Shifting and tilting towards enhanced piezoelectricity in high-temperature ceramics: an average structure study of (1 − x)BiFe2/8Ti3/8Mg3/8O3–xPbTiO3 through X-ray and neutron diffraction

A comprehensive report is provided of the average structure of a high Curie temperature ferroelectric ceramic, (1 − x )BiFe 2/8 Ti 3/8 Mg 3/8 O 3 – x PbTiO 3 (BFTM– x PT) when x = 0.25–0.375 at room temperature. Both neutron and synchrotron X-ray powder diffraction data were collected and combined Rietveld refinements were completed. These data revealed that, of the compositions studied, BFTM– x PT crystallizes as mixed phase material. At x = 0.25–0.275, the average structure of each phase is best described by space groups R 3 c and Cc . At 0.30 ≥ x ≥ 0.35, a morphotropic phase boundary is present and is best modelled by space groups P 4 mm and Cc , where space group Cc is the dominant phase. As the concentration of PbTiO 3 increases, the amount of octahedral tilting decreases and x = 0.375 exhibits a loss of octahedral tilting and crystallizes in space groups P 4 mm and Cm . An updated phase diagram at room temperature of this novel system is given and structural intricacies responsible for its piezoelectric properties are revealed.