Long- and short-range structure studies of KBT-KBZ solid-solutions using synchrotron radiation

Abstract

The relaxor ferroelectric K_0.5Bi_0.5TiO₃ has been synthesised in a solid-solution series with K_0.5Bi_0.5ZrO₃, as K_0.5Bi_0.5Ti_1−xZr_xO₃. High-resolution synchrotron X-ray powder diffraction and X-ray absorption near edge structure spectroscopy were used to characterise the long-range average and local structural behaviour. Rietveld refinements against diffraction data show that a pseudocubic tetragonal region exists across the whole solid-solution series, with truly cubic symmetry only observed at x = 1 (pure KBZ). Variable-temperature diffraction data for x = 0 (pure KBT) showed a broad ferroelectric transition from tetragonal to cubic symmetry at approximately 683 K with a coexistence of both phases close to that temperature, accompanied by a marked volume contraction. Ti K-edge data showed that Zr doping has a minimal effect on Ti off-centering, and revealed no evidence for local clustering. Metal L-edges showed that Ti⁴⁺ cations remain off-centered with increasing Zr content, while Zr⁴⁺ cations approach a higher-symmetry coordination environment, most likely due to the increased size of the Zr atoms. Although there is a minimal effect on actual Ti-offsets, an effective dilution of these environments by Zr doping leads to a reduction in polar domains and a diminished ferroelectric response.