Influence of Nb5+ ions on phase transitions and polar disorder above TC in PbZrO3 studied by Raman spectroscopy

Micro-Raman light scattering experiments on PbZrO3 (PZO) single crystal doped with Nb5+ have been investigated. Special attention was paid to the paraelectric (PE) phase in which nominally forbidden first-order Raman spectra were detected at temperatures far above the phase transition T-C. Complex Raman spectra were observed in the vicinity of three structural phase transitions. These results mainly from the coexistence of phases with different symmetries in a wide temperature range below T-C. The Raman measurements have been compared with dielectric and optical observations and proved that polar nanoregions in a centrosymmetric lattice appear well above T-C. It was shown that doping ABO(3) perovskites with heterovalent ions like Nb5+ unbalances charge neutrality of the lattice and strongly extends the temperature range of polar regions. The investigations performed point out that in the PE matrix the interaction between electrons and lattice vibrations, as recently suggested for pure PZO, plays an important role.