Role of dynamic polar nanoregions in heterovalent perovskite relaxor: Inelastic light scattering study of ferroelectric Ti rich Pb(Zn1/3Nb2/3)O3-PbTiO3

Abstract

The role of dynamic polar nanoregions (PNRs) of (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-100xPT) single crystals with the PT content x = 0.15 (i.e., higher than above the morphotropic phase boundary composition x ∼ 0.09) has been investigated using inelastic light scattering. The remarkable anomaly of the longitudinal acoustic mode is clearly observed in the vicinity of the cubic-tetragonal phase transition temperature at the TC-T = 481 K. A broad central peak (CP) appears below the Burns temperature TB ∼ 700 K. Upon cooling, the relaxation time determined from the CP width clearly shows a critical slowing down when approaching TC-T in contrast with the suppressed slowing down previously observed in PZN-7PT [S. Tsukada and S. Kojima, Phys. Rev. B 78, 144106 (2008)]. These facts are due to the existence of dynamic PNRs and the disappearance of chemically ordered regions resulting from a higher PT content in the solid solution. In the cubic phase, the local symmetry breaking caused by the PNRs was observed by Raman scattering. The initial size of dynamic PNRs is about 3 nm just below TB, and it increases significantly upon cooling below the intermediate temperature T* ∼ 600 K, reaching 10 nm down to TC-T.