Phase transformations in La_2-xY_xMo₂O₉ (x = 0.05, x = 0.075): Temperature cycling and DRT analysis

Two members of ceramic samples of the so-called LAMOX family oxygen ionic conductors La_2-xY_xMo₂O₉ (x = 0.05, x = 0.075) were investigated by means of broadband impedance spectroscopy. It was found that the compound with x = 0.05 is characterized not only by a typical jump of ionic conductivity at the temperature of α ↔ β phase transition (for LAMOX at around 800–830 K), but also by an anomalous fall in the range from 740 to 760 K. The analysis of impedance and XRD data showed that the later anomaly is related to the phase transition from metastable β^′ to α phase. Formalism of the distribution of relaxation times (DRT) was used to examine these anomalies. In the vicinity of α ↔ β the DRT function consisted of two clearly separable peaks, indicating the coexistence of α and β phases. In specific cases of β^′ → α and β → β^′ transitions, only one DRT peak, which broadens at the temperatures of transition, was observed.