Novel cubic-phase pyrochlore Sb(III)(2)Sn(IV)(2)O-7 transformed from Sn(II)(2)Sb(V)(2)O-7: First-principles calculation-based prediction and experimental evidence

摘要

The performance of semiconductors highly depends on their crystal structures, and most semiconductors have more than one kind of crystal structure. In our previous work, Sn(II)(2)Sb(V)(2)O-7 with cubic-phase pyrochlore A(2)B(2)O(7) structure was successfully prepared by an ion-exchange process. However, in many other cubic-phase pyrochlore A(2)B(2)O(7) semiconductors, A(3+)/B4+ was another possible combination. In this work, a novel structure of cubic-phase pyrochlore A(2)B(2)O(7) antimony tin oxide, Sb(III)(2)Sn(IV)(2)O-7, was successfully predicted by first-principles calculations, which were started from the chemical compositions of Sn2Sb2O7. The structures and electronic properties of Sn(II)(2)Sb(V)(2)O-7 and Sb(III)(2)Sn(IV)(2)O-7 were then analyzed by combining first-principles calculations with particle swarm optimization algorithm and Bader charge analysis. It was indicated that compared with cubic-phase pyrochlore tin antimonate Sn(II)(2)Sb(V)(2)O-7, cubic-phase pyrochlore antimony stannate Sb(III)(2)Sn(IV)(2)O-7 was more stable due to the lower total energy, thus predicting the possible structural transformation from metastable Sn(II)(2)Sb(V)(2)O-7 to Sb(III)(2)Sn(IV)(2)O-7. Furthermore, delta-sol calculations showed that the band gap of Sb(III)(2)Sn(IV)(2)O-7 was larger than that of Sn(II)(2)Sb(V)(2)O-7. The above results of theoretical calculations were validated by the successful preparation of the predicted Sb(III)(2)Sn(IV)(2)O-7 via annealing treatment on Sn(II)(2)Sb(V)(2)O-7, and by the instrumental characterizations (X-ray diffraction patterns, X-ray photoelectron spectra, and UV-Vis spectra) on the two structures. (C) 2016 Elsevier Ltd. All rights reserved.