Morphotropic Phase Boundary Perovskites High Strain Piezoelectrics And Dielectric Ceramics PDF Download

The current generation of textured piezoelectric ceramics are primarily limited in high power applications by low coercive fields (Ec), low tetragonal to rhombohedral phase transition temperatures (Trt), and low Curie temperatures (TC). Over the past decade, numerous studies have shown that both Pb(In1/2Nb1/2)O3-Pb(Zn1/3Nb2/3)O3-PbTiO3 (PIN-PZN-PT) and Pb(Yb1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PYN-PMN-PT) ceramics both have higher Ec's and phase transition temperatures. However, random PIN-PZN-PT and PYN-PMN-PT ceramics show comparably low piezoelectricity compared to textured Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 and Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics. To realize high-strain textured piezoelectrics with coercive fields and phase transition temperatures that exceed those of the current generation, this dissertation explores the processing, templated grain growth, and electromechanical properties of random and textured PIN-PZN-PT and PYN-PMN-PT ceramics. A major challenge in the development of textured PIN-PZN-PT ceramics is the synthesis of phase pure perovskite powder. The role of ZnO-doping was investigated in the phase formation of perovskite PIN-PZN-PT powder. ZnO dopant concentrations of 0.04 -- 0.83 mol% increased the rate of perovskite formation and resulted in nearly phase pure powder. ZnO doping promoted perovskite formation by increasing the reactivity of an intermediate Zn-based pyrochlore phase by substituting on Nb5+ sites and forming oxygen vacancies. Because of the associated oxygen control, it is shown that phase pure powder can be achieved during synthesis. The role of ZnO-doping was related to the densification and electromechanical properties of PIN-PZN-PT ceramics. ZnO-doping enhanced the rate and degree of sintering of PIN-PZN-PT due to the formation of oxygen vacancies. Incorporation of Zn2+ into the perovskite lattice increased the tetragonal character of PIN-PZN-PT, resulting in an increased Curie temperature and tetragonal splitting of the 200 peaks. Sintering in flowing oxygen reduced the solubility of Zn2+ into the perovskite lattice and resulted in the formation of rhombohedral PIN-PZN-PT perovskite. Oxygen sintering resulted in ZnO-doped PIN-PZN-PT ceramics with a large piezoelectric coefficient (d33 ~ 550 pC/N), large coercive field (Ec ~ 13 kV/cm), and high rhombohedral to tetragonal phase transition temperature (Trt ~ 165°C). It was determined that PIN-PZN-PT does not nucleate on barium titanate templates and thus texturing by TGG was not successful. High PYN-content PYN-PMN-PT ceramics are challenging to texture due to limited grain growth. A PbO-CuO liquid phase was shown to promote the grain growth of 21PYN-41PMN-38PT ceramics barium titanate platelets, and thus enable templated grain growth of high Ec PYN-PMN-PT ceramics. Texturing increased the strain behavior by 83% compared to random 21PYN-41PMN-38PT ceramics. Textured 21PYN-41PMN-38PT had a high coercive field of 13.9 kV/cm and high TC of 224°C. The composition of textured high coercive field PYN-PMN-PT was related to electromechanical property enhancements. Increasing the rhombohedral character of PYN-PMN-PT increases the degree of intrinsic piezoelectricity, which reduces the strain hysteresis. Texturing the morphotropic phase boundary composition, 20PYN-46PYN-34PT, resulted in an 81% increase in peak strain to 0.18% while texturing tetragonal 20PYN-40PMN-40PT resulted in a 45% increase in peak strain to 0.16%. These results reveal that ceramic composition and stresses associated with residual template particles are critical factors in the resulting electromechanical performance of texture-engineered ceramics.