Superconductivity in three-layer Na0.3CoO2·1.3H2O

The observation of superconductivity at 4.3 K in a new crystalline form of Na_0.3CoO₂·1.3H₂O is reported. The new superconductor has three layers of CoO₆ octahedral per crystallographic unit cell, in contrast to the previously reported two-layer superconductor. The three-layer cell occurs because the relative orientations of neighboring CoO₂ layers are distinctly different from what is seen in the two-layer superconducting phase. This type of structural difference in materials that are otherwise chemically and structurally identical is not possible to attain on the layered copper oxide superconductors. The synthesis and stability of the new phase are described.     

Structure and dielectric properties of (Na0.50Bi0.50)1−xBaxTiO3: 0≤x≤0.10

Solid solution of (1−x)Na_0.5Bi_0.5TiO₃-xBaTiO₃ is investigated in the composition range 0.00≤x≤0.10. It is shown that the system exhibits rhombohedral structure up to x=0.055 and then becomes ‘nearly cubic’ for x≥0.06. Temperature dependent dielectric measurements reveals three peaks in the imaginary part of the dielectric constant for compositions exhibiting rhombohedral as well as ‘nearly cubic’ structures. The first of these three peaks exhibits Vogel-Fulcher type relaxation behaviour.     

Thermal parameters of MgSO4·7H2O and NiSO4·7H2O crystals added with urea and thiourea

Pure and impurity-added (with urea and thiourea) MgSO₄·7H₂O and NiSO₄·7H₂O single crystals were grown by the free-evaporation method from aqueous solutions. Density was measured by the flotation method. X-ray diffraction data were collected for powder samples and used for the estimation of thermal parameters like Debye-Waller factor, mean-square amplitude of vibration, Debye temperature and Debye frequency. The thermal parameters do not vary in a particular order with respect to impurity concentration, which could be attributed to the random disturbance created by the impurity molecules in the hydrogen-bonding system of the MgSO₄·7H₂O and NiSO₄·7H₂O lattices.     

Crystal structure of the quaternary compound CuTa2InTe4 from X-ray powder diffraction

The crystal structure of the new quaternary compound CuTa₂InTe₄ was studied using X-ray powder diffraction data. The powder pattern refined by the Rietveld method indicates that this material crystallizes in the tetragonal system with space group I-4¯2m (No. 121), Z=2, and unit cell parameters a=6.1963(2) Å, c=12.4164(4) Å, c/a=2.00 and V=476.72(3) Å³. The structural and instrumental refinement of 28 parameters led to R_p=10.4%, R_wp=11.1%, R_exp=6.8% and χ²=2.7 for 96 independent reflections.     

Compression behavior of the delafossite-type metallic oxide PdCoO2 below 10 GPa

The compression behavior of delafossite-type metallic oxide PdCoO₂ below 10 GPa has been investigated by in situ high pressure X-ray diffraction measurement using synchrotron radiation. It is found that the delafossite-type structure of PdCoO₂ is stable below 10 GPa. It should be noted that compression behavior of PdCoO₂ is anisotropic. Pressure dependence of the lattice parameters indicates that the a-axis is more compressible than the c-axis. The lattice parameter ratio c/a in the hexagonal unit increases with increasing pressure. The calculated zero-pressure bulk modulus is 224 GPa. It is found that the above characteristic compression behaviors of PdCoO₂ are the same as those of the delafossite CuFeO₂. The compressibilities of the a-axis of both PdCoO₂ and CuFeO₂ are highly different although those of the c-axis are almost the same.     

Synthesis and thermal stability of Zn3N2 powder

This paper reports that Zn₃N₂ powder of high quality has been synthesized by a nitridation reaction of Zn powder with NH₃ gas (flow rate 500 ml/min) at the nitridation temperature of 600 °C for 120 min. X-ray diffraction indicates that Zn₃N₂ is cubic in structure with the lattice constant being a=9.788 Å. X-ray photoelectron spectroscopy shows the differences of chemical bonding states between Zn₃N₂ and ZnO, and confirms the formation of N-Zn bonds. Thermal gravimetric analysis and differential thermal analysis are employed to investigate the thermal decomposition behavior of Zn₃N₂ powder. It is found that Zn₃N₂ is unstable when exposed to open air above 500 °C.     

Chemical Synthesis of C3N and BC2N Compounds

A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride （CC14）, boron tribromide （BBr3）, lithium nitride （Li3N） and sodium as reactants has been carried out at the temperature of 400℃. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C-N with an amorphous, structure; the other is piece-like polycrystalline B-C-N with the hexagonal structure. Their determined compositions are close to C3N and BC2N, respectively.     

Extended X-ray absorption fine-structure (EXAFS) of a complex oxide structure: a full multiple scattering analysis of the Au L3-edge EXAFS of Au2O3

Crystalline Au₂O₃ was obtained by hydrothermal synthesis at 3000 atm and its extended X-ray absorption fine-structure (EXAFS) at the Au L₃-edge was measured at room temperature. A detailed full multiple scattering (MS) analysis using FEFF8 theory shows that only a small number of scattering paths contribute significantly to the EXAFS of Au₂O₃. Because of the complex unit cell (low local symmetry) of the Au₂O₃ structure, contributions of MS paths are almost negligible. The results indicate that FEFF8 theory provides a good reference for the analysis of Au-O phases.     

Demineralisation of a semianthracite char with molten salts/HCl: A study by X-ray diffraction

The effects of chemical heat treatments of a semianthracite char (AC) on the composition of the mineral fraction of the material are investigated. The starting char was first treated with a mixture of LiCl/KCl or LiCl/KCl/CaO at 743, 873 or 1173 K and the products obtained were then washed thoroughly with distilled water. A small fraction of these samples were treated with 10⁻³ M HCl solution. The composition changes were studied by X-ray diffraction. The predominant mineral components initially present in the starting char are quartz, mullite, muscovite and/or kaolinite and oldhamite. The treatments of AC resulted in significant changes in the mineral fraction of the material, in particular when LiCl/KCl/CaO was used. In this case, spurrite, γ-calcium orthosilicate and gehlenite were formed, which were eliminated by treatment with 10⁻³ M HCl solution.     

Structural phase transition of ScSb and YSb with a NaCl-type structure at high pressures

By use of synchrotron radiation, powder X-ray diffraction of ScSb and YSb with a NaCl-type structure has been studied up to 45 GPa at room temperature. A first-order phase transition from the NaCl-type (B1) to a CsCl-type structure (B2) began to occur at around 28 GPa for ScSb and at around 26 GPa for YSb. Crystal data of the high-pressure phase of both antimonides are obtained. The high-pressure structural behavior of ScSb and YSb is similar to that of heavier LnSb (Ln=Dy-Lu). The B1-B2 transition for ScSb and YSb can be understood according to the rigid sphere model. The bulk moduli of ScSb and YSb are about 58 GPa at ambient pressure.     

Pressure-induced phase transitions of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure

By use of synchrotron radiation the powder X-ray diffraction of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure has been studied up to 60 GPa at room temperature. First-order phase transitions with the crystallographic change were found at around 20 GPa for LaAs, and 57 GPa for LuAs. The high-pressure form of LaAs is a tetragonal structure and can be viewed as a distorted CsCl-type structure. The atoms in the tetragonal structure are located at La: 0, 0, 0; As: 1/2, 1/2, 1/2. The space group is P4/mmm. The structural change to the tetragonal structure occurs with the volume collapse of about 10%. The structure of these high-pressure phases of LuAs is unknown. The volume vs. pressure curves for LaAs and LuAs are fitted by a Birch equation of state. The bulk moduli of both arsenides are 92±6 GPa for LaAs and 85±3 GPa for LuAs. The high-pressure structural behavior of LaX (X=P, As and Sb) and LnAs (Ln=lanthanide) with the NaCl-type structure is discussed.     

Negative thermal expansion and phase transition behaviour in Ag2O

The structure of Ag₂O has been studied between 5 and 300 K using both high resolution synchrotron X-ray and neutron powder diffraction methods. Ag₂O exhibits strong negative thermal expansion below 200 K and the cell volume is only weakly temperature dependent between 200 and 300 K. There is evidence for a first order phase transition below 35 K in Ag₂O and this is apparently related to displacive disorder of the Ag cations. This disorder contributes to the observed NTE.     

On the symmetry and structure of the double perovskites Ba2LnRuO6 (Ln=La, Pr and Nd)

The structures of the double perovskites Ba₂LnRuO₆ (Ln=La, Pr and Nd) at room temperature were re-investigated by profile analysis of X-ray diffraction data. It has been shown that neither the triclinic nor the monoclinic P2₁/n space group correctly describes their structures. Ba₂LaRuO₆ is actually rhombohedral, space group , cell parameters a=6.03196(10) Å and α=60.298(2)°. On the other hand, both Ba₂PrRuO₆ and Ba₂NdRuO₆ are found to be cubic, space group , with the cell parameters a=8.48416(6) and 8.47061(5) Å, respectively.     

Effect of ion nitriding on the crystal structure of 3 mol% Y2O3-doped ZrO2 thin-films prepared by the sol-gel method

We investigated the effect of ion nitriding on the crystal structure of 3 mol% Y₂O₃-doped ZrO₂ (3YSZ) thin-films prepared by the sol-gel method. For this purpose, we used X-ray diffractometry to determine the crystalline phases, the lattice parameters, the crystal sizes, and the lattice microstrains, and glow discharge-optical emission spectroscopy to obtain the depth profiles of the elemental chemical composition. We found that nitrogen atoms substitute oxygen atoms in the 3YSZ crystal, thus leading to the formation of unsaturated-substitutional solid solutions with reduced lattice parameters and Zr_0.94Y_0.06O_1.72N_0.17 stoichiometric formula. We also found that ion nitriding does not affect the grain size, but does generate lattice microstrains due to the increase in point defects in the crystalline lattice.     

Structure and electrical conductivity of a novel inorganic solid electrolyte: Na14.5[Al(PO4)2F2]2.5[Ti(PO4)2F2]0.5 (NATP)

A novel inorganic solid electrolyte with a layered framework structure stable up to 1043 K, Na_14.5[Al(PO₄)₂F₂]_2.5[Ti(PO₄)₂F₂]_0.5 (NATP), has been hydrothermally prepared and characterized by single-crystal and powder X-ray diffraction techniques, X-ray fluorescence (XRF) analysis, IR spectroscopic measurement, thermogravimetric and differential thermal analysis (TGA and DTA). NATP crystallizes in the acentric hexagonal space group P3 with a=10.448(2), b=10.448(2), , Z=1, containing a large number of Na⁺ cations in the interlamellar space and the cavities of its framework. There are six different crystallographic Na⁺ cationic sites, in which 8% Na(5) and 12% Na(6) sites are vacant. Electrical conductivity measurements show that Na⁺ cations exhibit a high mobility with two domains for the electrical conductivity versus temperature.     

Residual surface stress measurements in YBa2Cu3Ox superconductors

XRD and residual surface stress (sin² ψ) measurements were carried out on YBa₂Cu₃O_x superconductors with varying oxygen stoichiometry (6.3 < x < 7.0). Slopes of the surface strain versus sin² ψ were plotted against oxygen content for certain reflections. Compressional surface stress has been found along the c-axis, while a tensile surface stress has been observed along the ab-plane. Both surface stresses were found to vary slightly with oxygen content. These findings qualitatively agree with a very small hydrostatic pressure effect on T_c for fully oxygenated YBa₂Cu₃O_x (x = 7) compared to oxygen deficient material at the surface.     

Synthesis of PEO/4Hb-TaS2 layered nanocomposite

Single-phase layered nanocomposite containing 4Hb-TaS₂ and poly(ethylene oxide) [PEO] has been first synthesized by using the exfoliation-adsorption technique. It has been characterized by powder X-ray diffraction (XRD) and electrical dc resistivity measurements. As the product exhibited lattice expansions along the stacking direction, PEO was intercalated into 4Hb-TaS₂ galleries.     

Physico-chemical characterization of electrochemical deposit of Ca10(PO4)6(OH)2 on copper surfaces

Surface modification of biomaterials to improve biocompatibility without changing their bulk properties is desired for many clinical applications and has become an emerging technology in biomaterial research and industry. In the present study, a sample electrochemical method of coating the solid surfaces of copper, with a film of apatite, was developed. Thin layer of calcium phosphate crystals formed on the surfaces of copper, was carried out by electrochemical methods, and characterized by XRD, infrared spectroscopy and chemical analysis.     

Ab initio calculations and experimental determination of the structure of Cr2AlC

We have calculated the equilibrium volume and the density of states (DOS) of Cr₂AlC for antiferromagnetic (AFM), ferromagnetic (FM) and paramagnetic (PM) configurations by ab initio total energy calculations. Based on a comparison of the cohesive energies as well as the DOS for all three magnetic configurations we have identified the FM configuration to be metastable. Furthermore, we report the structural characterization of polycrystalline Cr₂AlC thin films grown by magnetron sputtering. Our calculated interplanar distances and equilibrium volume for the PM and AFM configurations are in good agreement with our experiment. The charge density distribution suggests that the chemical bonding between Cr and C in Cr₂AlC is very similar to the one in cubic CrC.     

Synthesis and structure of aluminum substituted MoSi2

Mo(Si_1−xAl_x)₂ compositions have been prepared by a modified SHS route under pressure. The compositional phase analysis indicates a body centered tetragonal C11_b phase below x<0.05 substitution, above which a biphasic region of C11_b and C40 structure coexists. Occurrence of pure hexagonal C40 phase is observed for x>0.1. The aluminum substitution leads to a continuous increase in the lattice parameters in both these structures. In the biphasic region, redistribution of aluminum concentration takes place with the evolution of aluminum rich C40 phase as indicated by energy dispersive X-ray analysis and supported by micro-hardness measurements.