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

Bi-0.5(Na0.825K0.175)(0.5)TiO3 (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 degrees C. 100-200 nm BNKT17.5 powders with homogeneous composition and few aggregation can be obtained by calcining dried gels at 750 degrees C for 2h. 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 degrees C. The BNKT17.5 ceramics sintered at 1150 degrees C provide optimum dielectric and piezoelectric properties. The dielectric constant Er and piezoelectric constant d(33) attain the values of 925 and 164 pC/N, respectively, while the electromechanical coupling factor k(p) 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. (C) 2010 Elsevier B.V. All rights reserved.