Phase Equilibrium of the In₂O₃−TiO₂−MO (M = Ca, Sr) Systems and the Structure of In₆Ti₆CaO₂₂

Abstract

The phase relationships of the In 2 O 3 −TiO 2 −CaO and In 2 O 3 −TiO 2 −SrO systems have been studied at 1350 °C in air. The In 2 O 3 −TiO 2 −CaO system contains a ternary compound Ti 6 In 6 CaO 22 crystallizing in an incommensurate structure. The In 2 O 3 −TiO 2 −SrO system, on the other hand, is a simple ternary phase diagram without any ternary phases. The structure of Ti 6 In 6 CaO 22 can be expressed by an incommensurate composite model that consists of two subsystems: the first subsystem, containing the InO 6 octahedral layer and the Ti atoms in the TiO x layer, is rather rigid and can be reasonably represented with the averaged structure within the main lattice, a = 5.951(1) Å, b 1 = 3.422(1) Å, c = 6.352(1) Å, and β = 108.32(1)°; the second subsystem, consisting of only the O2 atoms in the TiO x layer, can be expressed with a smaller subcell, a = 5.951(1) Å, b 2 = 2.464(1) Å, c = 6.352(1) Å, and β = 108.32(1)°. The overall structure was refined in the superspace group C 2/ m (0 β 0) s 0, β = q / b * = 0.389(1) by using the program, JANA2000. The modulation of the structure is prominent in the second subsystem. Ti 6 In 6 CaO 22 is a semiconductor with a band gap of about 3.5 eV and its electrical conductivity depends strongly on the oxygen partial pressure with the activation energy of about 1.88, 1.76, and 1.48 eV respectively in the air, oxygen, and argon atmosphere.