Effect of Hydrostatic Pressure on the Phase Transitions in Monoclinic and Tetragonal RbD2PO4Crystals

The effect of hydrostatic pressure was studied for the phase transitions in the two forms of RbD 2 PO 4 ; monoclinic (ferrielectric) and tetragonal (ferroelectric) crystals. In monoclinic crystal, the I-II and II-III transition temperatures mono-tonically decrease with increasing pressure, and the phase boundaries are represented by a quadric form of T c = T 0 c + K p +γ p 2 with the parameters of T 0 c , K , and γ being 102.5°C, -50 deg GPa -1 , -39 deg GPa -2 for the I-II transition and 41.8°C, -24 deg GPa -1 , -15 deg GPa -2 for the II-III transition, respectively. A pressure-induced phase of IV was newly observed above about 0.7 GPa. The transition to phase IV shows marked first order character. In tetragonal RbD 2 PO 4 , the ferroelectric Curie temperature monotonically decreases with increasing pressure with the initial slope of -47 deg GPa - 1 . The slope of the Curie temperature against pressure seems to decrease as pressure increases above about 0.3 GPa.