Evolutions of chemical and polar structures and electric properties in the Barium-Lead Zirconate-Titanate (BPZT) system

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(Thesis) M.Sc.
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Ceramics of the perovskite (1-x)[Ba(Zr0.30Ti0.70)O3] - x[Pb(Zr0.30Ti0.70)O3] (BZT-PZT) solid solution were prepared by solid state reaction method with complete solubility throughout the series. The ceramics were examined by X-ray diffraction and dielectric spectroscopy to investigate the crystal structure, phase transition and electric properties. The XRD results reveal that all ceramics exhibit a pure perovskite structure, and with increasing x, the cubic phase gradually transforms into a tetragonal phase. Detailed structural analysis and Rietveld refinements based on XRD data. The dielectric permittivity was measured as a function of frequency (0.1 Hz - 100 kHz) in the temperature range of 123 K to 573 K. For 0 < x < 0.40, the ceramics exhibit a typical relaxor behaviour. With the increase of the PZT concentration, the temperature of the dielectric maximum (Tmax) shows a non-monotonic variation, which first decreases and then increases at a critical composition (xC1 = 0.10). The maximum of dielectric permittivity (e’max) at Tmax shows frequency dispersion following the Vogel-Fulcher law. The difference between Tmax and the fitting parameter TVF, (Tmax-TVF), first increases and then decreases at another critical composition (xC2 = 0.30), with the increase of PZT concentration, showing the same trend as the shift of Tmax with frequency (DTmax). The high-temperature slope of the diffuse dielectric peak (T > Tmax) is scaled by the empirical Lorenz-type quadratic relation. The transition from the high-temperature paraelectric state, in which the dielectric constant follows the Curie-Weiss law, to the ergodic cluster state is found to occur over all the studied compositions. Single crystals of (Ba1-xPbx)(Zr1-yTiy)O3 were grown by a high-temperature solution growth method using (PbO + B2O3) as a flux upon slow cooling from 1100 °C. The size of the as-grown crystals varies from 1 to 5 mm. The X-ray powder diffraction analysis shows that the crystals have a tetragonal perovskite structure. The composition of the crystal is found to be (Ba0.46Pb0.54)(Zr0.12Ti0.88)O3 by X-ray photoelectron spectroscopy (XPS). The measurements of dielectric properties indicate that the crystal undergoes a single phase transition from the cubic to the tetragonal phase at Curie temperature, TC = 554 K, upon heating. Polarized light microscopic studies of the domain structure confirm that the crystals are of tetragonal symmetry at room temperature. A typical ferroelectric hysteresis loop is displayed at room temperature, indicating the ferroelectric nature of the (Ba0.46Pb0.54)(Zr0.12Ti0.88)O3 crystals.
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Thesis advisor: Ye, Zuo-Guang
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