Influences of the crystallographic phases on the piezoelectric properties of PZN-PT single crystals

Single crystals of lead-based relaxor ferroelectric solid solutions, in particular, lead zinc niobium titanium oxide 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 solid solutions are closely related to the morphotropic phase boundary (MPB) effects and the formation of macro-domain states which results from the substitution of Ti4+ ions for the complex ions (Zn1/3Nb2/3)4+ on the B-site of the perovskite structure facilitating their use in ultrasonics and underwater communications. Hence growth of PZNT (91/9) single crystals at morphotropic phase boundary has been carried out by flux technique using PbO as flux. The grown crystals are light yellow in color showing arrowhead morphology and approximately has dimensions 5x5x2 mm3. The X-ray diffraction results of the grown crystals show that the peaks correspond to perovskite phases. Even though the strong crystal anisotropy of truly rhombohedral crystals is enough to explain the piezoelectric response of PZN-PT because of the near degeneracy of two of more phases near the MPB, it is to be noted that the monoclinic phases composed of very finely twinned rhombohedral and tetragonal domains at the MPB are responsible for the piezoelectric properties of PZN-PT and they act as inhibitors to facilitate the polarization rotation. From the dielectric measurements it is evident that the Curie temperature Tc is about 180 deg C and loss factor (tan δ) is 0.24. From the hysteresis loop measurements, an increase in the values of remanent polarization (Pr) and coercive field (Ec) was observed due to the effect of poling. Electromechanical coupling factor (k33)calculated from the impedance spectra was 79 % and the piezoelectric coefficient d33 was 2110 pC/N for the (001) oriented plate. (author)