Oxygen vacancy micrometric enrichment in high-performance lead-free piezoelectric ceramic (Bi0.5Na0.5)0.94Ba0.06TiO3: A synchrotron radiation study

A multiscale description of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT6) ceramic is presented. High piezoelectric and electromechanical parameters (d₃₃ = 167 pC/N, k_t = 48.6%) were experimentally determined. The ceramic’s crystal structure, after poling, was determined from synchrotron X-ray diffraction. The Rietveld analysis reveals a highly textured BNBT6 perovskite with R3c symmetry. μ-X ray fluorescence on both unpoled and poled ceramics provided evidence of micrometric inhomogeneities in the elemental fluorescence intensities. μ-X ray absorption near edge spectroscopy (μ-XANES) at Ti K-edge spectra present anomalous absorption intensities in some energy intervals. First-principles modeling and linear combination analysis of μ-XANES spectra suggest local variations in the structure of the oxygen octahedron around titanium. The integrated analysis of experiments points toward the existence of micrometric clusters with an enrichment of Bi-O vacancies, distributed randomly at distances of tens of microns. Mentioned microstructural characteristics are consistent with the experimentally determined high piezoelectric and electromechanical parameters.