Resolving the controversies about the ‘nearly cubic’ and other phases of Sr_1−xCa_xTiO₃(0≤x≤1): I. Room temperature structures

Abstract

Results of a powder x-ray diffraction study are presented to show that the so-called 'nearly cubic' phase region of Sr(1-x)Ca(x)TiO(3), in fact, corresponds to two different types of crystal structures. The 'nearly cubic' phase occurring in the composition range 0.35<x<0.41 is antiferroelectric in nature and its most plausible space group is Pbcm, while the crystal structure of the 'nearly cubic' phase for 0.41≤x<0.70 belongs to the space group Pbnm. This space group persists up to x = 1.0, even though the 'nearly cubic'-like features disappear for x≥0.70. There are two other phase boundaries which occur around 0.05<x<0.06 and 0.35<x<0.36 and correspond to the change of structures with space groups Pm3m to Ibmm and Ibmm to Pbcm, respectively.