal nanoantenna in order to create a diffractionless metasurface able to absorb light in the 3-5 μm spectral range. This study is conducted with angle-resolved reflectivity measurements obtained with a Fourier transform infrared spectrometer. A first design is based on a perturbation of a periodic arrangement, leading to a significant reduction of the radiative losses. Then, a random assembly of nanoantennas is built following a Poisson-disk distribution of given density, in order to obtain a nearly perfect cluttered assembly with optical properties of a homogeneous material.

  13. Nanodosimetric track structure in homogeneous extended beams.

    PubMed

    Conte, V; Moro, D; Colautti, P; Grosswendt, B

    2015-09-01

    Physical aspects of particle track structure are important in determining the induction of clustered damage in relevant subcellular structures like the DNA and higher-order genomic structures. The direct measurement of track-structure properties of ionising radiation is feasible today by counting the number of ionisations produced inside a small gas volume. In particular, the so-called track-nanodosimeter, installed at the TANDEM-ALPI accelerator complex of LNL, measures ionisation cluster-size distributions in a simulated subcellular structure of dimensions 20 nm, corresponding approximately to the diameter of the chromatin fibre. The target volume is irradiated by pencil beams of primary particles passing at specified impact parameter. To directly relate these measured track-structure data to radiobiological measurements performed in broad homogeneous particle beams, these data can be integrated over the impact parameter. This procedure was successfully applied to 240 MeV carbon ions and compared with Monte Carlo simulations for extended fields. PMID:25848108

  14. Homogeneously dispersed multimetal oxygen-evolving catalysts.

    PubMed

    Zhang, Bo; Zheng, Xueli; Voznyy, Oleksandr; Comin, Riccardo; Bajdich, Michal; García-Melchor, Max; Han, Lili; Xu, Jixian; Liu, Min; Zheng, Lirong; García de Arquer, F Pelayo; Dinh, Cao Thang; Fan, Fengjia; Yuan, Mingjian; Yassitepe, Emre; Chen, Ning; Regier, Tom; Liu, Pengfei; Li, Yuhang; De Luna, Phil; Janmohamed, Alyf; Xin, Huolin L; Yang, Huagui; Vojvodic, Aleksandra; Sargent, Edward H

    2016-04-15

    Earth-abundant first-row (3d) transition metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution. These gelled FeCoW oxyhydroxides exhibit the lowest overpotential (191 millivolts) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation after more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between tungsten, iron, and cobalt in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER. PMID:27013427

  15. The homogeneity conjecture for supergravity backgrounds

    NASA Astrophysics Data System (ADS)

    Figueroa-O'Farrill, José Miguel

    2009-06-01

    These notes record three lectures given at the workshop "Higher symmetries in Physics", held at the Universidad Complutense de Madrid in November 2008. In them we explain how to construct a Lie (super)algebra associated to a spin manifold, perhaps with extra geometric data, and a notion of privileged spinors. The typical examples are supersymmetric supergravity backgrounds; although there are more classical instances of this construction. We focus on two results: the geometric constructions of compact real forms of the simple Lie algebras of type B4, F4 and E8 from S7, S8 and S15, respectively; and the construction of the Killing superalgebra of eleven-dimensional supergravity backgrounds. As an application of this latter construction we show that supersymmetric supergravity backgrounds with enough supersymmetry are necessarily locally homogeneous.

  16. RF Spectroscopy on a Homogeneous Fermi Gas

    NASA Astrophysics Data System (ADS)

    Yan, Zhenjie; Mukherjee, Biswaroop; Patel, Parth; Struck, Julian; Zwierlein, Martin

    2016-05-01

    Over the last two decades RF spectroscopy has been established as an indispensable tool to probe a large variety of fundamental properties of strongly interacting Fermi gases. This ranges from measurement of the pairing gap over tan's contact to the quasi-particle weight of Fermi polarons. So far, most RF spectroscopy experiments have been performed in harmonic traps, resulting in an averaged response over different densities. We have realized an optical uniform potential for ultracold Fermi gases of 6 Li atoms, which allows us to avoid the usual problems connected to inhomogeneous systems. Here we present recent results on RF spectroscopy of these homogeneous samples with a high signal to noise ratio. In addition, we report progress on measuring the contact of a unitary Fermi gas across the normal to superfluid transition.

  17. Analysis of homogeneous turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Leonard, A. D.; Hill, J. C.; Mahalingam, S.; Ferziger, J. H.

    1988-01-01

    Full turbulence simulations at low Reynolds numbers were made for the single-step, irreversible, bimolecular reaction between non-premixed reactants in isochoric, decaying homogeneous turbulence. Various initial conditions for the scalar field were used in the simulations to control the initial scalar dissipation length scale, and simulations were also made for temperature-dependent reaction rates and for non-stoichiometric and unequal diffusivity conditions. Joint probability density functions (pdf's), conditional pdf's, and various statistical quantities appearing in the moment equations were computed. Preliminary analysis of the results indicates that compressive strain-rate correlates better than other dynamical quantities with local reaction rate, and the locations of peak reaction rates seem to be insensitive to the scalar field initial conditions.

  18. Soliton production with nonlinear homogeneous lines

    SciTech Connect

    Elizondo-Decanini, Juan M.; Coleman, Phillip D.; Moorman, Matthew W.; Petney, Sharon Joy Victor; Dudley, Evan C.; Youngman, Kevin; Penner, Tim Dwight; Fang, Lu; Myers, Katherine M.

    2015-11-24

    Low- and high-voltage Soliton waves were produced and used to demonstrate collision and compression using diode-based nonlinear transmission lines. Experiments demonstrate soliton addition and compression using homogeneous nonlinear lines. We built the nonlinear lines using commercially available diodes. These diodes are chosen after their capacitance versus voltage dependence is used in a model and the line design characteristics are calculated and simulated. Nonlinear ceramic capacitors are then used to demonstrate high-voltage pulse amplification and compression. The line is designed such that a simple capacitor discharge, input signal, develops soliton trains in as few as 12 stages. We also demonstrated output voltages in excess of 40 kV using Y5V-based commercial capacitors. The results show some key features that determine efficient production of trains of solitons in the kilovolt range.

  19. Soliton production with nonlinear homogeneous lines

    DOE PAGESBeta

    Elizondo-Decanini, Juan M.; Coleman, Phillip D.; Moorman, Matthew W.; Petney, Sharon Joy Victor; Dudley, Evan C.; Youngman, Kevin; Penner, Tim Dwight; Fang, Lu; Myers, Katherine M.

    2015-11-24

    Low- and high-voltage Soliton waves were produced and used to demonstrate collision and compression using diode-based nonlinear transmission lines. Experiments demonstrate soliton addition and compression using homogeneous nonlinear lines. We built the nonlinear lines using commercially available diodes. These diodes are chosen after their capacitance versus voltage dependence is used in a model and the line design characteristics are calculated and simulated. Nonlinear ceramic capacitors are then used to demonstrate high-voltage pulse amplification and compression. The line is designed such that a simple capacitor discharge, input signal, develops soliton trains in as few as 12 stages. We also demonstrated outputmore » voltages in excess of 40 kV using Y5V-based commercial capacitors. The results show some key features that determine efficient production of trains of solitons in the kilovolt range.« less

  20. Homogeneous catalyst formulations for methanol production

    DOEpatents

    Mahajan, Devinder; Sapienza, Richard S.; Slegeir, William A.; O'Hare, Thomas E.

    1991-02-12

    There is disclosed synthesis of CH.sub.3 OH from carbon monoxide and hydrogen using an extremely active homogeneous catalyst for methanol synthesis directly from synthesis gas. The catalyst operates preferably between 100.degree.-150.degree. C. and preferably at 100-150 psia synthesis gas to produce methanol. Use can be made of syngas mixtures which contain considerable quantities of other gases, such as nitrogen, methane or excess hydrogen. The catalyst is composed of two components: (a) a transition metal carbonyl complex and (b) an alkoxide component. In the simplest formulation, component (a) is a complex of nickel tetracarbonyl and component (b) is methoxide (CH.sub.3 O.sup.-), both being dissolved in a methanol solvent system. The presence of a co-solvent such as p-dioxane, THF, polyalcohols, ethers, hydrocarbons, and crown ethers accelerates the methanol synthesis reaction.