Structure and electrical properties of [(Na0.825K0.175)0.5Bi0.5]1+xTiO₃piezoceramics with A-site nonstoichiometry

A type of nonstoichiometric piezoceramics, [(Na0.825K0.175)0.5Bi0.5]1+x TiO3 (BKNT-x, x = 0–0.009), was synthesized by the conventional sintering method. The effects of Bi3+, Na+ and K+ content on the structure and electrical properties of 0.825Bi0.5Na0.5TiO3-0.175Bi0.5K0.5TiO3 piezoceramics were investigated.The XRD patterns demonstrated that BKNT-x piezoceramics form a solid solution without a secondary phase. Meanwhile, SEM micrographs indicated that excess [(Na0.825K0.175)0.5Bi0.5]2+ suppresses grain growth and that BKNT-x ceramics become considerably denser. BKNT-0.002 ceramics offer the following enhanced properties: d33 = 154 pC/N, kp = 33%, εr = 1087, tanδ = 0.036, and Qm = 116. This improvement of properties is most likely related to the dense structure and the maintenance of morphotropic phase boundaries through the introduction of a proper A-site cation excess. For ceramics containing volatile elements, stoichiometric control is an efficacious method of enhancing performance.