Solid-phase equilibria in the system NiOMn2O3O2

Abstract A complete phase diagram is presented for the system NiOMn2O3O2 showing the phases which can exist in the air or pure oxygen at temperatures between 600 and 1200°C. Six phases are observed: rock-salt phase Ni1−sMns O ≤ s ≤ 0·025), an ordered rock-salt phase Ni6MnO8, an ilmenite phase Ni2−pMnpO3 (1 ≤ p ≤ 1·06), a cubic spinel phase Ni3−yMnyO4 (1·725 ≤ y ≤ 3·000), a tetragonal spinel phase Ni3−yMnyO4 (2·895 ≤ y ≤ 3·000) and a C-rare-earth-oxide or α-Mn2O3 phase Mn2−zNizO3 (O ≤ z ≤ 0·230). Argument is drawn to show that all the phases except the simple rock-salt probably contain manganese in the +4 oxidation state.