Structural characterization of delithiated LiVO2

Structural characteristics of delithiated LiVO₂ prepared by chemical and electrochemical methods have been examined by powder X-ray diffraction techniques. Electrochemical data and structural analyses of Li_1?xVO₂ samples show that, for x ? 0.3, removal of lithium from the layered LiVO₂ structure (space $\text{group = R}\text{3}\text{?}\text{m}$) results in a rearrangement of the vanadium ions in the cubic-close-packed oxygen lattice. In Li_0.22VO₂ approximately one-third of the vanadium ions are located in octahedral sites left vacant in the lithium layer. This results in a stabilized structure with near-cubic lattice constants.     

Single crystal growth and characterization of nearly stoichiometric LiVO2

LiVO₂ undergoes an imperfectly understood orbital ordering transition near 500 K resulting in a loss of magnetic moment below the transition. Studies of the transition have been hampered by a lack of high-quality stoichiometric single crystals. Here we report the growth and basic characterization of large, nearly stoichiometric LiVO₂ single crystals. The crystals were characterized by magnetic susceptibility, electrical resistivity, differential scanning calorimetry, and specific heat measurements over a temperature range from 2 to 650 K. A first-order phase transition with large hysteresis near T_t≈500 K was observed in all measurements. An anisotropy of the order of 100 was observed in the in-plane versus out-of-plane resistivity, and the inferred semiconducting energy gap was 0.18 eV for T<T_t and 0.14 eV for T<T_t. Electron diffraction experiments were performed on LiVO₂ single crystals at temperatures below and above T_t. Superlattice reflections were observed below T_t and disappeared upon heating above the phase transition temperature. Upon cooling below T_t, the supperlattice spots reappeared. Bright field electron micrographs indicate that the crystals develop a roughly hexagonal network of cracks.     

Metal-ion distribution and magnetic structure of Fe-substituted cobaltite spinel: FeCo2O4

The metal ion distribution of FeCo₂O₄ (cubic spinel) which was quenched from 900°C in air was determined to be ($\text{Fe}$³⁺_0.18$\text{Co}$²⁺_0.82) [$\text{Fe}$³⁺_0.82$\text{Co}$²⁺_0.18 Co^III+_1.0] O₄ with the neutron diffraction method. The oxygen spacial parameter u was determined to be 0.382 ± 0.002. The magnetic structure was explained as a Néel type ferrimagnet and the origin of the spontaneous magnetization was attributed to the uncompensation of the spins between A- and B-site of the spinel lattice. The magnetic moment per molecule was estimated to be 0.70 μB.     

Aqueous slip casting of MgAl2O4 spinel powder

A stoichiometric MgAl ₂ O ₄ spinel (MAS) powder was synthesized by calcining a compacted mixture of aboldsymbol{alpha} -Al ₂ O ₃ and calcined caustic MgO at 1400°C for 1 h and was surface treated against hydrolysis using an ethanol solution of H ₃ PO ₄ and Al(H ₂ PO ₄ ) ₃ after fine grinding. Aqueous suspensions with 41–45 vol.% treated powder were prepared using tetra methyl ammonium hydroxide (TMAH) and an ammonium salt of polyacrylic acid (Duramax D-3005) as dispersing agents. These stable suspensions were consolidated in plaster moulds by slip casting (SC) route for the first time. For comparison purposes, the treated powder was also compacted by die-pressing technique after converting into freeze-dried granules and sintered along with slip cast samples at 1550–1650°C for 1–2 h. The MAS ceramics fabricated by slip casting and die-pressing exhibited comparable properties.     

X-ray investigation of the solid solution Zn1−XCuXCr2S4 with spinel structure

The phase diagram of the quasibinary system of the semiconducting ZnCr₂S₄ and the metallic CuCr₂S₄ has been studied with the help of X-ray powder photographs of quenched samples and high temperature X-ray diffraction patterns. At ambient temperature the mutual solid solubility of both sulfide spinels is only small with x < 0.1 and > 0.9. But the interchangeability of ZnCr₂S₄ and CuCr₂S₄ increases with increasing temperature, and at temperatures above 630°C a complete series of mixed crystals is formed, which, however, cannot be quenched to room temperature without decomposition. The limited solid solubility of chalcide spinels containing copper is discussed in terms of size factor and valence state of the ions under investigation.     

A neutron diffraction study of the ferrimagnetic spinel NiCo2O4

Neutron-diffraction experiments at 4.2K on a polycrystalline sample of the spinel NiCo₂O₄ prepared at 320°C revealed 92% occupancy of the tetrahedral (A) sites by cobalt and Neel ferrimagnetism with mean A-site and B-site moments 〈μ_A〉 = 2.29(9)μ_B and 〈μ_B〉 = ?0.97(13)μ_B. Diffuse scattering and electron microscopy demonstrated variations with position in the Ni/Co ratio. These and literature-magnetization data are interpreted with the assumption that the σ-bonding d orbitals form itinerant-electron states with overlapping energies for A-site Co²⁺ and B-site Ni²⁺ configurations. The formal valencies for these ions become low-spin Co_A^(3?δ)+ and Ni_B^(2+δ)+, where δ increases with externally applied field H.     

硅元素掺杂改性尖晶石型锰酸锂的研究进展

尖晶石锰酸锂(LiMn₂O₄)具有理论比容量高、热稳定性高、价格低廉、循环性能良好等特点,深受研究者的亲睐,目前已有固相法、燃烧合成法和共沉淀等多种制备方法。为了进一步改善该材料的循环性能,研究者提出了元素掺杂的策略,元素掺杂改性是基于改变材料的晶体结构或材料中部分元素的平均价态来提高材料的电化学性能和结构的稳定性。Si⁴⁺掺杂可以取代材料中的部分Mn⁴⁺,从而使材料产生Jahn-Teller效应的离子数降低和尖晶石锰酸锂的八面体体积扩大,提高电化学性能。为此,综述了近几年来单一硅元素掺杂及硅与其他元素复合掺杂改性尖晶石型锰酸锂正极材料的研究进展。     

金属Ag对NiFe2O4尖晶石性能的影响

制备了不同金属Ag含量的Ag-NiFe2O4金属陶瓷,利用扫描电子显微镜观察显微组织,由X射线衍射分析化学成分,研究了Ag的添加量对其体积密度、气孔率、热震性、导电率以及腐蚀速率的影响,试验结果表明,抗热震性和导电能力随着Ag含量的增加而增强,导电率的提高和腐蚀率的增大仍是一对突出的矛盾.单一通过添加金属Ag不可能使导电率和腐蚀率都满足要求.     

Crystal structure of Li2 CaUF8

Compound Li₂CaUF₈ is tetragonal. The unit cell, with $\text{a}\text{=5.2290(12)}\text{A}\text{?}$,$\text{c}\text{=11.0130(18)}\text{A}\text{?}$, contains two formula units and the space group is I$\text{bar}\text{?}$m2. The crystal structure has been solved from single crystal diffractometer data by Patterson and Fourier synthesis and refined by a least-squares method. The final value of R is 0.062 for 602 reflections. The cationic distribution is the same as in the scheelite structure, with an additional cationic ordering. Moreover, we observe that the fluorine atoms are randomly distributed at two half occupied sites.     

Synthesis and structural characterization of the normal spinel Li[Ni2]O4

Room-temperature electrochemical extraction of lithium from nearly stoichiometric, layered LiNiO₂ gives the solid-solution system Li_1?xNiO₂. Monitoring the temperature dependence of the X-ray-diffraction pattern of Li_0.5NiO₂ has revealed a first-order transformation above 150°C to the cubic, normal spinel phase Li[Ni₂]O₄. This spinel phase is stable to 300°C     

The crystal structure of LiScS2 and NaScS2

LiScS₂ and NaScS₂ were prepared and the structure was determined by X-ray powder work. The observed α-NaFeO₂ structure for these compounds is discussed in relation to other ABS₂ compounds.     

Synthesis and magnetic behavior of spinel FeAl2O4 nanoparticles

Nanocrystalline FeAl₂O₄ has been synthesized from furnace heating of corresponding iron and aluminium acetylacetonate complexes. The nanoparticles obtained were characterized using powder X-ray diffraction (XRD), EDX and transmission electron microscopy (TEM). The particles were faceted with a diameter in the range of 10-20 nm. The magnetic property of the FeAl₂O₄ nanoparticles was studied for the first time by plotting M vs H hysteresis curves, at different temperature and also by recording the temperature dependence of zero-field-cooled M_ZFC and field-cooled M_FC magnetization curves. On decreasing the temperature to 4 K, the magnetization shows deviation from linear behavior.     

Preferred orientation of NiAl2O4 spinel grown on sapphire

The orientation relationships between the spinel nickel aluminate (NiAl₂O₄) and the aluminum oxide single crystal from which it is grown have been investigated. A variety of sapphire surface orientations were used. The nickel source was primarily nickel vapor, but nickel metal was also used. The large grained spinel layer growing in contact with the sapphire is highly textured, and a thinner fine grained layer on its outer surface is only lightly textured. Two principal textures were observed: for sapphire surfaces oriented near the basal plane, the {111} spinel is parallel to the (0001) sapphire; for surfaces oriented away from the basal plane the {111} spinel is parallel to the {1120} sapphire. In both cases the directions 〈110〉 spinel and 〈1010〉 sapphire are aligned. Considerable twinning and several secondary textures have also been seen.     

The crystal structure of the intercalates SnTaS2 and SnNbS2

The crystal structure of SnTaS₂ was determined by X-ray and neutron powder diffraction. SnTaS₂ is hexagonal, $\text{a}\text{=3.307}\text{A}\text{?}$, $\text{c}\text{=17.442}\text{A}\text{?}$, space group P6₃/mmc with Ta and Sn at special positions. Ta is in trigonal-prismatic coordination by sulfur forming TaS₂ slabs; Sn is linearly coordinated by sulfur atoms of adjacent TaS₂ slabs. X-ray powder diffraction showed that SnNbS₂ is isostructural with SnTaS₂.     

FP-LAPW study of the fundamental properties of the cubic spinel CdAl2O4

We have investigated the structural, elastic, electronic, optical and thermodynamic properties of the cubic spinel CdAl₂O₄ using accurate ab initio calculations. Computed equilibrium structural parameters are in good agreement with the available experimental data. Single-crystals elastic parameters are calculated for pressure up to 30 GPa using a conserving-volume total energy-strain method. Isotropic elastic parameters for ideal polycrystalline CdAl₂O₄ aggregates are computed in the framework of the Voigt-Reuss-Hill approximation. Result for band structure using the Engel-Vosko scheme of the GGA shows a significant improvement over the common GGA functionals. Optical spectra have been calculated for the energy range 0-30 eV. The peaks and structures in the optical spectra are assigned to interband transitions. Pressure dependence of the band gaps, static dielectric constant and static refractive index are also investigated. Pressure and thermal effects on some macroscopic properties are predicted using the quasi-harmonic Debye model.     

Preparation of a new Cu-substituted cobaltite spinel : CuCo2O4

CuCo₂O₄ spinel with tetragonal distortion was synthesized under high temperature-pressure conditions. Its calculated lattice constants were a = 8.154 and $\text{c}\text{= 7.875}\text{A}\text{?}$ ($\text{c}\text{a}\text{= 0.966}$ at room temperature). An antiferromagnetic ordering occurred at 24K and the effctive Bohr magneton of 1.74 showed that the copper ion was divalent state. From crystallographic and magnetic measurements, the copper cobaltite was expressed as (Cu²⁺) [Co₂^III]O₄.     

Crystal structure of K4[H2J2O10].8H20

Crystals of K₄ [H₂J₂O₁₀] 8H₂O belong to the triclinic system, space group P 1 with a = 7.161 (2) $\text{A}\text{?}\text{, b}\text{= 10,553}$ (5) $\text{A}\text{?}\text{, c}\text{= 7,081}$ (2) $\text{A}\text{?}\text{, α = 98°1′}$, β = 117°8′, γ = 90°6′ and Z = 1. The crystal structure has been determined on the basis of photographic data from 877 independent reflections, with the final R value of 6,6%. The iodine atoms are surrounded by a distorted octahedra consisting of five oxygen atoms and one OH group. The average J-O distance is 2.03 Å. There are 2 independent K atoms in the structure. K(1) has a coordination number of eight, while K(2) is surrounded by 6 (5 water molecules + one OH group) nearest neighbours.     

Crystal structure of LuRuB2

Ternary metal borides of the formula MTB₂ have been synthesized in a new structure for M=Sc, Y, Tb, Dy, Ho, Er, Tm, Lu, and T=Ru, Os. Single crystal x-ray diffraction data on LuRuB₂ were refined on an orthorhombic unit cell, space group Pnma, Z=4, and yielded an R factor equal to 0.085. All metal atoms are coplanar with short bond distances of 3.10Å between rare earth atoms which are arranged in zig-zag chains.     

Crystal structure of a metal excess spinel : Cu1.10Cr1.30Sn0.70S3.90

The compound Cu_1.10Cr_1.30Sn_0.70S_3.90 has been studied by neutron diffraction. It belongs to the spinel structural type, but the formula indicates a copper excess with respect to the ideal spinel composition. The structural refinements have been performed according to the Rietveld method. Chromium and tin are located on the 16d octahedral sites (B-sublattice of the spinel structure). 0.95 copper occupy the 8a tetrahedral sites (A-sublattice) whereas 0.15 copper is found on the 16c octahedral sites which would be unoccupied in an ideal stoichiometric spinel. The R value is 3.6 %. The excess spinel is found to slowly release the copper excess leading to Cu₂S formation. The question whether short metal-metal distances or epitaxy phenomenon are involved is discussed.     

Studies of glass structure in the TeO2  Fe2O3 system

Some structure characteristics of glasses in the TeO₂Fe₂O₃ system have been studied by means of Moessbauer and IR spectroscopy and positron annihilation. Discussion is been made about the character of the chemical bonds and structuring of the glasses on the basis of the experimental data obtained.