Enhanced spontaneous polarization in Sr and Ca co-doped BaTiO3 ceramics

The dielectric and ferroelectric properties of (Ba_xSr_1−x)_0.77Ca_0.23TiO₃ ceramics with x=1 to 0.7 were studied and compared with those of Ba_xSr_1−xTiO₃ and Ba_0.77Ca_0.23TiO₃ ceramics. It has been found that Sr doping of the Ba_0.77Ca_0.23TiO₃ ceramics causes a drastic decrease of the Curie temperature, just like Sr doping of pure BaTiO₃ ceramics, demonstrating a cell volume effect. However, the (Ba_xSr_1−x)_0.77Ca_0.23TiO₃ ceramics with x=0.9 and 0.8 have larger spontaneous polarization than those of the corresponding Ba_xSr_1−xTiO₃ and Ba_0.77Ca_0.23TiO₃ ceramics, along with sufficient insulating properties. The enhancement of their polarization was explained by the increase of the lattice parameter c/a ratio due to the lattice distortion and strain developed in the ceramics.