CeAlO3 and Ce1−xRxAlO3 (R=La, Nd) solid solutions: Crystal structure, thermal expansion and phase transitions

The crystal structures of CeAlO3 and the solid solutions Ce1−xRxAlO3 (R=La, Nd), and their thermal behaviour in a wide temperature range of 12−1200 K have been precisely determined by means of in situ high-resolution X-ray powder diffraction technique applying synchrotron radiation, thermal analysis and magnetic measurements. The unique sequence of the reversible phase transitions I4/mcm↔Imma↔R3¯c↔Pm3¯m has been detected in CeAlO3 and solid solutions formed in the pseudo-binary system CeAlO3–LaAlO3. In the Ce1−xNdxAlO3 system, the samples with x=0.3 and 0.5 compositions undergo three phase transformations I2/m↔Imma↔R3¯c↔Pm3¯m, whereas for the Ce-rich sample Ce0.9Nd0.1AlO3 four successive transitions are observed: I4/mcm↔I2/m↔Imma↔R3¯c↔Pm3¯m. Crystal structure parameters of all structural polymorphs of CeAlO3 and solid solutions based on them as well as their thermal evolution are reported. Based on in situ powder diffraction and DTA/DSC data, the phase diagrams of the pseudo-binary systems CeAlO3–LaAlO3 and CeAlO3–NdAlO3 are constructed together with a combined phase diagram, where the transition temperatures are presented as a function of the average radius of rare-earth cations.