The influence of uniaxial compressive stress on the small signal direct piezoelectric coefficient of hard and soft Pb(Zr,Ti)O3 at the morphotropic phase boundary was investigated as a function of temperature from 25 °C to 450 °C. The stress- and temperature-dependent piezoelectric data indicate that stress is capable of either directly or indirectly modifying the orientation of polar defects in the crystal lattice and reduce the internal bias field. At higher temperatures, the mobility of polar defects was found to increase, corresponding to a two-step decrease in the direct piezoelectric coefficient and a decrease in the frequency dispersion. Quenching experiments were used to elucidate the role of the internal bias field on the stress-dependent piezoelectric response. ; Author preprint