The nonlinear, complex, inducedpiezoelectric response of Pb(Mg1/3Nb2/3)O3-PbTiO3 relaxors Solid solutions ͑1Ϫx͒Pb͑Mg 1/3 Nb 2/3 ͒O 3 -xPbTiO 3 with 0.20рxр0.40 were studied using impedance measurements and high resolution x-ray powder diffraction. The dependence of the real and imaginary parts of the dielectric constant with temperature was investigated on unpoled and poled ceramics, showing several transition points. The temperature dependence of the unit-cell parameters showed the onset of two successive spontaneous phase transitions: cubic→tetragonal →rhombohedral. A coexistence of both ferroelectric phases was evidenced in a large temperature and composition range. The dielectric and structural properties were interpreted in terms of relaxor→ferroelectric spontaneous phase transition. An intermediate behavior between a relaxor and a real ferroelectric was evidenced. A partial phase diagram was proposed including both structural and dielectric informations.

Relaxor single crystals PZN-9%PT have been cut and poled along [ 1 101] direction for which the spontaneous polarization P s is approximately parallel to the poling field E p . The piezoelectric matrix of the monoclinic single-domain (1M state) has been determined, in the approximation of an orthorhombic symmetry. The shear mode (15) along [101], gives the highest electromechanical coupling factor k 15 (>80%) and the largest piezoelectric coefficient d 15 ($3200 pC/N). The properties of the disoriented 1M state have been calculated from a change of axes. The maximum of d ' 33 is obtained along a direction close to [001]. This is due to the very large value of d 15 compared to d 33 in the basic 1M state. On the other hand the transverse piezoelectric coefficient along [uv0] for the [001] disoriented P s single domain presents a strong anisotropy. Finally, in the [001] domain engineered configuration, an important extrinsic contribution of the domain coexistence is evidenced by comparing calculated and measured coefficients.

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