INVESTIGATIONS ON ELECTRONICALLY CONDUCTING OXIDE SYSTEMS .20. MGNIMNO4 AND PROPERTIES OF MGZNIMN2-ZO4 SPINELS

Substitution of magnesium(II) for manganese in the series MgzIINiIIMnzIVMn2-2zIIIO4 (0 less-than-or-equal-to z less-than-or-equal-to 1) yields spinels whose stability is increased in comparison with NiMn2O4 (z = 0). Below 730-degrees-C in air the latter compound is decomposed by oxidation, forming alpha-Mn2O3 and NiMnO3. MgNiMnO4 (Z = 1) is found to be stable on annealing at 450-degrees-C. The change in electrical conductivity in the series from sigma-20-degrees-c = 5 x 10(-4) OMEGA-1 cm-1 (E-sigma = 0.325 eV) for NiMn2O4 (Z = 0) to sigma-20-degrees-c = 5 x 10(-7) OMEGA-1 cm-1 (E-sigma = 0.392 eV) for MgNiMnO4 (z = 1) is discussed.