ORDER-DISORDER TRANSITION OF OXYGEN VACANCY IN THE BROWNMILLERITE SYSTEM

Order-disorder transition temperature (T-d) of the system (Ba1-xSrx)(2 )In2O5 and Ba-2(In1-xGax)(2)O-5 was investigated by means of electrica l conductivity measurements and dilatometry. It was found that the sub stitution of Sr2+ for Ba2+ increased the T-d, and the substitution of Ga3+ for In3+ decreased the T-d, at which the increasing rate of the e lectrical conductivity decreased. A tolerance factor, which has been u sed for the perovskite-type structure, was applied for the present bro wnmillerite systems, in order to understand the T-d shift. As the tole rance factor approached 1, the T-d decreased linearly. (C) 1998 Elsevi er Science B.V. All rights reserved.