Fano resonance and relaxor behavior in Pr doped SrTiO3: A Raman spectroscopic investigation

Highlights: • The electric dipoles remains present well above the characteristic relaxor temperatures. • The local octahedral tilt angle modulates around 505K allowing growth of Polar nano regions (PNRs). • It is shown that the paraelectric to relax or ferroelectric phase transition in this compound is random polarizability instability driven phenomenon which has been correlated with the local octahedral tilt angle. The phenomenon of relaxor ferroelectrics is studied through detailed Raman spectroscopy on polycrystalline Sr_1-xPr_xTiO₃ (x = 0.01–0.17) samples. The polar mode was observed up to very high temperature ~1000 K indicating presence of dipoles well above the characteristic relaxor temperatures and they develop a short range correlation at 505 K leading to formation of PNRs. Below 505 K, the TO₂ polar mode anomalously soften along with Fano resonance and changes in the octahedral tilt angle. This establishes growth of local polar order associated with local structural phase transition at T ~505 K. The local TiO₆ octahedral tilt scales with the intensity of the polar mode and hence can be used as an order parameter for relaxor transition. It is shown that the paraelectric to relaxor ferroelectric phase transition in this compound is random polarizability instability driven phenomenon which has been correlated with the local octahedral tilt angle.