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DOE OSTI2023

Magnetic structures and excitations in sawtooth olivine chalcogenides Mn 2 SiX 4 (X = S, Se)

The Mn lattice in olivine chalcogenide Mn 2 SiX 4 (X = S, Se) compounds forms a sawtooth, which is of special interest in magnetism owing to the possibility of realizing flat bands in magnon spectra, a key component in magnonics. In this work, we investigate the Mn 2 SiX 4 olivines using magnetic susceptibility, and X-ray and neutron diffraction. We have determined the average and local crystal structures of Mn 2 SiS 4 and Mn 2 SiSe 4 using synchrotron X-ray, neutron diffraction, and X-ray total scattering data followed by Rietveld and pair distribution function analyses. It is found from the pair distribution function analysis that the Mn triangle that constitutes the sawtooth is isosceles in Mn 2 SiS 4 and Mn 2 SiSe 4 . The temperature evolution of magnetic susceptibility of Mn 2 SiS 4 and Mn 2 SiSe 4 shows anomalies below 83 K and 70 K, respectively, associated with magnetic ordering. From the neutron powder diffraction measurements the magnetic space groups of Mn 2 SiS 4 and Mn 2 SiSe 4 are found to be Pnma and Pnm'a', respectively. Here, we find that the Mn spins adopt a ferromagnetic alignment on the sawtooth in both Mn 2 SiS 4 and Mn 2 SiSe 4 but along different crystallographic directions for the S and the Se compounds. From the temperature evolution of Mn magnetic moments obtained from refining neutron diffraction data, the transition temperatures are accurately determined as T N (S) = 83(2) K and T N (Se) = 70.0(5) K. Broad diffuse magnetic peaks are observed in both the compounds, and are prominently seen close to T N , suggesting the presence of a short-range magnetic order. The magnetic excitations studied using inelastic neutron scattering reveal a magnon excitation with an energy corresponding to approximately 4.5 meV in both S and Se compounds. Spin correlations are observed to persist up to 125 K much above the ordering temperature and we suggest the possibility of short-range spin correlations responsible for this.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Magnetic and magnetocaloric properties of La{sub 0.85}(Na{sub 1−x}K{sub x}){sub 0.15}MnO{sub 3} ceramics produced by reactive spark plasma sintering

La{sub 0.85}(Na{sub 1−x}K{sub x}){sub 0.15}MnO{sub 3} (0 ≤ x ≤ 1) ceramics were synthesized from the raw La(OH){sub 3}, NaOH, KOH, and MnO{sub 2} powders using Reactive Spark Plasma Sintering. All the compounds were obtained as pure, dense, and ultrafine grained pellets. The Rietveld refinement of the X-Ray powder diffraction shows that all our synthesized samples are single phase and crystallize in the distorted rhombohedral system with R-3c space group. The thermal variation of their magnetization under a magnetic applied field of 50 mT shows a paramagnetic to ferromagnetic transition at a Curie temperature very close to room temperature. The magnetic entropy change, deduced from magnetization measurements versus magnetic applied field up to 5 T at several temperatures exhibits a maximum |ΔS{sub M}|{sub max} which slightly increases with increasing K content. The relative cooling power values, inferred from the |ΔS{sub M}| vs T peak broadening, vary slightly with the potassium content, reaching, values between 316 and 289 Jkg{sup −1}, in an applied magnetic field of 5 T, when x increases from 0 to 1. Technically, these large values make the prepared materials very promising for domestic magnetic refrigeration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Structural investigation of the temperature-stable relaxor dielectric Ba 0.8 Ca 0.2 TiO 3 -Bi(Mg 0.5 Ti 0.5 )O 3

Aberration corrected scanning transmission electron microscopy (STEM) and electron diffraction have been used to disclose local structure and nano-chemistry in a Ca modified BaTiO 3 -Bi(Mg 0.5 Ti 0.5 )O 3 relax or dielectric ceramic which exhibits high and near-invariant relative permittivity over a wide temperature range. High resolution, synchrotron X-ray diffraction indicated a globally cubic structure ($Pm$$\overline{3}$$m$), but direct atomic-scale imaging by STEM revealed local tetragonal distortions. Nanopolar clusters were identified from B-site atomic displacement vectors measured relative to oxygen ion positions along < 100 > and < 110 > zone axes of integrated differential phase contrast (iDPC) STEM images, highlighting cluster sizes of 2–5 nm. Chemical analysis by STEM-energy dispersive X-ray spectroscopy and full pattern refinements of X-ray powder diffraction data each implied high levels of Bi vacancies within the matrix. The possibility that these A-site vacancies modulate the nanopolar structure and promote flattening of the permittivity-temperature response in this class of dielectric is discussed.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Structural analysis and ferroelectric properties of Fe doped BaTiO{sub 3}

The polycrystalline samples of Fe doped BaTiO{sub 3} (BTO) with compositional formula BaTi{sub 1-x}Fe{sub x}O{sub 3} (x = 0, 0.03, 0.04 and 0.05) were prepared by solid-state reaction route. The influence of the Fe content on the structural, vibrational and electric properties of BaTiO{sub 3} was investigated using X-ray powder diffraction (XRD), Raman spectroscopy and Polarization techniques. XRD analysis indicates the formation of single-phase tetragonal structure for all the prepared samples. Tetragonal cubic structure with space group P4mm of all samples is further approved by Rietveld refinement. Room temperature Raman spectra of pure BaTiO{sub 3} show four active modes of vibration whose intensity decreases with increasing Fe doping. Small shift in Raman modes and increment in the line width has been observed with the doping ions. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Incommensurate spin density wave and magnetocaloric effect in the metallic triangular lattice HoAl 2 Ge 2

Here, we report the magnetic structure and the magnetocaloric effect (MCE) of the ternary compound HoAl 2 Ge 2 with a trigonal CaAl 2 Si 2 -type crystal structure. A neutron powder diffraction experiment reveals that HoAl 2 Ge 2 exhibits an incommensurate spin density wave (SDW) with a propagation vector k=(0.23,0,0.06). The special arrangement of magnetic moments in HoAl 2 Ge 2 induces interesting physical phenomena and large magnetocaloric effects. The rise in resistivity at low temperatures indicates the effect of the SDW state in the electronic transport. The maximum magnetic-entropy change is –16.1J/kg K under a magnetic field change of 0–70 kOe for an isotropic HoAl 2 Ge 2 powder and it increases to –17.9J/kg K for a single crystal when the magnetic field (H) is applied parallel to the ab plane. A large rotating magnetic-entropy change of –5.1J/kg K for H=20 kOe in a HoAl 2 Ge 2 single crystal is obtained, which is closely associated to the magnetic anisotropy of the SDW order and its response to the external magnetic field. We discuss the large MCE in terms of the field-induced metamagnetic transition from the incommensurate SDW order to the ferromagnetic order. Our study establishes the triangular lattice R Al 2 Ge 2 (R=rare-earth elements) as a unique family of compounds to explore the existence of the incommensurate spin density waves and the correlated physical properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

A new glass-free LTCC microwave ceramic – (1 − x) Li{sub 2.08}TiO{sub 3} + xLiF

Graphical abstract: - Highlights: • Sintering temperature of Li{sub 2}TiO{sub 3} was reduced to 900 °C by doping with LiF and excessive lithium. • A new glass-free LTCC microwave ceramic – (1 − x) Li{sub 2.08}TiO{sub 3} + xLiF was obtained. • The obtained LTCC material exhibited excellent microwave dielectric properties. - Abstract: The structure and microstructure of the (1 − x) Li{sub 2.08}TiO{sub 3} + xLiF (0.11 ≤ x ≤ 0.14) ceramics were studied by X-ray powder diffraction (XRD), thermal dilatometry and scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied with a network analyzer. All samples exhibited single monoclinic phase. The sintering temperature was successfully reduced to about 900 °C/2 h for the LiF-doped Li{sub 2.08}TiO{sub 3} specimens. The dielectric permittivity slightly decreased, whereas the Q × f value changed little, with the increase in LiF dopant. The temperature coefficient of resonant of frequency (τ{sub f}) value changed from positive to negative with increasing x, and a near zero value was obtained at x = 0.13 composition. Optimized microwave dielectric properties with ε{sub r} = ∼22.8, Q × f = ∼63,000 GHz and τ{sub f} = ∼1.0 ppm/°C for x = 0.13 composition sintered at 900 °C/2 h. The XRD and back scattering SEM analysis showed that the ceramic was compatible with Ag powders after sintering at 900 °C/2 h.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Isothermal sections of the quasi-ternary systems Ag{sub 2}S(Se)–Ga{sub 2}S(Se){sub 3}–In{sub 2}S(Se){sub 3} at 820 K and the physical properties of the ternary phases Ga{sub 5.5}In{sub 4.5}S{sub 15}, Ga{sub 6}In{sub 4}Se{sub 15} and Ga{sub 5.5}In{sub 4.5}S{sub 15}:Er{sup 3+}, Ga{sub 6}In{sub 4}Se{sub 15}:Er{sup 3+}

Isothermal sections of the quasi-ternary systems Ag{sub 2}S(Se)–Ga{sub 2}S(Se){sub 3}–In{sub 2}S(Se){sub 3} at 820 K were compared. Along the 50 mol% Ag{sub 2}S(Se), both systems feature continuous solid solutions with the chalcopyrite structure. Along the 17 mol% Ag{sub 2}S(Se), the interactions at the AgIn{sub 5}S(Se){sub 8}–'AgGa{sub 5}S(Se){sub 8}' sections are different. In the Ag{sub 2}S–Ga{sub 2}S{sub 3}–In{sub 2}S{sub 3} system the existence of the layered phase AgGa{sub x}In{sub 5–x}S{sub 8}, 2.25≤x≤2.85, was confirmed (S.G. P6{sub 3}mc). The Ag{sub 2}Se–Ga{sub 2}Se{sub 3}–In{sub 2}Se{sub 3} system features the formation of solid solution (up to 53 mol% Ga{sub 2}Se{sub 3}) based on AgIn{sub 5}Se{sub 8} (S.G. P-42m). Crystal structure, atomic coordinates were determined by powder diffraction method for samples from the homogeneity region of AgIn{sub 5}Se{sub 8}. Specific conductivities of the crystals Ga{sub 6}In{sub 4}Se{sub 15} (1.33·10{sup −6} Ω{sup −1} m{sup −1}), Ga{sub 5.94}In{sub 3.96}Er{sub 0.1}Se{sub 15} (3.17·10{sup −6} Ω{sup −1} m{sup −1}), Ga{sub 5.5}In{sub 4.5}S{sub 15} (7.94·10{sup −6} Ω{sup −1} m{sup −1}), Ga{sub 5.46}In{sub 4.47}Er{sub 0.07}S{sub 15} (1·10{sup −9} Ω{sup −1} m{sup −1}) were measured at room temperature. Optical absorption and photoconductivity spectra were recorded in the range 400–760 nm. The introduction of erbium leads to an increase in the absorption coefficient and to the appearance of absorption bands at 530, 660, 810, 980, 1530 nm. - Highlights: • Nature of solid solutions in Ag{sub 2}S(Se)–Ga{sub 2}S(Se){sub 3}–In{sub 2}S(Se){sub 3} (820 K) were discussed. • Crystal structures of ternary and quaternary compounds were discussed. • Specific conductivity, optical properties of four single crystals were measured. • Photoconductivity of the Ga{sub 5.5}In{sub 4.5}S{sub 15} in the range 400–760 nm were recorded.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2010

Synthesis of flower-like Boehmite (AlOOH) via a simple solvothermal process without surfactant

Boehmite (AlOOH) with hierarchical flower-like structures was synthesized by the solvothermal reaction of AlCl{sub 3}.6H{sub 2}O in the presence of ethanol and toluene at 200 {sup o}C for 24 h. The product was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that boehmite with flower-like nanostructures, which aggregated together by the weak hydrogen bonds, was formed through dissolution-deposition process of boehmite microcrystals and the toluene has a great effect on the morphology of product in the reaction system. Meanwhile, the {gamma}-Al{sub 2}O{sub 3} was also obtained by calcination of above product at 500 {sup o}C for 2 h, and the flower-like morphology kept no change. The surface area of {gamma}-Al{sub 2}O{sub 3} powder was determined to be 166.8 m{sup 2}/g by N{sub 2} adsorption measurement. The possible formation mechanism of flower-like boehmite nanostructures was proposed and discussed.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Microstrain in tetragonal lead-zirconate-titanate: The effect of pressure on the ionic displacements

Piezoelectric materials respond to external stimuli by adjusting atomic positions. In solid-solutions, the changes occurring in atomic scale are very complex since the short- and long-range order are different. Standard methods used in diffraction data analysis fail to model the short-range order accurately. Pressure-induced cation displacements in ferroelectric Pb(Zr{sub 0.45}Ti{sub 0.55})O{sub 3} perovskite oxide are modeled by starting from a short-range order. We show that the model gives the average structure correctly and properly describes the local structure. The origin of the microstrain in lead zirconate titanate is the spatially varying Zr and Ti concentration and atomic distances, which is taken into account in the simulation. High-pressure neutron powder diffraction and simulation techniques are applied for the determination of atomic positions and bond-valences as a function of pressure. Under hydrostatic pressure, the material loses its piezoelectric properties far before the transition to the cubic phase takes place. The total cation valence +6 is preserved up to 3.31 GPa by compensating the increasing B-cation valence by decreasing Pb-displacement from the high-symmetry position. At 3.31 GPa, Pb-displacement is zero and the material is no more ferroelectric. This is also the pressure at which the Pb-valence is minimized. The average structure is still tetragonal. The model for microstrain predicts that the transition occurs over a finite pressure range: Pb-displacements are spatially varying and follow the distribution of Zr and Ti ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Open porous BiVO{sub 4} nanomaterials: Electronspinning fabrication and enhanced visible light photocatalytic activity

Highlights: • BiVO{sub 4} nanofibers were successfully fabricated by electrospinning method. • PVP was used to adjust the viscosity and increase spinnability of the electrospinning sol. • BiVO{sub 4} nanofibers were used for the degradation of MB. • Compared to the submicron sized BiVO4, BiVO{sub 4} nanofibers show superior photocatalytic activity. - Abstract: Witnessed by X-ray powder diffraction (XRD), Raman, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies, BiVO{sub 4} nanofibers and porous nanostructures were successfully fabricated by electrospinning method using NH{sub 4}VO{sub 3} and Bi(NO{sub 3}){sub 3} as starting materials. Polyvinylpyrrolidinone (PVP) was used to tune the viscosity and spinnability of the electrospinning sol. The slow decomposition and combustion of PVP matrix prevented rapid crystal growth of BiVO{sub 4} nanostructures leading to considerably small crystallite size (approximately 19.1–28.3 nm) with less surface defects after two hours calcination at varying temperatures. This paid great tributes to the superior visible light photocatalytic activity when compared to the submicron sized BiVO{sub 4} prepared in the absence of PVP.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Resolving the Chemical Formula of Nesquehonite via NMR Crystallography, DFT Computation, and Complementary Neutron Diffraction

Nesquehonite is a magnesium carbonate mineral relevant to carbon sequestration envisioned for carbon capture and storage of CO 2 . Its chemical formula remains controversial today, assigned as either a hydrated magnesium carbonate [MgCO 3 · 3H 2 O], or a hydroxy- hydrated- magnesium bicarbonate [Mg(HCO 3 )OH · 2H 2 O]. Here, the resolution of this controversy is central to understanding this material‘s thermodynamic, phase, and chemical behavior. In an NMR crystallography study, using rotational-echo double-resonance 13 C{ 1 H} (REDOR), 13 C- 1 H distances are determined with precision, and the combination of 13 C static NMR lineshapes and density functional theory (DFT) calculations are used to model different H atomic coordinates. [MgCO 3 · 3H 2 O] is found to be accurate, and evidence from neutron powder diffraction bolsters these assignments. Refined H positions can help understand how H-bonding stabilizes this structure against dehydration to MgCO 3 . More broadly, these results illustrate the power of NMR crystallography as a technique for resolving questions where X-ray diffraction is inconclusive.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Effect of annealing temperature on structure and electrical properties of topological insulator Bi{sub 2}Te{sub 3}

Bi{sub 2}Te{sub 3} samples were prepared by precipitation method. The samples were annealed in evacuated quartz tubes and were treated at different temperature for different duration of time. Effects of annealing temperature and time on the structure of Bi{sub 2}Te{sub 3} were studied in detail. The Bi{sub 2}Te{sub 3} samples annealed at temperature 300°C and 450°C for 48Hrs, 72Hrs and 96Hrs were selected for the present study. The structure of Bi{sub 2}Te{sub 3} and related phases were investigated by the X-ray powder diffraction technique. Morphology and chemical compositions of the samples were investigated by scanning electron microscope and energy dispersive X-ray spectroscopy respectively. All the samples were indexed in rhombohedral crystal structure, with a space group R-3m. The structure consists of repeated quintuple layers of atoms, Te2-Bi-Te1-Bi-Te2 stacking along the z-axis of the unit cell. Electrical properties of the sample annealed at 300°C for 96Hrs was evaluated by measurements of the electrical resistivity and magnetoresistance. The magnetoresistance data at low temperature (1.5 to 50 K) were analyzed to investigate weak antilocalization (WAL) effect. MR data followed the Hikami–Larkin–Nagaoka (HLN) equation with a fit parameter α close to −1 as expected for topological surface states at 1.5 K, but for other temperatures the small oscillations were observed which may be due to the phenomena like Shubnikov-de Hass effect.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Crystal structure of perfluorononanoic acid, C 9 HF 17 O 2

The crystal structure of perfluorononanoic acid (PFNA) was solved via parallel tempering using synchrotron powder diffraction data obtained from the Brockhouse X-ray Diffraction and Scattering (BXDS) Wiggler Lower Energy (WLE) beamline at the Canadian Light Source. PFNA crystallizes in monoclinic space group P2 1 /c (#14) with lattice parameters a = 26.172(1) Å, b = 5.6345(2) Å, c = 10.9501(4) Å, and β = 98.752(2)°. The crystal structure is composed of dimers, with pairs of PFNA molecules connected by hydrogen bonds via the carboxylic acid functional groups. The Rietveld-refined structure was compared to a density functional theory-optimized structure, and the root-mean-square Cartesian difference was larger than normally observed for correct powder structures. The powder data likely exhibited evidence of disorder which was not successfully modeled.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

DOE OSTI2012

Syntheses and crystal structures of the quaternary uranium lanthanide oxyselenides UYb{sub 2}O{sub 2}Se{sub 3} and U{sub 2}Ln{sub 2}O{sub 4}Se{sub 3} (Ln=Pr, Sm, Gd)

Single crystals of the new uranium lanthanide oxyselenide compounds UYb{sub 2}O{sub 2}Se{sub 3} and U{sub 2}Ln{sub 2}O{sub 4}Se{sub 3} (Ln=Pr, Sm, Gd) have been synthesized from an Sb{sub 2}Se{sub 3} flux. The structures have been determined from single-crystal X-ray diffraction data. UYb{sub 2}O{sub 2}Se{sub 3} is isostructural to UYb{sub 2}O{sub 2}S{sub 3}. The structure comprises layers of edge-sharing YbSe{sub 6} octahedra and double layers of disordered (U/Ln)O{sub 4}Se{sub 4} square antiprisms. The U{sub 2}Ln{sub 2}O{sub 4}Se{sub 3} (Ln=Pr, Sm, Gd) compounds are isostructural to U{sub 2}Ln{sub 2}O{sub 4}S{sub 3} (Ln=La-Gd) whose structure had been deduced previously from X-ray powder diffraction data. In the structure a dodecahedron of four O atoms and four Se atoms surrounds a site primarily occupied by U and a distorted bicapped octahedron of five Se atoms and three O atoms surrounds a site primarily occupied by the lanthanide. These compounds represent the first examples of quaternary uranium oxyselenides. - Graphical abstract: The U{sub 2}Ln{sub 2}O{sub 4}Se{sub 3} (Ln=Pr, Sm, Gd) structure: primarily U sites are in black, primarily Ln sites are in blue, O red, Se orange. Highlights: Black-Right-Pointing-Pointer Single crystals of the new compounds UYb{sub 2}O{sub 2}Se{sub 3} and U{sub 2}Ln{sub 2}O{sub 4}Se{sub 3} (Ln=Pr, Sm, Gd) have been synthesized. Black-Right-Pointing-Pointer These compounds represent the first examples of quaternary uranium oxyselenides. Black-Right-Pointing-Pointer U is surrounded by a dodecahedron or square prism of four O atoms and four Se atoms

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Experimental and Theoretical Studies on a High Pressure Monoclinic Phase of Ammonia Borane

The effect of pressure on the structure of ammonia borane NH{sub 3}BH{sub 3} (AB) was investigated using a combination of high pressure X-ray diffraction (XRD) and density functional theory (DFT). In situ XRD was performed up to 15.0 GPa at room temperature in a diamond anvil cell, and two first-order phase transitions were observed at 1.6 and 12.9 GPa. The ambient pressure I4mm structure transformed into the high pressure Cmc2{sub 1} phase at 1.6 GPa, and then experienced a second-order isostructural phase transition at 5 GPa, and further developed into a monoclinic P2{sub 1} (Z = 4) phase at 12.9 GPa. The structure of the high pressure P2{sub 1} phase was solved by powder diffraction data and further optimized using DFT calculations. The high pressure phase transitions were found to be reversible upon releasing pressure. The behavior of the N-H {hor_ellipsis} H-B dihydrogen bonding framework, inter- and intramolecular interactions at high pressure was also investigated. The origin of the phase transition at 12.9 GPa is attributed to the reorganization of the dihydrogen bonding network and the change in the rotational dynamics of the NH{sub 3} and BH{sub 3} groups.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Influence of gradual cobalt substitution on lithium nickel phosphate nano-scale composites for high voltage applications

The carbon-free LiNiPO{sub 4} and cobalt doped LiNi{sub 1−x}Co{sub x}PO{sub 4}/C (x = 0.0–1.0) were synthesized and investigated for high voltage applications (> 4 V) for Li-ion batteries. Nano-scale composites were prepared by handy sol–gel approach using citric acid under slightly reductive gas atmosphere (Ar-H{sub 2}, 85:15%). Structural and morphological characteristics of the powders were revealed by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and inductively coupled plasma (ICP). Except for a small impurity phase (Ni{sub 3}P), phase pure samples crystallized in the olivine-lattice structure with a linear relationship between lattice parameters (a, b and c) and chemical composition. The FE-SEM images proved that LiNiPO{sub 4}/C particles (50–80 nm) did not agglomerate, and showed that as the cobalt content was higher agglomeration had increased. The electrochemical properties of all electrodes were investigated by galvanostatic charge–discharge measurements. Substitution of Ni{sup 2} {sup +} by Co{sup 2} {sup +} caused higher electronic conductivities and showed more effective Li{sup +} ion mobility. When the cobalt content is 100%, the capacity reached to a higher level (146.2 mA h g{sup −} {sup 1}) and good capacity retention of 85.1% at the end of the 60 cycles was observed. The cycling voltammogram (CV) revealed that LiCoPO{sub 4}/C electrode improved the electrochemical properties. The Ni{sup 3} {sup +}–Ni{sup 2} {sup +} redox couple was not observed for carbon free LiNiPO{sub 4}. Nevertheless, it was observed that carbon coated LiNiPO{sub 4} sample exhibits a significant oxidation (5.26 V)–reduction (5.08 V) peaks. With this study, characteristics of the LiNi{sub 1−x}Co{sub x}PO{sub 4}/C series were deeply evaluated and discussed. - Highlights: • Structural, morphological and electrochemical effects of Co doped LiNi{sub 1−} {sub x}Co{sub x}PO{sub 4}/C electrodes are investigated. • Cheap, effective and simple sol–gel approach is used. • After the 60th cycle, capacity retention is almost 87% for LiCoPO{sub 4}/C electrode. • LiNiPO{sub 4}/C sample exhibits a distinctive oxidation (5.26 V)–reduction (5.08 V) peaks.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Direct Production of Ferrochrome by Segregation Reduction of Chromite in the Presence of Calcium Chloride

A solid reduction process is described whereby chromite is reduced with the help of calcium chloride to produce ferrochrome alloy powders with high metal recovery. The process involves segregation reduction of chromite using graphite as the reductant and calcium chloride as the segregation catalyst. Experiments were performed in the temperature range of 1200–1400 °C to evaluate the influences of various design parameters using both a thermogravimetric analyzer and an electric tube furnace with continuous off-gas analysis. The reduced products were characterized by scanning electron microscopy, X-ray powder diffraction, synchrotron X-ray absorption spectroscopy, and were subjected to wet chemical analysis. It was concluded that the addition of calcium chloride not only accelerated the carbothermic reduction of chromite but also promoted the formation and growth of individual ferrochrome alloy particles. The alloy formation within chromite particles was minimized, enabling the effective separation of ferrochrome alloy particles from the unwanted gangue without the need for fine grinding. Majority of the calcium chloride remained in a recoverable form, with a small percentage (<10 wt %) consumed by reacting with the siliceous gangue forming wadalite. Pure ferrochrome alloy powders were successfully produced with high metal recovery using elutriating separation.

36 MATERIALS SCIENCE↗

DOE OSTI2011

In-situ Dehydration Studies of Fully K- Rb- and Cs-exchanged Natrolites

In-situ synchrotron X-ray powder diffraction studies of K-, Rb-, and Cs-exchanged natrolites between room temperature and 425 C revealed that the dehydrated phases with collapsed frameworks start to form at 175, 150, and 100 C, respectively. The degree of the framework collapse indicated by the unit-cell volume contraction depends on the size of the non-framework cation: K-exchanged natrolite undergoes an 18.8% unit-cell volume contraction when dehydrated at 175 C, whereas Rb- and Cs-exchanged natrolites show unit-cell volume contractions of 18.5 and 15.2% at 150 and 100 C, respectively. In the hydrated phases, the dehydration-induced unit-cell volume reduction diminishes as the cation size increases and reveals increasingly a negative slope as smaller cations are substituted into the pores of the natrolite structure. The thermal expansion of the unit-cell volumes of the dehydrated K-, Rb-, and Cs-phases have positive thermal expansion coefficients of 8.80 x 10{sup -5} K{sup -1}, 1.03 x 10{sup -4} K{sup 01}, and 5.06 x 10{sup -5} K{sup -1}, respectively. Rietveld structure refinements of the dehydrated phases at 400 C reveal that the framework collapses are due to an increase of the chain rotation angles, {Psi}, which narrow the channels to a more elliptical shape. Compared to their respective hydrated structures at ambient conditions, the dehydrated K-exchanged natrolite at 400 C shows a 2.2-fold increase in {Psi}, whereas the dehydrated Rb- and Cs-natrolites at 400 C reveal increases of {Psi} by ca. 3.7 and 7.3 times, respectively. The elliptical channel openings of the dehydrated K-, Rb-, to Cs-phases become larger as the cation size increases. The disordered non-framework cations in the hydrated K-, Rb-, and Cs-natrolite order during dehydration and the subsequent framework collapse. The dehydrated phases of Rb- and Cs-natrolite can be stabilized at ambient conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗