In situ Raman and electric modulus study of NBT-ST-KNN ceramics: An insight into temperature evolution of relaxor dynamics

Results obtained in this work concerning a well-established relaxor system, (0.8- x )(Na 0.5 Bi 0.5 )TiO 3 -0.2SrTiO 3 - x (K 0.5 Na 0.5 )NbO 3 ( x = 0.005, 0.01, 0.04 and 0.1) will definitely provide rich insights into the creation and thermal relaxation of the polar nanoregions (PNRs), the entities responsible for unique relaxor response. The major highlights of this paper are: • In-situ Raman and electric modulus studies to probe into the thermal response of PNRs. • Local structure changes from polar R3c + weakly polar P4bm (≈T F-R ) to P4bm (≥ T m ). • T F-R , T m and T B derived from Raman study show good agreement with dielectric result. • Shoulder response in M"(f) graph in addition to bulk peak depicts the presence of PNRs. • Non-Debye type of behavior in M"(f) interpreted in terms of stretched exponent β. Polar nanoregions (PNRs) are often argued to be the key factor in enhancing the functional properties of relaxor-based ferroelectrics. The creation and relaxation of these polar entities are believed to be strongly temperature-dependent, but the explanation is still unclear. In this investigation we have chosen a well-established relaxor system (0.8- x )(Na 0.5 Bi 0.5 )TiO 3 -0.2SrTiO 3 - x (K 0.5 Na 0.5 )NbO 3 ; ( x = 0.005, 0.01, 0.04 and 0.1) to probe into the thermal dynamics of PNRs using in-situ Raman and electric modulus formalism. The Raman spectra segregate into different temperature zones corresponding to ferroelectric-relaxor transition (T F-R ), maximum dielectric constant (T m ) and Burn’s temperature (T B ). A closer introspection of width and position of peak peaks around these temperatures depicts the existence of local structural heterogeneities. Further, the frequency-dependent electric modulus, M"(f) study demarcates high-frequency shoulder (related to PNR relaxation) from intermediate frequency peak corresponding to bulk response. Analysis of Z"(f) and M"(f) predict temperature evolution of long-range ordered regions to localized relaxations.