Phase relations in the pseudo ternary system In2O3-TiO2-BO (B: Zn, Co and Ni) at 1200 °C in air

Phase relations in the pseudo ternary systems In₂O₃-TiO₂-ZnO, In₂O₃-TiO₂-CoO and In₂O₃-TiO₂-NiO at 1200 °C in air were determined by means of a classic quenching method. In₆Ti₆BO₂₂ (B: Zn, Co and Ni) which has the monoclinic In(Fe_1/4Ti_3/4)O_27/8-type of structure with a 4-dimensional super space group exists in a stable form. There exist homologous phases In_1+x(Ti_1/2Zn_1/2)_1−xO₃(ZnO)_m (m: natural number, 0<x ≤ 1) having the InGaO₃(ZnO)_m-type of the layered crystal structures such as In_1+x(Ti_1/2Zn_1/2)_1−xO₃(ZnO) (0.12 ≤ x ≤ 0.29), In_1+x(Ti_1/2Zn_1/2)_1−x(ZnO)₂ (0.12 ≤ x ≤ 0.50), In_1+x(Ti_1/2Zn_1/2)_1−xO₃(ZnO)₃ (0.15 ≤ x ≤ 0.84), In_1+x(Ti_1/2Zn_1/2)_1−x(ZnO)₄ (0.15 ≤ x ≤ 1), In_1+x(Ti_1/2Zn_1/2)_1−xO₃(ZnO)₅ (0.15 ≤ x ≤ 1), In_1+x(Ti_1/2Zn_1/2)_1−x(ZnO)₆ (0.15 ≤ x ≤ 1), In_1+x(Ti_1/2Zn_1/2)_1−xO₃(ZnO)₇ (0.15 ≤ x ≤ 1), In_1+x(Ti_1/2Zn_1/2)_1−x(ZnO)₈ (?<x ≤ 1), In_1+x(Ti_1/2Zn_1/2)_1−xO₃(ZnO)₉ (0.15 ≤ x ≤ 1), In_1+x(Ti_1/2Zn_1/2)_1−x(ZnO)₁₀ (?<x ≤ 1), and In_1+x(Ti_1/2Zn_1/2)_1−xO₃(ZnO)₁₁ (0.15 ≤ x ≤ 1)… without an upper limit of m in the pseudo ternary system In₂O₃-TiO₂-ZnO. All the ions are on the trigonal lattice points, the In(III) is in the octahedral coordination with the oxygen and the {In_x(Ti_1/2Zn_1/2)_1−xZn_m} is in the trigonalbipyramidal coordination with oxygen in the crystal structures of each homologous compound. They have R3¯m (No. 166) for m = odd or P63/mmc (No. 194) for m = even in space group. Lattice constants for each of the homologous compounds as a hexagonal setting and In₆Ti₆BO₂₂ as the monoclinic system were determined by means of the powder X-ray diffraction method at room temperature. The temperature dependence of resistivity for In_1+x(Ti_1/2Zn_1/2)_1−x(ZnO)₄ (0.15 ≤ x ≤ 1) showed semiconducting-like behavior for all samples examined at T(K) = 2–300. The resistivity increased systematically with decreasing x (0.7 ≤ x ≤ 1), and it was found that samples where x ≤ 0.7 became insulators. The optical band gap E_g (eV) of In_1+x(Ti_1/2Zn_1/2)_1−x(ZnO)₄ has been estimated from the diffuse reflection spectra for the whole range of x (0.15 ≤ x ≤ 1). A minimum value of 2.0717 eV for x = 1 and a maximum one of 3.066 eV for x = 0.15 were observed. Dependence of the crystal structures of the InAO₃(BO), In(Ti_1/2B_1/2)O₃(B′O) and stability of In₆Ti₆BO₂₂ upon the constituent cations in the pseudo quaternary system In₂O₃-TiO₂-A₂O₃-BO (A: Fe, Ga and Cr; B, B′: Mg, Zn, Co, Ni, Ca and Sr) were discussed in terms of their ionic radii and site preference effects.