Effects of oxygen content and heating rate on phase transition behavior in Bi2(V0.95Ti0.05)O5.475−x

Abstract The phase transition behavior of oxide-ion conductor Bi 2 (V 0.95 Ti 0.05 )O 5.475− x , which has various thermal histories and sample forms, has been studied by means of differential scanning calorimetry. Thermogravimetric analysis revealed that the oxygen content per compositional formula varied with the applied thermal treatment, although no significant structural difference was observed by X-ray diffraction (XRD) analysis. The phase transition behavior from α f to β f and from β f to γ f , observed at a heating rate of 10 K min −1 , are markedly affected by the sample preparation. For example, the endothermic peak of the transition from α f to β f appeared at around 400 °C for quenched powder and at around 320 °C for powder cooled at 0.5 K min −1 . The trend of the transition temperatures can be qualitatively explained in terms of oxygen content, i.e. , Bi 2 (V 0.95 Ti 0.05 )O 5.475− x with less oxygen content exhibits the transition from α f to β f at a higher temperature and the transition from β f to γ f at a lower temperature. We confirmed the two types of transition behavior from α f to β f depending on heating rate of DSC and high-temperature X-ray diffraction (HT-XRD) analysis. At rapid heating rates of 10 and 40 K min −1 , α f transformed to β f directly. Meanwhile, at a slow heating rate of 2 K min −1 , the β f precipitated from α f because slow heating allowed the diffusion of Ti and oxygen vacancies induced by the aliovalent doping. This suggests that the small differences of atomic arrangement also affect the phase transition behavior because additional elements have preferable crystallographic sites in α f and β f .