In situ Raman scattering studies of pressure-temperature phase diagrams in antiferroelectric xCaSnO₃-modified NaNbO₃ ceramics

As one of the classic antiferroelectrics, high complexity of a NaNbO₃ structure sequence attracts great attention in the ferroelectric physics field. Here, temperature-pressure phase diagrams as a function of a CaSnO₃ content for antiferroelectric (1-x)NaNbO₃-xCaSnO₃ ceramics have been improved by Raman spectroscopy. We clarify structural order of phase transitions on CaSnO₃-modified NaNbO₃ ceramics within the temperature range of 80-840 K by discussing the anomalies of lattice and phonon dynamics. The doping effect of CaSnO₃ on the P-R phase transition has been summarized from the decreased critical temperature from 660 to 580 K. The intermediate phase at 480 K was recognized as an incommensurate phase. In addition, the anomalous pressure with respect to phonon frequency at the stress field of 0-25 GPa also provides the evidence of structural transformations at 6.55 and 10.05 GPa. Upon increasing the CaSnO₃ content, phase transition moves to a lower pressure range. This work would provide the powerful supplement of phase transitions for the broad NaNbO₃-based crystalline family with Raman scattering.