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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on CaTiO3 by Materials Project

CaTiO3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.45 Å) and four longer (2.71 Å) Ca–O bond lengths. Ti4+ is bonded to six O2- atoms to form corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 0–26°. There is two shorter (1.96 Å) and four longer (1.97 Å) Ti–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Ti4+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ca2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaTiO3 by Materials Project

CaTiO3 is Orthorhombic Perovskite-like structured and crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. Ca2+ is bonded in a 11-coordinate geometry to five O2- atoms. There are one shorter (2.33 Å) and four longer (2.45 Å) Ca–O bond lengths. Ti4+ is bonded to six O2- atoms to form corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 21–28°. There is four shorter (1.97 Å) and two longer (1.98 Å) Ti–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Ti4+ atoms. In the second O2- site, O2- is bonded in a 5-coordinate geometry to one Ca2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaTiO3 by Materials Project

CaTiO3 is (Cubic) Perovskite structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ca2+ is bonded to twelve equivalent O2- atoms to form CaO12 cuboctahedra that share corners with twelve equivalent CaO12 cuboctahedra, faces with six equivalent CaO12 cuboctahedra, and faces with eight equivalent TiO6 octahedra. All Ca–O bond lengths are 2.75 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 CaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Ti–O bond lengths are 1.94 Å. O2- is bonded in a distorted linear geometry to four equivalent Ca2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaTiO3 by Materials Project

CaTiO3 is Ilmenite structured and crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent O2- atoms to form distorted CaO6 pentagonal pyramids that share corners with nine equivalent TiO6 octahedra, edges with three equivalent CaO6 pentagonal pyramids, and a faceface with one TiO6 octahedra. The corner-sharing octahedra tilt angles range from 38–64°. There are three shorter (2.30 Å) and three longer (2.44 Å) Ca–O bond lengths. Ti4+ is bonded to six equivalent O2- atoms to form distorted TiO6 octahedra that share corners with nine equivalent CaO6 pentagonal pyramids, edges with three equivalent TiO6 octahedra, and a faceface with one CaO6 pentagonal pyramid. There are three shorter (1.90 Å) and three longer (2.13 Å) Ti–O bond lengths. O2- is bonded in a distorted see-saw-like geometry to two equivalent Ca2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaTiO3 by Materials Project

CaTiO3 is Orthorhombic Perovskite structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 12-coordinate geometry to six O2- atoms. There are a spread of Ca–O bond distances ranging from 2.35–2.78 Å. In the second Ca2+ site, Ca2+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of Ca–O bond distances ranging from 2.51–2.97 Å. Ti4+ is bonded to six O2- atoms to form corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 18–27°. There are a spread of Ti–O bond distances ranging from 1.96–1.98 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and two equivalent Ti4+ atoms. In the second O2- site, O2- is bonded in a 5-coordinate geometry to three Ca2+ and two equivalent Ti4+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Studies on the compositional dependent structural and electrical properties of CaTiO3-modified K0.5Na0.5NbO3 piezoelectric system

Lead-free piezoelectric ceramics of (1 − x)K0.5Na0.5NbO3-xCaTiO3 were fabricated, and their crystal structure, microstructure, and electrical properties were systematically studied. Rietveld refinement of the x-ray diffraction data and Raman spectroscopic analyses revealed a composition-dependent structural phase transition: three phase transitions, namely, from a pure orthorhombic phase for x ≤ 0.02 to a mixed phase of orthorhombic and tetragonal phases (0.03 ≤ x ≤ 0.08) and finally another mixed phase of tetragonal + cubic for x = 0.10 and 0.15 at room temperature (RT). The morphological study reveals a decrease in grain size along with a more uniform distribution of grains as the concentration of CaTiO3 (CT) increases; notably, a homogeneous distribution of grains is observed for x = 0.05. The temperature-dependent dielectric properties show two phase transitions, from orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC), for unmodified K0.5Na0.5NbO3 (KNN). However, both the phase transition temperatures (TO-T and TC) decrease, and the transition peaks broaden with an increase in CT substitution, and for x > 0.06, the TO-T shifted below RT. The broadening of the transition peak at TO-T may be due to the relaxation behavior. Among the prepared samples, the 5 mol. % CT-modified KNN shows the optimum electrical properties (d33 = 114 pC/N, ɛr = 412, and 2Pr = 15.25 μC/cm2) at RT. The enhanced electrical properties for x = 0.05 are due to the coexistence of orthorhombic and tetragonal phases, facilitating easy polarization rotation and flattening of the free energy profile. A phase diagram has been constructed based on the information gathered from the temperature-dependent dielectric measurements, RT x-ray diffraction, and Raman spectroscopy data and is discussed in detail.

Physics↗
DOE OSTI2020

A Thermodynamic Investigation of Ni on Thin-Film Titanates (ATiO3)

Thin, ~1-nm films of CaTiO3, SrTiO3, and BaTiO3 were deposited onto MgAl2O4 by Atomic Layer Deposition (ALD) and then studied as catalyst supports for ~5 wt % of Ni that was added to the perovskite thin films by Atomic Layer Deposition. Scanning Transmission Electron Microscopy demonstrated that both the Ni and the perovskites uniformly covered the surface of the support following oxidation at 1073 K, even after redox cycling, but large Ni particles formed following a reduction at 1073 K. When compared to Ni/MgAl2O4, the perovskite-containing catalysts required significantly higher temperatures for Ni reduction. Equilibrium constants for Ni oxidation, as determined from Coulometric Titration, indicated that the oxidation of Ni shifted to lower PO2 on the perovskite-containing materials. Based on Ni equilibrium constants, Ni interactions are strongest with CaTiO3, followed by SrTiO3 and BaTiO3. The shift in the equilibrium constant was shown to cause reversible deactivation of the Ni/CaTiO3/MgAl2O4 catalyst for CO2 reforming of CH4 at high CO2 pressures, due to the oxidation of the Ni.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Dielectric Resonator Design for Low Power and Low Temperature Microwave Plasma

Waveguide-based microwave plasmas generally operate at high temperatures (2000 - 6000K)[1], making it difficult to directly interface solid materials with the plasma without significant thermal damage. Dielectric microwave resonators (DMRs), long studied for wave-based manipulation of electromagnetic radiation for telecom and optics, can focus radiation to extremely small mode volumes, creating intense localized fields with low-power input.[2] This phenomenon can be used for applications ranging from efficient plasma electronics to near-ambient plasma-materials interactions. Such DMR-based plasmas have been demonstrated a handful of times in the literature, but the majority of research towards this utilize the lowest frequency resonance mode.[3], [4], [5] By carefully controlling the geometry of cylindrical resonators, a variety of electromagnetic modes can be excited. In this work, COMSOL Multiphysics simulations are used to study the electric field enhancement and absorption properties of CaTiO3 DMRs as a function of geometry and excitation frequency. Whereas previous studies have utilized the HEM111 resonance frequency to drive low power plasma excitation, we find that higher order resonance frequencies are more effective at field enhancement and result in less power loss within the dielectric material, hence less wasted heating. The effectiveness of these modes is also geometry dependent and can be computationally optimized for plasma generation. Complementing these computational efforts, we demonstrate a new closed-system reactor design built in a WR-650 waveguide and experimentally demonstrate the formation of atmospheric argon microwave plasma using < 30 W input power on DMR dimers. We observe a shifting resonance frequency as the DMRs heat in response to microwave excitation and develop a Python-based lock-in mechanism to effectively track the DMR resonance over time, leading to stable plasma operation. We use infrared thermal imaging to monitor the temperature of the DMR dimers and surrounding quartz chamber, demonstrating thermal temperatures < 60 degreesC. Finally, we utilize optical emission spectroscopy (OES) to probe the plasma properties as a function of the resonance mode.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Investigation of Rh–titanate (ATiO 3 ) interactions on high-surface-area perovskite thin films prepared by atomic layer deposition

Thin, ~1 nm films of CaTiO 3 , SrTiO 3 , and BaTiO 3 were deposited onto MgAl 2 O 4 by Atomic Layer Deposition (ALD) and studied as catalyst supports for Rh. Scanning Transmission Electron Microcopy (STEM) and X-Ray Diffraction (XRD) demonstrated that the films had the perovskite structure and formed uniform coatings stable up to 1073 K. Rh, added by ALD, interacted strongly with CaTiO 3 and somewhat less strongly with SrTiO 3 , while Rh on BaTiO 3 was similar to Rh on unmodified MgAl 2 O 4 . STEM measurements of Rh on CaTiO 3 films showed Rh remained well dispersed after repeated oxidations and reductions at 1073 K; however, the Rh was inactive for CO-oxidation. Rh formed small particles on SrTiO 3 films and was active for CO oxidation after reduction at 1073 K. The reducibility and catalytic activity of Rh/BaTiO 3 /MgAl 2 O 4 were similar to that of Rh/MgAl 2 O 4 . Evidence from CO-TPR, FTIR, and XPS all indicated that the degree of interaction between Rh and the three perovskite films can be ranked in the following order: Rh/CaTiO 3 /MgAl 2 O 4 > Rh/SrTiO 3 /MgAl 2 O 4 > Rh/BaTiO 3 /MgAl 2 O 4 . Here, bulk ex-solution catalysts, synthesized by reduction of ATi 0.98 Rh 0.02 O 3 (A = Ca, Sr, and Ba), were also examined for comparison.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗