Cтруктура дефектов, электронная зонная структура и фазовый переход полупроводник--металл в кобальтите PrBaCo-=SUB=-2-=/SUB=-O-=SUB=-5.5-=/SUB=-: ab initio PAW-подход

The calculations of electronic band structure of the cobaltite PrBaCo2O5+d for the content of oxygen near 5.5 have been performed using the first-principle PAW method. It has been shown that the semiconductor-metal transition near 5+d=5.5 is associated with the conversion of cobalt atoms in octahedral oxygen surrounding from high to low spin state and the similar atoms in pyramidal surrounding from the low to high spin state. The metal conductivity appears due to raising of the energy of pyramidal Co eg antibonding states. As a result these states turn up at the Fermi level thus defining the conductivity. The effect of oxygen content deviation from 5.5 on the band structure and conductivity has been studies. It is shown that the semiconductor-metal transition can be observed in the narrow range of 5+d below 5.5.

XAFS Study of Iron and Nickel Speciation in Complex Sodium Aluminophosphate Based Glasses

ABSTRACTIron and nickel oxidation state and coordination in complex sodium aluminophosphate based glasses suggested as potential matrices for immobilization of legacy high level waste currently stored in stainless steel tanks at PA «Mayak» (Ural reg., Russia) were determined by X-ray absorption fine structure spectroscopy (XAFS: XANES/EXAFS). The glasses containing (wt.%) 20-30 Na2O, 6-12 Al2O3, 40-52 P2O5, 2-5 Fe2O3, 1-3 NiO, 0-6 B2O3, 10-15 other waste oxides produced by quenching of their melts were fully amorphous or contained minor Fe and Ni free phases. Fe in the glasses was found to be predominantly trivalent with an average Fe-O distance and a coordination number (CN) in the first shell of 1.94 to 1.97 Å and 5.2 to 5.8, respectively, mostly in octahedral oxygen environment. Ni is divalent in all the glasses and has in the first shell an average Ni-O distance and CN of 1.97 to 2.03 Å and 4.9 to 5.6, respectively. The first shell of both Fe and Ni is somewhat distorted. The second and further coordination shells are weakly appeared exhibiting no clustering and homogeneous distribution of Fe and Ni ions in the glass network. The data on Fe obtained are in good agreement with those from Mössbauer study of same glasses. After annealing glasses were partly devitrified and interpretation of XAFS data is strongly complicated due to Fe and Ni partitioning among crystalline and vitreous phases.

Lithium diaquanickel(II)catena-borodiphosphate(V) monohydrate

The title borophosphate LiNi(H2O)2[BP2O8]·H2O was synthesized under hydrothermal conditions. The crystal structure is isotypic with the Mg analogue and features helical [BP2O8]3−borophosphate ribbons, constructed by BO4(2 symmetry) and PO4tetrahedra. The borate groups share all their oxygen apices with adjacent phosphate tetrahedra. The ribbons are connectedviaNi2+cations that are located on twofold rotation axes. The cations have a slightly distorted octahedral oxygen coordination by four O atoms from the anion and by two water molecules. The voids within the helices are occupied by Li+cations, likewise located on twofold rotation axes, in an irregular environment of five O atoms. The structure is stabilized by O—H...O hydrogen bonds between coordinated or uncoordinated water molecules and O atoms that are part of the helices.

High-pressure Synthesis and Crystal Structure of the Vanadium Orthoborate VBO3

The vanadium orthoborate VBO3 was synthesized under high-pressure / high-temperature conditions of 7.5 GPa and 1250 °C in a Walker-type multianvil apparatus. The crystal structure was determined on the basis of single crystal X-ray diffraction data, collected at r. t. The title compound crystallizes in the trigonal calcite structure, space group R3̄c, with the lattice parameters a = 462.0(1) and c = 1450.9(3) pm. Within the trigonal planar BO3 groups, the B-O distance is 138.8(3) pm. The vanadium atoms have a slightly distorted octahedral oxygen coordination (V-O: 202.3(2) pm).

Multianvil High-Pressure Synthesis And Crystal Structure Of β-YbBO3

β-Ytterbium borate (β-YbBO3) was synthesized under high-pressure in a Walker-type multianvil apparatus at 2.2 GPa and 1400 °C. The title-compound crystallizes in the trigonal calcite structure, space group R3̄̄c. Single crystal X-ray data yielded a = 492.1(2), c = 1630.5(9) pm, wR2 = 0.0344 for 165 F2 values and 11 variable parameters. Within the trigonal planar BO3 groups the B-O distance is 137.8(4) pm. The ytterbium atoms have a slightly distorted octahedral oxygen coordination (Yb-O: 224.4(2) pm)

Investigations of The Local Structure in Lithium Nickel Cobalt Oxide Cathode Materials

ABSTRACTWe have studied the modifications of structural and physical properties which occur during delithiation of lithium-nickel-cobalt oxide cathode materials. Long-range and short-range orders have been investigated using XRD, Raman and FTIR spectroscopies. Different samples LixNi0.7Co0.3O2 (0.5≤x_≤1) were prepared by electrochemical lithium deintercalation from LixNi0.7Co0.3O2. Electrochemical extraction of lithium was carried out using Li/LiCIO4 in PC/LixNi0.7Co0.3O2 cells in the potentiometric method with potential step of 10 mV. During the first charge of the Li//LixNi0.7Co0.3O2 cell, the change in the cathode structure was followed by x-ray powder diffraction and vibrational spectroscopies at room temperature. A good correlation is found between XRD data and the local environment of the host lattice. Detailled analysis of vibrational spectra shows that the octahedral oxygen environment of Li+ ions remains stable in the investigated domain of concentration.

Neue Einsichten zur Stabilisierung des Hulsit-Strukturtyps am Beispiel von MnII,2MnIII(BO3)O2 und MnIISrMnIII(BO3)O3 / New Insights into the Stabilization of the Hulsite Structure During Crystal Structure Determination of MnII2MnIII(BO3)O2 and MnIISrMnIII(BO3)O2

The compounds MnII2MnIII(BO3)O2 (I) and MnIISrMnIII(BO3)O2 (II) were prepared by using a B2O3 flux technique. Single crystals were investigated by X-ray diffraction. I showed orthorhombic symmetry, space group D92h - Pbam (No. 55), a = 926.0; b = 1241.5; c = 304.96pm ; Z = 4 and II monoclinic symmetry, space group C12h - P2/m (No. 10), a = 1107.5; b = 311.04; c = 542.93 pm, β = 95,10(2)°; Z = 2. MnII2MnIII(BO3)O2 i is isotypic with the mineral Ludwigite while MnnIISrMnmIII(BO3)O2 is isostructural with the mineral Hulsite. In the structure of MnII2Mnlll(BO3)O2 (I) all metal point positions showed octahedral oxygen coordination, one point position is occupied by Mn3+ . The structure of Mnll2Sr2Mnlll2(BO3)2O4 (II) contains five octahedrally coordinated metal sites, three of them statistically occupied by Mn2+ or Mn 3+ and Sr2+. The incorperation of Sr2+ seems to be responsible for the Hulsite structure. Both structures contain isolated, trigonal planar BO3 units and oxygen atoms that are not coordinated to boron.

Synthese und röntgenographische Charakterisierung von zwei neuen Verbindungen des Ludwigit-Strukturtyps: Co5Sn(BO3)2O4 und Co5Mn(BO3 )2O4/Synthesis and X -Ray Characterization of Two New Compounds with Ludwigite-Structure: Co5Sn(BO3)2O4 and Co5Mn(BO3)2O4

The compounds Co5Sn(BO3)2O4 (I) and Co5Mn(BO3)2O4 (II) were prepared by using a B2O3 flux technique. Single crystals were investigated by X-ray diffraction and showed orthorhombic symmetry, space group D2h9-Pbam (No. 55), I a = 944.4; b = 1233.8; c = 310.5 pm; Z = 2 and II a = 925.07; b = 1241.67; c = 305.24 pm; Z = 2. Both compounds are isotypic to the mineral Ludwigite. All metal point positions show an octahedral oxygen coordination. Co2+ and M4+ (M = Sn or Mn) occupy one point position statistically. Both structures contain isolated, trigonal planar BO3 units and oxygen atoms that are not coordinated to boron.