Chemical composition and tolerance factor at the morphotropic phase boundary in (Bi0.5Na0.5)TiO3-based piezoelectric ceramics

A quantitative relationship between the morphotropic phase boundary (MPB) composition and the tolerance factor (t) in (Bi0.5Na0.5)TiO3 (BNT)-based piezoelectric ceramics was established. The t value of the MPB compositions in BNT-based ceramics is around 0.990-0.993 and is independent of the types of added compounds. In order to experimentally demonstrate this, two piezoelectric ceramic systems (1-x)(Bi0.5Na0.5)TiO3-x(Ba1-aSra)TiO3, a = 0.05 and 0.3 (BNBST5-x and BNBST30-x, x < 12%), were used. XRD patterns and lattice parameter investigations revealed that these two systems formed solid solutions within the studied stoichiometry and showed a rhombohedral-tetragonal phase transformation. Both the structural analysis and electrical property measurements indicated that the MPB compositions were BNBST5-6 and BNBST30-8 and their corresponding t values were 0.9900 and 0.9903, respectively. The results confirmed the relation between the MPB composition and t value and provide a method for designing new piezoelectric materials.