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

Abstract

The relaxor ferroelectric K 0.5 Bi 0.5 TiO 3 has been synthesised in a solid-solution series with K 0.5 Bi 0.5 ZrO 3, as K 0.5 Bi 0.5 Ti 1-x Zr x O 3. 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). Variableerature 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 Ti 4+ cations remain off-centered with increasing Zr content, while Zr 4+ 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.