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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
DOE OSTI2024

Epitaxial (Al x Ga 1-x-y In y ) 2 O 3 Alloys Lattice Matched to Monoclinic Ga 2 O 3 Substrates

We have epitaxially stabilized a series of monoclinic (Al x Ga 1-x-y In y ) 2 O 3 alloys by careful choice of molecular beam epitaxy growth conditions, which balance alloy growth with suboxide desorption. The films are pseudomorphic to (010) β-Ga 2 O 3 substrates at thicknesses up to 150 nm with compositions ranging from (Al 0.01 Ga 0.83 In 0.16 ) 2 O 3 to (Al 0.24 Ga 0.75 In 0.03 ) 2 O 3 . The absorption edge shifts from approximately 4.62-5.14 eV with coincidently increasing Al and decreasing In mole fractions. J-V measurements reveal an increase in resistivity over four orders of magnitude with a maximum value of 4.2 x 10 5 Ω-cm for (Al 0.17 Ga 0.76 In 0.07 ) 2 O 3 , which has nearly identical lattice parameters (both in-plane and out-of-plane) to the underlying β-Ga 2 O 3 . Scanning transmission electron microscopy of this sample reveals a mostly uniform and single crystalline film, though we identify areas of non-uniform In incorporation and some γ-phase inclusions. This work demonstrates the feasibility of thick layers lattice-matched to β-Ga 2 O 3 with increased bandgap compared to phase-separation limited (Al,Ga) 2 O 3 . These alloys can enable higher bandgap epitaxial dielectrics and high sheet charge density transistors by increasing the conduction band offset with respect to β-Ga 2 O 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Nonstoichiometry and Defects in Hydrothermally Synthesized ε-LiVOPO 4

ε-LiVOPO 4 has been synthesized through the hydrothermal method by adjusting the pH of the hydrothermal solution and the reaction temperature. This phase is formed between 180 and 220 °C, as diamond-like crystals around 10–15 μm in size. X-ray diffraction (XRD) analysis shows that hydrothermal ε-LiVOPO 4 lattice parameters a and b linearly decrease, while c linearly increases when the synthesis temperature increases. Thermogravimetric analysis with mass spectroscopy reveals 1.5 to 0.5% water loss at about 350 °C for ε-LiVOPO 4 synthesized at 180 and 220 °C, suggesting water or protons incorporation into the structure. Magnetic studies reveal ferrimagnetism in hydrothermal ε-LiVOPO 4 below 10 K, as opposed to antiferromagnetic ordering below 14 K found in samples synthesized at high temperature. In-situ XRD upon heating of the hydrothermal ε-LiVOPO 4 synthesized at 180, 200, and 220 °C reveals that the temperature dependences of their lattice parameters merge at about 500 °C; furthermore, at the same temperature the structure reversibly changes from triclinic to monoclinic. The lattice parameters and the magnetic properties of the hydrothermal samples heated to 750 °C are similar to those of solid-state synthesized ε-LiVOPO 4 . Based on structure and composition analysis, we suggest that hydrothermal samples can be described as an ε-Li 1+ x H y V 1– z OPO 4 ( x , y , z < 0.1) solid solution. The electrochemical characterization of hydrothermal ε-LiVOPO 4 reveals the first cycle capacity of about 300 mAh/g, which holds for about five cycles, gradually decreasing thereafter. The low-voltage region does not reveal voltage plateaus corresponding to Li 1.5 VOPO 4 and Li 1.75 VOPO 4 phases found in the solid-state material, further suggesting structural disorder in the low-temperature samples evidenced from the lattice parameters and the magnetic properties.

25 ENERGY STORAGE↗
DOE OSTI2019

Appearance of Griffiths-Like Phase in a New Pyrochlore Compound La{sub 2}Mn{sub 2}O{sub 7−δ}

The La{sub 2}Mn{sub 2}O{sub 7 − δ} compound was prepared using ceramic method. The X-ray diffraction study revealed that this compound crystallized in pyrochlore oxide–type monoclinic structure with the P2/M space group. Concerning the magnetization measurements, they showed a paramagnetic (PM) behavior at high temperature and a ferromagnetic (FM) transition near 167 K. As for the magnetic measurements, they demonstrated the possible existence of a Griffiths-like phase, which was observed for the first time, to our knowledge, in a pyrochlore oxide-type A{sub 2}B{sub 2}O{sub 7}. This originality can be due to the competition between the AFM and FM interactions of the Mn ions, induced by oxygen deficiency. The critical isotherm analyses indicated that the 3D-Heisenberg was the most acceptable model in the case of our compound.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Optical and photoluminensce properties of Eu{sup 2+}-activated strontium magnesium silicate phosphors using different rare earth co-activators

Nanostructured powders of Sr{sub 1.96}MgSi{sub 2}O{sub 7}:Eu{sub 0.01}{sup 2+}, R{sub 0.01}{sup 3+} (R{sup 3+ }= Er{sup 3+}, Tm{sup 3+} and Tb{sup 3+}) have been fabricated via urea combustion technique. XRD results implied that tetragonal Sr{sub 2}MgSi{sub 2}O{sub 7} was the major phase whereas monoclinic Sr{sub 2}SiO{sub 4} and SrSiO{sub 3} were the minor phases. Meanwhile, field emission SEM textures showed the hollow spherical network-like shape structures filled with fused interconnections for the Sr{sub 1.96}MgSi{sub 2}O{sub 7}:Eu{sub 0.01}{sup 2+} sample. It has been recognized that the replacement of Sr{sup 2+} with co-dopant R{sup 3+} ions e.g. Er{sup 3+}, Tm{sup 3+} and Tb{sup 3+} considerably help obtaining homogeneous structure as well. The values of band gap energy and calculated refractive index were ultimately dependant on the ionic radius of R{sup 3+} co-doping ion. It has been suggested that the divalent activator ion (Eu{sup 2+}) was responsible for the number of PL emission spectra, while the trivalent co-activator ions (R{sup 3+}) were the key reasons for variations in the broadening and intensity of PL emission spectra.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Characterization of CuO/n–Si pn junction synthesized by successive ionic layer adsorption and reaction method

Transparent conducting Copper oxide CuO thin films were successfully synthesized on glass and n-type Silicon substrates by successive ionic layer adsorption and reaction method. The crystal structure, surface texture, optical and electrical properties were studied. The results revealed that the deposited CuO thin films at different cycles number (5, 10, 15), have polycrystalline structure nature with monoclinic phase, and the crystallite size increases with the increase of cycles number. The average roughness and the root mean square values increase with increasing cycles number. The optical energy band gap and Urbach energy was decrement from 2.33 eV and 1.2 eV for 5 cycles to 2.1 eV and 0.82 eV for 15 cycles. The electrical properties of Ni/CuO/n–Si pn junction were studied using current–voltage (I–V) measurements. The barrier heights (Φ{sub B}) of Ni/CuO/n–Si thin films were calculated and its values are (0.716, 0.736, 0.723) eV, for 5, 10 and 15 cycles respectively with an applied bias voltage of 3 V.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Ag-doped HfO{sub 2} thin films via sol–gel dip coating method

In this study, undoped and Ag-doped HfO{sub 2} thin films were deposited on glass substrates by means of sol–gel dip coating method. These films were then thermally annealed at 500 °C for 1 h. The structural and optical properties of undoped and Ag-doped HfO{sub 2} thin films were characterized by X-ray diffraction, UV–Vis spectrometry and scanning electron microscope. The results of this analysis were compared and interpreted with the results obtained in literature by various methods of coating with HfO{sub 2}. The X-ray diffraction peaks of the films paired with monoclinic HfO{sub 2} crystalline peaks. The refractive indices of the films decreased with doping Ag, at 500 nm wavelengths. The optical band gap values of Ag-doped HfO{sub 2} thin films increased with doping Ag. The porous structures were observed on the surface films, especially with 5% Ag doping.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Comparative In Vitro Evaluation Between Zirconia and Veneer Ceramic Materials Using Different Techniques

Zirconia surface treatment using different techniques could be employed to overcome the delamination issue reported between veneering ceramic materials and the corresponding zirconia core. The study subjected yttria partially stabilized zirconia core material to grinding and sandblasting as a first surface treatment. An airbrush gun spraying technique was used to coat a uniform thin layer of veneering ceramic (IPS e.max Ceram and Noritake Cerabien ZR) on the core materials followed by performing laser scanning as a second surface treatment. The specimens were investigated for surface topography, interface analysis, elemental compositions, phase transformation, and fracture mode patterns using profilometer, SEM, EDS, XRD, and stereomicroscope. The impact of laser scanning on the shear bond strength before and after storage of specimens in artificial saliva was also studied. Transformable tetragonal phase to monoclinic was predominant in sandblasted specimens followed by laser scanning with observation of micro-cracks at interface. The grinding followed by laser scanning yielded satisfactory outcomes in terms of the presence of coating property. The phase transformation was not detected through the latter technique. The technique greatly enhanced the roughness property and bond strength values which might be considered as a reliable application to improve the longevity of fixed dental crowns in load bearing areas.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Assessment of mechanical, thermal properties and crystal shapes of monoclinic tricalcium silicate from atomistic simulations

The two most common polymorphs in industrial alite, M1 and M3, were characterized at the molecular scale. Different methods were employed and discussed to assess mechanical properties and specific heat of both polymorphs. The calculated homogenized elastic moduli and specific heat were found in good agreement with experimental measurements. A comparative analysis of spacial Youngs modulus reveal isotropic and anisotropic spacial distribution for M{sub 1} and M{sub 3} respectively. A more isotropic compressive strength is also reported for M{sub 1} when compared to M{sub 3} polymorph. Cleavage energies computation allowed to proposed equilibrium shapes for both polymorph, with significant differences. While the lowest cleavage energies were found along (100) and (001) for both polymorphs, the constructed M1 crystal possesses 3 independent facets, against seven for the M3 polymorph.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Detailed in situ ATR-FTIR spectroscopy study of the early stages of C-S-H formation during hydration of monoclinic C3S

The early stages of tricalcium silicate hydration has been studied by in situ ATR-FTIR spectroscopy. A method for data reduction based on background correction and subtraction of spectra of pure components is presented, which makes it possible to describe the kinetic evolution of the calcium silicate hydrate phase upon hydration with great detail. The results obtained are in full agreement with recently reported, detailed solid-state NMR spectroscopy measurements. As ATR-FTIR spectroscopy does not require any isotope enrichment in order to increase the signal intensities and is a widely available technique, we suggest that our study opens up an avenue towards detailed in situ characterization of hydrating cementitious systems and hydrating systems in general.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Superconductivity in MgTa 2 S 5

Superconductivity in the new compound, MgTa 2 S 5 , is reported. Its crystal structure was indexed to space group $C$2/$m$, which is monoclinic with lattice parameters $a$ = 5.784(5) $\mathring{A}$, $b$ = 12.680(3) $\mathring{A}$, and $c$ = 6.106(5) $\mathring{A}$, with $β$ = 112.64°. Electrical resistivity reveals metallic behavior with $ρ$(296 K) = 5.2 mΩ cm and bulk superconductivity below $T$ $c$ = 1 K. Measurements of the specific heat C reveal the electronic specific heat coefficient $γ$ = 11.1(5) mJ/mol K 2 , a jump in $C$ at $T$ $c$ illustrating bulk superconductivity, and an energy gap associated with the superconducting state of $E$ $g$ = 0.25(3) meV. MgTa 2 S 5 can be classified as a BCS superconductor. In conclusion, an unidentified minority phase present in the sample (~ 4%) exhibits a superconducting phase transition near 2.6 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

PDRG1 predicts a poor prognosis and facilitates the proliferation and metastasis of colorectal cancer

Highlights: • PDRG1 is overexpressed in colorectal cancer tissues and is associated with poor prognosis of colorectal cancer patients. • PDRG1 regulates the proliferation, apoptosis, cell cycle progression and metastasis of colorectal cancer cells. • PDRG1 promotes the proliferation, migration and invasion of colorectal cancer via p21-mediated cell cycle progression. The incidence and mortality of colorectal cancer (CRC) is increasing yearly and CRC patients are becoming younger in global. Evidences have revealed the carcinogenic effect of p53 and DNA damage-regulated gene 1 (PDRG1) in several types of tumors. However, its biological function is yet to be investigated in CRC. This study aimed to unveil the prooncogenic role of PDRG1 in CRC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Techniques for Polytypic Transformations in Silicon Carbide

Abstract—: Two main polytype transformations in silicon carbide, namely, 2H → 6H and 3C → 6H, have been studied by ab initio methods. It has been shown that the intermediate phases with trigonal symmetry P3m1 and monoclinic symmetry Cm make it much easier to move the close-packed layers in such transitions by breaking them up into separate stages. It has been found that these two polytype transformations proceed in completely different ways. The links being relocated noticeably tilted compared to their initial position at the transition 2H → 6H, which allows the compression of the SiC links in the plane (11 2-bar 0). The transition 3C → 6H is carried out through the formation of Si–Si and C–C auxiliary links, living for a short time and helping densely packed layers to swap places. As a result, the activation barrier of the transformation 2H → 6H (1.7 eV/atom) is significantly less than the activation barrier of the transformation 3C → 6H (3.6 eV/atom), which means that the second transition should occur at the temperatures by 750–800°C higher than the first one. The energy profiles of this polytypic transformations, as well as the geometry of all intermediate and transition phases have been calculated. It has been shown that all the transition states have monoclinic symmetry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Heat Effect Due to Monoclinic-to-Orthorhombic Phase Transition in Ultrahigh Molecular Weight Polyethylene

We analyze heat effects associated with the solid-state phase transition in ultrahigh molecular weight polyethylene from the unstable monoclinic phase into thermodynamically stable orthorhombic phase. The model proposed here for the structure of supramolecular formations of monoclinic phase does not contradict to earlier X-ray diffraction data for this polymer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Spectral and Structural Characteristics of (Lu{sub 1 –} {sub x}Eu{sub x}){sub 2}(WO{sub 4}){sub 3} Tungstates

The structure, luminescence, and IR absorption spectra of (Lu{sub 1 –} {sub x}Eu{sub x}){sub 2}(WO{sub 4}){sub 3} solid solutions are studied in a wide range of europium concentrations (0 ≤ x ≤ 1). As the europium concentration increases, two types of crystalline phases sequentially alternate. An orthorhombic phase (space group Pbcn) of tungstate solid solutions is observed at 0 ≤ x < 0.5. In the range 0.5 ≤ x ≤ 0.8, along with the orthorhombic phase, a monoclinic phase (space group C2/c) appears; at x > 0.8, the solid solution has a monoclinic structure. The correspondence between the structure and spectral characteristics of these compounds is found. A change in the structure state leads to not only changes in luminescence spectra, but also in tungstate luminescence excitation spectra. In connection with the hydrophilicity of (Lu{sub 1 –} {sub x}Eu{sub x}){sub 2}(WO{sub 4}){sub 3} solid solutions, the water adsorption isotherm for tungstate samples and its effect on their spectral and structural characteristics is studied. It is found that the luminescence maximum under resonant excitation of Eu{sup 3+} ions is observed in samples with monoclinic structure C2/c at x ~ 0.9.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Strain Localization during Diametral Compression of ZrO{sub 2}(Y{sub 2}O{sub 3}) Ceramics

Deformation behavior of ZrO{sub 2}−Y{sub 2}O{sub 3} ceramics under conditions of diametral compression has been studied by method of digital image correlation. Spatiotemporal patterns of strain localization along the axis of a deformed sample (ε{sub xx}(x)) and across this axis (ε{sub yy}(y)) were obtained. It is established that the ε{sub xx} and ε{sub yy} deformations accumulated during the diametral compression test are inhomogeneously distributed over the sample. This is manifested by variation of the microstructure characteristics such as the size of the coherently diffracting domains of a tetragonal phase and microstresses and leads to the tetragonal–monoclinic phase transformation. This pattern of strain localization is correlated with the observed inhomogeneity of microstresses arising in the material volume.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evidence for a short-range chemical order of Ge atoms and its critical role in inducing a giant magnetocaloric effect in Gd 5 Si 1.5 Ge 2.5

Crystal structure and magnetic properties of Gd 5 Si 1.5 Ge 2.5 and Gd 4.9 Zr 0·1 Si 1.5 Ge 2.5 were investigated using high-energy X-ray diffraction and magnetic measurements. Results showed that a Zr substitution for 2% Gd reduces unit cell volumes of a room-temperature monoclinic and a low-temperature orthorhombic lattice and a difference between them at a magnetostructural transition. At a microscopic level, the Zr substitution increases length of disconnected interlayer T–T bonds of the monoclinic lattice at the expense of length of connected interlayer T–T bonds (T = Si, Ge). These opposing changes of the interlayer T–T bonds provided evidence for existence of a short-range chemical order of Ge atoms in lattices of Gd 5 Si 1.5 Ge 2.5 and its weakening by the Zr substitution. Magnetic measurements revealed that the Zr substitution brings about a change of the magnetic structure and a reduction of a giant magnetocaloric effect of Gd 5 Si 1.5 Ge 2.5 . Based on such structural and magnetic changes due to the Zr substitution, we propose a relation between the short-range chemical order and the total entropy change at the magnetostructural transition. Finally, using this relation, a giant magnetocaloric effect and an annealing effect observed over a wide range of Gd 5 (Si,Ge) 4 composition can be explained quantitatively.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In-situ observation of single-phase compositionally-complex oxide formation during high-pressure and high-temperature synthesis

Compositionally-complex oxides (CCOs) with equal or non-equal atomic ratios of multi-principal cations are single-phase solid solutions and possess unique structural characteristics and correlated possibilities for tailorable and exceptional functionalities. However, breakdown of single-phase structure and phase separation impair widespread adoption of CCOs under in-service environments. Here, in-situ phase transformation during high-pressure and high-temperature synthesis of an exemplary CCO (CeZrHf) 0.852 (YbY) 0.148 O 2-δ is for the first time clarified by using synchrotron X-ray energy dispersive diffraction. During synthesizing at ~4.5 GPa inside a large-volume press, ZrO 2 and HfO 2 gradually initiate lattice diffusion as monoclinic (022) and (220) peaks collapse and merge completely at 973 K; CeO 2 starts diffusing as the dramatic intensity change of cubic (220) peak above 1073 K, causing a metastable phase formation; single-phase solid solution ultimately forms at 1673 K. Importantly, the results revealed provide in-depth understanding of phase transformation dynamics and insights for novel design paradigm of CCOs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Lattice Dynamics and Structural Phase Transitions in Eu 2 O 3

Using the density functional theory, we study the structural and lattice dynamical properties of europium sesquioxide (Eu 2 O 3 ) in the cubic, trigonal, and monoclinic phases. The obtained lattice parameters and energies of the Raman modes show a good agreement with the available experimental data. The Eu-partial phonon density of states calculated for the cubic structure is compared with the nuclear inelastic scattering data obtained from a 20 nm thick Eu 2 O 3 film deposited on a YSZ substrate. A small shift of the experimental spectrum to higher energies results from a compressive strain induced by the substrate. On the basis of lattice and phonon properties, we analyze the mechanisms of structural transitions between different phases of Eu 2 O 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗