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16 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on In2O3 by Materials Project

In2O3 is Corundum structured and crystallizes in the trigonal R-3c space group. The structure is three-dimensional. In3+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge, face, and corner-sharing InO6 octahedra. The corner-sharing octahedra tilt angles range from 49–63°. There are three shorter (2.16 Å) and three longer (2.29 Å) In–O bond lengths. O2- is bonded to four equivalent In3+ atoms to form a mixture of distorted edge and corner-sharing OIn4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on In2O3 by Materials Project

In2O3 is Corundum-like structured and crystallizes in the cubic Ia-3 space group. The structure is three-dimensional. there are two inequivalent In3+ sites. In the first In3+ site, In3+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing InO6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are a spread of In–O bond distances ranging from 2.17–2.26 Å. In the second In3+ site, In3+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing InO6 octahedra. The corner-sharing octahedral tilt angles are 55°. All In–O bond lengths are 2.21 Å. O2- is bonded to four In3+ atoms to form a mixture of distorted edge and corner-sharing OIn4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on In2O3 by Materials Project

In2O3 is Corundum-like structured and crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. there are two inequivalent In3+ sites. In the first In3+ site, In3+ is bonded to six O2- atoms to form a mixture of distorted face, edge, and corner-sharing InO6 octahedra. The corner-sharing octahedra tilt angles range from 48–65°. There are a spread of In–O bond distances ranging from 2.14–2.31 Å. In the second In3+ site, In3+ is bonded to six O2- atoms to form a mixture of face, edge, and corner-sharing InO6 octahedra. The corner-sharing octahedra tilt angles range from 49–71°. There are a spread of In–O bond distances ranging from 2.18–2.29 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four In3+ atoms to form a mixture of distorted edge and corner-sharing OIn4 trigonal pyramids. In the second O2- site, O2- is bonded to four In3+ atoms to form a mixture of distorted edge and corner-sharing OIn4 tetrahedra. In the third O2- site, O2- is bonded to four In3+ atoms to form a mixture of distorted edge and corner-sharing OIn4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on In2O3 by Materials Project

In2O3 is Stibnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent In3+ sites. In the first In3+ site, In3+ is bonded to seven O2- atoms to form a mixture of distorted edge, face, and corner-sharing InO7 pentagonal bipyramids. There are a spread of In–O bond distances ranging from 2.20–2.44 Å. In the second In3+ site, In3+ is bonded to seven O2- atoms to form a mixture of distorted edge and corner-sharing InO7 pentagonal bipyramids. There are a spread of In–O bond distances ranging from 2.20–2.38 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four In3+ atoms to form distorted OIn4 trigonal pyramids that share corners with four equivalent OIn5 square pyramids, corners with seven equivalent OIn5 trigonal bipyramids, corners with four equivalent OIn4 trigonal pyramids, edges with three equivalent OIn5 square pyramids, and a faceface with one OIn5 trigonal bipyramid. In the second O2- site, O2- is bonded to five In3+ atoms to form OIn5 square pyramids that share corners with eight equivalent OIn5 trigonal bipyramids, corners with four equivalent OIn4 trigonal pyramids, edges with four equivalent OIn5 square pyramids, edges with two equivalent OIn5 trigonal bipyramids, and edges with three equivalent OIn4 trigonal pyramids. In the third O2- site, O2- is bonded to five In3+ atoms to form distorted OIn5 trigonal bipyramids that share corners with eight equivalent OIn5 square pyramids, corners with seven equivalent OIn4 trigonal pyramids, edges with two equivalent OIn5 square pyramids, edges with four equivalent OIn5 trigonal bipyramids, and a faceface with one OIn4 trigonal pyramid.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on In2O3 by Materials Project

In2O3 is Corundum-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. In3+ is bonded to six O2- atoms to form a mixture of distorted corner, edge, and face-sharing InO6 octahedra. The corner-sharing octahedra tilt angles range from 51–72°. There are a spread of In–O bond distances ranging from 2.16–2.33 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent In3+ atoms to form a mixture of distorted corner and edge-sharing OIn4 tetrahedra. In the second O2- site, O2- is bonded to four equivalent In3+ atoms to form a mixture of distorted corner and edge-sharing OIn4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Advances in Molecular Beam Epitaxy Growth of Ultra-Wide Bandgap Ga2O3 Based Alloys

Gallium oxide (Ga2O3) is an emerging ultra-wide bandgap semiconductor material that has attracted attention for its potential to outperform existing SiC and GaN based devices operating at high breakdown voltages and high temperature. Isovalent alloying of In and Al in Ga2O3 provides the ability to engineer bandgap energy and strain of the material. Alloying with Al increases the bandgap energy and the theoretically achievable Baliga's figure of merit, a key measure of a material's ultimate performance limits for high power switching devices. Alloying with In introduces compressive strain and can be used to counteract the tensile strain of Al incorporation. The resulting (AlxGa1-x-yIny)2O3 alloy can be lattice-matched to commercially available Ga2O3 wafers and has a tunable bandgap energy greater than that of Ga2O3, 4.76 eV. Such lattice-matched material can be grown arbitrarily thick without the detrimental effects of elastic strain and relaxation, making it suitable for high voltage diodes and transistors. However, efforts to synthesize isovalent alloys are complicated by their tendency to phase separate into corundum Al2O3 or bixbyite In2O3. Literature reports of the quaternary (AlxGa1-x-yIny)2O3 are limited to <1% unintentional indium incorporation in In-catalyzed (AlxGa1-x)2O3. The primary limitation to quaternary growth is the limited incorporation of indium at elevated growth temperatures. This limited incorporation is due to both the volatility of indium oxide and Al and Ga cation exchange reactions which replace indium in In2O3. We report on the development of a novel high-throughput molecular beam epitaxy (MBE) technique to screen the growth conditions for the ternary alloy (InyGa1-y)2O3, and the application of these findings to the first successful synthesis of phase pure monoclinic (AlxGa1-x-yIny)2O3 by MBE. By leveraging the unique sub-oxide chemistry of Ga2O3 and in-situ monitoring of crystal properties by reflection high-energy electron diffraction (RHEED), a cyclical growth and etch-back method is developed and applied to rapidly characterize the (InyGa1-y)2O3 growth space. This cyclical method provides approximately 10x increase in experimental throughput and up to 46x improvement in Ga2O3 substrate utilization. Appropriate growth conditions for monoclinic (InyGa1- y)2O3 are identified by machine learning analysis of RHEED patterns and targeted growths are characterized ex-situ to confirm improved In incorporation. These growth conditions are then combined with established (AlxGa1-x)2O3 growth conditions to grow quaternary (AlxGa1-x-yIny)2O3 with Al mole fractions ranging from 1.4% - 24.4% and In mole fractions ranging from 3.1% to 15.5%. The chemical and optical properties of the alloys are investigated by XRD, XPS, and spectroscopic ellipsometry. A lattice-matched (AlxGa1-x-yIny)2O3 alloy is examined by 4D-STEM and the chemical and physical uniformity of Al and In incorporation are discussed.

alloy↗
DOE OSTI2026

Microstructure and Composition of Passivating Interfaces in Silicon Heterojunction Solar Modules Weathered in Different Climates

Sanyo/Panasonic patented silicon heterojunction with intrinsic thin layer (HIT) solar cells in the 1990's, which demonstrated world record photovoltaic (PV) efficiency around 2014 and inspired the newer generations of silicon heterojunction technology (SHJ) as well as the current world record back-contact PV cell designs. The high-quality passivation strategy, utilizing ultra-thin layers of hydrogenated amorphous silicon (a-Si:H), leads to high voltages and long carrier lifetimes, but these qualities may degrade over time as the modules operate outdoors. Here, we investigate local microstructure and composition at the interface layers of cells from HIT modules weathered in a hot, humid climate (Florida, USA) and temperate climate (Colorado, USA) for 10 years. We employ a comprehensive set of high-resolution electron microscopy imaging and spectroscopy to directly resolve structure and composition in these cells down to the nanoscale. We show features such as alignment of the In2O3 transparent conducting oxide and a-Si:H layers on the textured c-Si facets, interfacial oxidation at the a-Si:H/c-Si and In2O3/a-Si:H interfaces, and twinned c-Si resulting from epitaxial growth into the a-Si:H layer. Our results raise potential degradation mechanisms in these outdoor-weathered modules, but the root cause of electrical loss remains uncertain due to the very small changes in aged samples. This study shows that many atomic scale features at the In2O3/a-Si:H/c-Si interfaces are surprisingly robust, and the electrical losses with aging may either be attributed to other pathways or be very sensitive to the subtle chemical and microstructural features observed here.

14 SOLAR ENERGY↗
DOE OSTI2024

Computational Insights into Phase Equilibria Between Wide-Gap Semiconductors and Contact Materials

Novel wide-band-gap semiconductors are needed for next-generation power electronics, but there is a gap between a promising material and a functional device. Finding stable (metal) contacts is one of the major challenges that is currently dealt with mainly via trial and error. Herein, we computationally investigate the thermochemistry and phase coexistence at the junction between three wide-gap semiconductors, ..beta..-Ga2O3, GeO2, and GaN, and possible contact materials. The pool of possible contacts includes 47 elemental metals and a set of 4 common, n-type transparent conducting oxides (ZnO, TiO2, SnO2, and In2O3). We use first-principles thermodynamics to model the Gibbs free energies of chemical reactions as a function of gas pressure (pO2/pN2) and equilibrium temperature. We deduce whether a semiconductor/contact interface will be stable at relevant conditions or a chemical reaction between them is to be expected, possibly influencing the long-term reliability and performance of devices. We generally find that most elemental metals tend to oxidize or nitridize and form various interface oxide/nitride layers. Exceptions include select late- and post-transition metals and, in the case of GaN, also the alkali metals, which are predicted to exhibit stable coexistence, although in many cases at relatively low gas partial pressures. Similar is true for the transparent conducting oxides, for which, in most cases, we predict a preference toward forming ternary oxides when in contact with ..beta..-Ga2O3 and GeO2. The only exception is SnO2, which we find to form stable contacts with both oxides. Finally, we show how the same approach can be used to predict gas partial pressure vs temperature phase diagrams to help direct synthesis of ternary compounds. We believe these results provide a valuable guidance in selecting contact materials to wide-gap semiconductors and suitable growth conditions.

contact materials↗
DOE OSTI2023

General Kinetic Model for pH Dependence of Proton-Coupled Electron Transfer: Application to an Electrochemical Water Oxidation System

The pH dependence of proton-coupled electron transfer (PCET) reactions, which are critical to many chemical and biological processes, is a powerful probe for elucidating their fundamental mechanisms. Herein, a general, multichannel kinetic model is introduced to describe the pH dependence of both homogeneous and electrochemical PCET reactions. According to this model, a weak pH dependence can arise from the competition among multiple sequential and concerted PCET channels involving different forms of the redox species, such as protonated and deprotonated forms, as well as different proton donors and acceptors. The contribution of each channel is influenced by the relative populations of the reactant species, which often depend strongly on pH, leading to complex pH dependence of PCET apparent rate constants. This model is used to explain the origins of the experimentally observed weak pH dependence of the electrochemical PCET apparent rate constant for a ruthenium-based water oxidation catalyst attached to a tin-doped In2O3 (ITO) surface. The weak pH dependence is found to arise from the intrinsic differences in the rate constants of participating channels and the dependence of their relative contributions on pH. This model predicts that the apparent maximum rate constant will become pH-independent at higher pH, which is confirmed by experimental measurements. Our analysis also suggests that the dominant channels are electron transfer at lower pH and sequential PCET via electron transfer followed by fast proton transfer at higher pH. Furthermore, this work highlights the importance of considering multiple competing channels simultaneously for PCET processes.

Catalysts↗
DOE OSTI2020

Interfacial control of oxygen vacancy doping and electrical conduction in thin film oxide heterostructures

Systems and methods of reversibly controlling the oxygen vacancy concentration and distribution in oxide heterostructures consisting of electronically conducting In2O3 films grown on ionically conducting Y2O3-stabilized ZrO2 substrates. Oxygen ion redistribution across the heterointerface is induced using an applied electric field oriented in the plane of the interface, resulting in controlled oxygen vacancy (and hence electron) doping of the film and possible orders-of-magnitude enhancement of the film's electrical conduction. The reversible modified behavior is dependent on interface properties and is attained without cation doping or changes in the gas environment in contact with the sample.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mechanistic understanding of support effect on the activity and selectivity of indium oxide catalysts for CO 2 hydrogenation

Herein we present a mechanistic study on the support effect (ZrO 2 and CeO 2 ) of In 2 O 3 catalysts in CO 2 hydrogenation by a combined experimental and computational approach. Kinetic experiments and surface characterization suggested that the activity of In 2 O 3 catalysts cannot be simply correlated with the abundance of surface oxygen vacancies (O v ) formed by either H 2 -reduction or thermal treatment, which has been frequently invoked in previous studies. The support effect should originate from the electronic interactions between In 2 O 3 and the support oxide, rather than geometric factors or the difference in the particle size of In 2 O 3 . Theoretical modelling revealed that surface O v facilitate the formation and stabilization of the formate (HCOO*) intermediate. While a carbonate-like structure is favored for CO 2 adsorption on CeO 2 -supported or unsupported In 2 O 3 catalysts, CO 2 tends to bind strongly in a bent configuration on the O v site at the In 2 O 3 -ZrO 2 interface. The distinct CO 2 adsorption structures on different supported In 2 O 3 catalysts may account for the different reaction energy profiles in the subsequent hydrogenation reactions, especially the rate-limiting step, i.e., hydrogenation of HCOO* to CH 2 O* and methoxy (CH 3 O*). The relatively higher methanol selectivity of In 2 O 3 catalyst supported on ZrO 2 with respect to that on CeO 2 are suggested to stem from the greater energy difference (Δ$E_a$) between the parallel hydrogenation and C-O bond cleavage of HCOO*, which leads to the formation of methanol and CO, respectively. We report this study underlines the important role of metal-oxide-interface in determining the catalytic behavior of oxide-supported In 2 O 3 catalysts in CO 2 conversion.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2025

Pd-promoted reduction and restructuring of an In 2 O 3 -based catalyst for CO 2 hydrogenation at room temperature

An unconventional reaction mechanism in an In 2 O 3 /Pd(1 1 1) inverse model catalyst for the CO 2 hydrogenation reaction has been uncovered: In 2 O 3 is partially reduced at room temperature in a reaction atmosphere as a result of its direct contact with Pd(1 1 1), which is an efficient H 2 splitter. The reduction induces changes in surface free energy, leading to a dynamical restructuring at the In 2 O 3 /Pd(1 1 1) interface via formation of InO x and outward diffusion of Pd, as revealed by ambient pressure X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and density functional theory simulations. This dynamical restructuring eventually promotes the growth of 2D InPd y O x nanodomains as the catalytically active phase and the exclusive formation of methanol upon hydrogenation of CO 2 at room temperature. A comparable high selectivity toward CH 3 OH was found in more realistic bulk catalytic systems (2 wt% Pd/In 2 O 3 catalyst and commercial CZA catalyst). Scanning tunneling microscopy under ultrahigh vacuum and ambient pressure reaction atmospheres further reveals the structural dynamics at the InO x /Pd(1 1 1) interface, where we follow in situ the evolution of the InO x particles on Pd(1 1 1) and the mobility of the InPd y O x nanodomains in a CO 2 + H 2 environment. The present findings of the formation of a mixed oxide phase in a dynamically restructuring metal/reducible-oxide interface indicate further implications for other heterogeneous catalytic systems beyond the present CO 2 hydrogenation example and highlight the importance of in situ investigations.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Randomly Layered Superstructure of In 2 O 3 Truncated Nano-Octahedra and Its High-Pressure Behavior

This study outlines the synthesis and characterization of a unique superlattice composed of vertex-truncated indium oxide (In 2 O 3 ) nano-octahedra, along with an exploration of its response to high-pressure conditions. Here, using a bright-field transmission electron microscope (BF-TEM), we determined an average circumradius of 15.2 nm for these octahedral building blocks. The resilience and response of the superlattice to pressure variations, peaking at 18.01 GPa, were examined by employing synchrotron-based Wide-Angle X-ray Scattering (WAXS) and Small-Angle X-ray Scattering (SAXS) techniques. The WAXS data revealed no phase transitions, reinforcing the stability of the 2D superlattice comprised of random layers in alignment with a 2D p31m symmetry. Notably, the SAXS data unveiled a pressure-induced, irreversible octahedron translation and ligand interaction occurring within the random layer. Through our examination of these pressure-sensitive behaviors, we identified a distinctive translation model inherent to octahedra and observed modulation in the superlattice cell parameter induced by pressure. This research signifies a noteworthy progression in deciphering the intricate behaviors of 2D superlattices under high-pressure conditions.

36 MATERIALS SCIENCE↗