Synthesis and Characterization of Piezo-/ferroelectric Lead Zirconate-Titanate (PZT) Single Crystals and Related Ternary Ceramics

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(Thesis) Ph.D.
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Author: Xie, Yujuan
PbZr1-xTixO3 (PZT) single crystals with compositions across the morphotropic phase boundary (MPB) have been successfully grown by a top-seeded solution growth (TSSG) technique. The growth conditions are optimized in terms of chemical, thermodynamic and kinetic parameters. The growth temperature is found to be the key factor for controlling the composition of the crystals. The PbZr0.54Ti0.46O3 crystals exhibit the best properties, with a piezoelectric coefficient d33=1223pC/N, an electromechanical coupling factor k33=0.8, a high coercive field Ec=7kV/cm and a high Curie temperature TC=395°C, making them a potentially material for high temperature and high power electromechanical transducer applications. The availability of the PZT single crystals has allowed us to perform a series of characterization of their physical properties. Dielectric measurements of the PbZr0.80Ti0.20O3 crystal show that the phase transition between rhombohedral octahedron-tilted (R3c) and untilted (R3m) phases is of the first order, which is evidenced by a thermal hysteresis upon heating and cooling. The tricritical behaviour of this composition is revealed by the birefringence measurements, showing a slightly discontinuous phase transition in (001)cub platelet and a continuous phase transition in the (110)cub platelet. The domain structures and phase transitions of the PZT single crystals with compositions near the MPB are investigated by polarized microscopy (PLM). Continuous polarization rotation within the (110)cub plane was observed in both PbZr0.58Ti0.42O3 and PbZr0.54Ti0.46O3 crystals. Tetragonal nanodomains observed in the PbZr0.54Ti0.46O3 crystal can be explained by Imry and Ma's random field theory, which suggests that quenched random field related to structural disorder can break the system into nanodomains that are more energetically favored. In our search for new lead-reduced piezoelectric materials, the ternary ceramics of Bi(Zn1/2Ti1/2)O3-PbZrO3-PbTiO3 [BZT-PZ-PT] were synthesized and investigated. The introduction of BZT into the PZT binary system brings the MPB to a lower PT content and enlarges the composition range of the MPB region. Enhanced piezoelectric and ferroelectric properties are obtained in the MPB region with the highest BZT content (=15mole%), with d33=275pC/N, Pr=33μC/cm2 and Ec=26 kV/cm.
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Thesis advisor: Ye, Zuo-Guang
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