High pressure Raman spectroscopic studies of the relaxor ferroelectric 0.85Pb(Zn1/3Nb2/3)O3-0.15PbTiO3

In situ Raman spectroscopic measurements have been carried out at high pressure up to 33 GPa using a diamond anvil cell to investigate the structural transitions in relaxor ferroelectric 0.85Pb(Zn1/3Nb2/3)O3-0.15PbTiO3. Raman modes are found to be broad due to substitutional disorder at the B-site of the perovskite. Evolution of spectra with pressure gives evidence for structural instabilities around 2.2, 6.3, and 14.6 GPa. New modes at 343 and 376 cm−1 appear across the transition at 6.3 GPa, characteristic of the high pressure antiferrodistortive rhombohedral phase (PII). The pressure dependence of mode frequency, width of the Raman bands, and integrated intensity of structurally sensitive A1(TO) mode at 272 cm−1 are obtained; their effect on polar ordering and structural transitions are discussed. The disappearance of the mode around 200 cm−1 and the appearance of a new one around 120 cm−1 are evident around 14.6 GPa, and these are attributed to a possible new phase PIII. The reported pressure-induced suppression of diffuse x-ray scattering on Pb-based relaxors is consistent with the observed Raman features.