Phase coexistence in Sr0.70Ca0.30TiO3 studied through electron diffraction

A detailed structural study employing electron diffraction in selected area (SAD) and convergent beam electron diffraction (CBED) modes, followed by Rietveld analysis of the powder X-ray diffraction (XRD) data, has been carried out to identify the correct space group and to investigate the possible phase coexistence in Sr0.70Ca0.30TiO3 (SCT30) ceramics. The occurrence of distinctly two types of wide-angle CBED patterns and the presence of mutually perpendicular A2 type GM-lines in the forbidden reflections do show the coexistence of Pnma phase and a new orthorhombic phase with space group P21212 in SCT30. The occurrence of P21212 orthorhombic phase in SCT30 appears to be a result of distortion in addition with the rigid tilt of BO6 octahedra. It so appears that the possibility of occurrence of P21212 for distorted perovskite structures is yet to be theoretically investigated.

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