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

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posted on 19.04.2005 by Zhaofei Li, Junliang Sun, Liping You, Huan Jiao, Guobao Li, Xiping Jing, Fuhui Liao, Jianhua Lin
The phase relationships of the In2O3−TiO2−CaO and In2O3−TiO2−SrO systems have been studied at 1350 °C in air. The In2O3−TiO2−CaO system contains a ternary compound Ti6In6CaO22 crystallizing in an incommensurate structure. The In2O3−TiO2−SrO system, on the other hand, is a simple ternary phase diagram without any ternary phases. The structure of Ti6In6CaO22 can be expressed by an incommensurate composite model that consists of two subsystems:  the first subsystem, containing the InO6 octahedral layer and the Ti atoms in the TiOx layer, is rather rigid and can be reasonably represented with the averaged structure within the main lattice, a = 5.951(1) Å, b1 = 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 TiOx layer, can be expressed with a smaller subcell, a = 5.951(1) Å, b2 = 2.464(1) Å, c = 6.352(1) Å, and β = 108.32(1)°. The overall structure was refined in the superspace group C2/m(0β0)s0, β = q/b* = 0.389(1) by using the program, JANA2000. The modulation of the structure is prominent in the second subsystem. Ti6In6CaO22 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.

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