Search

The crystal structure of the new ternary phosphideTm5Pd9P7 was determined from powder X‐ray diffraction data: space group P6‾ , a=9.9971(2), c=3.94371(8) Å, RI=0.0518, Rp=0.0667, Rp=0.0667, wRp=0.1065. The crystal structure of the phosphide Tm5Pd9P7 is closely related with the Zr2Fe12P7‐type, and is formed by combination of two types of structural units with the compositions [TmPd6P3] and [TmTm3Pd3P3] mutually displaced by 1/2 along the c axis. Connection of the last units forms the trigonal prisms [Tm6] around P3 atoms in the crystallographic position 1a (0 0 0). The isotypic ternary phosphide Lu5Pd9P7 was synthesized (a=9.9934(7), c=3.9207(4) Å). The electronic and bonding properties of Tm5Pd9P7 are obtained from tight binding linear muffin‐tin orbital (TB‐LMTO) calculations and a crystal orbital Hamiltonian population (COHP) bonding analysis. These analyses show strong covalent bonding within (Pd9P7)15− nanotubes which are ionically bound via the Tm atoms to three dimensional network. [ABSTRACT FROM AUTHOR]

We explored under what conditions perovskite oxides ABO3 adopt a polar or an antiferrodistortive structure from the viewpoint of the tolerance factor τ and the orbital interactions of the empty orbitals of the A and B cations with the filled orbitals of their surrounding O2- ions. Polar structures require the presence of a substantial size-mismatch as well as strong cation-anion orbital interactions at A or B cation sites. A tetragonal polar structure is preferred when the A cation empty orbitals are extended or when the B-cation empty orbitals are contracted. A trigonal polar structure is favored in opposite cases. An antiferrodistortive structure is found for perovskites with weak size-mismatch or those with substantial size-mismatch if both A and B cations do not generate strong cation-anion orbital interactions. Antiferrodistortive structures result from interactions involving the A cations with the O4 squares of the face-sharing AO8 square-prisms in a two-in-two-out manner, and are found only when the A/O cation-anion interactions are substantial. [ABSTRACT FROM AUTHOR]

The new ternary intermetallic phase, BaPtCd2, was synthesized by solid-state reaction from direct combination of the elements in a stoichiometric mixture. The reaction was done at 850 °C for 15 h, followed by an equilibration at 600 °C for 4 d. The crystal structure was determined by X-ray diffraction method on a single crystal. BaPtCd2 is isotypic to MgCuAl2 and crystallizes in the orthorhombic space group Cmcm [ a = 4.467(2), b = 11.143(4), c = 8.240(3) Å, V = 410.2(3) Å3, and Z = 4]. Barium atoms are linked together forming zigzag chains. Cadmium atoms are bonded to each other forming six-membered rings of platinum centered boat and anti-boat conformations. BaPtCd2 contains 16 electrons per formula unit and belongs to the electron poorest compounds with MgCuAl2 type structure. Calculations based on the linear muffin-tin orbitals method in the atomic spheres approximation show that significant bonding states in BaPtCd2 are unoccupied. [ABSTRACT FROM AUTHOR]

The new ternary intermetallic phase, BaPtCd2, was synthesized by solid-state reaction from direct combination of the elements in a stoichiometric mixture. The reaction was done at 850 °C for 15 h, followed by an equilibration at 600 °C for 4 d. The crystal structure was determined by X-ray diffraction method on a single crystal. BaPtCd2 is isotypic to MgCuAl2 and crystallizes in the orthorhombic space group Cmcm [ a = 4.467(2), b = 11.143(4), c = 8.240(3) Å, V = 410.2(3) Å3, and Z = 4]. Barium atoms are linked together forming zigzag chains. Cadmium atoms are bonded to each other forming six-membered rings of platinum centered boat and anti-boat conformations. BaPtCd2 contains 16 electrons per formula unit and belongs to the electron poorest compounds with MgCuAl2 type structure. Calculations based on the linear muffin-tin orbitals method in the atomic spheres approximation show that significant bonding states in BaPtCd2 are unoccupied. [ABSTRACT FROM AUTHOR]

The dynamical properties of EuTiO3 are investigated to gain insight into its precursor effects analogous to those observed in many other perovskite oxides. In spite of the fact that a competition between the long wave length transverse optic mode and the zone boundary acoustic mode is absent, which makes the mode-mode coupling inessential, acoustic instabilities on limited spatial regions appear well above TS. This confirms the notion that dynamic forerunners are inherent and precede any phase transition in cubic perovskite oxides. [ABSTRACT FROM AUTHOR]

The dynamical properties of EuTiO3 are investigated to gain insight into its precursor effects analogous to those observed in many other perovskite oxides. In spite of the fact that a competition between the long wave length transverse optic mode and the zone boundary acoustic mode is absent, which makes the mode-mode coupling inessential, acoustic instabilities on limited spatial regions appear well above TS. This confirms the notion that dynamic forerunners are inherent and precede any phase transition in cubic perovskite oxides. [ABSTRACT FROM AUTHOR]

The new low valent iridiumindiumoxogallate Ir2In12Ga4O15 was prepared by heating intimate mixtures of Ir, In, In2O3, and Ga2O3 in a platinum crucible under an atmosphere of argon (1400 K, 70 h). The compound has an orange color. X-ray powder diffraction patterns can be indexed on the basis of a primitive orthorhombic unit cell with lattice parameters a = 1954.5(1) pm, b = 674.0(1) pm, and c = 745.9(1) pm. The crystal structure of Ir2In12Ga4O15 was solved from powder diffraction data and refined using the Rietveld method ( Pnn2, R(prof.) = 4.4 %, R(int.) = 2.5 %). Ir2In12Ga4O15 is according to [IrIn5In2/2]9+2[GaO4]5-2[Ga2O7]8- an ortho-gallate- pyro-gallate with chains of corner sharing [IrIn7]9+ polyhedra, [GaO4]5-2 tetrahedra, and [Ga2O7]8- double tetrahedra. The Ir-In distances within the IrIn7 polyhedra are shorter than in Ir-In intermetallic phases and lie between 256-261 pm. [ABSTRACT FROM AUTHOR]

The new low valent iridiumindiumoxogallate Ir2In12Ga4O15 was prepared by heating intimate mixtures of Ir, In, In2O3, and Ga2O3 in a platinum crucible under an atmosphere of argon (1400 K, 70 h). The compound has an orange color. X-ray powder diffraction patterns can be indexed on the basis of a primitive orthorhombic unit cell with lattice parameters a = 1954.5(1) pm, b = 674.0(1) pm, and c = 745.9(1) pm. The crystal structure of Ir2In12Ga4O15 was solved from powder diffraction data and refined using the Rietveld method ( Pnn2, R(prof.) = 4.4 %, R(int.) = 2.5 %). Ir2In12Ga4O15 is according to [IrIn5In2/2]9+2[GaO4]5-2[Ga2O7]8- an ortho-gallate- pyro-gallate with chains of corner sharing [IrIn7]9+ polyhedra, [GaO4]5-2 tetrahedra, and [Ga2O7]8- double tetrahedra. The Ir-In distances within the IrIn7 polyhedra are shorter than in Ir-In intermetallic phases and lie between 256-261 pm. [ABSTRACT FROM AUTHOR]

Orchid colored powder samples of Cs2AgF4 were prepared by a solid state reaction from CsF and AgF2. The diffuse reflectance spectrum of a powder sample of Cs2AgF4 was measured in the UV/Vis region. It shows three broad bands, two in the visible-light region at 650 nm, 500 nm and one in the UV region at 259 nm. The bands are assigned to F 2p → Ag 4d and Ag 4d → Ag 4d transitions. The optical band gap for Cs2AgF4 determined from the UV/Vis diffuse reflectance spectrum is approx. 2.17 eV. In order to interpret the observed absorptions, the theoretical absorption spectrum of Cs2AgF4 was obtained from density functional calculations. [ABSTRACT FROM AUTHOR]

Orchid colored powder samples of Cs2AgF4 were prepared by a solid state reaction from CsF and AgF2. The diffuse reflectance spectrum of a powder sample of Cs2AgF4 was measured in the UV/Vis region. It shows three broad bands, two in the visible-light region at 650 nm, 500 nm and one in the UV region at 259 nm. The bands are assigned to F 2p → Ag 4d and Ag 4d → Ag 4d transitions. The optical band gap for Cs2AgF4 determined from the UV/Vis diffuse reflectance spectrum is approx. 2.17 eV. In order to interpret the observed absorptions, the theoretical absorption spectrum of Cs2AgF4 was obtained from density functional calculations. [ABSTRACT FROM AUTHOR]

We explored under what conditions perovskite oxides ABO3 adopt a polar or an antiferrodistortive structure from the viewpoint of the tolerance factor τ and the orbital interactions of the empty orbitals of the A and B cations with the filled orbitals of their surrounding O2- ions. Polar structures require the presence of a substantial size-mismatch as well as strong cation-anion orbital interactions at A or B cation sites. A tetragonal polar structure is preferred when the A cation empty orbitals are extended or when the B-cation empty orbitals are contracted. A trigonal polar structure is favored in opposite cases. An antiferrodistortive structure is found for perovskites with weak size-mismatch or those with substantial size-mismatch if both A and B cations do not generate strong cation-anion orbital interactions. Antiferrodistortive structures result from interactions involving the A cations with the O4 squares of the face-sharing AO8 square-prisms in a two-in-two-out manner, and are found only when the A/O cation-anion interactions are substantial. [ABSTRACT FROM AUTHOR]