Prediction of ground-state structures and order-disorder phase transitions in II-III spinel oxides: A combined cluster-expansion method and first-principles study

Ground-state structures of six II-III spinel oxides are predicted by combining the cluster expansion method and first principles calculations. The ground states of MgGa2O4 and MgIn2O4 are found to be inverse spinels with a tetragonal lattice, whereas those of MgAl2O4, ZnAl2O4, ZnGa2O4, and ZnIn2O4 are normal spinels with a cubic lattice. Order-disorder transition behaviors are examined using Monte Carlo simulations. The order-disorder transition to exchange octahedral and tetrahedral cations takes place as commonly accepted. In inverse spinels, a new kind of transition to exchange II and III cations in octahedral sites can be recognized, which has not been reported experimentally. Their transition temperatures are evaluated.