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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

In situ study of rotating lattice single–crystal formation in Sb 2 S 3 glass by Laue μXRD

Single–crystal architectures in glass, formed by a solid–solid transformation via laser heating, are novel solids with a rotating lattice. To understand the process of lattice formation that proceeds via crystal growth, we have observed in situ Sb 2 S 3 crystal formation under X–ray irradiation with simultaneous Laue micro X–ray diffraction (μXRD) pattern collection. By translating the sample with respect to the beam, we form rotating lattice single (RLS) crystal lines with a consistently linear relationship between the rotation angle and distance from nucleation site. The lines begin with a seed crystal, followed by a transition region comprising of sub–grain or very similarly oriented grains, followed by the presence of a rotating lattice single crystal of unrestricted length. Here, the results demonstrate that the primary cause of lattice rotation within RLS crystals is the densification accompanying the glass → crystal transformation, rather than stresses produced from the difference in thermal expansion coefficient of the two phases or paraelectric → ferroelectric transition during cooling to ambient temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tape casting and characterizations of MgO ceramics

Herein we report a high density MgO ceramic substrate produced by the tape casting technology. The tape casting formulation and process produced a uniform tape free of cracking. Y 2 O 3 and SiO 2 were used as the sintering aid for the pressureless sintering of the green tape. X-ray diffraction phase identification indicates that MgO is the main phase, while both Y 2 O 3 and SiO 2 sintering aids react with MgO to form MgY 4 Si 3 O 13 as the second phase. Liquid phase sintering occurs in the temperature range from 1030°C to ~1500°C, which is confirmed by the simultaneous Thermal Gravitation Analysis/ Differential Scanning Calorimeter (TGA/DSC) and the percent linear shrinkage and densification. A 96.5% theoretical density was achieved by presureless sintering at 1650°C for 2 hours, which was further increased to a fully dense structure using hotisostatic- pressing(HIP) at 1650°C and 207 MPa in argon. Scanning electron microscopy (SEM) and energy dispersive(EDS) spectroscopic analysis on the HIP’ed sample show that MgY 4 Si 3 O 13 is located at the MgO grain boundary and the sample has a fully dense structure. The refractive indices and extinction coefficient were measured on the HIP’ed sample along with thermal properties and dielectric properties. Thermal diffusivity and heat capacity were measured to calculate the thermal conductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mass Transport in Binary TiO 2 :SiO 2 and GeO 2 :SiO 2 Direct Ink Write Glasses

The mass transport mechanisms of Ti in TiO 2 :SiO 2 and Ge in GeO 2 :SiO 2 direct ink write, additively manufactured glasses were studied. Due to the low solubility of Ti in SiO2 and high melting point of TiO 2 relative to SiO 2 , Ti transport was found to occur via solid state interdiffusion between adjoining SiO 2 and TiO 2 precursor particles. The diffusivity of titanium in SiO 2 measured over typical sintering temperatures (1000-1300 °C) using Rutherford backscattering spectrometry was D = 9.1 × 10 -7 [m2/sec] exp ($\frac{378[\frac{kJ}{mol}]}{RT}$. This provides an estimate of ~30 nm for the diffusion length under typical sintering conditions (2 hrs. at 1200 °C). Although Ti and Ge have similar diffusivities in SiO 2 glass at low concentrations, GeO 2 was found to be much more mobile during the sintering of printed GeO 2 :SiO 2 green bodies. This was evident in glasses with phase separated GeO 2 regions over length scales of ~10 μm and in experiments involving binary xerogels in which GeO 2 migrated over ~10 μm through cracked, porous SiO 2 layers. Large phase separated regions and long transport lengths in GeO 2 :SiO 2 suggest that the transport of GeO 2 occurs prior to the densification of the SiO 2 matrix via an alternative mechanism such as capillary flow. These results inform important considerations in the design of index modifying inks for the direct ink write process, namely initial precursor phase, mutual solubility with the base SiO 2 glass, and mass transport throughout the sintering process.

36 MATERIALS SCIENCE↗
DOE OSTI2022

High-entropy boride–carbide ceramics by sequential boro/carbothermal synthesis

We report a dual-phase high-entropy boride/carbide ceramic with fine grain size was synthesized by a sequential boro/carbothermal process. In the first step, a Hf-Nb-Ta-Ti-Zr-containing carbide was synthesized by carbothermal reduction of oxides followed by reaction of the carbide with B4C and ZrH2 to convert part of the carbide to boride. The resulting composition was ~29 vol% high-entropy boride with an average grain size of ~1.1 µm. Solid solution formation occurred at the densification temperature of 1900°C resulting in a relative density higher than 99%. The Vickers’ hardness was 26.5 ± 1.4 GPa. This is the first report of synthesizing dual-phase boride-carbide high-entropy ceramics from carbothermally synthesized, high-entropy carbide powders.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Structure-mechanical properties correlation in bulk LiPON glass produced by nitridation of metaphosphate melts

The glassy solid electrolyte Lithium phosphorous oxynitride (LiPON) has been widely researched in thin film solid state battery format due to its outstanding stability when cycled against lithium. In addition, recent reports show thin film LiPON having interesting mechanical behaviors, especially its ability to resist micro-scale cracking via densification and shear flow. Here, in the present study, we have produced bulk LiPON glasses with varying nitrogen contents by ammonolysis of LiPO 3 melts. The resulting compositions were determined to be LiPO 3-3z/2 N z , where 0 ≤ z ≤ 0.75, and the z value of 0.75 is among the highest ever reported for this series of LiPON glasses. The short-range order structures of the different resulting compositions were characterized by infrared, Raman, 31 P magic angle spinning nuclear magnetic resonance, and X-ray photoelectron spectroscopies. Instrumented nano-indentation was used to measure mechanical properties. It was observed that similar to previous studies, both trigonally coordinated (N t ) and doubly bonded (N d ) N co-exist in the glasses in about the same amounts for z ≤ 0.36, the limit of N content in most previous studies. For glasses with z > 0.36, it was found that the fraction of the N t increased significantly while the fraction of N d correspondingly decreased. The incorporation of nitrogen increased both the elastic modulus and hardness of the glass by approximately a factor of 1.5 when N/P ratio reaches 0.75. At the same time, an apparent embrittlement of the glass was observed due to nitridation, which was revealed by nanoindentation with an extra sharp nanoindenter tip.

25 ENERGY STORAGE↗
DOE OSTI2025

Ta–Zr carbides: Synthesis advances via carbothermal reduction and defect evolution observed through transmission electron microscopy ion irradiation

The thermodynamic stability of six distinct compositions within the Zr—Ta—C ternary system is investigated in this study, marking the first report of their synthesis through carbothermic reduction in vacuum. A prolonged annealing process at 2200°C enabled high densification and phase equilibrium. Detailed phase identification and microstructural characterization through microscopy and X-ray diffraction techniques revealed clear compositional trends and stable phase formations. Two compositions ((Ta 0.2 Zr 0.8 )C 0.6 and (Ta 0.5 Zr 0.5 )C 1 ) were selected for ion irradiation experiments using 200 keV Kr + at 600°C—representing the first-ever irradiation study on the Zr—Ta—C system. The findings indicated defect accumulation and nanoscale cavity formation without any evidence of amorphization, highlighting the system's structural stability under irradiation. Together, the synthesis and irradiation results provide a basis for further investigation of the system and suggest its relevance for applications under extreme environments.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Ion-induced effects on grain boundaries and a-Si:H tissue quality in microcrystalline silicon films

Microcrystalline silicon films have been deposited by means of the remote expanding thermal plasma. The effect of ion bombardment on the microcrystalline silicon film properties has been investigated by applying an RF bias to the deposition substrate. The application of the RF substrate bias resulted in the formation of an additional plasma in front of the substrate holder. Neither the SiH{sub 4} depletion nor the growth flux was significantly enhanced upon substrate biasing, which suggests that (the composition of) the growth precursor flux is unaffected and that the ion-film interaction mechanisms were responsible for the observed material changes. Moderate bias conditions (i.e., dc bias voltages up to {approx}70 V) led to an improved grain boundary passivation and densification of the amorphous silicon tissue, as concluded from the analysis of the infrared Si-H{sub x} stretching modes. These improvements have been ascribed to ion-induced Si surface atom displacement, which enhances the surface diffusion length of the growth precursors. More-energetic ion bombardment (i.e., under applied dc bias voltages of {approx}60 V and higher) resulted in enhanced (di)vacancy incorporation via ion-induced Si bulk atom displacement. The film crystallinity was found not to be affected by the ion bombardment, although a reduced crystallite size was observed under ion bombardment conditions where Si bulk displacement had been sufficiently activated. The extent of the ion-film interaction mechanism has been enhanced by increasing the ion-to-Si deposition flux ratio. Under specific ion bombardment conditions, i.e., dc bias voltage in the range of 40-70 V and ion/Si arrival rate {approx}0.20, microcrystalline silicon films have been obtained which, on the basis of the Si-H{sub x} stretching modes, are qualified as solar-grade, i.e., the intergranular space is filled with a dense amorphous silicon tissue which completely passivates the crystalline grain boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Hardness, elastic modulus, and wear resistance of hafnium oxide-based films grown by atomic layer deposition

The investigation of mechanical properties of atomic layer deposition HfO{sub 2} films is important for implementing these layers in microdevices. The mechanical properties of films change as a function of composition and structure, which accordingly vary with deposition temperature and post-annealing. This work describes elastic modulus, hardness, and wear resistance of as-grown and annealed HfO{sub 2}. From nanoindentation measurements, the elastic modulus and hardness remained relatively stable in the range of 163–165 GPa and 8.3–9.7 GPa as a function of deposition temperature. The annealing of HfO{sub 2} caused significant increase in hardness up to 14.4 GPa due to film crystallization and densification. The structural change also caused increase in the elastic modulus up to 197 GPa. Wear resistance did not change as a function of deposition temperature, but improved upon annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Tailoring nanopore formation in atomic layer deposited ultrathin films [Nanopore formation in atomic layer deposited ultrathin films]

Selectivity is a critical attribute of catalysts used in manufacturing of essential and fine chemicals. An excellent way to induce selectivity in catalysts is by using ultrathin films with tailored nanoporosity. For instance, nanopores can be created in atomic layer deposition (ALD) ultrathin over-coatings on supported metal nanoparticles by subjecting the coatings to high temperature annealing. These nanopores expose the active surface of the underlying metal nanoparticles. The dimensions of these nanopores can be tuned to impart shape selectivity: only reactants or products with a specific size or shape can fit inside the pore. In this work, the authors explore the underlying mechanism driving nanopore formation in ALD films. Ultrathin films of ALD TiO 2 (similar to 2.5 nm thick) and ALD Al 2 O 3 (similar to 4.9 nm thick) were deposited on nonporous gamma-Al 2 O 3 nanoparticles. The pore formation and evolution were monitored in situ during thermal annealing using small-angle x-ray scattering (SAXS), and the crystallinity was monitored by in situ x-ray diffraction. A correlation between the nanopore formation and amorphous to crystalline phase transitions in the ALD layers was observed. The authors hypothesize that the pores form through the relaxation of stress induced by densification of the ALD films during the phase transitions. In conclusion, the authors developed a mathematical model to evaluate this hypothesis and found remarkable agreement between the model and the SAXS measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2010

An Assessment of Molecular Dynamic Force Fields for Silica for Use in Simulating Laser Damage Mitigation

We compare force fields (FF's) that have been used in molecular dynamic (MD) simulations of silica in order to assess their applicability for use in simulating IR-laser damage mitigation. Although pairwise FF?s obtained by fitting quantum mechanical calculations such as the BKS and CHIK potentials have been shown to reproduce many of the properties of silica including the stability of silica polymorphs and the densification of the liquid, we show that melting temperatures and fictive temperatures are much too high. Softer empirical force fields give liquid and glass properties at experimental temperatures but may not predict all properties important to laser mitigation experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Ultrastrong colloidal crystal metamaterials engineered with DNA

Lattice-based constructs, often made by additive manufacturing, are attractive for many applications. Typically, such constructs are made from microscale or larger elements; however, smaller nanoscale components can lead to more unusual properties, including greater strength, lighter weight, and unprecedented resiliencies. Here, solid and hollow nanoparticles (nanoframes and nanocages; frame size: ~15 nanometers) were assembled into colloidal crystals using DNA, and their mechanical strengths were studied. Nanosolid, nanocage, and nanoframe lattices with identical crystal symmetries exhibit markedly different specific stiffnesses and strengths. Unexpectedly, the nanoframe lattice is approximately six times stronger than the nanosolid lattice. Nanomechanical experiments, electron microscopy, and finite element analysis show that this property results from the buckling, densification, and size-dependent strain hardening of nanoframe lattices. Last, these unusual open architectures show that lattices with structural elements as small as 15 nanometers can retain a high degree of strength, and as such, they represent target components for making and exploring a variety of miniaturized devices.

42 ENGINEERING↗
DOE OSTI2025

Imaging quantum melting in a disordered 2D Wigner solid

Two-dimensional strongly interacting electrons crystalize into a solid phase known as the Wigner crystal at low densities and form a Fermi liquid at high densities. At intermediate densities, the two-dimensional solid evolves into a strongly correlated liquid phase around a critical density. We observed this quantum melting of a disordered Wigner solid in bilayer molybdenum diselenide (MoSe2) using a noninvasive scanning tunneling microscopy imaging technique. At low densities, the Wigner solid forms nanocrystalline domains pinned by local disorder. It exhibits a quantum densification behavior with increased densities in the solid phase. Above a threshold density, the Wigner solid melts locally and enters a mixed phase in which solid and liquid regions coexist. The liquid regions expand and form a percolation network at even higher densities.

Xiang, Ziyu↗
DOE OSTI2015

Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} laser ceramics: Influence of the size of yttrium oxide particles on sintering

The influence of the size of Y{sub 2}O{sub 3} powder particles on the structure formation and densification of Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} phase. Bulk swelling of pressed samples during sintering of 2.94Y{sub 2}O{sub 3}-0.06Nd{sub 2}O{sub 3}-5Al{sub 2}O{sub 3} powders with the size ratio of the initial particles R(Al{sub 2}O{sub 3}/Y{sub 2}O{sub 3}) ∼ 5 is observed. The application of different-sized powders (R ∼ 2.5) provides quantitative ratios between phases in the 3Y{sub 2}O{sub 3}-5Al{sub 2}O{sub 3} system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} have been obtained by the solid-phase sintering of oxide powders (R ∼ 2.5). The slope efficiency for 1 at % Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} laser ceramics is found to be 33%.

36 MATERIALS SCIENCE↗
DOE OSTI2016

High-precision measurements of the compressibility of chalcogenide glasses at a hydrostatic pressure up to 9 GPa

The volumes of glassy germanium chalcogenides GeSe{sub 2}, GeS{sub 2}, Ge{sub 17}Se{sub 83}, and Ge{sub 8}Se{sub 92} are precisely measured at a hydrostatic pressure up to 8.5 GPa. The stoichiometric GeSe{sub 2} and GeS{sub 2} glasses exhibit elastic behavior in the pressure range up to 3 GPa, and their bulk modulus decreases at pressures higher than 2–2.5 GPa. At higher pressures, inelastic relaxation processes begin and their intensity is proportional to the logarithm of time. The relaxation rate for the GeSe{sub 2} glasses has a pronounced maximum at 3.5–4.5 GPa, which indicates the existence of several parallel structural transformation mechanisms. The nonstoichiometric glasses exhibit a diffuse transformation and inelastic behavior at pressures above 1–2 GPa. The maximum relaxation rate in these glasses is significantly lower than that in the stoichiometric GeSe{sub 2} glasses. All glasses are characterized by the “loss of memory” of history: after relaxation at a fixed pressure, the further increase in the pressure returns the volume to the compression curve obtained without a stop for relaxation. After pressure release, the residual densification in the stoichiometric glasses is about 7% and that in the Ge{sub 17}Se{sub 83} glasses is 1.5%. The volume of the Ge{sub 8}Se{sub 92} glass returns to its initial value within the limits of experimental error. As the pressure decreases, the effective bulk moduli of the Ge{sub 17}Se{sub 83} and Ge{sub 8}Se{sub 92} glasses coincide with the moduli after isobaric relaxation at the stage of increasing pressure, and the bulk modulus of the stoichiometric GeSe{sub 2} glass upon decreasing pressure noticeably exceeds the bulk modulus after isobaric relaxation at the stage of increasing pressure. Along with the reported data, our results can be used to draw conclusions regarding the diffuse transformations in glassy germanium chalcogenides during compression.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

High-precision measurements of the compressibility and the electrical resistivity of bulk g-As{sub 2}Te{sub 3} glasses at a hydrostatic pressure up to 8.5 GPa

High-precision studies of the volume and the electrical resistivity of g-As{sub 2}Te{sub 3} glasses at a high hydrostatic pressure up to 8.5 GPa at room temperature are performed. The glasses exhibit elastic behavior in compression only at a pressure up to 1 GPa, and a diffuse structural transformation and inelastic density relaxation (logarithmic in time) begin at higher pressures. When the pressure increases further, the relaxation rate passes through a sharp maximum at 2.5 GPa, which is accompanied by softening the relaxing bulk modulus, and then decreases, being noticeable up to the maximum pressure. When pressure is relieved, an unusual inflection point is observed in the baric dependence of the bulk modulus near 4 GPa. The polyamorphic transformation is only partly reversible and the residual densification after pressure release is 2%. In compression, the electrical resistivity of the g-As{sub 2}Te{sub 3} glasses decreases exponentially with increasing pressure (at a pressure up to 2 GPa); then, it decreases faster by almost three orders of magnitude in the pressure range 2–3.5 GPa. At a pressure of 5 GPa, the electrical resistivity reaches 10{sup –3} Ω cm, which is characteristic of a metallic state; this resistivity continues to decrease with increasing pressure and reaches 1.7 × 10{sup –4} Ω cm at 8.1 GPa. The reverse metal–semiconductor transition occurs at a pressure of 3 GPa when pressure is relieved. When the pressure is decreased to atmospheric pressure, the electrical resistivity of the glasses is below the initial pressure by two–three orders of magnitude. Under normal conditions, both the volume and the electrical resistivity relax to quasi-equilibrium values in several months. Comparative structural and Raman spectroscopy investigations demonstrate that the glasses subjected to high pressure have the maximum chemical order. The glasses with a higher order have a lower electrical resistivity. The polyamorphism in the As{sub 2}Te{sub 3} glasses is caused by both structural changes and chemical ordering. The g-As{sub 2}Te{sub 3} compound is the first example of glasses, where the reversible metallization under pressure has been studied under hydrostatic conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of the Thermal Conditions of Fabrication and Treatment on the Optical Properties of In{sub 2}O{sub 3} Films

In{sub 2}O{sub 3} films on Al{sub 2}O{sub 3} (012) substrates are fabricated by dc magnetron sputtering at various temperatures (20–600°C). The effect of annealing and the substrate temperature on the film properties are studied by the ellipsometric method and the optical transmission method. Refractive-index profiles are constructed and band gaps for direct and indirect transitions are found. It is established that annealing leads to densification of the film material and unifies the refractive index. Annealing also decreases and unifies the energies of band-to-band transitions, which can be explained by lowering the influence of barriers in annealed films. However, the band gap for direct transitions varies greater than for indirect transitions. This fact can be associated with the mechanism of indirect transitions, notably, the participation of phonons facilitates interband transitions even if they are hindered by extra barriers caused by grain boundaries. The latter can be indirect evidence of the actuality of indirect transitions in indium oxide.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Structural Reliability of Cathode Contact Materials in Planar SOFCs

Despite significant developments in material and stack design technologies to enhance performance, the long-term mechanical reliability of solid oxide fuel cells remained an issue. The contact between electrodes and interconnects (especially the cathode side) was identified as one of the weakest links in present generation planar solid oxide fuel cells. Computational modeling was used to gain valuable insights on the cathode contact sintering mechanics and bond reliability. A continuum viscous sintering model was incorporated into a commercial finite element analysis code to simulate contact material densification and evaluate the bond and stack mechanical reliability due to developed stresses from the contact layer sintering. The parameters required for the cathode contact material constitutive model were extracted from experiments conducted for the contact material development at PNNL. The effects of contact layer thickness and sintering conditions like temperature and pressure on the stack stresses and reliability were investigated.

SOFC, FEA, Reliability↗
DOE OSTI2019

Secondary Pore Network Design Optimization Analytical Diffusion Model for Lithium Ion Battery

Fast ion transport along the electrode thickness is required for Lithium ion battery (LIB) to sustain continuous high-rate discharge or charge currents, which is a desired feature for the fast charging of electric vehicle batteries. Advance in LIB electrode manufacturing allows to control, to a certain extent, the electrode microstructure architecture in order to improve the macroscopic performances of these devices. For instance, several groups have experimentally tested architectures tailored specifically to increase the through plane ionic diffusion in regards for fast charge application by adding channels or groove-like large pores oriented along the electrode thickness. These voids do not replace the existing pores of the electrode microstructure but consist in a second, coarser, pore network, called the secondary pore network (SPN). The model quantifies the impact of SPN on ionic diffusion with a composite electrode through a simple analytical approach, considering various pore channel geometries and comparing to standard electrodes with identical gravimetric and identical volumetric specific theoretical capacity. The goal is to find optimal SPN design parameters according to three optimization objectives aiming to balance the improved overall through-plane, thanks to the coarse aligned channels, and the degraded in-plane diffusion, due to the porous matrix densification required to maintain gravimetric and volumetric specific theoretical capacity. The analytical model must be considered as a pre-screening tool to quickly investigate large design space, that can be refined later with more complex electrochemical CPU-expensive numerical models.

Usseglio Viretta, Francois↗