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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Electrical and Optical Property of Ferroelectric BaTiO3:Eu

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.

Park, Yeonjoon↗
NASA NTRS1993

Thin film processing of photorefractive BaTiO3

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.

Schuster, Paul R.↗
NASA NTRS1982

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

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.

Dharmadhikari, V. S.↗
NASA NTRS2014

A General Reliability Model for Ni-BaTiO3-Based Multilayer Ceramic Capacitors

The evaluation of multilayer ceramic capacitors (MLCCs) with Ni electrode and BaTiO3 dielectric material for potential space project applications requires an in-depth understanding of their reliability. A general reliability model for Ni-BaTiO3 MLCC is developed and discussed. The model consists of three parts: a statistical distribution; an acceleration function that describes how a capacitor's reliability life responds to the external stresses, and an empirical function that defines contribution of the structural and constructional characteristics of a multilayer capacitor device, such as the number of dielectric layers N, dielectric thickness d, average grain size, and capacitor chip size A. Application examples are also discussed based on the proposed reliability model for Ni-BaTiO3 MLCCs.

statistical modeling↗
NASA NTRS2014

A General Reliability Model for Ni-BaTiO3-Based Multilayer Ceramic Capacitors

The evaluation for potential space project applications of multilayer ceramic capacitors (MLCCs) with Ni electrode and BaTiO3 dielectric material requires an in-depth understanding of the MLCCs reliability. A general reliability model for Ni-BaTiO3 MLCCs is developed and discussed in this paper. The model consists of three parts: a statistical distribution; an acceleration function that describes how a capacitors reliability life responds to external stresses; and an empirical function that defines the contribution of the structural and constructional characteristics of a multilayer capacitor device, such as the number of dielectric layers N, dielectric thickness d, average grain size r, and capacitor chip size A. Application examples are also discussed based on the proposed reliability model for Ni-BaTiO3 MLCCs.

statistical modeling↗
NASA NTRS2015

Insulation Resistance Degradation in Ni-BaTiO3 Multilayer Ceramic Capacitors

Insulation resistance (IR) degradation in Ni-BaTiO3 multilayer ceramic capacitors has been characterized by the measurement of both time to failure and direct-current (DC) leakage current as a function of stress time under highly accelerated life test conditions. The measured leakage current-time dependence data fit well to an exponential form, and a characteristic growth time SD can be determined. A greater value of tau(sub SD) represents a slower IR degradation process. Oxygen vacancy migration and localization at the grain boundary region results in the reduction of the Schottky barrier height and has been found to be the main reason for IR degradation in Ni-BaTiO3 capacitors. The reduction of barrier height as a function of time follows an exponential relation of phi (𝑡)=phi (0)e(exp -2Κt), where the degradation rate constant 𝐾=𝐾o𝑒(𝐸𝑘/𝑘𝑇) is inversely proportional to the mean time to failure (MTTF) and can be determined using an Arrhenius plot. For oxygen vacancy electromigration, a lower barrier height phi(0) will favor a slow IR degradation process, but a lower phi(0) will also promote electronic carrier conduction across the barrier and decrease the insulation resistance. As a result, a moderate barrier height phi(0) (and therefore a moderate IR value) with a longer MTTF (smaller degradation rate constant 𝐾) will result in a minimized IR degradation process and the most improved reliability in Ni-BaTiO3 multilayer ceramic capacitors.

dielectric degradation↗
DOE OSTI2020

Materials Data on BaTiO3 by Materials Project

BaTiO3 crystallizes in the orthorhombic Amm2 space group. The structure is two-dimensional and consists of two BaTiO3 sheets oriented in the (0, 1, 0) direction. Ba2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are two shorter (2.56 Å) and four longer (3.07 Å) Ba–O bond lengths. Ti4+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.75 Å) and one longer (1.82 Å) Ti–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ba2+ and one Ti4+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Ba2+ and one Ti4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

7.86 kV GaN-on-GaN PN power diode with BaTiO3 for electrical field management

Devices based on gallium nitride (GaN) have great potential for high power switching applications due to the high breakdown field and high electron mobility. In this work, we present a vertical GaN-on-GaN PN power diode using high dielectric constant material, BaTiO3, for electrical field management and high breakdown voltages, in together with an optimized guard-ring and field plate design. Numerical simulation shows that with high-k dielectrics implemented, the peak electrical field at the PN interface is mitigated from 3.5 to 3.1 MV/cm under a reverse bias of −9.05 kV. The device design with BaTiO3 shows a breakdown voltage of 9.65 kV or about 600 V improvement. The fabricated diodes with a 57 μm thick drift layer demonstrate a breakdown voltage of 7.86 kV on a bulk GaN substrate. The device has an on-resistance of 2.8 mΩ cm2 and a Baliga figure of merit of 22 GW/cm2.

Physics↗
NASA NTRS1971

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

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.

Mountvala, A. J.↗
NASA NTRS1983

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

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

Dharmadhikari, V. S.↗
NASA NTRS2012

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

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.

Liu, David Donhang↗
DOE OSTI2020

Materials Data on BaTiO3 by Materials Project

BaTiO3 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Ba2+ is bonded in a linear geometry to two equivalent O2- atoms. Both Ba–O bond lengths are 2.52 Å. Ti4+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Ti–O bond lengths are 2.06 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to two equivalent Ti4+ and two equivalent O2- atoms. Both O–O bond lengths are 2.06 Å. In the second O2- site, O2- is bonded to two equivalent Ba2+ and four equivalent O2- atoms to form distorted corner-sharing OBa2O4 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaTiO3 by Materials Project

BaTiO3 is (Cubic) Perovskite structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ba2+ is bonded to twelve equivalent O2- atoms to form BaO12 cuboctahedra that share corners with twelve equivalent BaO12 cuboctahedra, faces with six equivalent BaO12 cuboctahedra, and faces with eight equivalent TiO6 octahedra. All Ba–O bond lengths are 2.85 Å. Ti4+ is bonded to six equivalent O2- atoms to form TiO6 octahedra that share corners with six equivalent TiO6 octahedra and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Ti–O bond lengths are 2.02 Å. O2- is bonded in a distorted linear geometry to four equivalent Ba2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaTiO3 by Materials Project

BaTiO3 is (Cubic) Perovskite structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. Ba2+ is bonded to twelve equivalent O2- atoms to form BaO12 cuboctahedra that share corners with twelve equivalent BaO12 cuboctahedra, faces with six equivalent BaO12 cuboctahedra, and faces with eight equivalent TiO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.79–3.00 Å. Ti4+ is bonded to six equivalent O2- atoms to form TiO6 octahedra that share corners with six equivalent TiO6 octahedra and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 10°. There are three shorter (1.87 Å) and three longer (2.22 Å) Ti–O bond lengths. O2- is bonded in a 2-coordinate geometry to four equivalent Ba2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaTiO3 by Materials Project

BaTiO3 is (Cubic) Perovskite structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional and consists of one titanium molecule and one BaO3 framework. In the BaO3 framework, Ba2+ is bonded to six equivalent O2- atoms to form corner-sharing BaO6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ba–O bond lengths are 2.32 Å. O2- is bonded in a linear geometry to two equivalent Ba2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaTiO3 by Materials Project

BaTiO3 crystallizes in the orthorhombic C222_1 space group. The structure is three-dimensional. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with nine BaO12 cuboctahedra, corners with three equivalent TiO6 octahedra, faces with seven BaO12 cuboctahedra, and faces with seven TiO6 octahedra. The corner-sharing octahedra tilt angles range from 7–9°. There are a spread of Ba–O bond distances ranging from 2.83–3.08 Å. In the second Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with twelve BaO12 cuboctahedra, faces with six equivalent BaO12 cuboctahedra, and faces with eight TiO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.88–2.93 Å. There are two inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three equivalent BaO12 cuboctahedra, corners with three equivalent TiO6 octahedra, faces with seven BaO12 cuboctahedra, and a faceface with one TiO6 octahedra. The corner-sharing octahedra tilt angles range from 5–10°. There are a spread of Ti–O bond distances ranging from 1.86–2.17 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six equivalent TiO6 octahedra and faces with eight BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 5–10°. There are a spread of Ti–O bond distances ranging from 1.88–2.17 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted L-shaped geometry to four Ba2+ and two equivalent Ti4+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to four Ba2+ and two Ti4+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to four Ba2+ and two Ti4+ atoms. In the fourth O2- site, O2- is bonded in a 6-coordinate geometry to four Ba2+ and two equivalent Ti4+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to four Ba2+ and two Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaTiO3 by Materials Project

BaTiO3 is (Cubic) Perovskite structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with twelve equivalent BaO12 cuboctahedra, faces with six equivalent BaO12 cuboctahedra, and faces with eight equivalent TiO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.81–3.00 Å. Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with six equivalent TiO6 octahedra and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 3–11°. There are a spread of Ti–O bond distances ranging from 1.83–2.38 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to four equivalent Ba2+ and two equivalent Ti4+ atoms. In the second O2- site, O2- is bonded in a 1-coordinate geometry to four equivalent Ba2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaTiO3 by Materials Project

BaTiO3 is (Cubic) Perovskite structured and crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with twelve equivalent BaO12 cuboctahedra, faces with six equivalent BaO12 cuboctahedra, and faces with eight equivalent TiO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.79–3.06 Å. Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six equivalent TiO6 octahedra and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 8–13°. There are a spread of Ti–O bond distances ranging from 1.85–2.28 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 6-coordinate geometry to four equivalent Ba2+ and two equivalent Ti4+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to four equivalent Ba2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗