The dielectric, elastic, and piezoelectric properties of a niobium-doped $\mathrm{Pb}{\mathrm{Zr}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_3$ ceramic with a composition located near the morphotropic phase boundary have been studied from $25\text{to}400°\mathrm{C}$. A strong softening of the elastic coefficients was observed far below the temperature corresponding to the dielectric permittivity maximum, $T_{\epsilon \max }=366°\mathrm{C}$. The steep decrease of the stiffness coefficient $c_{44}$ from $400\text{to}350°\mathrm{C}$ is probably a stepwise anomaly which is expected at an improper ferroelastic transition. In addition, it was found that all macroscopic piezoelectric activity had disappeared well above $T_{\epsilon \max }$. This is explained by the combined effects of compositional fluctuations in the $\mathrm{Zr}∕\mathrm{Ti}$ sublattice and the presence of polar nanoregions. The elastic properties have an anomaly at the temperature at which the lattice becomes predominantly centrosymmetric. The piezoelectric activity vanishes when the polar nanoregions reach a critical size below which they can no longer interact coherently through the nonpolar matrix to induce a macroscopic piezoelectric response.

• Received 5 October 2005

DOI:https://doi.org/10.1103/PhysRevB.73.144114