Vapor pressure and thermodynamic properties of MgIn₂O₄

Abstract

The vapor pressure of pure indium, and the sum of the pressures of (In) and (In₂O) species over the condensed phase mixture {In} + 〈MgIn₂O₄〉 + 〈MgO〉, have been measured by the Knudsen effusion technique in the temperature range 1095–1350 K. The materials under study were contained in a zirconia crucible, which had a Knudsen orifice along the vertical wall. The major vapor species over the condensed phase mixture were identified as (In) and (In₂O) using a mass-spectrometer. The vapor pressure of (In₂O) corresponding to the reaction, 4 {In} +(MgIn₂O₄)→(MgO)+3(In₂O) was deduced from the experimental results; log p=−13.600⁄T+7.62(±0.03) atm The standard free energy of formation of the inverse spinel 〈MgIn₂O₄〉 from its component oxides, is given by, (Mgo)+(In₂O₃)→(MgIn₂O₄) δG°=−6190+0.06T (±400)cal The entropy of transformation of 〈In₂O₃〉 from the C rare-earth structure to the corundum structure is evaluated from the measured entropy of formation of (MgIn₂O₄) and a semi-empirical correlation for the entropy of formation of spinel phases from component oxides with rock-salt and corundum structures.