Evolutionary Algorithm-Based Crystal Structure Prediction of Cu_xZn_yO_z Ternary Oxides

Binary zinc(II) oxide (ZnO) and copper(II) oxide (CuO) are used in a number of applications, including optoelectronic and semiconductor applications. However, no crystal structures have been reported for ternary Cu-Zn-O oxides. In that context, we investigated the structural characteristics and thermodynamics of Cu_xZn_yO_z ternary oxides to map their experimental feasibility. We combined evolutionary crystal structure prediction and quantum chemical methods to investigate potential Cu_xZn_yO_z ternary oxides. The USPEX algorithm and density functional theory were used to screen over 4000 crystal structures with different stoichiometries. When comparing compositions with non-magnetic Cu^I ions, magnetic Cu^II ions, and mixed Cu^I-Cu^II compositions, the magnetic Cu₂Zn₂O₄ system is thermodynamically the most favorable. At ambient pressures, the thermodynamically most favorable ternary crystal structure is still 2.8 kJ/mol per atom higher in Gibbs free energy compared to experimentally known binary phases. The results suggest that thermodynamics of the hypothetical Cu_xZn_yO_z ternary oxides should also be evaluated at high pressures. The predicted ternary materials are indirect band gap semiconductors.