The effect of local ordering on the structure phase transition in disordered KTa1/2Nb1/2O3 from first principles studies

First principles density functional theory (DFT) was applied to investigate the effect of B site cations ordering on the structure phase transition in disordered KTa1/2Nb1/2O3 (KTN) solid solution. Several 20- and 40-atom ordered supercells with composition KTN have been studied. The calculated results are in good agreement with the available experimental and theoretical data. The stable ferroelectric and antiferroelectric states are observed in the relaxed ordered KTN supercells, which are caused by the off-center displacements of B site cations. It is found that different chemical order of B site cations result in different phases in the ordered KTN cells. In conclusion, the local ordering of B site cations significantly influence the structure phase transition of disordered KTN.