Noboru Kimizuka

Structures of LuFeO3(ZnO)m (m = 1, 4, 5 and 6)

The structures of the title compounds, iron lutetium zinc oxides, can be described as a close packing of O atoms, with Lu atoms in octahedral voids and Fe and Zn atoms in tetrahedral voids. Blocks constituting m+1 layers of Fe and/or Zn atoms along the c axis are alternately stacked with single layers of Lu along the c axis

Structure of Ga2O3(ZnO)6: a member of the homologous series Ga2O3(ZnO)m

The structure of Ga(2)O(3)(ZnO)(6) was determined using single-crystal X-ray diffraction techniques in the space group Cmcm. The metal ion sublattice resembles some of the Zn ions in the wurtzite ZnO structure. The oxygen ion sublattice in Ga(2)O(3)(ZnO)(6) also resembles some of the O ions in ZnO. Structural relationships between Ga(2)O(3)(ZnO)(6) and ZnO are discussed, illustrating the process for obtaining the centrosymmetric Ga(2)O(3)(ZnO)(6) structure from the noncentrosymmetric ZnO. Structures of phases in the homologous series Ga(2)O(3)(ZnO)(m) are predicted on the basis of the structural data for Ga(2)O(3)(ZnO)(6). The structures of even m are constructed by simply extending the structure units seen in Ga(2)O(3)(ZnO)(6), while those of odd m consist of structure units which are of different types from those used for even m.

Superspace description of the homologous series Ga2O3(ZnO)m

A unified description for the structures of the homologous series Ga(2)O(3)(ZnO)(m), gallium zinc oxide, is presented using the superspace formalism. The structures were treated as a compositely modulated structure consisting of two subsystems. One is constructed with metal ions and the other with O ions. The ideal model is given, in which the displacive modulations of ions are well described by the zigzag function with large amplitudes. Alternative settings are also proposed which are analogous to the so-called modular structures. The validity of the model has been confirmed by refinements for phases with m = 6 and m = 9 in the homologous series. A few complex phenomena in real structures are taken into account by modifying the ideal model.

Electrical, optical, and thermoelectric properties of Ga2O3(ZnO)9

The physical properties of the sintered sample of Ga2O3(ZnO)9, a member of the homologous series Ga2O3(ZnO)m and recently found to have new structures, were investigated. The material was found to be a new transparent conducting oxide, and is composed of relatively abundant and inexpensive elements compared to indium. The electrical conductivity of a sintered low 57% density sample, 13 S cm−1 as fired at 1723 K, could be varied by postheating in air or a reducing gas (H2 3% : Ar 97%) flow. The changes in conductivity were associated with the variations of absorbance in the visible light range, while the optical band gap, or the absorption edge, was almost unchanged. The thermoelectric properties showed n-type behavior. It was relatively easy to vary the thermoelectric properties through redox treatments, and reversibility was also observed. The maximum figure of merit Z reaches a value of close to 10−4 K−1 at 660 K for a sample with density of only 73%. The potential of Ga2O3(ZnO)9 as a thermoelectric material appears to be similar to or even greater than the related In2O3(ZnO)m system, and since Ga2O3(ZnO)9 has an advantage in the abundance of constituent elements, it is revealed to be a promising system for further investigations.

Orthorhombic InFe0.33Ti0.67O3.33

The title compound, indium iron titanium oxide, is closely related to InFeO 3 , having a hexagonal structure which consists of alternating layers of InO 6 octahedra and FeO 5 trigonal bipyramids. According to substitution of Ti 4+ for Fe 3+ , excess O atoms are introduced into the Fe-O trigonal lattice plane of InFeO 3 . The inplane arrangement of O atoms can be described as partial occupation on a honeycomb lattice, although large displacement parameters indicate local shifts of 0 atoms due to repulsive interactions between them.

Structure of (Ga2O3)2(ZnO)13 and a unified description of the homologous series (Ga2O3)2(ZnO)(2n + 1).

The structure of (Ga(2)O(3))(2)(ZnO)(13) has been determined by a single-crystal X-ray diffraction technique. In the monoclinic structure of the space group C2/m with cell parameters a = 19.66 (4), b = 3.2487 (5), c = 27.31 (2) Å, and β = 105.9 (1)°, a unit cell is constructed by combining the halves of the unit cell of Ga(2)O(3)(ZnO)(6) and Ga(2)O(3)(ZnO)(7) in the homologous series Ga(2)O(3)(ZnO)(m). The homologous series (Ga(2)O(3))(2)(ZnO)(2n + 1) is derived and a unified description for structures in the series is presented using the (3+1)-dimensional superspace formalism. The phases are treated as compositely modulated structures consisting of two subsystems. One is constructed by metal ions and another is by O ions. In the (3 + 1)-dimensional model, displacive modulations of ions are described by the asymmetric zigzag function with large amplitudes, which was replaced by a combination of the sawtooth function in refinements. Similarities and differences between the two homologous series (Ga(2)O(3))(2)(ZnO)(2n + 1) and Ga(2)O(3)(ZnO)(m) are clarified in (3 + 1)-dimensional superspace. The validity of the (3 + 1)-dimensional model is confirmed by the refinements of (Ga(2)O(3))(2)(ZnO)(13), while a few complex phenomena in the real structure are taken into account by modifying the model.