The piezoelectric and dielectric properties of Ca-additive Sm-modified PbTiO₃ ceramics intended for surface acoustic wave devices

Sm-modified lead titanate ceramics with a composition of (Pb_0.88-x Ca_xSm_0.08 (Ti_0.98Mn_0.02) O₃; x=0.11∼0.17 were prepared by conventional mixed -oxide method. The dielectric and piezoelectric properties of these doped ceramics were measured at room temperature. Microstructural and compositional analyses have been carried out using SEM and XRD. The Curie point (T_c) was studied by measuring the dielectric behavior as a function of temperature. The experiments successfully showed that Ca additive not only reduce the lattice anisotropy but is also helpful in providing a higher thickness electromechanical coupling coefficient, k_t (>0.57), than that of conventional PbTiO₃ based ceramics while still keeping a small planar electromechanical coupling coefficient, k_p. In addition, the Ca additive produced a higher phase velocity and high electromechanical coupling coefficient. The SAW properties of our samples (V_p and k²) are better than those of commercially-made PZT and PT samples.