Relaxor-PT based ferroelectric single crystals Pb(Zn1/3Nb 2/3)O3-PbTiO3 (PZNT) and Pb(Mg 1/3Nb2/3)O3-PbTiO3 (PMNT) offer high performance with ultra-high electromechanical coupling factors k33s > 0.9 and piezoelectric coefficients d33s > 1500 pC/N. However, the usage temperature range of these perovskite single crystals is limited by T RT-the rhombohedral to tetragonal phase transition temperature, which occurs at significantly lower temperatures than the Curie temperature T C, a consequence of curved morphotropic phase boundaries (MPBs). Furthermore, these ←001→-oriented crystals exhibit low mechanical quality Q and coercive fields, restricting their usage in high-power applications. In this survey, recent developments on binary and ternary perovskite relaxor-PT crystal systems are reviewed with respect to their temperature usage range. General trends of dielectric and piezoelectric properties of relaxor-PT crystal systems are discussed in relation to their respective TC/TRT. In addition, two approaches have been implemented to improve mechanical Q, including acceptor dopants, analogous to hard polycrystalline ceramics, and anisotropic domain engineering, enabling lowloss crystals with high coupling for high-power applications. © 2010 IEEE.