Reinvestigation of Pressure-Induced II–III Transitions in Ferroelectric Ca₂Sr(C₂H₅COO)₆ and Ca₂Pb(C₂H₅COO)₆

Abstract

The pressure induced ferroelectric II to ferroelectric III phase transitions in Ca₂Sr(C₂H₅COO)₆ (DSP) and Ca₂Pb(C₂H₅COO)₆ (DLP) crystals were reinvestigated by polarizing microscope observation and dielectric constant measurements. The phase transitions were observed without passing through the first order phase boundaries to avoid possible effects of strains. At room temperature transitions from optically uniaxial to biaxial states were found at 0.68±0.10 GPa in DSP and 0.60±0.10 GPa in DLP. Dielectric constant measurements indicated that the transition in DLP corresponds to the II–III transition while that in DSP to a new pressure induced phase of IV. The results indicate that phase III in DLP is not isostructural with phase II in contrast to early expectation.