High pressure Raman studies on ABO₃ perovskite type structure compound PbHfO₃ to 40 GPa: pressure-induced phase transitions

Abstract

Lead hafnate (PbHfO₃), an ABO₃ perovskite family antiferroelectric (AFE), has been investigated up to 40 GPa by high pressure Raman scattering in the diamond anvil cell. In the range 0 to 40 GPa three pressure-induced phase transitions are found to occur, near 2, 7 and 15 GPa, as revealed by changes in the Raman spectra features at the above pressures. At pressures above 20 GPa the Raman peaks become very weak and the background scattering becomes very strong. Optical observations under a microscope show that the color of the samples changes from colorless to deep orange by about 40 GPa. We believe that this is connected with the downward motion of the d-band of the transition metal ion. The possible role of the electronic structure in the pressure-induced phase transitions is discussed. The phase transitions are subtle, and optical observations of the domain patterns (AFE domains) indicate that the high pressure phases II and III and possibly also IV are all AFE. X-Ray diffraction studies on PbHfO₃ up to 52 GPa reported in the accompanying paper are in broad agreement with the high pressure Raman study.