Elastic response of (1-x)Ba(Ti0.8Zr0.2)O3 - x(Ba0.7Ca0.3)TiO3 (x = 0.45-0.55) and the role of the intermediate orthorhombic phase in enhancing the piezoelectric coupling

The elastic response of (Ba,Ca)(Ti,Zr)O3 at compositions where the piezoelectric effect is maximized has been measured by different methods between 1 Hz and 250 kHz and compared with that of PZT at the middle of its morphotropic phase boundary. In all cases, the compliance is peaked at the border between the tetragonal (T) and the orthorhombic (O) phases, intermediate between the T and the low-temperature rhombohedral phase. The anomalies do not exhibit dependence on frequency and their relative amplitude is 200-300 times larger than the losses, demonstrating that they are intrinsic rather than due to the domain wall motion. This also demonstrates the role of an intermediate O or monoclinic phase in enhancing the transverse instability and piezoelectric coupling at a (morphotropic) phase boundary between R and T phases.