Phase transitions in A-site substituted perovskite compounds: The (Ca1–2xNaxLax)TiO3 (0⩽x⩽0.5) solid solution

The (Ca1–2xNaxLax)TiO3 (image) A-site substituted perovskite compounds have been synthesized and characterized by XRD and Raman spectroscopy at room temperature. The XRD powder diffraction study suggests that the end-member Na1/2La1/2TiO3 crystallizes in the tetragonal space group I4/mcm. The phase transition from Pbnm to I4/mcm is located between image and image and is driven by the variation of ionic radii at the A-site. The observed Raman modes are in agreement with group theory analysis, and the relationships between the behavior of structural parameters (e.g. Ti–O–Ti bond angle), indicated by long-range order, and the corresponding Raman frequency shifts and intensity evolution, indicated by short-range order, are established and discussed in terms of the radius effect and the mass effect.