The structural properties of Bi_0.75Pr_0.25O_1.5 have been investigated by powder X-ray and neutron diffraction as a function of temperature up to around 800 °C. A layered rhombohedral structure is confirmed throughout the temperature range studied, with an order-disorder type phase transition (β₂ ↔ β₁) at ca. 730 °C. This transition is accompanied by partial migration of the oxide ions from the fluorite-like blocks of the layered structure to interstitial sites in the van der Waals gap between blocks. A reversible step change in total conductivity, associated with the phase transition, is preceded by non-linear behaviour observed in the Arrhenius plot of total conductivity at lower temperatures. A theoretical model based on a modification of the “cube-root” model successfully describes the conductivity data through the phase transition, showing the transition to involve a jump in inter-planar conductivity correlated with the appearance of interstitial oxide ions in the van der Waals gap. While the “cube root” model has been successfully used to explain phase transitions in classic 3-dimensional ionic conductors, the present study represents the first example of application of this model to a lower dimensional system.

通过粉末X射线和中子衍射研究了Bi _0.75 Pr _0.25 O _1.5的结构性质随温度的变化，最高温度约为800°C。在整个研究的温度范围内的层状菱形结构被确认，与有序-无序型相转变（β ₂ ↔β ₁）在 730℃。这种转变伴随着氧化物离子从层状结构的萤石状块的部分迁移到块之间范德华间隙中的间隙位置。总电导率可逆的阶跃变化（与相变相关）是在较低温度下在总电导率的阿伦尼乌斯图中观察到的非线性行为。基于“立方根”模型的修改的理论模型成功地描述了通过相变的电导率数据，显示了涉及平面内电导率跃迁的跃迁，该跃迁与范德华兹中的间隙氧化物离子的出现有关间隙。尽管“立方根”模型已成功用于解释经典3维离子导体中的相变，