Effect of hydrostatic pressure on the structural phase transitions in CH₃NH₃PbX₃(X = Cl, Br, I)

The dielectric properties and the effect of hydrostatic pressure on the successive phase transitions have been studied for single crystal CH3NH3PbX3 (X: Cl, Br, I). Anisotropic anomalies in dielectric constant at phase transitions are obtained. The pressure (p)-temperature (T) phase diagrams are shown for the three CH3NH3PbX3 crystals. The intermediate tetragonal phase of CH3NH3PbCl3 and the lower-temperature tetragonal phase (space group: P4/mmm) in CH3NH3PbBr3 become narrower as pressure increases and disappear at around 100 MPa. There appears a pressure-induced phase above about 360 MPa and 90 MPa in CH3NH3PbBr3 and CH3NH3PbI3, respectively. On the other hand, CH3NH3PbCl3 does not show a pressure-induced phase up to about 700 MPa and the p-T phase diagram is different from those of the Br- and I-salts. A common reduced p-T phase diagram is proposed for CH3NH3PbBr3 and CH3NH3PbI3 and discussed.