A combined X-ray diffraction and Raman scattering study of the phase transitions in Sr1−xCaxTiO3 (x=0.04, 0.06, and 0.12)

Results of powder X-ray diffraction and Raman scattering studies on the phase transitions in Sr1−xCaxTiO3 (SCT) are presented for image, 0.06 and 0.12 in the temperature range 8–473 K. It is proposed that the space group of SCT in the composition range image is image with image tilt system and not image with image tilt system, as assumed by earlier workers. The lowering of the crystal symmetry from image to image is supported by the observation of additional Raman lines, in agreement with the factor group analysis for the image space group. The structural Eg mode, characteristics of the non-cubic phase, is shown to be present even in the cubic phases of image and image but not of image indicating the change in the local structure of the cubic phase of SCT for image. The presence of symmetry forbidden TO2 mode in the Raman spectra of the cubic phase of SCT for image and its absence for image provides yet another characteristic feature distinguishing the image and image space groups. The implications of the change in the tilt system from image to image on the development of the polar order is also discussed.