Single crystals of Pb(Sc1/2Nb1/2)O3 (PSN) were grown by a high-temperature solution method using (PbO + B2O3) as flux. X-ray diffraction (XRD) indicates a pure perovskite phase without B-site ordering. Polarized light microscopy shows that the crystals are of rhombohedral symmetry at room temperature and become cubic at 112 oC on heating which is the Curie temperature (TC). A relaxor-to-ferroelectric phase transition is confirmed by dielectric spectroscopy. Frequency-dependent permittivity is also observed, revealing relaxor behavior. Poling the crystal at room temperature does not change TC but suppresses the permittivity. A typical ferroelectric hysteresis loop is obtained at room temperature, indicating the ferroelectric nature of the PSN crystal.A new antiferroelectric solid solution ceramics of (1-x)PbZrO3-xPb(Zn1/2W1/2)O3 [(1-x)PZ-xPZnW, with x = 0 - 10%] has been prepared by conventional solid state reaction method. XRD reveals the perovskite structure of the (1-x)PZ-xPZnW ceramics. TC decreases when the percentage of PZnW increases. Meanwhile, another transition related to the transformation from antiferroelectric (AFE) to an intermediate ferroelectric (FE) phase was observed and its transition temperature (TAFE-FE) decreases from 213 oC for x = 0 to 58 oC for x = 0.10. A typical FE hysteresis loop was obtained, indicating the FE nature of the intermediate phase.The 0.97PbZrO3-0.03Pb(Zn1/2W1/2)O3 (97%PZ-3%PZnW) ceramic was used to study the intermediate FE phase. The temperature dependence of dielectric permittivity was studied. TC on cooling and heating are both 212 oC, indicating a second-order phase transition. Another phase transition below TC was observed, from the AFE phase at room temperature to an intermediate phase at higher temperature. This transition shows thermal hysteresis on cooling and heating, representing a first-order phase transition. Within the temperature range of the intermediate phase, ferroelectric hysteresis loops were displayed and a non-centrosymmetric structure was revealed by second harmonic generation, which indicates the FE nature for the intermediate phase. High resolution XRD and the subsequent refinement results show that the intermediate FE phase is rhombohedral (R3m) and the AFE phase is orthorhombic (Pbam). A phase diagram of the (1-x)PbZrO3-xPb(Zn1/2W1/2)O3 solid solution has been established.
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Thesis advisor: Ye, Zuo-Guang
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