Phase structure and electric properties of Bi0.5(Na0.825K0.175)0.5TiO3 ceramics prepared by a sol–gel method

Bi0.5(Na0.825K0.175)0.5TiO3 (BNKT17.5) lead-free piezoelectric powders were prepared by the sol–gel process. Thermal analysis and XRD patterns reveal that the BNKT17.5 powders possess pure perovskite phase above 600 °C. 100–200 nm BNKT17.5 powders with homogeneous composition and few aggregation can be obtained by calcining dried gels at 750 °C for 2 h. Moreover, BNKT17.5 ceramics were fabricated by conventional sintering of as-prepared BNKT17.5 powders. The SEM micrographs show that ceramics have a dense microstructure with a fine grain size at 1150 °C. The BNKT17.5 ceramics sintered at 1150 °C provide optimum dielectric and piezoelectric properties. The dielectric constant ɛr and piezoelectric constant d33 attain the values of 925 and 164 pC/N, respectively, while the electromechanical coupling factor kp exhibits the value of 0.27. The results confirm the sol–gel process as a advantageous route in fabricating uniform and good electric properties of BNKT17.5 ceramics.