THERMOPOWER ANALYSIS OF SUBSTITUTED NICKEL MANGANITE SPINELS

Information about the distribution of cations between tetrahedral (A) and octahedral (B) sites in the spinel structure of NiMn2O4 and some s ubstituted spinel phases are derived from thermopower measurements in connection with some ion distribution models. The cubic spinel NiMn2O4 is characterized by a high degree of inversion coupled with dispropor tionation of Mn(III) with formation of Mn(II) on tetrahedral and Mn(IV ) on octahedral sites. Spinels of the series LizNiMn2-zO4 show increas ed concentrations of Mn(IV) on the B-sites and the Mn(II) content on t he A-sites is reduced FeNiMnO4 is dominated by partial Fe octahedral s ite occupation connected with Mn disproportionation.