PREPARATION AND ELECTRICAL-PROPERTIES OF MONOPHASE CUBIC SPINEL, MN1.5CO0.95NI0.55O4, DERIVED FROM ROCK-SALT TYPE OXIDE

The purpose of this study was to prepare a sintered body consisting of monophase cubic spinel type oxide, Mn1.5Co0.95Ni0.55O4, and to evalua te its electrical properties. It was found that cooling from 1400 to 1 000 degrees C in nitrogen did not affect the preservation of the sinte red rock salt type oxide formed at 1400 degrees C. A crack free sinter ed body of monophase cubic spinel may be obtained by heat treatment at 1000 degrees C in air, using a specimen cooled from 1400 degrees C at a rate of 500 degrees C min(-1). A heat treatment time in air at 1000 degrees C of more than 48 h was required to convert the rock salt typ e structure into a perfect cubic spinel structure. The electrical cond uctivity, sigma, of the sintered cubic spinel oxide synthesized in thi s work was found to be stable at 100 and 200 degrees C in air and at 1 00, 200 and 300 degrees C in nitrogen. The sintered spinel oxide was a p-type semiconductor, based on small polaron hopping conduction. The intrinsic hole concentration, n, was estimated to be constant, with a value of 1.6-1.8 x 10(28) m(-3). The mobility, mu, increased exponenti ally with increasing annealing temperature in both atmospheres, sugges ting that the change in sigma is dependent on mu.