Solid-state synthesis of modified (Bi0.5Na0.5)TiO3 piezoelectric nanocrystalline ceramics and evaluating their properties

The piezoelectric nanocrystalline ceramics of (Bi0.5Na0.5) TiO3, 0.94(Bi0.5Na0.5) TiO3–0.06BaTiO3, 0.82(Bi0.5Na0.5) TiO3–0.18(Bi0.5K0.5) TiO3 and 0.85(Bi0.5Na0.5) TiO3–0.144(Bi0.5K0.5)TiO3–0.006BaTiO3 (abbreviated as BNT, BNBT6, BNKT18 and BNT–BT–BKT, respectively) have been synthesized by a modified solid state approach using high-energy planetary ball-milling. The crystal structures of ceramics were determined using X-ray diffraction (XRD) method and that the microstructures as well as the morphology of the sintered ceramic specimens were observed using scanning-electron microscopy (SEM). The dielectric coefficient was also calculated based on its relation with a constant capacitance measured by an electrical circuit on the basis of the Wetston–Bridge and the piezoelectric coefficient (d33) measured with a d33-meter. On the calcination of powders the XRD results showed that the perovskite phase was formed perfectly and the crystallite sizes of BNT, BNBT6, BNKT18 and BNT–BT–BKT were estimated at about >100, 55, 36 and 63 nm, respectively. Also, the crystallite sizes of the calcinated BNT powders over the course of 5, 10, 20, 30 and 40 h of ball-milling were estimated at about 86, 82, 72, 53, 81 nm, respectively. Moreover, the results of XRD and SEM analysis of the sintered powders at 750–1150 °C confirmed the positive effect of nanocrystalline formation during ball-milling in decreasing the sintering temperature and increasing the density of the sintered samples. Furthermore, electrical calculations such as dielectric and piezoelectric coefficients showed that the modified BNKT18 nanocrystalline ceramic sintered at 1150 °C was to have the best values of dielectric (εr=792 at 1 kHz) and piezoelectric coefficients (d33=85.9 pC/N) in comparison with the other synthesized piezoelectric ceramics.