The influences of compressive stress on the dielectric and ferroelectric properties of Fe3+/Nb5+ hybrid-doped barium titanate (BaTiO3) ceramics were investigated. Superimposed compressive stress had a pronounced effect on the electrical properties of the ceramics. The response of low-field dielectric properties to stress changed from soft to hard piezoelectric behavior with increasing Nb5+ content. While ferroelectric properties decreased with stress, hardening behavior was observed with increasing Nb5+ content in hybrid-doped BaTiO3 ceramics. A mechanism based on induced change in the acceptor valence by the donor dopant in hybrid-doped BaTiO3 ceramics was proposed to explain the results obtained.

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Promising piezoelectric properties have been reported recently for lead-free 0.96(K0.48Na0.52Nb0.95Sb0.05)-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (KNNS-BNKZ) ceramics. The presence of coexisting ferroelectric rhombohedral and tetragonal phases is thought to play a key role in their functional properties, but a thorough understanding is currently lacking. In this experiment, (1-x)KNNS-(x)BNKZ ceramics with x = 0 to 0.05 were prepared by the mixed-oxide method. High resolution synchrotron x-ray powder diffraction (SXPD) measurements reveal that the addition of BNKZ into KNNS ceramics leads to an increase of the rhombohedral-orthorhombic phase transition temperature (TR-O) and a reduction of the orthorhombic-tetragonal phase transition temperature (TO-T) leading to orthorhombic-tetragonal and rhombohedral-tetragonal phase coexistence at room temperature for compositions with x = 0.02 and 0.04, respectively. By combining the results of the SXPD measurements with microstructural examination using SEM, evidence is also found for the occurrence of chemical heterogeneity, which could provide an additional means to control the functional properties. The structural observations are correlated with changes in the dielectric properties, obtained as permittivity-temperature plots, and variations in the polarisation and coercive field values, obtained from measurements of the ferroelectric hysteresis loops.

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In this work, an X-ray Absorption Spectroscopy (XAS) measurement was employed to determine the local structure of Mn in BaTiO 3 . A combination of Synchrotron X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EX-AFS) experiments was performed on Mn-doped BaTiO 3 samples. The BaTi 1 -x Mn2) were used for the XAS experiment. XAS spectra at the Mn K-edge were recorded in transmission mode. The spectra were collected at ambient temperature with a Ge(111) double crystal monochromator and recorded after performing an energy calibration. The features of the measured Mn K-edge XANES and EXAFS were both consistent with Mn on the Ti site and inconsistent with Mn on other sites. In addition, the dielectric and ferroelectric properties results also supported the possible Mn T i substitution in BaTiO 3 material. The clear agreement between the two measured synchrotron XAS spectra, as well as supporting electrical results, was by far the strongest evidence of Mn substituting for Ti in BaTiO 3 structure.