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Abstract

Phase ordering in the mixed-valence oxide Sb2O4 has been examined by density functional theory (DFT) calculations. We find that the ground-state total energies of the two phases (alpha and beta) are almost degenerate and are highly sensitive to the choice of the approximation to the exchange correlation (xc) functional used in our calculations. Interestingly, with the inclusion of the zero-point energy corrections, the a phase is predicted to be the ground state polymorph for most xc functionals used. We also illustrate the pronounced stereochemical activity of Sb in these polymorphs of Sb2O4, setting an exception to the Keve and Skapski rule. Here, we find that the actual bonding in the alpha phase is more asymmetric, while the anomalous stability of the beta phase could be rationalized from kinetic considerations. We find a non-negligible activation barrier for this alpha, beta phase transition, and the presence of a saddle point (beta phase) supports the separation of Sh(III) over a continuous phase transition, as observed in experiments.