Multi-scale effects of poling on structure-property relationships in lead magnesium niobate-lead titanate single crystals

Ferroelectric Pb(Mg1/3Nb2/3)O 3-PbTiO3 (PMN-PT) single crystals are the most promising candidates for the next generation of ultrasonic devices. These materials have superior properties (d33= 3000 PC/N, d31= -1800 pC/N, d15= 5000 pC/N, k33 >0.90) when compared with conventional PZT ceramics. The outstanding properties of ferroelectric piezoelectrics depend in large part on the domain reorientation process known as poling. In this thesis, the multi-scale effects of poling on structure-property relationships are investigated, as a function of crystallographic orientation and temperature, for compositions in the morphotropic phase boundary (MPB) region. Thermal softening and expansion coefficients were determined by dilatometry, and a unique direction was discovered along one of the crystallographic equivalent <001> directions, even for unpoled melt-grown crystals. Values of dielectric constant (K33) tripled along the unique direction for compositions near the MPB, compared with the other orthogonal directions. Poling along <001> doubled K33 at room temperature (from K33≈2000 to ≈5000) for compositions near the critical point, and increased over ten-fold (from K33≈1200 to ≈14000) for compositions near the MPB. Room temperature poling also affected the domain structure, and the phase transformation characteristics.; Onsets in non-linearity for thermal strain and Curie-Weiss behavior were found to correlate with the Burns temperature. Diffuse dielectric phase anomalies for compositions close to the critical point were attributed to a convergence of three phases rather than classic relaxor behavior. In addition, hyper-Raman measurements revealed softening of a new composition-independent non-polar mode at the Burns temperature.; A never-before-seen superlattice in the MPB region was revealed by XRD in the transmission mode. Poling increased the average significance of the superlattice, signifying a structural contribution to the super-structure. The effects of poling on domain and crystallographic structure, and on phase transformation behavior, are reported. The use of PMN-PT piezoelectric crystals is dependent on successful poling methods.