Relaxor behavior of K_0.5La_0.5Bi₂Ta₂O₉ ceramics

Potassium lanthanum bismuth tantalate (K_0.5La_0.5Bi₂Ta₂O₉), a new relaxor ferroelectric was synthesized via the solid-state reaction route. X-ray structural studies along with Rietveld refinement confirmed it to be an n = 2 member of the Aurivillius family of oxides and the refined lattice parameters are a = 5.512 (2) nm, b = 5.504 (2) nm and c = 25.072 (4) nm. The appearance of 1 / 2 {h 00} and 1 / 2 {h k 0} type superlattice reflections in the electron diffraction patterns reflected the presence of ordered polar regions. A broad dielectric peak associated with frequency dependent dielectric maximum temperature was observed. The value of the diffuseness parameter γ = 1.93, obtained from the fit of a modified Curie-Weiss law established the relaxor nature of the title compound. The dielectric relaxation obeyed the Vogel-Fulcher relation wherein E_a = 0.06 eV and T_{v f} = 396 K. The relaxor behavior was attributed to the local polar ordering on A-sites.