Anomalous dispersion X-ray diffraction study of Pb/Bi ordering/disordering states in PbTiO₃-based perovskite oxides

Synchrotron radiation-based anomalous dispersion X-ray powder diffraction (ADSPD) was carried out to reveal the Pb/Bi ordering/disordering states in a series of PbTiO₃-based negative thermal expansion materials (1 - x)PbTiO₃ - xBiFeO₃ (x = 0.1, 0.3, 0.5) and (1 - x)PbTiO₃ - xBi(Zn_1/2Ti_1/2)O₃ (x = 0.1, 0.2, 0.3). It gives strong evidence of the disordered Pb/Bi distributions in these compositions, which is consistent with electron diffraction studies. Combined with binding energy calculation, we show that the disordered nature of Pb/Bi distributions is likely to be attributed to the similar electron configurations of Pb²⁺ and Bi³⁺ as well as their comparable coordinate environments in perovskite structures. The results of this study may be helpful to better understand the structure-property relationship in Pb/Bi-containing perovskites and are useful for further developing underlying physics in relevant materials.