  First-order, rhombohedral to orthorhombic, stress-induced phase transitions
have been evidenced by bulk charge-stress measurements and X-ray diffraction
derived lattice strain measurements in [001]c-poled PZN-4.5PT. The transitions
are induced by uniaxial, compressive loads applied either along or
perpendicular to the poling direction. In each case, they occur via rotation of
the polar vector in the Cm monoclinic plane and the induced lattice strain is
hysteretic yet reversible. Although no depoling is observed in the transverse
mode, net depolarization is observed under longitudinal stress which is
important for the use of [001]c-poled PZN-PT and PMN-PT single crystals in
Tonpilz-type underwater projectors.
