Next-generation sonar projectors rely on piezoelectric single crystals such as lead magnesium niobate–lead titanate to induce mechanical strain and generate ever greater acoustic output, but the performance of these materials under high-power operation is not well understood. As the electrical driving force increases, the linear piezoelectric relationships give way to nonlinear, amplitude-dependent properties. Such behavior is impossible to predict solely from small signal, linear measurements. This work has characterized the behavior of single crystals by examining the dynamic relaxation from initial strain levels of 0.1 to 0.2%. Strain-dependent values of the mechanical quality factor and resonance frequency are reported for single crystals, and these properties are compared with conventional high-power piezoceramics.