V. G. Zubkov

Defect crystal structure of new TiO(OH)2 hydroxide and related lithium salt Li2TiO3

Crystal structures of TiO(OH)(2) and Li(2)TiO(3) have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li(2)TiO(3) salt obtained at 700 degrees C reveals stacking faults of LiTi(2) metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3(1)12. The possibility to stabilise this imperfect state increases the mobility of the Li(+) ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)(2). The crystal structure of TiO(OH)(2) belongs to the layered double hydroxide structure type with the 3R(1) sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)(2)OTi(2)O(OH)(2)]. TiO(OH)(2) is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.

Synthesis and structural, magnetic and electrical characterisation of the reduced oxoniobates BaNb8O14, EuNb8O14, Eu2Nb5O9 and EuxNbO3 (x = 0.7, 1.0)

Abstract Powder samples of the reduced oxoniobates Eu0.7NbO3, EuNbO3, Eu2Nb5O9, EuNb8O14 and BaNb8O14 have been synthesised. EuNbO3 and Eu0.7NbO3 adopt the perovskite type structure (space group Pm3m) with unit cell parameters a = 4.021(1) and 3.981(3) A , respectively. Eu2Nb5O9 exhibits an intergrowth structure which can be described as alternating slabs of NbO and EuNbO3. It crystallises in P4 mmm with a = 4.131(1) and c = 12.043(5) A . EuNb8O14 and the here synthesised modification of BaNb8O14 is isostructural with SrNb8O14. The structures of EuNb8O14 and BaNb8O14 have been refined from X-ray powder diffraction data with the Rietveld technique. They have the unit cell parameters a = 9.2272(1), b = 10.2647(2), c = 5.9381(1) and a = 9.3451(1), b = 10.2689(2), c = 5.9470(4) A , (space group Pbam), respectively. In all the studied compounds AO12 cuboctahedra (A = Eu, Ba) form either chains (in ANb8O14), double layers (in Eu2Nb5O9) or three-dimensional nets (in EuNbO3 and Eu0.7NbO3). Magnetic susceptibility measurements show temperature independent paramagnetism for BaNb8O14, while the susceptibilities of the Eu niobates follow Curie-Weiss laws with effective magnetic moments in good agreement with the expected μeff = 7.9 μB for Eu2+. Eu0.7NbO3 and Eu1.0NbO3 exhibit ferromagnetic ordering below 4 K. BaNb8O14 and EuNb8O14 are semiconductors, while Eu2Nb5O9, EuNbO3 and Eu0.7NbO3 are metallic.

Superconducting properties of the atomically disordered MgB2 compound

The effect of disorder induced by neutron irradiation in a nuclear reactor (thermal neutron fluence 1×1019cm−2) on the superconducting transition temperature Tc and the upper critical field Hc2 of polycrystalline MgB2 samples was investigated. Despite the appreciable radiation-induced distortions (more than ten displacements per atom), the initial crystal structure (C32) was retained. The temperature Tc decreased from 38 to 5 K upon irradiation and was practically completely restored after the subsequent annealing at a temperature of 70°C. A weak change in the dHc2/dT derivative upon irradiation is explained by the fact that the irradiated samples are described by the “pure” limit of the theory of disordered superconductors. The suppression of Tc upon disordering may be due to the isotropization of the originally anisotropic (or multicomponent) superconducting gap or to a decrease in the density of electronic states at the Fermi level.

Crystal structure of the low-temperature form of K3PO4

The crystal structure of the low-temperature form of K3PO4 has been determined for the first time using neutron diffraction (Rietveld method) and Raman spectroscopy: orthorhombic cell (sp. gr. Pnma, Z = 4), lattice parameters a = 1.12377(2) nm, b = 0.81046(1) nm, c = 0.59227(1) nm. The structure is made up of isolated [PO4] tetrahedra, with the potassium ions in between.

Crystal structure and optical properties of germanates Ln2Ca(GeO3)4 (Ln = Gd, Ho, Er, Yb, Y)

This paper reports on the results of structural and optical investigations of a new class of layered compounds Ln2Ga(GeO3)4 (Ln = Gd, Ho, Er, Yb, Y), which are promising for the use in photonics as converters of laser radiation.

Crystal structure and magnetic properties of a one dimensional complex oxide ca3nimno6

Abstract The results of structural refinements and magnetic properties of one-dimensional oxide Ca 3 NiMnO 6 are presented. The structure of Ca 3 NiMnO 6 was solved by Rietveld analysis of powder neutron date in space group R -3 c with a =9.1227(9) A, c =10.5811(17) A, z=6 (type of K 4 CdCl 6 ). Infinite chains of MnO 6 octahedra and (Ni,Mn)O 6 trigonal prisms sharing faces run parallel to the c axis. The chains are separated by Ca 2+ cations, which are located in a distorted square antiprismatic environment. Magnetic susceptibility obeys the Curie-Weiss law at 300–600 K with μ eff value 5.00 μ B consistent with the valence cationic combination Ni 2+ -Mn 4+ . Magnetic measurements display the antiferromagnetic ordering in Ca 3 NiMnO 6 at 16 K.

New elaboration technique, structure and physical properties of infinite-layer Sr1−xLnxCuO2(Ln = Nd, Pr)

Abstract The infinite-layer compounds of the (Sr, Ln)CuO 2 family have been prepared by a new synthesis method from the low-pressure phase of SrCuO 2 and NdCuO 2 as starting materials. The crystal structure, microstructure and superconductivity of these samples have been studied with use of neutron powder diffraction, optical micrographs, energy-dispersive X-ray analysis. magnetic-susceptibility and electrical-resistivity measurements. The ratio of the lattice constants a/c as an empirical parameter for the existence of superconductivity in the electron-doped infinite-layer compounds is discussed.

Synthesis, crystal structure, and luminescence properties of CaY2Ge3O10:Ln3+, Ln = Eu, Tb

The crystal structure and luminescence properties of CaY2Ge3O10:Ln3+ (Ln = Eu, Tb) germanates synthesized via a conventional solid-state reaction and an ethylenediaminetetraacetic acid complexing process are studied. The CaY2 − xLnxGe3O10 (Ln = Eu, Tb; x = 0–1.0, 2.0; Δx = 0.1) solid solutions have a monoclinic structure (space group P21/c, Z = 4), in which dopant ions occupy three nonequivalent noncentrosymmetric sites with different Ca2+/Ln3+ ratios. The effect of the synthesis methods, dopant concentrations, and excitation wavelengths on the luminescence properties of the compounds obtained is determined.

Synthesis and crystal structure of the pyrovanadate Na2ZnV2O7

The compound Na 2 ZnV 2 O 7 with an akermanite-type structure has been synthesized. It has a tetragonal unit cell, a =8.2711(4), c =5.1132(2) A, and crystallizes with P -42 1 m symmetry, Z =2. Its crystal structure has been refined from a combination of X-ray and neutron powder diffraction data. The structure contains layers of corner-sharing VO 4 and ZnO 4 tetrahedra, the former in pairs forming pyrovanadate V 2 O 7 units. The sodium atoms are positioned between the layers, with a distorted antiprismatic coordination of oxygen atoms.

Band structure of the superconducting MgB2 compound and modeling of related ternary systems

Band structure of a novel superconductor—magnesium diboride—is studied by the self-consistent FP-LMTO method. Density of states near the Fermi level of MgB2 and its electronic properties are governed by the metal-like boron 2p orbitals in the planar network of boron atoms. The modification of the band structure of MgB2 upon doping the boron (with Be, C, N, and O substitutional impurities) and the magnesium (with Be, Ca, Li, and Na substitutional impurities) sublattices or upon the introduction of structural vacancies (boron nonstoichiomety) is analyzed. The electronic structures of MgB2 and hypothetical CaB2 are also studied as functions of pressure.