STUDY BY THERMOGRAVIMETRY, ELECTRICAL-CONDUCTIVITY AND IR SPECTROMETRY OF THE PHASE-TRANSITION FOR MANGANESE CATION DEFICIENT SPINELS

Thermogravimetry, electrical conductivity and IR spectrometry were used to study the crystal structure change of the metastable manganese cation deficient spinels that occur during the oxidation of manganese ions above 500 degree C. The kinetics of the transformation is governed by a nucleation growth mechanism with an activation energy varying with the amount of Mn**3** plus ions. The nature of the inversion products depends on the manganese substitution extent. For a substitution extent x less than 0. 72 a phase with a corundum structure which is a solid solution of alpha -(MnFe)(//2O//3 and for x greater than 0. 72 a mixture of two phases alpha -(MnFe)//2O//3 plus Mn//2O//3 of orthorhombic structure.