Piezoelectric, ferroelectric, and relaxor-ferroelectric materials are key components in a range of technologies including sonar, ultrasound, radio frequency (RF) filters, accelerometers, motion sensors, micropositioning systems, and mechanical energy harvesting devices . Characteristic for these materials is the coupling of mechanical and electrical properties. In the direct piezoelectric effect, an applied stress σ j induces a polarization P i at a fixed electrical field E, d i,j = (∂P i /∂σ j ) E . Here, d i,j are the piezoelectric coefficients; i = {x, y, z} are the field directions (by convention the polar direction is set to i = 3 = z); j are the elastic tensor directions, indicated with Voigt indicies runing from 1 to 6, i.e j = {xx, yy, zz, yz, xz, xy}. In the converse piezoelectric effect, d i,j = (∂ε i /∂E j )