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Sample records for creates homogenous batio3

  1. Effects of ultrasonication and conventional mechanical homogenization processes on the structures and dielectric properties of BaTiO3 ceramics.

    PubMed

    Akbas, Hatice Zehra; Aydin, Zeki; Yilmaz, Onur; Turgut, Selvin

    2017-01-01

    The effects of the homogenization process on the structures and dielectric properties of pure and Nb-doped BaTiO3 ceramics have been investigated using an ultrasonic homogenization and conventional mechanical methods. The reagents were homogenized using an ultrasonic processor with high-intensity ultrasonic waves and using a compact mixer-shaker. The components and crystal types of the powders were determined by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses. The complex permittivity (ε('), ε″) and AC conductivity (σ') of the samples were analyzed in a wide frequency range of 20Hz to 2MHz at room temperature. The structures and dielectric properties of pure and Nb-doped BaTiO3 ceramics strongly depend on the homogenization process in a solid-state reaction method. Using an ultrasonic processor with high-intensity ultrasonic waves based on acoustic cavitation phenomena can make a significant improvement in producing high-purity BaTiO3 ceramics without carbonate impurities with a small dielectric loss.

  2. Ferroelectric and ferromagnetic properties in BaTiO3 thin films on Si (100)

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Punugupati, Sandhyarani; Prater, John T.; Hunte, Frank; Narayan, Jagdish

    2014-09-01

    In this paper, we report on the epitaxial integration of room temperature lead-free ferroelectric BaTiO3 thin (˜1050 nm) films on Si (100) substrates by pulsed laser deposition technique through a domain matching epitaxy paradigm. We employed MgO and TiN as buffer layers to create BaTiO3/SrRuO3/MgO/TiN/Si (100) heterostructures. C-axis oriented and cube-on-cube epitaxial BaTiO3 is formed on Si (100) as evidenced by the in-plane and out-of-plane x-ray diffraction, and transmission electron microscopy. X-ray photoemission spectroscopic measurements show that Ti is in 4(+) state. Polarization hysteresis measurements together with Raman spectroscopy and temperature-dependent x-ray diffraction confirm the room temperature ferroelectric nature of BaTiO3. Furthermore, laser irradiation of BaTiO3 thin film is found to induce ferromagnetic-like behavior but affects adversely the ferroelectric characteristics. Laser irradiation induced ferromagnetic properties seem to originate from the creation of oxygen vacancies, whereas the pristine BaTiO3 shows diamagnetic behavior, as expected. This work has opened up the route for the integration of room temperature lead-free ferroelectric functional oxides on a silicon platform.

  3. Strain of a BaTiO3 single crystal caused by the converse flexoelectric effect

    NASA Astrophysics Data System (ADS)

    Rumyantseva, E. D.; Zalesskii, V. G.

    2016-04-01

    The inhomogeneous strain induced by a homogeneous external electric field (the converse flexoelectric effect) has been studied in a thin BaTiO3 single crystal slab. The type of inhomogeneous strain (cylindrical and spherical bending) has been determined via the interference method, and its dependence on the applied filed is measured, as well. The influence of the domain structure on this effect has also been shown.

  4. 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.

  5. Nanoscale symmetry fluctuations in ferroelectric barium titanate, BaTiO3.

    PubMed

    Shao, Yu Tsun; Zuo, Jian Min

    2017-08-01

    Crystal charge density is a ground-state electronic property. In ferroelectrics, charge is strongly influenced by lattice and vice versa, leading to a range of interesting temperature-dependent physical properties. However, experimental determination of charge in ferroelectrics is challenging because of the formation of ferroelectric domains. Demonstrated here is the scanning convergent-beam electron diffraction (SCBED) technique that can be simultaneously used for imaging ferroelectric domains and identifying crystal symmetry and its fluctuations. Results from SCBED confirm the acentric tetragonal, orthorhombic and rhombohedral symmetry for the ferroelectric phases of BaTiO3. However, the symmetry is not homogeneous; regions of a few tens of nanometres retaining almost perfect symmetry are interspersed in regions of lower symmetry. While the observed highest symmetry is consistent with the displacive model of ferroelectric phase transitions in BaTiO3, the observed nanoscale symmetry fluctuations are consistent with the predictions of the order-disorder phase-transition mechanism.

  6. Structural Transformation of Hexagonal (0001)BaTiO3 Ceramics to Tetragonal (111)BaTiO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Watanabe, Takayuki; Shimada, Mikio; Aiba, Toshiaki; Yabuta, Hisato; Miura, Kaoru; Oka, Kengo; Azuma, Masaki; Wada, Satoshi; Kumada, Nobuhiro

    2011-09-01

    A ceramic slurry that contains a 6H-type Ba(Ti0.95Mn0.05)O3 powder was casted into a plaster mold under 10 T magnetic field to form a green compact of (0001)-oriented Ba(Ti0.95Mn0.05)O3. After sintering the green compact at 1300 °C in air, it was confirmed that the (0001)-oriented 6H-type perovskite structure transformed to a (111)-oriented 3C-type perovskite structure. The structural transformation was again examined using hexagonal BaTiO3 prepared by reducing pseudo-cubic BaTiO3 powder in H2 atmosphere. In this case, the preferred (0001) orientation was not confirmed for the green compacts. After sintering the green compacts at 1300 °C in air, mixed crystal orientations of (100)/(001) and (111) were observed for the resultant tetragonal BaTiO3 ceramics. This (100)/(001) orientation was suppressed by annealing the hexagonal BaTiO3 powder at 1000 °C before slip-casting, leading to highly (111)-oriented ceramics. It was found that the green compacts of (0001)-oriented hexagonal BaTiO3 can transform into (111)-oriented tetragonal BaTiO3 ceramics, maintaining the macroscopic crystal orientations due to a similar atomic stacking along [0001] of 6H-type BaTiO3 and [111] of 3C-type BaTiO3.

  7. Structural and magnetic studies of Co and Fe implanted BaTiO 3 crystals

    NASA Astrophysics Data System (ADS)

    Khalitov, N. I.; Khaibullin, R. I.; Valeev, V. F.; Dulov, E. N.; Ivoilov, N. G.; Tagirov, L. R.; Kazan, S.; Şale, A. G.; Mikailzade, F. A.

    2012-02-01

    Singly-charged Co or Fe ions with energy 40 keV were implanted into single-domain ferroelectric plates of barium titanate (BaTiO 3) with high fluences in the range of (0.5-1.5) × 10 17 ion/cm 2 to create new magnetoelectric materials. Scanning electron microscopy (SEM) and conversion electron Mössbauer spectroscopy (CEMS) studies have shown that high-fluence implantation with 3d-ions results in formation of cobalt or iron nanoparticles in the near-surface irradiated region of perovskite-type crystal. With increasing the fluence, the both Co- and Fe-implanted BaTiO 3 samples reveal at first superparamagnetic, and then ferromagnetic properties at room temperature. Analysis of magnetic hysteresis loops measured in the in-plane and out-of-plane geometries have shown that ferromagnetic BaTiO 3:Co(Fe) nanocomposite layers display the "easy plane" magnetic anisotropy similar to that found for thin granular magnetic films. Together with our previous observation of the magnetoelectric effect in these samples, our structural and magnetic investigations show that the ion implantation is suitable to synthesize the desired magnetoelectric nanocomposite materials.

  8. Ferroelectric BaTiO3 nanoparticles: biosynthesis and characterization.

    PubMed

    Jha, Anal K; Prasad, K

    2010-01-01

    A new low-cost, green and reproducible Lactobacillus sp. assisted biosynthesis of BaTiO(3) nanoparticles is reported. X-ray and transmission electron microscopy analyses are performed to ascertain the formation of BaTiO(3) nanoparticles. The apparent crystallite size and lattice strain are estimated from Williamson-Hall approach. XRD analysis of the compound indicated the formation of a single-phase tetragonal structure. Individual nanoparticles as well as a few aggregate having the size of 20-80 nm are found. A possible involved mechanism for the biosynthesis of nano-BaTiO(3) has also been proposed in which ROS as well as partial pressure of gaseous hydrogen (rH(2)) of the culture solution seems to play an important role in the process. Remarkable enhancement in dielectric properties was observed in BaTiO(3)/polyvinylidene fluoride (PVDF) nanocomposite.

  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. 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.

  12. Enhancement of p-type conductivity in nanocrystalline BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Guo, Xin; Pithan, Christian; Ohly, Christian; Jia, Chun-Lin; Dornseiffer, Jügen; Haegel, Franz-Hubert; Waser, Rainer

    2005-02-01

    Undoped BaTiO3 ceramic samples with an average grain size of ˜35nm were prepared and the electrical properties investigated. The defect structure is dominated by acceptor impurities; therefore, the conductivity of nanocrystalline BaTiO3 is of p-type. Comparing with microcrystalline BaTiO3, the conductivity of nanocrystalline BaTiO3 is about 1 to 2 orders of magnitude higher and the activation energy remarkably lower, which is ascribed to a greatly reduced oxidation enthalpy in nanocrystalline BaTiO3 (˜0.3 versus ˜0.92eV for microcrystalline BaTiO3).

  13. Electrical and Optical Property of Ferroelectric BaTiO3:Eu

    NASA Technical Reports Server (NTRS)

    Park, Yeonjoon; Grichener, Alexander; Jensen, Jacob; Choi, Sang H.

    2005-01-01

    We studied various electrical and optical properties of Europium (1 atomic %) incorporated BaTiO3 film on n-Si(100) substrate. The thin film structure was analyzed by X-ray diffraction. Film thickness and optical refractive index were measured with an ellipsometer. P-E hysteresis measurement shows the remnant polarization of 37 micro C/sq cm in BaTiO3:Eu film. C-V measurements on the pure BaTiO3 film show recovery of capacitance across sweeping voltage ranges with a narrow transition zone due to the polarization change. On the other hand, C-V and I-V measurements on the BaTiO3:Eu film show that Europium incorporation increases positively charged states in the BaTiO3 layer such that BaTiO3:Eu/n-Si interface behaves like a leaky p-n junction.

  14. Dimension effects on the dielectric properties of fine BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Hou, Zhi-Wen; Kang, Ai-Guo; Ma, Wei-Qing; Zhao, Xiao-Long

    2014-11-01

    It is found that the core-shell structured grains are easy to produce for fine grain doped BaTiO3 ceramics in the sintering process. We study the influence of the core-shell structure on the Curie—Weiss temperature and dielectric properties of BaTiO3 ceramics by using effective medium approximation (EMA). Considering the second approximation, the dielectric properties of fine grain doped BaTiO3 ceramics are consistent with experimental data.

  15. 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.

  16. Electric and Mechanical Switching of Ferroelectric and Resistive States in Semiconducting BaTiO3-δ Films on Silicon.

    PubMed

    Gómez, Andrés; Vila-Fungueiriño, José Manuel; Moalla, Rahma; Saint-Girons, Guillaume; Gázquez, Jaume; Varela, María; Bachelet, Romain; Gich, Martí; Rivadulla, Francisco; Carretero-Genevrier, Adrián

    2017-08-15

    Materials that can couple electrical and mechanical properties constitute a key element of smart actuators, energy harvesters, or many sensing devices. Within this class, functional oxides display specific mesoscale responses which often result in great sensitivity to small external stimuli. Here, a novel combination of molecular beam epitaxy and a water-based chemical-solution method is used for the design of mechanically controlled multilevel device integrated on silicon. In particular, the possibility of adding extra functionalities to a ferroelectric oxide heterostructure by n-doping and nanostructuring a BaTiO3 thin film on Si(001) is explored. It is found that the ferroelectric polarization can be reversed, and resistive switching can be measured, upon a mechanical load in epitaxial BaTiO3-δ /La0.7 Sr0.3 MnO3 /SrTiO3 /Si columnar nanostructures. A flexoelectric effect is found, stemming from substantial strain gradients that can be created with moderate loads. Simultaneously, mechanical effects on the local conductivity can be used to modulate a nonvolatile resistive state of the BaTiO3-δ heterostructure. As a result, three different configurations of the system become accessible on top of the usual voltage reversal of polarization and resistive states. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. 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

  18. Electron-relaxation-mode interaction in BaTiO3:Nb

    NASA Astrophysics Data System (ADS)

    Maglione, M.; Belkaoumi, M.

    1992-02-01

    Dielectric relaxation was previously reported in BaTiO3 and BaTiO3:Fe single crystals at radio frequencies [M. Maglione et al., Phys. Rev. B 40, 11 441 (1989)]. We have measured the dielectric dispersion in four BaTiO3:Nb samples (xNb<0.3 at. %) as a function of frequency (10

  19. BaTiO3-Based Non-Reducible Low-Loss Dielectric Ceramics

    NASA Astrophysics Data System (ADS)

    Nakamura, Tomoyuki; Sano, Harunobu; Konoike, Takehiro; Tomono, Kunisaburo

    1999-09-01

    Dielectrics composed of BaTiO3-rare earth oxide-MgO havebeenstudied to design a non-reducible low-loss dielectricmaterial. Curie temperatures of dielectrics composed ofBaTiO3 Gd2O3 MgO were lowered by Gd2O3, which provided thedielectrics with low power loss. It was found that the addition ofBaZrO3 to BaTiO3 Gd2O3 MgO decreased the capacitance change withtemperature. Gd2O3 diffused easily into BaTiO3, but, it could noteasily diffuse into BaTiO3 to which BaZrO3 had been added. It wasconsidered that BaZrO3 prevented the Gd2O3 diffusion into BaTiO3,resulting the remains of ferroelectricity and reduced capacitancechange. Thus non-reducible and low power loss X7R dielectricceramics were developed.

  20. Electrocaloric effect in BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Cao, Hai-Xia; Li, Zhen-Ya

    2009-11-01

    The modified transverse Ising model taking into account the four-spin exchange interaction and quantum fluctuation, as well as the mechanical constraint of the substrate, is constructed and applied to investigate the electrocaloric effect (ECE) in BaTiO3 thin films. It is found that the temperature dependence of ECE strongly depends on both the four-spin exchange interaction and quantum fluctuation. Most importantly, we achieve the adiabatic temperature change ΔT =11.78 K at Tm=490 K, which can be comparable with that observed experimentally in PbZr0.95Ti0.05O3 thin films and ferroelectric polymers. Furthermore, the internal stresses resulting from the clamping effect of the substrate play a crucial role in the ECE of ferroelectric films. Control of the misfit stress by appropriate choice of substrate provides an effective means to improve the adiabatic temperature change for use in cooling or thermodielectric power conversion devices.

  1. Synthesis and Characterization of Bowl-Like Single-Crystalline BaTiO3 Nanoparticles

    PubMed Central

    2010-01-01

    Novel bowl-like single-crystalline BaTiO3 nanoparticles were synthesized by a simple hydrothermal method using Ba(OH)2·8H2O and TiO2 as precursors. The as-prepared products were characterized by XRD, Raman spectroscopy, SEM and TEM. The results show that the bowl-like BaTiO3 nanoparticles are single-crystalline and have a size about 100–200 nm in diameter. Local piezoresponse force measurements indicate that the BaTiO3 nanoparticles have switchable polarization at room temperature. The local effective piezoelectric coefficient is approximately 28 pm/V. PMID:20596350

  2. Direct writing of three-dimensional woodpile BaTiO3 structures

    NASA Astrophysics Data System (ADS)

    Li, Jijiao; Li, Bo; Wu, Hongya; Zhou, Ji

    2014-05-01

    Barium titanate (BaTiO3) woodpile structures with designed, three-dimensional (3D) geometry have been fabricated by direct-writing assembly techniques. Concentrated BaTiO3 inks with suitable rheological properties were prepared to enable the fabrication of the complex 3D structures. It was demonstrated that BaTiO3 inks with a total solids volume fraction of 0.41 are shear thinning and have a high storage modulus 1 × 105Pa with a yield stress of 300 Pa. Additionally, the woodpile lattice structures exhibited an excellent self-supporting feature.

  3. Ferroelectric control of magnetism in BaTiO3/Fe heterostructures via interface strain coupling

    NASA Astrophysics Data System (ADS)

    Sahoo, Sarbeswar; Polisetty, Srinivas; Duan, Chun-Gang; Jaswal, Sitaram S.; Tsymbal, Evgeny Y.; Binek, Christian

    2007-09-01

    Reversible control of magnetism is reported for a Fe thin film in proximity of a BaTiO3 single crystal. Large magnetization changes emerge in response to ferroelectric switching and structural transitions of BaTiO3 controlled by applied electric fields and temperature, respectively. Interface strain coupling is the primary mechanism altering the induced magnetic anisotropy. As a result, coercivity changes up to 120% occur between the various structural states of BaTiO3 . Up to 20% coercivity change is achieved via electrical control at room temperature. Our all solid state ferroelectric-ferromagnetic heterostructures open viable possibilities for technological applications.

  4. Children Creating Ways To Represent Changing Situations: On the Development of Homogeneous Spaces.

    ERIC Educational Resources Information Center

    Nemirovsky, Ricardo; Tierney, Cornelia

    2001-01-01

    Focuses on children creating representations on paper for situations that change over time. Articulates the distinction between homogeneous and heterogeneous spaces and reflects on children's tendency to create hybrids between them. (Author/MM)

  5. Oxygen loss, semiconductivity, and positive temperature coefficient of resistance behavior in undoped cation-stoichiometric BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Beltrán, H.; Cordoncillo, E.; Escribano, P.; Sinclair, D. C.; West, A. R.

    2005-11-01

    Stoichiometric BaTiO3 ceramics fabricated from sol-gel-derived powders and sintered at temperatures <=1100 °C are highly insulating and electrically homogeneous. At higher sintering temperatures, samples gradually lose oxygen and the conductivity increases as a consequence. The latter phenomena are very sensitive to the furnace atmosphere and are partially reversible during cooling when partial reoxidation can occur. This results in ceramics that are often electrically heterogeneous with insulating surfaces or grain boundaries but semiconducting grain cores. In samples that were heated at 1450 °C in N2 and quenched, a positive temperature coefficient of resistance (PTCR) effect was observed, associated with an additional impedance arising from space-charge effects. These results demonstrate that, depending on sample processing, insulating cation-stoichiometric BaTiO3 can instead be semiconducting and under certain circumstances, exhibit a PTCR effect, without the need for donor dopant additives.

  6. Consequences of Ca multisite occupation for the conducting properties of BaTiO3

    NASA Astrophysics Data System (ADS)

    Zulueta, Y. A.; Dawson, J. A.; Leyet, Y.; Anglada-Rivera, J.; Guerrero, F.; Silva, R. S.; Nguyen, Minh Tho

    2016-11-01

    In combination with the dielectric modulus formalism and theoretical calculations, a newly developed defect incorporation mode, which is a combination of the standard A- and B-site doping mechanisms, is used to explain the conducting properties in 5 mol% Ca-doped BaTiO3. Simulation results for Ca solution energies in the BaTiO3 lattice show that the new oxygen vacancy inducing mixed mode exhibits low defect energies. A reduction in dc conductivity compared with undoped BaTiO3 is witnessed for the incorporation of Ca. The conducting properties of 5 mol% Ca-doped BaTiO3 are analyzed using molecular dynamics and impedance spectroscopy. The ionic conductivity activation energies for each incorporation mode are calculated and good agreement with experimental data for oxygen migration is observed. The likely existence of the proposed defect configuration is also analyzed on the basis of these methods.

  7. Pyroelectric response of spray-deposited BaTiO3 thin film

    NASA Astrophysics Data System (ADS)

    Peale, Robert E.; Oladeji, Isaiah O.; Smith, Evan M.; Vasilyev, Vladimir; Alhasan, Sarmad Fawzi Hamza; Abouelkhair, Hussain; Todorovski, Dalibor; Kimani, Martin; Cleary, Justin W.

    2016-09-01

    Pyroelectric photoresponse of aqueous spray deposited thin films containing BaTiO3 nano-crystals is reported. X-ray diffraction data indicate the presence of hexagonal BaTiO3 nano-crystals with 20 nm crystalline domains in a matrix of some as yet unidentified nano-crystalline material. When the film is annealed at 600 C, the X-ray pattern changes significantly and indicates a conversion to one of the non-hexagonal phases of BaTiO3 as well as a complete change in the matrix. With suitable amplifier, the measured photoresponse was 40V/W. Ferroelectric hysteresis on a film with significant presence of hexagonal BaTiO3 shows saturated polarization which is about 5-times smaller than for the bulk tetragonal phase. A potential application is a patternable infrared detector for photonic and plasmonic devices, such as chip-scale spectral sensors.

  8. Light Sensitive Lattice Defects In BaTiO3 Containing Fe

    NASA Astrophysics Data System (ADS)

    Possenriede, Ewald; Schirmer, Ortwin F.; Godefroy, Genevieve; Maillard, Alain

    1989-01-01

    Electron spin resonance spectra, which can consistently be explained by the models Fe4+ - Vo and Fe5+ - vBa, have been observed with BaTiO3 containing Fe. Also Fe3+ and - Fe3+ - Vo have been identified. All these centers as well as several unidentified ones are observed to change their charge states under illumination. They thus are possibly in involved in photorefractive processes in BaTiO3 containing Fe.

  9. Ab initio calculations of BaTiO3 (111) surfaces

    NASA Astrophysics Data System (ADS)

    Eglitis, R. I.

    2013-11-01

    The article presents the results of calculations of polar (111) surface relaxations and energetics using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. Using a hybrid B3LYP approach, the surface relaxation has been calculated for the two possible Ti and BaO3 BaTiO3 (111) surface terminations. For both Ti- and BaO3-terminated BaTiO3 (111) surfaces, the upper layer atoms relax inward. The second layer atoms, with the sole exception of Ti-terminated BaTiO3 (111) surface Ba atom, relax outward. The calculated surface relaxation energy for Ti-terminated BaTiO3 (111) surface is more than two times larger than the surface relaxation energy for BaO3-terminated BaTiO3 (111) surface. The surface energy for Ti-terminated BaTiO3 (111) surface (7.28 eV/cell) is smaller, than the surface energy for BaO3-terminated (111) surface (8.40 eV/cell).

  10. Atomistic description for temperature-driven phase transitions in BaTiO3

    NASA Astrophysics Data System (ADS)

    Qi, Y.; Liu, S.; Grinberg, I.; Rappe, A. M.

    2016-10-01

    Barium titanate (BaTiO3) is a prototypical ferroelectric perovskite that undergoes the rhombohedral-orthorhombic-tetragonal-cubic phase transitions as the temperature increases. In this paper, we develop a classical interatomic potential for BaTiO3 within the framework of the bond-valence theory. The force field is parametrized from first-principles results, enabling accurate large-scale molecular dynamics (MD) simulations at finite temperatures. Our model potential for BaTiO3 reproduces the temperature-driven phase transitions in isobaric-isothermal ensemble (N P T ) MD simulations. This potential allows for the analysis of BaTiO3 structures with atomic resolution. By analyzing the local displacements of Ti atoms, we demonstrate that the phase transitions of BaTiO3 exhibit a mix of order-disorder and displacive characters. Besides, from a detailed observation of structural dynamics during phase transition, we discover that the global phase transition is associated with changes in the equilibrium value and fluctuations of each polarization component, including the ones already averaging to zero, Contrary to the conventional understanding that temperature increase generally causes bond-softening transition, the x -polarization component (the one which is polar in both the orthorhombic and the tetragonal phases) exhibits a bond-hardening character during the orthorhombic-to-tetragonal transition. These results provide further insight about the temperature-driven phase transitions in BaTiO3.

  11. Controlled orientation of molecular-beam-epitaxial BaTiO3 on Si(001) using thickness engineering of BaTiO3 and SrTiO3 buffer layers

    NASA Astrophysics Data System (ADS)

    Hsu, Min-Hsiang Mark; Van Thourhout, Dries; Pantouvaki, Marianna; Meersschaut, Johan; Conard, Thierry; Richard, Olivier; Bender, Hugo; Favia, Paola; Vila, Maria; Cid, Rosalia; Rubio-Zuazo, Juan; Castro, German R.; Van Campenhout, Joris; Absil, Philippe; Merckling, Clement

    2017-06-01

    Monolithically integrating BaTiO3 on silicon substrates has attracted attention because of the wide spectrum of potential novel applications ranging from electronics to photonics. For optimal device performance, it is important to control the BaTiO3 domain orientation during thin film preparation. Here, we use molecular beam epitaxy to prepare crystalline BaTiO3 on Si(001) substrates using a SrTiO3 buffer layer. A systematic investigation is performed to understand how to control the BaTiO3 domain orientation through the thickness engineering of the SrTiO3 buffer layer and the BaTiO3 layer itself. This provides different possibilities for obtaining a given BaTiO3 orientation as desired for a specific device application.

  12. Direct detection of cysteine using functionalized BaTiO3 nanoparticles film based self-powered biosensor.

    PubMed

    Selvarajan, Sophia; Alluri, Nagamalleswara Rao; Chandrasekhar, Arunkumar; Kim, Sang-Jae

    2017-05-15

    Simple, novel, and direct detection of clinically important biomolecules have continuous demand among scientific community as well as in market. Here, we report the first direct detection and facile fabrication of a cysteine-responsive, film-based, self-powered device. NH2 functionalized BaTiO3 nanoparticles (BT-NH2 NPs) suspended in a three-dimensional matrix of an agarose (Ag) film, were used for cysteine detection. BaTiO3 nanoparticles (BT NPs) semiconducting as well as piezoelectric properties were harnessed in this study. The changes in surface charge properties of the film with respect to cysteine concentrations were determined using a current-voltage (I-V) technique. The current response increased with cysteine concentration (linear concentration range=10µM-1mM). Based on the properties of the composite (BT/Ag), we created a self-powered cysteine sensor in which the output voltage from a piezoelectric nanogenerator was used to drive the sensor. The potential drop across the sensor was measured as a function of cysteine concentrations. Real-time analysis of sensor performance was carried out on urine samples by non-invasive method. This novel sensor demonstrated good selectivity, linear concentration range and detection limit of 10µM; acceptable for routine analysis. Copyright © 2016 Elsevier B.V. All rights reserved.

  13. Study of electro-caloric effect in Ca and Sn co-doped BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Upadhyay, Sanjay Kumar; Fatima, Iram; Raghavendra Reddy, V.

    2017-04-01

    The present work deals with the study of structural, ferroelectric, dielectric and electro-caloric effects in lead free ferroelectric polycrystalline Ba1-x Ca x Ti0.95Sn0.05O3 (x  =  2, 5 and 10%) i.e. Ca, Sn co-doped BaTiO3 (BTO). Phase purity of the samples is confirmed from x-ray data by using Rietveld refinement. 119Sn Mössbauer reveals homogenous phase as well as iso-valent substitution of Sn at Ti site. Enhancements in ferroelectric and dielectric properties have been observed. Indirect method which is based on Maxwell equation has been used to determine the electro-caloric (EC) effect in the studied ferroelectric ceramics and maximum EC coefficient is observed for Ba0.95Ca0.05Ti0.95Sn0.05O3.

  14. Synthesis of transparent BaTiO3 nanoparticle/polymer composite film using DC field

    NASA Astrophysics Data System (ADS)

    Kondo, Yusuke; Okumura, Yasuko; Oi, Chifumi; Sakamoto, Wataru; Yogo, Toshinobu

    2008-10-01

    Transparent BaTiO3 nanoparticle/polymer composite films were synthesized from titanium-organic film and barium ion in aqueous solution under direct current (DC) field. Titanium-organic precursor was synthesized from titanium isopropoxide, acetylacetone and methacrylate derivative. The UV treatment was effective to increase the anti-solubility of the titanium-organic film during DC processing. BaTiO3 nanoparticles were crystallized in the precursor films on stainless substrates without high temperature process, as low as 40°C. The crystallite size of BaTiO3 increased with increasing reaction temperature from 40 to 50 °C at 3.0 V/cm. BaTiO3 nanoparticles also grew in size with increasing reaction time from 15 min to 45 min at 3.0 V/cm and 50 °C. Transparent BaTiO3 nanoparticle/polymer films were synthesized on stainless substrates at 3.0 V/cm and 50°C for 45 min.

  15. Single crystalline BaTiO3 thin films synthesized using ion implantation induced layer transfer

    NASA Astrophysics Data System (ADS)

    Park, Young-Bae; Diest, Kenneth; Atwater, Harry A.

    2007-10-01

    Layer transfer of BaTiO3 thin films onto silicon-based substrates has been investigated. Hydrogen and helium ions were co-implanted to facilitate ion-implantation-induced layer transfer of films from BaTiO3 single crystals. From thermodynamic equilibrium calculations, we suggest that the dominant species during cavity nucleation and growth are H2, H+, H2O, Ba2+ and Ba-OH, and that the addition of hydrogen to the Ba-Ti-O system can effectively suppress volatile oxide formation during layer transfer and subsequent annealing. After ion implantation, BaTiO3 layers contain microstructural defects and hydrogen precipitates in the lattice, but after layer transfer, the single crystal is found to be stoichiometric. Using direct wafer bonding and layer splitting, single crystal BaTiO3 thin films were transferred onto amorphous Si3N4 and Pt substrates. Micro-Raman spectroscopy indicated that the density of defects generated by ion implantation in BaTiO3 can be significantly reduced during post-transfer annealing, returning the transferred layer to its single crystal state. Characterization using piezoresponse force microscopy shows that the layer transferred thin films are ferroelectric, with domain structures and piezoresponse characteristics similar to that of bulk crystals.

  16. 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.

  17. 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.

  18. Nanoparticle-Based Magnetoelectric BaTiO3-CoFe2O4 Thin Film Heterostructures for Voltage Control of Magnetism.

    PubMed

    Erdem, Derya; Bingham, Nicholas S; Heiligtag, Florian J; Pilet, Nicolas; Warnicke, Peter; Vaz, Carlos A F; Shi, Yanuo; Buzzi, Michele; Rupp, Jennifer L M; Heyderman, Laura J; Niederberger, Markus

    2016-11-22

    Multiferroic composite materials combining ferroelectric and ferromagnetic order at room temperature have great potential for emerging applications such as four-state memories, magnetoelectric sensors, and microwave devices. In this paper, we report an effective and facile liquid phase deposition route to create multiferroic composite thin films involving the spin-coating of nanoparticle dispersions of BaTiO3, a well-known ferroelectric, and CoFe2O4, a highly magnetostrictive material. This approach offers great flexibility in terms of accessible film configurations (co-dispersed as well as layered films), thicknesses (from 100 nm to several μm) and composition (5-50 wt % CoFe2O4 with respect to BaTiO3) to address various potential applications. A detailed structural characterization proves that BaTiO3 and CoFe2O4 remain phase-separated with clear interfaces on the nanoscale after heat treatment, while electrical and magnetic studies indicate the simultaneous presence of both ferroelectric and ferromagnetic order. Furthermore, coupling between these orders within the films is demonstrated with voltage control of the magnetism at ambient temperatures.

  19. 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.

  20. 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.

  1. X-ray absorption spectroscopy on epitaxial BaTiO3 thin film

    NASA Astrophysics Data System (ADS)

    Panchal, Gyanendra; Shukla, D. K.; Choudhary, R. J.; Reddy, V. Raghavendra; Phase, D. M.

    2017-05-01

    We report the soft X-ray absorption spectroscopy (XAS) on pulsed laser deposition (PLD) grown epitaxial BaTiO3 thin film on (001) oriented SrTiO3 substrate. X-ray diffraction studies confirm that film is grown along the [001] direction and is compressed along surface normal. XAS around O K edge and Ti L3,2 edges performed on BaTiO3 thin film along with bulk BaTiO3 depicts considerable changes in crystal field parameters in thin film form due to strain present in the film. Modifications observed in t2g and eg sub bands of Ti ions are explained considering structural anisotropies present in the thin film.

  2. Dielectric Properties of BaTiO3-Based Ceramics under High Electric Field

    NASA Astrophysics Data System (ADS)

    Tsurumi, Takaaki; Adachi, Hiroshige; Kakemoto, Hirofumi; Wada, Satoshi; Mizuno, Youichi; Chazono, Hirokazu; Kishi, Hiroshi

    2002-11-01

    The dielectric properties under a high electric field (ac-field) of BaTiO3-based ceramics with core grains, shell grains and core-shell grains were compared with those of multilayer ceramic capacitors (MLCCs) with these three kinds of grains. The MLCCs with the X7R specification had a core-shell structure, and the relative dielectric permittivity (\\varepsilonr) of the dielectric layers in the MLCCs increased with increasing ac-field. Similar behavior was observed in the MLCCs consisting of only cores, indicating that the core predominantly determined the dielectric properties of MLCCs under high ac-fields. The dielectric properties of MLCCs and ceramic plates consisting of only shell grains showed that the shell was the relaxor ferroelectrics. A slight change in the shell composition yielded a large shift of the peak temperature of \\varepsilonr. The shell improved the temperature stability of \\varepsilonr at low temperatures under low ac-fields. In a ceramic plate with relatively large BaTiO3 grains (approximately 3 μm), the maximum \\varepsilonr was observed at a moderate ac-field, which was explained from the electric displacement vs electric field hysteresis curves of ferroelectric BaTiO3. The MLCCs and ceramics plates with fine BaTiO3 grains (0.4 to 0.5 μm) showed similar dielectric behavior to the MLCC with the core-shell structure. The size effect of BaTiO3 played an important role in determining the temperature stability of \\varepsilonr. For future MLCCs with very thin dielectric layers, a microstructure with fine BaTiO3 grains and grain boundary layers of the shell was proposed.

  3. Conduction Mechanisms in Multiferroic Multilayer BaTiO3/NiFe2O4/BaTiO3 Memristors

    NASA Astrophysics Data System (ADS)

    Samardzic, N.; Bajac, B.; Srdic, V. V.; Stojanovic, G. M.

    2017-10-01

    Memristive devices and materials are extensively studied as they offer diverse properties and applications in digital, analog and bio-inspired circuits. In this paper, we present an important class of memristors, multiferroic memristors, which are composed of multiferroic multilayer BaTiO3/NiFe2O4/BaTiO3 thin films, fabricated by a spin-coating deposition technique on platinized Si wafers. This cost-effective device shows symmetric and reproducible current-voltage characteristics for the actuating voltage amplitude of ±10 V. The origin of the conduction mechanism was investigated by measuring the electrical response in different voltage and temperature conditions. The results indicate the existence of two mechanisms: thermionic emission and Fowler-Nordheim tunnelling, which alternate with actuating voltage amplitude and operating temperature.

  4. 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.

  5. 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.

  6. 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.

  7. Photoinduced charge transfer properties and photocatalytic activity in Bi2O3/BaTiO3 composite photocatalyst.

    PubMed

    Fan, Haimei; Li, Haiyan; Liu, Bingkun; Lu, Yongchun; Xie, Tengfeng; Wang, Dejun

    2012-09-26

    A series of Bi(2)O(3)/BaTiO(3) composite photocatalysts with different mass ratios of Bi(2)O(3) vs BaTiO(3) were prepared by an impregnating-annealing method. X-ray diffraction (XRD), high-resolution transmission electron microscopic (HRTEM), and UV-vis diffuse reflection spectroscopy (DRS) confirmed that Bi(2)O(3) and BaTiO(3) coexisted in the composites. The results of surface photovoltage (SPV) experiments showed enhancements of photovoltaic response in composites, which indicated a higher separation efficiency of photoinduced charges due to the establishment of an efficient interfacial electric field between Bi(2)O(3) and BaTiO(3) in the composites. The consistency of phtocatalytic activity and photovoltaic response intensity of photocatalysts showed that the efficiency interfacial electric field between Bi(2)O(3) and BaTiO(3) played an important role in improving the degradation efficiency of Rhodamine B (RhB). The 60%-Bi(2)O(3)/BaTiO(3) sample with the best activity was found by optimizing the mass ratios of Bi(2)O(3) vs. BaTiO(3). On the basis of the work function (WF) measurements, a reasonable energy band diagram was proposed for BaTiO(3)/Bi(2)O(3) composite. It would be helpful in designing and constructing high efficiency heterogeneous semiconductor photocatalyst.

  8. Nanogenerator power output: influence of particle size and crystallinity of BaTiO3

    NASA Astrophysics Data System (ADS)

    Nutal Schädli, Gian; Büchel, Robert; Pratsinis, Sotiris E.

    2017-07-01

    Lead-free piezoelectric nanogenerators made with BaTiO3 offer an attractive energy harvesting solution towards portable, battery-free medical devices such as self-powered pacemakers. Here, we assembled nanogenerators made of thin, flexible poly(vinylidene fluoride-co-hexafluoropropylene) films containing either polycrystalline BaTiO3 nanoparticles of various sizes or commercial monocrystalline particles of 64 or 278 nm in average diameter. The nanoparticles were prepared by hydrogen-driven flame aerosol technology and had an average diameter of 24-50 nm with an average crystal size of about 10 nm. The rapid cooling during nanoparticle formation facilitated the synthesis of polycrystalline, multi-domain, piezoelectrically active tetragonal BaTiO3 with a high c/a lattice ratio. Using these particles, 2 μm thin polymer nanocomposites were formed, assembled into nanogenerators that exhibited a 1.4 V time-averaged output, almost twice that of the best commercial BaTiO3 particles. That output was maintained stable for over 45 000 cycles with each cycle corresponding to a heartbeat of 60 bpm. The exceptional piezoelectric performance of these nanogenerators is traced to their constituent polycrystalline nanoparticles, having high degree of domain orientation upon poling and exhibiting the flexoelectric effect, polarization induced by a strain gradient.

  9. First-principles calculations on the four phases of BaTiO3.

    PubMed

    Evarestov, Robert A; Bandura, Andrei V

    2012-04-30

    The calculations based on linear combination of atomic orbitals basis functions as implemented in CRYSTAL09 computer code have been performed for cubic, tetragonal, orthorhombic, and rhombohedral modifications of BaTiO(3) crystal. Structural and electronic properties as well as phonon frequencies were obtained using local density approximation, generalized gradient approximation, and hybrid exchange-correlation density functional theory (DFT) functionals for four stable phases of BaTiO(3). A comparison was made between the results of different DFT techniques. It is concluded that the hybrid PBE0 [J. P. Perdew, K. Burke, M. Ernzerhof, J. Chem. Phys. 1996, 105, 9982.] functional is able to predict correctly the structural stability and phonon properties both for cubic and ferroelectric phases of BaTiO(3). The comparative phonon symmetry analysis in BaTiO(3) four phases has been made basing on the site symmetry and irreducible representation indexes for the first time. Copyright © 2012 Wiley Periodicals, Inc.

  10. Hydrothermal synthesis of BaTiO 3 nanoparticles using a supercritical continuous flow reaction system

    NASA Astrophysics Data System (ADS)

    Hayashi, Hiromichi; Noguchi, Takio; Islam, Nazrul M.; Hakuta, Yukiya; Imai, Yusuke; Ueno, Nobuhiko

    2010-06-01

    Highly crystalline BaTiO 3 nanoparticle was synthesized rapidly by hydrothermal reaction in supercritical water using a continuous flow reactor. The reactants of TiO 2 sol (or TiCl 4)/Ba(NO 3) 2 mixed solution and KOH solution were used as starting materials and that was heated quickly up to 400 °C under the pressure of 30 MPa for 8 ms as reaction time. The XRD results revealed that the crystal phase of the obtained particles was cubic BaTiO 3, indicating that the hydrothermal reaction in supercritical water was successfully proceeded under present reaction conditions. Primarily particle size of the BaTiO 3 nanoparticle was determined by means of BET surface area, as small as less than 10 nm with decreasing the reaction pH. In contrast, dispersed particle size in solution measured by DLS (dynamic light scattering) technique decreased from 260 to 90 nm with increasing the reactants concentration. Aggregation of BaTiO 3 nanoparticles might be depressed in the presence of coexisting nitrate anions.

  11. BaTiO3/SrTiO3 heterostructures for ferroelectric field effect transistors

    NASA Astrophysics Data System (ADS)

    Shoron, Omor F.; Raghavan, Santosh; Freeze, Christopher R.; Stemmer, Susanne

    2017-06-01

    Integration of ultrathin ferroelectric thin films with semiconductors is of interest for negative capacitance transistors that exhibit internal voltage gain, which may allow for scaling the supply voltage of low power circuits. In this study, BaTiO3 thin films were grown on doped SrTiO3 channels using molecular beam epitaxy. The BaTiO3 films are ferroelectric despite their low thickness (˜10 nm). Parallel plate capacitor devices exhibit anti-clockwise hysteresis, and a comparison with reference structures without BaTiO3 shows that the polarization in the BaTiO3 thin films is switchable and controls the charge density in the channel. Field effect transistors were fabricated to study the effect of ferroelectricity on the transistor characteristics. Anti-clockwise hysteresis and a shift in threshold-voltage are observed in the output characteristics of the transistors. These properties make these heterostructures a suitable system for studying negative capacitance effects.

  12. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  14. 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

    2016-01-08

    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.

  15. 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.

  16. High-Energy-Density Polymer Nanocomposites Composed of Newly Structured One-Dimensional BaTiO3@Al2O3 Nanofibers.

    PubMed

    Pan, Zhongbin; Yao, Lingmin; Zhai, Jiwei; Fu, Dezhou; Shen, Bo; Wang, Haitao

    2017-02-01

    Flexible electrostatic capacitors are potentially applicable in modern electrical and electric power systems. In this study, flexible nanocomposites containing newly structured one-dimensional (1D) BaTiO3@Al2O3 nanofibers (BT@AO NFs) and the ferroelectric polymer poly(vinylidene fluoride) (PVDF) matrix were prepared and systematically studied. The 1D BT@AO NFs, where BaTiO3 nanoparticles (BT NPs) were embedded and homogeneously dispersed into the AO nanofibers, were successfully synthesized via an improved electrospinning technique. The additional AO layer, which has moderating dielectric constant, was introduced between BT NPs and PVDF matrixes. To improve the compatibility and distributional homogeneity of the nanofiller/matrix, dopamine was coated onto the nanofiller. The results show that the energy density due to high dielectric polarization is about 10.58 J cm(-3) at 420 MV m(-1) and the fast charge-discharge time is 0.126 μs of 3.6 vol % BT@AO-DA NFs/PVDF nanocomposite. A finite element simulation of the electric-field and electric current density distribution revealed that the novel-structured 1D BT@AO-DA NFs significantly improved the dielectric performance of the nanocomposites. The large extractable energy density and high dielectric breakdown strength suggest the potential applications of the BT@AO-DA NFs/PVDF nanocomposite films in electrostatic capacitors and embedded devices.

  17. Quasi-zero lattice mismatch and band alignment of BaTiO3 on epitaxial (110)Ge

    NASA Astrophysics Data System (ADS)

    Hudait, M. K.; Zhu, Y.; Jain, N.; Maurya, D.; Zhou, Y.; Priya, S.

    2013-07-01

    Growth, structural, and band alignment properties of pulsed laser deposited amorphous BaTiO3 on epitaxial molecular beam epitaxy grown (110)Ge layer, as well as their utilization in low power transistor are reported. High-resolution x-ray diffraction demonstrated quasi-zero lattice mismatch of BaTiO3 on (110)Ge. Cross-sectional transmission electron microscopy micrograph confirms the amorphous nature of BaTiO3 layer as well as shows a sharp heterointerface between BaTiO3 and Ge with no traceable interfacial layer. The valence band offset, ΔEv, of 1.99 ± 0.05 eV at the BaTiO3/(110)Ge heterointerface is measured using x-ray photoelectron spectroscopy. The conduction band offset, ΔEc, of 1.14 ± 0.1 eV is calculated using the bandgap energies of BaTiO3 of 3.8 eV and Ge of 0.67 eV. These band offset parameters for carrier confinement and the interface chemical properties of the BaTiO3/(110)Ge system are significant advancement towards designing Ge-based p-and n-channel metal-oxide semiconductor field-effect transistors for low-power application.

  18. Comparison of rheological, mechanical, electrical properties of HDPE filled with BaTiO3 with different polar surface tension

    NASA Astrophysics Data System (ADS)

    Su, Jun; Zhang, Jun

    2016-12-01

    In this work, three types of coupling agents: isopropyl trioleic titanate (NDZ105), vinyltriethoxysilane (SG-Si151), 3-aminopropyltriethoxysilane (KH550) were applied to modify the surface tension of Barium titanate (BaTiO3) particles. The Fourier transform infrared (FT-IR) spectra confirm the chemical adherence of coupling agents to the particle surface. The long hydrocarbon chains in NDZ105 can cover the particle surface and reduce the polar surface tension of BaTiO3 from 37.53 mJ/m2 to 7.51 mJ/m2, turning it from hydrophilic to oleophilic properties. The short and non-polar vinyl groups in SG-Si151 does not influence the surface tension of BaTiO3, but make BaTiO3 have both hydrophilic and oleophilic properties. The polar amino in KH550 can keep BaTiO3 still with hydrophilic properties. It is found that SG-Si151 modified BaTiO3 has the lowest interaction with HDPE matrix, lowering the storage modulus of HDPE composites to the greatest extent. As for mechanical properties, the polar amino groups in KH550 on BaTiO3 surface can improve the adhesion of BaTiO3 with HDPE matrix, which increases the elongation at break of HDPE composites to the greatest extent. In terms of electrical properties, the polar amino groups on surface of BaTiO3 can boost the dielectric properties of HDPE/BaTiO3 composites and decrease the volume resistivity of HDPE/BaTiO3 composites. The aim of this study is to investigate how functional groups affect the rheological, mechanical and electrical properties of HDPE composites and to select a coupling agent to produce HDPE/BaTiO3 composites with low dielectric loss, high dielectric constant and elongation at break.

  19. Enhancement of nonlinear optical properties of BaTiO3 nanoparticles by the addition of silver seeds.

    PubMed

    Yust, Brian G; Razavi, Neema; Pedraza, Francisco; Elliott, Zakary; Tsin, Andrew T; Sardar, Dhiraj K

    2012-11-19

    Barium titanate (BaTiO3) is a technologically important material because of its nonlinear properties, such as its strong second harmonic generation and high third order susceptibility. While many nonlinear effects have been extensively studied on the bulk scale, there are still questions regarding the strength of nonlinear effects in nanoparticles. The nonlinear properties of BaTiO3 nanoparticles and nanorods have been studied using the closed aperture z-scan technique. Silver was then grown photochemically on the surface of the BaTiO3 nanoparticles, and it was found that the third order susceptibility increases dramatically.

  20. Eu-Doped BaTiO3 Powder and Film from Sol-Gel Process with Polyvinylpyrrolidone Additive

    PubMed Central

    García-Hernández, Margarita; García-Murillo, Antonieta; de J. Carrillo-Romo, Felipe; Jaramillo-Vigueras, David; Chadeyron, Geneviève; De la Rosa, Elder; Boyer, Damien

    2009-01-01

    Transparent BaTiO3:Eu3+ films were prepared via a sol-gel method and dip-coating technique, using barium acetate, titanium butoxide, and polyvinylpyrrolidone (PVP) as modifier viscosity. BaTiO3:Eu3+ films ~500 nm thick, crystallized after thermal treatment at 700 ºC. The powders revealed spherical and rod shape morphology. The optical quality of films showed a predominant band at 615 nm under 250 nm excitation. A preliminary luminescent test provided the properties of the Eu3+ doped BaTiO3. PMID:19865533

  1. DFT study of Ag and La codoped BaTiO3

    NASA Astrophysics Data System (ADS)

    Maldonado, Frank; Stashans, Arvids

    2017-03-01

    Density functional theory and generalized gradient approximation including a Hubbard-like term was used in the present work to analyse structure as well as electronic and electrical properties of Ag and La codoped BaTiO3 material. Intrinsic oxygen vacancy defect has been taken into consideration throughout the calculations. Results on atomic shifts indicate the significance of Coulomb electrostatic interaction in finding equilibrium state of the system. It is shown that the n-type electrical conductivity should be expected as a result of codoping. Computed concentrations of free-carriers manifest the advantage of codoping procedure compared to the single impurity doping in the BaTiO3 crystal. It is also shown that oxygen vacancy alone can produce the n-type conductivity.

  2. 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.

  3. Interface charge behaviors of BaTiO3 film heterostructures with various crystal orientations

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Ouyang, Jun; Cheng, Hongbo; Yang, Qian; Kang, Limin; Zhang, Hua; Hu, Fangren

    2017-02-01

    Heteroepitaxial BaTiO3 ferroelectric films with (001), (110), and (111) orientations were grown on SrRuO3-buffered SrTiO3 substrates by magnetron sputtering. The leakage current and interface charge behaviors were systematically investigated. Without a discernible orientation-dependence behavior, the leakage current behaviors were all well described by a modified Schottky-contact model. On the basis of this theory, the interface charge state parameters, including dynamic dielectric constant, potential barriers, depletion layer width, effective space-charge density and hole concentration, and their evolution behaviors were analyzed in detail. They all exhibited anisotropic characteristics and were proved to be essentially attributed to the macrophysical properties of BaTiO3 film heterostructures.

  4. First-principles calculations on thermodynamic properties of BaTiO3 rhombohedral phase.

    PubMed

    Bandura, Andrei V; Evarestov, Robert A

    2012-07-05

    The calculations based on the linear combination of atomic orbitals have been performed for the low-temperature phase of BaTiO(3) crystal. Structural and electronic properties, as well as phonon frequencies were obtained using hybrid PBE0 exchange-correlation functional. The calculated frequencies and total energies at different volumes have been used to determine the equation of state and thermal contribution to the Helmholtz free energy within the quasiharmonic approximation. For the first time, the bulk modulus, volume thermal expansion coefficient, heat capacity, and Grüneisen parameters in BaTiO(3) rhombohedral phase have been estimated at zero pressure and temperatures form 0 to 200 K, based on the results of first-principles calculations. Empirical equation has been proposed to reproduce the temperature dependence of the calculated quantities. The agreement between the theoretical and experimental thermodynamic properties was found to be satisfactory. Copyright © 2012 Wiley Periodicals, Inc.

  5. XMCD studies of thin Co films on BaTiO3.

    PubMed

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

    2015-08-19

    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.

  6. 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.

  7. Formation of new structural states in compressed BaTiO3 nanopowders

    NASA Astrophysics Data System (ADS)

    Shmyt'ko, I. M.; Frolov, D. D.; Aronin, A. S.; Ganeeva, G. R.; Kedrov, V. V.

    2017-06-01

    The structural changes in BaTiO3 nanocrystal powder and tablets have been probed via X-ray diffraction, scanning electron and transmission microscopy, and differential calorimetry after successive hightemperature annealing in air. It is shown that, beginning with the annealing temperature of 1200°C, significant amount of the Ba2TiO4 phase forms in the tablets together with the BaTiO3 phase. This phase is equilibrium one; it practically vanishes when the annealing temperature decreases to 700-600°C; and this phase practically restored to the initial state when the annealing temperature is again increased to 1200°C. Annealing the powders causes no formation of new phases, but an increase in their crystallite sizes. A probable reason of the emergence of Ba2TiO4 phase in tablets and its absence in free powder is discussed, as well.

  8. Donor-doping effect in BaTiO 3 ceramics using positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Mohsen, M.; Krause-Rehberg, R.; Massoud, A. M.; Langhammer, H. T.

    2003-10-01

    Temperature-dependent measurements using positron lifetime spectroscopy (PLS) were carried out to study various defects in polycrystalline donor doped BaTiO 3 (BT) samples. Annealing under different donor-doping level of La and Y were performed. At high doping level, it was found that with increasing doping level the average lifetime increases. This is attributed to the interplay of complexes containing oxygen vacancies VO and other vacancies, such as VBa, VTi as well as grain boundaries.

  9. Structural evolution of BaTiO(3) nanocrystals synthesized at room temperature.

    PubMed

    Rabuffetti, Federico A; Brutchey, Richard L

    2012-06-06

    Sub-10 nm BaTiO(3) nanocrystals were synthesized at room temperature via the vapor diffusion sol-gel method, and their structural evolution during nucleation and growth stages was followed using a series of techniques that probe the atomic structure on different length and time scales. Special emphasis was placed on assessing the evolution of the local symmetry and structural coherence of the resulting nanocrystals, as these are the structural bases for cooperative properties such as ferroelectricity. Although the room-temperature crystal structure of the fully grown nanocrystals appears cubic to Rietveld analysis of synchrotron X-ray diffraction data, Raman spectroscopy and pair distribution function analysis demonstrate the presence of non-centrosymmetric regions arising from the off-centering of the titanium atoms. This finding demonstrates that accounting for diffuse scattering is critical when attempting the structural characterization of nanocrystals with X-ray diffraction. The local symmetry of acentric regions present in BaTiO(3) nanocrystals, particularly structural correlations within an individual unit cell and between two adjacent unit cells, is best described by a tetragonal P4mm space group. The orthorhombic Amm2 space group also provides an adequate description, suggesting both types of local symmetry can coexist at room temperature. The average magnitude of the local off-center displacements of the titanium atoms along the polar axis is comparable to that observed in bulk BaTiO(3), and their coherence length is on the order of 16 Å. The presence of local dipoles suggests that a large amount of macroscopic polarization can be achieved in nanocrystalline BaTiO(3) if the coherence of their ferroelectric coupling is further increased.

  10. Ferroelectric control of magnetism in BaTiO3/Fe heterostructures

    NASA Astrophysics Data System (ADS)

    Sahoo, Sarbeswar; Polisetty, Srinivas; Duan, Chun Gang; Jaswal, Sitaram; Tsymbal, Evgeny; Binek, Christian

    2008-03-01

    Multiferroics can offer the possibility to manipulate the cross coupled order parameters by conjugate electric and magnetic fields. Switching off ferromagnetic order by an electric field for instance promises significant impact in the design of novel spintronic devices. Here we report on the reversible control of magnetism for a Fe thin film in proximity of a BaTiO3 single-crystal. Large magnetization changes emerge in response to ferroelectric switching and structural transitions of BaTiO3 controlled by applied electric fields and temperature, respectively.^ Interface strain coupling is the primary mechanism altering the induced magnetic anisotropy. As a result, coercivity changes up to 120% occur between the various structural states of BaTiO3. Up to 20% coercivity change is achieved via electrical control at room temperature. Our all solid state ferroelectric-ferromagnetic heterostructures open viable possibilities for new technological applications. ^S. Sahoo, S. Polisetty, C.-G. Duan, S. S. Jaswal, E. Y. Tsymbal, and Ch. Binek, Phys. Rev. B 76, 092108 (2007).

  11. Deposition barium titanate (BaTiO3) doped lanthanum with chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Iriani, Y.; Jamaludin, A.; Nurhadi, N.

    2016-11-01

    Deposition of Barium Titanate (BaTiO3) thin films used Chemical Solution Deposition (CSD) method and prepared with spin coater. BaTiO3 is doped with lanthanum, 1%, 2%, and 3%. The thermal process use annealing temperature 900°C and holding time for 3 hours. The result of characterization with x-ray diffraction (XRD) equipment show that the addition of La3+ doped on Barium Titanate caused the change of angle diffraction.The result of refine with GSAS software shows that lanthanum have been included in the structure of BaTiO3. Increasing mol dopant La3+ cause lattice parameter and crystal volume become smaller. Characterization result using Scanning Electron Microscopy (SEM) equipment show that grain size (grain size) become smaller with increasing mole dopant (x) La3+. The result of characterization using Sawyer Tower methods show that all the samples (Barium Titanante and Barium Titanate doped lanthanum) are ferroelectric material. Increasing of mole dopant La3+ cause smaller coercive field and remanent polarization increases.

  12. Observation of self poling in BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Lubomirsky, Igor; Chang, David T.; Stafsudd, Oscar M.

    1999-05-01

    The dependence of ferroelectric properties of sol-gel derived BaTiO3 thin (0.35 μm) films on various Si substrates was investigated. It was found that only films deposited on p+ Si (1020cm-3 B, 2% Ge) are (110) oriented and possess a few percent of the spontaneous polarization of single-crystal BaTiO3. The direction of polarization self restored after being reversed by external bias or heated above the Curie temperature. It was found that the pyroelectric coefficient was not zero above the Curie point, which indicated that the films are permanently subjected to an electric field, which originates from the contact potential between the film and the substrate. This conclusion was confirmed by surface photovoltage spectroscopy. Orientation of the films was attributed to the presence of Ge in the substrate, which decreased lattice mismatch between the (100) vector of the Si substrate and (110) vector of BaTiO3. The possibility of a paraelectric to ferroelectric transition driven by an electric field due to the contact potential difference must be taken into account for dynamic random access memory applications.

  13. Optical properties of pulsed-laser deposited BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Xu, Jie; Durisin, Daniel P.; Auner, Gregory W.

    2005-04-01

    Thin films of barium titanate (BaTiO3) have been grown on Si (100) and UV fused silica substrates using KrF pulsed-laser deposition (PLD). The films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV/VIS/NIR spectroscopy. Smooth and stoichiometric films were grown on Si (100) substrate at O2 pressure range of 10-30 mTorr and substrate temperature of 600°C-620°C. The XRD patterns of the films revealed the polycrystalline peaks with a preferential orientation. The optical properties of BaTiO3 films were investigated in terms of UV-VIS transmission spectrum of the films deposited on UV fused silica substrate. The spectral dependences of refractive index and absorption coefficient, and the thickness of the films have been calculated from optical transmission measurements using the envelope method. The band gap energy (Eg) of BaTiO3 films was found to be 3.35eV.

  14. Surface chemistry and infrared absorbance changes during ZnO atomic layer deposition on ZrO2 and BaTiO3 particles

    NASA Astrophysics Data System (ADS)

    Ferguson, J. D.; Weimer, A. W.; George, S. M.

    2005-01-01

    ZnO atomic layer deposition (ALD) was achieved using sequential exposures of Zn(CH2CH3)2 and H2O on ZrO2 and BaTiO3 particles at 450 K. The surface chemistry of ZnO ALD was monitored in vacuum using Fourier transform infrared spectroscopy. The BaTiO3 and ZrO2 particles initially displayed vibrational features consistent with surface hydroxyl (-OH) groups. Zn(CH2CH3)2 exposure removed the surface hydroxyl groups and created Zn(CH2CH3)* surface species. The subsequent H2O exposure removed the Zn(CH2CH3)* surface species and produced ZnOH* surface species. Repeating the Zn(CH2CH3)2 and H2O exposures in an ABAB... reaction sequence at 450 K progressively deposited ZnO. Because ZnO is a semiconductor, the background infrared absorbance increased with the number of AB cycles during the deposition of the ZnO film. The increasing background infrared absorbance during long Zn(CH2CH3)2 exposures also revealed that the Zn(CH2CH3)2 reaction is not self-limiting. The background absorbance was modulated dramatically by the presence of ethyl (-CH2CH3) or hydroxyl (-OH) groups on the surface of the growing ZnO film. The infrared absorbance was higher with hydroxyl (-OH) groups and lower with ethyl (-CH2CH3) groups on the ZnO surface. The background absorbance changes were not linear with surface coverage. The large changes in absorbance after low reactant exposure suggested that the most reactive surface sites may be most influential in affecting the film conductance. Transmission electron microscopy (TEM) was used to examine the ZnO films deposited on the ZrO2 and BaTiO3 particles. The TEM images revealed ZrO2 and BaTiO3 particles encapsulated by conformal ZnO films. The ZnO films had a thickness of ~43 A˚ after 20 AB reaction cycles and ~65 A˚ after 30 AB reaction cycles, respectively. These TEM images are consistent with a ZnO ALD growth rate at 450 K of ~2.2 A˚/AB cycle.

  15. 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

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

    DOE PAGES

    Torgersen, Jan; Acharya, Shinjita; Dadlani, Anup Lal; ...

    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

  17. 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.

  18. Novel Piezoelectric Paper‐Based Flexible Nanogenerators Composed of BaTiO3 Nanoparticles and Bacterial Cellulose

    PubMed Central

    Zhang, Guangjie; Liao, Qingliang; Zhang, Zheng; Liang, Qijie; Zhao, Yingli; Zheng, Xin

    2015-01-01

    A piezoelectric paper based on BaTiO3 (BTO) nanoparticles and bacterial cellulose (BC) with excellent output properties for application of nanogenerators (NGs) is reported. A facile and scalable vacuum filtration method is used to fabricate the piezoelectric paper. The BTO/BC piezoelectric paper based NG shows outstanding output performance with open‐circuit voltage of 14 V and short‐circuit current density of 190 nA cm−2. The maximum power density generated by this unique BTO/BC structure is more than ten times higher than BTO/polydimethylsiloxane structure. In bending conditions, the NG device can generate output voltage of 1.5 V, which is capable of driving a liquid crystal display screen. The improved performance can be ascribed to homogeneous distribution of piezoelectric BTO nanoparticles in the BC matrix as well as the enhanced stress on piezoelectric nanoparticles implemented by the unique percolated networks of BC nanofibers. The flexible BTO/BC piezoelectric paper based NG is lightweight, eco‐friendly, and cost‐effective, which holds great promises for achieving wearable or implantable energy harvesters and self‐powered electronics. PMID:27774389

  19. Novel Piezoelectric Paper-Based Flexible Nanogenerators Composed of BaTiO3 Nanoparticles and Bacterial Cellulose.

    PubMed

    Zhang, Guangjie; Liao, Qingliang; Zhang, Zheng; Liang, Qijie; Zhao, Yingli; Zheng, Xin; Zhang, Yue

    2016-02-01

    A piezoelectric paper based on BaTiO3 (BTO) nanoparticles and bacterial cellulose (BC) with excellent output properties for application of nanogenerators (NGs) is reported. A facile and scalable vacuum filtration method is used to fabricate the piezoelectric paper. The BTO/BC piezoelectric paper based NG shows outstanding output performance with open-circuit voltage of 14 V and short-circuit current density of 190 nA cm(-2). The maximum power density generated by this unique BTO/BC structure is more than ten times higher than BTO/polydimethylsiloxane structure. In bending conditions, the NG device can generate output voltage of 1.5 V, which is capable of driving a liquid crystal display screen. The improved performance can be ascribed to homogeneous distribution of piezoelectric BTO nanoparticles in the BC matrix as well as the enhanced stress on piezoelectric nanoparticles implemented by the unique percolated networks of BC nanofibers. The flexible BTO/BC piezoelectric paper based NG is lightweight, eco-friendly, and cost-effective, which holds great promises for achieving wearable or implantable energy harvesters and self-powered electronics.

  20. Enhanced actuation performance of piezoelectric fiber composites induced by incorporated BaTiO3 nanoparticles in epoxy resin

    NASA Astrophysics Data System (ADS)

    Wu, Mingliang; Yuan, Xi; Luo, Hang; Chen, Haiyan; Chen, Chao; Zhou, Kechao; Zhang, Dou

    2017-05-01

    Piezoelectric fiber composites (PFCs) have attracted much interest owing to their flexibility and toughness compared with conventional monolithic piezoceramic wafers. The free strain values and actuation property of PFCs strongly depend on the active electric field applied in Pb(Zr1 - xTix)O3 (PZT) fibers. Reducing the dielectric constant mismatch between PZT fiber and the assembling epoxy resin would greatly increase the active electric field in PZT fiber. Therefore, BaTiO3 (BT) nanoparticles were introduced into the epoxy resin to enhance the dielectric constant. Homogeneous dispersion of BT nanoparticles and tight adhesion with the epoxy resin were achieved through a surface modification by dopamine. The maximum dielectric constant of dopamine modified BT/epoxy (BT@Dop/epoxy) nanocomposites was 10.38 with 12 wt% BT@Dop content at 1 kHz. The maximum free strain of PFCs reached 1820 ppm with 6 wt% BT@Dop content, while PFCs assembled by pure epoxy showed 790 ppm at the same processing condition. The tip displacement of cantilever beam actuated by PFCs reached the peak of 19 mm at the resonance frequency with 6 wt% BT@Dop, which was improved by 90% comparing to PFCs with pure epoxy.

  1. Local Structure of BiFeO3-BaTiO3 Mixture

    NASA Astrophysics Data System (ADS)

    Yoneda, Yasuhiro; Yoshii, Kenji; Kohara, Shinji; Kitagawa, Shuji; Mori, Shigeo

    2008-09-01

    Local structure analysis of (1-x)BiFeO3-xBaTiO3 mixture was carried out by a synchrotron radiation X-ray pair-distribution function (PDF) method. The PDF peak is resolved as a doublet owing to the presence of two phases with distinct local structures. The randomness of the off-center displacement of Bi atoms was different in these two phases, one was an average structure and the other a disordered rhombohedral structure. The volume fraction of each phase changed with BaTiO3 composition.

  2. Fraunhofer diffraction to determine the twin angle in single-crystal BaTiO3.

    PubMed

    Melnichuk, Mike; Wood, Lowell T

    2003-08-01

    We present a new method for determining the electrically induced twin angle alpha of a (100) bulk single crystal of barium titanate (BaTiO3) using a nondestructive optical technique based on Fraunhofer diffraction. The technique required two steps that were performed simultaneously. First, we analyzed the diffracted light intensity captured with a line camera. Second, we measured the size of the diffracting element by analyzing images of crystal's surface taken with a CCD camera. The value obtained for the twin angle is 0.67 degrees +/- 0.05 degrees, which compares favorably with the theoretical value of 0.63 degrees.

  3. Electric-field-induced domain intersection in BaTiO3 single crystal

    NASA Astrophysics Data System (ADS)

    He, Ming; Wang, Mengxia; Zhang, Zhihua

    2017-03-01

    Large-angle convergent beam electron diffraction was used to determine the directions of polarization vectors in a BaTiO3 single crystal. Domain intersections driven by an electric field were investigated by in situ transmission electron microscopy. The dark triangles observed in the domain intersection region can be accounted for by dislocations and the strain field. Domains nucleate at the domain tip depending on the dislocations and strain field to relieve the accumulated stress. Schematic representations of the intersecting domains and the microscopic structure are given, clarifying the special electric-field-induced domain structure.

  4. Intensity dependent absorption/transparency of a reducing BaTiO3

    NASA Astrophysics Data System (ADS)

    Chang, J. Y.; Garrett, M. H.; Jenssen, H. P.; Warde, C.

    1993-12-01

    We report intensity dependent absorption and transparency as a function of wavelength for barium titanate. The BaTiO3 crystal examined has an as-grown, light-blue color due to an absorption centered at 690 nm, and when reduced in a partial pressure of 10-15 atm of oxygen it has a yellow-orange color due to an absorption centered at 470 nm. Both energy levels are active in the reduced sample as revealed in the spectrum of the intensity dependent changes in absorption.

  5. Inverse barocaloric effects in ferroelectric BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Stern-Taulats, E.; Lloveras, P.; Barrio, M.; Defay, E.; Egilmez, M.; Planes, A.; Tamarit, J.-LI.; Mañosa, Ll.; Mathur, N. D.; Moya, X.

    2016-09-01

    We use calorimetry to identify pressure-driven isothermal entropy changes in ceramic samples of the prototypical ferroelectric BaTiO3. Near the structural phase transitions at ˜400 K (cubic-tetragonal) and ˜280 K (tetragonal-orthorhombic), the inverse barocaloric response differs in sign and magnitude from the corresponding conventional electrocaloric response. The differences in sign arise due to the decrease in unit-cell volume on heating through the transitions, whereas the differences in magnitude arise due to the large volumetric thermal expansion on either side of the transitions.

  6. 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.

  7. Electromagnetic properties and microwave absorption properties of BaTiO 3-carbonyl iron composite in S and C bands

    NASA Astrophysics Data System (ADS)

    Rui-gang, Yang

    2011-07-01

    BaTiO3 powders are prepared by sol-gel method. The carbonyl iron powder is prepared via thermal decomposition of iron pentacarbonyl. Then BaTiO3-carbonyl iron composite with different mixture ratios was prepared using the as-prepared material. The structure, morphology, and properties of the composites are characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, scanning electron microscopy (SEM), and a network analyzer. The complex permittivity and reflection loss of the composites have been measured at different microwave frequencies in S- and C-bands employing vector network analyzer model PNA 3629D vector. The effect of the mass ratio of BaTiO3/carbonyl iron on the microwave loss properties of the composites is investigated. A possible microwave absorbing mechanism of BaTiO3-carbonyl iron composite has been proposed. The BaTiO3-carbonyl iron composite can find applications in suppression of electromagnetic interference, and reduction of radar signature.

  8. Impact of Fe on structural modification and room temperature magnetic ordering in BaTiO3

    NASA Astrophysics Data System (ADS)

    Rajan, Soumya; Gazzali, P. M. Mohammed; Chandrasekaran, G.

    2017-01-01

    Ba1 - xFexTiO3 (x = 0, 0.005, 0.01) polycrystalline ceramics are prepared using solid state reaction method. Structural studies through XRD, Raman and XPS confirm single tetragonal phase for BaTiO3 whereas a structural disorder tends to intervene with the introduction of smaller Fe ions which reduces the tolerance factor and tetragonality ratio. Grain size of the samples is estimated using SEM micrographs with ImageJ software and chemical composition is confirmed using EDX spectra. Raman spectra measured in the temperature range of 303 K to 573 K showers light on the structural phase transition exploiting a significant disappearance of the 306 cm- 1 mode. Further, structural analyses suggest the entry of Fe into the B-site upon increasing its concentration in BaTiO3. The dopant sensitive modes lying at around 640 cm- 1 and 650 cm- 1 are assigned to lattice strain. A reduction in ferroelectric to paraelectric transition temperature is observed with a transformation from diffused type to normal ferroelectric upon the increased Fe content. The oxidation state of Fe in the BaTiO3 lattice has been decided using EPR Spectra precisely. Room temperature magnetic ordering is observed in Fe substituted BaTiO3 using PPMS. The coexistence of ferroelectric and magnetic ordering is established in the present study for optimized Fe substituted BaTiO3.

  9. Quantitative study of band structure in BaTiO3 particles with vacant ionic sites

    NASA Astrophysics Data System (ADS)

    Oshime, Norihiro; Kano, Jun; Ikeda, Naoshi; Teranishi, Takashi; Fujii, Tatsuo; Ueda, Takeji; Ohkubo, Tomoko

    2016-10-01

    Levels of the conduction band minimum and the valence band maximum in ion-deficient BaTiO3 particles were investigated with optical band gap and ionization energy measurements. Though it is known that the quantification of the band structure in an insulator is difficult, due to the poor electrical conductivity of BaTiO3, systematic variation in the band energy levels was found that correlated with the introduction of vacancies. Photoelectron yield spectroscopy provided direct observation of the occupancy level of electrons, which is altered by the presence of oxygen and barium vacancies. In addition, the conduction band deviation from the vacuum level was determined by optical reflectance spectroscopy. Our results show that: (1) Introduction of oxygen vacancies forms a donor level below the conduction band. (2) The conduction band is shifted to a lower level by a larger number of oxygen vacancies, while the valence band also shifts to a lower level, due to the reduction in the density of O 2p orbitals. (3) Introduction of barium vacancies widens the band gap. Since barium vacancies can induce a small number of oxygen vacancies with accompanying charge compensation, this behavior suppresses any large formation of donor levels in the gap states, indicating that cation vacancies can control the number of both donor and acceptor levels.

  10. 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.

  11. 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.

  12. Understanding the peculiarities of the piezoelectric effect in macro-porous BaTiO3

    PubMed Central

    Roscow, James I.; Topolov, Vitaly Yu.; Bowen, Christopher R.; Taylor, John; Panich, Anatoly E.

    2016-01-01

    Abstract This work demonstrates the potential of porous BaTiO3 for piezoelectric sensor and energy-harvesting applications by manufacture of materials, detailed characterisation and application of new models. Ferroelectric macro-porous BaTiO3 ceramics for piezoelectric applications are manufactured for a range of relative densities, α = 0.30–0.95, using the burned out polymer spheres method. The piezoelectric activity and relevant parameters for specific applications are interpreted by developing two models: a model of a 3–0 composite and a ‘composite in composite’ model. The appropriate ranges of relative density for the application of these models to accurately predict piezoelectric properties are examined. The two models are extended to take into account the effect of 90° domain-wall mobility within ceramic grains on the piezoelectric coefficients d3j*. It is shown that porous ferroelectrics provide a novel route to form materials with large piezoelectric anisotropy d33*d31*>>1 at 0.20 ≤ α ≤ 0.45 and achieve a high squared figure of merit d33* g33*. The modelling approach allows a detailed analysis of the relationships between the properties of the monolithic and porous materials for the design of porous structures with optimum properties. PMID:27933117

  13. 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

  14. Interface enhanced functionalities in BaTiO3/CaTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Wu, Xifan

    2014-03-01

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

  15. Fabrication of BaTiO3 Thin Films Using Modified Chemical Solutions and Sintering Method

    NASA Astrophysics Data System (ADS)

    Tanaka, Kiyotaka; Suzuki, Kazuyuki; Kato, Kazumi

    2008-09-01

    BaTiO3 thin films were fabricated at 650 °C by single sintering using additive-free and diethanolamine (DEA)-modified alkoxide solutions. The BaTiO3 thin films derived from the DEA-modified solution had a flat surface and an rms roughness below 2.5 nm. The grain size on Pt/Ti/SiO2/Si substrates single-sintered at 650 °C for 100 min was estimated to be about 34 to 43 nm. We succeeded in obtaining the electric properties of Pt/BaTiO3/Pt capacitors by single sintering at 650 °C for 1 min. The dielectric constant ɛr and dielectric loss tan δ at 1 MHz were 110 and 0.05, respectively. On the other hand, the grain size on SiO2/Si substrates single-sintered at 650 °C for 100 min reached about 55 to 62 nm. For the thickness and Fourier-transform infrared (FT-IR) spectra of the gel films, it was found that the thickness of the gel films at around 200 °C derived from the DEA-modified solution became abnormally thick and that the intermediate compounds generated during the decomposition of DEA remained in the gel films.

  16. Understanding the peculiarities of the piezoelectric effect in macro-porous BaTiO3.

    PubMed

    Roscow, James I; Topolov, Vitaly Yu; Bowen, Christopher R; Taylor, John; Panich, Anatoly E

    2016-01-01

    This work demonstrates the potential of porous BaTiO3 for piezoelectric sensor and energy-harvesting applications by manufacture of materials, detailed characterisation and application of new models. Ferroelectric macro-porous BaTiO3 ceramics for piezoelectric applications are manufactured for a range of relative densities, α = 0.30-0.95, using the burned out polymer spheres method. The piezoelectric activity and relevant parameters for specific applications are interpreted by developing two models: a model of a 3-0 composite and a 'composite in composite' model. The appropriate ranges of relative density for the application of these models to accurately predict piezoelectric properties are examined. The two models are extended to take into account the effect of 90° domain-wall mobility within ceramic grains on the piezoelectric coefficients [Formula: see text]. It is shown that porous ferroelectrics provide a novel route to form materials with large piezoelectric anisotropy [Formula: see text] at 0.20 ≤ α ≤ 0.45 and achieve a high squared figure of merit [Formula: see text] [Formula: see text]. The modelling approach allows a detailed analysis of the relationships between the properties of the monolithic and porous materials for the design of porous structures with optimum properties.

  17. 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

    2016-03-04

    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.

  18. Radiation effect on domain and defect structure of BaTiO3 crystals

    NASA Astrophysics Data System (ADS)

    Fesenko, Evgeni G.; Lisinska-Czekaj, Agata; Czekaj, Dionizy; Surowiak, Zygmunt

    2003-10-01

    BaTiO3 single crystals were obtained by Remeika-method from solutions of melted salts and oxides. Radioactive Co60 isotope was employed as a source of γ-radiation. Three different radiation doses were applied: 1.2 x 107 rad, 3.0 x 108 rad, and 1.3 x 107 rad. Temperature of single crystals during irradiation did not exceed 313 K. A few batches of crystals were subjected to irradiation, namely: single crystals with natural surface (after the crystal was grown), single crystals with the etched surface layer and single crystals which had been subjected to an influence of the strong direct and alternating electric fields before exposure. Both domain and defect structure of single crystals was investigated by the etching method, decorating method, optical microscopy and scanning electron microscopy. It has been found that irradiation causes destabilization of the domain walls of the head-to-head-type with a negative charge screening spontaneous polarization (Ps). The negative domains in a positive matrix, which did not grow through the whole crystal body, were found to decay under the influence of radiation. In a place previously occupied by decaying negative domains, defect clusters are observed. The investigations have shown that there is a close correlation between the domain structure and the defect structure of BaTiO3 crystals.

  19. Enhanced resistive memory in Nb-doped BaTiO3 ferroelectric diodes

    NASA Astrophysics Data System (ADS)

    Jin, Qiao; Zheng, Chunyan; Zhang, Yongcheng; Lu, Chaojing; Dai, Jiyan; Wen, Zheng

    2017-07-01

    In this study, we report on enhanced resistive memory in BaTiO3-based ferroelectric diodes due to the doping of donors. A large ON/OFF current ratio of ˜2000, about two orders of magnitude higher than that of Au/BaTiO3/SrRuO3, is achieved in a Au/Nb:BaTiO3/SrRuO3 diode at room temperature. This can be ascribed to the enhanced ferroelectric-modulation on the potential barrier at the Nb:BaTiO3/SrRuO3 interface associated with the (NbTi4+ 5 +) . donors, which gives rise to an efficient control of device transport between a bulk-limited current in the ON state and an interface-limited Schottky emission in the OFF state. In contrast, the resistance switching is suppressed in a Au/Fe:BaTiO3/SrRuO3 device since the (FeTi4+ 3 +) ' acceptors suppress semiconducting character of the BaTiO3 thin film and make the polarization-modulation of the band diagram negligible. The present work facilitates the design of high-performance resistive memory devices based on ferroelectric diodes with controllable charged defects.

  20. 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.

  1. First-principles study for vacancy-induced magnetism in nonmagnetic ferroelectric BaTiO3.

    PubMed

    Cao, D; Cai, M Q; Zheng, Yue; Hu, W Y

    2009-12-14

    The possibilities of vacancy-induced magnetism in perovskite BaTiO(3) are investigated by first-principles calculations. Calculated results show that both titanium and oxygen vacancies could induce magnetism, but the barium vacancy did not induce magnetism. New and interesting magnetic properties of half-metallic magnetism are found in BaTiO(3) induced by the Ti-vacancy. Based on the density of states and the spin charge density distribution of BaTiO(3), we discuss the different origins of magnetism induced by the partial spin-polarized O 2p states around Ti vacancies and the partially filled d-states Ti around the oxygen vacancies. The discrepancy between the magnetic moments in the cubic phase and the tetragonal phase is due to anisotropic spin polarization induced by structure distortions. Our calculations would enable exploring magneto-electric coupling in nonmagnetic ferroelectric oxides.

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

    DOE PAGES

    Kumah, D. P.; Dogan, M.; Ngai, J. H.; ...

    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

  3. Studies of local structural distortions in strained ultrathin BaTiO3 films using scanning transmission electron microscopy.

    PubMed

    Park, Daesung; Herpers, Anja; Menke, Tobias; Heidelmann, Markus; Houben, Lothar; Dittmann, Regina; Mayer, Joachim

    2014-06-01

    Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.

  4. Improving dielectric properties of BaTiO3/poly(vinylidene fluoride) composites by employing core-shell structured BaTiO3@Poly(methylmethacrylate) and BaTiO3@Poly(trifluoroethyl methacrylate) nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Xianhong; Zhao, Sidi; Wang, Fang; Ma, Yuhong; Wang, Li; Chen, Dong; Zhao, Changwen; Yang, Wantai

    2017-05-01

    Polymer based dielectric composites were fabricated through incorporation of core-shell structured BaTiO3 (BT) nanoparticles into PVDF matrix by means of solution blending. Core-shell structured BT nanoparticles with different shell composition and shell thickness were prepared by grafting methacrylate monomer (MMA or TFEMA) onto the surface of BT nanoparticles via surface initiated atom transfer radical polymerization (SI-ATRP). The content of the grafted polymer and the micro-morphology of the core-shell structured BT nanoparticles were investigated by thermo gravimetric analyses (TGA) and transmission electron microscopy (TEM), respectively. The dielectric properties were measured by broadband dielectric spectroscopy. The results showed that high dielectric constant and low dielectric loss are successfully realized in the polymer based composites. Moreover, the type of the grafted polymer and its content had different effect on the dielectric constant. In detail, the attenuation of dielectric constant was 16.6% for BT@PMMA1/PVDF and 10.7% for BT@PMMA2/PVDF composite in the range of 10 Hz to 100 kHz, in which the grafted content of PMMA was 5.5% and 8.0%, respectively. However, the attenuation of dielectric constant was 5.5% for BT@PTFEMA1/PVDF and 4.0% for BT@PTFEMA2/PVDF composite, in which the grafted content of PTFEMA was 1.5% and 2.0%, respectively. These attractive features of BT@PTFEMA/PVDF composites suggested that dielectric ceramic fillers modified with fluorinated polymer can be used to prepare high performance composites, especially those with low dielectric loss and high dielectric constant.

  5. 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.

  6. 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.

  7. 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

  8. Size dependent nonlinear optical absorption in BaTiO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Woldu, Tesfakiros; Raneesh, B.; Sreekanth, P.; Ramana Reddy, M. V.; Philip, Reji; Kalarikkal, Nandakumar

    2015-04-01

    We present nonlinear optical absorption properties of BaTiO3 nanoparticles of different sizes prepared by the modified polymer precursor method. Structural properties of the samples were characterized using XRD and TEM, and optical properties by UV-visible light absorption. Nonlinear optical properties of the samples were measured by the single-beam open aperture Z-scan technique using 5 ns laser pulses at 532 nm. Results show that all samples exhibit a size dependent nonlinear optical response. Optical limiting efficiency increases with grain size and has a strong dependence on the structural phase of the particles. Nonlinear optical absorption is found to be enhanced when the particles undergo a transition from the cubic to the tetragonal phase.

  9. Contradictory nature of Co doping in ferroelectric BaTiO3

    DOE PAGES

    Ponath, Patrick; O’Hara, Andrew; Cao, Hai-Xia; ...

    2016-11-11

    The growth of Co-substituted BaTiO3 (BTO) films on Ge(001) substrates by molecular beam epitaxy is demonstrated in this paper. Energy-dispersive x-ray spectroscopy and transmission electron microscopy images confirm the uniform Co distribution. However, no evidence of magnetic ordering is observed in samples grown for Co concentrations between 2% and 40%. Piezoresponse force microscopy measurements show that a 5% Co-substituted BTO sample exhibits ferroelectric behavior. First-principles calculations indicate that while Co atoms couple ferromagnetically in the absence of oxygen vacancies, the occurrence of oxygen vacancies leads to locally antiferromagnetically coupled complexes with relatively strong spin coupling. Finally, the presence of amore » significant amount of oxygen vacancies is suggested by x-ray photoelectron spectroscopy measurements.« less

  10. Imprint control of BaTiO3 thin films via chemically induced surface polarization pinning

    DOE PAGES

    Lee, Hyungwoo; Kim, Tae Heon; Patzner, Jacob J.; ...

    2016-02-22

    Surface-adsorbed polar molecules can significantly alter the ferroelectric properties of oxide thin films. Thus, fundamental understanding and controlling the effect of surface adsorbates are crucial for the implementation of ferroelectric thin film devices, such as ferroelectric tunnel junctions. Herein, we report an imprint control of BaTiO3 (BTO) thin films by chemically induced surface polarization pinning in the top few atomic layers of the water-exposed BTO films. Our studies based on synchrotron X-ray scattering and coherent Bragg rod analysis demonstrate that the chemically induced surface polarization is not switchable but reduces the polarization imprint and improves the bistability of ferroelectric phasemore » in BTO tunnel junctions. Here, we conclude that the chemical treatment of ferroelectric thin films with polar molecules may serve as a simple yet powerful strategy to enhance functional properties of ferroelectric tunnel junctions for their practical applications.« less

  11. 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.

  12. Imprint Control of BaTiO3 Thin Films via Chemically Induced Surface Polarization Pinning.

    PubMed

    Lee, Hyungwoo; Kim, Tae Heon; Patzner, Jacob J; Lu, Haidong; Lee, Jung-Woo; Zhou, Hua; Chang, Wansoo; Mahanthappa, Mahesh K; Tsymbal, Evgeny Y; Gruverman, Alexei; Eom, Chang-Beom

    2016-04-13

    Surface-adsorbed polar molecules can significantly alter the ferroelectric properties of oxide thin films. Thus, fundamental understanding and controlling the effect of surface adsorbates are crucial for the implementation of ferroelectric thin film devices, such as ferroelectric tunnel junctions. Herein, we report an imprint control of BaTiO3 (BTO) thin films by chemically induced surface polarization pinning in the top few atomic layers of the water-exposed BTO films. Our studies based on synchrotron X-ray scattering and coherent Bragg rod analysis demonstrate that the chemically induced surface polarization is not switchable but reduces the polarization imprint and improves the bistability of ferroelectric phase in BTO tunnel junctions. We conclude that the chemical treatment of ferroelectric thin films with polar molecules may serve as a simple yet powerful strategy to enhance functional properties of ferroelectric tunnel junctions for their practical applications.

  13. Magnetic properties of self-assembled Fe nanoislands on BaTiO3(001)

    NASA Astrophysics Data System (ADS)

    Govind, R. K.; Hari Babu, V.; Chiang, C.-T.; Magnano, E.; Bondino, F.; Denecke, R.; Schindler, K.-M.

    2013-11-01

    The coercivity and saturation magnetization of ultrathin films of Fe on a BaTiO3(001) single crystal substrate have been determined using magneto-optic Kerr effect (MOKE) and X-ray magnetic circular dichroism (XMCD) as a function of annealing temperature. Films deposited at room temperature exhibit bulk-like properties, whereas with increasing annealing temperature coercivity increases and saturation magnetization decreases. Investigations with scanning electron microscopy (SEM) and low-energy electron diffraction (LEED) reveal that annealing causes a morphology transformation from a continuous flat film, which completely covers the substrate, to nanoislands via self-assembled growth. The morphology and size of the islands imply stronger pinning of domain walls or complex magnetic structures as the origin of their particular magnetic properties.

  14. 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.

  15. Tuning the caloric response of BaTiO3 by tensile epitaxial strain

    NASA Astrophysics Data System (ADS)

    Grünebohm, Anna; Marathe, Madhura; Ederer, Claude

    2016-08-01

    We investigate the effect of epitaxial strain on the electrocaloric effect (ECE) in BaTiO3 by means of ab-initio-based molecular-dynamics simulations. We show that tensile strain can be used to optimize the operation range for ferroic cooling. Strain in the range of ≤ 1% can be used to shift the operation temperature by several hundreds of kelvin both to higher and lower temperatures, depending on the direction of the external field. In addition, the transformation between multi-domain and mono-domain states, induced by an in-plane electric field, results in an additional peak of the adiabatic temperature change at lower temperatures, and a broad temperature interval where the caloric response scales linearly with the applied field strength, even up to very high fields.

  16. Significantly Enhanced Energy Storage Density by Modulating the Aspect Ratio of BaTiO3 Nanofibers

    NASA Astrophysics Data System (ADS)

    Zhang, Dou; Zhou, Xuefan; Roscow, James; Zhou, Kechao; Wang, Lu; Luo, Hang; Bowen, Chris R.

    2017-03-01

    There is a growing need for high energy density capacitors in modern electric power supplies. The creation of nanocomposite systems based on one-dimensional nanofibers has shown great potential in achieving a high energy density since they can optimize the energy density by exploiting both the high permittivity of ceramic fillers and the high breakdown strength of the polymer matrix. In this paper, BaTiO3 nanofibers (NFs) with different aspect ratio were synthesized by a two-step hydrothermal method and the permittivity and energy storage of the P(VDF-HFP) nanocomposites were investigated. It is found that as the BaTiO3 NF aspect ratio and volume fraction increased the permittivity and maximum electric displacement of the nanocomposites increased, while the breakdown strength decreased. The nanocomposites with the highest aspect ratio BaTiO3 NFs exhibited the highest energy storage density at the same electric field. However, the nanocomposites with the lowest aspect ratio BaTiO3 NFs achieved the maximal energy storage density of 15.48 J/cm3 due to its higher breakdown strength. This contribution provides a potential route to prepare and tailor the properties of high energy density capacitor nanocomposites.

  17. Significantly Enhanced Energy Storage Density by Modulating the Aspect Ratio of BaTiO3 Nanofibers.

    PubMed

    Zhang, Dou; Zhou, Xuefan; Roscow, James; Zhou, Kechao; Wang, Lu; Luo, Hang; Bowen, Chris R

    2017-03-23

    There is a growing need for high energy density capacitors in modern electric power supplies. The creation of nanocomposite systems based on one-dimensional nanofibers has shown great potential in achieving a high energy density since they can optimize the energy density by exploiting both the high permittivity of ceramic fillers and the high breakdown strength of the polymer matrix. In this paper, BaTiO3 nanofibers (NFs) with different aspect ratio were synthesized by a two-step hydrothermal method and the permittivity and energy storage of the P(VDF-HFP) nanocomposites were investigated. It is found that as the BaTiO3 NF aspect ratio and volume fraction increased the permittivity and maximum electric displacement of the nanocomposites increased, while the breakdown strength decreased. The nanocomposites with the highest aspect ratio BaTiO3 NFs exhibited the highest energy storage density at the same electric field. However, the nanocomposites with the lowest aspect ratio BaTiO3 NFs achieved the maximal energy storage density of 15.48 J/cm(3) due to its higher breakdown strength. This contribution provides a potential route to prepare and tailor the properties of high energy density capacitor nanocomposites.

  18. Significantly Enhanced Energy Storage Density by Modulating the Aspect Ratio of BaTiO3 Nanofibers

    PubMed Central

    Zhang, Dou; Zhou, Xuefan; Roscow, James; Zhou, Kechao; Wang, Lu; Luo, Hang; Bowen, Chris R.

    2017-01-01

    There is a growing need for high energy density capacitors in modern electric power supplies. The creation of nanocomposite systems based on one-dimensional nanofibers has shown great potential in achieving a high energy density since they can optimize the energy density by exploiting both the high permittivity of ceramic fillers and the high breakdown strength of the polymer matrix. In this paper, BaTiO3 nanofibers (NFs) with different aspect ratio were synthesized by a two-step hydrothermal method and the permittivity and energy storage of the P(VDF-HFP) nanocomposites were investigated. It is found that as the BaTiO3 NF aspect ratio and volume fraction increased the permittivity and maximum electric displacement of the nanocomposites increased, while the breakdown strength decreased. The nanocomposites with the highest aspect ratio BaTiO3 NFs exhibited the highest energy storage density at the same electric field. However, the nanocomposites with the lowest aspect ratio BaTiO3 NFs achieved the maximal energy storage density of 15.48 J/cm3 due to its higher breakdown strength. This contribution provides a potential route to prepare and tailor the properties of high energy density capacitor nanocomposites. PMID:28332636

  19. Two-wave mixing and energy transfer in BaTiO3 application to laser beamsteering

    NASA Astrophysics Data System (ADS)

    Rak, D.; Ledoux, I.; Huignard, J. P.

    1984-03-01

    Energy transfer between the two recording beams in a BaTiO3 photorefractive crystal is analyzed as a function of the following parameters: incident beams ratio, spatial frequency, pump beam intensity. Exponential gain coefficients of approximately 20/cm are reached for optimized holographic recording conditions. Application of the energy transfer to a new method of laser beam deflection is proposed.

  20. 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.

  1. First-Principles Calculation of Solution Energy of Alkaline-Earth Metal Elements to BaTiO3

    NASA Astrophysics Data System (ADS)

    Moriwake, Hiroki; Hirayama, Tsukasa; Ikuhara, Yuichi; Tanaka, Isao

    2007-10-01

    Quantitative analysis of the solution energy of alkaline-earth metal elements to perovskite-type BaTiO3 was carried out by a first-principles calculation combined with thermodynamics theory. The solution energies of neutral solute and a compensated solute with an oxygen vacancy were systematically calculated. They were obtained for two cation sites and four thermodynamical conditions with different chemical potentials of constituent atoms. Both Ca and Sr preferably occupy the Ba site of BaTiO3. On the other hand, Mg occupies the Ti site. This corresponds well to the widely accepted experimental findings regarding site preference. Moreover, under the condition of coexising BaO, CaO and BaTiO3, energy difference between the Ba-site solution and O-vacancy compensated Ti-site solution of Ca ions has been found to be smaller than that of Sr. Under this condition, the O-vacancy compensated Ti-site solution of Ca should be favorable compared with that of Sr. The same number of oxygen vacancies as Ca ions occupying Ti sites can be introduced. This also explains well experimental feature of the Ca-doped BaTiO3-based nonreducible multilayer ceramics capacitor (MLCC) materials regarding solution site of the Ca ion and abundance of O-vacancy.

  2. BaTiO3 integration with nanostructured epitaxial (100), (110), and (111) germanium for multifunctional devices.

    PubMed

    Hudait, Mantu K; Zhu, Yan; Jain, Nikhil; Maurya, Deepam; Zhou, Yuan; Varghese, Ron; Priya, Shashank

    2013-11-13

    Ferroelectric-germanium heterostructures have a strong potential for multifunctional devices. Germanium (Ge) is attractive due to its higher electron and hole mobilities while ferroelectric BaTiO3 is promising due to its high relative permittivity, which can make next-generation low-voltage and low-leakage metal-oxide semiconductor field-effect transistors. Here, we investigate the growth, structural, chemical, and band alignment properties of pulsed laser deposited BaTiO3 on epitaxial (100)Ge, (110)Ge, and (111)Ge layers. Cross-sectional transmission electron microscopy micrographs show the amorphous nature of the BaTiO3 layer and also show a sharp heterointerface between BaTiO3 and Ge. The appearance of strong Pendellösung oscillation fringes from high-resolution X-ray diffraction implies the presence of parallel and sharp heterointerfaces. The valence band offset relation of ΔEV(100) ≥ ΔEV(111) > ΔEV(110) and the conduction band offset relation of ΔE(C)(110) > ΔE(C)(111) ≥ ΔE(C)(100) on crystallographically oriented Ge offer significant advancement for designing new-generation ferroelectric-germanium-based multifunctional devices.

  3. Magnetic and electrical properties of CuFe2O4/BaTiO3 bilayer thin films

    NASA Astrophysics Data System (ADS)

    Yoon, Dong Jin; Hwang, Sung-Ok; Koo, Chang Young; Lee, Jai-Yeoul; Lee, Hee Young; Ryu, Jungho

    2013-04-01

    The magnetic and the electrical properties of CuFe2O4/BaTiO3 thin films grown on highly-textured Pt(111)/TiO2/SiO2/Si(100) substrates were studied. Sintered BaTiO3 and CuFe2O4 pellets prepared by the conventional mixed oxide process were used as targets during deposition by using the ion-beam sputtering and the pulsed laser deposition techniques. The film structure is of a bilayer type, where the BaTiO3 layer lies underneath the CuFe2O4 layer. The CuFe2O4/BaTiO3 film stack was then annealed at a temperature between 700 and 750 °C, followed by either FC (fast-cooling) or SC (slow-cooling) treatment. The ferroelectric and the electrical properties were measured using a ferroelectric test system, a digital multimeter, and an impedance analyzer. The Magnetic hysteresis (M-H) behavior at room temperature was measured using a vibration sample magnetometer (VSM), and the maximum saturation magnetization ( M s ) and coercivity ( H c ) values were 700 emu/cm3 and 325 Oe, respectively.

  4. Strain mediated magnetoelectric coupling in a NiFe2O4-BaTiO3 multiferroic composite

    NASA Astrophysics Data System (ADS)

    Gorige, Venkataiah; Kati, Raju; Yoon, D. H.; Kumar, P. S. Anil

    2016-10-01

    In this paper we demonstrate significant magnetoelectric coupling in ferrimagnetic, NiFe2O4, and ferroelectric, BaTiO3, multiferroic composite bulk materials by measuring temperature dependent magnetization. X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy data show that the two phases coexist with a highly crystalline and sharp interface without any detectable impurities, which enables significant magnetoelectric (ME) coupling. The temperature dependent magnetization data of the composite clearly show the jumps in magnetization curves at the structural phase transitions of BaTiO3, thereby indicating their origin in ME coupling. The change in coercivity of composite sample in different ferroelectric phases of BaTiO3 has been observed compared to the NiFe2O4 sample. The different lattice strains corresponding to different ferroelectric phases of BaTiO3 could be the driving force for modulating the magnetization and coercivity of the composite material. This is clear evidence of strain mediated ME coupling in ferrimagnetic and ferroelectric composite materials.

  5. Enhanced strain effect of aged acceptor-doped BaTiO3 ceramics with clamping domain structures

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Zhou, Zhiyong; Zhao, Xiaobo; Liu, Zhen; Liang, Ruihong; Dong, Xianlin

    2017-03-01

    A clamping domain structure is proposed to improve the amount of non-180° domain switching in BaTiO3 based piezoelectric ceramics. Experimental results show a large unipolar strain of 0.23% at 5 kV/mm in aged 0.5 mol. % Mn doped BaTiO3 ceramics with clamping domain structures, and the normalized strain (d33*= Smax/Emax) reaches 600 pm/V at low electric fields of 2 or 3 kV/mm. In contrast, pure BaTiO3 ceramics with clamping domain structures exhibit no clear polarization constriction or strain enhancement at 3 kV/mm. Electron paramagnetic resonance spectra verify the existence of titanium vacancies, Mn2+ and Mn4+, in 0.5 mol. % Mn doped BaTiO3 ceramics. These results indicate that the enhanced strain effect can be attributed to the combined effect of the clamping domain structure and stabilization of defect dipoles. This method provides a general way to obtain large strain in ferroelectrics.

  6. Ferroelectric BaTiO3 dipole induced charge transfer enhancement in dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Feng, Keyuan; Liu, Xiaoyan; Si, Donghui; Tang, Xiao; Xing, An; Osada, Minoru; Xiao, Peng

    2017-05-01

    BaTiO3/TiO2 nanocomposite films with varied amount of BaTiO3 are fabricated and applied as photoanodes for dye-sensitized solar cells (DSCs) and demonstrated enhanced power conversion efficiency. Ferroelectricity of BaTiO3 in the film after subjected to a annealing process up to 450 °C is examined by Switching Spectroscopy Piezoresponse Force Microscopy (SSPFM). The highest performance is achieved in 1.0 wt% BaTiO3 addition as a result of increased photocurrent density (Jsc) and fill factor (FF), regardless of reduction of dye-loading. Electrochemical impedance spectroscopy (EIS) measurements at different bias voltages (≦Voc) in dark suggest that ferroelectric dipole induced electric field has positive effects on enhancing electron mobility and suppressing charge recombination. Although more detailed experiments are needed in designing of the nanocomposite films for compensating characteristics of dye-loading and electron mobility, introduction of ferroelectric dipole induced electric field into the photoanode would be a good strategy in achieving further improvement of power conversion efficiency of DSCs through improved charge transfer properties.

  7. Influences of annealing temperature on structural characterization and magnetic properties of Mn-doped BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Phan, The-Long; Zhang, P.; Grinting, D.; Yu, S. C.; Nghia, N. X.; Dang, N. V.; Lam, V. D.

    2012-07-01

    Polycrystalline samples of BaTiO3 doped with 2.0 at. % Mn were prepared by solid-state reaction at various temperatures (Tan) ranging from 500 to 1350 °C, used high-pure powders of BaCO3, TiO2, and MnCO3 as precursors. Experimental results obtained from x-ray diffraction patterns and Raman scattering spectra reveal that tetragonal Mn-doped BaTiO3 starts constituting as Tan ≈ 500 °C. The Tan increase leads to the development of this phase. Interestingly, there is the tetragonal-hexagonal transformation in the crystal structure of BaTiO3 as Tan ≈ 1100 °C. Such the variations influence directly magnetic properties of the samples. Besides paramagnetic contributions of Mn2+ centers traced to electron spin resonance, the room-temperature ferromagnetism found in the samples is assigned to exchange interactions taking place between Mn3+ and Mn4+ ions located in tetragonal BaTiO3 crystals.

  8. Local structural investigation of Eu(3+)-doped BaTiO3 nanocrystals.

    PubMed

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

    2014-03-07

    A structural investigation of sub-15 nm xEu:BaTiO3 nanocrystals (x = 0-5 mol%) was conducted to determine the distribution of the Eu(3+) 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 Eu(3+) ion. The solubility limit of the Eu(3+) 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 Eu(3+) for Ba(2+)via creation of a Ti(4+) vacancy at low europium concentrations (<1 mol%), and with the substitution of Eu(3+) for both Ba(2+) and Ti(4+) 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.

  9. Stabilisation des phases monocristallines quadratique et cubique dans BaTiO3

    NASA Astrophysics Data System (ADS)

    Amami, J.; Goutaudier, C.; Trabelsi-Ayadi, M.; Boulon, G.

    2004-12-01

    Single crystals of Ba1-xYbxTiO3 and Ba1-xSrxTiO3 with tetragonal structure were grown by the floating zone (FZ) method using an LHPG (Laser Heated Pedestal Growth) technique. The grown crystals, typically 1 mm in diameter and 8 mm in length, were yellowish transparent. Substitution of more than 2.5 at % Sr for Ba in BaTiO3 and addition of 3 to 5 at % Ln (Ln= Yb, Eu), were effective in preventing the formation of the hexagonal phase. The Eu3+ emission spectra recorded at room temperature demonstrate a significant intensity enhancement of the 5D0 → 7F1 magnetic dipolar transition compared to the 5D0 → 7F2 electric dipolar transition. Les fibres monocristallines de Ba1-xYbxTiO3 et Ba1-xSrxTiO3 de structure quadratique ont été préparées par la méthode de la zone flottante (FZ) en utilisant la technique LHPG (Laser Heated Pedestal Growth). Les échantillons élaborés, de dimensions 1mm x 8 mm, sont jaunâtres et transparentes. La substitution du baryum par plus de 2,5 mol% de Sr dans BaTiO3 et le dopage de 3 à 5 mol% de Ln (Ln = Yb, Eu) évitent la formation de la phase hexagonale. Le spectre d’émission de Eu3+ enregistré à température ambiante montre le changement de structure traduit par la forte intensité de la transition dipolaire magnétique 5D0 → 7F1 comparée à celle de la transition dipolaire électrique 5D0 → 7F2.

  10. 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.

  11. Tailoring the structure and thermoelectric properties of BaTiO3via Eu(2+) substitution.

    PubMed

    Xiao, Xingxing; Widenmeyer, Marc; Xie, Wenjie; Zou, Tianhua; Yoon, Songhak; Scavini, Marco; Checchia, Stefano; Zhong, Zhicheng; Hansmann, Philipp; Kilper, Stefan; Kovalevsky, Andrei; Weidenkaff, Anke

    2017-05-31

    A series of Ba1-xEuxTiO3-δ (0.1 ≤ x ≤ 0.9) phases with ∼40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu(2+) substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 Å (equal to ∼5 unit cells) deviations from the cubic structure model (Pm3[combining macron]m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3-δ. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along 〈110〉 of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1-xEuxTiO3-δ. From the obtained density of states a significant reduction of the band gap by the presence of filled Eu(2+) 4f states at the top of the valence band was observed. The physical property measurements revealed that barium-europium titanates exhibit n-type semiconducting behavior and at high temperature the electrical conductivity strongly depended on the Eu(2+) content. Activation energies calculated from the electrical conductivity and Seebeck coefficient data indicate that at high temperatures (800 K < T < 1123 K) the conduction mechanism of Ba1-xEuxTiO3-δ (0.1 ≤ x ≤ 0.9) is a polaron hopping when 0 < x ≤ 0.6 and is a thermally activated process when 0.6 < x < 1. Besides, the thermal conductivity increases with increasing Eu(2+) concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3-δ showed a ZT value of 0.24 at 1123 K.

  12. 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.

  13. DFT study of BaTiO3 (001) surface with O and O2 adsorption

    NASA Astrophysics Data System (ADS)

    Rakotovelo, G.; Moussounda, P. S.; Haroun, M. F.; Légaré, P.; Rakotomahevitra, A.; Parlebas, J. C.

    2007-06-01

    Progress of scanning tunneling microscopy (STM) allowed to handle various molecules adsorbed on a given surface. New concepts emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces and adsorbed molecules at an atomic scale is thus particularly invaluable. In this work, within the framework of density functional theory (DFT), we present an electronic and structural ab initio study of a BaTiO3 (001) surface (perovskite structure) in its paraelectric phase. As far as we know the atomic and molecular adsorption of oxygen at surface is then analyzed for the first time in the literature. Relaxation is taken into account for several layers. Its analysis for a depth of at least four layers enables us to conclude that a reasonable approximation for a BaTiO3 (001) surface is provided with a slab made up of nine plans. The relative stability of two possible terminations is considered. By using a kinetic energy cut off of 400 eV, we found that a surface with BaO termination is more stable than with TiO2 termination. Consequently, a surface with BaO termination was chosen to adsorb either O atom or O2 molecule and the corresponding calculations were performed with a coverage 1 on a (1×1) cell. A series of cases with O2 molecule adsorbed in various geometrical configurations are also analyzed. For O2, the most favorable adsorption is obtained when the molecule is placed horizontally, with its axis, directed along the Ba-Ba axis and with its centre of gravity located above a Ba atom. The corresponding value of the adsorption energy is -9.70 eV per molecule (-4.85 eV per O atom). The molecule is then rather extended since the O O distance measures 1.829 Å. By comparison, the adsorption energy of an O atom directly located above a Ba atom is only -3.50 eV. Therefore we are allowed to conclude that the O O interaction stabilizes atomic adsorption. Also the local densities of states (LDOS) corresponding to various situations are discussed in the present paper. Up to now, we are not aware of experimental data to be compared to our calculated results.

  14. Dielectric Properties of BaTiO3 Codoped with Er2O3 and MgO

    NASA Astrophysics Data System (ADS)

    Hwang, Jin Hyun; Choi, Sang Keun; Han, Young Ho

    2001-08-01

    The effect of Er2O3 and MgO addition on the dielectric properties of BaTiO3 ceramics was studied in a reduced atmosphere. MgO effectively prevented the material from being reduced and suppressed grain growth. An X7R material with moderate temperature dependence was developed by the addition of MgO with higher than 2.0 mol% Er2O3 to BaTiO3, which is ascribed to the decrease in grain size and the grain core-grain shell structure. In the presence of equimolar amount of B-site metal ions, there was no evidence to support the incorporation of Er ions into the octahedral and dodecahedral cation sites.

  15. Local control of magnetic anisotropy in transcritical permalloy thin films using ferroelectric BaTiO3 domains

    NASA Astrophysics Data System (ADS)

    Fackler, Sean W.; Donahue, Michael J.; Gao, Tieren; Nero, Paris N. A.; Cheong, Sang-Wook; Cumings, John; Takeuchi, Ichiro

    2014-11-01

    We investigated the local coupling between dense magnetic stripe domains in transcritical permalloy (tPy) thin films and ferroelectric domains of BaTiO3 single crystals in a tPy/BaTiO3 heterostructure. Two distinct changes in the magnetic stripe domains of tPy were observed from the magnetic force microscopy images after cooling the heterostructure from above the ferroelectric Curie temperature of BaTiO3 (120 °C) to room temperature. First, an abrupt break in the magnetic stripe domain direction was found at the ferroelectric a-c-domain boundaries due to an induced change in in-plane magnetic anisotropy. Second, the magnetic stripe domain period increased when coupled to a ferroelectric a-domain due to a change in out-of-plane magnetic anisotropy. Micromagnetic simulations reveal that local magnetic anisotropy energy from inverse magnetostriction is conserved between in-plane and out-of-plane components.

  16. 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.

  17. p-Electron Magnetism in anion doped BaTiO3-xXx (X=C,N,B)

    NASA Astrophysics Data System (ADS)

    Gruber, Christoph; Osvaldo Bedolla Velazquez, Pedro; Redinger, Josef; Mohn, Peter; Marsman, Martijn

    2012-02-01

    We present VASP calculations using the HSE functional for carbon, nitrogen, and boron doped BaTiO3-xXx (X=C,N,B). We calculate a 40-atom supercell and replace one oxygen atom by C,N, or B. For all three substituents we find a magnetically ordered groundstate which is insulating for C and N and halfmetallic for B. The changes in the electronic structure between the undoped and the doped case are dominated by the strong crystal field effects together with the large band splitting for the impurity p-bands. Using an MO picture we give an explanation for the pronounced changes in the electronic structure between the insulating non-magnetic state and the as well insulating magnetic state for doped BaTiO3. p-element doped perovskites could provide a new class of materials for various applications ranging from spin-electronics to magneto-optics.

  18. Accelerated search for BaTiO3-based piezoelectrics with vertical morphotropic phase boundary using Bayesian learning

    PubMed Central

    Xue, Dezhen; Balachandran, Prasanna V.; Yuan, Ruihao; Hu, Tao; Qian, Xiaoning; Dougherty, Edward R.; Lookman, Turab

    2016-01-01

    An outstanding challenge in the nascent field of materials informatics is to incorporate materials knowledge in a robust Bayesian approach to guide the discovery of new materials. Utilizing inputs from known phase diagrams, features or material descriptors that are known to affect the ferroelectric response, and Landau–Devonshire theory, we demonstrate our approach for BaTiO3-based piezoelectrics with the desired target of a vertical morphotropic phase boundary. We predict, synthesize, and characterize a solid solution, (Ba0.5Ca0.5)TiO3-Ba(Ti0.7Zr0.3)O3, with piezoelectric properties that show better temperature reliability than other BaTiO3-based piezoelectrics in our initial training data. PMID:27821777

  19. Microstructure and ferroelectricity of BaTiO3 thin films on Si for integrated photonics

    NASA Astrophysics Data System (ADS)

    Kormondy, Kristy J.; Popoff, Youri; Sousa, Marilyne; Eltes, Felix; Caimi, Daniele; Rossell, Marta D.; Fiebig, Manfred; Hoffmann, Patrik; Marchiori, Chiara; Reinke, Michael; Trassin, Morgan; Demkov, Alexander A.; Fompeyrine, Jean; Abe, Stefan

    2017-02-01

    Significant progress has been made in integrating novel materials into silicon photonic structures in order to extend the functionality of photonic circuits. One of these promising optical materials is BaTiO3 or barium titanate (BTO) that exhibits a very large Pockels coefficient as required for high-speed light modulators. However, all previous demonstrations show a noticable reduction of the Pockels effect in BTO thin films deposited on silicon substrates compared to BTO bulk crystals. Here, we report on the strong dependence of the Pockels effect in BTO thin films on their microstructure, and provide guidelines on how to engineer thin films with strong electro-optic response. We employ several deposition methods such as molecular beam epitaxy and chemical vapor deposition to realize BTO thin films with different morphology and crystalline structure. While a linear electro-optic response is present even in porous, polycrystalline BTO thin films with an effective Pockels coefficient r eff = 6 pm V-1, it is maximized for dense, tetragonal, epitaxial BTO films (r eff = 140 pm V-1). By identifying the key structural predictors of electro-optic response in BTO/Si, we provide a roadmap to fully exploit the linear electro-optic effect in novel hybrid oxide/semiconductor nanophotonic devices.

  20. Interactions between Mn dopant and oxygen vacancy for insulation performance of BaTiO3

    NASA Astrophysics Data System (ADS)

    Chikada, Shunsuke; Kubota, Teppei; Honda, Atsushi; Higai, Shin'ichi; Motoyoshi, Yasuhiro; Wada, Nobuyuki; Shiratsuyu, Kosuke

    2016-10-01

    We performed first-principles calculations and electron spin resonance (ESR) measurements on Mn-doped perovskite BaTiO3 (BT) ceramics in order to investigate the interactions between Mn dopant and O vacancy (VO). We discovered the following two. First, VOs are stabilized at the nearest neighbor O site of Mn at a Ti site and this results in the suppression of VO diffusion. Second, electrons generated by the formation of VOs are trapped in unoccupied Mn-3d orbitals in the BT bandgap. This indicates that the valence state of Mn changes according to the VO density. We synthesized Mn-doped BT by varying the partial pressure of O2 gas and examined the Mn valence states with ESR measurements. We successfully observed that the majority type of Mn ions (2+, 3+, and 4+) depends on O2 gas pressure of the firing atmosphere. According to these theoretical and experimental investigations, we concluded that Mn dopants have two effects, i.e., VO and electron carrier trapping. Moreover, the mechanisms of Mn doping in BT improved the insulation resistance, and the reliability of BT-based ceramic capacitors/condensers were thoroughly examined.

  1. 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.

  2. Structural, Magnetic and Dielectric Properties of Fe-DOPED BaTiO3 Solids

    NASA Astrophysics Data System (ADS)

    Guo, Zhengang; Yang, Lihong; Qiu, Hongmei; Zhan, Xuedan; Yin, Jinhua; Cao, Lipeng

    The structural, ferroelectric and magnetic properties of bulk perovskite Fe-doped BaTiO3 (BFTO) prepared by standard solid-state reaction have been investigated. X-ray diffraction (XRD) identifies the tetragonal structure of BFTO samples. Rietveld refinements of XRD data indicates that the doping ions led to ab-plane expansion and out-of-ab-plane shrinkage of the BFTO phases. X-ray photoelectron spectroscopy (XPS) measurements for the prepared samples reveals that Fe3+ and Fe4+ ions replaces Ti4+ ions in the crystal lattice to form single-phase BFTO solids. The results of the temperature-dependent dielectric properties and magnetic hysteresis loops for the BFTO solids show simultaneously the ferroelectric order and ferromagnetic order at room temperature. The doping of magnetic element Fe brings about ferromagnetic order for the samples, and the measured magnetic moment for each Fe atom increases from 0.70 μB to 1.55 μB in BFTO samples. The origin of ferromagnetism of the BFTO samples should be attributed to the double exchange interactions of Fe3+-O2-Fe4+ ions.

  3. Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3

    DOE PAGES

    Chen, F.; Zhu, Y.; Liu, S.; ...

    2016-11-22

    The dynamical processes associated with electric field manipulation of the polarization in a ferroelectric remain largely unknown but fundamentally determine the speed and functionality of ferroelectric materials and devices. Here in this paper we apply subpicosecond duration, single-cycle terahertz pulses as an ultrafast electric field bias to prototypical BaTiO3 ferroelectric thin films with the atomic-scale response probed by femtosecond x-ray-scattering techniques. We show that electric fields applied perpendicular to the ferroelectric polarization drive large-amplitude displacements of the titanium atoms along the ferroelectric polarization axis, comparable to that of the built-in displacements associated with the intrinsic polarization and incoherent across unitmore » cells. This effect is associated with a dynamic rotation of the ferroelectric polarization switching on and then off on picosecond time scales. These transient polarization modulations are followed by long-lived vibrational heating effects driven by resonant excitation of the ferroelectric soft mode, as reflected in changes in the c-axis tetragonality. The ultrafast structural characterization described here enables a direct comparison with first-principles-based molecular-dynamics simulations, with good agreement obtained.« less

  4. Ab initio study of the BaTiO3/Ge interface

    NASA Astrophysics Data System (ADS)

    Dogan, Mehmet; Ismail-Beigi, Sohrab

    2017-08-01

    We present a comprehensive first-principles study of BaTiO3 ultrathin films epitaxially grown on Ge(001). We recently reported on the experimental realization of this system and analyzed the 2 ×1 structural distortions in the BTO thin film which may give rise to technologically relevant functional properties [D. P. Kumah et al., Phys. Rev. Lett. 116, 106101 (2016), 10.1103/PhysRevLett.116.106101]. In this work, we describe the structural and electronic properties of the experimentally observed interface configuration, as well as a distinct metastable interface configuration with a higher out-of-plane polarization. We show that these two distinct interface structures can be made energetically degenerate by choosing a top electrode with an appropriate work function, thus enabling, in principle, an epitaxial ferroelectric thin film oxide. We analyze the interface chemistry and electronic structure and show that in the two polarization states the bands align differently, indicating a strong ferroelectric field effect. We also show that, surprisingly, in the intrinsic limit for the semiconductor, switching the oxide polarization state can cause the dominant charge carrier to switch between electrons and holes. The coupling of ferroelectric switching in the oxide with charge carrier type modulation in the semiconductor may have novel technological applications.

  5. Soft-mode spectroscopy in cubic BaTiO3 by hyper-Raman scattering

    NASA Astrophysics Data System (ADS)

    Vogt, H.; Sanjurjo, J. A.; Rossbroich, G.

    1982-11-01

    Hyper-Raman scattering from cubic BaTiO3 is studied to clarify the controversies about the low-frequency dielectric response in this material. Applying the fluctuation-dissipation theorem, we obtain the imaginary part ɛ''(Ω) of the dielectric function in the wave-number range from 3 to 150 cm-1. ɛ''(Ω) can be adequately described by a classical single-oscillator dispersion formula. In approaching the Curie temperature, we find a continuous decrease of the mode frequency Ω0. The relative damping constant γΩ0 exceeds 2, so that the mode may be referred to as intermediate between oscillator and relaxator. Because of the high damping ɛ''(Ω) can be formally written as the sum of two overdamped oscillator contributions. This would lead to the concept of a soft-mode saturation and an extra dispersion mechanism as has been recently inferred from the far-infrared reflectivity spectrum. However, we do not find any evidence for this mode splitting and, so far, regard it as artificial.

  6. Phase transitions in BaTiO3 under uniaxial compressive stress: Experiments and phenomenological analysis

    NASA Astrophysics Data System (ADS)

    Schader, Florian H.; Khakpash, Nasser; Rossetti, George A.; Webber, Kyle G.

    2017-02-01

    The relative permittivity of polycrystalline BaTiO3 was measured from -150 °C to 250 °C at compressive bias stresses up to -500 MPa. Mechanical loading shifted the rhombohedral-orthorhombic, orthorhombic-tetragonal, and tetragonal-cubic phase transition temperatures and produced a pronounced broadening of the dielectric softening in the vicinity of all three transitions. The inter-ferroelectric rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions were found to be less stress sensitive than the ferroelectric-paraelectric transition occurring between tetragonal and cubic phases at the Curie point. The application of compressive stress resulted in a strong suppression of the relative permittivity, such that at the highest applied stress of -500 MPa, the permittivity in the single phase regions away from the phase transitions was found to display only a weak dependence on temperature between -100 °C and 125 °C. The experimental observations closely followed the predictions of a 2-4-6 Landau polynomial wherein the dielectric stiffness and higher-order dielectric stiffness coefficients are linear functions of uniaxial stress.

  7. Electrical and magnetic properties of hexagonal BaTiO3-δ

    NASA Astrophysics Data System (ADS)

    Kolodiazhnyi, T.; Belik, A. A.; Wimbush, S. C.; Haneda, H.

    2008-02-01

    The electrical resistivity, Hall coefficient, and magnetic susceptibility of n -type hexagonal BaTiO3-δ (hex-BaTiO3-δ) have been measured in the 5-400K temperature range. Above 200K this compound undergoes a transition from an insulating to a semiconducting state. Below 140K Hall effect data indicate the existence of an energy gap of approximately 43meV separating the localized electron ground state from the conduction band. Magnetic measurements reveal a strong magnetic anomaly in hex-BaTiO3-δ with a maximum in the susceptibility at around 160-200K . This anomaly is quite similar to that of the hexagonal BaMg1/3Ru2/3O3 which may indicate that the electron ground state in hex-BaTiO3-δ is comprised of spin singlet Ti3+-Ti3+ dimers. We further propose that the thermal dissociation of these dimers is responsible for the change in the electron transport mechanism in hex-BaTiO3-δ .

  8. Dielectric relaxation behavior of acceptor (Mg)-doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Kwon, Sang-Hoon; Hur, Kang-Heon

    2011-04-01

    Dielectric relaxation behavior of acceptor (Mg)-doped BaTiO3 ceramics was investigated with the increase of Mg concentration up to 0.6 mol. % in the temperature rang of 120 ˜ 540 °C. In the high temperature range above 320 °C, the activation energies of dielectric relaxation (Eτ) showed nearly similar values of ˜ 1.2 eV irrespective of Mg concentration. However, in the low temperature range below 320 °C, they continuously decreased from ˜ 1.2 eV and then saturated to ˜ 0.4 eV with the increase of Mg concentration. The activation energies of electrical conduction (Eσ) of the bulk grain evaluated by impedance analysis also showed almost the same behavior. Such coincidence demonstrates that the observed dielectric behaviors are caused by the space charge polarization at grain boundaries by conducting charge carriers. The disappearance of the dielectric relaxation in submicrometer fine-grain specimen also supports this mechanism. The variation of Eτ and Eσ with the increase of Mg concentration in the low temperature range was supposed to be caused by the dominant hopping conduction between ionized acceptor (MgTi″) and neutral or hole-trapped acceptor (MgTi×).

  9. Microstructure and ferroelectricity of BaTiO3 thin films on Si for integrated photonics.

    PubMed

    Kormondy, Kristy J; Popoff, Youri; Sousa, Marilyne; Eltes, Felix; Caimi, Daniele; Rossell, Marta D; Fiebig, Manfred; Hoffmann, Patrik; Marchiori, Chiara; Reinke, Michael; Trassin, Morgan; Demkov, Alexander A; Fompeyrine, Jean; Abel, Stefan

    2017-02-17

    Significant progress has been made in integrating novel materials into silicon photonic structures in order to extend the functionality of photonic circuits. One of these promising optical materials is BaTiO3 or barium titanate (BTO) that exhibits a very large Pockels coefficient as required for high-speed light modulators. However, all previous demonstrations show a noticable reduction of the Pockels effect in BTO thin films deposited on silicon substrates compared to BTO bulk crystals. Here, we report on the strong dependence of the Pockels effect in BTO thin films on their microstructure, and provide guidelines on how to engineer thin films with strong electro-optic response. We employ several deposition methods such as molecular beam epitaxy and chemical vapor deposition to realize BTO thin films with different morphology and crystalline structure. While a linear electro-optic response is present even in porous, polycrystalline BTO thin films with an effective Pockels coefficient r eff = 6 pm V(-1), it is maximized for dense, tetragonal, epitaxial BTO films (r eff = 140 pm V(-1)). By identifying the key structural predictors of electro-optic response in BTO/Si, we provide a roadmap to fully exploit the linear electro-optic effect in novel hybrid oxide/semiconductor nanophotonic devices.

  10. In situ studies on ferroelectric BaTiO3 interface

    NASA Astrophysics Data System (ADS)

    Shin, Junsoo; Braun Nascimento, Von; Plummer, Ward; Zhang, Jiandi; Borisevich, Albina; Meunier, Vincent; Kalinin, Sergei; Baddorf, Arthur

    2012-02-01

    Ferroelectric phase stability in ferroelectric films is critically dependent on the surface and interface phenomena, especially governed by electrostatic depolarization energy. Predictions for the minimum critical film thickness for ferroelectricity have continuously decreased down to few unit cells. We have examined surface/interface atomic structures of ultrathin BaTiO3 (BTO) films grown on conductive SrRuO3 (SRO) and Nb-doped SrTiO3. The surface structure of BTO/SRO was refined using in-situ Low Energy Electron Diffraction (LEED) I-V, resulting to observation of polar distortion in ultrathin (>= 4 ML) BTO films. The in-situ Scanning Tunneling Microscopy (STM) has been performed prior and after BTO deposition on SRO. However, the unusual 2x2 reconstruction is observed for 1-2 ML BTO films and bare SRO by STM. The surface reconstruction of SRO bottom electrode is shown to affect the interface of films deposited subsequently which could be reflected in ultrathin film properties. The in-situ LEED I-V structural studies on 1-2 ML BTO interface have been performed without SRO layer, which kept ultrathin BTO films from the preclusion of reconstructed SRO films.

  11. 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).

  12. BaTiO3-based nanolayers and nanotubes: first-principles calculations.

    PubMed

    Evarestov, Robert A; Bandura, Andrei V; Kuruch, Dmitrii D

    2013-01-30

    The first-principles calculations using hybrid exchange-correlation functional and localized atomic basis set are performed for BaTiO(3) (BTO) nanolayers and nanotubes (NTs) with the structure optimization. Both the cubic and the ferroelectric BTO phases are used for the nanolayers and NTs modeling. It follows from the calculations that nanolayers of the different ferroelectric BTO phases have the practically identical surface energies and are more stable than nanolayers of the cubic phase. Thin nanosheets composed of three or more dense layers of (0 1 0) and (0 1 1[overline]) faces preserve the ferroelectric displacements inherent to the initial bulk phase. The structure and stability of BTO single-wall NTs depends on the original bulk crystal phase and a wall thickness. The majority of the considered NTs with the low formation and strain energies has the mirror plane perpendicular to the tube axis and therefore cannot exhibit ferroelectricity. The NTs folded from (0 1 1[overline]) layers may show antiferroelectric arrangement of Ti-O bonds. Comparison of stability of the BTO-based and SrTiO(3)-based NTs shows that the former are more stable than the latter. Copyright © 2012 Wiley Periodicals, Inc.

  13. Atomic and electronic structure of the BaTiO3 -Ge (001) interface

    NASA Astrophysics Data System (ADS)

    Fredrickson, Kurt; Ponath, Patrick; Posadas, Agham; McCartney, Martha; Aoki, Toshihiro; Smith, David; Demkov, Alexander

    2014-03-01

    There is tremendous interest in putting perovskite oxides, such as SrTiO3 (STO) or BaTiO3 (BTO), on semiconductors due to their very high permitivitties. BTO can be grown directly on Ge using an approach similar to the growth of STO in Si. To date, very little is known about the atomic and electronic structure of the BTO-Ge interface. We use molecular beam epitaxy to grow BTO with in-plane polarization directly on Ge(001) using a Sr Zintl buffer layer. This results in an atomically flat, oxygen- and carbon-free Ge surface with very sharp (2x1) reconstruction as observed with reflection high energy electron diffraction. Using scanning transmission electron microscopy, we are able to precisely determine the atomic geometry of the interface, with the exception of the exact positions of the oxygen atoms. In situx-ray photoemission spectroscopy is used to analyze the oxidation state of the interfacial Ge and to determine the valence band offset at the interface. We use density functional theory to determine placement of interfacial O and calculate the valence band offset. The theoretical valence band offset is in good agreement with the photoemission data, strongly suggesting the correctness of the interface geometry. We calculate the effect of O vacancies and ionic substitution at the interfacial layer on the valence band offsets.

  14. Scale-bridging simulations of surfaces and defects in BaTiO3

    NASA Astrophysics Data System (ADS)

    Greco, Andrea; Tangney, Paul; Freeland, John; Mostofi, Arash

    2014-03-01

    BaTiO3 (BTO) is a ferroelectric perovskite oxide that is of particular interest in thin-film form for its technological application in tunable nanoelectronic devices. The dielectric properties of BTO thin films depend on many different factors, among which the presence of oxygen vacancies is believed to be one of the most important. Oxygen vacancies, however, are difficult to characterize directly in experiments and usually even their concentration is unknown. On the one hand, first-principles simulations based on density-functional theory (DFT) are invaluable for providing insight into the role of defects in materials and, in principle, could be used for the study of oxygen vacancies in BTO thin films. On the other hand, the large length and time-scales associated with structures and processes in realistic surfaces are well beyond the scope of DFT calculations. To overcome some of these limitations we use DFT in conjunction with a computationally efficient classical interatomic force field that has been fitted to DFT energies, forces and stresses in bulk BTO. We assess the transferability of this potential to defects and surfaces. We then use it to study the prevalence of oxygen vacancies and their structures, both in bulk BTO and near BTO surfaces. Support from the CDT in Theory and Simulation of Materials (Imperial College of London) and Argonne National Laboratory is thankfully acknowledged.

  15. Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Punugupati, Sandhyarani; Prater, John T.; Narayan, Jagdish

    2016-04-01

    We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO3 (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba0.4Sr0.6TiO3 (BST). The epitaxial integration of BST (˜800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A1TO3 mode (at 521.27 cm-1) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping.

  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. 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

  18. 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.

  19. Self-Pumped Phase-Conjugate Twyman-Green Interferometry Using a BaTiO3 Crystal

    DTIC Science & Technology

    1991-12-01

    mirrors without the need of additional high quality optics normally needed for this type of testing using conventional Twyman -Green interferometers ...conjugate interferometer is a highly sensitive test for collimation. vii SELF-PUMPED PHASE-CONJUGATE TWYMAN -GREEN INTERFEROMETRY USING A BaTiO 3...surfaces. Determining the quality of optical components by the use of interferometry was pioneered by Twyman in 1918, and the Twyman -Green interferometer

  20. The Effects of Spark-Plasma Sintering (SPS) on the Microstructure and Mechanical Properties of BaTiO3/3Y-TZP Composites

    PubMed Central

    Li, Jing; Cui, Bencang; Wang, Huining; Lin, Yuanhua; Deng, Xuliang; Li, Ming; Nan, Cewen

    2016-01-01

    Composite ceramics BaTiO3/3Y-TZP containing 0 mol %, 3 mol %, 5 mol %, 7 mol %, and 10 mol % BaTiO3 have been prepared by conventional sintering and spark-plasma sintering (SPS), respectively. Analysis of the XRD patterns and Raman spectra reveal that the phase composition of t-ZrO2, m-ZrO2, and BaTiO3 has been obtained. Our results indicate that SPS can be effective for the decrease in grain size and porosity compared with conventional sintering, which results in a lower concentration of m-ZrO2 and residual stress. Therefore, the fracture toughness is enhanced by the BaTiO3 phase through the SPS technique, while the behavior was impaired by the piezoelectric second phase through conventional sintering. PMID:28773445

  1. X-ray absorption fine structure analysis of molybdenum added to BaTiO3-based ceramics used for multilayer ceramic capacitors

    NASA Astrophysics Data System (ADS)

    Ogata, Yoichiro; Shimura, Tetsuo; Ryu, Minoru; Iwazaki, Yoshiki

    2017-04-01

    The effect of slight molybdenum doping of perovskite-type BaTiO3-based ceramics on the reliability of a multilayer ceramic capacitor (MLCC) and on the valence state of molybdenum in the BaTiO3-based ceramics has been investigated by highly accelerated lifetime tests and X-ray absorption fine structure analysis. The molybdenum added to the BaTiO3-based ceramics is located at Ti sites and improves the highly accelerated lifetime and lowers the initial dielectric resistivity in MLCCs. Through sintering in a reducing atmosphere, which is an important process in the fabrication of BaTiO3-based MLCCs, the oxidation state of the molybdenum added could be adjusted from +6 to a value close to +4.

  2. High ferroelectric polarization in c-oriented BaTiO3 epitaxial thin films on SrTiO3/Si(001)

    NASA Astrophysics Data System (ADS)

    Scigaj, M.; Chao, C. H.; Gázquez, J.; Fina, I.; Moalla, R.; Saint-Girons, G.; Chisholm, M. F.; Herranz, G.; Fontcuberta, J.; Bachelet, R.; Sánchez, F.

    2016-09-01

    The integration of epitaxial BaTiO3 films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO3/LaNiO3/SrTiO3 heterostructure is grown monolithically on Si(001). The BaTiO3 films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm2. This result paves the way towards the fabrication of lead-free BaTiO3 ferroelectric memories on silicon platforms.

  3. High dielectric constant associated with the strain-induced phase transition of an ordered assembly of BaTiO3 nanocubes under three-dimensional clamping

    NASA Astrophysics Data System (ADS)

    Yasui, Kyuichi; Mimura, Ken-ichi; Izu, Noriya; Kato, Kazumi

    2017-02-01

    Numerical calculations of the Gibbs function for an ordered assembly of BaTiO3 nanocubes (nanocrystals) under three-dimensional clamping have revealed that the phase transition from a tetragonal to cubic crystal structure can take place at room temperature at some misfit strain associated with a tilt angle of the attached nanocubes. The phase transition is second-order due to the three-dimensional clamping. Near and at the phase transition, the dielectric constant becomes extremely high owing to the second-order transition. This is considered to be the reason for the high dielectric constant of an assembly at room temperature, which has been experimentally observed. An ordered assembly of BaTiO3 nanocubes under rigid three-dimensional clamping is a completely different system from the normal nanocrystalline (polycrystalline) BaTiO3 ceramics under elastic clamping and from a BaTiO3 epitaxial thin film under two-dimensional clamping.

  4. High ferroelectric polarization in c-oriented BaTiO3 epitaxial thin films on SrTiO3/Si(001)

    DOE PAGES

    Scigaj, M.; Chao, C. H.; Gázquez, J.; ...

    2016-09-21

    The integration of epitaxial BaTiO3 films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO3/LaNiO3/SrTiO3 heterostructure is grown monolithically on Si(001). The BaTiO3 films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm2. Lastly, this result paves the way towards the fabrication of lead-free BaTiO3 ferroelectric memories on silicon platforms.

  5. Preparation and characterization of self-assembled percolative BaTiO3-CoFe2O4 nanocomposites via magnetron co-sputtering.

    PubMed

    Yang, Qian; Zhang, Wei; Yuan, Meiling; Kang, Limin; Feng, Junxiao; Pan, Wei; Ouyang, Jun

    2014-04-01

    BaTiO3-CoFe2O4 composite films were prepared on (100) SrTiO3 substrates by using a radio-frequency magnetron co-sputtering method at 750 °C. These films contained highly (001)-oriented crystalline phases of perovskite BaTiO3 and spinel CoFe2O4, which can form a self-assembled nanostructure with BaTiO3 well-dispersed into CoFe2O4 under optimized sputtering conditions. A prominent dielectric percolation behavior was observed in the self-assembled nanocomposite. Compared with pure BaTiO3 films sputtered under similar conditions, the nanocomposite film showed higher dielectric constants and lower dielectric losses together with a dramatically suppressed frequency dispersion. This dielectric percolation phenomenon can be explained by the 'micro-capacitor' model, which was supported by measurement results of the electric polarization and leakage current.

  6. 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.

  7. Reduced overpotentials for electrocatalytic water splitting over Fe- and Ni-modified BaTiO3.

    PubMed

    Artrith, Nongnuch; Sailuam, Wutthigrai; Limpijumnong, Sukit; Kolpak, Alexie M

    2016-10-26

    Water electrolysis is a key technology for the replacement of fossil fuels by environmentally friendly alternatives, but state-of-the-art water oxidation catalysts rely on rare elements such as Pt groups and other noble metals. In this article, we employ first-principles calculations to explore the potential of modified barium titanate (BaTiO3), an inexpensive perovskite oxide that can be synthesized from earth-abundant precursors, for the design of efficient water oxidation electrocatalysts. Our calculations identify Fe and Ni doping as a means to improve the electrical conductivity and to reduce the overpotential required for water oxidation over BaTiO3. Based on computed Pourbaix diagrams and pH/potential-dependent surface phase diagrams, we further show that BaTiO3 is stable under reaction conditions and is not sensitive with respect to poisoning by reaction intermediates and hydrogen adsorption. This proof of concept demonstrates that even minor compositional modifications of existing materials may greatly improve their catalytic activity, a fact that is often neglected when larger composition spaces are screened.

  8. Current understanding of structure-processing-property relationships in BaTiO3-Bi(M)O3 dielectrics

    DOE PAGES

    Beuerlein, Michaela A.; Kumar, Nitish; Usher, Tedi -Marie; ...

    2016-09-01

    Here, as part of a continued push for high permittivity dielectrics suitable for use at elevated operating temperatures and/or large electric fields, modifications of BaTiO3 with Bi(M)O3, where M represents a net-trivalent B-site occupied by one or more species, have received a great deal of recent attention. Materials in this composition family exhibit weakly coupled relaxor behavior that is not only remarkably stable at high temperatures and under large electric fields, but is also quite similar across various identities of M. Moderate levels of Bi content (as much as 50 mol%) appear to be crucial to the stability of themore » dielectric response. In addition, the presence of significant Bi reduces the processing temperatures required for densification and increases the required oxygen content in processing atmospheres relative to traditional X7R-type BaTiO3-based dielectrics. Although detailed understanding of the structure–processing–property relationships in this class of materials is still in its infancy, this article reviews the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO3-Bi(M)O3 dielectrics as well as the processing challenges and opportunities associated with these materials.« less

  9. Design and preparation of stress-free epitaxial BaTiO3 polydomain films by RF magnetron sputtering

    PubMed Central

    Zhang, Wei; Yuan, Meiling; Wang, Xianyang; Pan, Wei; Wang, Chun-Ming; Ouyang, Jun

    2012-01-01

    Domain structures of BaTiO3 thick films grown on (100) SrTiO3 single-crystal substrates were engineered using an RF magnetron sputtering deposition process. By tuning the sputtering power and cooling rate and using an off-axis sputtering technique to prepare conducting perovskite oxide bottom electrode with heteroepitaxial quality, we have deposited epitaxial tetragonal single-domain and polydomain BaTiO3 films with a self-assembled three-domain architecture. The electrical properties and microstructure of the BaTiO3 films were characterized, and a c/a1/a2 cellular polydomain structure was clearly observed in as-grown films by optical microscopy. Such a polydomain structure was a consequence of a complete relaxation of misfit stresses of the film. Engineering of this self-assembled microstructure has great potential in providing large, field-tunable pyroelectric and electromechanical responses in next-generation microelectronic devices and micro-electro-mechanical systems (MEMS). PMID:27877494

  10. Enhancement of Magnetoelectric Coupling in CoGaxFe2-xO4/BaTiO3 Composite

    NASA Astrophysics Data System (ADS)

    Ni, Yan; Zhang, Zhen; Jiles, David; Nlebedim, Cajetan

    2015-03-01

    Multiferroic materials exhibit magnetoelectric coupling and promise new device applications including magnetic sensors, generators and filters. An effective method for developing magnetoelectric (ME) materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, enhancement of magnetoelectric coupling was found by systematically studying the electrical and magnetic properties of CoGaxFe2-xO4/BaTiO3 composite. It is found that Ga doping not only stabilizes the magnetic phase of composites but also increases the sensitivity of magnetoelastic response by 30%. Moreover, Ga doping reduces the electrical conductivity and the dielectric loss of composite. An enhancement of the electrostrain with doping Ga is also observed in CoGaxFe2-xO4/BaTiO3 (x =0.3). As both the sensitivity of magnetostriction and the change in the electric field with strain increase, the ME voltage coefficient also increase. Thus, our work is beneficial for the application of CoFe2O4/BaTiO3-based multiferroic materials. This work was supported by the USDoE, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. The research was performed at Ames Laboratory, operated for the USDoE by Iowa State University (contract # DE-AC02-07CH11358)

  11. The characterization of silicone type dielectric elastomer filled with nano sized BaTiO3 particles

    NASA Astrophysics Data System (ADS)

    Liu, Liwu; Zhang, Wei; Bo, Tao; Zhao, Wei; Lv, Xiongfei; Li, Jinrong; Zhang, Zhen

    2015-04-01

    In this paper, the characterization and electromechanical stability behavior of nano sized BaTiO3 particle filled dielectric elastomer has been analyzed experimentally and theoretically. The free energy function involving a new dielectric energy density function and Mooney-Rivlin elastic strain energy function has been used to carry out the analysis. To give a comprehensive dielectric energy function, the influence of the BaTiO3 weight fraction on the dielectric property of the dielectric elastomer has been considered. The analytical results show that with the increasing weight fraction of BaTiO3 or the electrostrictive factor, the critical electric field of silicone elastomer decreases, i.e. the elastomer's stability is reduced. Meanwhile, with the increasing material constant ratio k which is the ratio of the two material constants appeared in the Mooney-Rivilin elastic strain energy function, the critical nominal electric field will increase. These results are useful in not only helping us to understand the influence of the filled nano-BaTiO3 particles on the electromechanical stability of silicone dielectric elastomer, but also giving great guidance to obtain specific dielectric elastomer actuators to meet the demand of users by changing the dielectric property of the elastomer.

  12. Ferroelectric BaTiO3 thin films on Ti substrate fabricated using pulsed-laser deposition.

    PubMed

    He, J; Jiang, J C; Liu, J; Collins, G; Chen, C L; Lin, B; Giurgiutiu, V; Guo, R Y; Bhalla, A; Meletis, E I

    2010-09-01

    We report on the fabrication of ferroelectric BaTiO3 thin films on titanium substrates using pulsed laser deposition and their microstructures and properties. Electron microscopy studies reveal that BaTiO3 films are composed of crystalline assemblage of nanopillars with average cross sections from 100 nm to 200 nm. The BaTiO3 films have good interface structures and strong adhesion with respect to Ti substrates by forming a rutile TiO2 intermediate layer with a gradient microstructure. The room temperature ferroelectric polarization measurements show that the as-deposited BTO films possess nearly the same spontaneous polarization as the bulk BTO ceramics indicating formation of ferroelectric domains in the films. Successful fabrication of such ferroelectric films on Ti has significant importance for the development of new applications such as structural health monitoring spanning from aerospace to civil infrastructure. The work can be extended to integrate other ferroelectric oxide films with various promising properties to monitor the structural health of materials.

  13. Large Spin Splitting and Interfacial States in a Bi /BaTiO3(001 ) Rashba Ferroelectric Heterostructure

    NASA Astrophysics Data System (ADS)

    Lutz, P.; Figgemeier, T.; El-Fattah, Z. M. Abd; Bentmann, H.; Reinert, F.

    2017-04-01

    The fabrication of hybrid systems in which specific physical properties of materials are coupled provides a setting to explore alternative functionality in condensed matter physics. Here, we realize the formation of spin-polarized electronic states, arising from a strong spin-orbit interaction, on the prototype ferroelectric BaTiO3(001 ) by epitaxial growth of ultrathin bismuth layers. Low-energy electron diffraction shows that the films grow along the Bi(0001) orientation and form two twinned and 90°-rotated domains. Using angle-resolved photoelectron spectroscopy, we directly confirm the presence of metallic electronic states with large spin splitting in the bulk band gap of the substrate. At a low film thickness of approximately 4 monolayers, we observe the emergence of an interface state close to the Fermi energy that features a holelike dispersion near the X ¯ point of BaTiO3(001 ) . Our results demonstrate the formation of low-dimensional electronic states with large spin splitting coupled to a BaTiO3 substrate, with importance for the exploration of spin manipulation at interfaces based on ferroelectricity.

  14. Epitaxial growth and magnetic properties of ultrathin iron oxide films on BaTiO3(001)

    NASA Astrophysics Data System (ADS)

    Hari Babu, V.; Govind, R. K.; Schindler, K.-M.; Welke, M.; Denecke, R.

    2013-09-01

    The growth and magnetic properties of ultrathin iron oxide films on BaTiO3(001) substrate have been studied by low energy electron diffraction, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and magneto-optic Kerr effect experiments. The iron oxide films were prepared by both simultaneous oxidation and postgrowth oxidation methods. Assuming a surface structure close to Fe3O4[100], the unit cell was found to be epitaxially grown on BaTiO3[100] unit cell due to small lattice mismatch between the film and the substrate. The films exhibit a uniaxial magnetic anisotropy with the easy-axis along Fe3O4[11¯0] direction. For the films on or above 1.7 nm thickness, the XMCD shows characteristic contributions from different Fe site occupations similar to those of the bulk Fe3O4. On the other hand, the XAS line shape and XMCD of the films in the thickness range 1.2-1.6 nm indicate the lesser occupation of Fe2+ octahedral sites associated with the formation of γ-Fe2O3 phase at lower thicknesses. Our investigations offer further insight into the structure, interface, and magnetic properties of the Fe3O4/BaTiO3 as an interesting system for technological applications.

  15. Electrical Properties of Nd-Doped BaTiO3 PTC Ceramics Prepared by Hydrothermal Synthesis

    NASA Astrophysics Data System (ADS)

    Hashishin, T.; Sato, E.; Umeki, S.; Kojima, K.; Tamaki, J.

    2011-10-01

    Nd-doped BaTiO3 nanopowders with ca. 200 nm in average diameter were prepared by hydrothermal synthesis at 200 and 240 °C for 24 h. Neodymium (III) nitrate hexahydrate (Nd(NO3)3·6H2O) as a donor dopant was added to the powder mixtures of barium hydroxide (Ba(OH)2) and titanium dioxide (TiO2) ranging from 0.25 to 0.45 mol%. A green compact of the powder mixtures obtained was heated at 1340 °C for 2 h with/without three steps of ramp heating processes. Sintered without these steps, 0.35 mol% Nd-doped BaTiO3 with the resistivity of 124 ohm·cm at R. T. indicated insufficient PTCR effect; resistance change of 3 × 102 in the vicinity of Curie temperature. On the other hand, a pellet of 0.35 mol% Nd-doped BaTiO3 sintered via the step-heating process exhibited the large resistance change of 7.5 × 103.

  16. Design and preparation of stress-free epitaxial BaTiO3 polydomain films by RF magnetron sputtering.

    PubMed

    Zhang, Wei; Yuan, Meiling; Wang, Xianyang; Pan, Wei; Wang, Chun-Ming; Ouyang, Jun

    2012-06-01

    Domain structures of BaTiO3 thick films grown on (100) SrTiO3 single-crystal substrates were engineered using an RF magnetron sputtering deposition process. By tuning the sputtering power and cooling rate and using an off-axis sputtering technique to prepare conducting perovskite oxide bottom electrode with heteroepitaxial quality, we have deposited epitaxial tetragonal single-domain and polydomain BaTiO3 films with a self-assembled three-domain architecture. The electrical properties and microstructure of the BaTiO3 films were characterized, and a c/a1/a2 cellular polydomain structure was clearly observed in as-grown films by optical microscopy. Such a polydomain structure was a consequence of a complete relaxation of misfit stresses of the film. Engineering of this self-assembled microstructure has great potential in providing large, field-tunable pyroelectric and electromechanical responses in next-generation microelectronic devices and micro-electro-mechanical systems (MEMS).

  17. Design and preparation of stress-free epitaxial BaTiO3 polydomain films by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Yuan, Meiling; Wang, Xianyang; Pan, Wei; Wang, Chun-Ming; Ouyang, Jun

    2012-06-01

    Domain structures of BaTiO3 thick films grown on (100) SrTiO3 single-crystal substrates were engineered using an RF magnetron sputtering deposition process. By tuning the sputtering power and cooling rate and using an off-axis sputtering technique to prepare conducting perovskite oxide bottom electrode with heteroepitaxial quality, we have deposited epitaxial tetragonal single-domain and polydomain BaTiO3 films with a self-assembled three-domain architecture. The electrical properties and microstructure of the BaTiO3 films were characterized, and a c/a1/a2 cellular polydomain structure was clearly observed in as-grown films by optical microscopy. Such a polydomain structure was a consequence of a complete relaxation of misfit stresses of the film. Engineering of this self-assembled microstructure has great potential in providing large, field-tunable pyroelectric and electromechanical responses in next-generation microelectronic devices and micro-electro-mechanical systems (MEMS).

  18. 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.

  19. 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.

  20. High rate capability of a BaTiO3-decorated LiCoO2 cathode prepared via metal organic decomposition

    NASA Astrophysics Data System (ADS)

    Teranishi, Takashi; Katsuji, Naoto; Yoshikawa, Yumi; Yoneda, Mika; Hayashi, Hidetaka; Kishimoto, Akira; Yoda, Koji; Motobayashi, Hidefumi; Tasaki, Yuzo

    2016-10-01

    Metal organic decomposition (MOD) using octylic acid salts was applied to synthesize a BaTiO3-LiCoO2 (BT-LC) composite powder. The Ba and Ti octylates were utilized as metal precursors, in an attempt to synthesize homogeneous BT nanoparticles on the LC matrix. The BT-LC composite, having a phase-separated composite structure without any impurity phase, was successfully obtained by optimizing the MOD procedure. The composite prepared using octylate precursors exhibited a sharper distribution and better dispersibility of decorated BT particles. Additionally, the average particle size of the decorated BTs using metal octylate was reduced to 23.3 nm, compared to 44.4 nm from conventional processes using Ba acetate as well as Ti alkoxide as precursors. The composite cathode displayed better cell performance than its conventional counterpart; the discharge capacity of the metal octylate-derived specimen was 55.6 mAh/g at a 50C rate, corresponding to 173% of the capacity of the conventional specimen (32.2 mAh/g). The notable improvement in high rate capability obtained in this study, compared with the conventional route, was attributed to the higher density of the triple junction formed by the BT-LC-electrolyte interface.

  1. Effect of BaTiO3 nano-particles on breakdown performance of propylene carbonate.

    PubMed

    Hou, Yanpan; Zhang, Zicheng; Zhang, Jiande; Liu, Zhuofeng; Song, Zuyin

    2015-05-01

    As an alternative to water, propylene carbonate (PC) has a good application prospect in the compact pulsed power sources for its breakdown strength higher than that of water, resistivity bigger than 10(9) Ω m, and low freezing temperature (-49 °C). In this paper, the investigation into dielectric breakdown of PC and PC-based nano-fluids (NFs) subjected to high amplitude electric field is presented with microsecond pulses applied to a 1 mm gap full of PC or NFs between spherical electrodes. One kind of NF is composed of PC mixed with 0.5-1.4 vol. % BaTiO3 (BT) nano-particles of mean diameter ≈100 nm and another is mixed with 0.3-0.8 vol. % BT nano-particles of mean diameter ≈30 nm. The experimental results demonstrate the rise of permittivity and improvement of the breakdown strength of NFs compared with PC. Moreover, it is found that there exists an optimum fraction for these NFs corresponding to tremendous surface area in nano-composites with finite mesoscopic thickness. In concrete, the dielectric breakdown voltage of NFs is 33% higher than that of PC as the volume concentration of nano-particles with a 100 nm diameter is 0.9% and the breakdown voltage of NFs is 40% higher as the volume concentration of nano-particles with a 30 nm diameter is 0.6%. These phenomena are considered as the dielectric breakdown voltage of PC-based NFs is increased because the interfaces between nano-fillers and PC matrices provide myriad trap sites for charge carriers, which play a dominant role in the breakdown performance of NFs.

  2. Hierarchical interfaces induce high dielectric permittivity in nanocomposites containing TiO2@BaTiO3 nanofibers

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Chen, Weiwei; Wang, Jianjun; Shen, Yang; Gu, Lin; Lin, Yuanhua; Nan, Ce-Wen

    2014-05-01

    Interface issues are common and crucial in nanocomposites or nanohybrid systems since the interface area is enormous on the nanoscale. In the 0-3 dimensional polymer nanocomposites, in which nano-inclusions (0-dimension) are embedded in a 3-dimensionally connected polymer matrix, enhanced dielectric permittivity could be induced by the interfacial polarization at the interfaces between the nano-inclusions and the polymer matrix. In this contribution, we propose and demonstrate that the topological structure of the interface plays an equally important role as the area of the interface in determining the dielectric polarization of polymer nanocomposites. TiO2 nanofibers embedded with BaTiO3 nanoparticles are prepared via electrospinning and then fused with polyvinyl difluoride (PVDF) into polymer nanocomposite films. Modulation of hierarchical interfaces is thus achieved for these nanocomposites. The confinement of these additional interfaces inside the TiO2 nanofibers leads to percolated networks formed by the interfacial regions. The dielectric permittivity of the polymer nanocomposites is thus enhanced by ~300% over the PVDF matrix at a low filler loading of 11 vol%. A phase-field simulation study indicates that the enhanced dielectric permittivity could be attributed to the increased polarization in the percolated interfacial regions inside the TiO2 nanofibers. The instantaneous electrical breakdown of the TiO2@BaTiO3 nanofibers studied by the in situ transmission electron microscopy method further reveals the striking feature that the breakdown behavior of the nanofibers changes from semiconductive to metallic with the incorporation of insulating BaTiO3 nanoparticles.Interface issues are common and crucial in nanocomposites or nanohybrid systems since the interface area is enormous on the nanoscale. In the 0-3 dimensional polymer nanocomposites, in which nano-inclusions (0-dimension) are embedded in a 3-dimensionally connected polymer matrix, enhanced dielectric permittivity could be induced by the interfacial polarization at the interfaces between the nano-inclusions and the polymer matrix. In this contribution, we propose and demonstrate that the topological structure of the interface plays an equally important role as the area of the interface in determining the dielectric polarization of polymer nanocomposites. TiO2 nanofibers embedded with BaTiO3 nanoparticles are prepared via electrospinning and then fused with polyvinyl difluoride (PVDF) into polymer nanocomposite films. Modulation of hierarchical interfaces is thus achieved for these nanocomposites. The confinement of these additional interfaces inside the TiO2 nanofibers leads to percolated networks formed by the interfacial regions. The dielectric permittivity of the polymer nanocomposites is thus enhanced by ~300% over the PVDF matrix at a low filler loading of 11 vol%. A phase-field simulation study indicates that the enhanced dielectric permittivity could be attributed to the increased polarization in the percolated interfacial regions inside the TiO2 nanofibers. The instantaneous electrical breakdown of the TiO2@BaTiO3 nanofibers studied by the in situ transmission electron microscopy method further reveals the striking feature that the breakdown behavior of the nanofibers changes from semiconductive to metallic with the incorporation of insulating BaTiO3 nanoparticles. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00703d

  3. Hierarchical interfaces induce high dielectric permittivity in nanocomposites containing TiO2@BaTiO3 nanofibers.

    PubMed

    Zhang, Xin; Chen, Weiwei; Wang, Jianjun; Shen, Yang; Gu, Lin; Lin, Yuanhua; Nan, Ce-Wen

    2014-06-21

    Interface issues are common and crucial in nanocomposites or nanohybrid systems since the interface area is enormous on the nanoscale. In the 0-3 dimensional polymer nanocomposites, in which nano-inclusions (0-dimension) are embedded in a 3-dimensionally connected polymer matrix, enhanced dielectric permittivity could be induced by the interfacial polarization at the interfaces between the nano-inclusions and the polymer matrix. In this contribution, we propose and demonstrate that the topological structure of the interface plays an equally important role as the area of the interface in determining the dielectric polarization of polymer nanocomposites. TiO2 nanofibers embedded with BaTiO3 nanoparticles are prepared via electrospinning and then fused with polyvinyl difluoride (PVDF) into polymer nanocomposite films. Modulation of hierarchical interfaces is thus achieved for these nanocomposites. The confinement of these additional interfaces inside the TiO2 nanofibers leads to percolated networks formed by the interfacial regions. The dielectric permittivity of the polymer nanocomposites is thus enhanced by ∼300% over the PVDF matrix at a low filler loading of 11 vol%. A phase-field simulation study indicates that the enhanced dielectric permittivity could be attributed to the increased polarization in the percolated interfacial regions inside the TiO2 nanofibers. The instantaneous electrical breakdown of the TiO2@BaTiO3 nanofibers studied by the in situ transmission electron microscopy method further reveals the striking feature that the breakdown behavior of the nanofibers changes from semiconductive to metallic with the incorporation of insulating BaTiO3 nanoparticles.

  4. Enhancement of output performance through post-poling technique on BaTiO3/PDMS-based triboelectric nanogenerator

    NASA Astrophysics Data System (ADS)

    Ali, Danish; Yu, Bin; Duan, Xiaochao; Yu, Hao; Zhu, Meifang

    2017-02-01

    In the modern era, the invention of new energy sources is important in order to make advances possible in electronic media. A triboelectric nanogenerator (TENG) is considered to be strong design that converts mechanical power into electrical power, using organic (polymer) or inorganic (lead, ceramic etc) materials to initiate the triboelectrification process, followed by charge separation. In this study, a lead-free BaTiO3/PDMS-Al-based TENG was fabricated by mixing tetragonal ferroelectric BaTiO3 nanocrystals in a PDMS matrix to make a composite for a working electrode film. It is worth noting that a new post- poling process has been introduced to align the dipole structures in the BaTiO3 nanocrystals, and to attain a high electron density on the surface of the working electrode film. The output was recorded up to 375 V and 6 μA of close circuit voltage and short circuit current, respectively, at a current density of 0.3 μA cm-2 and an effective power equal to 2.25 mW at a load resistance of 100 MΩ, and is four times higher than a PDMS-Al-based TENG. This study also reveals the hidden locks that will enable other inorganic materials with a dipole structure to enhance their output using the post-poling technique. The TENG has a vast field of applications due to its stability, the flexibility of its thin films and its biocompatibility. It is also an aid for exploring new TENG devices with enhanced output performance.

  5. Enhancement of output performance through post-poling technique on BaTiO3/PDMS-based triboelectric nanogenerator.

    PubMed

    Ali, Danish; Yu, Bin; Duan, Xiaochao; Yu, Hao; Zhu, Meifang

    2017-02-17

    In the modern era, the invention of new energy sources is important in order to make advances possible in electronic media. A triboelectric nanogenerator (TENG) is considered to be strong design that converts mechanical power into electrical power, using organic (polymer) or inorganic (lead, ceramic etc) materials to initiate the triboelectrification process, followed by charge separation. In this study, a lead-free BaTiO3/PDMS-Al-based TENG was fabricated by mixing tetragonal ferroelectric BaTiO3 nanocrystals in a PDMS matrix to make a composite for a working electrode film. It is worth noting that a new post- poling process has been introduced to align the dipole structures in the BaTiO3 nanocrystals, and to attain a high electron density on the surface of the working electrode film. The output was recorded up to 375 V and 6 μA of close circuit voltage and short circuit current, respectively, at a current density of 0.3 μA cm(-2) and an effective power equal to 2.25 mW at a load resistance of 100 MΩ, and is four times higher than a PDMS-Al-based TENG. This study also reveals the hidden locks that will enable other inorganic materials with a dipole structure to enhance their output using the post-poling technique. The TENG has a vast field of applications due to its stability, the flexibility of its thin films and its biocompatibility. It is also an aid for exploring new TENG devices with enhanced output performance.

  6. Electron paramagnetic resonance of Nb-doped BaTiO3 ceramics with positive temperature coefficient of resistivity

    NASA Astrophysics Data System (ADS)

    Jida, Shin'suke; Miki, Toshikatsu

    1996-11-01

    Paramagnetic centers in Nb-doped BaTiO3 ceramics are measured at 77-500 K by electron paramagnetic resonance (EPR) for investigating the role of the centers on the well-known positive temperature coefficient of resistivity (PTCR) effect (PTCR at the Curie temperature). EPR detects four signals; an anisotropically broad singlet signal at g=2.005, a sextet signal due to Mn2+, a Cr3+ signal, and a Ti3+ signal. The former two signals arise in the rhombohedral and cubic phases, but disappear in the tetragonal and orthorhombic phases. The Cr3+ signal appears in all of the phases, while the Ti3+ signal is detected only at low temperatures. The singlet signal also arises in undoped, barium-deficient BaTiO3 ceramics, therefore the signal is attributable to barium-vacancy-associated centers rather than Nb4+ ions or Fe3+ ions proposed by several authors. In this article, we propose that the singlet signal is due to vacancy-pairs of VBa-F+ type, i.e., the vacancy pair of VBa-VO capturing one electron. The electrical resistivity data show a polaronic character of low-temperature conduction and a high resistivity jump around the Curie temperature. The low-temperature polaronic conduction is explained in terms of electron-hopping between Ti4+ and Ti3+ ions. The resistivity jump at the Curie temperature occurs along with the EPR intensity increase of the singlet signal, the Mn2+ signal and the Cr3+ signal. We conclude that the PTCR of Nb-doped BaTiO3 ceramics is strongly associated with the trap activation of the VBa-VO vacancy-pairs and manganese centers at the tetragonal-to-cubic transition.

  7. Interface Control of Ferroelectricity in an SrRuO3 /BaTiO3 /SrRuO3 Capacitor and its Critical Thickness.

    PubMed

    Shin, Yeong Jae; Kim, Yoonkoo; Kang, Sung-Jin; Nahm, Ho-Hyun; Murugavel, Pattukkannu; Kim, Jeong Rae; Cho, Myung Rae; Wang, Lingfei; Yang, Sang Mo; Yoon, Jong-Gul; Chung, Jin-Seok; Kim, Miyoung; Zhou, Hua; Chang, Seo Hyoung; Noh, Tae Won

    2017-05-01

    The atomic-scale synthesis of artificial oxide heterostructures offers new opportunities to create novel states that do not occur in nature. The main challenge related to synthesizing these structures is obtaining atomically sharp interfaces with designed termination sequences. In this study, it is demonstrated that the oxygen pressure (PO2) during growth plays an important role in controlling the interfacial terminations of SrRuO3 /BaTiO3 /SrRuO3 (SRO/BTO/SRO) ferroelectric (FE) capacitors. The SRO/BTO/SRO heterostructures are grown by a pulsed laser deposition method. The top SRO/BTO interface, grown at high PO2 (around 150 mTorr), usually exhibits a mixture of RuO2 -BaO and SrO-TiO2 terminations. By reducing PO2, the authors obtain atomically sharp SRO/BTO top interfaces with uniform SrO-TiO2 termination. Using capacitor devices with symmetric and uniform interfacial termination, it is demonstrated for the first time that the FE critical thickness can reach the theoretical limit of 3.5 unit cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Interface Control of Ferroelectricity in an SrRuO3/BaTiO3/SrRuO3 Capacitor and its Critical Thickness

    DOE PAGES

    Shin, Yeong Jae; Kim, Yoonkoo; Kang, Sung -Jin; ...

    2017-03-03

    Here, the atomic-scale synthesis of artificial oxide heterostructures offers new opportunities to create novel states that do not occur in nature. The main challenge related to synthesizing these structures is obtaining atomically sharp interfaces with designed termination sequences. In this study, it is demonstrated that the oxygen pressure (PO2) during growth plays an important role in controlling the interfacial terminations of SrRuO3/BaTiO3/SrRuO3 (SRO/BTO/SRO) ferroelectric (FE) capacitors. The SRO/BTO/SRO heterostructures are grown by a pulsed laser deposition method. The top SRO/BTO interface, grown at high PO2 (around 150 mTorr), usually exhibits a mixture of RuO2-BaO and SrO-TiO2 terminations. By reducing PO2,more » the authors obtain atomically sharp SRO/BTO top interfaces with uniform SrO-TiO2 termination. Using capacitor devices with symmetric and uniform interfacial termination, it is demonstrated for the first time that the FE critical thickness can reach the theoretical limit of 3.5 unit cells.« less

  9. Growth of Nanoscale BaTiO3/SrTiO3 Superlattices by Molecular-Beam Epitaxy

    DTIC Science & Technology

    2008-05-01

    can be achieved for SrTiO3.16 We found this method to also work for BaTiO3. An ex- ample of typical shuttered RHEED oscillations during the growth...to obtain atomically abrupt interfaces. For this reason we have used the method developed by Koster et al.13 to prepare TiO2-terminated (001) SrTiO3...sub- strates. An atomic force microscopy (AFM) image of a typical TiO2-terminated SrTiO3 substrate surface pre- pared by us using this method is shown

  10. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    NASA Astrophysics Data System (ADS)

    Xun, Wei; Hao, Xiang; Pan, Tao; Zhong, Jia-Lin; Ma, Chun-Lan; Hou, Fang; Wu, Yin-Zhong

    2017-07-01

    Based on first-principles calculations, the BaTiO3(BTO) film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

  11. Structure and dielectric properties of composite material based on surface-modified BaTiO3 nanoparticles in polystyrene

    NASA Astrophysics Data System (ADS)

    Emelianov, Nikita

    2015-01-01

    This article reports on studies of the structure and dielectric properties of composites materials based on BaTiO3 nanoparticles in the polymer matrix. It is shown that nanoparticles of barium titanate obtained by peroxide method, have surface enriched hydroxyl (-OH) groups, which allow the formation of strong chemical bonds with the molecules of surfactant. This surface modification prevents agglomeration of nanoparticles, which leads to heterogeneity of mechanical and dielectric properties of the composites. It is shown that the effective dielectric constant for the studied composite material agrees well with the modified Kerner equation for the volume content of nanoparticles within the range from 5 to 35%.

  12. Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment(Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Sharma, Dipika; Satsangi, Vibha R.; Dass Kaura, Sahab; Shrivastav, Rohit; Waghmare, Umesh V.

    2016-10-01

    Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment Dipika Sharmaa, Vibha R. Satsangib, Rohit Shrivastava, Umesh V. Waghmarec, Sahab Dassa aDepartment of Chemistry, Dayalbagh Educational Institute, Agra-282 110 (India) bDepartment of Physics and Computer Sciences, Dayalbagh Educational Institute, Agra-282 110 (India) cTheoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore-560 064 (India) * Phone: +91-9219695960. Fax: +91-562-2801226. E-mail: drsahabdas@gmail.com. Study on photoelectrochemical activity of pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction has been carried out using DFT based band offsets and charge carriers effective mass calculations and their experimental verification. The results of DFT calculations show that BaTiO3 and Cu2O have staggered type band alignment after the heterojunction formation and high mobility of electrons in Cu2O as compared to the electrons in BaTiO3. Staggered type band edges alignment and high mobility of electrons and holes improved the separation of photo-generated charge carriers in BaTiO3/Cu2O heterojunction. To validate the theoretical results experiments were carried out on pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction with varying thickness of Cu2O. All samples were characterized by X- Ray Diffractometer, SEM and UV-Vis spectrometry. Nanostructured thin films of pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction were used as photoelectrode in the photoelectrochemical cell for water splitting reaction. Maximum photocurrent density of 1.44 mA/cm2 at 0.90 V/SCE was exhibited by 442 nm thick BaTiO3/Cu2O heterojunction photoelectrode Increased photocurrent density and enhanced photoconversion efficiency, exhibited by the heterojunction may be attributed to improved conductivity and enhanced separation of the photogenerated carriers at the BaTiO3/Cu2O interface. The experimental results and first-principles calculations compare well, thus suggesting that such calculations have the potential to be used in screening various metal oxide heterojunction before performing the experiments thereby saving precious chemicals, time and energy. Keywords: Photoelectrochemical, Water splitting, heterojunction, Cu2O, BaTiO3 References: [1] Surbhi Choudhary, et al. Nanostructured bilayered thin films in photoelectrochemical water splitting - A review: International Journal of Hydrogen Energy, (2012). [2] Dipika Sharma, Anuradha Verma, V.R. Satsangi, Rohit shrivastav, Sahab Dass Nanostructured SrTiO3 thin films sensitized by Cu2O for Photoelectrochemical Hydrogen Generation. International journal of Hydrogen Energy;42:,4230-4241, 2014.

  13. 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.

  14. 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

  15. 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

    2016-04-28

    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.

  16. Epitaxial BaTiO3(100) films on Pt(100): a low-energy electron diffraction, scanning tunneling microscopy, and x-ray photoelectron spectroscopy study.

    PubMed

    Förster, Stefan; Huth, Michael; Schindler, Karl-Michael; Widdra, Wolf

    2011-09-14

    The growth of epitaxial ultrathin BaTiO(3) films on a Pt(100) substrate has been studied by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and x-ray photoelectron spectroscopy (XPS). The films have been prepared by radio-frequency-assisted magnetron sputter deposition at room temperature and develop a long-range order upon annealing at 900 K in O(2). By adjusting the Ar and O(2) partial pressures of the sputter gas, the stoichiometry was tuned to match that of a BaTiO(3)(100) single crystal as determined by XPS. STM reveals the growth of continuous BaTiO(3) films with unit cell high islands on top. With LEED already for monolayer thicknesses, the formation of a BaTiO(3)(100)-(1 × 1) structure has been observed. Films of 2-3 unit cell thickness show a brilliant (1 × 1) LEED pattern for which an extended set of LEED I-V data has been acquired. At temperatures above 1050 K the BaTiO(3) thin film starts to decay by formation of vacancy islands. In addition (4 × 4) and (3 × 3) surface reconstructions develop upon prolonged heating.

  17. 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).

  18. On the terahertz dielectric response of cubic BaTiO3: Coexistence of displacive and order-disorder dynamics

    NASA Astrophysics Data System (ADS)

    Deng, Hai-Yao

    2012-10-01

    Two distinct modes with frequencies below 150 cm-1 were recently observed in cubic BaTiO3 (Ponomareva I. et al., Phys. Rev. B, 77 (2008) 012102). One of these modes perfectly softens to zero while the other saturates at about 60 cm-1 as the ferroelectric transition is approached. In the present work, we interpret these modes employing two widely recognized elements: nano-size tetragonal precursors forming in the cubic phase and an eight-well potential model for Ti ions due to Comes, Lambert and Guinier (Solid State Commun., 6 (1968) 715). We show that the frequency squared of the saturating mode (SM), which exists in the cubic phase, and that of an E-symmetry mode (EM), which exists in the tetragonal phase, fall on a single curve, ˜33 cm-2K-1(T - T*), thereby suggesting connections between the lattice dynamics across the ferroelectric transition. T* is predicted and confirmed to coincide with the tetragonal-orthorhombic transition temperature of 290 K. The perfectly softening mode (PSM) is argued to be associated with the re-orientational motions of tetragonal precursors. The complex dielectric function is calculated without free inputs and the result agrees satisfactorily with measurements. The SM is characterized as a resonant mode, whereas the PSM as a relaxational mode, confirming that both order-disorder and displacive dynamics coexist in cubic BaTiO3.

  19. Polarization-induced interfacial coupling modulations in BaTiO3/GaN heterojunction devices

    NASA Astrophysics Data System (ADS)

    Bhat, Thirumaleshwara N.; Pandey, B. K.; Krupanidhi, S. B.

    2017-07-01

    We report on the ferroelectric polarization-induced switchable interfacial coupling modulations in BaTiO3/GaN heterojunction transport behaviour. The ferroelectric barium titanate, BaTiO3 (BTO) was integrated with polar semiconductor gallium nitride (GaN). BTO with a tetragonal structure was deposited on a wurtzite (0 0 0 1) epitaxial GaN/c-Al2O3 substrate by pulsed laser deposition, which was further confirmed by x-ray diffraction and Raman spectroscopy. BTO/GaN heterojunctions with resistive switching behaviour exhibited modulations in transport characteristics due to the interfacial coupling. The ferroelectric nature and interfacial coupling effect of this heterojunction was confirmed with the help of piezo-response force microscopy. A valence band offset of 0.82 eV and conduction band offset of 0.62 eV were obtained for BTO/GaN heterojunctions by x-ray photo-electron spectroscopy. This interfacial coupling phenomenon was analysed and its effect on the carrier conduction in the heterojunction was investigated by band alignment studies.

  20. 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).

  1. Effect of microwave heating on BaTiO3:Nb ceramics with positive temperature coefficient of resistivity

    NASA Astrophysics Data System (ADS)

    Jida, Shin'suke; Suemasu, Takeshi; Miki, Toshikatsu

    1999-08-01

    The microwave heating technique is employed for obtaining high performance positive temperature coefficient of resistivity (PTCR) ceramics of Nb-doped BaTiO3 with a low resistivity at room temperature and a high resistivity jump above the Curie temperature. The grains of the BaTiO3:Nb ceramics prepared by microwave sintering are as large as 20-50 μm even when the Nb content exceeds 0.2 at. %, whereas such large grain size has never been obtained at this high content of Nb by ordinary sintering with an electric furnace. The large grains are also obtained by subjecting the heavily Nb-doped ceramics composed of fine grains to postheating with microwave after ordinary sintering. The room-temperature resistivity decreases down below 10 Ω cm and the PTCR character is obtained by postannealing in air. The mechanism of grain growth by microwave heating is discussed in terms of nonuniform temperature distribution of specimens during heating. The experimental data indicate that the microwave heating technique and the employment of a dopant that forms donor levels even at high doping levels will enable to develop high performance PTCR ceramics.

  2. Complementary resistive switching in BaTiO3/NiO bilayer with opposite switching polarities

    NASA Astrophysics Data System (ADS)

    Li, Shuo; Wei, Xianhua; Lei, Yao; Yuan, Xincai; Zeng, Huizhong

    2016-12-01

    Resistive switching behaviors have been investigated in the Au/BaTiO3/NiO/Pt structure by stacking the two elements with different switching types. The conducting atomic force microscope measurements on BaTiO3 thin films and NiO thin films suggest that with the same active resistive switching region, the switching polarities in the two semiconductors are opposite to each other. It is in agreement with the bipolar hysteresis I-V curves with opposite switching polarities for single-layer devices. The bilayer devices show complementary resistive switching (CRS) without electroforming and unipolar resistive switching (URS) after electroforming. The coexistence of CRS and URS is mainly ascribed to the co-effect of electric field and Joule heating mechanisms, indicating that changeable of resistance in this device is dominated by the redistribution of oxygen vacancies in BaTiO3 and the formation, disruption, restoration of conducting filaments in NiO. CRS in bilayer with opposite switching polarities is effective to solve the sneak current without the introduction of any selector elements or an additional metal electrode.

  3. High calcination of ferroelectric BaTiO3 doped Fe nanoceramics prepared by a solid-state sintering method

    NASA Astrophysics Data System (ADS)

    Samuvel, K.; Ramachandran, K.

    2015-07-01

    This study examined the effects of the combination of starting materials on the properties of solid-state reacted BaTiO3 using two different types of BaCO3 and TiO2. In addition, the effect of mechanochemical activation by high energy milling and the Ba/Ti molar ratio on the reaction temperature, particle size and tetragonality were investigated. The TiO2 phase and size plays a major role in increasing the reaction temperature and particle size. With the optimum selection of starting materials and processing conditions, BaTiO3 with a particle size <200 nm (Scherrer's formula) and a tetragonality c/a of approximately 1.007 was obtained. Broadband dielectric spectroscopy is applied to investigate the electrical properties of disordered perovskite-like ceramics in a wide temperature range. From the X-ray diffraction analysis it was found that the newly obtained BaTi0.5Fe0.5O3 ceramics consist of two chemically different phases. The electric modulus M∗ formalism used in the analysis enabled us to distinguish and separate the relaxation processes, dominated by marked conductivity in the ε∗(ω) representation. Interfacial effects on the dielectric properties of the samples have been understood by Cole-Cole plots in complex impedance and modulus formalism. Modulus formalism has identified the effects of both grain and grain boundary microstructure on the dielectric properties, particularly in solid state routed samples.

  4. Piezoelectric tuning of exchange bias in a BaTiO3/Co/CoO heterostructure

    NASA Astrophysics Data System (ADS)

    Polisetty, S.; Echtenkamp, W.; Jones, K.; He, X.; Sahoo, S.; Binek, Ch.

    2010-10-01

    Piezoelectrically controlled strain is used for electric tuning of exchange-bias fields. A generic exchange-bias Co/CoO bilayer is deposited on the surface of a ferroelectric and thus piezoelectric BaTiO3 substrate which allows to apply electrically and thermally tunable stress in the adjacent ferromagnetic Co thin film. The stress-induced strain alters foremost the magnetic anisotropy of the Co film and by that the magnetization orientation at the Co/CoO interface modifying the exchange-bias field. This results in a pronounced electrically induced weakening of the exchange bias but also includes the possibility of tuning the exchange-bias field through a subtle sign change from regular negative to positive values. The electrically controlled crossover from negative to positive exchange bias is consistently observed at various temperatures in the rhombohedral phase of BaTiO3 . This complex electric field dependence of the exchange-bias field is the result of the long-range nature of strain and interpreted through competition between ferromagnetic and antiferromagnetic exchange at the Co/CoO interface. Our data suggest competition between regular negative and positive exchange bias. Weakening of negative exchange bias originates from noncollinear alignment of the Co and CoO interface magnetizations. Positive exchange bias is activated when stress induces antiferromagnetic exchange through atomic displacements changing the exchange paths at the Co/CoO interface.

  5. 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)

  6. Hole-trapping effect on thermoelectric power of mixed ionic electronic conductor BaTiO3.

    PubMed

    Yoo, H-I

    2005-11-21

    The effect of hole-trapping on the thermopower of a mixed ionic electronic conductor, e.g., BaTiO3, is analyzed in terms of irreversible thermodynamics by taking trapped holes as a fourth kind of electronic charge carrier in addition to free electrons, free holes and mobile oxide ions. It is found that the effect manifests itself in two ways: thermostatically in the ionic thermopower via the thermodynamic factor and dynamically in the electronic thermopower via the electrical conductivity contribution of the trapped holes. The thermopowers of both 99.995% pure, undoped and 1.8 m/o Al-doped BaTiO3, that were measured against oxygen activity in the range of -18 < log aO2 < or = 0 at elevated temperatures of 800 degrees to 1100 degrees C [H.-I. Yoo and C. R. Song, J. Electroceram., 2001, 6, 61, ref. 6], are reanalyzed by taking into account the hole-trapping for the doped case. It is found that while the reduced heats-of-transport of free electrons and holes are, respectively, close to their thermal energy k(B)T (k(B) being the Boltzmann constant), that of trapped holes is close to their migration energy that is essentially the same as the trapping energy onto the acceptors doped, 1.04 eV.

  7. A review of molecular beam epitaxy of ferroelectric BaTiO3 films on Si, Ge and GaAs substrates and their applications

    DOE PAGES

    Mazet, Lucie; Yang, Sang Mo; Kalinin, Sergei V.; ...

    2015-06-30

    SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide-semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Lastly, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics,more » which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric.« less

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

    DOE PAGES

    Jeong, I.-K.; Lee, Seunghun; Jeong, Se-Young; ...

    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

  9. A review of molecular beam epitaxy of ferroelectric BaTiO3 films on Si, Ge and GaAs substrates and their applications

    PubMed Central

    Mazet, Lucie; Yang, Sang Mo; Kalinin, Sergei V; Schamm-Chardon, Sylvie; Dubourdieu, Catherine

    2015-01-01

    SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide–semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Finally, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric. PMID:27877816

  10. Single-crystal-like, c-axis oriented BaTiO3 thin films with high-performance on flexible metal templates for ferroelectric applications

    NASA Astrophysics Data System (ADS)

    Shin, Junsoo; Goyal, Amit; Jesse, Stephen; Kim, Dae Ho

    2009-06-01

    Epitaxial, c-axis oriented BaTiO3 thin films were deposited using pulsed laser ablation on flexible, polycrystalline Ni alloy tape with biaxially textured oxide buffer multilayers. The high quality of epitaxial BaTiO3 thin films with P4mm group symmetry was confirmed by x-ray diffraction. The microscopic ferroelectric domain structure and the piezoelectric domain switching in these films were confirmed via spatially resolved piezoresponse mapping and local hysteresis loops. Macroscopic measurements demonstrate that the films have well-saturated hysteresis loops with a high remanent polarization of ˜11.5 μC/cm2. Such high-quality, single-crystal-like BaTiO3 films on low-cost, polycrystalline, flexible Ni alloy substrates are attractive for applications in flexible lead-free ferroelectric devices.

  11. 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.

  12. A review of molecular beam epitaxy of ferroelectric BaTiO3 films on Si, Ge and GaAs substrates and their applications.

    PubMed

    Mazet, Lucie; Yang, Sang Mo; Kalinin, Sergei V; Schamm-Chardon, Sylvie; Dubourdieu, Catherine

    2015-06-01

    SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide-semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Finally, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric.

  13. 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.

  14. Engineered Unique Elastic Modes at a BaTiO3=ð2 × 1Þ-Geð001Þ Interface

    SciTech Connect

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

    2016-03-07

    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.

  15. 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

  16. First-principles determination of chemical potentials and vacancy formation energies in PbTiO3 and BaTiO3

    NASA Astrophysics Data System (ADS)

    Alahmed, Zeyad; Fu, Huaxiang

    2007-12-01

    Formation energies of different neutral vacancies ( VPb , VTi , VO , and VBa ) in tetragonal PbTiO3 and tetragonal BaTiO3 are studied by means of first-principles pseudopotential calculations. Using thermodynamic laws, we also analytically determine the constraints that yield valid chemical potentials for atomic reservoirs in equilibrium with ferroelectric solids, and examine how the energies of vacancy formation may be modified by varying reservoir conditions. We further contrast the defect energetics in BaTiO3 with those in PbTiO3 , revealing notable differences. Detailed findings of this study are rather lengthy and are summarized in Sec. 4 .

  17. Ultrahigh energy density of polymer nanocomposites containing BaTiO3@TiO2 nanofibers by atomic-scale interface engineering.

    PubMed

    Zhang, Xin; Shen, Yang; Zhang, Qinghua; Gu, Lin; Hu, Yuhan; Du, Jiawen; Lin, Yuanhua; Nan, Ce-Wen

    2015-02-04

    Atomic-scale interface engineering in BaTiO3@TO2 nanofibers (TiO2 nano-fibers embedded with BaTiO3 nano-particles) leads to concurrent enhancement of electric displacement and breakdown strength in poly(vinylidene fluoride) (PVDF)-based nanocomposites. An ultrahigh energy density of ≈20 J cm(-3) is achieved with only 3 vol% nanofibers, which is by far the highest discharged energy density of PVDF-based nanocomposites. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Dielectric response and structure of in-plane tensile strained BaTiO3 thin films grown on the LaNiO3 buffered Si substrate

    NASA Astrophysics Data System (ADS)

    Qiao, Liang; Bi, Xiaofang

    2008-02-01

    Highly (001)-textured BaTiO3 films were grown epitaxially on the LaNiO3 buffered Si substrate. A strong in-plane tensile strain has been revealed by using x-ray diffraction and high resolution transmission electron microscopy. The BaTiO3 film has exhibited a small remnant polarization, indicating the presence of ca1/ca2/ca1/ca2 polydomain state in the film. Temperature dependent dielectric permittivity has demonstrated that two phase transitions occurred at respective temperatures of 170 and 30°C. The result was discussed in detail based on the misfit strain-temperature phase diagrams theory.

  19. Interface induced out-of-plane magnetic anisotropy in magnetoelectric BiFeO3-BaTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Lazenka, Vera; Jochum, Johanna K.; Lorenz, Michael; Modarresi, Hiwa; Gunnlaugsson, Haraldur P.; Grundmann, Marius; Van Bael, Margriet J.; Temst, Kristiaan; Vantomme, André

    2017-02-01

    Room temperature magnetoelectric BiFeO3-BaTiO3 superlattices with strong out-of-plane magnetic anisotropy have been prepared by pulsed laser deposition. We show that the out-of-plane magnetization component increases with the increasing number of double layers. Moreover, the magnetoelectric voltage coefficient can be tuned by varying the number of interfaces, reaching a maximum value of 29 V/cm Oe for the 20×BiFeO3-BaTiO3 superlattice. This enhancement is accompanied by a high degree of perpendicular magnetic anisotropy, making the latter an ideal candidate for the next generation of data storage devices.

  20. Fabrication of Stretchable Nanocomposites with High Energy Density and Low Loss from Cross-Linked PVDF Filled with Poly(dopamine) Encapsulated BaTiO3.

    PubMed

    Xie, Yunchuan; Yu, Yangyang; Feng, Yefeng; Jiang, Wanrong; Zhang, Zhicheng

    2017-01-25

    In this report, a simple solution-cast method was employed to prepare poly(dopamine) (PDA) encapsulated BaTiO3 (BT) nanoparticle (PDA@BT) filled composites using PVDF matrix cross-linked by the free radical initiator. The effects of both the particle encapsulation and matrix cross-linking on the mechanical and dielectric properties of the composites were carefully investigated. The results suggested that the introduction of BT particles improved permittivity of the composites to ∼30 at 100 Hz when particle contents of only 7 wt % were utilized. This was attributed to the enhanced polarization, which was induced by high permittivity ceramic particles. Compared to bare BT, PDA@BT particles could be dispersed more homogeneously in the matrix, and the catechol groups of PDA layer might form chelation with free ions present in the matrix. The latter might depress the ion conduction loss in the composites. Other results revealed that the formation of hydrogen-bonding between the PDA layer and the polymer, especially the chemical cross-linking across the matrix, resulted in increased Young' modulus by ∼25%, improved breakdown strength by ∼40%, and declined conductivity by nearly 1 order of magnitude when compared to BT filled composites. The composite films filled with PDA@BTs indicated greater energy storage capacities by nearly 190% when compared to the pristine matrix. More importantly, the excellent mechanical performance allowed the composite films to adopt uni- or biaxially stretching, a crucial feature required for the realization of high breakdown strength. This work provided a facile strategy for fabrication of flexible and stretchable dielectric composites with depressed dielectric loss and enhanced energy storage capacity at low filler loadings (<10 wt %).

  1. 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.

  2. Creation and destruction of morphotropic phase boundaries through electrical poling: a case study of lead-free (Bi(1/2)Na(1/2))TiO3-BaTiO3 piezoelectrics.

    PubMed

    Ma, Cheng; Guo, Hanzheng; Beckman, Scott P; Tan, Xiaoli

    2012-09-07

    We report the first direct evidence that the morphotropic phase boundary in ferroelectric materials, along with the associated strong piezoelectricity, can be created, destroyed, or even replaced by another morphotropic phase boundary through phase transitions during electrical poling. The real-time evolution of crystal structure and domain morphology during the poling-induced phase transitions in (Bi(1/2)Na(1/2))TiO3}BaTiO3 is observed with in situ transmission electron microscopy. These observations elucidate the microstructural origin of the macroscopic piezoelectricity's dependence on the poling field and previously unexplained strain behaviors. This study demonstrates that the ferroelectric-to-ferroelectric transitions during the poling process can completely alter the morphotropic phase boundaries and, hence, must be comprehensively investigated when interpreting the microscopic mechanism of macroscopic piezoelectric behaviors.

  3. Piezoelectric anisotropy and energy-harvesting characteristics of novel sandwich layer BaTiO3 structures

    NASA Astrophysics Data System (ADS)

    Roscow, James I.; Topolov, Vitaly Yu; Taylor, John T.; Bowen, Christopher R.

    2017-10-01

    This paper presents a detailed modelling and experimental study of the piezoelectric and dielectric properties of novel ferroelectric sandwich layer BaTiO3 structures that consist of an inner porous layer and dense outer layers. The dependencies of the piezoelectric coefficients {d}3j* and dielectric permittivity {\\varepsilon }33* σ of the sandwich structure on the bulk relative density α are analysed by taking into account an inner layer with a porosity volume fraction of 0.5–0.6. The observed changes in {d}3j* and {\\varepsilon }33* σ are interpreted within the framework of a model of a laminar structure whereby the electromechanical interaction of the inner porous layer and outer dense layers have an important role in determining the effective properties of the system. The porous layer is represented as a piezocomposite with a 1–3–0 connectivity pattern, and the composite is considered as a system of long poled ceramic rods with 1–3 connectivity which are surrounded by an unpoled ceramic matrix that contains a system of oblate air pores (3–0 connectivity). The outer monolithic is considered as a dense poled ceramic, however its electromechanical properties differ from those of the ceramic rods in the porous layer due to different levels of mobility of 90° domain walls in ceramic grains. A large anisotropy of {d}3j* at α = 0.64–0.86 is achieved due to the difference in the properties of the porous and monolithic layers and the presence of highly oblate air pores. As a consequence, high energy-harvesting figures of merit {d}3j* {g}3j* are achieved that obey the condition {d}33* {g}33* /({d}31* {g}31* )∼ {10}2 at {d}33* {g}33* ∼ {10}-12 {{{Pa}}}-1, and values of the hydrostatic piezoelectric coefficients {d}h* ≈ 100 {{pC}} {{{N}}}-1 and {g}h* ≈ 20 {{mV}} {{m}} {{{N}}}-1 are achieved at α= 0.64–0.70. The studied BaTiO3-based sandwich structures has advantages over highly anisotropic PbTiO3-type ceramics as a result of the higher piezoelectric activity of ceramic BaTiO3 and can be used in piezoelectric sensor, energy-harvesting and related applications.

  4. Second-harmonic generation of single BaTiO3 nanoparticles down to 22 nm diameter.

    PubMed

    Kim, Eugene; Steinbrück, Andrea; Buscaglia, Maria Teresa; Buscaglia, Vincenzo; Pertsch, Thomas; Grange, Rachel

    2013-06-25

    We investigate the second-harmonic generation (SHG) signal from single BaTiO3 nanoparticles of diameters varying from 70 nm down to 22 nm with a far-field optical microscope coupled to an infrared femtosecond laser. An atomic force microscope is first used to localize the individual particles and to accurately determine their sizes. Power and polarization-dependent measurements on the individual nanoparticles reveal a diameter range between 30 and 20 nm, where deviations from bulk nonlinear optical properties occur. For 22 nm diameter particles, the tetragonal crystal structure is not applicable anymore and competing effects due to the surface to volume ratio or crystallographic modifications are taking place. The demonstration of SHG from such small nanoparticles opens up the possibilities of using them as bright coherent biomarkers. Moreover, our work shows that measuring the SHG of individual nanoparticles reveals critical material properties, opening up new possibilities to investigate ferroelectricity at the nanoscale.

  5. Ferroelectric BaTiO3 thin films on Ni metal tapes using NiO as buffer layer

    NASA Astrophysics Data System (ADS)

    Yuan, Z.; Liu, J.; Weaver, J.; Chen, C. L.; Jiang, J. C.; Lin, B.; Giurgiutiu, V.; Bhalla, A.; Guo, R. Y.

    2007-05-01

    Ferroelectric BaTiO3 (BTO) thin films were deposited on NiO buffered polycrystalline Ni tapes by pulsed laser deposition. Microstructural studies by x-ray diffractometer and transmission electron microscopy reveal that the as-grown BTO films have the nanopillar structures with an average size of approximately 80nm in diameter and the good interface structures with no interdiffusion or reaction. The dielectric and ferroelectric property measurements exhibit that the BTO films have a relatively large dielectric constant, a small dielectric loss, and an extremely large piezoelectric response with a symmetric hysteresis loop. These excellent properties indicate that the as-fabricated BTO films are promising for the development of the structural health monitoring systems.

  6. 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.

  7. 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.

  8. Vacancy-induced magnetism in BaTiO3(001) thin films based on density functional theory.

    PubMed

    Cao, Dan; Cai, Meng-Qiu; Hu, Wang-Yu; Yu, Ping; Huang, Hai-Tao

    2011-03-14

    The origin of magnetism induced by vacancies on BaTiO(3)(001) surfaces is investigated systematically by first-principles calculations within density-functional theory. The calculated results show that O vacancy is responsible for the magnetism of the BaO-terminated surface and the magnetism of the TiO(2)-terminated surface is induced by Ti vacancy. For the BaO-terminated surface, the magnetism mainly arises from the unpaired electrons that are localized in the O vacancy basin. In contrast, for the TiO(2)-terminated surface, the magnetism mainly originates from the partially occupied O-2p states of the first nearest neighbor O atoms surrounding the Ti vacancy. These results suggest the possibility of implementing magneto-electric coupling in conventional ferroelectric materials.

  9. 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.

  10. 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.

  11. Piezoelectric and Triboelectric Dual Effects in Mechanical-Energy Harvesting Using BaTiO3/Polydimethylsiloxane Composite Film.

    PubMed

    Suo, Guoquan; Yu, Yanhao; Zhang, Zhiyi; Wang, Shifa; Zhao, Ping; Li, Jianye; Wang, Xudong

    2016-12-21

    Piezoelectric and triboelectric nanogenerators have been developed as rising energy-harvesting devices in the past few years to effectively convert mechanical energy into electricity. Here, a novel hybrid piezo/triboelectric nanogenerator based on BaTiO3 NP/PDMS composite film was developed in a simple and low-cost way. The effects of the BTO content and polarization degree on the output performance were systematically studied. The device with 20 wt % BTO in PDMS and a 100-μm-thick film showed the highest output power. We also designed three measurement modes to record hybrid, triboelectric, and piezoelectric outputs separately with a simple structure that has only two electrodes. The hybrid output performance is higher than the tribo- and piezoelectric performances. This work will provide not only a new way to enhance the output power of nanogenerators, but also new opportunities for developing built-in power sources in self-powered electronics.

  12. Nanocrystalline ferroelectric BaTiO3/Pt/fused silica for implants synthetized by pulsed laser deposition method

    NASA Astrophysics Data System (ADS)

    Jelínek, Miroslav; Drahokoupil, Jan; Jurek, Karel; Kocourek, Tomáš; Vaněk, Přemysl

    2017-09-01

    The thin-films of BaTiO3 (BTO)/Pt were prepared to test their potential as coatings for titanium-alloy implants. The nanocrystalline BTO/Pt bi-layers were successfully synthesized using fused silica as substrates. The bi-layers were prepared using KrF excimer laser ablation at substrate temperatures (Ts) ranging from 650 °C to 750 °C. The microstructure and composition of the deposits were investigated by scanning electron microscope, x-ray diffraction and wavelength dispersive x-ray spectroscopy methods. The electrical characterization of the Pt/BTO/Pt capacitors indicated ferroelectric-type response in BTO films containing (40-140) nm-sized grains. The technology, microstructure, and functional response of the layers are presented in detail.

  13. Raman tensor elements for tetragonal BaTiO3 and their use for in-plane domain texture assessments

    NASA Astrophysics Data System (ADS)

    Deluca, Marco; Higashino, Masayuki; Pezzotti, Giuseppe

    2007-08-01

    A quantitative assessment of c-axis oriented domains in a textured BaTiO3 (BT) single crystal has been carried out by polarized Raman microprobe spectroscopy. The relative intensity modulation of the Raman phonon modes has been theoretically modeled as a function of crystal rotation and linked to the volume fraction of c-axis oriented domains. Raman tensor elements have also been experimentally determined for the Ag and B1 vibrational modes. As an application, the internal in-plane texture and the volume fraction of c-oriented domains in the BT single crystal have been nondestructively visualized by monitoring the relative intensity of Ag and B1 Raman modes.

  14. Ferroelectric instabilities and enhanced piezoelectric response in Ce modified BaTiO3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Brajesh, Kumar; Kalyani, Ajay Kumar; Ranjan, Rajeev

    2015-01-01

    The crystal structure, ferroelectric, and piezoelectric behaviors of the Ba(Ti1-xCex)O3 solid solution have been investigated at close composition intervals in the dilute concentration regime. Ce concentration as low as 2 mol. % induces tetragonal-orthorhombic instability and coexistence of the phases, leading to enhanced high-field strain and direct piezoelectric response. Detailed structural analysis revealed tetragonal + orthorhombic phase coexistence for x = 0.02, orthorhombic for 0.03 ≤ x ≤ 0.05, and orthorhombic + rhombohedral for 0.06 ≤ x ≤ 0.08. The results suggest that Ce-modified BaTiO3 is a potential lead-free piezoelectric material.

  15. Micropatterning of Ni particles on a BaTiO3 green sheet using a self-assembled monolayer.

    PubMed

    Masuda, Y; Koumura, T; Okawa, T; Koumoto, K

    2003-07-01

    We studied surface modification of ceramic BaTiO(3) green sheets including polyvinylbutyral (PVB) as an organic binder and successfully fabricated a patterned self-assembled monolayer (SAM) which has a region of amino groups and a region of silanol groups on the green sheet. The patterned SAM was then immersed in water containing Ni particles that show negative zeta potential in water. Ni particles were attracted to the amino groups of the patterned SAM that show positive zeta potential by attractive electrostatic interaction. Consequently, a micropattern of Ni particles was achieved using a SAM at room temperature in water. This process can be used to fabricate a thin uniform internal Ni electrode for miniaturized high-performance multilayer ceramic capacitors (MLCC).

  16. 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.

  17. Domain wall contribution to the electrocaloric effect in BaTiO3 nanoparticle: a phase-field investigation

    NASA Astrophysics Data System (ADS)

    Li, B.; Wang, J. B.; Zhong, X. L.; Wang, F.; Liu, B. L.; Zhou, Y. C.

    2013-02-01

    The domain wall contribution to the electrocaloric effect (ECE) in the BaTiO3 (BTO) nanoparticle at room temperature is investigated using a phase-field model combined with thermodynamics analysis. The results show that the domain structure which relates to the size has a significant effect on the ECE in the BTO nanoparticle. When the size of the BTO nanoparticle decreases, the domain structure undergoes a transition from a multidomain structure to a monodomain structure. In the multidomain BTO nanoparticle, the adiabatic temperature change increases with increasing of the domain wall density and domain wall width. In the monodomain BTO nanoparticle, the adiabatic temperature change almost retains constant with the value of 0.95 K which is smaller than that in the multidomain structure. The variation of the adiabatic temperature change at different domain structure is attributed to the domain wall contribution to ECE.

  18. The electrocaloric effect around the orthorhombic- tetragonal first-order phase transition in BaTiO3

    NASA Astrophysics Data System (ADS)

    Bai, Yang; Ding, Kai; Zheng, Guang-Ping; Shi, San-Qiang; Cao, Jiang-Li; Qiao, Lijie

    2012-06-01

    This paper demonstrates the electrocaloric effect (ECE) around BaTiO3's orthorhombic-tetragonal first-order phase transition. By manipulating a field-induced transition of a metastable phase in the thermal hysteresis zone, a huge exothermic or endothermic peak appears after first applying or removing electric fields because of the energy change of lattice structure. A large ECE of ΔT/E = 1.4K.m/MV, equaling to latent heat, is achieved under 10kV/cm at 10°C. The entropy change for polarization ordering alone induces an ECE two orders of magnitude lower under the same condition. It confirms the dominant factor to ECE of the energy flow due to the structural phase transition.

  19. The giant electrocaloric effect and high effective cooling power near room temperature for BaTiO3 thick film

    NASA Astrophysics Data System (ADS)

    Bai, Yang; Zheng, Guang-Ping; Ding, Kai; Qiao, Lijie; Shi, San-Qiang; Guo, Dong

    2011-11-01

    The electrocaloric effect (ECE) of BaTiO3 multilayer thick film was investigated by direct calorimetric measurement. The ECE increases monotonically with the enhancement of applied field. The maximum ECE occurs above Tc and shifts to higher temperature with increasing applied field. Under an ultrahigh field of 800 kV/cm, it exhibits a giant ECE of ΔT = 7.1 K and ΔS = 10.1 J/kg . K at 80 °C. The ECE heat follows a general power-law relation with the varying rate of applied field within a certain range. A high cooling power (˜50 W/kg) is achieved based on the net-cooling resulting from the different varying rates of rising and falling fields.

  20. Polar distortion in ultrathin BaTiO3 films studied by in situ LEED I-V

    NASA Astrophysics Data System (ADS)

    Shin, Junsoo; Nascimento, V. B.; Borisevich, A. Y.; Plummer, E. W.; Kalinin, S. V.; Baddorf, A. P.

    2008-06-01

    Phase stability in nanoscale ferroelectrics is governed by the interplay of electrostatic depolarization energy, domain formation, adsorption, and surface band bending. Using in situ low-energy electron-diffraction intensity versus voltage (LEED I-V ), we have characterized 4 and 10 ML BaTiO3 films, grown using pulsed laser deposition with fully compressive strain on a SrRuO3/SrTiO3 substrate. LEED I-V reveals a single surface dead layer and a monodomain vertically polarized state below. The single orientation is attributed to the intrinsic imprint asymmetry and the stability of a polarized phase to compensation of depolarizing charges by dipoles induced by surface stress.

  1. The coupled effects of oxygen defect and crystallographic orientation on the electromechanical properties of BaTiO3 nanowires

    NASA Astrophysics Data System (ADS)

    Ghorbanali, Saeed; Shahraki, Mehran Gholipour

    2017-02-01

    Influence of oxygen vacancies on electromechanical properties of individual BaTiO3 (BTO) nanowires (NWs) is investigated, using molecular dynamics simulations. The simulations were performed for defected 0-4% oxygen vacancy defects) tetragonal NWs with axial directions of [001] and [110]. Results show an increase in spontaneous polarization and piezoelectric constant of the individual NWs due to increasing oxygen vacancy concentration, and a decrease in yield stress and Young's modulus. It seems that in individual BTO NWs the softening effect of the oxygen vacancies overcomes the pinning effect and results in enhancement of piezoelectric constant and spontaneous polarization. Results also show that yield stress and Young's modulus of the NWs with axial direction of [001] are higher than those for NWs with axial direction of [110] while it is reverse for spontaneous polarization and piezoelectric constant.

  2. Laser Ablated and RF Sputtered BaTiO3 Thin Films for Use in Superconducting RF MEM Switches

    SciTech Connect

    Hijazi, Y.; Bogozi, A.; Brzhezinskaya, M.; Martinez, J.; Noel, J.; Lawrence, L.; Fairweather, D.; Vargas, J.; Vlasov, Yu.; Larkins, G.; Hanna, D.; Kennedy, R.; Stampe, P.

    2004-06-28

    In this work an investigative study of the crystal structure of BaTiO3 thin films prepared using two techniques (laser ablation and RF magnetron sputtering) is presented. These films are to be used as the insulation layer in a capacitively shunted superconducting RF MEM switch with an insertion loss of better than 0.05 dB and an isolation of 30 dB at 3 GHz. Using X-Ray diffraction, the aim of the study is to compare the quality of the sputtered and laser ablated films produced, and study their effect on the RF and mechanical performance of the switch. The crystal structure is expected to have an effect on the effective dielectric constant of the films, which in turn will affect the electrical performance of the switch. This work will report on these results and serve to further enhance the electrical performance of our MEM switches.

  3. Effectiveness of BaTiO3 dielectric patches on YBa2Cu3O7 thin films for MEM switches

    DOE PAGES

    Vargas, J.; Hijazi, Y.; Noel, J.; ...

    2014-05-12

    A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO3 dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO3 insulation layer. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO3 layer. The effect examination of surface morphology will be presented using characterization techniques as x-ray diffraction,more » SEM and AFM for an optimum switching device. The thin film is made of YBa2Cu3O7 deposited on LaAlO3 substrate by pulsed laser deposition. In our work, the dielectric material sputtering pressure is set at 9.5x10-6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate BaTiO3 patches will be shown as part of the results. These novel surface patterns will in turn be used in modelling other RF MEM switch devices such as distributed-satellite communication system operating at cryogenic temperatures.« less

  4. Magnetoelectric effect in laminate composites of Tb1-xDyxFe2-y and Fe-doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Zhang, Ning; Fan, Junfeng; Rong, Xiaofang; Cao, Hongxia; Wei, Jianjun

    2007-03-01

    Fe-doped BaTiO3 has been synthesized with sol-gel technique. Its transformation point of ferroelectric to paraelectric and the latent heat of the transformation were observed at 103.27 °C and 169.9 J/mol, respectively. They are a little less than those for pure BaTiO3. Bonded layered composites Tb1-xDyxFe2-y/BaTi0.99Fe0.01O3 have been fabricated. Their magnetoelectric (ME) effect has been investigated. The transverse ME voltage coefficient for the bilayer Tb1-xDyxFe2-y-BaTi0.99Fe0.01O3 and the trilayer Tb1-xDyxFe2-y-BaTi0.99Fe0.01O3-Tb1-xDyxFe2-y can reach 578 (mv Oe-1 cm-1) and 2100 (mv Oe-1 cm-1), respectively, under a bias magnetic field of 350 Oe at room temperature. Those are about 50% larger than those for the bilayer and trilayer composed by pure BaTiO3. It suggests that the doped BaTiO3 can be a new choice of piezoelectrics to compose ME composites.

  5. First principles study of Ca in BaTiO3 and Bi0.5Na0.5TiO3

    NASA Astrophysics Data System (ADS)

    Fongkaew, Ittipon; T-Thienprasert, Jiraroj; Limpijumnong, Sukit

    2015-11-01

    BaTiO3-Bi0.5Na0.5TiO3 is one of the promising candidates as a high-temperature relaxor with a high Curie temperature and several preferred dielectric characteristics. It has been found experimentally for a long time that adding calcium to BaTiO3-Bi0.5Na0.5TiO3 improves its temperature characteristic of the capacitance [J. Electron. Mater. 39, 2471]. In this study, Calcium (Ca) defects in perovskite BaTiO3 and Bi0.5Na0.5TiO3 have been studied based on first-principles calculations. In both BaTiO3 and Bi0.5Na0.5TiO3, our calculations showed that Ca atom energetically prefers to substitute for the cations, that is Ba, Bi, Na and Ti, depending on the growth conditions. In most cases, Ca predominantly substitutes on the A-site without providing additional electrical carriers (serve as either neutral defects or self-compensating defects). The growth conditions where Ca can be forced to substitute for B-site (with limited amount) and the conditions where Ca can be forced to serve as an acceptor are identified. Details of the local structures, formation energies and electronic properties of these Ca defects are reported.

  6. Preparation and characterization of self-assembled percolative BaTiO3–CoFe2O4 nanocomposites via magnetron co-sputtering

    PubMed Central

    Yang, Qian; Zhang, Wei; Yuan, Meiling; Kang, Limin; Feng, Junxiao; Pan, Wei; Ouyang, Jun

    2014-01-01

    BaTiO3–CoFe2O4 composite films were prepared on (100) SrTiO3 substrates by using a radio-frequency magnetron co-sputtering method at 750 °C. These films contained highly (001)-oriented crystalline phases of perovskite BaTiO3 and spinel CoFe2O4, which can form a self-assembled nanostructure with BaTiO3 well-dispersed into CoFe2O4 under optimized sputtering conditions. A prominent dielectric percolation behavior was observed in the self-assembled nanocomposite. Compared with pure BaTiO3 films sputtered under similar conditions, the nanocomposite film showed higher dielectric constants and lower dielectric losses together with a dramatically suppressed frequency dispersion. This dielectric percolation phenomenon can be explained by the ‘micro-capacitor’ model, which was supported by measurement results of the electric polarization and leakage current. PMID:27877664

  7. Effectiveness of BaTiO 3 dielectric patches on YBa 2 Cu 3 O 7 thin films for MEM switches

    DOE PAGES

    Vargas, J.; Hijazi, Y.; Noel, J.; ...

    2014-05-12

    A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO3 dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO3 insulation layer. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO3 layer. The effect examination of surface morphology will be presented using characterization techniques as x-ray diffraction,more » SEM and AFM for an optimum switching device. The thin film is made of YBa2Cu3O7 deposited on LaAlO3 substrate by pulsed laser deposition. In our work, the dielectric material sputtering pressure is set at 9.5x10-6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate BaTiO3 patches will be shown as part of the results. These novel surface patterns will in turn be used in modelling other RF MEM switch devices such as distributed-satellite communication system operating at cryogenic temperatures.« less

  8. 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.

  9. Polarization-Mediated Modulation of Electronic and Transport Properties of Hybrid MoS2-BaTiO3-SrRuO3 Tunnel Junctions.

    PubMed

    Li, Tao; Sharma, Pankaj; Lipatov, Alexey; Lee, Hyungwoo; Lee, Jung-Woo; Zhuravlev, Mikhail Y; Paudel, Tula R; Genenko, Yuri A; Eom, Chang-Beom; Tsymbal, Evgeny Y; Sinitskii, Alexander; Gruverman, Alexei

    2017-02-08

    Hybrid structures composed of ferroelectric thin films and functional two-dimensional (2D) materials may exhibit unique characteristics and reveal new phenomena due to the cross-interface coupling between their intrinsic properties. In this report, we demonstrate a symbiotic interplay between spontaneous polarization of the ultrathin BaTiO3 ferroelectric film and conductivity of the adjacent molybdenum disulfide (MoS2) layer, a 2D narrow-bandgap semiconductor. Polarization-induced modulation of the electronic properties of MoS2 results in a giant tunneling electroresistance effect in the hybrid MoS2-BaTiO3-SrRuO3 ferroelectric tunnel junctions (FTJs) with an OFF-to-ON resistance ratio as high as 10(4), a 50-fold increase in comparison with the same type of FTJs with metal electrodes. The effect stems from the reversible accumulation-depletion of the majority carriers in the MoS2 electrode in response to ferroelectric switching, which alters the barrier at the MoS2-BaTiO3 interface. Continuous tunability of resistive states realized via stable sequential domain structures in BaTiO3 adds memristive functionality to the hybrid FTJs. The use of narrow band 2D semiconductors in conjunction with ferroelectric films provides a novel pathway for development of the electronic devices with enhanced performance.

  10. 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.

  11. 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

  12. Effects of X-Ray Irradiation and Barium Deficiency on Grain Boundary States in BaTiO3:Ta Ceramics

    NASA Astrophysics Data System (ADS)

    Uchida, Yoshiharu; Kai, Ayako; Murata, Takuya; Miki, Toshikatsu

    2004-02-01

    The effects of x-irradiation and Ba deficiency in BaTiO3:Ta ceramics were investigated in conjunction with the mechanism of an abrupt increase in electrical resistivity at the Curie temperature Tc, which was called the mode-I positive temperature coefficient of resistivity (PTCR). X-irradiation decreases the resistivity and the potential barrier height at grain boundaries in the rhombohedral and cubic specimens, but increases the ESR intensity of a singlet signal at g=2.005. On the other hand, introducing Ba deficiency increases the room-temperature resistivity ρRT and the magnitude of resistivity jump ρmode-I at Tc, but both ρRT and ρmode-I become to decrease when Ba deficiency exceeds 0.03 at%. In highly Ba-deficient specimens, the singlet ESR signal also decreases with increasing Ba deficiency. For explaining the irradiation effects, we proposed two models. One is the hole-recombination model, in which trapped-electrons at VBa-associated acceptor levels recombine with the holes created by irradiation. The other is the electron-detrapping model for the electrons trapped by acceptor levels. The explanation of the effects of x-irradiation and Ba deficiency was attempted by assuming VBa-associated centers (VBa, VBa-VO, VBa-F and VBa-F+). We conclude that predominant acceptor states at grain boundaries are VBa-VO-type defects. It is considered that the mode-I PTCR originats from critical changes in the density of states (DOS) of VBa-VO and the Fermi energy at tetragonal-to-cubic transition. This type of trap activation may lead to the formation of VBa-F+ and VBa-F from VBa-VO.

  13. Hybridization and electron-phonon coupling in ferroelectric BaTiO3 probed by resonant inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Fatale, S.; Moser, S.; Miyawaki, J.; Harada, Y.; Grioni, M.

    2016-11-01

    We investigated the ferroelectric perovskite material BaTiO3 by resonant inelastic x-ray scattering (RIXS) at the Ti L3 edge. We observe with decreasing temperature a transfer of spectral weight from the elastic to the charge-transfer spectral features, indicative of increasing Ti 3 d -O 2 p hybridization. When the incident photon energy selects transitions to the Ti 3 d eg manifold, the quasielastic RIXS response exhibits a tail indicative of phonon excitations. A fit of the spectral line shape by a theoretical model allows us to estimate the electron-phonon coupling strength M ˜0.25 eV, which places BaTiO3 in the intermediate coupling regime.

  14. Dielectric and magnetic characterization of the mixed system (BaTiO3)x(NiFe2O4)1-x

    NASA Astrophysics Data System (ADS)

    Riesco, R.; Peiteado, M.; Bernardo-Maestro, B.; Caballero, A. C.; Cebollada, F.; de Frutos, J.; Gonzalo, J. A.; Aragó, C.

    2015-10-01

    Ceramic composites of the mixed system (BaTiO3)x(NiFe2O4)1-x (x = 1, 0.8, 0.65, 0.6, 0.5, 0.2, 0) have been prepared by hydrothermal synthesis and characterized through dielectric and magnetic measurements. It is shown that, when compared with the first-order phase transition of pure BaTiO3, the ferroelectric response of this mixed system is dramatically smeared by the presence of ferrite and eventually disappears around x ≈ 0.65. The peak of the dielectric constant becomes increasingly smoothed with composition, also diminishing its maximum value as the frequency increases. Moreover, the magnetic behavior is not suppressed by the presence of the ferroelectric perovskite and just qualitative changes occur in the hysteresis parameters on the whole compositional range.

  15. Annealing control of magnetic anisotropy and phase separation in CoFe2O4-BaTiO3 nanocomposite films

    NASA Astrophysics Data System (ADS)

    Rafique, Mohsin; Herklotz, A.; Guo, E.-J.; Roth, R.; Schultz, L.; Dörr, K.; Manzoor, Sadia

    2013-12-01

    Multiferroic heteroepitaxial nanocomposite films of BaTiO3 and CoFe2O4 (CFO) have been grown by pulsed laser deposition employing alternating ablation of two ceramic targets. Films grown at temperatures between 650 °C and 710 °C contain columnar CFO grains about 10-20 nm in diameter embedded in a BaTiO3 matrix. The very strong vertical compression of these grains causes large perpendicular magnetic anisotropy. Post-growth annealing treatments above the growth temperature gradually release the compression. This allows one to tune the stress-induced magnetic anisotropy. Additionally, annealing leads to substantial enhancement of the saturation magnetization MS. Since MS of a pure CFO film remains unchanged by a similar annealing procedure, MS is proposed to depend on the volume fraction of the obtained CFO phase. We suggest that MS can be utilized to monitor the degree of phase separation in nanocomposite films.

  16. Microstructure and dielectric properties of nano-grained X7R type BaTiO3 ceramic capacitors sintered by 2.45 GHz microwave

    NASA Astrophysics Data System (ADS)

    Chen, Cheng-Sao; Chou, Chen-Chia

    2007-12-01

    Systematic investigation on the effects of microwave sintering on the characteristics of nano-grained BaTiO3 (BT) capacitor materials co-doped with yttrium (Y) and magnesium (Mg) elements was carried out. The granular structure in these materials was observed to be relatively insensitive to the sintering temperature and soaking time. The nano-sized BaTiO3 capacitor materials possessing X7R dielectric constant-temperature (K-T) characteristics have been obtained over a wide range of sintering conditions. Transmission electron microscope (TEM) examinations revealed that the detailed microstructural study of these materials is extremely complicated. The unique K-T properties of the materials are ascribed to the duplex structure in the samples, namely finer grains of paraelectric phase and larger grains of ferroelectric phase.

  17. 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.

  18. Temperature-dependent far-infrared reflectance of an epitaxial (BaTiO3)8/(SrTiO3)4 superlattice

    NASA Astrophysics Data System (ADS)

    Železný, V.; Caha, O.; Soukiassian, A.; Schlom, D. G.; Xi, X. X.

    2017-06-01

    Infrared reflectance spectra of the polar optic phonons in a [(BaTiO3)8/(SrTiO3)4] 50 superlattice over the temperature range 8 to 650 K are reported. The spectra exhibit lattice vibration features typical of the perovskite constituents, BaTiO3 and SrTiO3. Using the effective medium approximation for multilayer systems and a fitting procedure, we were able to successfully simulate the infrared reflectivity of the superlattice structures and extract the parameters and dielectric functions of the phonons. When applied at varying temperatures, this approach provides the parameters of the zone-center polar phonons and their temperature dependence. Comparing these results with x-ray diffraction we identified some anomalies in phonon behavior related to the phase transitions that the superlattice undergoes.

  19. Crystal structure and the paraelectric-to-ferroelectric phase transition of nanoscale BaTiO3.

    PubMed

    Smith, Millicent B; Page, Katharine; Siegrist, Theo; Redmond, Peter L; Walter, Erich C; Seshadri, Ram; Brus, Louis E; Steigerwald, Michael L

    2008-06-04

    We have investigated the paraelectric-to-ferroelectric phase transition of various sizes of nanocrystalline barium titanate (BaTiO3) by using temperature-dependent Raman spectroscopy and powder X-ray diffraction (XRD). Synchrotron X-ray scattering has been used to elucidate the room temperature structures of particles of different sizes by using both Rietveld refinement and pair distribution function (PDF) analysis. We observe the ferroelectric tetragonal phase even for the smallest particles at 26 nm. By using temperature-dependent Raman spectroscopy and XRD, we find that the phase transition is diffuse in temperature for the smaller particles, in contrast to the sharp transition that is found for the bulk sample. However, the actual transition temperature is almost unchanged. Rietveld and PDF analyses suggest increased distortions with decreasing particle size, albeit in conjunction with a tendency to a cubic average structure. These results suggest that although structural distortions are robust to changes in particle size, what is affected is the coherency of the distortions, which is decreased in the smaller particles.

  20. Enhanced piezoelectric and mechanical properties of AlN-modified BaTiO3 composite ceramics.

    PubMed

    Xu, Dan; Wang, Lidong; Li, Weili; Wang, Wei; Hou, Yafei; Cao, Wenping; Feng, Yu; Fei, Weidong

    2014-07-14

    BaTiO3-xAlN (BT-xAlN) composite ceramics were prepared by conventional solid state reaction sintering. The effects of the AlN content on the crystalline structures, densities, and electrical and mechanical properties of the BT ceramics were investigated. The BT-1.5%AlN ceramic exhibits a good piezoelectric constant of 305 pC N(-1) and an improved Vickers hardness of 5.9 GPa. The enhanced piezoelectricity originates from interactions between defect dipoles and spontaneous polarization inside the domains due to the occurrence of local symmetry, caused by the preferential distribution of the Al(3+)-N(3-) pairs vertical to the c axis. The hardening of the material is attributed to the improved density, and particle and grain boundary strengthening. Our work indicates that if a suitable doping ion pair is designed, lead-free ceramic systems prepared from ordinary raw materials by a conventional sintering method have a high probability of exhibiting good piezoelectric and mechanical properties simultaneously.

  1. Observation of ferroelectricity at room temperature in ~1 nm thick conducting BaTiO3-δ

    NASA Astrophysics Data System (ADS)

    Lee, Seungran; Baasanforj, L.; Chang, Jungwon; Hwang, Inwoong; Kim, Jungrae; Shim, Seungbo; Song, Jonghyun; Kim, Jinhee

    Efforts to search for new and multi-functionalities in thin-film systems have led important findings of unknown phenomena and functionality which do not appear in bulk systems. As film growth technique is advanced, one can decrease the film thickness even thinner down to ~ nm, its unique physical properties are still appearing. For example, the superconducting metallic state of an LaAlO3/SrTiO3 (LAO/STO) heterostructure was found where LAO is about 3-4 unit cells (uc). An SrRuO3 film exhibited its ferromagnetic metallicity down to 4-6 uc; a few years later, its ferromagnetism was found to be disappeared at 2-3 uc. Meanwhile, theoretical methods have predicted existence of ferroelectrical properties mostly in prototype ferroelectric BaTiO3 (BTO): 3-6 uc. However, experimental verification to find such predicted thickness was hindered by large leakage current. Here we observed that ~1 nm-thick conducting BTO fillms show ferroelectric switching at room temperature (RT), and BTO films are fully-strained on LAO/STO heterostructures thicker than 5 nm thickness. Our experimental results will enlarge applicable functional oxide devices for future applications.

  2. BaTiO3 based relaxor ferroelectric epitaxial thin-films for high-temperature operational capacitors

    NASA Astrophysics Data System (ADS)

    Kumaragurubaran, Somu; Nagata, Takahiro; Takahashi, Kenichiro; Ri, Sung-Gi; Tsunekawa, Yoshifumi; Suzuki, Setsu; Chikyow, Toyohiro

    2015-04-01

    The epitaxial growth of 0.6[BaTiO3]-0.4[Bi(Mg2/3Nb1/3)O3] (BT-BMN) relaxor ferroelectric thin-films on (100) Nb doped SrTiO3 substrates has been achieved and the structure is investigated for high-temperature capacitor applications. The post growth annealing decreases the oxygen vacancy and other defects in BT-BMN films, resulting in the enhancement of dielectric constant. An insertion of intermediate SrRuO3 layers as an electrode instead of Pt, sandwiching the film, is found to be more effective in enhancing the dielectric constant. A very high dielectric constant exceeding 400 was achieved from high-temperature annealed film and the film showed an excellent dielectric constant stability of below 11% in the temperature range of 80-400 °C. This will enable smaller, high-temperature tolerant, monolithically integrated thin-film capacitors on power semiconductor devices.

  3. Positive and negative electrocaloric effect in BaTiO3 in the presence of defect dipoles

    NASA Astrophysics Data System (ADS)

    Ma, Yang-Bin; Grünebohm, Anna; Meyer, Kai-Christian; Albe, Karsten; Xu, Bai-Xiang

    2016-09-01

    The influence of defect dipoles on the electrocaloric effect (ECE) in acceptor doped BaTiO3 is studied by means of lattice-based Monte-Carlo simulations using a Ginzburg-Landau type effective Hamiltonian. Oxygen vacancy-acceptor associates are described by fixed local dipoles with orientation parallel or antiparallel to the external field. By a combination of canonical and microcanonical simulations the ECE is directly evaluated. Our results reveal that in the case of antiparallel defect dipoles the ECE can be positive or negative depending on the dipole density. Moreover, a transition from a negative to positive ECE can be observed when the external field increases. These transitions are due to the delicate interplay of internal and external fields and are explained by the domain structure evolution and related field-induced entropy changes. The results are in good qualitative agreement to those obtained by molecular dynamics simulations employing an ab initio based effective Hamiltonian. Finally, a modified electrocaloric cycle, which makes use of the negative ECE in the presence of defect dipoles, is proposed to enhance the cooling effect.

  4. 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.

  5. 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.

  6. Fabrication of Micro Accelerometer Using Screen Printed BaTiO3 Film on a Ceramic Substrate and Its Characterization

    NASA Astrophysics Data System (ADS)

    Suzuki, Masato; Kobayashi, Yuta; Aoyagi, Seiji; Tajiri, Hiroyuki; Nagahata, Takaya

    The concept of MEMS sensors directly fabricated on a ceramic substrate, which can be used for a package of end product, was proposed. As one of such sensors, a micro accelerometer utilizing a fringe capacitance formed in a ferroelectric material was focused on. For this sensor, in stead of a previously used bulk PZT plate, a screen-printed BaTiO3 (BTO) film on a ceramic alumina substrate was herein employed. A screen-printing method can save the amount of raw material of the film, because a comparatively thick film can be deposited only on a specified area. Moreover, BTO does not contain harmful lead material. The optimal condition for fabricating a BTO film on an alumina substrate with minimum unwanted surface defects was experimentally searched. The number of defects was decreased by employing a metal barrier of Pt layer underneath BTO, and by setting the annealing temperature for crystallization to a higher value of 1,400°C. A comparatively high relative dielectric constant of εr =926 was achieved. An accelerometer using a BTO film was practically fabricated. The sensitivity of it was estimated as 0.1 pF/g, which is degraded a little compare with the previously developed accelerometer using a PZT plate; however, the order is same.

  7. Rapid stability of ferroelectric polarization in the Ca, Ce hybrid doped BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Shujuan; Zhang, Lixue; Wang, Jiping; Shi, Xiujing; Zhao, Yingying; Zhang, Dawei

    2016-12-01

    In this work, we report a rapid stability phenomenon of ferroelectric polarization in the Ca, Ce hybrid doped BaTiO3 ceramics (BCaxT+BTCe8) (x = 10, 20, 24, 30 mol%) prepared by separate doping Ca2+ and Ce4+ ions. Double hysteresis loops are identified in the aged BCaxT+BTCe8 samples; meanwhile, the polarization of these loops present a rapid decrease within very short aging time (about 1 h), and then the polarization remains almost unchanged over the followed ~1000 h. This phenomenon is not reported in previous researches. Raman scattering spectrum indicates that oxygen vacancies are generated because of Ca2+ ions entering into Ti sites partly in the BCaxT+BTCe8 samples, and then the oxygen vacancies are quantitatively characterized by half of the Ce3+ content through the XPS test. The emergence of the aging phenomenon is explained through the defect dipole reorientation mechanism. The larger radius of Ca2+ ions is further discussed as a possible reason for the rapid stability phenomenon of ferroelectric polarization. It may provide an effective design method from the viewpoint of the ionic radius to accelerate polarization stability, and thus to facilitate the possible practical applications of the aging effect.

  8. Effect of sintering temperature and oxygen atmosphere on electrocaloric effect of BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Ren, Xue-Chong; Nie, Wei-Li; Bai, Yang; Qiao, Li-Jie

    2015-09-01

    This paper demonstrates the effect of sintering parameters on the electrocaloric effect (ECE) in BaTiO3 ferroelectric ceramics, especially the sintering temperature and atmosphere. The samples were prepared by solid-state reaction method. With the rise of sintering temperature from 1200 °C to 1350 °C, the grain size increases remarkably and the densification is improved. The 1350 °C sintered sample has better ferroelectricity and higher latent heat for ferroelectric-paraelectric phase transition than those of the 1200 °C sintered sample. Correspondingly, it exhibits much better ECE. If the sample is sintered in pure oxygen, instead of in air, all ferroelectricity, dielectric strength and ECE are further enhanced. The sample sintered at 1350 °C in oxygen exhibits an excellent ECE performance with ΔTmax = 1.37 K and ΔSmax = 1.75 J/kg K. Contribution to the Topical Issue "Materials for Dielectric Applications", edited by Maciej Jaroszewski and Sabu Thomas.

  9. Rapid stability of ferroelectric polarization in the Ca, Ce hybrid doped BaTiO3 ceramics

    PubMed Central

    Liu, Shujuan; Zhang, Lixue; Wang, Jiping; Shi, Xiujing; Zhao, Yingying; Zhang, Dawei

    2016-01-01

    In this work, we report a rapid stability phenomenon of ferroelectric polarization in the Ca, Ce hybrid doped BaTiO3 ceramics (BCaxT+BTCe8) (x = 10, 20, 24, 30 mol%) prepared by separate doping Ca2+ and Ce4+ ions. Double hysteresis loops are identified in the aged BCaxT+BTCe8 samples; meanwhile, the polarization of these loops present a rapid decrease within very short aging time (about 1 h), and then the polarization remains almost unchanged over the followed ~1000 h. This phenomenon is not reported in previous researches. Raman scattering spectrum indicates that oxygen vacancies are generated because of Ca2+ ions entering into Ti sites partly in the BCaxT+BTCe8 samples, and then the oxygen vacancies are quantitatively characterized by half of the Ce3+ content through the XPS test. The emergence of the aging phenomenon is explained through the defect dipole reorientation mechanism. The larger radius of Ca2+ ions is further discussed as a possible reason for the rapid stability phenomenon of ferroelectric polarization. It may provide an effective design method from the viewpoint of the ionic radius to accelerate polarization stability, and thus to facilitate the possible practical applications of the aging effect. PMID:28004752

  10. Integrated silicon nanophotonics: structure and electro-optic properties of BaTiO3 on Si(001)

    NASA Astrophysics Data System (ADS)

    Kormondy, Kristy; Fallegger, Florian; Abel, Stefan; Popoff, Youri; Ponath, Patrick; Posadas, Agham; Sousa, Marilyne; Caimi, Daniele; Siegwart, Heinz; Uccelli, Emanuele; Czornomaz, Lukas; Marchiori, Chiara; Fompeyrine, Jean; Demkov, Alexander

    2015-03-01

    High-quality epitaxial BaTiO3 (BTO) on Si has emerged as a promising material for future electro-optic (EO) devices based on BTO's large effective Pockels coefficient. In order to achieve strong EO coupling, a film must have (1) correct crystallographic orientation with respect to the applied electric field, and (2) low leakage current in the film to sustain a strong electric field. We report on the EO response of BTO films deposited on Si by molecular beam epitaxy. O2 rapid thermal anneal at 600C for 30 min ensures full oxidation of BTO for minimal leakage current with minor change in crystalline structure. EO characterization was performed by analyzing changes of the polarization of a laser beam transmitted through pairs of lithographically defined electrodes. The EO response shows signatures of ferroelectric domains with in-plane polarization. Comparison with normalized responses of c-axis and a-axis films illustrate that a strong EO response is observed even for a mixed film. These results quantify the relationship between BTO structure and EO properties, an important step towards future silicon photonic devices based on ferroelectric oxides.

  11. 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.

  12. Electrocaloric effect in BaTiO3 at all three ferroelectric transitions: Anisotropy and inverse caloric effects

    NASA Astrophysics Data System (ADS)

    Marathe, Madhura; Renggli, Damian; Sanlialp, Mehmet; Karabasov, Maksim O.; Shvartsman, Vladimir V.; Lupascu, Doru C.; Grünebohm, Anna; Ederer, Claude

    2017-07-01

    We study the electrocaloric (EC) effect in bulk BaTiO3 (BTO) using molecular dynamics simulations of a first principles-based effective Hamiltonian, combined with direct measurements of the adiabatic EC temperature change in BTO single crystals. We examine in particular the dependence of the EC effect on the direction of the applied electric field at all three ferroelectric transitions, and we show that the EC response is strongly anisotropic. Most strikingly, an inverse caloric effect, i.e., a temperature increase under field removal, can be observed at both ferroelectric-ferroelectric transitions for certain orientations of the applied field. Using the generalized Clausius-Clapeyron equation, we show that the inverse effect occurs exactly for those cases where the field orientation favors the higher temperature/higher entropy phase. Our simulations show that temperature changes of around 1 K can, in principle, be obtained at the tetragonal-orthorhombic transition close to room temperature, even for small applied fields, provided that the applied field is strong enough to drive the system across the first-order transition line. Our direct EC measurements for BTO single crystals at the cubic-tetragonal and at the tetragonal-orthorhombic transitions are in good qualitative agreement with our theoretical predictions, and in particular confirm the occurrence of an inverse EC effect at the tetragonal-orthorhombic transition for electric fields applied along the [001] pseudocubic direction.

  13. Substantial enhancement of energy storage capability in polymer nanocomposites by encapsulation of BaTiO3 NWs with variable shell thickness.

    PubMed

    Wang, Guanyao; Huang, Yanhui; Wang, Yuxin; Jiang, Pingkai; Huang, Xingyi

    2017-08-09

    Dielectric polymer nanocomposites have received keen interest due to their potential application in energy storage. Nevertheless, the large contrast in dielectric constant between the polymer and nanofillers usually results in a significant decrease of breakdown strength of the nanocomposites, which is unfavorable for enhancing energy storage capability. Herein, BaTiO3 nanowires (NWs) encapsulated by TiO2 shells of variable thickness were utilized to fabricate dielectric polymer nanocomposites. Compared with nanocomposites with bare BaTiO3 NWs, significantly enhanced energy storage capability was achieved for nanocomposites with TiO2 encapsulated BaTiO3 NWs. For instance, an ultrahigh energy density of 9.53 J cm(-3) at 440 MV m(-1) could be obtained for nanocomposites comprising core-shell structured nanowires, much higher than that of nanocomposites with 5 wt% raw ones (5.60 J cm(-3) at 360 MV m(-1)). The discharged energy density of the proposed nanocomposites with 5 wt% mTiO2@BaTiO3-1 NWs at 440 MV m(-1) seems to rival or exceed those of some previously reported nanocomposites (mostly comprising core-shell structured nanofillers). More notably, this study revealed that the energy storage capability of the nanocomposites can be tailored by the TiO2 shell thickness. Finite element simulations were employed to analyze the electric field distribution in the nanocomposites. The enhanced energy storage capability should be mainly attributed to the smoother gradient of dielectric constant between the nanofillers and polymer matrix, which alleviated the electric field concentration and leakage current in the polymer matrix. The methods and results herein offer a feasible approach to construct high-energy-density polymer nanocomposites with core-shell structured nanowires.

  14. The effects of sintering temperature on dielectric constant of Barium Titanate (BaTiO3)

    NASA Astrophysics Data System (ADS)

    Sandi, DianisaKhoirum; Supriyanto, Agus; Anif; Jamaluddin; Iriani, Yofentina

    2016-02-01

    Barium Titanate (BT) has been synthesized using solid-state reaction method. Raw materials are Barium Carbonate (BaCO3) and Titanium Dioxide (TiO2). These materials are mixed for 6 h and sintered at a temperature of 1000oC, 1100oC, and 1200oC for 2 h. The sintering temperature was varied to investigate its effects on microstructure and dielectric constant of BT. The XRD patterns showed that BT becomes homogenous, with the large lattice parameter as the increase of sintering temperature. The crystal structure of BT is tetragonal. The crystalline size and crystallinity of BT at a sintering temperature of 1000oC are 37 nm and 97%. Those values for BT at a sintering temperature of 1100oC are 38 nm and 96%. At a sintering temperature of 1200oC, the values are 41 nm and 97%. The dielectric constant of BT at a sintering temperature of 1000oC, 1100oC, and 1200oC are 148, 163, and 185, respectively. It can be concluded that sintering temperature affects microstructure and dielectric constant of BT. High sintering temperature produces a high dielectric constant of BT. It indicates that crystalline size increases.

  15. Hydrothermal synthesis and properties of NiFe2O4@BaTiO3 composites with well-matched interface

    PubMed Central

    Zhou, Jian-Ping; Lv, Li; Liu, Qian; Zhang, Yu-Xiang; Liu, Peng

    2012-01-01

    NiFe2O4@BaTiO3 multiferroic composite particles were produced by a simple hydrothermal method in two steps: preparing NiFe2O4 nanoparticles and then synthesizing core-shell nanocomposites. Multiferroic composite ceramics were sintered from these powders. X-ray diffraction, Raman scattering and energy dispersive x-ray analyses indicated that the core-shell composites with a NiFe2O4 core and BaTiO3 shell were formed in the hydrothermal environment. Different types of sharp interfaces were self-assembled owing to the minimization of direct elastic energy. The saturation magnetization of the composites linearly increased with the NiFe2O4 content while the dielectric constant decreased. A dielectric peak appeared at around 460 °C because of the oxygen vacancies in the BaTiO3 ceramics. It resulted in an enhancement of magnetic permeability in the composites, indicating magnetoelectric coupling that was also observed by direct magnetoelectric measurements. PMID:27877501

  16. 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

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

    DOE PAGES

    Qiao, Q.; Zhang, Y.; Contreras-Guerrero, Rocio; ...

    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

  18. Dielectric performance of high permitivity nanocomposites: impact of polystyrene grafting on BaTiO 3 and TiO 2

    DOE PAGES

    Grabowski, Christopher A.; Fillery, Scott P.; Koerner, Hilmar; ...

    2016-09-22

    Polymer nanocomposites are a promising concept to improve energy storage density of capacitors, but realizing their hypothetical gains has proved challenging. The introduction of high permittivity fillers often leads to reduction in breakdown strength due to field exclusion, which intensifies the applied electric field within the polymer matrix near nanoparticle interfaces. This has prompted research in developing new nanoparticle functionalization chemistries and processing concepts to maximize particle separation. Herein, we compare the dielectric performance of blended nanocomposites to matrix free assemblies of hairy (polymer-grafted) nanoparticles (HNPs) that exhibit comparable overall morphology. The dielectric breakdown strength of polystyrene-grafted BaTiO3 (PS@BaTiO3) systemsmore » was over 40% greater than a blended nanocomposite with similar loading (~25% v/v BaTiO3). Hairy nanoparticles with TiO2 cores followed similar trends in breakdown strength as a function of inorganic loading up to 40% v/v. Dielectric loss for PS@BaTiO3 HNPs was 2-5 times lower than analogous blended films for a wide frequency spectrum (1 Hz to 100 kHz). For BaTiO3 content above 7% v/v, grafting the polymer chains to the nanoparticle significantly improved energy storage density and efficiency, likely due to the polymer canopy mitigating interfacial transport and restricting particle-particle hot-spots by establishing a finite minimum particle separation.« less

  19. A first-principles study on the mechanism of screening depolarizing field in two-dimensional BaTiO3 nanosheets

    NASA Astrophysics Data System (ADS)

    Gao, Haigen; Yue, Zhenxing; Li, Longtu

    2016-03-01

    A first-principles method is employed to study the mechanism of screening depolarizing field in two-dimensional BaTiO3 nanosheets. The geometric structures and ferroelectric properties show that the low-dimensional BaTiO3 with thickness m = 3 is a freestanding ultrathin film. Therefore, the scale of BaTiO3 nanosheets is defined as m = 1 and 2. The stable domain period corresponding to m = 1, 2, and 3 is 2, 2, and 6, respectively. When m = 1 and 2, only the spontaneous polarizations perpendicular to the surfaces are observed, and they are ˜6 and 15 μC/cm2, respectively. This indicates that the depolarizing field still has an effect on spontaneous polarizations. The difference in macroscopic charge density distribution between ferroelectric and paraelectric phases reveals that a dipole is formed at the ferroelectric domain wall, which leads to a decrease in the depolarizing field in the direction [001]. As a consequence, the critical thickness disappears.

  20. Structures and properties of La- and Sm-doped BaTiO3 sputtered films: Post-annealing and dopant effects

    NASA Astrophysics Data System (ADS)

    Wu, C. H.; Chu, J. P.; Chang, W. Z.; John, V. S.; Wang, S. F.; Lin, C. H.

    2008-01-01

    200-nm-thick La- and Sm-doped BaTiO3 thin films with A /B ratio of unity fabricated by magnetron sputtering on the Pt /Ti/SiO2/Si substrate have been characterized. The effects of post-annealing and the amount of dopant on structure and electrical properties were studied. X-ray diffraction studies reveal that the films annealed at 750°C show tetragonal BaTiO3 crystal structure without any detectable second phase formation. X-ray photoelectron spectroscopy results confirm that La substitutes the A site and Sm is in the B site in lightly doped films. La2O3 or Sm2O3 is present in the BaTiO3 structure when the dopant content is more than 1.4at.% La or 1.0% Sm. The permittivity increases with increasing annealing temperature up to 750°C due to the coarse grains and better crystallinity. The leakage current property is found to vary with the type of dopant.

  1. 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

    2015-01-07

    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.

  2. Biocompatibility and osteogenesis of the castor bean polymer doped with silica (SiO2) or barium titanate (BaTiO3) nanoparticles.

    PubMed

    Nacer, Renato Silva; Silva, Baldomero Antonio Kato da; Poppi, Rodrigo Ré; Silva, Dheywid Karlos Mattos; Cardoso, Vinicius Saura; Delben, José Renato Jurkevicz; Delben, Angela Antonia Sanches Tardivo

    2015-04-01

    To evaluate the biocompatibility and osteogenesis of castor oil polymer doped with SiO2 or BaTiO3 nanoparticles. Twenty four male rats Wistar were submitted to bone defect filled with castor oil polymer. The animals were distributed in two experimental groups had been formed with 12 animals each: Group 1 - Castor oil polymer doped with 0.30 grams of SiO2 replacing 0.30 grams of CaCO3. Group 2 - Castor oil polymer doped with 0.30 grams of BaTiO3 replacing 0.30 grams of CaCO3. Euthanasia occurred 30 and 60 days after surgery and the femurs were sent to histological analysis and MEV. The implants were biocompatible and allowed for progressive osteogenesis through osteoconduction in both observation periods. There was significant bone neoformation at 30 and 60 days in both groups within the histomorphometric evaluation, but group 1's osteogenesis was lesser in the 30 and 60-day periods observed when compared to the animals of group 2. The MEV morphometric evaluation evidenced a lesser percentage of osseous tissue filling within the BaTiO2-doped polymer. The castor oil polymer doped with SiO2 or BaTiO3 remained biocompatible and allowed for progressive osteogenesis in both observation periods.

  3. Excited configurations of hydrogen in the BaTiO3 -xHx perovskite lattice associated with hydrogen exchange and transport

    NASA Astrophysics Data System (ADS)

    Ito, T. U.; Koda, A.; Shimomura, K.; Higemoto, W.; Matsuzaki, T.; Kobayashi, Y.; Kageyama, H.

    2017-01-01

    Excited configurations of hydrogen in the oxyhydride BaTiO3 -xHx (x =0.1 -0.5 ), which are considered to be involved in its hydrogen transport and exchange processes, were investigated by positive muon spin relaxation spectroscopy using muonium (Mu) as a pseudoisotope of hydrogen. Muons implanted into the BaTiO3 -xHx perovskite lattice were mainly found in two qualitatively different metastable states. One was assigned to a highly mobile interstitial protonic state, which is commonly observed in perovskite oxides. The other was found to form an entangled two spin-1/2 system with the nuclear spin of an H- ion at the anion site. The structure of the (H,Mu) complex agrees well with that of a neutralized center containing two H- ions at a doubly charged oxygen vacancy, which was predicted to form in the SrTiO3 -δ perovskite lattice by a computational study [Y. Iwazaki et al., APL Mater. 2, 012103 (2014), 10.1063/1.4854355]. Above 100 K, interstitial Mu+ diffusion and retrapping to a deep defect were observed, which could be a rate-limiting step of macroscopic Mu/H transport in the BaTiO3 -xHx lattice.

  4. 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.

  5. 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

  6. Preparation and Characterization of BaTiO3-PbZrTiO3 Coating for Pyroelectric Energy Harvesting

    NASA Astrophysics Data System (ADS)

    Raghavendra, R. M.; Praneeth, K. P. S. S.; Dutta, Soma

    2017-01-01

    Harvesting energy from waste heat is a promising field of research as there are significant energy recovery opportunities from various waste thermal energy sources. The present study reports pyroelectric energy harvesting using thick film prepared from a (x)BaTiO3-(1 - x)PbZr0.52Ti0.48O3 (BT-PZT) solid solution. The developed BT-PZT system is engineered to tune the ferro to paraelectric phase transition temperature of it in-between the phase transition temperature of BaTiO3 (393 K) and PbZrTiO3 (573 K) with higher pyroelectric figure-of-merit (FOM). The temperature-dependent dielectric behavior of the material has revealed the ferro- to paraelectric phase transition at 427 K with a maximum dielectric constant of 755. The room-temperature (298 K) pyroelectric coefficient (Pi) of the material was obtained as 738.63 μC/m2K which has yielded a significantly high FOM of 1745.8 J m-3 K-2. The enhancement in pyroelectric property is attributed to the morphotopic phase transition between tetragonal and rhombohedral PZT phases in the BT-PZT system. The developed BT-PZT system is capable of generating a power output of 1.3 mW/m2 near the Curie temperature with a constant rate (0.11 K/s) of heating. A signal conditioning circuit has been developed to rectify the time-varying current and voltage signals obtained from the harvester during heating cycles. The output voltage generated by the pyroelectric harvester has been stored in a capacitor for powering wearable electronics.

  7. 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).

  8. Diffraction studies for stoichiometry effects in BaTiO3 grown by molecular beam epitaxy on Ge(001)

    NASA Astrophysics Data System (ADS)

    Hsu, Min-Hsiang Mark; Merckling, Clement; El Kazzi, Salim; Pantouvaki, Marianna; Richard, Oliver; Bender, Hugo; Meersschaut, Johan; Van Campenhout, Joris; Absil, Philippe; Van Thourhout, Dries

    2016-12-01

    In this work, we present a systematic study of the effect of the stoichiometry of BaTiO3 (BTO) films grown on the Ge(001) substrate by molecular-beam-epitaxy using different characterization methods relying on beam diffraction, including reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and selected-area electron diffraction in transmission electron microscopy. Surprisingly, over a wide range of [Ba]/[Ti] ratios, as measured by the Rutherford backscattering spectrometry, all the BTO layers exhibit the same epitaxial relationship <100>BTO(001)//<110>Ge(001) with the substrate, describing a 45° lattice rotation of the BTO lattice with respect to the Ge lattice. However, varying the [Ba]/[Ti] ratio does change the diffraction behavior. From RHEED patterns, we can derive that excessive [Ba] and [Ti] generate twinning planes and a rougher surface in the non-stoichiometric BTO layers. XRD allows us to follow the evolution of the lattice constants as a function of the [Ba]/[Ti] ratio, providing an option for tuning the tetragonality of the BTO layer. In addition, we found that the intensity ratio of the 3 lowest-order Bragg peaks I(001)/I(002), I(101)/I(002), and I(111)/I(002) derived from ω - 2θ scans characteristically depend on the BTO stoichiometry. To explain the relation between observed diffraction patterns and the stoichiometry of the BTO films, we propose a model based on diffraction theory explaining how excess [Ba] or [Ti] in the layer influences the diffraction response.

  9. Enhancement of tetragonal anisotropy and stabilisation of the tetragonal phase by Bi/Mn-double-doping in BaTiO3 ferroelectric ceramics.

    PubMed

    Yabuta, Hisato; Tanaka, Hidenori; Furuta, Tatsuo; Watanabe, Takayuki; Kubota, Makoto; Matsuda, Takanori; Ifuku, Toshihiro; Yoneda, Yasuhiro

    2017-04-03

    To stabilise ferroelectric-tetragonal phase of BaTiO3, the double-doping of Bi and Mn up to 0.5 mol% was studied. Upon increasing the Bi content in BaTiO3:Mn:Bi, the tetragonal crystal-lattice-constants a and c shrank and elongated, respectively, resulting in an enhancement of tetragonal anisotropy, and the temperature-range of the ferroelectric tetragonal phase expanded. X-ray absorption fine structure measurements confirmed that Bi and Mn were located at the A(Ba)-site and B(Ti)-site, respectively, and Bi was markedly displaced from the centrosymmetric position in the BiO12 cluster. This A-site substitution of Bi also caused fluctuations of B-site atoms. Magnetic susceptibility measurements revealed a change in the Mn valence from +4 to +3 upon addition of the same molar amount of Bi as Mn, probably resulting from a compensating behaviour of the Mn at Ti(4+) sites for donor doping of Bi(3+) into the Ba(2+) site. Because addition of La(3+) instead of Bi(3+) showed neither the enhancement of the tetragonal anisotropy nor the stabilisation of the tetragonal phase, these phenomena in BaTiO3:Mn:Bi were not caused by the Jahn-Teller effect of Mn(3+) in the MnO6 octahedron, but caused by the Bi-displacement, probably resulting from the effect of the 6 s lone-pair electrons in Bi(3+).

  10. 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.

  11. Dielectric properties and microstructure of sintered BaTiO3 fabricated by using mixed 150-nm and 80-nm powders with various additives

    NASA Astrophysics Data System (ADS)

    Oh, Min Wook; Kang, Jae Won; Yeo, Dong Hun; Shin, Hyo Soon; Jeong, Dae Yong

    2015-04-01

    Recently, the use of small-sized BaTiO3 particles for ultra-thin MLCC research has increased as a method for minimizing the dielectric layer's thickness in thick film process. However, when particles smaller than 100 nm are used, the reduced particle size leads to a reduced dielectric constant. The use of nanoparticles, therefore, requires an increase in the amount of additive used due to the increase in the specific surface area, thus increasing the production cost. In this study, a novel method of coating 150-nm and 80-nm BaTiO3 powders with additives and mixing them together was employed, taking advantage of the effect obtained through the use of BaTiO3 particles smaller than 100 nm, to conveniently obtain the desired dielectric constant and thermal characteristics. Also, the microstructure and the dielectric properties were evaluated. The additives Dy, Mn, Mg, Si, and Cr were coated on a 150-nm powder, and the additives Dy, Mn, Mg, and Si were coated on 80-nm powder, followed by mixing at a ratio of 1:1. As a result, the microstructure revealed grain formation according to the liquid-phase additive Si; additionally, densification was well realized. However, non-reducibility was not obtained, and the material became a semiconductor. When the amount of added Mn in the 150-nm powder was increased to 0.2 and 0.3 mol%, insignificant changes in the microstructure were observed, and the bulk density after mixing was found to have increased drastically in comparison to that before mixing. Also, non-reducibility was obtained for certain conditions. The dielectric property was found to be consistent with the densification and the grain size. The mixed composition #1-0.3 had a dielectric constant over 2000, and the result somewhat satisfied the dielectric constant temperature dependency for X6S.

  12. Electronic and optical properties of BaTiO3 across tetragonal to cubic phase transition: An experimental and theoretical investigation

    NASA Astrophysics Data System (ADS)

    Mishra, Vikash; Sagdeo, Archna; Kumar, Vipin; Warshi, M. Kamal; Rai, Hari Mohan; Saxena, S. K.; Roy, Debesh R.; Mishra, Vinayak; Kumar, Rajesh; Sagdeo, P. R.

    2017-08-01

    Temperature dependent diffuse reflectance spectroscopy measurements were carried out on polycrystalline samples of BaTiO3 across the tetragonal to cubic structural phase transition temperature (TP). The values of various optical parameters such as band gap (Eg), Urbach energy (Eu), and Urbach focus (E0) were estimated in the temperature range of 300 K to 480 K. It was observed that with increasing temperature, Eg decreases and shows a sharp anomaly at TP. First principle studies were employed in order to understand the observed change in Eg due to the structural phase transition. Near TP, there exist two values of E0, suggesting the presence of electronic heterogeneity. Further, near TP, Eu shows metastability, i.e., the value of Eu at temperature T is not constant but is a function of time (t). Interestingly, it is observed that the ratio of Eu (t=0)/Eu (t = tm), almost remains constant at 300 K (pure tetragonal phase) and at 450 K (pure cubic phase), whereas this ratio decreases close to the transition temperature, which confirms the presence of electronic metastability in the pure BaTiO3. The time dependence of Eu, which also shows an influence of the observed metastability can be fitted with the stretched exponential function, suggesting the presence of a dynamic heterogeneous electronic disorder in the sample across TP. First principle studies suggest that the observed phase coexistence may be due to a very small difference between the total cohesive energy of the tetragonal and the cubic structure of BaTiO3. The present work implies that the optical studies may be a sensitive probe of disorder/heterogeneity in the sample.

  13. Enhancement of tetragonal anisotropy and stabilisation of the tetragonal phase by Bi/Mn-double-doping in BaTiO3 ferroelectric ceramics

    PubMed Central

    Yabuta, Hisato; Tanaka, Hidenori; Furuta, Tatsuo; Watanabe, Takayuki; Kubota, Makoto; Matsuda, Takanori; Ifuku, Toshihiro; Yoneda, Yasuhiro

    2017-01-01

    To stabilise ferroelectric-tetragonal phase of BaTiO3, the double-doping of Bi and Mn up to 0.5 mol% was studied. Upon increasing the Bi content in BaTiO3:Mn:Bi, the tetragonal crystal-lattice-constants a and c shrank and elongated, respectively, resulting in an enhancement of tetragonal anisotropy, and the temperature-range of the ferroelectric tetragonal phase expanded. X-ray absorption fine structure measurements confirmed that Bi and Mn were located at the A(Ba)-site and B(Ti)-site, respectively, and Bi was markedly displaced from the centrosymmetric position in the BiO12 cluster. This A-site substitution of Bi also caused fluctuations of B-site atoms. Magnetic susceptibility measurements revealed a change in the Mn valence from +4 to +3 upon addition of the same molar amount of Bi as Mn, probably resulting from a compensating behaviour of the Mn at Ti4+ sites for donor doping of Bi3+ into the Ba2+ site. Because addition of La3+ instead of Bi3+ showed neither the enhancement of the tetragonal anisotropy nor the stabilisation of the tetragonal phase, these phenomena in BaTiO3:Mn:Bi were not caused by the Jahn-Teller effect of Mn3+ in the MnO6 octahedron, but caused by the Bi-displacement, probably resulting from the effect of the 6 s lone-pair electrons in Bi3+. PMID:28367973

  14. First-principles investigations on polytypes of BaTiO3: Hybrid calculations and pressure dependences

    NASA Astrophysics Data System (ADS)

    Seo, Yu-Seong; Ahn, Jai Seok

    2013-06-01

    We report our first-principles investigations on three polytypes of BaTiO3 (BTO): a paraelectric phase with cubic Pm-3 m structure and two ferroelectric (FE) phases with tetragonal P4 mm and rhombohedral R3 m structures. We compared the structural and the electrical properties of BTO obtained by using various approaches: e.g., the Hartree-Fock (HF) theory, the density functional theory (DFT) with the local density approximation (LDA) or with the two generalized gradient approximations (two GGAs: PWGGA and PBE), and three hybrid functionals of the HF and the DFT (B3LYP, B3PW, and PBE0). For the P4 mm structure, the two GGAs and the hybrid functionals reproduced the cell volumes, but slightly overestimated the c/a ratio. The hybrid functionals provided accurate predictions for the experimental energy gaps, but slightly underestimated the experimental dielectric constants. The calculated dielectric constants were inversely proportional to the c/a ratios for the P4 mm structure (or the c H / a H ratio for the R3 m structure), irrespective of the functional choice. Also, the over-estimated polarization could be ascribed to a super-tetragonality in the GGA/hybrid functionals. The pressure dependences for the cell parameters, fractional atomic displacements, energy gaps, dielectric constants, and FE polarizations were calculated by using the B3PW hybrid functional. As pressure was increased, the polarization decreased monotonically until it reached zero at a critical pressure of ˜ 20 GPa for both the P4 mm and the R3 m structures. Anomalous behaviors were also observed in the atomic movements and the polarizations for the P4 mm structure: δ Ti , the fractional coordinate of Ti, showed a sign reversal at pressures below -8 GPa while the polarization showed a maximum at -2 GPa and then decreased with decreasing pressure. However, such effects were not observed for the R3 m structure: the polarization monotonically increased with decreasing pressure. Such behaviors of the polarizations, together with super-tetragonality/super-trigonality, are discussed.

  15. Pressure dependence of the phonon spectrum in BaTiO3 polytypes studied by ab initio calculations

    NASA Astrophysics Data System (ADS)

    Seo, Yu-Seong; Ahn, Jai Seok

    2013-07-01

    We report the first principles investigations on the phonons of three polytypes of BaTiO3 (BTO): paraelectric (PE) cubic Pm3¯m and two ferroelectric (FE) phases, tetragonal P4mm and rhombohedral R3m. The phonon frequencies were calculated using various exchange-correlation functionals, including density functional theory, Hartree-Fock approximation, and their hybrids were reviewed. The pressure-induced interplays between the modes from individual phases were explored by calculating the phonon modes as a function of pressure, P from -15 to 230 GPa. The pressure-sensitive modes of the FE phases showed softening and converged to the modes of the PE phase at pressures below ˜10 GPa. These results on the FE phases can be interpreted as phonon precursors for a change in symmetry from low- to high-symmetry and partly as a theoretical explanation for the pressure-induced mode-coupling behaviors reported by Sood [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.51.8892 51, 8892 (1995)]. As pressure is applied further beyond ˜50 GPa to the cubic PE phase, the lowest F1u mode softens again and diverges into two separate modes of tetragonal FE P4mm at above ˜150 GPa. These phonon-branching behaviors at high pressures provide a clear reconfirmation of the re-entrant ferroelectricity predicted in earlier papers [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.95.196804 95, 196804 (2005); Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.74.180101 74, 180101 (2006); Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.85.054108 85, 054108 (2012)]. The high-pressure-re-entrant FE polarization was not found in the rhombohedral structure. Instead, the centrosymmetric R3¯m phase was favored at above ˜30 GPa. The phonon modes calculated for the phonon-propagation vectors in the high-symmetry directions show that the Pm3¯m phase exhibits polar instability at the Γ point and nonpolar instability at the X, M, and R points under high pressure.

  16. Direct observation of the critical relaxation of polarization clusters in BaTiO3 using a pulsed x-ray laser technique.

    PubMed

    Namikawa, K; Kishimoto, M; Nasu, K; Matsushita, E; Tai, R Z; Sukegawa, K; Yamatani, H; Hasegawa, H; Nishikino, M; Tanaka, M; Nagashima, K

    2009-11-06

    We have developed a new method to investigate the relaxation time of the dipole moment in polarization clusters in BaTiO3. Time correlation of speckle intensities was measured by the use of a double pulsed soft x-ray laser. The evolution of the relaxation time of the dipole moment near the Curie temperature (T(C)) was investigated. The maximum relaxation time (approximately 90 ps) is shown to appear at a temperature of 4.5 K above the T(C), being coincident with the one where the maximum polarization takes place. This method is widely applicable to any other critical decay processes at phase transitions.

  17. Influences of Orientation on Magnetoelectric Coupling at La1-x Sr x MnO3/BaTiO3 Interface from Ab Initio Calculations

    NASA Astrophysics Data System (ADS)

    Nguyen, Thuy Trang; Yamauchi, Kunihiko; Oguchi, Tamio; Hoang, Nam Nhat

    2017-01-01

    An ab initio study on the magnetoelectric coupling at interfaces of ferromagnetic perovskite Sr-doped LaMnO3 (LSMO) and ferroelectric perovskite BaTiO3 (BTO) with (001) and (111) perovskite orientations is presented. It was found that the interfaces with both orientations exhibit significant magnetoelectric couplings. The effects of the orientation on the magnetoelectric coupling are discussed on the basis of the electronic structure, suggesting that the enhancement of electrostatic-screening-induced magnetoelectric coupling at the (111) interface in comparison with the (001) interface is mainly due to strengthened interfacial coupling.

  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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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.

  20. Poly(vinylidene fluoride) polymer based nanocomposites with enhanced energy density by filling with polyacrylate elastomers and BaTiO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Yu, Ke; Bai, Yuanyuan; Zhou, Yongcun; Niu, Yujuan; Wang, Hong

    2014-02-01

    Polyacrylate elastomers were introduced into poly(vinylidene fluoride) polymer-based nanocomposites filled with BaTiO3 nanoparticles and the three-phase nanocomposite films were prepared. The energy discharged of the nanocomposite with 3 vol. % polyacrylate elastomers is 8.8 J/cm3, approximately 11% higher compared to that of the nanocomposite without adding polyacrylate elastomers. Large elastic deformation of the polyacrylate elastomers increases Maxwell-Wagner-Sillars interfacial polarization and space charge polarization of the nanocomposites with the electric field increasing, which results in increased maximum polarization and energy discharged of the nanocomposites.

  1. 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.

  2. Evolution of structure in Na0.5Bi0.5TiO3 single crystals with BaTiO3

    SciTech Connect

    Ge, Wenwei; Luo, Chengtao; Zhang, Qinhui; Ren, Yang; Li, Jiefang; Luo, Haosu; Viehland, D.

    2014-10-20

    The structural, dielectric, and piezoelectric properties of Na0.5Bi0.5TiO3-x mol. %BaTiO3 (NBT-x%BT) crystals have been investigated. The dielectric and piezoelectric properties of NBT-x%BT were enhanced near x¼5–7. High resolution synchrotron x-ray powder diffraction studies revealed the presence of a phase boundary between monoclinic (Cc) and tetragonal (P4bm) phases near x¼5–7, where the dielectric and piezoelectric properties were enhanced.

  3. Electric modulation of magnetization at the BaTiO3/La0.67Sr0.33MnO3 interfaces

    NASA Astrophysics Data System (ADS)

    Lu, H.; George, T. A.; Wang, Y.; Ketsman, I.; Burton, J. D.; Bark, C.-W.; Ryu, S.; Kim, D. J.; Wang, J.; Binek, C.; Dowben, P. A.; Sokolov, A.; Eom, C.-B.; Tsymbal, E. Y.; Gruverman, A.

    2012-06-01

    We report large (>10%) magnetization modulation by ferroelectric polarization reversal in the ferroelectric-ferromagnetic BaTiO3/La0.67Sr0.33MnO3 (BTO/LSMO) heterostructures. We find that the electrically induced change in magnetization is limited to the BTO/LSMO interface but extends about 3 nm deep into the LSMO layer—far beyond the expected screening length of metallic LSMO. It is suggested that this effect is due to a metal-insulator transition occurring at the BTO/LSMO interface as a result of electrostatic doping.

  4. 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

  5. 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.

  6. Ultra high energy density nanocomposite capacitors using surface-functionalized BaTiO3 nanowires and PVDF-TrFE-CFE

    NASA Astrophysics Data System (ADS)

    Tang, Haixiong; Lin, Yirong; Sodano, Henry A.

    2012-04-01

    High energy density capacitors are critically important in advanced electronic devices and electric power systems due to their reduced weight, size and cost to meet desired applications. Nanocomposites hold strong potential for increased performance, however, the energy density of most nanocomposites is still low compared to commercial capacitors and neat polymers. Here, high energy density nanocomposite capacitors are fabricated using surface-functionalized high aspect ratio barium titanate (BaTiO3) nanowires (NWs) in a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) matrix. These nanocomposites have 63.5% higher dielectric permittivity compared to previous nanocomposites with BaTiO3 nanoparticles and also have high breakdown strength. At a 17.5% volume fraction, the nanocomposites show more than 145.3% increase in energy density above that of the pure P(VDF-TrFE- CFE) polymer (10.48 J/cm3 compared to 7.21 J/cm3). This value is significant and exceeds those reported for the conventional polymer-ceramic composites; it is also more than two times larger than high performance commercial materials. The findings of this research could lead to broad interest due to the potential for fabricating next generation energy storage devices.

  7. Dielectric responses of modified BaTiO3 ceramics in multilayer ceramic capacitors to the combined uniaxial stress and dc bias field

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Yue, Zhenxing; Gui, Zhilun; Li, Longtu

    2008-10-01

    Dielectric measurements of modified BaTiO3 in a multilayer ceramic capacitor (MLCC) show that the application of external uniaxial stress perpendicular to electric field in a MLCC can lead to a slight increase in the dielectric permittivity. The additional application of a dc bias results in a significantly suppressed dielectric permittivity in the temperature range from 228 to 453 K. These observations can be explained as a result of domain wall movements in grains with a core-shell structure, due to the combined stress and dc bias field. As the dc bias increased up to 5.6 MV/m, the Curie peak, which has diffuse phase transition characteristics in the absence of dc bias, becomes sharper, and two new peaks are induced at about 250 and 315 K. Furthermore, the first order paraelectric-ferroelectric phase transition of the modified BaTiO3 ceramic becomes stronger with increasing dc bias when a uniaxial stress is also applied.

  8. Lattice screening of the polar catastrophe and hidden in-plane polarization in KNbO3/BaTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    García-Fernández, Pablo; Aguado-Puente, Pablo; Junquera, Javier

    2013-02-01

    We have carried out first-principles simulations, based on density functional theory, to obtain the atomic and electronic structure of (001) BaTiO3/KNbO3 interfaces in an isolated slab geometry. We tried different types of structures including symmetric and asymmetric configurations and variations in the thickness of the constituent materials. The spontaneous polarization of the layer-by-layer non-neutral material (KNbO3) in these interfaces cancels out almost exactly the “built-in” polarization responsible for the electronic reconstruction. As a consequence, the so-called polar catastrophe is quenched and all the simulated interfaces are insulating. A model, based on the modern theory of polarization and basic electrostatics, allows an estimation of the critical thickness for the formation of the two-dimensional electron gas between 33 and 36 KNbO3 unit cells. We also demonstrate the presence of an unexpected in-plane polarization in BaTiO3 localized at the p-type TiO2/KO interface, even under in-plane compressive strains. We expect this in-plane polarization to remain hidden due to angular averaging during quantum fluctuations unless the symmetry is broken with small electric fields.

  9. 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

  10. Comparative study of conduction-band and valence-band edges of TiO2, SrTiO3, and BaTiO3 by ionization potential measurements

    NASA Astrophysics Data System (ADS)

    Fujisawa, Jun-ichi; Eda, Takumi; Hanaya, Minoru

    2017-10-01

    Here, we report the energy positions of the conduction-band and valence-band edges of anatase titanium dioxide (TiO2), strontium titanate (SrTiO3), and barium titanate (BaTiO3). From the photoelectron yield spectra, the ionization potentials of anatase TiO2, SrTiO3, and BaTiO3 were estimated to be ca. 7.25, 6.90, 7.05 eV, respectively, which correspond to the top of the valence band of each titanium oxide. From these data and their band gaps, it was found that the bottoms of the conduction bands of SrTiO3 and BaTiO3 are positioned above that of anatase TiO2 by 0.40 and 0.23 eV, respectively.

  11. 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.

  12. Light and magnetic field double modulation on the resistive switching behavior in BaTiO3/FeMn/BaTiO3 trilayer films

    NASA Astrophysics Data System (ADS)

    Li, Hongwei; Wu, Shuxiang; Hu, Ping; Li, Dan; Wang, Gaili; Li, Shuwei

    2017-07-01

    An obvious resistive switching (RS) was observed in BaTiO3/FeMn/BaTiO3 (BFB) trilayer films under different conditions. The RS effect was enhanced in light irradiation and restrained in magnetic field. The ratio of high resistance to low resistance of samples annealed at 500 °C is larger than 1500, and the samples showed a good stability. SET and RESET voltages decrease with increasing illumination intensity, but the ON/OFF ratio showed an inverse tendency. Conduction mechanisms in low resistance and high resistance were determined to be Ohmic and space charge limited conduction (SCLC) mechanism, respectively. A redistribution of oxygen vacancies and bound magnetic polaron (BMP) were used for explanation of the mechanism of RS behavior in this system under light irradiation and magnetic field, respectively.

  13. 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.

  14. Crystal structure and polarization hysteresis properties of ferroelectric BaTiO3 thin-film capacitors on (Ba,Sr)TiO3-buffered substrates

    NASA Astrophysics Data System (ADS)

    Maki, Hisashi; Noguchi, Yuji; Kutsuna, Kazutoshi; Matsuo, Hiroki; Kitanaka, Yuuki; Miyayama, Masaru

    2016-10-01

    Ferroelectric BaTiO3 (BT) thin-film capacitors with a buffer layer of (Ba1- x Sr x )TiO3 (BST) have been fabricated on (001) SrTiO3 (STO) single-crystal substrates by a pulsed laser deposition method, and the crystal structure and polarization hysteresis properties have been investigated. X-ray diffraction reciprocal space mapping shows that the BST buffer effectively reduces the misfit strain relaxation of the BT films on SrRuO3 (SRO) electrodes. The BT capacitor with the SRO electrodes on the BST (x = 0.3) buffer exhibits a well-saturated hysteresis loop with a remanent polarization of 29 µC/cm2. The hysteresis loop displays a shift toward a specific field direction, which is suggested to stem from the flexoelectric coupling between the out-of-plane polarization and the strain gradient adjacent to the bottom interface.

  15. Influence of Cooling Duration on the PTCR Effect of Sm3+-doped BaTiO3-based Ceramics Sintered in a Reducing Atmosphere

    NASA Astrophysics Data System (ADS)

    Cheng, Xuxin; Xiaoxia, L.; Chen, Xiaoming

    2017-06-01

    The influence of cooling duration on the electrical properties and the positive temperature coefficient of resistance (PTCR) characteristics of Sm-doped BaTiO3 (BST) ceramics fired at 1200 °C for 30 min in a reducing atmosphere and deoxidized at 800 °C for 1 h were investigated. The cooling duration influenced the PTCR characteristics of the BST specimens. The room-temperature resistivity of the samples firstly reduced and then increased with the increase in the content of Sm2O3. A long cooling duration resulted in low resistivity of the BST ceramics. Meanwhile, the room-temperature resistivity of the BST ceramics decreased with an increase in cooling duration. Furthermore, the S2 samples exhibited a remarkable PTCR effect. The samples exhibited a resistance jump greater than 3.2 orders of magnitude and a low room-temperature resistivity of 228.4Ω·cm.

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

    DOE PAGES

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; ...

    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. Lastly, 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.

  17. 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.

  18. Theoretical Study of the BaTiO3 Powder’s Volume Ratio’s Influence on the Output of Composite Piezoelectric Nanogenerator

    PubMed Central

    Zhou, Xi; Xu, Qi; Bai, Suo; Qin, Yong; Liu, Weisheng

    2017-01-01

    The combination of the piezoelectric materials and polymer is an effective way to make the piezoelectric nanogenerator (PENG) possess both the polymer’s good flexibility and ferroelectric material’s high piezoelectric coefficient. The volume ratio of ferroelectric material in the composite is an important factor that determines the PENG’s output performance. In this paper, the BaTiO3/polydimethylsiloxane (PDMS) composite PENG was demonstrated as having an optimal volume ratio (46%) at which the PENG can output its highest voltage, and this phenomenon can be ascribed to the trade-off between the composite PENG’s top electrode charge and its capacitance. These results are of practical importance for the composite PENG’s performance optimization. PMID:28598406

  19. Effects of BaTiO3 and SrTiO3 as the buffer layers of epitaxial BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Wang, Can; Tian, ShiLu; Zhou, Yong; Ge, Chen; Guo, HaiZhong; He, Meng; Jin, KuiJuan; Yang, GuoZhen

    2017-06-01

    BiFeO3 (BFO) thin films with BaTiO3 (BTO) or SrTiO3 (STO) as buffer layer were epitaxially grown on SrRuO3-covered SrTiO3 substrates. X-ray diffraction measurements show that the BTO buffer causes tensile strain in the BFO films, whereas the STO buffer causes compressive strain. Different ferroelectric domain structures caused by these two strain statuses are revealed by piezoelectric force microscopy. Electrical and magnetical measurements show that the tensile-strained BFO/BTO samples have reduced leakage current and large ferroelectric polarization and magnetization, compared with compressively strained BFO/STO. These results demonstrate that the electrical and magnetical properties of BFO thin films can be artificially modified by using a buffer layer.

  20. Numerical Estimation of the Dependence of Dielectric Constant of BaTiO3 Thick Films on Grain-Size Distribution

    NASA Astrophysics Data System (ADS)

    Yamashita, Kimihiro; Yamazaki, Shozo; Koumoto, Kunihito; Yanagida, Hiroaki

    1981-10-01

    An exponential function of the grain size was assumed in calculating the apparent (total) dielectric constant of BaTiO3 thick films with the average grain diameter known. The function was tested and estimated experimentally, for cases where the grain sizes were calculated using the following methods; the two-dimensional diameter analysis, the Schwartz-Saltykov method and Oel’s method for converting a two-dimensional grain distribution to a spacial grain sizedistribution. Using the present assumed function and the extended logarithmic mixing rule to combine the dielectric constants of individual grains, the grain-size distribution-dependence of the dielectric constant was successfully simulated. From the simulated results it was concluded that the dielectric constants of coarse grains of thick films increase with increase of grain size in the range from room temperature up to 135°C.

  1. Structural and Optical properties of poly-crystalline BaTiO3 and SrTiO3 prepared via solid state route

    NASA Astrophysics Data System (ADS)

    Jarabana, Kanaka M.; Mishra, Ashutosh; Bisen, Supriya

    2016-10-01

    Polycrystalline BaTiO3 (BTO) and SrTiO3 (STO) were synthesized by solid state route method and properties of made polycrystalline were characterized by X-Ray diffraction (XRD), Raman Spectroscopy & FTIR Spectroscopy. XRD analysis shows that samples are crystalline in nature. In Raman Spectroscopy measurement, the experiment has been done with the help of JOBIN-YOVN HORIBA LABRAM HR800 single monochromator, which is coupled with a “peltier cooled” charge coupled device (CCD). Raman Spectroscopy at low temperature measurement shows the phase transition above & below the curie temperature in samples. Fourier transform Infrared spectroscopy was used to determine the Ti-O bond length position.

  2. 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

    2015-12-09

    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.

  3. 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

  4. 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.

  5. Atomic and Electronic Structure of the BaTiO3(001) (5×5)R26.6° Surface Reconstruction

    NASA Astrophysics Data System (ADS)

    Martirez, John Mark P.; Morales, Erie H.; Saidi, Wissam A.; Bonnell, Dawn A.; Rappe, Andrew M.

    2012-12-01

    This contribution presents a study of the atomic and electronic structure of the (5×5)R26.6° surface reconstruction on BaTiO3 (001) formed by annealing in ultrahigh vacuum at 1300 K. Through density functional theory calculations in concert with thermodynamic analysis, we assess the stability of several BaTiO3 surface reconstructions and construct a phase diagram as a function of the chemical potential of the constituent elements. Using both experimental scanning tunneling microscopy (STM) and scanning tunneling spectroscopy measurements, we were able to further narrow down the candidate structures, and conclude that the surface is either TiO2-Ti3/5, TiO2-Ti4/5, or some combination, where Ti adatoms occupy hollow sites of the TiO2 surface. Density functional theory indicates that the defect states close to the valence band are from Ti adatom 3d orbitals (≈1.4eV below the conduction band edge) in agreement with scanning tunneling spectroscopy measurements showing defect states 1.56±0.11eV below the conduction band minimum (1.03±0.09eV below the Fermi level). STM measurements show electronic contrast between empty and filled states’ images. The calculated local density of states at the surface shows that Ti 3d states below and above the Fermi level explain the difference in electronic contrast in the experimental STM images by the presence of electronically distinctive arrangements of Ti adatoms. This work provides an interesting contrast with the related oxide SrTiO3, for which the (001) surface (5×5)R26.6° reconstruction is reported to be the TiO2 surface with Sr adatoms.

  6. Atomic and Electronic Structure of the BaTiO(3)(001) (sqrt[5] × sqrt[5])R26.6° Surface Reconstruction.

    PubMed

    Martirez, John Mark P; Morales, Erie H; Saidi, Wissam A; Bonnell, Dawn A; Rappe, Andrew M

    2012-12-21

    This contribution presents a study of the atomic and electronic structure of the (sqrt[5] × sqrt[5])R26.6° surface reconstruction on BaTiO(3) (001) formed by annealing in ultrahigh vacuum at 1300 K. Through density functional theory calculations in concert with thermodynamic analysis, we assess the stability of several BaTiO(3) surface reconstructions and construct a phase diagram as a function of the chemical potential of the constituent elements. Using both experimental scanning tunneling microscopy (STM) and scanning tunneling spectroscopy measurements, we were able to further narrow down the candidate structures, and conclude that the surface is either TiO(2)-Ti(3/5), TiO(2)-Ti(4/5), or some combination, where Ti adatoms occupy hollow sites of the TiO(2) surface. Density functional theory indicates that the defect states close to the valence band are from Ti adatom 3d orbitals (≈ 1.4 eV below the conduction band edge) in agreement with scanning tunneling spectroscopy measurements showing defect states 1.56 ± 0.11 eV below the conduction band minimum (1.03 ± 0.09 eV below the Fermi level). STM measurements show electronic contrast between empty and filled states' images. The calculated local density of states at the surface shows that Ti 3d states below and above the Fermi level explain the difference in electronic contrast in the experimental STM images by the presence of electronically distinctive arrangements of Ti adatoms. This work provides an interesting contrast with the related oxide SrTiO(3), for which the (001) surface (sqrt[5] × sqrt[5])R26.6° reconstruction is reported to be the TiO(2) surface with Sr adatoms.

  7. 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.

  8. Ab initio hybrid DFT calculations of BaTiO3, PbTiO3, SrZrO3 and PbZrO3 (111) surfaces

    NASA Astrophysics Data System (ADS)

    Eglitis, Roberts I.

    2015-12-01

    The results of ab initio calculations for polar BaTiO3, PbTiO3, SrZrO3 and PbZrO3 (111) surfaces using the CRYSTAL code are presented. By means of the hybrid B3LYP approach, the surface relaxation has been calculated for two possible B (B = Ti or Zr) or AO3 (A = Ba, Pb or Sr) BaTiO3, PbTiO3, SrZrO3 and PbZrO3 (111) surface terminations. According to performed B3LYP calculations, all atoms of the first surface layer, for both terminations, relax inwards. The only exception is a small outward relaxation of the PbO3-terminated PbTiO3 (111) surface upper layer Pb atom. B3LYP calculated surface energies for BaO3, PbO3, SrO3 and PbO3-terminated BaTiO3, PbTiO3, SrZrO3 and PbZrO3 (111) surfaces are considerably larger than the surface energies for Ti (Zr)-terminated (111) surfaces. Performed B3LYP calculations indicate a considerable increase of Tisbnd O (Zrsbnd O) chemical bond covalency near the BaTiO3, PbTiO3, SrZrO3 and PbZrO3 (111) surface relative to the BaTiO3, PbTiO3, SrZrO3 and PbZrO3 bulk. Calculated band gaps at the Γ-point near the PbTiO3, SrZrO3 and PbZrO3 (111) surfaces are reduced, but near BaTiO3 (111) surfaces increased, with respect to the BaTiO3, PbTiO3, SrZrO3 and PbZrO3 bulk band gap at the Γ-point values.

  9. Theory of Isotope Effects in Quantum Paraelectric SrTiO3 and KTaO3 and in Ferroelectric BaTiO_3

    NASA Astrophysics Data System (ADS)

    Ceresoli, Davide; Tosatti, Erio

    2004-03-01

    Quantum fluctuations -- responsible in quantum paraelectric perovskites like SrTiO3 and KTaO3 for the suppression of displacive ferroelectricity otherwise present at the classical level -- can be reduced by substitution with heavier isotopes. By replacing ^16O with ^18O Itoh et al. [1] demonstrated that ferroelectricity can in fact be dramatically restored up to T_c=23 K in SrTiO_3. Theoretically this effect was described by Bishop et al. [2] and to some extent by Roussev et al. [3] at the qualitative level. Recently Yamada et al. [4] also studied isotope substitution in this way as well as a pseudo-spin hamiltonian formalism. We undertook the task of addressing this problem at a more quantitative level, based on a full electronic structure starting point. Density functional calculations and subsequent first principles phonon spectrum calculations were performed for SrTiO_3, KTaO_3, and also for BaTiO3 at their experimental cubic lattice spacings. An unstable k=0 TO phonon mode was found for all of them, indicating classical ferroelectricity as expected. Anharmonic Ginzburg-Landau parameters were also extracted from the energy changes obtained after introduction in the ab-initio calculations of static stabilizing ferroelectric distortions. Subsequently, gaussian fluctuations, both quantum and thermal, were introduced on top of the classical T=0 ferroelectric state by treating the effect of the anharmonic terms within a self-consistent harmonic approximation as done by earlier workers [2,3,4]. Our results correctly indicate the onset of isotope-induced ferroelectricity in SrTiO3 but not in KTaO_3, and also predict an increase of Tc by about 30 K in BaTiO3 that agrees well with earlier Quantum Monte Carlo studies by Zhong et al. [5]. Substitution of nuclei other than oxygen with heavier isotopes is also predicted to enhance ferroelectricity (although much less so than oxygen), at variance with recent claims [6]. M. Itoh, R. Wang, Y. Inaguma, T. Yamaguchi, Y-J. Shan and T. Nakamura, Phys. Rev. Lett. 82, 3540 (1999). A. Bussmann-Holder, H. Büttner and A. R. Bishop, J. Phys. Cond. Matt. 12, L115 (2000). R. Roussev and A. J. Millis, Phys. Rev. B 67, 014105 (2003). Y. Yamada, N. Todoroki and S. Miyashita, cond-mat/0311385 W. Zhong and D. Vanderbilt, Phys. Rev. B 53, 5047 (1996). T. Hidaka and K. Oka, Phys. Rev. B 35, 8502 (1987).

  10. Elemental intermixing within an ultrathin SrRuO3 electrode layer in epitaxial heterostructure BaTiO3/SrRuO3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Zhang, H. B.; Qi, R. J.; Ding, N. F.; Huang, R.; Sun, L.; Duan, C. G.; Fisher, Craig A. J.; Chu, J. H.; Ikuhara, Y.

    2016-01-01

    Aberration corrected scanning transmission electron microscopy is used to directly observe atom columns in an epitaxial BaTiO3 thin film deposited on a 3.6 nm-thick SrRuO3 electrode layer above an SrTiO3 (001) substrate. Compositional gradients across the heterointerfaces were examined using electron energy-loss spectroscopy techniques. It was found that a small amount of Ba and Ti had diffused into the SrRuO3 layer, and that this layer contained a non-negligible concentration of oxygen vacancies. Such point defects are expected to degrade the electrode's electronic conductivity drastically, resulting in a much longer screening length. This may explain the discrepancy between experimental measurements and theoretical estimates of the ferroelectric critical thickness of a BaTiO3 ferroelectric barrier sandwiched between metallic SrRuO3 electrodes, since theoretical calculations generally assume ideal (stoichiometric) perovskite SrRuO3.

  11. 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.

  12. Integration of ferroelectric BaTiO3 with Ge: The role of a SrTiO3 buffer layer investigated using aberration-corrected STEM

    NASA Astrophysics Data System (ADS)

    Wu, HsinWei; Lu, Sirong; Aoki, Toshihiro; Ponath, Patrick; Ekerdt, John G.; Demkov, Alexander A.; McCartney, Martha R.; Smith, David J.

    2017-06-01

    The integration of semiconductors with ferroelectrics having a controlled polarization direction is an ongoing and challenging topic of research. In this work, BaTiO3 (BTO)/SrTiO3 (STO) heterostructures were grown by molecular beam epitaxy either directly with STO substrates or by using 2-nm-thick STO buffer layers on Ge(001) substrates. Sharp, chemically abrupt interfaces and c-axis-oriented BTO films for both types of heterostructures were observed using aberration-corrected scanning transmission electron microscopy and elemental mapping. Anti-phase boundaries as well as ⟨100⟩ misfit dislocations were present in the BTO/STO samples, with the offsets of the dislocation cores varying by distances between 1 and 5 nm away from the BTO/STO interface. Conversely, misfit dislocations were not observed in the BTO/STO/Ge structure although vertical anti-phase boundaries were still common. Overall, the results emphasize the benefits of identifying a suitable buffer layer to ensure the growth of a high quality material having the desired out-of-plane ferroelectric polarization.

  13. Nanostructured lead-free ferroelectric Na0.5Bi0.5TiO3-BaTiO3 whiskers: synthesis mechanism and structure.

    PubMed

    Maurya, Deepam; Petkov, Valeri; Kumar, Ashok; Priya, Shashank

    2012-05-14

    Nanostructured lead-free ferroelectric Na(0.5)Bi(0.5)TiO(3)-BaTiO(3) (NBTBT) whiskers with a high aspect ratio were synthesized topochemically using Na(2)Ti(6)O(13) (NTO) as a host structure for the first time. High energy X-ray diffraction coupled with an atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of the lead-free NBTBT whiskers, which was found to be rhombohedral, i.e. a ferroelectric enabling type. High resolution transmission electron microscopic (HRTEM) analysis revealed local monoclinic-type structural distortions, indicating a modulated structure at the nanoscale in the morphotropic phase boundary (MPB) composition of the lead-free NBTBT whiskers. The structural rearrangement during the synthesis of the lead-free NBTBT whiskers was found to occur via translation of the edge shared octahedra of NTO into a corner sharing coordination. High temperature morphological changes that depict the disintegration of the isolated whiskers into their individual grains due to the higher grain boundary energy have been found to occur in close analogy with Rayleigh-type instability.

  14. 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.

  15. Double hysteresis in BaTiO3/PbZr0.2Ti0.8O3 ferroelectric bilayer thin film

    NASA Astrophysics Data System (ADS)

    Salev, Pavel; Grigoriev, Alexei

    2015-03-01

    We observed two hysteresis loops in BaTiO3/PbZr0.2Ti0.8O3 (BTO/PZT) bilayer thin film. The first loop with polarization of 27 μ C/cm2 was measured in the applied voltage of +/- 20 V. The second hysteresis loop with polarization of 76 μ C/cm2 was measured in the applied voltage of +/- 55 V. Both hysteresis loops showed characteristic shape with concave region followed by saturation region in the broad range of applied voltage frequencies providing strong evidence for ferroelectric origin of both loops. We performed computational analysis of BTO/PZT bilayer based on Landau-Ginzburg-Devonshire model including contributions of electronic band structure. We found an increased concentration of free charge carriers at the interface between BTO and PZT which provides compensation for the bound charge due to polarization mismatch of the layers. Moreover, as the free charge effectively screens polarization in one layer from another, polarization switching of individual layers can be possible. This leads to the conclusion that two hysteresis loops can be a result of polarization switching of the individual layers.

  16. Inhomogeneous crystallinity and its influence on piezoelectricity of Bi12TiO20-BaTiO3 polar composites fabricated by thermal gradient sintering

    NASA Astrophysics Data System (ADS)

    Yu, Dan; Zhao, Minglei; Wang, Chunlei; Wang, Lihai; Yan, Shirui; Wang, Yafei; Gai, Zhigang

    We have previously described the enhancement of piezoelectricity in low crystallinity Bi12TiO20-BaTiO3 (BTO-BT) nanocomposites. This poses a question regarding the effect of the crystallinity on piezoelectricity. Here, the variation of crystallinity and structure that was developed along the temperature gradient was confirmed. The magnitude of the piezoelectric constant was found to have great relationship with the crystallinity and distortion of BiO5 polyhedra of amorphous Bi12TiO20. The highest piezoelectric constant of 13pC/N was obtained together with the lowest crystallinity and highest degree of distortion of BiO5 polyhedra. These results highlight the key role of the amorphous phase and further confirm the importance of distortion of BiO5 polyhedra in influencing the piezoelectricity. In this view, one may also expect that macroscopic polarity could be improved by increasing the amorphous content and the degree distortion of the BiO5 bonding units in the system.

  17. 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.

  18. Multiferroic behavior on nanometric La2/3Ca1/3MnO3 / BaTiO3 bilayers

    NASA Astrophysics Data System (ADS)

    Prieto, Pedro; Ordoñez, John Edward; Gomez, Maria Elena; Lopera, Wilson

    2014-03-01

    We have deposited bilayers of the FM La2/3Ca1/3MnO3 and FE BaTiO3 as a route to design systems with artificial magnetoelectric coupling on LCMO/BTO/Nb:STO system. We maintain a fixed magnetic layer thickness (tLCMO = 48 nm) and varying the thickness of the ferroelectric layer (tBTO = 20, 50, 100 nm). We analyze the influence of the thickness ratio (tBTO/ tLCMO) in electrical and magnetic properties of manganite. From X-ray diffraction analysis we observed that the samples grew textured. Magnetization and transport measurements indicate a possible multiferroic behavior in the bilayer. We found an increase in the Curie and metal-insulator transition temperature in the bilayer in comparison with those for LCMO (48nm)/STO. Hysteresis loops on bilayers show ferromagnetic behavior. This work has been supported by the ``El Patrimonio Autónomo Fondo Nacional de Financiamiento para CT&I FJC'' Colciencias-CENM Research Projects: No. 1106-48-925531 and CI7917-CC 10510 contract 0002-2013 COLCIENCIAS-UNIVALLE.

  19. Correlated rattling-ion origins of dielectric properties in reentrant dipole glasses BaTiO3-BiScO3

    NASA Astrophysics Data System (ADS)

    Krayzman, Victor; Levin, Igor; Woicik, Joseph C.; Bridges, Frank

    2015-11-01

    The local structure of the pseudo-cubic solid solution 0.6BaTiO3-0.4BiScO3, which exhibits reentrant dipole-glass behavior, has been determined using the Reverse Monte Carlo method to simultaneously fit (1) neutron and X-ray total scattering data (including the corresponding real-space pair-distribution functions), (2) Bi and Sc extended X-ray absorption fine structure, and (3) patterns of diffuse scattering in electron diffraction. These structural refinements revealed the multi-site probability density distributions for both Bi (14-sites) and Ti (8 sites), whereas Ba and Sc featured normal unimodal distributions. Bi atoms are displaced along both the <111> and <100> directions, while Ti atoms are shifted along <111>. Correlated dynamic hopping of Bi and Ti over their corresponding split sites combined with chemical disorder is proposed as the origin of the strong frequency dispersion observed in dielectric measurements. The existence of split sites also explains the reentrant dipole-glass behavior reported for this system.

  20. 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.

  1. 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.

  2. Phase Evolution and Nucleus Growth Observation of Solid-State BaTiO3 Powder Prepared by High-Energy Bead Milling for Raw Material Mixing

    NASA Astrophysics Data System (ADS)

    Lee, Ting-Tai; Huang, Chi-Yuen; Chang, Che-Yuan; Lin, Shih-Pin; Su, Che-Yi; Lee, Chun-Te; Fujimoto, Masayuki

    2011-09-01

    The solid-state synthesis, phase evolution, and nucleus growth of the barium titanate (BaTiO3, BT) powder were investigated in this study. Rapid nucleus growth and precursor phase formation of BT were observed at a relatively low temperature of 600 °C by mixing BaCO3 (2 m2/g) and TiO2 (7 m2/g) with a high-energy bead mill. The decomposition of BaCO3 and the formation of the Ba2TiO4 phase were identified by transmission electron microscopy (TEM). On the basis of this observation, the weight loss observed at 600 °C in the derivative thermogravimetry (DTG) curve could also be explained. Furthermore, with increasing calcination temperature, single cubic BT with less than 80 nm fine nuclei/crystallites was observed at 900 °C, and tetragonal BT (c/a > 1.008) with an average particle size of 0.4 µm was obtained at 1000 °C. With regard to the dielectric properties of sintered ceramics, the relative permittivity (ɛr) increased with calcination temperature, and the Curie point also shifted to a progressively higher temperature. However, BT nucleus samples (with low calcination temperatures of 800 and 900 °C) could not satisfy the X7R requirement (Electric Industries Association Standard, the tolerance of capacitance from -55 to +125 °C is ±15%) until calcination temperature increased to 1000 °C.

  3. 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.

  4. Magnetic behavior of La2/3Ca1/3MnO3 / BaTiO3 bilayers

    NASA Astrophysics Data System (ADS)

    Ordonez, John E.; Gomez, Maria E.; Lopera, Wilson; Marin, Lorena; Pardo, Jose A.; Morellon, Luis; Algarabel, Pedro; Prieto, Pedro

    2013-03-01

    We have grown ferroelectric BaTiO3(BTO) and ferromagnetic La2/3Ca1/3MnO3 (LCMO) onto (001) SrTiO3 and Nb:SrTiO3 by pulsed laser deposition (PLD) at pure oxygen atmosphere, and a substrate temperature of 820° C, seeking for a multiferroic behavior in this structure. From x-ray diffraction (XRD) we found lattice parameter aBTO=4.068 Å, and aLCMO=3.804 Å, for each individual layer. In the BTO/LCMO bilayer, (002)-Bragg peak for BTO maintain its position whereas (002) LCMO peak shift to lower Bragg angle indicating a strained LCMO film. Magnetization measurements reveal an increase in the Curie temperature from 170 K to 220 K for the bilayer when LCMO (t = 47 nm) is deposited on BTO (t=52 nm) film, while depositing the BTO (50 nm) above LCMO (48 nm) the Curie temperature remains at values close to that obtained for a LCMO single layer (~175 K), deposited under identical growth parameters This work has been supported by Instituto de Nanociencias de Aragón, Zaragoza, Spain, ``El Patrimonio Autónomo Fondo Nacional de Financiamiento para CT&I FJC'' COLCIENCIAS-CENM Contract RC 275-2011 and Research Project COLCIENCIAS-UNIVALLE.

  5. Fabrication and optical properties of InGaN/GaN multiple quantum well light emitting diodes with amorphous BaTiO3 ferroelectric film

    NASA Astrophysics Data System (ADS)

    Peng, Jing; Wu, Chuan-Ju; Sun, Tang-You; Zhao, Wen-Ning; Wu, Xiao-Feng; Liu, Wen; Wang, Shuang-Bao; Jie, Quan-Lin; Xu, Zhi-Mou

    2012-06-01

    BaTiO3 (BTO) ferroelectric thin films are prepared by the sol-gel method. The fabrication and the optical properties of an InGaN/GaN multiple quantum well light emitting diode (LED) with amorphous BTO ferroelectric thin film are studied. The photoluminescence (PL) of the BTO ferroelectric film is attributed to the structure. The ferroelectric film which annealed at 673 K for 8 h has the better PL property. The peak width is about 30 nm from 580 nm to 610 nm, towards the yellow region. The mixed electroluminescence (EL) spectrum of InGaN/GaN multiple quantum well LED with 150-nm thick amorphous BTO ferroelectric thin film displays the blue-white light. The Commission Internationale De L'Eclairage (CIE) coordinate of EL is (0.2139, 0.1627). EL wavelength and intensity depends on the composition, microstructure and thickness of the ferroelectric thin film. The transmittance of amorphous BTO thin film is about 93% at a wavelength of 450 nm-470 nm. This means the amorphous ferroelectric thin films can output more blue-ray and emission lights. In addition, the amorphous ferroelectric thin films can be directly fabricated without a binder and used at higher temperatures (200 °C-400 °C). It is very favourable to simplify the preparation process and reduce the heat dissipation requirements of an LED. This provides a new way to study LEDs.

  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. 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.

  8. Oxygen Partial Pressure during Pulsed Laser Deposition: Deterministic Role on Thermodynamic Stability of Atomic Termination Sequence at SrRuO3/BaTiO3 Interface.

    PubMed

    Shin, Yeong Jae; Wang, Lingfei; Kim, Yoonkoo; Nahm, Ho-Hyun; Lee, Daesu; Kim, Jeong Rae; Yang, Sang Mo; Yoon, Jong-Gul; Chung, Jin-Seok; Kim, Miyoung; Chang, Seo Hyoung; Noh, Tae Won

    2017-08-16

    With recent trends on miniaturizing oxide-based devices, the need for atomic-scale control of surface/interface structures by pulsed laser deposition (PLD) has increased. In particular, realizing uniform atomic termination at the surface/interface is highly desirable. However, a lack of understanding on the surface formation mechanism in PLD has limited a deliberate control of surface/interface atomic stacking sequences. Here, taking the prototypical SrRuO3/BaTiO3/SrRuO3 (SRO/BTO/SRO) heterostructure as a model system, we investigated the formation of different interfacial termination sequences (BaO-RuO2 or TiO2-SrO) with oxygen partial pressure (PO2) during PLD. We found that a uniform SrO-TiO2 termination sequence at the SRO/BTO interface can be achieved by lowering the PO2 to 5 mTorr, regardless of the total background gas pressure (Ptotal), growth mode, or growth rate. Our results indicate that the thermodynamic stability of the BTO surface at the low-energy kinetics stage of PLD can play an important role in surface/interface termination formation. This work paves the way for realizing termination engineering in functional oxide heterostructures.

  9. Synthesis of BaTiO3 and Ba(ZrxTi1-X)O3 by using the soft combustion method

    NASA Astrophysics Data System (ADS)

    Ahmad, Atiqah; Razak, Khairunisak Abdul

    2017-07-01

    In this work, barium titanate, BaTiO3 (BT) and Zr doped BT, BaZrxTi1-xO3 (BZT) with powders were successfully produced using the soft combustion method. Barium nitrate and titanium (IV) isopropoxide were used as the starting materials while zirconium (IV) oxynitrate hydrate as the doping precursors, and glycine as the combustion agent. The produced powders were pressed into 12 mm diameter pellets by using 150 MPa cold press. The effect of Zr dopant in BT was studied with molar ratio of x = 0.00, 0.03, 0.05, 0.08 and 0.10. The phase presence was identified using X-ray diffractometer. Morphology of powders and sintered pellets was observed using a scanning electron microscope. Density of the sintered pellets was measured by using Archimedes' principle, while dielectric properties were analysed by using an LCR meter. Pure perovskite BT and BZT structure were obtained after sintering at 1400 °C for 5 h. BZT with x = 0.03 has grain size of 3.9 µm and shows the highest dielectric constant of 525, compared to undoped BT that has the average grain size of 4.2 µm with dielectric constant 223. The results is in agreement with microstructure observation and density of the sample.

  10. Potential and piezoelectric response imaging of 180^o domain of atomically ordered clean surfaces of BaTiO3 single crystals in UHV

    NASA Astrophysics Data System (ADS)

    Watanabe, Yukio; Kaku, S.; Matsumoto, D.; Cheong, S. W.

    2009-03-01

    We report the electrostatic and piezoelectric properties of the clean, free surface of BaTiO3 single crystal in ultra high vacuum (UHV) The topographic imaging by AFM confirmed that the surface is atomically wellordered exhibiting clear one-lattice-height atomic steps. The amplitude and the phase image of piezoelectric response microscopy (PFM) identified 180^o domains. The electrostatic potential mapping by Kelvin force microscopy (KFM) of these domains revealed that the shapes of the domains agreed exactly with the PFM images, which confirms the correctness of the standard 180^o domain theory and disagrees with closure domains. However, the potential difference of upward and downward domain is approx. 0.1V, which is 100 times smaller than the value estimated by the standard theory. Similar measurements with changing temperature across Curie temperature show that this result cannot be explained by the compensation of the spontaneous polarization by contamination or oxygen deficiency or ionic conduction). The present results suggest that an intrinsic electrostatic shielding mechanism exists for 180^o domains, which is consistent with the reports of surface electron/hole layers [1]. [4pt] [1] Watanabe et al. PRL86332(2001);Ferroelectr.367, 23(2008) We acknowledge JSPS No.19340084.

  11. Flexoelectric characterization of BaTiO3-0.08Bi(Zn1/2Ti1/2)O3

    NASA Astrophysics Data System (ADS)

    Huang, Shujin; Kim, Taeyang; Hou, Dong; Cann, David; Jones, Jacob L.; Jiang, Xiaoning

    2017-05-01

    Flexoelectricity, the linear coupling between the strain gradient and the induced electric polarization, has been widely studied as a substitution for piezoelectricity among ceramic lead-free materials. Its potential in micro/nano-scale sensing has especially gained attention, outweighing the performance of cutting edge lead-based piezoelectric materials. In this letter, the flexoelectric coefficient of lead-free ceramic BaTiO3-0.08Bi(Zn1/2Ti1/2)O3 (BT-8BZT) was investigated in the transverse mode. The thermal dependence of flexoelectricity in BT-8BZT was investigated at temperatures ranging from 25 °C to 200 °C, and the results were compared with those of BaxSr1-xTiO3 (BST) ceramics. The effective μ12 of BT-8BZT is ˜25 μC/m at room temperature and can remain as high as ˜13 μC/m at 200 °C. This result suggests that BT-8BZT can be effectively used for micro/nano-sensing within a broad range of temperatures.

  12. 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.

  13. An impedance spectroscopy study of magnetodielectric coupling in BaTiO3-CoFe2O4 nanostructured multiferroics

    NASA Astrophysics Data System (ADS)

    Acevedo, Ulises; Lopez-Noda, Rene; Breitwieser, Romain; Calderon, Francisco; Ammar, Souad; Valenzuela, Raul

    2017-05-01

    Granular BaTiO3-CoFe2O4 (BTO-CFO) nanocomposites were prepared by combining polyol synthesis and spark plasma sintering (SPS). This method allows samples with a high density and a very small grain size (less than 150 nm), and thus a large interface area between phases. In order to study the involved magnetoelectric effects, the impedance response of these nanomaterials was measured in the 5 Hz-10 MHz frequency range, under 0-7.5 kOe magnetic applied fields, and in the 40-170°C temperature range. The best agreement to model these results by an equivalent circuit was achieved by means of three parallel RC arrangements connected in series; by their RC values, these circuits are representative of grain boundaries. An association between each RC circuit and each interface (or grain boundary), i. e., BTO-BTO, BTO-CFO, and CFO-CFO, is proposed on the basis of their temperature and magnetic behavior.

  14. Characterization of Fe-doped SrTiO3/BaTiO3 multilayer films and their ethanol sensing applications

    NASA Astrophysics Data System (ADS)

    Supasai, Thidarat; Wisitsoraat, Anurat; Hodak, Satreerat

    2010-03-01

    Fe-doped SrTiO3/BaTiO3 multilayer films have been deposited on alumina substrate using a sol-gel spin coating technique. The field effect scanning electron microscope photographs revealed a mixture of round and facet-shaped crystals in the undoped films. This microstructure disappeared in Fe-doped films which adopted a more porous sponge-like structure. The grain size of the films decreased from 300 nm for undoped films to 100 nm and 70 nm with Fe doping concentrations of 4 and 8 wt%, respectively. The absorption edge energy for X-rays by Fe was found to be about 7121 eV consistent with Fe^2+ oxidation state. Interdigitated electrodes were applied on these films for ethanol gas sensing application. A sensitivity figure of merit based on the relative change in the resistance of the Fe-doped films 8 wt% film was found to be in the 1-3 range for ethanol doses of 100-1000 ppm when operating at 250 C and in the range of 3-10 when the operating temperature was 350 C.

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

    DOE PAGES

    Ni, Yan; Zhang, Zhen; Nlebedim, Cajetan I.; ...

    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

  16. Self-assembled core-shell CoFe2O4@BaTiO3 particles loaded P(VDF-HFP) flexible films with excellent magneto-electric effects

    NASA Astrophysics Data System (ADS)

    Zhou, Ling; Fu, Qiuyun; Zhou, Dongxiang; Zheng, Zhiping; Hu, Yunxiang; Luo, Wei; Tian, Yahui; Wang, Chaohong; Xue, Fei; Tang, Xiahui

    2017-07-01

    Flexible composited multiferroic films with excellent magnetic-electric effects were prepared. The films were composed of self-assembled CoFe2O4@BaTiO3 core-shell nanoparticle fillers and a poly(vinylidene fluoride-co-hexafluoropropene) matrix. The CoFe2O4@BaTiO3 core-shell particles were prepared using a hydrolysis-hydrothermal method. The surface modification of CoFe2O4 with the cationic surfactant cetyltrimethyl ammonium bromide promoted the BaTiO3 nanocrystals' self-assembly precipitation. Compared with the films loaded by bare CoFe2O4, the films filled with core-shell particles exhibited reduced leakage current density, enhanced dielectric properties, ferroelectric (FE) polarization, and magneto-electric (ME) effects. An excellent ME voltage coefficient of 1835 mV/cm Oe was measured at a DC bias field of -3500 Oe and an AC magnetic field of 3.5 Oe with a frequency of 45 kHz. This enhancement of ME effects was attributed to the large FE-ferromagnetic (FM) interface to volume and the increment of induced polarization, which were originated from the efficient impediment of the aggregation of FM fillers in the core-shell matrix.

  17. First-principles study of multiferroic properties of Fe3O4/SrTiO3 and Fe3O4/BaTiO3 [001] superlattices

    NASA Astrophysics Data System (ADS)

    Park, Min Sik; Freeman, A. J.

    2007-03-01

    Multiferroic superlattices are good candidates for the study of the interplay between magnetism and ferroelectricity, and important for multifunctional device applications operating at room temperature. Recently, it was found that the magnetoresistance arising at the Fe3O4/BaTiO3 barrier is strongly bias dependent. We calculated the physical properties for multiferroic superlattices of spinel Fe3O4 (as a ferrimagnet) and perovskite SrTiO3, and BaTiO3 (as ferroelectric materials) by using first-principles density functional calculations with the highly precise full-potential linearized augmented plane wave (FLAPW) method. At the interface, the half-metallicity of bulk Fe3O4 is destroyed, and magnetic moments that are different from bulk Fe are obtained. The ferroelectric instability of BaTiO3 near the interface is also discussed. M. Ziese, A. Bollero, I. Panagiotopoulos, and N. Moutis, Appl. Phys. Lett., 88, 212502 (2006). Wimmer, Krakauer, Weinert, Freeman, Phys.Rev.B, 24, 864 (1981).

  18. Methodical thermolysis of [Ba2Ti2(thd)4(OnPr)8(nPrOH)2] under autogenous pressure followed by combustion for the synthesis of dielectric tetragonal BaTiO3 nanopowder.

    PubMed

    Pol, Vilas G; Thiyagarajan, P; Moreno, Jose M Calderon; Popa, Monica; Kessler, Vadim G; Gohil, Suresh; Seisenbaeva, Gulaim A

    2009-07-06

    The tetragonal BaTiO(3) nanopowder is synthesized in a solvent-less, efficient process by the thermolysis of a single [Ba(2)Ti(2)(thd)(4)(OnPr)(8)(nPrOH)(2)] precursor in a closed reactor at 700 degrees C under autogenous pressure, followed by combustion. This paper compiles the synthesis of the [Ba(2)Ti(2)(thd)(4)(OnPr)(8)(nPrOH)(2)] precursor, its analysis by mass spectrometry, and implementation for the fabrication of dielectric tetragonal BaTiO(3) nanopowder by controlled efficient thermal decomposition. The as-prepared, intermediate, and final forms of the obtained nanomaterials are systematically analysed by XRD, Raman, and EDS measurements to gain structural and compositional information. Employing HR-SEM, TEM, and HR-TEM techniques, the morphological changes during the structural evolution of all the phases are pursued. The mechanistic elucidation for the fabrication of BaTiO(3) nanopowder is developed on the basis of TGA and DTA data obtained for the initial [Ba(2)Ti(2)(thd)(4)(OnPr)(8)(nPrOH)(2)] reactant as well as the as-prepared BaCO(3) with amorphous Ti phase.

  19. Ferroelectric substrate effects on the magnetism, magnetotransport, and electroresistance of La0.7Ca0.3MnO3 thin films on BaTiO3

    NASA Astrophysics Data System (ADS)

    Alberca, A.; Munuera, C.; Tornos, J.; Mompean, F. J.; Biskup, N.; Ruiz, A.; Nemes, N. M.; de Andres, A.; León, C.; Santamaría, J.; García-Hernández, M.

    2012-10-01

    La0.7Ca0.3MnO3 optimally doped epitaxial films were grown on ferroelectric BaTiO3 substrates. Electronic transport (magnetoresistance and electroresistance) and magnetic properties showed important anomalies in the temperature interval between 60 and 150 K, below the metal-insulator transition. Scanning probe microscopy revealed changes in BaTiO3 surface morphology at those temperatures. La0.7Ca0.3MnO3 thickness is a critical factor: 120-Å-thick films showed large anomalies sensitive to electric poling of the BaTiO3, whereas the behavior of 150-Å-thick films is closer to that of the reference La0.7Ca0.3MnO3 samples grown on SrTiO3. We propose that, through inhomogenous strain and electric polarization effects, the ferroelectric substrate induces an inhomogenous spin distribution in the magnetic layer. This would imply the coexistence of in-plane and out-of-plane ferromagnetic patches in La0.7Ca0.3MnO3, possibly interspersed with antiferromagnetic regions, as it has recently been theoretically predicted. Substrate poling effects are investigated, and a magnetoelectric coupling is demonstrated.

  20. Microscopic distribution of metal dopants and anion vacancies in Fe-doped BaTiO3-δ single crystals

    NASA Astrophysics Data System (ADS)

    Chakraborty, Tanushree; Meneghini, Carlo; Aquilanti, Giuliana; Ray, Sugata

    2013-06-01

    A detailed microscopic structural study on two single crystalline dilute magnetic oxides, BaTi0.95Fe0.05O3-δ with and without perceptible δ, has been carried out. Although it has been reported earlier that varying δ significantly affects high temperature ferromagnetism, the real distribution/redistribution of vacancies and dopant Fe ions inside the 6H hexagonal structure was never probed. This study reveals that oxygen vacancies reduce the dopant Fe3+ ions to Fe2+ and mostly accumulate around these Fe2+ ions. Another distinct trend is the tendency of the dopant Fe ions to get closer instead of being distributed randomly, thereby creating {{Fe}}_{2}^{2+}{{O}}_{9-{\\delta }^{\\prime}} like dimers within the 6H hexagonal unit cell. This experimental observation definitively confirms previous hypotheses based on theoretical models.

  1. Dielectric behaviour of BaTiO3-based ceramic multilayer capacitors under high dc bias field

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Yue, Zhenxing; Zhao, Jianqiang; Wen, Hai; Wang, Xiaohui; Li, Longtu

    2006-08-01

    The dielectric behaviour of X7R-MLCCs with different active layers under high dc bias field (up to 6.25 MV m-1) has been investigated in the whole measurement temperature range from 213 to 453 K. The results show that as the dc bias field increases, the dielectric permittivity in the whole measurement range and the frequency dispersion at lower temperature are both suppressed, while dielectric loss initially decreases till the temperature reaches about 423 K and subsequently remains invariable. These results are attributed to the response of the core-shell structure in grains to the applied dc bias field. Furthermore, the dielectric permittivity of X7R-MLCCs with more dielectric layers is more significantly affected because of a more powerful pinning effect of the residual stress between the dielectric layer and the Ni electrode on the migration of the domain walls and the influence of created interfaces on dielectric properties of the dielectric materials close to the interface. The Curie peaks for two samples shift towards higher temperature at a rate 0.55 × 10-5 K m V-1 in the presence of the dc bias field. It is more significant that an interesting field-induced transition from paraelectric phase to ferroelectric phase in the shell part was found at about 323 K and Curie temperature.

  2. 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

  3. The Effects of Gd/Nd Co-Doping on the Microstructure and Dielectric Properties of BaTiO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Tang; Bin; Zhang; ShuRen; Zhou; XiaoHua

    2009-11-01

    In order to obtain X7R (-55 to 125 °C, ΔC/C = ±15% or less) ceramics sintered at a middle temperature, the effects of Gd2O3 and Nd2O3 additives on the microstructure and dielectric properties of BaTiO3 (BT)-Nb2O5-ZnO-borosilicate system were investigated. When the amount of Gd2O3 was stable, the dielectric constant at room temperature (ɛ25 °C) monotonously decreased as the Nd2O3 content increased from 0.1 to 0.7 wt %. Minimal influence was observed on the high temperature coefficient of capacitance (TCC125 °C). In contrast, when the Nd2O3 content remained unchanged and Gd2O3 was increased, the dielectric constant ɛ25 °C at room temperature first declined and then increased and the TCC125 °C value decreased. Additionally, the TCC125 °C value of BT ceramics was positively correlated to the micro-stress. For Gd/Nd co-doped ceramics, TCC125 °C value was determined only by the Gd2O3 content. BT ceramics sintered at 1140 °C in air have the following properties: ɛ25 °C> 3000, tan δ≤1.0%, ρ≥1011 Ω·cm and ΔC/C (-55 to +125 °C) ≤ ±7.5%.

  4. Dielectric Properties and Microstructures of Low-Temperature-Sintered BaTiO3-Based Ceramics with CuBi2O4 Sintering Aid

    NASA Astrophysics Data System (ADS)

    Hasegawa, Tomoyuki; Otagiri, Tadashi

    2006-09-01

    The low-temperature sintering of BaTiO3 (BT) ceramics was investigated by conventional ceramics processing using a CuBi2O4 sintering aid, and the dielectric properties and microstructures of the ceramics were examined. BT powders without CuBi2O4 could not be fully densified at sintering temperatures lower than 1300 °C. However, the addition of CuBi2O4 markedly enhanced the sinterbility of BT powders, and the sintering temperature decreased from 1300 to 920 °C. This may be due to the promotion of liquid-phase sintering. 6.0 wt % CuBi2O4-added BT ceramics sintered at 920 °C exhibited a high density of 5.95 g/cm3. Moreover, to obtain dielectric ceramics with a stable temperature coefficient of capacitance, the effects of ZnO addition on the dielectric properties and microstructures of low-temperature-sintered BT ceramics with a CuBi2O4 sintering aid were also studied. It was found that the addition of ZnO was very effective for improving the temperature coefficient of capacitance and reducing the dielectric loss of the low-temperature-sintered specimens. This is attributable to the microstructural change involving the formation of a core-shell structure, as shown by transmission electron microscopy and X-ray energy-dispersive spectrometry (TEM-EDS). Therefore, a high dielectric constant of 1900, a low dielectric loss of 0.6% and a stable temperature coefficient of capacitance (X7R EIA standard of Δ C/C25 {\\degC}=± 15% in the temperature range from -55 to +125 °C) were obtained for 1.0 wt % ZnO-added BT ceramics with 6.0 wt % CuBi2O4 sintered at 930 °C for 2 h.

  5. High dielectric constant and low dielectric loss hybrid nanocomposites fabricated with ferroelectric polymer matrix and BaTiO3 nanofibers modified with perfluoroalkylsilane

    NASA Astrophysics Data System (ADS)

    Zhang, Xianhong; Ma, Yuhong; Zhao, Changwen; Yang, Wantai

    2014-06-01

    Interfacial interaction and compatibility between the ceramic dielectric and polymer matrix have strong impact on the dielectric permittivity and dielectric loss of their composites. In this work, we presented a simple strategy to fabricate flexible dielectric composite of high dielectric constant BaTiO3 (BT) nanofiber and ferroelectric poly(vinylidene fluoride) (PVDF) matrix. The electrospun BT nanofiber was sintered at about 800 °C to form perovskite crystalline. Fluorosilane 1H,1H,2H,2H-perfluorooctyltrimethoxysilane was used to introduce a short perfluoroalkyl chain to the surface of BT nanofiber by silane coupling. The effects of content of modified BT nanofiber on the dielectric performance of the composites were investigated by broadband dielectric spectroscopy. The results in comparison with pure PVDF showed that the dielectric constant increased about 2 times (from 10 to 22) and dielectric loss tan δ reduced about 50% (from 0.12 to 0.06) when the loading of modified BT nanofiber was up to 20 v%. In the same loading fraction of BT nanofibers (10 v%), the dielectric loss of fluorosilane modified sample (tan δ = 0.08) was lower than that of unmodified one (tan δ = 0.1). In the range of 20-100 °C, the k showed almost no dependence on the temperature. However, the dielectric loss revealed a trend of decreasing at first and increased later with the increasing of temperature, and reached the lowest value (tanδ = 0.01) at about 60 °C.

  6. An evidence of trap activation for positive temperature coefficient of resistivity in BaTiO3 ceramics with substitutional Nb and Mn as impurities

    NASA Astrophysics Data System (ADS)

    Miki, Toshikatsu; Fujimoto, Akira; Jida, Shin'suke

    1998-02-01

    The mechanism of the electrical resistivity increase above the Curie temperature TC [so-called positive temperature coefficient of resistivity (PTCR) effect] in BaTi1-x-yNbxMnyO3 ceramics is studied with the temperature-dependent resistivity and electron paramagnetic resonance (EPR) data and the calculated energy levels of various Mn-associated centers. The activation energy of trapped electrons at grain boundary interface states is deduced from the resistivity data. The deduced value is found to be nearly equal to the activation energy of Mn2+ and/or singlet EPR signals. This indicates that the EPR signals arising at the cubic phase are due to trapped-electron centers at grain boundaries, and that the centers responsible for the EPR signals contribute to the rise of grain boundary barrier above TC. The PTCR mechanism is separately discussed for mode I of abrupt resistivity jump at TC and mode II of moderate resistivity increase at higher temperatures. From the analyses of resistivity and EPR data, we found that mode II PTCR is well explained by the Heywang model, but mode I PTCR is hardly explained only by the effect of spontaneous polarization proposed by Jonker. Defect models of Mn-VO, Mn-VO-Mn, and Mn-O-Nb-VO type are proposed for Mn associated centers and VBa-VO or VO-VTi-VO type for cation-vacancy-associated centers, taking the local electroneutrality requirement for stable defects and the electronic energy change of substitutional Mn by phase transitions into account. Changes of the electronic energy levels of such defects by phase transitions successfully explain not only the PTCR and EPR data but also the degraded PTCR by incomplete or overabundant oxidation. A part of the Mn-VO centers formed at low Mn contents release electrons at the tetragonal phase forming Mn3+-VO with an effective charge of +1 to act as a charge compensator for negatively charged acceptors at the grain boundary, but the Mn-VO centers hardly act as acceptor-type electron-trapping centers at the cubic phase. At high Mn concentrations, the Mn-VO-Mn type di-Mn center acts as an acceptor-type electron-trapping center at both tetragonal and cubic phases. A trap activation occurs in one type of Mn-O-Mn-VO centers at the tetragonal-to-cubic transition. We conclude that the trap activaiton of the Mn interface states by the tetragonal-to-cubic transition significantly contributes to the PTCR effect of BaTiO3 ceramics with a high content of Mn.

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

    DOE PAGES

    Yue -Wei Yin; Tao, Jing; Huang, Wei -Chuan; ...

    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

  8. 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.

  9. Étude théorique de la photoconductivité et de l'absorption photoinduite de BaTiO{3} et de KNbO{3} dopés au fer

    NASA Astrophysics Data System (ADS)

    Khatib, D.; Radoua, A.; Krätzig, E.

    1998-11-01

    Calculation of conductivity, and study of photoconductivity and light induced absorption in a iron doped BaTiO3 and KNbO3 are performed at many light intensities. The results are interpreted with the help of two impurity levels bands model. This model allows as to calculate a dark conductivity, to explain behaviour of the photoconductivity with a regard to the light intensities, and to study the light induced absorption coefficient by using impurities concentrations. Le calcul de la conductivité et l'étude de la photoconductivité et de l'absorption photoinduite dans BaTiO3 et KNbO3 dopés au fer sont effectués pour différentes intensités d'éclairement. Les résultats sont interprétés à l'aide d'un modèle de bandes à deux niveaux d'impuretés. Il permet de calculer la conductivité, d'expliquer le comportement de la photoconductivité vis a vis de l'intensité de l'éclairement, et d'étudier le coefficient d'absorption photoinduite, en utilisant les concentrations des impuretés.

  10. 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.

  11. 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

  12. 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.

  13. Type-I pseudo-first-order phase transition induced electrocaloric effect in lead-free Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Feng; Chen, Guorui; Liu, Xing; Zhai, Jiwei; Shen, Bo; Li, Shandong; Li, Peng; Yang, Ke; Zeng, Huarong; Yan, Haixue

    2017-05-01

    In this study, the electrocaloric effect (ECE) of Bi0.5Na0.5TiO3-0.06BaTiO3 (BNT-0.06BT) ceramic has been directly measured using a home-made adiabatic calorimeter. The maximum adiabatic temperature change (ΔT) approaches 0.86 K under an electric field of 5 kV/mm at 110 °C, which provides experimental evidence for optimizing the ECE near the type-I pseudo-first-order phase transition (PFOPT). Most importantly, a considerable ΔT value can be maintained over a wide temperature range well above the temperature of the PFOPT under a high electric field. In addition, ΔT is closely related to the structural transition and electric field strength. This work provides a guideline to investigate the high ECE in BNT-based ferroelectric ceramics for applications in cooling technologies.

  14. Electric-field-induced phase transformation at a lead-free morphotropic phase boundary: Case study in a 93%(Bi0.5Na0.5)TiO3-7% BaTiO3 piezoelectric ceramic

    NASA Astrophysics Data System (ADS)

    Daniels, John E.; Jo, Wook; Rödel, Jürgen; Jones, Jacob L.

    2009-07-01

    The electric-field-induced strain in 93%(Bi0.5Na0.5)TiO3-7%BaTiO3 polycrystalline ceramic is shown to be the result of an electric-field-induced phase transformation from a pseudocubic to tetragonal symmetry. High-energy x-ray diffraction is used to illustrate the microstructural nature of the transformation. A combination of induced unit cell volumetric changes, domain texture, and anisotropic lattice strains are responsible for the observed macroscopic strain. This strain mechanism is not analogous to the high electric-field-induced strains observed in lead-based morphotropic phase boundary systems. Thus, systems which appear cubic under zero field should not be excluded from the search for lead-free piezoelectric compositions.

  15. Crystal Structural Analyses of Ferrielectric Tetragonal (Bi1/2Na1/2)TiO3-7%BaTiO3 Powders and Single Crystals

    NASA Astrophysics Data System (ADS)

    Kitanaka, Yuuki; Ogino, Motohiro; Hirano, Kiyotaka; Noguchi, Yuji; Miyayama, Masaru; Kagawa, Yutaka; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Torii, Shuki; Kamiyama, Takeshi

    2013-09-01

    We have investigated the crystal structure of (Bi1/2Na1/2)TiO3-7%BaTiO3 (BNT-7%BT) by high-resolution neutron powder diffraction (NPD) and high-energy synchrotron radiation X-ray diffraction (SR-XRD) analyses. The NPD study revealed that the BNT-7%BT crystals have a single-phase tetragonal structure with P4bm symmetry. The crystal structure refined by the Rietveld method was found to be similar to the ferrielectric P4bm phase reported for BNT at a high temperature of 673 K. The SR-XRD analyses for single crystals of BNT-7%BT demonstrated that the P4bm phase remains as a stable phase in the crystals even after a high electric field is applied for poling, which is different from the structural analysis of ceramics by Ma et al. [Phys. Rev. Lett. 109 (2012) 107602].

  16. 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.

  17. Enhanced piezoelectric properties of lead-free 0.935(Bi0.5Na0.5)TiO3-0.065BaTiO3 thin films fabricated by using pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Park, J. S.; Lee, M. H.; Kim, D. J.; Do, D.; Kim, M.-H.; Kim, J. S.; Song, T. K.; Kim, S. W.; Choi, H. I.; Jang, K. W.; Hwang, I. R.; Park, B. H.

    2013-04-01

    0.935(Bi0.5Na0.5)TiO3-0.065BaTiO3 (BNT-BT) thin films have been grown on Pt(111)/Ti/SiO2/Si substrates by using a pulsed laser deposition method. Deposition conditions of oxygen pressure and deposition temperature were changed. The BNT-BT thin film deposited at 750 °C and 300 mTorr exhibited a slim hysteresis loop with a remnant polarization (2 P r ) of 11 µC/cm2 and a low leakage current density of 7.3 × 10-5 A/cm2 at 98 kV/cm. The piezoelectric responses of the thin films were investigated using piezoelectric force microscopy with a lock-in amplifier. The thin films exhibited piezoelectric properties with a d 33, f value of 168 pm/V.

  18. 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.

  19. Giant strain in lead-free piezoceramics Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3 system

    NASA Astrophysics Data System (ADS)

    Zhang, Shan-Tao; Kounga, Alain Brice; Aulbach, Emil; Ehrenberg, Helmut; Rödel, Jürgen

    2007-09-01

    Piezoelectric actuators convert electrical into mechanical energy and are implemented for many large-scale applications such as piezoinjectors and ink jet printers. The performance of these devices is governed by the electric-field-induced strain. Here, the authors describe the development of a class of lead-free (0.94-x)Bi0.5Na0.5TiO3-0.06BaTiO3-xK0.5Na0.5NbO3 ceramics. These can deliver a giant strain (0.45%) under both unipolar and bipolar field loadings, which is even higher than the strain obtained with established ferroelectric Pb(Zr ,Ti)O3 ceramics and is comparable to strains obtained in Pb-based antiferroelectrics.

  20. 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).

  1. Regional Homogeneity

    PubMed Central

    Jiang, Lili; Zuo, Xi-Nian

    2015-01-01

    Much effort has been made to understand the organizational principles of human brain function using functional magnetic resonance imaging (fMRI) methods, among which resting-state fMRI (rfMRI) is an increasingly recognized technique for measuring the intrinsic dynamics of the human brain. Functional connectivity (FC) with rfMRI is the most widely used method to describe remote or long-distance relationships in studies of cerebral cortex parcellation, interindividual variability, and brain disorders. In contrast, local or short-distance functional interactions, especially at a scale of millimeters, have rarely been investigated or systematically reviewed like remote FC, although some local FC algorithms have been developed and applied to the discovery of brain-based changes under neuropsychiatric conditions. To fill this gap between remote and local FC studies, this review will (1) briefly survey the history of studies on organizational principles of human brain function; (2) propose local functional homogeneity as a network centrality to characterize multimodal local features of the brain connectome; (3) render a neurobiological perspective on local functional homogeneity by linking its temporal, spatial, and individual variability to information processing, anatomical morphology, and brain development; and (4) discuss its role in performing connectome-wide association studies and identify relevant challenges, and recommend its use in future brain connectomics studies. PMID:26170004

  2. Electrical characterization and analysis of the degradation of electrode Schottky barriers in BaTiO3 dielectric materials due to hydrogen exposure

    NASA Astrophysics Data System (ADS)

    Heidary, Damoon Sohrabi Baba; Qu, Weiguo; Randall, Clive A.

    2015-03-01

    Hydrogen gas creates a highly damaging environment that degrades electrical properties in oxide based dielectrics and piezoelectrics. In this study, the degradation resistivity due to hydrogen gas in a barium titanate X7R dielectric is designed and processed for base metal electrode capacitors. The present paper is devoted to I-V measurements and the loss of resistivity in the electrode Schottky barriers. The DC degradation and asymmetries noted in I-V forward and reverse biasing conditions were assumed to be hydrogen ion interstitials, locally creating donor substitutions. Thermionic and field emission conductivity mechanisms are applied to model the I-V data; the conductivity is controlled by the Schottky barrier heights and hydrogen ions localizing at the interfaces. Finally, a mechanism was proposed for resistivity degradation due to exposure to hydrogen gas. The proposed mechanism predicts the degradation should be reversible, and its validity was examined by recovery tests.

  3. Positive Temperature Coefficient of Resistivity Effect of Semiconducting BaTiO3-(Bi1/2Na1/2)TiO3 Ceramics Prepared by a Wet-Chemistry Route

    NASA Astrophysics Data System (ADS)

    Xiang, Ping-Hua; Takeda, Hiroaki; Shiosaki, Tadashi

    2007-10-01

    Without any additional donor dopants, BaTiO3-(Bi1/2Na1/2)TiO3 (BT-BNT) positive temperature coefficient of resistivity (PTCR) ceramics were successfully prepared by a wet-chemistry route. With 2 mol % BNT addition, the obtained BT-BNT ceramics had semiconductivity and exhibited a PTCR behavior at about 155 °C. The onset temperature of the PTCR effect increased to ˜165 °C for the 4 mol % BNT added samples. Room-temperature resistivity ρRT increased with the content of BNT added and the ceramics changed from a semiconductor to an insulator, which was consistent with the variation of the microstructure. The temperature of resistivity anomaly in BT-BNT ceramics also increased with increasing BNT content. A small amount of manganese (Mn) dopant was found to improve the PTCR effect in the BT-BNT system. The possible mechanism underlying the PTCR effect in BT-BNT ceramics was proposed.

  4. Study of dielectric behavior of ternary mixtures of epoxy/titanates (MgTiO3, CaTiO3, SrTio3 and BaTiO3) with carbon black

    NASA Astrophysics Data System (ADS)

    Khouni, Habib; Bouzit, Nacerdine; Jiménez, Juan Pablo Martinez; Bouamar, Mohamed

    2016-12-01

    The aim of this paper is to study and to model the dielectric behavior of various ternary composites prepared with epoxy resin (RE), one type of titanates (magnesium titanate MgTiO3, calcium titanate CaTiO3, strontium titanate SrTiO3, and barium titanate BaTiO3) with carbon black (CB). The study has therefore been focused on the effect of adding carbon black to titanate included in an epoxy matrix. The effects have been quantified according to the volume fraction of carbon black. In this work, we present a method based on nonlinear optimization for determining the permittivity of the every constituent, in order to minimize systematic errors and mount the effect of carbon black. The time domain reflectometry (TDR) approach is used to characterize the samples under test in the range from DC to 10 GHz. The conductivity behavior study is performed at a low frequency of 400 MHz, throughout this work. We explain the carbon black effect on the ternary mixtures by using the substitution principle for predicting their dielectric behavior. The experimental results confirm the concordance with the modified Lichtenecker mixture law. To predict the electromagnetic behavior of the ternary composites in quantitative manner, we use a numerical optimization method for identification the parameters of the theoretical model. Finally, these materials find their interest in the miniaturization of electronic components used in microelectronic and telecommunication applications.

  5. Temperature-induced local and average structural changes in BaTiO3-xBi(Zn1/2Ti1/2)O3 solid solutions: The origin of high temperature dielectric permittivity

    NASA Astrophysics Data System (ADS)

    Hou, Dong; Usher, Tedi-Marie; Zhou, Hanhan; Raengthon, Natthaphon; Triamnak, Narit; Cann, David P.; Forrester, Jennifer S.; Jones, Jacob L.

    2017-08-01

    The existence of local tetragonal distortions is evidenced in the BaTiO3-xBi(Zn1/2Ti1/2)O3 (BT-xBZT) relaxor dielectric material system at elevated temperatures. The local and average structures of BT-xBZT with different compositions are characterized using in situ high temperature total scattering techniques. Using the box-car fitting method, it is inferred that there are tetragonal polar clusters embedded in a non-polar pseudocubic matrix for BT-xBZT relaxors. The diameter of these polar clusters is estimated as 2-3 nm at room temperature. Sequential temperature series fitting shows the persistence of the tetragonal distortion on the local scale, while the average structure transforms to a pseudocubic paraelectric phase at high temperatures. The fundamental origin of the temperature stable permittivity of BT-xBZT and the relationship with the unique local scale structures are discussed. This systematic structural study of the BT-xBZT system provides both insight into the nature of lead-free perovskite relaxors, and advances the development of a wide range of electronics with reliable high temperature performance.

  6. 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.

  7. Relaxation dynamics of lead-free (Na1/2Bi1/2)TiO3-BaTiO3 single crystals studied by Brillouin scattering

    NASA Astrophysics Data System (ADS)

    Lee, Byoung Wan; Ko, Jae-Hyeon; Li, Xiaobing; Luo, Haosu

    2016-10-01

    The acoustic properties of 0.95(Na1/2Bi1/2)TiO3-0.05BaTiO3 (NBT-0.05BT) single crystals were investigated in a hypersonic frequency range and compared to those of archetypal relaxor Pb(Mg1/3Nb2/3)O3 (PMN). Temperature dependences of the Brillouin frequency shift of the longitudinal acoustic (LA) mode, as well as its half width, of NBT-5%BT and PMN exhibited diffuse and broad anomalies over a wide temperature range, which were related to the softening of the sound velocity and substantial increase in the hypersonic damping toward the dielectric maximum temperature. These broad acoustic anomalies of unpoled NBT-0.05BT suggest the existence of noncentrosymmetric polar nanoregions in the paraelectric phase which do not evolve into a long-range ferroelectric order. The calculated relaxation times of NBT-0.05BT exhibited much longer values compared to those of PMN, which suggests that the size of polar nanoregions of NBT-0.05BT is larger than that of PMN.

  8. 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).

  9. Electric properties of high strain textured Na 0.5Bi 0.5TiO 3-BaTiO 3-K 0.5Na 0.5NbO 3 thick films

    NASA Astrophysics Data System (ADS)

    Fu, Fang; Zhai, Jiwei; Xu, Zhengkui; Bai, Wangfeng; Yao, Xi

    2011-05-01

    Textured (1 - x)(0.94Na 0.5Bi 0.5TiO 3 - 0.06BaTiO 3) - xK 0.5Na 0.5NbO 3 (abbreviated as NBT-BT-KNN) thick film on platinum substrate was prepared via tape casting method. The structure and electrical properties of the thick films were investigated. The results show that the thick films possess typical polycrystalline perovskite structures and the orientation degree reached to 75%. The remnant polarization ( Pr) and coercive field ( Ec) were optimized to 11.2 μC/cm 2 and 12.8 kV/cm for x = 0.02 thick film. The dielectric properties of NBT-BT-KNN thick films as a function of temperature were also investigated. With the addition of KNN, the Td (depolarization temperature) and TC (Curie temperature) are all decreased. Meanwhile, the dielectric constant is increased with the addition of the KNN at room temperature. The piezoelectric constant of the thick film was calculated from unipolar electric field-induced strain curve. With the addition of KNN, the d33 value increased and reached to the maximum value of 349 pm/V for x = 0.02 thick film.

  10. 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.

  11. Influence of the concentration in Fe-doped BaTiO 3 on magnetoelectric couping of layered composites BaTi 1-xFe xO 3-Tb 1-yDy yFe 2-z

    NASA Astrophysics Data System (ADS)

    Zhang, Ning; Wei, Jianjin

    Perovskites BaTi 1-xFe xO 3 has been synthesized with the concentration x ranging from 0.01 to 0.02. Their transformation point of ferroelectric to paraelectric and the corresponding latent heat of the phase transformation were observed to decrease with increasing the doping level of Fe 3+. Bonded layered composites BaTi 1-xFe xO 3-Tb 1-yDy yFe 2-z have been fabricated and their magnetoelectric effect has been investigated. The sample containing a layer of perovskite BaTi 0.985Fe 0.015O 3 was found to show the maximum transverse ME voltage coefficient, which is about 1422 mV Oe -1 cm -1 under a magnetic field of 1580 Oe, in these bilayers. Analysis shows that the Fe-doped BaTiO 3 with doping level at about 1.5% should have largest piezoelectric coefficient in these ceramics BaTi 1-xFe xO 3.

  12. 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.

  13. Time and frequency-dependence of the electric field-induced phase transition in BaTiO3-BiZn1/2Ti1/2O3

    NASA Astrophysics Data System (ADS)

    Iamsasri, Thanakorn; Esteves, Giovanni; Choe, Hyeokmin; Vogt, Marco; Prasertpalichat, Sasiporn; Cann, David P.; Gorfman, Semën; Jones, Jacob L.

    2017-08-01

    The time and frequency dependence of the electric field-induced phase transition in BaTiO3-BiZn1/2Ti1/2O3 was studied using in situ X-ray diffraction. The kinetics of the field-induced phase transition between cubic and tetragonal phases was described using a modified Kolmogorov-Avrami-Ishibashi (KAI) equation. Unlike previous works, for which some assumptions (e.g., unimodal and Gaussian) on the distribution of transition rates are needed, the present work utilized Bayesian inference and a Markov chain Monte Carlo algorithm to obtain the distribution of transition rates empirically without a priori assumption on the distribution. The results show that the transition rate coefficient increases as the frequency of applied field increases. The mean value of exponent n in the modified-KAI equation was close to 1, implying that the field-induced phase transition is site saturated and the growth of the induced phase occurred primarily from the surface.

  14. 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.

  15. Enhanced torsional actuation and stress coupling in Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 lead-free piezoceramic system

    DOE PAGES

    Berik, Pelin; Maurya, Deepam; Kumar, Prashant; ...

    2017-01-09

    This paper is concerned with the development of a piezoelectric d15 shear-induced torsion actuator made of a lead-free piezoceramic material exhibiting giant piezoelectric shear stress coefficient (e15) and piezoelectric transverse shear actuation force comparable to that of leadbased shear-mode piezoceramics. The Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 (NBT-BTMn) composition exhibited excellent properties as a torsional transducer with piezoelectric shear stress coefficient on the order of 11.6 C m–2. The torsional transducer, consisting of two oppositely polarized NBT-BT-Mn d15 mode piezoceramic shear patches, provided a rate of twist of 0.08 mm m–1 V–1 under quasi-static 150 V drive. The high value of piezoelectric shear d15more » coefficient in NBT-BT-Mn sample further demonstrated its potential in practical applications. Lastly, these results confirm that the lead-free piezoceramics can be as effective as their lead-based counterparts.« less

  16. Electronic structures and abnormal phonon behaviors of cobalt-modified Na0.5Bi0.5TiO3-6%BaTiO3 single crystals

    NASA Astrophysics Data System (ADS)

    Huang, T.; Zhang, P.; Xu, L. P.; Chen, C.; Zhang, J. Z.; Hu, Z. G.; Luo, H. S.; Chu, J. H.

    2016-10-01

    Optical properties, electronic structures, and structural variations of x wt% cobalt (Co) doped Na0.5Bi0.5TiO3-6%BaTiO3 (x=0%, 0.5%, 0.8%) single crystals have been studied by temperature-dependent optical ellipsometry and Raman spectra from 250 to 650 K. Based on the temperature evolution of electronic transitions (Ecp1 and Ecp2) and the phonon modes involving Ti-O vibrations, two critical temperature points exhibit an increasing trend with Co dopants, which are related to structural variations for ferroelectric to anti-ferroelectric, and anti-ferroelectric to paraelectric transition, respectively. Additionally, distinguishing abnormal phonon behaviors can be observed from Raman spectra for the crystal of x=0.5% and 0.8%, which show reverse frequency shift of the modes involving Ti-O vibration. It can be ascribed to different relative concentration of Co2+ and Co3+ in the crystals, which has been confirmed by X-ray Photoelectron Spectroscopy data.

  17. Thermally stable electrostrains of morphotropic 0.875NaNbO3-0.1BaTiO3-0.025CaZrO3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Qi, He; Zuo, Ruzhong; Fu, Jian; Dou, Mengxian

    2017-03-01

    The 0.875NaNbO3-0.1BaTiO3-0.025CaZrO3 relaxor ferroelectric ceramics were reported to exhibit thermally stable electrostrains (˜0.15% @ 6 kV/mm) from room temperature (RT) to ˜175 °C and comparable strain hysteresis (<13%) to that of typical lead-based piezoelectric ceramics. Dominant strain contribution mechanisms with increasing temperature were analyzed by means of temperature-dependent permittivity, polarization, and strain measurements and synchrotron x-ray diffraction. The rhombohedral (R) and tetragonal (T) morphotropic phase boundary provided a solid structural base for temperature-stable piezoelectric strains from RT to ˜140 °C. The growth of polar nanoregions (pseudocubic) into microdomains (R) and subsequent field-induced R-T phase transition, as well as large electrostrictive effects, sequentially contributed to high electrostrain levels in the proximity of the Curie temperature (from 140 to 175 °C). In addition, the observed low strain hysteresis was attributed to the small strain fraction from domain switching. These experimental results demonstrated that NaNbO3-based relaxor ferroelectrics might be potential lead-free materials for actuator applications.

  18. Enhanced torsional actuation and stress coupling in Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 lead-free piezoceramic system

    PubMed Central

    Berik, Pelin; Maurya, Deepam; Kumar, Prashant; Kang, Min Gyu; Priya, Shashank

    2017-01-01

    Abstract This paper is concerned with the development of a piezoelectric d 15 shear-induced torsion actuator made of a lead-free piezoceramic material exhibiting giant piezoelectric shear stress coefficient (e 15) and piezoelectric transverse shear actuation force comparable to that of lead-based shear-mode piezoceramics. The Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 (NBT-BT-Mn) composition exhibited excellent properties as a torsional transducer with piezoelectric shear stress coefficient on the order of 11.6 C m–2. The torsional transducer, consisting of two oppositely polarized NBT-BT-Mn d 15 mode piezoceramic shear patches, provided a rate of twist of 0.08 mm m–1 V–1 under quasi-static 150 V drive. The high value of piezoelectric shear d 15 coefficient in NBT-BT-Mn sample further demonstrated its potential in practical applications. These results confirm that the lead-free piezoceramics can be as effective as their lead-based counterparts. PMID:28179958

  19. Enhanced torsional actuation and stress coupling in Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 lead-free piezoceramic system.

    PubMed

    Berik, Pelin; Maurya, Deepam; Kumar, Prashant; Kang, Min Gyu; Priya, Shashank

    2017-01-01

    This paper is concerned with the development of a piezoelectric d15 shear-induced torsion actuator made of a lead-free piezoceramic material exhibiting giant piezoelectric shear stress coefficient (e15) and piezoelectric transverse shear actuation force comparable to that of lead-based shear-mode piezoceramics. The Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 (NBT-BT-Mn) composition exhibited excellent properties as a torsional transducer with piezoelectric shear stress coefficient on the order of 11.6 C m(-2). The torsional transducer, consisting of two oppositely polarized NBT-BT-Mn d15 mode piezoceramic shear patches, provided a rate of twist of 0.08 mm m(-1) V(-1) under quasi-static 150 V drive. The high value of piezoelectric shear d15 coefficient in NBT-BT-Mn sample further demonstrated its potential in practical applications. These results confirm that the lead-free piezoceramics can be as effective as their lead-based counterparts.

  20. Temperature-induced local and average structural changes in BaTiO 3 - x Bi(Zn 1/2 Ti 1/2 )O 3 solid solutions: The origin of high temperature dielectric permittivity

    DOE PAGES

    Hou, Dong; Usher, Tedi-Marie; Zhou, Hanhan; ...

    2017-08-11

    The existence of local tetragonal distortions is evidenced in the BaTiO3–xBi(Zn1/2Ti1/2)O3 (BT–xBZT) relaxor dielectric material system at elevated temperatures. The local and average structures of BT-xBZT with different compositions are characterized using in situ high temperature total scattering techniques. In using the box-car fitting method, it is inferred that there are tetragonal polar clusters embedded in a non-polar pseudocubic matrix for BT-xBZT relaxors. The diameter of these polar clusters is estimated as 2–3 nm at room temperature. Sequential temperature series fitting shows the persistence of the tetragonal distortion on the local scale, while the average structure transforms to a pseudocubicmore » paraelectric phase at high temperatures. Furthermore, the fundamental origin of the temperature stable permittivity of BT-xBZT and the relationship with the unique local scale structures are discussed. This systematic structural study of the BT-xBZT system provides both insight into the nature of lead-free perovskite relaxors, and advances the development of a wide range of electronics with reliable high temperature performance.« less

  1. Electrical Properties of Textured (Bi1/2K1/2)TiO3-BaTiO3 Lead-Free Piezoelectric Ceramics

    NASA Astrophysics Data System (ADS)

    Nemoto, Masahiro; Hiruma, Yuji; Nagata, Hajime; Takenaka, Tadashi

    2009-07-01

    The electrical properties of (1-x)(Bi1/2K1/2)TiO3-xBaTiO3 (BKT-BT100x) ceramics prepared by an ordinary solid-state reaction and a reactive templated grain growth (RTGG) method using platelike Bi4Ti3O12 particles as a template were investigated. The degree of orientation, F, which was determined by the Lotgering method using an X-ray diffraction pattern, achieved ≈83% in the textured BKT-BT10 ceramic. A textured BKT-BT10 ceramic with a homogeneous microstructure was obtained after a long sintering time. The field-induced strains and piezoelectric properties of the BKT-BT10 ceramic were improved by improving grain orientation. In particular, the piezoelectric strain constant, d33, and the normalized strain, d33*, of the textured BKT-BT10 ceramic in the direction parallel (∥) to the tape stacking direction were 121 pC/N and 211 pm/V (at 80 kV/cm), respectively.

  2. ESR, thermoelectrical and positron annihilation Doppler broadening studies of CuZnFe2O4-BaTiO3 composite

    NASA Astrophysics Data System (ADS)

    Hemeda, O. M.; Mahmoud, K. R.; Sharshar, T.; Elsheshtawy, M.; Hamad, Mahmoud A.

    2017-05-01

    Composite materials of Cu0.6Zn0.4Fe2O4 (CZF) and barium titanate (BT) with different concentrations were prepared by high energy ball milling method. The composite samples of CZF and BT were studied using Infrared, ESR and positron annihilation Doppler broadening (PADB) spectroscopy techniques as well as thermo-electric power measurements. The results confirm formation of the composite, and presence of two ferrimagnetic and ferroelectric phases, simultaneously. In addition, Fe-O bond for both tetrahedral and octahedral sites, population and distribution of cations at A and B sites are varied with BT content. The values of resonance field, line width of ESR spectrum and charge carrier concentration increase by increasing BT content. The value of the g factor for our samples with low BT content is greater than g-factor value of the isolated free electron. On the contrary, the g-factor values for samples with high BT content are smaller than the free isolated electron. PADB line-shape S-parameter suggests that there are increases of the density of the delocalized electrons, defect size and concentration caused by highly adding BT phase. In addition, PADB results confirm the homogeneity of composite phases and same structure of defects in BT-CZF composite samples.

  3. 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.

  4. 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…

  5. Homogeneous Atomic Fermi Gases

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Yan, Zhenjie; Patel, Parth B.; Hadzibabic, Zoran; Yefsah, Tarik; Struck, Julian; Zwierlein, Martin W.

    2017-03-01

    We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state: the striking consequence of Pauli blocking in momentum space for a degenerate gas. Cooling a spin-balanced Fermi gas at unitarity, we create homogeneous superfluids and observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas.

  6. Dielectric relaxation and Maxwell-Wagner interface polarization in Nb2O5 doped 0.65BiFeO3-0.35BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Tong; Hu, Jiacong; Yang, Haibo; Jin, Li; Wei, Xiaoyong; Li, Chunchun; Yan, Fei; Lin, Ying

    2017-02-01

    Electrical characterizations of Nb2O5 doped 0.65BiFeO3-0.35BaTiO3 (0.65BF-0.35BT) ceramic were carried out over broad temperature and frequency ranges through dielectric spectroscopy, impedance spectroscopy, and ac conductivity measurements. The dielectric constant and loss tangent are drastically reduced with introducing Nb2O5 into the 0.65BF-0.35BT system. Two dielectric anomalies are detected in the temperature regions of 100 °C ≤ T ≤ 280 °C and 350 °C ≤ T ≤ 480 °C, and the Curie temperature (TC) was confirmed in higher temperature region. A dielectric relaxation with large dielectric constants was detected near the TC. This dielectric relaxation becomes even stronger with the gradual increase in the Nb2O5 content. Impedance spectroscopy results clearly show the contributions of grains and grain boundaries in the frequency range of 100 Hz ≤ f ≤ 1 MHz, and the relaxation processes for grains and grain boundaries are non-Debye-type. The grain boundaries are more resistive than that of the grains, revealing the inhomogeneity in samples. The experimental results are well fitted based on a Maxwell-Wagner (MW) interfacial polarization model below 100 kHz, and the MW interfacial polarization effect becomes more and more obvious with the increase in the Nb2O5 content. The increase in dielectric constant is possibly related to space charge polarization, which is caused by charges accumulated at the interface between the grain and grain boundaries. Frequency dependence of the ac conductivity confirms the MW interfacial polarization effect below 100 kHz.

  7. Ab initio study of cross-interface electron-phonon couplings in FeSe thin films on SrTiO3 and BaTiO3

    DOE PAGES

    Wang, Y.; Linscheid, A.; Berlijn, T.; ...

    2016-04-22

    We study the electron-phonon coupling strength near the interface of monolayer and bilayer FeSe thin films on SrTiO 3 , BaTiO 3 , and oxygen-vacant SrTiO 3 substrates, using ab initio methods. The calculated total electron-phonon coupling strength λ = 0.2 – 0.3 cannot account for the high T c ~ 70 K observed in these systems through the conventional phonon-mediated pairing mechanism. In all of these systems, however, we find that the coupling constant of a polar oxygen branch peaks at q = 0 with negligible coupling elsewhere, while the energy of this mode coincides with the offset energymore » of the replica bands measured recently by angle-resolved photoemission spectroscopy experiments. But the integrated coupling strength for this mode from our current calculations is still too small to produce the observed high T c , even through the more efficient pairing mechanism provided by the forward scattering. We also arrive at the same qualitative conclusion when considering a checkerboard antiferromagnetic configuration in the Fe layer. In light of the experimental observations of the replica band feature and the relatively high T c of FeSe monolayers on polar substrates, our results point towards a cooperative role for the electron-phonon interaction, where the cross-interface interaction acts in conjunction with a purely electronic interaction. We then discuss a few scenarios where the coupling strength obtained here may be enhanced.« less

  8. Thickness dependence of ferroelectric stability in SrRuO3/BaTiO3/La0.7Sr0.3MnO3 ferroelectric tunnel junctions

    NASA Astrophysics Data System (ADS)

    Burton, J. D.; Tsymbal, Evgeny

    Ferroelectric tunnel junctions (FTJs) must meet key requirements in order to become viable device structures. One factor which can limit functionality is the thickness of the ferroelectric layer. The ferroelectric must be thin enough that a detectable tunnel current can flow through it, but if it is too thin, screening of the depolarization field by the electrodes will be insufficient for polarization stability. One mechanism to produce a large change in the tunneling resistance, i.e. a large tunneling electro resistance (TER), is to use asymmetric electrodes. This is disadvantageous from the point of view of switchability, however: the electric field due to the mismatch between metal work functions leads to a preference for one polarization state over the other and, in thinner FTJs, may render one of the polarization states unstable. To explore this effect we perform first-principles density functional calculations on SrRuO3/BaTiO3/La0.7Sr0.3MnO3 (SRO/BTO/LSMO) FTJs with varying BTO thicknesses. We find an energetic preference for polarization to point away from the LSMO electrode. FTJs with BTO thicknesses at or below 4 unit-cells polarization pointing toward LSMO is unstable, and therefore are unswitchable. Analysis reveals that, in addition to the work function mismatch, the difference in screening lengths and the intrinsic layer-by-layer polar nature of LSMO play a significant role in this instability. We will also present an analysis of these effects on the tunneling barrier profile as well as on the TER effect.

  9. 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).

  10. Ferroelectric properties of manganese doped (Bi1/2Na1/2)TiO3 and (Bi1/2Na1/2)TiO3-BaTiO3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Gallegos-Melgar, A.; Espinosa-Arbelaez, D. G.; Flores-Ruiz, F. J.; Lahmar, A.; Dellis, J.-L.; Lemée, N.; Espinoza-Beltran, F. J.; Muñoz-Saldaña, J.

    2015-12-01

    The effects of Manganese doped (Bi1/2Na1/2)TiO3 and (Bi1/2Na1/2)TiO3-BaTiO3 epitaxial thin films on the structure, dielectric, ferroelectric and piezoelectric properties are reported. The thin films were grown by pulsed laser deposition on (Lao.5Sr0.5)CoO3 (LSCO) electrode LaAlO3 (LAO) substrates using homemade ceramic targets. The (La0.5Sr0.5)CoO3 (LSCO)/LaAlO3/system was chosen based on the adequate coupling conditions to grow high quality epitaxial films with desired properties. The dielectric and ferroelectric properties are all self-consistent to each other, despite the morphotropic phase boundary effect in Mn doped BNT-BT thin film. Even when remanent polarizations of 17 and 25 μC/cm2 from BNT-Mn and BNT-BT-Mn thin films were respectively obtained from well-defined P-E hysteresis curves and the corresponding values of coercive field for BNT-Mn and BNT-BT-Mn thin films are 93 and 150 kV/cm, respectively, no significant changes are observed suggesting that the effect of MPB composition is not fully activated due to Mn additions. In the ceramics, the vibrational modes associated to Mn interactions with the oxygen octahedral were identified with Raman spectroscopy. Finally, the local piezoelectric constants (d33) as measured by PFM are 60 and 124 pm/V for BNT-Mn and BNT-BT-Mn thin films, respectively. Thus, BNT-Mn and BNT-BT-Mn thin films are potential candidates to be used in lead-free piezoelectric devices.

  11. 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).

  12. Preparation of 0.83(Bi0.5Na0.5)TiO3–0.17BaTiO3 thick films by screen printing

    NASA Astrophysics Data System (ADS)

    Sakai, Yuichi; Karaki, Tomoaki

    2017-10-01

    Preferentially oriented 0.83(Bi0.5Na0.5)TiO3–0.17BaTiO3 (BNT–17BT) thick films were prepared by adopting substrates with different thermal expansion coefficients, and the properties of the films were analyzed. The thick films were prepared by screen printing. The calcination temperature required to form BNT–17BT thick films without heterogeneous compounds was studied. The c-domain volume fraction (α c ) of the BNT–17BT thick films prepared on 3 mol % Y2O3-stabilized ZrO2 (YSZ) substrates with Pt bottom electrodes (BNT–17BT/YSZ) was larger than that of the BNT–17BT thick films prepared on Al2O3 substrates with Pt bottom electrodes (BNT–17BT/Al2O3) because the BNT–17BT/YSZ exhibited greater compressive stress than the BNT–17BT/Al2O3. The temperature dependence curves of the dielectric constants of the bulk ceramics and BNT–17BT/Al2O3 showed a shoulder with frequency dispersion at approximately 200 °C, whereas this shoulder was not observed in the curves of the BNT–17BT/YSZ. The remanent polarization (P r) of the BNT–17BT/YSZ was larger than that of the BNT–17BT/Al2O3. At temperatures higher than 180 °C, the P r of the BNT–17BT/YSZ was larger than that of the bulk ceramics. The P r of the BNT–17BT/YSZ was larger than that of the BNT–17BT/Al2O3 because the BNT–17BT/YSZ exhibited α c values larger than those of the BNT–17BT/Al2O3.

  13. Effects of vacancies on luminescence of Er-doped 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Lau, Chi Man; Wu, Xiao; Kwok, K. W.

    2015-07-01

    0.93Bi0.5Na0.5TiO3-0.07BaTiO3 ceramics doped with 0.01 mol Er3+ have been prepared and their photoluminescence (PL), ferroelectric, dielectric, and piezoelectric properties have been studied. By doping Er3+ at various sites, ceramics containing oxygen or cation vacancies have been prepared and their effects have been investigated. Ceramic containing no vacancy (i.e., doping Er3+ at the Bi3+ site) has also been prepared as a reference for the study. In addition to the reduction of the up-conversion PL emissions at 532, 547, and 660 nm, our results also reveal that oxygen vacancies can enhance, at the expense of the visible emissions, the near-infrared (1.44-1.66 μm) and mid-infrared (2.62-2.84 μm) down-conversion emissions. Similar results have also been observed for the ceramics containing cation vacancies, and the enhancement in the near-infrared emission becomes much more significant, reaching about 70% for the ceramic doped with Er3+ at the Na+ site. These should be attributed to the looping mechanism between the 4F7/2, 2H11/2, 4I9/2, and 4I11/2 levels facilitated by the cation vacancies and the efficient cross relaxations. The ceramics also exhibit reasonably good ferroelectric, dielectric, and piezoelectric properties, suggesting that they have great potential for multifunctional applications.

  14. Magnifying absolute instruments for optically homogeneous regions

    SciTech Connect

    Tyc, Tomas

    2011-09-15

    We propose a class of magnifying absolute optical instruments with a positive isotropic refractive index. They create magnified stigmatic images, either virtual or real, of optically homogeneous three-dimensional spatial regions within geometrical optics.

  15. Complete set of material constants of 0.95(Na0.5Bi0.5)TiO3-0.05BaTiO3 lead-free piezoelectric single crystal and the delineation of extrinsic contributions

    NASA Astrophysics Data System (ADS)

    Zheng, Limei; Yi, Xiujie; Zhang, Shantao; Jiang, Wenhua; Yang, Bin; Zhang, Rui; Cao, Wenwu

    2013-09-01

    Lead-free piezoelectric single crystal 0.95(Na0.5Bi0.5)TiO3 (NBT)-0.05BaTiO3 was grown by top-seeded solution growth method, which has rhombohedral symmetry with composition near morphotropic phase boundary. Full set of dielectric, piezoelectric, and elastic constants for [001]c poled domain-engineered single crystal was determined. Excellent electromechanical properties and low dielectric loss (d33 = 360 pC/N, d31 = -113 pC/N, d15 = 162 pC/N, k33 = 0.720, kt = 0.540, and tan δ = 1.1%) make it a good candidate to replace lead-based piezoelectric materials. The depolarization temperature (Td = 135 °C) is the highest among all NBT-based materials and its electromechanical coupling properties are very stable below Td. Extrinsic contributions to piezoelectric properties were investigated by Rayleigh analysis.

  16. 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

  17. Dielectric, piezoelectric, and ferroelectric properties of MnCO3-added 74(Bi(1/2)Na(1/2)) TiO3-20.8(Bi(1/2)K(1/2))TiO3-5.2BaTiO3 lead-free piezoelectric ceramics.

    PubMed

    Hu, Hanchen; Zhu, Mankang; Hou, Yudong; Yan, Hui

    2009-05-01

    74(Bi(1/2)Na(1/2))TiO3-20.8(Bi(1/2)K(1/2))TiO3-5.2BaTiO3-x MnCO3 lead-free piezoelectric ceramics were synthesized by conventional solid oxide routine. The tetragonal 74(Bi(1/2)Na(1/2))TiO3-20.8(Bi(1/2)K(1/2))TiO3-5.2 BaTiO3 (BNKB) exhibits high depolarization temperature T(d) of 195 degrees C; however, its properties are far from satisfactory for practical application and need to be improved. The experiments show that the addition of MnCO3 reduces the tetragonality c/a and increases the cell volume. In addition, it revealed that the suitable addition of MnCO3 promotes the sintering and increases the densities of BNKB ceramics. The addition of MnCO3 also enhances the relaxor behavior of BNKB ceramics due to the reconstruct of the disorder arrays. Due to the effect of the crystal lattice, grain growth, and relaxor behavior, the optimal electric properties were realized at MnCO3 addition x of 0.16: the dielectric permittivity epsilon(r) = 1047, dielectric dissipation tandelta = 0.022, piezoelectric strain d33 = 140 pC/N, mechanical coupling k(p) = 0.18, mechanical quality Q(m) = 89 while the depolarization temperature T(d) stays relatively high at 175 degrees C. The effect and mechanism of Mn doping on the electrical properties were discussed in detail.

  18. 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.

  19. Benchmarking monthly homogenization algorithms

    NASA Astrophysics Data System (ADS)

    Venema, V. K. C.; Mestre, O.; Aguilar, E.; Auer, I.; Guijarro, J. A.; Domonkos, P.; Vertacnik, G.; Szentimrey, T.; Stepanek, P.; Zahradnicek, P.; Viarre, J.; Müller-Westermeier, G.; Lakatos, M.; Williams, C. N.; Menne, M.; Lindau, R.; Rasol, D.; Rustemeier, E.; Kolokythas, K.; Marinova, T.; Andresen, L.; Acquaotta, F.; Fratianni, S.; Cheval, S.; Klancar, M.; Brunetti, M.; Gruber, C.; Prohom Duran, M.; Likso, T.; Esteban, P.; Brandsma, T.

    2011-08-01

    The COST (European Cooperation in Science and Technology) Action ES0601: Advances in homogenization methods of climate series: an integrated approach (HOME) has executed a blind intercomparison and validation study for monthly homogenization algorithms. Time series of monthly temperature and precipitation were evaluated because of their importance for climate studies and because they represent two important types of statistics (additive and multiplicative). The algorithms were validated against a realistic benchmark dataset. The benchmark contains real inhomogeneous data as well as simulated data with inserted inhomogeneities. Random break-type inhomogeneities were added to the simulated datasets modeled as a Poisson process with normally distributed breakpoint sizes. To approximate real world conditions, breaks were introduced that occur simultaneously in multiple station series within a simulated network of station data. The simulated time series also contained outliers, missing data periods and local station trends. Further, a stochastic nonlinear global (network-wide) trend was added. Participants provided 25 separate homogenized contributions as part of the blind study as well as 22 additional solutions submitted after the details of the imposed inhomogeneities were revealed. These homogenized datasets were assessed by a number of performance metrics including (i) the centered root mean square error relative to the true homogeneous value at various averaging scales, (ii) the error in linear trend estimates and (iii) traditional contingency skill scores. The metrics were computed both using the individual station series as well as the network average regional series. The performance of the contributions depends significantly on the error metric considered. Contingency scores by themselves are not very informative. Although relative homogenization algorithms typically improve the homogeneity of temperature data, only the best ones improve precipitation data

  20. Understanding the role of A-site and B-site cations on piezoelectric instability in lead--free (1-x) BaTiO3 -- xA(Cu1/3Nb2/3)O3 (A = Sr, Ca, Ba) solid solutions

    NASA Astrophysics Data System (ADS)

    Maurya, Deepam; Zhou, Yuan; Priya, Shashank

    2013-03-01

    This study provides fundamental understanding of the enhanced piezoelectric instability in lead-free piezoelectric (1-x) BaTiO3-xA(Cu1/3Nb2/3) O3(A: Sr, Ba and Ca and x = 0.0-0.03) solid solutions. These compositions were found to exhibit large longitudinal piezoelectric constant (d33) of ~330 pC/N and electromechanical planar coupling constant (kp) ~ 46% at room temperature. The X-ray diffraction coupled with atomic pair distribution functions (PDF)s indicated increase in local polarization. Raman scattering and electron paramagnetic resonance (EPR) analysis revealed that substitutions on A and B-site both substantially perturbed the local octahedral dynamics and resulted in localized nano polar regions with lower symmetry. The presence of nano domains and local structural distortions smears the Curie peak resulting in diffuse order-disorder type phase transitions. The effect of these distortions on the variations in physical property was modeled and analyzed within the context of nanodomains and phase transitions. *spriya@vt.edu The financial support from National Science Foundation and Office of Basic Energy Science, Department of Energy (Microscopy analysis) is gratefully acknowledged. The authors would also like to acknowledge the support from KIMS (new piezoelectric)

  1. 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.

  2. Dielectric and AC conductivity studies of Nd substituted 0.8BaTiO3-0.2(Bi0.5(1-x)Nd0.5xK0.5)TiO3 lead free ceramics

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    0.8BaTiO3 - 0.2(Bi0.5(1-x)Nd0.5xK0.5)TiO3 (0.01 ≤ x ≤ 0.06) lead free ceramic materials have been prepared by solid state reaction method and followed by high energy ball milling process. X-ray diffraction studies confirm the tetragonal structure of the materials at room temperature. Lattice parameters and density are decreasing with increase of Nd substitution. Microstructure studies were done by using Scanning electron microscope and it found that grain size is decreasing with increase of Nd substitution. Temperature and frequency dependent dielectric studies reveal relaxor behaviour of the materials. Dielectric constant, dielectric loss and Curie temperature are decreasing with Nd substitution. Maximum Curie temperature of 195°C was observed at 1MHz for x=0.01 Nd substituted sample. Degree of diffuseness was calculated from the modified Curie-Weiss law and it is increasing with Nd substitution. AC conductivity is increasing with increase of Nd substitution and observed maximum activation energy of 0.52 eV for x=0.02 Nd substituted sample.

  3. 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.…

  4. 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

  5. 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.

  6. Inverse focusing inside turbid media by creating an opposite virtual objective.

    PubMed

    Yu, Yeh-Wei; Chen, Szu-Yu; Lin, Che-Chu; Sun, Ching-Cherng

    2016-07-11

    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.

  7. 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.

  8. An Investigation of Dielectric, Piezoelectric Properties and Microstructures of Bi0.5Na0.5TiO3-BaTiO3-Bi0.5K0.5TiO3 Lead-Free Piezoelectric Ceramics Doped with K2AlNbO5 Compound

    NASA Astrophysics Data System (ADS)

    Liu, Gang; Jiang, Wentao; Liu, Kaihua; Liu, Xiaokui; Song, Chunlin; Yan, Yan; Jin, Li

    2017-08-01

    The effect of K2AlNbO5 compound acting as both donor and accepter on the phase, microstructures and electrical properties of the 0.9362(Bi0.5Na0.5)TiO3-0.0637BaTiO3-0.02(Bi0.5K0.5)TiO3 [(1- x)(0.9163BNT-0.0637BT-0.02BKT)- x(K2AlNbO5)] (BNKBT-1000 xKAN) ternary lead-free piezoelectric ceramics was systematically investigated. When doping content of K2AlNbO5 was varied from 0 to 0.009, the BNKBT-1000 xKAN ceramics showed a single perovskite structure, and the phase structure transferred from a rhombohedral-tetragonal coexistent morphotropic phase boundaries zone to a tetragonal zone. The x-ray photoelectron spectroscopy analysis indicated that the chemical valence of the Nb and Al element are 5+ and 3+, respectively. Strong relaxor characteristics were revealed by the temperature-dependent dielectric properties of the ceramics. Typical square polarization-electric field ( P- E) hysteresis loops were observed in the samples with doping content lower than 0.005. However, with further increasing the doping content ( x = 0.007 and 0.009), round P- E hysteresis loops were observed due to the high conductivity of these samples. Moreover, when the doping content was less than 0.005, the ceramic samples exhibited good piezoelectric properties. Specially, when the doping content was 0.001, the piezoelectric constant d 33 and electromechanical coupling coefficient k p of the sample were 197 pC/N and 22%, respectively. However, further addition would deteriorate both the dielectric and piezoelectric properties.

  9. Temperature dependence scaling behavior of the dynamic hysteresis in 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 ferroelectric ceramics

    NASA Astrophysics Data System (ADS)

    Patel, Satyanarayan; Chauhan, Aditi; Chauhan, Aditya; Vaish, Rahul

    2015-03-01

    Temperature dependent dynamic hysteresis of 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 (BNT-BT-ST) bulk ferroelectric ceramic was systematically studied. The scaling relations were estimated for corrective electric field ({{E}c}), remnant polarization ({{P}r}) and hysteresis loop area ≤ft( ≤ft< A \\right> \\right) as a function of temperature ≤ft( T \\right). It was observed that {{E}c}\\propto {{T}-0.6396}, {{P}r}\\propto {{T}-0.6849} and ≤ft< A \\right> \\propto {{T}-0.6446} for a constant magnitude of electric field ≤ft( E \\right). To understand the domain dynamics, back-switching polarization as a function of T is also predicted. The relation between back-switching polarization and temperature is estimated by well described Arrhenius law to evaluate the average activation energy. It also depends on the applied electric field; the relation fits well to a simple exponential decay function. The saturation polarization as a function of T was also evaluated to estimate the electrocaloric effect. It was found that electrocaloric effect and heat extract capacity in BNT-BT-ST ceramic is of a similar order to that observed in most other lead-free bulk ferroelectric ceramics. It can be said that BNT-BT-ST is also a promising material for solid state refrigeration. These results can be helpful to understand the temperature dependent hysteresis behavior and polarization switching in lead-free ferroelectric ceramics.

  10. Homogeneous, bioluminescent proteasome assays.

    PubMed

    O'Brien, Martha A; Moravec, Richard A; Riss, Terry L; Bulleit, Robert F

    2015-01-01

    Protein degradation is mediated predominantly through the ubiquitin-proteasome pathway. The importance of the proteasome in regulating degradation of proteins involved in cell-cycle control, apoptosis, and angiogenesis led to the recognition of the proteasome as a therapeutic target for cancer. The proteasome is also essential for degrading misfolded and aberrant proteins, and impaired proteasome function has been implicated in neurodegerative and cardiovascular diseases. Robust, sensitive assays are essential for monitoring proteasome activity and for developing inhibitors of the proteasome. Peptide-conjugated fluorophores are widely used as substrates for monitoring proteasome activity, but fluorogenic substrates can exhibit significant background and can be problematic for screening because of cellular autofluorescence or interference from fluorescent library compounds. Furthermore, fluorescent proteasome assays require column-purified 20S or 26S proteasome (typically obtained from erythrocytes), or proteasome extracts from whole cells, as their samples. To provide assays more amenable to high-throughput screening, we developed a homogeneous, bioluminescent method that combines peptide-conjugated aminoluciferin substrates and a stabilized luciferase. Using substrates for the chymotrypsin-like, trypsin-like, and caspase-like proteasome activities in combination with a selective membrane permeabilization step, we developed single-step, cell-based assays to measure each of the proteasome catalytic activities. The homogeneous method eliminates the need to prepare individual cell extracts as samples and has adequate sensitivity for 96- and 384-well plates. The simple "add and read" format enables sensitive and rapid proteasome assays ideal for inhibitor screening.

  11. Sources of Peer Group Homogeneity

    ERIC Educational Resources Information Center

    Cohen, Jere M.

    1977-01-01

    Investigates how adolescent friendship groups become homogeneous. Analysis of 49 student friendship groups indicates that homophilic selection is most important for group homogeneity, conformity pressures are somewhat important, and disproportionate group leaving contributes nothing to homogeneity. The conclusion is that the magnitude of peer…

  12. 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.

  13. 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.

  14. Homogeneous nucleation kinetics

    NASA Technical Reports Server (NTRS)

    Rasmussen, D. H.; Appleby, M. R.; Leedom, G. L.; Babu, S. V.; Naumann, R. J.

    1983-01-01

    Homogeneous nucleation kinetics are rederived in a manner fundamentally similar to the approach of classical nucleation theory with the following modifications and improvements. First, the cluster is a parent phase cluster and does not require energization to the parent state. Second, the thermodynamic potential used to describe phase stability is a continuous function along the pathway of phase decomposition. Third, the kinetics of clustering corresponds directly to the diffusional flux of monomers through the cluster distribution and are formally similar to classical theory with the resulting kinetic equation modified by two terms in the preexponential factor. These terms correct for the influence of a supersaturation dependent clustering within the parent phase and for the influence of an asymmetrical cluster concentration as a function of cluster size at the critical cluster size. Fourth, the supersaturation dependence of the nucleation rate is of the same form as that given by classical nucleation theory. This supersaturation dependence must however be interpreted in terms of a size dependent surface tension. Finally, there are two scaling laws which describe supersaturation to either constant nucleation rate or to the thermodynamically determined physical spinodal.

  15. Theoretical study of Ge/ BaTiO 3 Interfaces

    NASA Astrophysics Data System (ADS)

    Fredrickson, Kurt; Demkov, Alexander

    2011-03-01

    It has been shown (McKee et al., Phys. Rev. Lett. 81, 3014 (1998), and R. McKee, et al., Science 293 , 468 (2001)) that perovskite oxides SrTi O3 and BaTi O3 (BTO) can be grown epitaxially on Si and Ge, respectively. It would be interesting to achieve the reverse, i.e. to grow for example, Ge on BTO. It is not clear, however, whether one can achieve wetting of BTO by Ge. Theoretically, the energy of the Ge (001) surface is estimated to be anywhere between 591 and 1700 erg/cm2 and the surface energy of BTO is in the range of 1083-1496 erg/cm2 depending on termination and environment. The missing piece of information is the energy of the Ge/BTO interface. We examine five possible Ge/BTO interface structures and calculate their energies using density functional theory to determine which one has the lowest energy, and whether wetting can be achieved.

  16. Universum Inference and Corpus Homogeneity

    NASA Astrophysics Data System (ADS)

    Vogel, Carl; Lynch, Gerard; Janssen, Jerom

    Universum Inference is re-interpreted for assessment of corpus homogeneity in computational stylometry. Recent stylometric research quantifies strength of characterization within dramatic works by assessing the homogeneity of corpora associated with dramatic personas. A methodological advance is suggested to mitigate the potential for the assessment of homogeneity to be achieved by chance. Baseline comparison analysis is constructed for contributions to debates by nonfictional participants: the corpus analyzed consists of transcripts of US Presidential and Vice-Presidential debates from the 2000 election cycle. The corpus is also analyzed in translation to Italian, Spanish and Portuguese. Adding randomized categories makes assessments of homogeneity more conservative.

  17. Don't homogenize, synchronize.

    PubMed

    Sawhney, M

    2001-01-01

    To be more responsive to customers, companies often break down organizational walls between their units--setting up all manner of cross-business and cross-functional task forces and working groups and promoting a "one-company" culture. But such attempts can backfire terribly by distracting business and functional units and by contaminating their strategies and processes. Fortunately, there's a better way, says the author. Rather than tear down organizational walls, a company can make them permeable to information. It can synchronize all its data on products, filtering the information through linked databases and applications and delivering it in a coordinated, meaningful form to customers. As a result, the organization can present a single, unified face to the customer--one that can change as market conditions warrant--without imposing homogeneity on its people. Such synchronization can lead not just to stronger customer relationships and more sales but also to greater operational efficiency. It allows a company, for example, to avoid the high costs of maintaining many different information systems with redundant data. The decoupling of product control from customer control in a synchronized company reflects a fundamental fact about business: While companies have to focus on creating great products, customers think in terms of the activities they perform and the benefits they seek. For companies, products are ends, but for customers, products are means. The disconnect between how customers think and how companies organize themselves is what leads to inefficiencies and missed opportunities, and that's exactly the problem that synchronization solves. Synchronized companies can get closer to customers, sustain product innovation, and improve operational efficiency--goals that have traditionally been very difficult to achieve simultaneously.

  18. 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.

  19. Homogeneous crystal nucleation in polymers.

    PubMed

    Schick, Christoph; Androsch, R; Schmelzer, Juern W P

    2017-07-14

    The pathway of crystal nucleation significantly influences the structure and properties of semi-crystalline polymers. Crystal nucleation is normally heterogeneous at low supercooling, and homogeneous at high supercooling, of the polymer melt. Homogeneous nucleation in bulk polymers has been, so far, hardly accessible experimentally, and was even doubted to occur at all. This topical review summarizes experimental findings on homogeneous crystal nucleation in polymers. Recently developed fast scanning calorimetry, with cooling and heating rates up to 106 K s-1, allows for detailed investigations of nucleation near and even below the glass transition temperature, including analysis of nuclei stability. As for other materials, the maximum homogeneous nucleation rate for polymers is located close to the glass transition temperature. In the experiments discussed here, it is shown that polymer nucleation is homogeneous at such temperatures. Homogeneous nucleation in polymers is discussed in the framework of classical nucleation theory. The majority of our observations are consistent with the theory. The discrepancies may guide further research, particularly experiments to progress theoretical development. Progress in the understanding of homogeneous nucleation is much needed, since most of the modelling approaches dealing with polymer crystallization exclusively consider homogeneous nucleation. This is also the basis for advancing theoretical approaches to the much more complex phenomena governing heterogeneous nucleation. © 2017 IOP Publishing Ltd.

  20. Locally homogeneous pp-waves

    NASA Astrophysics Data System (ADS)

    Globke, Wolfgang; Leistner, Thomas

    2016-10-01

    We show that every n-dimensional locally homogeneous pp-wave is a plane wave, provided it is indecomposable and its curvature operator, when acting on 2-forms, has rank greater than one. As a consequence we obtain that indecomposable, Ricci-flat locally homogeneous pp-waves are plane waves. This generalises a classical result by Jordan, Ehlers and Kundt in dimension 4. Several examples show that our assumptions on indecomposability and the rank of the curvature are essential.

  1. Operator estimates in homogenization theory

    NASA Astrophysics Data System (ADS)

    Zhikov, V. V.; Pastukhova, S. E.

    2016-06-01

    This paper gives a systematic treatment of two methods for obtaining operator estimates: the shift method and the spectral method. Though substantially different in mathematical technique and physical motivation, these methods produce basically the same results. Besides the classical formulation of the homogenization problem, other formulations of the problem are also considered: homogenization in perforated domains, the case of an unbounded diffusion matrix, non-self-adjoint evolution equations, and higher-order elliptic operators. Bibliography: 62 titles.

  2. Homogeneous coordinates in motion correction.

    PubMed

    Zahneisen, Benjamin; Ernst, Thomas

    2016-01-01

    Prospective motion correction for MRI and other imaging modalities are commonly based on the assumption of affine motion, i.e., rotations, shearing, scaling and translations. In addition it often involves transformations between different reference frames, especially for applications with an external tracking device. The goal of this work is to develop a computational framework for motion correction based on homogeneous transforms. The homogeneous representation of affine transformations uses 4 × 4 transformation matrices applied to four-dimensional augmented vectors. It is demonstrated how homogenous transforms can be used to describe the motion of slice objects during an MRI scan. Furthermore, we extend the concept of homogeneous transforms to gradient and k-space vectors, and show that the fourth dimension of an augmented k-space vector encodes the complex phase of the corresponding signal sample due to translations. The validity of describing motion tracking in real space and k-space using homogeneous transformations only is demonstrated on phantom experiments. Homogeneous transformations allows for a conceptually simple, consistent and computationally efficient theoretical framework for motion correction applications. © 2015 Wiley Periodicals, Inc.

  3. Political homogeneity can nurture threats to research validity.

    PubMed

    Chambers, John R; Schlenker, Barry R

    2015-01-01

    Political homogeneity within a scientific field nurtures threats to the validity of many research conclusions by allowing ideologically compatible values to influence interpretations, by minimizing skepticism, and by creating premature consensus. Although validity threats can crop in any research, the usual corrective activities in science are more likely to be minimized and delayed.

  4. Proficiency testing in immunopathology: establishing the homogeneity of test material.

    PubMed

    Esterman, Adrian; Javanovich, Sue; McEvoy, Robert; Roberts-Thomson, Peter

    2005-04-01

    To develop a technique for homogeneity testing of serum aliquot samples suitable for use in the Quality Assurance Program in Clinical Immunology (QAP Pty Ltd). Albumin was selected as the surrogate protein marker for the product to be tested and the coefficient of dispersion (COD) calculated as the measure of homogeneity. To detect changes in the average level of homogeneity, cumulative sum control (cusum) charts were used. The COD(%) for each triplicate reading of albumin obtained from 34 specimens was normally distributed with a mean of 0.49% and a standard deviation of 0.25%. In industrial quality control schemes the action line is generally set at the upper 99% confidence limits, hence any triplicate sample would be considered to have acceptable homogeneity if the COD was < or = 1.08%. Cusum charts were created to monitor albumin homogeneity over time. The use of albumin measurement as the surrogate appears statistically suitable for homogeneity testing in QAP programs for immunodiagnostic testing. CUSUM charts are particularly useful to monitor such homogeneity testing.

  5. Dynamics of compact homogeneous universes

    SciTech Connect

    Tanimoto, M.; Koike, T.; Hosoya, A.

    1997-01-01

    A complete description of dynamics of compact locally homogeneous universes is given, which, in particular, includes explicit calculations of Teichm{umlt u}ller deformations and careful counting of dynamical degrees of freedom. We regard each of the universes as a simply connected four-dimensional space{endash}time with identifications by the action of a discrete subgroup of the isometry group. We then reduce the identifications defined by the space{endash}time isometries to ones in a homogeneous section, and find a condition that such spatial identifications must satisfy. This is essential for explicit construction of compact homogeneous universes. Some examples are demonstrated for Bianchi II, VI{sub 0}, VII{sub 0}, and I universal covers. {copyright} {ital 1997 American Institute of Physics.}

  6. Harmonic analysis of homogeneous networks.

    PubMed

    Wolfe, W J; Rothman, J A; Chang, E H; Aultman, W; Ripton, G

    1995-01-01

    We introduce a generalization of mutually inhibitory networks called homogeneous networks. Such networks have symmetric connection strength matrices that are circulant (one-dimensional case) or block circulant with circulant blocks (two-dimensional case). Fourier harmonics provide universal eigenvectors, and we apply them to several homogeneous examples: k-wta, k-cluster, on/center off/surround, and the assignment problem. We also analyze one nonhomogeneous case: the subset-sum problem. We present the results of 10000 trials on a 50-node k-cluster problem and 100 trials on a 25-node subset-sum problem.

  7. 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.

  8. 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.

  9. 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.

  10. Optimizing homogenization by chaotic unmixing?

    NASA Astrophysics Data System (ADS)

    Weijs, Joost; Bartolo, Denis

    2016-11-01

    A number of industrial processes rely on the homogeneous dispersion of non-brownian particles in a viscous fluid. An ideal mixing would yield a so-called hyperuniform particle distribution. Such configurations are characterized by density fluctuations that grow slower than the standard √{ N}-fluctuations. Even though such distributions have been found in several natural structures, e.g. retina receptors in birds, they have remained out of experimental reach until very recently. Over the last 5 years independent experiments and numerical simulations have shown that periodically driven suspensions can self-assemble hyperuniformally. Simple as the recipe may be, it has one important disadvantage. The emergence of hyperuniform states co-occurs with a critical phase transition from reversible to non reversible particle dynamics. As a consequence the homogenization dynamics occurs over a time that diverges with the system size (critical slowing down). Here, we discuss how this process can be sped up by exploiting the stirring properties of chaotic advection. Among the questions that we answer are: What are the physical mechanisms in a chaotic flow that are relevant for hyperuniformity? How can we tune the flow parameters such to obtain optimal hyperuniformity in the fastest way? JW acknowledges funding by NWO (Netherlands Organisation for Scientific Research) through a Rubicon Grant.

  11. 7 CFR 58.623 - Homogenizer.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing Practices), DEPARTMENT OF AGRICULTURE (CONTINUED) REGULATIONS AND STANDARDS UNDER THE....623 Homogenizer. Homogenizer shall comply with 3-A Sanitary Standards....

  12. 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.

  13. Coherence delay augmented laser beam homogenizer

    DOEpatents

    Rasmussen, P.; Bernhardt, A.

    1993-06-29

    The geometrical restrictions on a laser beam homogenizer are relaxed by ug a coherence delay line to separate a coherent input beam into several components each having a path length difference equal to a multiple of the coherence length with respect to the other components. The components recombine incoherently at the output of the homogenizer, and the resultant beam has a more uniform spatial intensity suitable for microlithography and laser pantogography. Also disclosed is a variable aperture homogenizer, and a liquid filled homogenizer.

  14. Coherence delay augmented laser beam homogenizer

    DOEpatents

    Rasmussen, Paul; Bernhardt, Anthony

    1993-01-01

    The geometrical restrictions on a laser beam homogenizer are relaxed by ug a coherence delay line to separate a coherent input beam into several components each having a path length difference equal to a multiple of the coherence length with respect to the other components. The components recombine incoherently at the output of the homogenizer, and the resultant beam has a more uniform spatial intensity suitable for microlithography and laser pantogography. Also disclosed is a variable aperture homogenizer, and a liquid filled homogenizer.

  15. On the decay of homogeneous isotropic turbulence

    NASA Astrophysics Data System (ADS)

    Skrbek, L.; Stalp, Steven R.

    2000-08-01

    wind tunnels and a water channel, the temporal decay of turbulence created by an oscillating grid in water and the decay of energy and vorticity created by a towed grid in a stationary sample of water. We also analyze decaying vorticity data we obtained in superfluid helium and show that decaying superfluid turbulence can be described classically. This paper offers a unified investigation of decaying isotropic, homogeneous turbulence that is based on accepted forms of the three-dimensional turbulent spectra and a variety of experimental decay data obtained in air, water, and superfluid helium.

  16. Homogeneous catalytic hydrogenolysis of biomass

    SciTech Connect

    Vasilakos, N.P.; Barreiros, M.T.

    1984-01-01

    Aqueous hydrogenation of cellulose in the presence of various homogeneous acidic catalysts was studied in a batch autoclave system at 250-350 degrees, residence times of 1-4 h, catalyst concentrations of less than 10% weight, and H pressures of less than 735 psi. The use of heterogeneous cocatalysts was also investigated. Under these conditions, less than 93% of the initial cellulose feed was converted, yielding mainly water-soluble components and gases rich in CO and CO2. C conversions to water-solubles and gases of less than 57% (on the basis of cellulose) were obtained, constituting in some cases improvements of more than 100% over the noncatalytic experiments. The conversion mechanism involved competing hydrolysis, pyrolysis, and hydrogenation reactions, the relative importance of which was strongly dependent on temperature. FeCl3 was the best overall catalyst, while molybdates displayed high selectivity toward hydrogenation.

  17. 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.

  18. Steps Towards a Homogenized Sub-Monthly Temperature Monitoring Tool

    NASA Astrophysics Data System (ADS)

    Rennie, J.; Kunkel, K.

    2015-12-01

    Land surface air temperature products have been essential for monitoring the evolution of the climate system. Before a temperature dataset is included in such reports, it is important that non-climatic influences be removed or changed so the dataset is considered homogenous. These inhomogeneities include changes in station location, instrumentation and observing practices. Very few datasets are free of these influences and therefore require homogenization schemes. While many homogenized products exist on the monthly time scale, few daily products exist, due to the complication of removing break points that are truly inhomogeneous rather than solely by chance (for example, sharp changes due to synoptic conditions). Since there is a high demand for sub-monthly monitoring tools, there is a need to address these issues. The Global Historical Climatology Network - Daily dataset provides a strong foundation of the Earth's climate on the daily scale, and is the official archive of daily data in the United States. While the dataset adheres to a strict set of quality assurance, no daily adjustments are applied. However, this dataset lays the groundwork for other products distributed at NCEI-Asheville, including the climate divisional dataset (nClimDiv), the North American monthly homogenized product (Northam) and the 1981-2010 Normals. Since these downstream products already provide homogenization and base period schemes, it makes sense to combine these datasets to provide a sub-monthly monitoring tool for the United States. Using these datasets already in existence, monthly adjustments are applied to daily data, and then anomalies are created using a base climatology defined by the 1981-2010 Normals. Station data is then aggregated to the state level and then regions defined by the National Climate Assessment. Ranks are then created to provide informational monitoring tools that could be of use for public dissemination. This presentation goes over the product, including

  19. Reciprocity theory of homogeneous reactions

    NASA Astrophysics Data System (ADS)

    Agbormbai, Adolf A.

    1990-03-01

    The reciprocity formalism is applied to the homogeneous gaseous reactions in which the structure of the participating molecules changes upon collision with one another, resulting in a change in the composition of the gas. The approach is applied to various classes of dissociation, recombination, rearrangement, ionizing, and photochemical reactions. It is shown that for the principle of reciprocity to be satisfied it is necessary that all chemical reactions exist in complementary pairs which consist of the forward and backward reactions. The backward reaction may be described by either the reverse or inverse process. The forward and backward processes must satisfy the same reciprocity equation. Because the number of dynamical variables is usually unbalanced on both sides of a chemical equation, it is necessary that this balance be established by including as many of the dynamical variables as needed before the reciprocity equation can be formulated. Statistical transformation models of the reactions are formulated. The models are classified under the titles free exchange, restricted exchange and simplified restricted exchange. The special equations for the forward and backward processes are obtained. The models are consistent with the H theorem and Le Chatelier's principle. The models are also formulated in the context of the direct simulation Monte Carlo method.

  20. Homogeneous modes of cosmological instantons

    SciTech Connect

    Gratton, Steven; Turok, Neil

    2001-06-15

    We discuss the O(4) invariant perturbation modes of cosmological instantons. These modes are spatially homogeneous in Lorentzian spacetime and thus not relevant to density perturbations. But their properties are important in establishing the meaning of the Euclidean path integral. If negative modes are present, the Euclidean path integral is not well defined, but may nevertheless be useful in an approximate description of the decay of an unstable state. When gravitational dynamics is included, counting negative modes requires a careful treatment of the conformal factor problem. We demonstrate that for an appropriate choice of coordinate on phase space, the second order Euclidean action is bounded below for normalized perturbations and has a finite number of negative modes. We prove that there is a negative mode for many gravitational instantons of the Hawking-Moss or Coleman{endash}De Luccia type, and discuss the associated spectral flow. We also investigate Hawking-Turok constrained instantons, which occur in a generic inflationary model. Implementing the regularization and constraint proposed by Kirklin, Turok and Wiseman, we find that those instantons leading to substantial inflation do not possess negative modes. Using an alternate regularization and constraint motivated by reduction from five dimensions, we find a negative mode is present. These investigations shed new light on the suitability of Euclidean quantum gravity as a potential description of our universe.

  1. Phosphoproteomic Analysis of Liver Homogenates

    PubMed Central

    Demirkan, Gokhan; Salomon, Arthur R.; Gruppuso, Philip A.

    2013-01-01

    Summary Regulation of protein function via reversible phosphorylation is an essential component of cell signaling. Our ability to understand complex phosphorylation networks in the physiological context of a whole organism or tissue remains limited. This is largely due to the technical challenge of isolating serine/threonine phosphorylated peptides from a tissue sample. In the present study, we developed a phosphoproteomic strategy to purify and identify phosphopeptides from a tissue sample by employing protein gel filtration, protein SAX (strong anion exchange) and SCX (strong cation exchange) chromatography, peptide SCX chromatography and TiO2 affinity purification. By applying this strategy to the mass spectrometry-based analysis of rat liver homogenates, we were able to identify with high confidence and quantify over four thousand unique phosphopeptides. Finally, the reproducibility of our methodology was demonstrated by its application to analysis of the mammalian Target of Rapamycin (mTOR) signaling pathways in liver samples obtained from rats in which hepatic mTOR was activated by refeeding following a period of fasting. PMID:22903715

  2. Magnetic field homogeneity of a conical coaxial coil pair.

    PubMed

    Salazar, F J; Nieves, F J; Bayón, A; Gascón, F

    2017-09-01

    An analytical study of the magnetic field created by a double-conical conducting sheet is presented. The analysis is based on the expansion of the magnetic field in terms of Legendre polynomials. It is demonstrated analytically that the angle of the conical surface that produces a nearly homogeneous magnetic field coincides with that of a pair of loops that fulfills the Helmholtz condition. From the results obtained, we propose an electric circuit formed by pairs of isolated conducting loops tightly wound around a pair of conical surfaces, calculating numerically the magnetic field produced by this system and its heterogeneity. An experimental setup of the proposed circuit was constructed and its magnetic field was measured. The results were compared with those obtained by numerical calculation, finding a good agreement. The numerical results demonstrate a significant improvement in homogeneity in the field of the proposed pair of conical coils compared with that achieved with a simple pair of Helmholtz loops or with a double solenoid. Moreover, a new design of a double pair of conical coils based on Braunbek's four loops is also proposed to achieve greater homogeneity. Regarding homogeneity, the rating of the analyzed configurations from best to worst is as follows: (1) double pair of conical coils, (2) pair of conical coils, (3) Braunbek's four loops, (4) Helmholtz pair, and (5) solenoid pair.

  3. Creating physics stars

    NASA Astrophysics Data System (ADS)

    Banks, Michael

    2013-07-01

    Korea has begun an ambitious 5bn plan to create 50 new institutes dedicated to fundamental research. Michael Banks meets physicist Se-Jung Oh, president of the Institute for Basic Science, to find out more.

  4. 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)

  5. 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.

  6. 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.

  7. Homogeneity and thermodynamic identities in geometrothermodynamics

    NASA Astrophysics Data System (ADS)

    Quevedo, Hernando; Quevedo, María N.; Sánchez, Alberto

    2017-03-01

    We propose a classification of thermodynamic systems in terms of the homogeneity properties of their fundamental equations. Ordinary systems correspond to homogeneous functions and non-ordinary systems are given by generalized homogeneous functions. This affects the explicit form of the Gibbs-Duhem relation and Euler's identity. We show that these generalized relations can be implemented in the formalism of black hole geometrothermodynamics in order to completely fix the arbitrariness present in Legendre invariant metrics.

  8. The Homogenization and Optimization of Thermoelectric Composites

    DTIC Science & Technology

    2015-04-17

    AFRL-OSR-VA-TR-2015-0090 The Homogenization and Optimization of Thermoelectric Composites Jiangyu Li UNIVERSITY OF WASHINGTON Final Report 04/17/2015...SUBTITLE The Homogenization and Optimization of Thermoelectric Composites 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-12-1-0325 5c. PROGRAM ELEMENT...behavior of thermoelectric composites using rigorous homogenization technique in this project. In the last three years, our accomplishment includes: (1

  9. Inhibitors of microsomal oxidations in insect homogenates

    PubMed Central

    Chakraborty, J.; Sissons, C. H.; Smith, J. N.

    1967-01-01

    1. Homogenates of insect tissues were assayed for enzymes capable of oxidizing p-nitrotoluene to p-nitrobenzoic acid. 2. Locust fat-body homogenate 10000g supernatant was an effective enzyme and required no added cofactors. 3. Homogenates of other insects or locust organs and 10000g sediment from locust fat-body were not active and inhibited microsomal oxidations carried out by locust fat-body or rabbit liver enzyme. 4. Inhibitory power was high in homogenates of whole flies and of fly heads or thoraces. 5. Inhibition appeared to involve both irreversible inactivation of enzyme and the removal of essential cofactors. PMID:4382105

  10. Benchmarking homogenization algorithms for monthly data

    NASA Astrophysics Data System (ADS)

    Venema, V. K. C.; Mestre, O.; Aguilar, E.; Auer, I.; Guijarro, J. A.; Domonkos, P.; Vertacnik, G.; Szentimrey, T.; Stepanek, P.; Zahradnicek, P.; Viarre, J.; Müller-Westermeier, G.; Lakatos, M.; Williams, C. N.; Menne, M. J.; Lindau, R.; Rasol, D.; Rustemeier, E.; Kolokythas, K.; Marinova, T.; Andresen, L.; Acquaotta, F.; Fratiannil, S.; Cheval, S.; Klancar, M.; Brunetti, M.; Gruber, C.; Prohom Duran, M.; Likso, T.; Esteban, P.; Brandsma, T.; Willett, K.

    2013-09-01

    The COST (European Cooperation in Science and Technology) Action ES0601: Advances in homogenization methods of climate series: an integrated approach (HOME) has executed a blind intercomparison and validation study for monthly homogenization algorithms. Time series of monthly temperature and precipitation were evaluated because of their importance for climate studies. The algorithms were validated against a realistic benchmark dataset. Participants provided 25 separate homogenized contributions as part of the blind study as well as 22 additional solutions submitted after the details of the imposed inhomogeneities were revealed. These homogenized datasets were assessed by a number of performance metrics including i) the centered root mean square error relative to the true homogeneous values at various averaging scales, ii) the error in linear trend estimates and iii) traditional contingency skill scores. The metrics were computed both using the individual station series as well as the network average regional series. The performance of the contributions depends significantly on the error metric considered. Although relative homogenization algorithms typically improve the homogeneity of temperature data, only the best ones improve precipitation data. Moreover, state-of-the-art relative homogenization algorithms developed to work with an inhomogeneous reference are shown to perform best. The study showed that currently automatic algorithms can perform as well as manual ones.

  11. A near-perfect invisibility cloak constructed with homogeneous materials.

    PubMed

    Li, Wei; Guan, Jianguo; Sun, Zhigang; Wang, Wei; Zhang, Qingjie

    2009-12-21

    A near-perfect, non-singular cylindrical invisibility cloak with diamond cross section is achieved by a two-step coordinate transformation. A small line segment is stretched and then blown up into a diamond space, and finally the cloak consisting of four kinds and eight blocks of homogeneous transformation media is obtained. Numerical simulations confirm the well performance of the cloak. The operation bandwidth of the cloak is also investigated. Our scheme is promising to create a simple and well-performed cloak in practice.

  12. 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,…

  13. Creating dedicated bioenergy crops

    USDA-ARS?s Scientific Manuscript database

    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...

  14. Creating a Classroom Newspaper.

    ERIC Educational Resources Information Center

    Buss, Kathleen, Ed.; McClain-Ruelle, Leslie, Ed.

    Based on the premise that students can learn a great deal by reading and writing a newspaper, this book was created by preservice instructors to teach upper elementary students (grades 3-5) newspaper concepts, journalism, and how to write newspaper articles. It shows how to use newspaper concepts to help students integrate knowledge from multiple…

  15. 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…

  16. 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…

  17. 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.…

  18. Creating Motivating Job Aids.

    ERIC Educational Resources Information Center

    Tilaro, Angie; Rossett, Allison

    1993-01-01

    Explains how to create job aids that employees will be motivated to use, based on a review of pertinent literature and interviews with professionals. Topics addressed include linking motivation with job aids; Keller's ARCS (Attention, Relevance, Confidence, Satisfaction) model of motivation; and design strategies for job aids based on Keller's…

  19. 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…

  20. Light-created chemiluminescence

    NASA Astrophysics Data System (ADS)

    Vasil'ev, Rostislav F.; Tsaplev, Yuri B.

    2006-11-01

    The results of studies of light-created chemiluminescence are described systematically. Conditions for the transformation of a dark chemical reaction into a chemiluminescence reaction are considered. Examples of photosensitised and photoinduced processes as well as of analytical applications are given.

  1. 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…

  2. Creating snags with explosives.

    Treesearch

    Evelyn L. Bull; Arthur D. Partridge; Wayne G. Williams

    1981-01-01

    The tops of ponderosa pine (Pinus ponderosa) trees were blown off with dynamite to create nest sites for cavity-nesting wildlife. The procedure included drilling a hole almost through the trunk, inserting the dynamite, and setting the charge with primacord and fuse. Trees were simultaneously innoculated with a decay organism. The average cost was $...

  3. 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…

  4. 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…

  5. 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…

  6. 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…

  7. Creating a Third Culture

    ERIC Educational Resources Information Center

    Weisbuch, Robert A.

    2008-01-01

    In this article, the author laments higher education's lack of concern towards the development of teaching in the public schools over the last half of the 20th century. Most of academe's work on the topic of teacher training has been done at the branches of state universities that needed to make money and create a niche. The author observes that…

  8. 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…

  9. 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.…

  10. Creating an Assessments Library

    ERIC Educational Resources Information Center

    Duncan, Greg; Gilbert, Jacqueline; Mackenzie, Mary; Meulener, Carol; Smith, Martin; Yetman, Beatrice; Zeppieri, Rosanne

    2006-01-01

    This article presents the steps taken over three years (2003-2006) by the Consortium for Assessing Performance Standards, a New Jersey Grant Project to create a database of thematically organized, integrated performance assessment tasks at the benchmark levels of proficiency, novice-mid, intermediate-low and pre-advanced as defined by the ACTFL…

  11. Creating Historical Drama.

    ERIC Educational Resources Information Center

    Cassler, Robert

    1990-01-01

    Describes creating for the National Archives Public Education Department a historical drama, "Second in the Realm," based on the story of the Magna Carta. Demonstrates the effectiveness of historical drama as a teaching tool. Explains the difficulties of writing such dramas and provides guidelines for overcoming these problems. (NL)

  12. [Teenagers creating art].

    PubMed

    Ahovi, Jonathan; Viverge, Agathe

    Teenagers need to interpret the world around them, sometimes in a completely different way to that in which, as children, they represented external reality. Some like drawing. They can use it to express their thoughts on death, sexuality or freedom. Their creative capacities are immense: they are creating art.

  13. 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,…

  14. Creating Motivating Job Aids.

    ERIC Educational Resources Information Center

    Tilaro, Angie; Rossett, Allison

    1993-01-01

    Explains how to create job aids that employees will be motivated to use, based on a review of pertinent literature and interviews with professionals. Topics addressed include linking motivation with job aids; Keller's ARCS (Attention, Relevance, Confidence, Satisfaction) model of motivation; and design strategies for job aids based on Keller's…

  15. 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…

  16. Creating Customer Delight.

    ERIC Educational Resources Information Center

    Black, Jim

    1995-01-01

    This article proposes that college admissions officers interested in improving service should focus on creating customer delight rather than simply satisfaction, studying the system when things go wrong rather than placing blame, establishing employee well-being as the highest priority of the organization, providing necessary tools and training…

  17. 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…

  18. Creating a Study Guide.

    ERIC Educational Resources Information Center

    Kelley, Laura C.

    2001-01-01

    Argues that making a theater study guide is an excellent in-class project, encouraging research, analysis, writing, and creative thinking. Offers a framework for creating one as a classroom project using John Steinbeck's "Of Mice and Men" as an example. Lists further resources. (SR)

  19. Creating an Effective Newsletter

    ERIC Educational Resources Information Center

    Shackelford, Ray; Griffis, Kurt

    2006-01-01

    Newsletters are an important resource or form of media. They offer a cost-effective way to keep people informed, as well as to promote events and programs. Production of a newsletter makes an excellent project, relevant to real-world communication, for technology students. This article presents an activity on how to create a short newsletter. The…

  20. 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…