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

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... raction (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. 2