Combining effects of TiO ₆ octahedron rotations and random electric fields on structural and properties in Na _0.5 Bi _0.5 TiO ₃

Abstract

Abstract The structural and dielectric properties of Na 0.5 Bi 0.5 TiO 3 (NBT) ceramics and crystals have been investigated and are compared to that of Pb(Zr 0.55 Ti 0.45 )O 3 (PZT55/45) and Pb(Mg 1/3 Nb 2/3 ) 0.72 Ti 0.28 O 3 (PMNT 72/28) ceramics. X‐ray diffraction (XRD) profiles for (100), (110), (111), (200), (220), and (222) (referred to cubic structure) reveal that the monoclinic structure with C c space group exists both in the NBT single crystal and ceramics. The diffraction profile obtained with high resolution laboratory XRD for the NBT single crystal can be well described, using C c model instead of R 3c model. The dielectric constant of NBT below T hump shows some similarity to that of PZT45/55 ceramics below 50°C in which oxygen octahedron rotations cause the frequency dispersion of the dielectric constant. The temperature‐dependent dielectric constant for NBT can be deconvolved into two independent processes. The lower temperature process shows a typical relaxor characteristic and follows the Vogel‐Fulcher relationship. The other process at higher temperature shows less frequency‐dependent behavior. Comparing the dielectric constant of NBT with that of PZT55/45 and PMNT72/28 reveals that both oxygen octahedral rotations and random electric fields play an important role in the frequency dispersion of the dielectric constant for NBT relaxor feroelectric.