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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Exploring the effects of climatic variables on monthly precipitation variation using a continuous wavelet-based multiscale entropy approach

Highlights: • Developed a wavelet transform entropy approach to study precipitation. • Multiscale entropy values were the basis for precipitation regionalization. • Various entropy-based bands were introduced to segregate the CWME values for each cluster. • The relationship between changes of CWME and mean monthly precipitation were investigated. • Central rain gauges of each cluster were used for further analysis. Understanding precipitation on a regional basis is an important component of water resources planning and management. The present study outlines a methodology based on continuous wavelet transform (CWT) and multiscale entropy (CWME), combined with self-organizing map (SOM) and k-means clustering techniques, to measure and analyze the complexity of precipitation. Historical monthly precipitation data from 1960 to 2010 at 31 rain gauges across Iran were preprocessed by CWT. The multi-resolution CWT approach segregated the major features of the original precipitation series by unfolding the structure of the time series which was often ambiguous. The entropy concept was then applied to components obtained from CWT to measure dispersion, uncertainty, disorder, and diversification of subcomponents. Based on different validity indices, k-means clustering captured homogenous areas more accurately, and additional analysis was performed based on the outcome of this approach. The 31 rain gauges in this study were clustered into 6 groups, each one having a unique CWME pattern across different time scales. The results of clustering showed that hydrologic similarity (multiscale variation of precipitation) was not based on geographic contiguity. According to the pattern of entropy across the scales, each cluster was assigned an entropy signature that provided an estimation of the entropy pattern of precipitation data in each cluster. Based on the pattern of mean CWME for each cluster, a characteristic signature was assigned, which provided an estimation of the CWME of a cluster across scales of 1–2, 3–8, and 9–13 months relative to other stations. The validity of the homogeneous clusters demonstrated the usefulness of the proposed approach to regionalize precipitation. Further analysis based on wavelet coherence (WTC) was performed by selecting central rain gauges in each cluster and analyzing against temperature, wind, Multivariate ENSO index (MEI), and East Atlantic (EA) and North Atlantic Oscillation (NAO), indeces. The results revealed that all climatic features except NAO influenced precipitation in Iran during the 1960–2010 period.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry

The mantle of Mars probably differentiated through the crystallization of a magma ocean during the first tens of million years (Ma) of Solar System evolution. However, the exact timescale of large-scale silicate differentiation of the martian mantle is debated, and in particular, it remains unclear when differentiation commenced. In this paper, we applied the short-lived 53 Mn- 53 Cr system to martian meteorites in order to date the onset of large-scale mantle differentiation on Mars. The new Cr isotope data demonstrate that martian meteorites exhibit no resolvable radiogenic 53 Cr variations, and instead have a uniform +20.2±1.2 (95% conf.) parts-per-million excess in 53 Cr/ 52 Cr relative to the terrestrial mantle. The investigated groups of martian meteorites are lithologically varied and derive from diverse mantle sources that probably had variable Mn/Cr. Hence, the lack of 53 Cr variability among martian meteorites demonstrates that silicate differentiation on Mars occurred after the extinction of 53 Mn. Provided that the sources of the martian meteorites have Mn/Cr variations that are typical of the terrestrial planets, this result implies that the onset of large-scale silicate differentiation must have occurred later than 20±5 Ma after Solar System formation. The onset of silicate differentiation on Mars inferred here is significantly later than time estimates for segregation of the martian core which conservatively occurred within <10 Ma after Solar System formation. Thus, the new Mn-Cr data imply that there was a small, but resolvable, time gap of at least 5 Ma between core formation and magma ocean solidification on Mars. If the age of core segregation is taken at face value, our results imply that the martian magma ocean remained mostly molten over several Ma. This inferred longevity of the magma ocean is inconsistent with thermal models predicting rapid (<1 Ma) solidification of the martian magma ocean. Although there is currently no unique solution to this conundrum, our results can potentially be explained by a protracted history of impact bombardment that delayed differentiation in a shallow magma ocean on Mars, or perhaps more readily, by the presence of an early and dense atmosphere that acted as an insulator and prevented the magma ocean from cooling quickly.

58 GEOSCIENCES↗
DOE OSTI2019

Age and origin of IIE iron meteorites inferred from Hf-W chronology

Non-magmatic iron meteorites, including the IIE group, can provide important insights into the history of metal-silicate differentiation and collisions on planetesimals. To better constrain the evolution of metal segregation and impacts on the IIE parent body, W isotopic data are reported for 10 IIE iron meteorites and a metal vein from the Portales Valley H6 chondrite. In addition, Pt isotopic data were obtained to quantify cosmic ray-induced neutron capture effects on W isotopes. After correction for these effects, the IIE iron meteorites exhibit variable pre-exposure 182W compositions, translating into Hf-W model age clusters of ~4–5 million years (Ma), ~10 Ma, ~15 Ma, and ~27 Ma after CAI formation. These distinct 182 W clusters likely represent samples from several discrete metallic melt pools on the IIE parent asteroid. The earliest metal segregation event at ~4–5 Ma was likely facilitated by 26 Al decay as an internal heat source. By contrast, the younger Hf-W model ages may not be chronologically meaningful, and probably reflect the effects of secondary mixing and re-equilibration of metal and silicates, likely facilitated by impacts on the IIE parent body. Thus, contrary to prior work, the Hf-W systematics of IIE iron meteorites do not require a protracted history of metal-silicate separation on the IIE parent body. Instead the results of this study are fully consistent with a single partial metal-silicate differentiation event driven by endogenic heating at ~4–5 Ma, followed by one or multiple impact events causing mixing and re-equilibration of metal and silicates at a later stage. As a result, the exact timing of these impact event(s) remains poorly constrained, but they most likely occurred in the first few tens of Ma of Solar System history.

58 GEOSCIENCES↗
DOE OSTI2016

Effects of solutes on dislocation nucleation from grain boundaries

When grain sizes are reduced to the nanoscale, grain boundaries (GB) become the dominant sources of the dislocations that enable plastic deformation. Here, we present the first molecular dynamics (MD) study of the effect of substitutional solutes on the dislocation nucleation process from GBs during uniaxial tensile deformation. A simple bi-crystal geometry is utilized in which the nucleation and propagation of dislocations away from a GB is the only active mechanism of plastic deformation. Solutes with atomic radii both larger and smaller than the solvent atomic radius were considered. Although the segregation sites are different for the two cases, both produce increases in the stress required to nucleate a dislocation. MD simulations at room temperature revealed that this increase in the nucleation stress is associated with changes of the GB structure at the emission site caused by dislocation emission, leading to increases in the heats of segregation of the solute atoms, which cannot diffuse to lower-energy sites on the timescale of the nucleation event. These results contribute directly to understanding the strength of nanocrystalline materials, and suggest suitable directions for nanocrystalline alloy design leading toward structural applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

High-Sensitivity C-Reactive Protein Complements Plasma Epstein-Barr Virus Deoxyribonucleic Acid Prognostication in Nasopharyngeal Carcinoma: A Large-Scale Retrospective and Prospective Cohort Study

Purpose: To evaluate the effects of combining the assessment of circulating high-sensitivity C-reactive protein (hs-CRP) with that of Epstein-Barr virus DNA (EBV DNA) in the pretherapy prognostication of nasopharyngeal carcinoma (NPC). Patients and Methods: Three independent cohorts of NPC patients (training set of n=3113, internal validation set of n=1556, and prospective validation set of n=1668) were studied. Determinants of disease-free survival, distant metastasis–free survival, and overall survival were assessed by multivariate analysis. Hazard ratios and survival probabilities of the patient groups, segregated by clinical stage (T1-2N0-1M0, T3-4N0-1M0, T1-2N2-3M0, and T3-4N2-3M0) and EBV DNA load (low or high) alone, and also according to hs-CRP level (low or high), were compared. Results: Elevated hs-CRP and EBV DNA levels were significantly correlated with poor disease-free survival, distant metastasis–free survival, and overall survival in both the training and validation sets. Associations were similar and remained significant after excluding patients with cardiovascular disease, diabetes, and chronic hepatitis B. Patients with advanced-stage disease were segregated by high EBV DNA levels and high hs-CRP level into a poorest-risk group, and participants with either high EBV DNA but low hs-CRP level or high hs-CRP but low EBV DNA values had poorer survival compared with the bottom values for both biomarkers. These findings demonstrate a significant improvement in the prognostic ability of conventional advanced NPC staging. Conclusion: Baseline plasma EBV DNA and serum hs-CRP levels were significantly correlated with survival in NPC patients. The combined interpretation of EBV DNA with hs-CRP levels led to refinement of the risks for the patient subsets, with improved risk discrimination in patients with advanced-stage disease.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2025

Tailoring Cu-Zr gradient nanoglass structures: Influence of nanoparticle size and cooling rates on glass-glass interfaces

The study of gradient nanoglasses (GNGs) has gained attention due to their unique mechanical properties and potential applications in advanced materials. This study employs molecular dynamics simulations to synthesize a GNG using Cu-Zr metallic glass nanoparticles (NPs) sized from 3 to 15 nm. The NPs were produced by melting and quenching metallic clusters at a relatively slow quench rate of 10 9 K/s. The synthesis of GNG is elucidated along with the characterization of its heterogeneous metallic glass nanostructure. A seamless GNG structure is formed through cold compression of Cu 64 Zr 36 amorphous NPs of varying sizes. The influence of NP size on the GNG structure is investigated, utilizing deeply relaxed NPs, which exhibit a characteristic Cu segregation pattern on their surfaces. The results highlight an increase in structural heterogeneity due to heterogeneous mass transport and the development of local composition and density variations caused by Cu segregation at glass-glass interfaces (GGIs). A reduction in NP size is correlated with decreased Cu atomic displacements and local density at GGIs, suggesting that larger NPs may produce stronger GGIs. This research presents a novel methodology for synthesizing heterogeneous metallic glasses, demonstrating the capacity to control and customize nanostructure heterogeneity through the manipulation of NP sizes and cooling rates. Furthermore, these findings enhance our understanding of structural evolution during nanoglass synthesis and lay the foundation for further exploration in nanomaterial synthesis and characterization.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis and properties of titanomagnetite (Fe3-xTixO4) nanoparticles: A tunable solid-state Fe(II/III) redox system

Titanomagnetite (Fe3-xTixO4) nanoparticles were synthesized by room temperature aqueous precipitation, in which Ti(IV) replaces Fe(III) and is charge compensated by conversion of Fe(III) to Fe(II) in the unit cell. A comprehensive suite of tools was used to probe composition, structure, and magnetic properties down to site-occupancy level, emphasizing distribution and accessibility of Fe(II) as a function of x. Synthesis of nanoparticles in the range 0 ≤ x ≤ 0.6 was attempted; Ti, total Fe and Fe(II) content were verified by chemical analysis. TEM indicated homogeneous spherical 10 12 nm particles. μ-XRD and Mössbauer spectroscopy on anoxic aqueous suspensions verified the inverse spinel structure and Ti(IV) incorporation in the unit cell up to x ≤ 0.38, based on Fe(II)/Fe(III) ratio deduced from the unit cell edge and Mössbauer spectra. Nanoparticles with a higher value of x possessed a minor amorphous secondary Fe(II)/Ti(IV) phase. XANES/EXAFS indicated Ti(IV) incorporation in the octahedral sublattice (B-site) and proportional increases in Fe(II)/Fe(III) ratio. XA/XMCD indicate these increases arise from increasing B-site Fe(II), and that these charge-balancing equivalents segregate to those B-sites near particle surfaces. Dissolution studies showed that this segregation persists after release of Fe(II) into solution, in amounts systematically proportional to x and thus the Fe(II)/Fe(III) ratio. A mechanistic reaction model was developed entailing mobile B-site Fe(II) supplying a highly interactive surface phase that undergoes interfacial electron transfer with oxidants in solution, sustained by outward Fe(II) migration from particle interiors and concurrent inward migration of charge-balancing cationic vacancies in a ratio of 3:1.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2025

A scalable multidimensional fully implicit solver for Hall magnetohydrodynamics

We propose an optimally performant fully implicit algorithm for the Hall magnetohydrodynamics (HMHD) equations based on multigrid-preconditioned Jacobian-free Newton-Krylov methods. HMHD is a challenging system to solve numerically because it supports stiff fast dispersive waves. The preconditioner is formulated using an operator-split approximate block factorization (Schur complement), informed by physics insight. We use a vector-potential formulation (instead of a magnetic field one) to allow a clean segregation of the problematic $\nabla$ x $\nabla$ x operator in the electron Ohm's law subsystem. This segregation allows the formulation of an effective damped block-Jacobi smoother for multigrid. We demonstrate by analysis that our proposed block-Jacobi iteration is convergent and has the smoothing property. The resulting HMHD solver is verified linearly with wave propagation examples, and nonlinearly with the GEM challenge reconnection problem by comparison against another HMHD code. We demonstrate the excellent algorithmic and parallel performance of the algorithm up to 16384 MPI tasks in two dimensions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Comparison of continuum and cross-core theories of dynamic strain aging

Dynamic strain aging (DSA) is the process of solute atoms segregating around dislocations on the timescale of loading. Continuum theories of DSA derived from elasticity theory have been shown to severely overpredict both the timescale and strengthening of DSA. Recently, cross-core theory was developed to reconcile this gap, invoking a special single-atomic-hop diffusion mechanism across the core of an extended dislocation. In this work, we show that the classical continuum theory expression for the rate of solute segregation is in error. After correcting this error, we show that continuum theory predictions match cross-core theory when the elevated diffusivity near the dislocation core is accounted for. Finally, our findings indicate that continuum theory is still a useful tool for studying dislocation-solute interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Response of nanostructured ferritic alloys to high-dose heavy ion irradiation

A latest-generation aberration-corrected scanning/transmission electron microscope (STEM) is used to study heavy-ion-irradiated nanostructured ferritic alloys (NFAs). Results are presented for STEM X-ray mapping of NFA 14YWT irradiated with 10 MeV Pt to 16 or 160 dpa at -100°C and 750°C, as well as pre-irradiation reference material. Irradiation at -100°C results in ballistic destruction of the beneficial microstructural features present in the pre-irradiated reference material, such as Ti-Y-O nanoclusters (NCs) and grain boundary (GB) segregation. Irradiation at 750°C retains these beneficial features, but indicates some coarsening of the NCs, diffusion of Al to the NCs, and a reduction of the Cr-W GB segregation (or solute excess) content. Ion irradiation combined with the latest-generation STEM hardware allows for rapid screening of fusion candidate materials and improved understanding of irradiation-induced microstructural changes in NFAs.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2017

Bubble evolution in Kr-irradiated UO 2 during annealing

Transmission electron microscopy observation of Kr bubble evolution in polycrystalline UO 2 annealed at high temperature was conducted in order to understand the inert gas behavior in oxide nuclear fuel. The average size of intragranular bubbles increased gradually from 0.8 nm in as-irradiated sample at room temperature to 2.6 nm at 1600 °C and the bubble size distribution changed from a uniform distribution to a bimodal distribution above 1300 °C. The size of intergranular bubbles increased more rapidly than intragranular ones and bubble denude zones near grain boundaries formed in all the annealed samples. It was found that high-angle grain boundaries held bigger bubbles than low angle grain boundaries. Complementary atomistic modeling was conducted to interpret the effects of grain boundary character on the Kr segregation. Lastly, the area density of strong segregation sites in the high-angle grain boundaries is much higher than that in the low angle grain boundaries.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

The role of ternary alloying elements in eutectoid transformation of U10Mo alloy part I. Microstructure evolution during arc melting and subsequent homogenization annealing in U9.8Mo0.2 X alloy ( X = Cr, Ni, Co)

This paper describes the microstructural evolution in an alloy of uranium with 10 wt.% molybdenum (U10Mo), with minor addition of a third alloying element, namely, Cr, Ni, or Co, at 0.2 wt.%. The microstructures of arc-melted buttons in the as-cast condition show significant Mo segregation. The segregation behavior of Cr, Ni, and Co was investigated through detailed scanning electron microscope imaging. A homogenization heat treatment at 900°C for 48 h results in uniform Mo distribution and associated grain growth in all of the four alloys that were fabricated. Further, formation of multiple phases was noted in U-9.8 wt.% Mo-0.2 wt.% Ni and U-9.8 wt.% Mo-0.2 wt.% Co alloys after the homogenization annealing step. The greatest grain-boundary-initiated eutectoid transformation as measured by % volume fraction was observed when the homogenized U-9.8 wt.% Mo-0.2 wt.% Ni alloy was aged at 500°C for 20 h. The least eutectoid transformation occurred in U10Mo.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Microstructure and fission products in the UCO kernel of an AGR-1 TRISO fuel particle after post irradiation safety testing

Tristructural isotropic (TRISO) coated particle fuel as a key fuel concept for the High Temperature Gas-cooled Reactors (HTGRs) and a candidate accident tolerant fuel (ATF) has been currently investigated under the US-DOE Advanced Gas Reactor (AGR) fuel development and qualification program. Over the past decades, extensive studies have been conducted to evaluate the fission product release, diffusion on Ag, Pd and Cd in the SiC layer and the TRISO coating system, and post-safety-test performance. However, to date, there are limited reported results on the fuel kernels’ response to irradiation with or without post irradiation high temperature annealing. To incrementally fulfill this knowledge gap extensive studies using transmission electron microscopes (TEM) and atom probe tomography (APT) were conducted on a TRISO fuel particle kernel with a 19.74% 235U enrichment, irradiated to 18.63% FIMA and subsequently subjected to post-safety testing at 1600ºC for 300 hours.. Microstructure characterizations, elemental analysis, and phase identification were conducted using conventional TEM and scanning TEM (STEM) imaging, energy-dispersive X-ray spectroscopy (EDS), selected-area electron diffraction (SAED) and atom probe tomography (APT). The following findings were made: (1) significant reconstructions and phase evolutions occurred in the irradiated and post-safety annealed fuel kernel, and its microstructure consists of two primary phases, namely a “high-Z (atomic mass)” UC phase and a “low-Z” UO phase, (2) no fission gas bubbles are identified within the fuel kernel, that can be attributed to the high temperature post safety annealing, (3) fission products Zr, Nb, Mo, Ru, Tc and Rh were found to preferentially segregate into UC phase or to form metallic precipitates, while the lanthanide fission products tend to stay in the solution of UO phase, (4) Pd was detected in the rod-shaped precipitates, (5) APT data reveals segregation of Te, Pd, and Ag at the UO and UC phase boundary, and (6) Pd is detected in both the UO and UC phases but with an enrichment in the former one.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Modified microstructures in proton irradiated dual phase 308L weldment filler material

In this study, the effect of proton irradiation on the microstructure of δ ferrite—γ austenite mixed phase 308L filler material in a 508–304 dissimilar metal weldment was investigated over a depth of 0 to 10 µm. Ni–Si–Mn G-phase precipitates were observed with SEM and TEM in δ ferrite but not in γ austenite. Our density functional theory based calculations show that the G/Fe interface energy in δ-Fe is significantly lower than that in γ-Fe (0.35 versus 1.25 J/m 2 ), which provides a thermodynamics-based explanation for our experimental observations of preferential formation of G-phase in δ ferrite. STEM-EDS, TEM dark field imaging, and diffraction patterns confirmed the Ni–Si–Mn enriched precipitates were G-phase precipitates with a stoichiometry of Mn 6 Ni 16 Si 7 . Intragranular voids and Ni–Si enriched clusters were observed in irradiated γ austenite. Additionally, Ni and Si segregation was observed along the void interfaces. In both cases, Ni–Si clusters and segregation to voids, selected area diffraction patterns did not reveal the existence of a second phase. Proton irradiation induced Cr depletion and Si and Ni enrichment at γ-γ austenite grain boundaries that was characterized with STEM/EDS.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Structural features of early fuel cycle taggant incorporation for intentional nuclear forensics

To develop strategies for incorporating transition metal taggants (Fe, Cr, and Ni) into oxide fuels and to understand how these taggant candidates persist through early fuel cycle processes, synthetic procedures are modified from established production routes to yield intentionally tagged early fuel cycle intermediates including uranyl nitrate hexahydrate (UNH, UO 2 (NO 3 ) 2 ·6H 2 O), uranyl peroxide tetrahydrate (studtite, UO 2 O 2 ·4H 2 O), and uranyl peroxide dihydrate (metastudtite, UO 2 O 2 ·2H 2 O). First, Fe, Cr, and Ni nitrate solutions are introduced to an aqueous solution of UNH followed by precipitation to produce tagged UNH. Then, studtite is precipitated from UNH followed by dehydration to metastudtite. Structural influences of taggant incorporation within all synthesized phases are investigated using powder X-ray diffraction (PXRD) and Raman spectroscopy to provide insight into crystallographic modifications resulting from the addition of tags to these early fuel cycle materials and elucidate the chemical form of taggants introduced at these stages. The possibility of segregation of taggant species into discrete phases within U matrices was examined using scanning electron microscopy with energy dispersive X-ray spectroscopy. Taggant concentrations in solid-phase materials were determined using inductively coupled plasma-optical emission spectroscopy. Observations from Raman spectroscopy and PXRD indicate that introducing transition metal tags during uranyl nitrate precipitation results in potential impurity phase segregation in UNH, but transition metal incorporation is suggested by results for tagged uranyl peroxide materials. Further, results from this study will inform strategies for optimizing taggant incorporation in UO 2 .

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Defect formation and transmutation behaviors in irradiated tungsten under thermal-neutron shielded and mixed spectrum conditions

Here, this study investigates the microstructural evolution of pure tungsten irradiated under thermal-neutron shielded and mixed spectrum conditions in the High Flux Isotope Reactor (HFIR). Four samples were irradiated at temperatures from 570 °C to 1130 °C up to 0.73 dpa. Neutron spectrum significantly influenced the accumulation of transmutation products, with Re+Os content estimated at ∼0.3–0.6% under thermal-neutron shielded conditions and ∼5.2% under the mixed spectrum condition. Irradiation temperature strongly influences tungsten’s microstructure, with dislocation loops and fine voids forming at lower temperatures and only larger voids and Re/Os segregation observed at higher temperature. Under thermal-neutron shielded conditions, dislocation loops and voids were observed at 570 °C and 790 °C. At the highest irradiation temperature (1130 °C), dislocation loops were no longer observed, while larger but less dense voids remained. Re and Os segregation to void surfaces was evident at 790 °C and 1130 °C, though no precipitation was observed. In contrast, under the mixed-spectrum condition, both spherical and needle-like Re/Os-rich precipitates were observed, frequently accompanied by large voids. Dislocation loops were not observed, but loop-like contrast within the precipitates suggests they may have nucleated on pre-existing loops. Irradiation-induced hardening was assessed for the shielded samples at 570 °C and 790 °C. Dispersed barrier hardening (DBH) analysis, based on TEM-resolved defects, revealed that voids were the dominant contributors to hardening, consistent with literature results. A schematic model is proposed to describe defect and precipitate evolution in tungsten under fusion-relevant transmutation-to-dpa conditions.

Dislocation loops↗
DOE OSTI2012

Hydrothermal synthesis of new rare earth silicate fluorides: A novel class of polar materials

Polar crystals provide an interesting avenue for materials research both in the structures they form and the properties they possess. This work describes the hydrothermal synthesis and structural characterization of three novel silicate fluorides. Compound (1), LiY{sub 3}(SiO{sub 4}){sub 2}F{sub 2} crystallizes in space group C2/c, with a=17.651(4) A, b=4.8868(10) A, c=11.625(2) A and {beta}=131.13(3) Degree-Sign . BaY{sub 2}(Si{sub 2}O{sub 7})F{sub 2} (2) crystallizes in space group P-1, with a=5.1576(10) A, b=6.8389(14) A, c=11.786(2) A, {alpha}=93.02(3) Degree-Sign , {beta}=102.05(3) Degree-Sign and {gamma}=111.55(3) Degree-Sign . Finally, the structure of Ba{sub 2}Y{sub 3}(SiO{sub 4}){sub 2}F{sub 5} (3) was determined in the polar orthorhombic space group Pba2, having unit cell parameters a=8.8864(18) A, b=12.764(3) A and c=5.0843(10) A. The structures are compared based on their building blocks and long range polarities. Aligned silicate tetrahedra segregated into a single layer in (3) impart the observed polarity. - Graphical abstract: The polar structure of Ba{sub 2}Y{sub 3}(SiO{sub 4}){sub 2}F{sub 5}. Highlights: Black-Right-Pointing-Pointer Natural yttrium silicate fluoride minerals are briefly reviewed. Black-Right-Pointing-Pointer The synthesis and structures of LiY{sub 3}(SiO{sub 4}){sub 2}F{sub 2}, BaY{sub 2}(Si{sub 2}O{sub 7})F{sub 2} and Ba{sub 2}Y{sub 3}(SiO{sub 4}){sub 2}F{sub 5} are discussed. Black-Right-Pointing-Pointer Ba{sub 2}Y{sub 3}(SiO{sub 4}){sub 2}F{sub 5} crystallizes in the polar space group Pba2. Black-Right-Pointing-Pointer Polarity occurs primarily through aligned silicate tetrahedra in a segregated layer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Structural studies of TiC{sub 1−x}O{sub x} solid solution by Rietveld refinement and first-principles calculations

The lattice parameters, structural stability and electronic structure of titanium oxycarbides (TiC{sub 1−x}O{sub x}, 0≤x≤1) solid solution were investigated by Rietveld refinement and first-principles calculations. Series of TiC{sub 1−x}O{sub x} were precisely synthesized by sintering process under the vacuum. Rietveld refinement results of XRD patterns show the properties of continuous solid solution in TiC{sub 1−x}O{sub x} over the whole composition range. The lattice parameters vary from 0.4324 nm to 0.4194 nm decreasing with increasing oxygen concentration. Results of first-principles calculations reveal that the disorder C/O structure is stable than the order C/O structure. Further investigations of the vacancy in Ti{sub 1−Va}(C{sub 1−x}O{sub x}){sub 1−Va} solid solution present that the structure of vacancy segregated in TiO-part is more stable than the disorder C/O structure, which can be ascribed to the Ti–Ti bond across O-vacancy and the charge redistributed around Ti-vacancy via the analysis of the electron density difference plots and PDOS. - Graphical abstract: XRD of series of titanium oxycarbides (TiC{sub 1−x}O{sub x}, 0≤x≤1) solid solution prepared by adjusting the proportion of TiO in the starting material. Highlights: • Titanium oxycarbides were obtained by sintering TiO and TiC under carefully controlled conditions. • Rietveld refinement results show continuous solid solution with FCC structure in TiC{sub 1−x}O{sub x}. • The disorder C/O structure is stable than the order C/O structure. • Introduction of vacancy segregated in TiO-part is more stable than disorder C/O structure. • Ti–Ti bond across O-vacancy and the charge redistributed around Ti-vacancy enhance structural stability.

36 MATERIALS SCIENCE↗