Structural and dielectric anomalies near the MPB region of Na0.5Bi0.5TiO3-SrTiO3 solid solution

摘要

In the present attempt, (1-x) NBT(Na0.5Bi0.5TiO3)-xST(SrTiO3) (x = 0.24-0.28) solid solutions are studied near the MPB region to investigate short-range structural and dielectric anomalies. X-ray diffraction study confirms the presence of MPB by the co-existence of rhombohedral (202), (122) and pseudocubic (002), (112) peaks at x = 0.25-0.26. For x = 0.24, the absence of pseudocubic peaks indicate the complete diffusion of cubic ST phase into the rhombohedral phase of pure NBT. RAMAN spectra exhibit the appearance of new vibrational modes at A and B sites by the splitting of bands in the NBT-ST at the MPB (x = 0.25-0.26), which are not detected for x < 0.25 and x > 0.26. This can be assigned to local ordering at the A-site cations (Bi/Na/Sr) and B-site TiO6 octahedral distortion, respectively. The high-temperature RAMAN spectra confirm the structural stability at up to 550 degrees C of all NBT-ST samples near the MPB. Dielectric transition temperature is shifted from 360 degrees C to 160 degrees C with ST and shows a single broad anomaly. The broadening of the dielectric peak with deviation from Curie-Weiss law proves the dielectric dispersion near the MPB region of NBT-ST. The MPB origin is the outcome of local imbalance due to chemical inhomogeneity at the A site and short-range disordering at the B site. This induces strain-charge disparity, which influences dielectric behavior.