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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 NTRS1986

Structural studies of gels and gel-glasses in the SiO2-GeO2 system using vibrational spectroscopy

GeO2 gel and gels in the SiO2-GeO2 system synthesized by the hydrolytic polycondensation of metal alkoxides have been studied by infrared and Raman spectroscopic techniques. The molecular structures, hydroxyl contents, and crystallinity of gels and gel-glasses in relation to the thermal history and GeO2 concentration were investigated. The binary compositions having up to 70 mol percent GeO2 were examined.

Mukherjee, Shyama P.↗
DOE OSTI2025

Measurement of electrical characteristics of Ge-based diodes with thermal GeO2 films exposed to controlled humidity conditions

We investigated the impact of the interaction between gas-phase water molecules and thermally oxidized GeO2 on Ge on the performance of metal–oxide–semiconductor (MOS) structures. A vacuum-integrated setup was developed to form MOS diodes with a GeO2/Ge structure that had been exposed to controlled humidity conditions and to subsequently measure their electrical characteristics in situ. The capacitance–voltage (C–V) curves exhibited a significant negative shift, indicating the generation of positive charges at the GeO2/Ge interface when the GeO2 surface was exposed to humidity levels above approximately 1%. According to a previous study using electron spectroscopy, this threshold corresponds to the humidity level at which molecular water begins to grow on a GeO2/Ge structure. It is likely that gas-phase water molecules infiltrating the GeO2 film bind to local OH sites via hydrogen bonding, leading to the formation of positive fixed charges at the GeO2/Ge interface.

Sano, Shuto↗
DOE OSTI2020

Materials Data on GeO2 by Materials Project

GeO2 is Hydrophilite-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Ge4+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing GeO6 octahedra. The corner-sharing octahedral tilt angles are 52°. There is four shorter (1.90 Å) and two longer (1.97 Å) Ge–O bond length. O2- is bonded in a distorted trigonal planar geometry to three equivalent Ge4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GeO2 by Materials Project

GeO2 crystallizes in the trigonal P3_121 space group. The structure is three-dimensional. Ge4+ is bonded in a distorted see-saw-like geometry to four equivalent O2- atoms. There are two shorter (2.03 Å) and two longer (2.11 Å) Ge–O bond lengths. O2- is bonded in a 3-coordinate geometry to two equivalent Ge4+ and one O2- atom. The O–O bond length is 1.54 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GeO2 by Materials Project

GeO2 crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. Ge4+ is bonded to six equivalent O2- atoms to form corner-sharing GeO6 octahedra. The corner-sharing octahedral tilt angles are 60°. All Ge–O bond lengths are 1.95 Å. O2- is bonded in a trigonal planar geometry to three equivalent Ge4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GeO2 by Materials Project

GeO2 is Rutile structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ge4+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing GeO6 octahedra. The corner-sharing octahedral tilt angles are 50°. There is four shorter (1.90 Å) and two longer (1.95 Å) Ge–O bond length. O2- is bonded in a distorted trigonal planar geometry to three equivalent Ge4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GeO2 by Materials Project

GeO2 is quartz (alpha) structured and crystallizes in the trigonal P3_121 space group. The structure is three-dimensional. Ge4+ is bonded to four equivalent O2- atoms to form corner-sharing GeO4 tetrahedra. There is two shorter (1.76 Å) and two longer (1.77 Å) Ge–O bond length. O2- is bonded in a bent 120 degrees geometry to two equivalent Ge4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GeO2 by Materials Project

GeO2 is low (alpha) Cristobalite structured and crystallizes in the tetragonal P4_12_12 space group. The structure is three-dimensional. Ge4+ is bonded to four equivalent O2- atoms to form corner-sharing GeO4 tetrahedra. There is two shorter (1.76 Å) and two longer (1.77 Å) Ge–O bond length. O2- is bonded in a bent 120 degrees geometry to two equivalent Ge4+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Glassy GeO2 obtained by the gel process

A comparison is made between GeO2 glass produced by the gel process and by a combined gel and thermal process. The latter appears to be more effective.

Voigt, Bernd↗
NASA NTRS1985

Sol-Gel Glasses

Multicomponent homogeneous, ultrapure noncrystalline gels/gel derived glasses are promising batch materials for the containerless glass melting experiments in microgravity. Hence, ultrapure, homogeneous gel precursors could be used to: (1) investigate the effect of the container induced nucleation on the glass forming ability of marginally glass forming compositions; and (2) investigate the influence of gravity on the phase separation and coarsening behavior of gel derived glasses in the liquid-liquid immiscibility zone of the nonsilicate systems having a high density phase. The structure and crystallization behavior of gels in the SiO2-GeO2 as a function of gel chemistry and thermal treatment were investigated. As are the chemical principles involved in the distribution of a second network former in silica gel matrix being investigated. The procedures for synthesizing noncrystalline gels/gel-monoliths in the SiO2-GeO2, GeO2-PbO systems were developed. Preliminary investigations on the levitation and thermal treatment of germania silicate gel-monoliths in the Pressure Facility Acoustic Levitator were done.

Mukherjee, S. P.↗
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↗
NASA NTRS1983

Ultrapure glass optical waveguide: Development in microgravity by the sol gel process

The sol-gel process for the preparation of homogeneous gels in three binary oxide systems was investigated. The glass forming ability of certain compositions in the selected oxide systems (SiO-GeO2, GeO2-PbO, and SiO2-TiO2) were studied based on their potential importance in the design of optical waveguide at longer wavelengths.

Mukherjee, S. P.↗
NASA NTRS1989

'Nose method' of calculating critical cooling rates for glass formation

The use of the so-called 'nose method' for computing critical cooling rates for glass formation is examined and compared with other methods, presenting data for the glass-forming systems SiO2, GeO2, and P2O5. It is shown that, for homogeneous crystallization, the nose-method will give an overestimate of Rc, a conclusion which was drawn after assessing the enfluence of a range of values for the parameters which control crystal growth and nucleation. The paper also proposes an alternative simple procedure (termed the 'cutoff method') for computing critical cooling rates from T-T-T diagrams, which was shown in the SiO2 and GeO2 systems to be superior to the nose method.

Weinberg, Michael C.↗
DOE OSTI2020

Local electrical degradations of solid-state electrolyte by nm-scale operando imaging of ionic and electronic transports

We report on degradation mechanisms of solid-state electrolyte (SSE) based on insights from nm-scale ionic conduction and electronic leakage for solid-state batteries. The significantly different local degradations revealed by nm-scale ionic and electronic transport imaging demonstrate the need for this nm-scale investigation. State-of-the-art lithium-ion conductive glass ceramic (Li 2 O–Al 2 O 3 –SiO 2 –P 2 O5–TiO2-GeO2) SSE shows at least two types of degradations spatially separated within the SSE, namely: (1) ionic conduction blocking and slight electronic leaking and (2) highly electronic shunting. Degradation was significantly suppressed by application of a Li-containing polyacrylonitrile thin coating on both sides of the ceramic SSE. With this coating, the ionic conduction was not reduced by the extensive cycling; instead, it improved slightly, although accompanied by a slight increase in electronic leaking. Our nm-scale transport imaging was achieved using an atomic force microscopy (AFM)-based half-cell setup and a logarithmic-scale amplifier with current sensitivity down to the fA (10-15 A) range. This half-cell setup consisting of an AFM-probe/SSE/Li structure can distinguish the ionic from the electronic current by flipping the bias-voltage polarity. This nm-scale operando imaging opens up novel characterization of ionic and electronic transport in the field of solid-state batteries.

42 ENGINEERING↗
DOE OSTI2022

Lead-Free Flexible Perovskite Solar Cells with Interfacial Native Oxide Have >10% Efficiency and Simultaneously Enhanced Stability and Reliability

Here we demonstrate an innovative compositional and interfacial engineering approach to achieve Pb-free flexible perovskite solar cells (f-PSCs) with an unprecedented combination of the highest efficiency reported to date (10.43%), together with enhanced operational stability and mechanical reliability. The key to this approach is alloying of an FASnI3 metal halide perovskite (MHP) thin film with Ge2+ to stabilize the Sn2+ oxidation state in the MHP, together with the use of a NiOx hole-transport layer. We show that this results in the in situ formation of a thin amorphous GeO2 native oxide layer at the NiOx/FASn0.9Ge0.1I3 interface. This layer not only passivates that critical interface but also enhances the interfacial mechanical bonding.

efficiency↗
DOE OSTI2020

Thermal conductivity of rutile germanium dioxide

Power electronics seek to improve power conversion of devices by utilizing materials with a wide bandgap, high carrier mobility, and high thermal conductivity. Due to its wide bandgap of 4.5 eV, b-Ga 2 O 3 has received much attention for high-voltage electronic device research. However, it suffers from inefficient thermal conduction that originates from its low-symmetry crystal structure. Rutile germanium oxide (r-GeO 2 ) has been identified as an alternative ultra-wide-bandgap (4.68 eV) semiconductor with predicted high electron mobility and ambipolar dopability; however, its thermal conductivity is unknown. Here, we characterize the thermal conductivity of r-GeO 2 as a function of temperature by first-principles calculations, experimental synthesis, and thermal characterization. The calculations predict an anisotropic phonon-limited thermal conductivity for r-GeO 2 of 37W m –1 K –1 along the a direction and 58W m –1 K –1 along the c direction at 300K where the phonon-limited thermal conductivity predominantly occurs via the acoustic modes. Experimentally, we measured the value of 51W m –1 K –1 at 300K for hot-pressed, polycrystalline r-GeO2 pellets. The measured value is close to our directionally averaged theoretical value, and the temperature dependence of ~1/T is also consistent with our theory prediction, indicating that thermal transport in our r-GeO 2 samples at room temperature and above is governed by phonon scattering. Furthermore, our results reveal that high-symmetry UWBG materials, such as r-GeO 2 , may be the key to efficient power electronics.

36 MATERIALS SCIENCE↗