Strain behavior and piezoelectric properties of relaxor-PbTiO3 based crystals have been studied under the combination of electric field and static uniaxial transverse compressive stress. The transverse piezoelectric coefficient, d32, for crystals well into the rhombohedral phase was found to increase with increasing stress due to a morphotropic phase boundary (MPB) effect, while the values for crystals with MPB composition exhibit a contrary trend that is associated with the phase transformation. In addition, an ac drive field was found to depolarize the crystals under stress. Of particular significance is that manganese-modified crystals show stable piezoelectric properties under ac drive field and stress, which has potential for transducer applications. © 2013 AIP Publishing LLC.