Preparation Of BT-CT-BZ Lead-free Piezoelectric Ceramics And Their Modification By Doping

This thesis was consisted of three parts. In part one, the 1 wt% Li-doped(Ba0.85Ca0.15)(Ti0.90Zr0.10)O3(BCZT) ceramics were fabricated by the citrate method. The effects of preparation processing of precursors, synthesis temperature on the crystal structure, micro-morphology and electrical properties were systematically investigated. The appropriate calcining temperature is determined to be between 600 and 700 ℃ according to the TG-DSC measurement results. XRD analysis manifests that the formation temperature of the pure perovskite structure for the Li-doped BCZT powders can be decreased greatly to below 700 ℃, and the Li-doped BCZT ceramics possess the coexistence of orthorhombic and tetragonal phase structure. The Li-doped BCZT ceramics exhibit excellent electrical properties, especially the samples calcined at 700 ℃ and sintered at 1500 ℃ possess the highest integrated ferroelectric properties. The pyroelectric coefficient is calculated by the static method, and the influence of calcining temperature on the pyroelectric properties of the Li-doped BCZT ceramics is studied. The samples calcined at 650 ℃ and sintered at 1500 ℃ possess the highest pyroelectric properties.In part two, the 1 mol% Sr and 1 mol% Sn co-doped(Ba0.84Ca0.15Sr0.01)(Ti0.90Zr0.09Sn0.01)O3(BCSTZS) ceramics were prepared by the conventional solid-state reaction method. The influences of sintering temperature on the structure and electrical properties were systematically investigated. XRD analysis indicates that the orthorhombic and tetragonal phases coexist in the BCSTZS ceramics at room temperature. When the sintering temperature increases from 1400 ℃ to 1550 ℃, the relative density increases and the microstructure becomes dense, leading to the improved integrated electrical properties. The BCSTZS ceramics sintered at 1550 ℃ exhibit the highest piezoelectric constant(d33=514 p C/N) and pyroelectric coefficient(p=1116.7 μC/K·m2). The environmental temperature exerts great influence on the electrostrain and piezoelectric properties of the BCSTZS ceramics. The safe usage temperature of the BCSTZS ceramics is determined below 70 ℃.In part three, the ferroelectric phase transitions of ferroelectric ceramics and single crystals were studied by Raman spectroscopy. The temperature-dependent Raman spectra confirm that the Li-doped BCZT ceramics and BCSTZS ceramics experience the orthorhombic ferroelectric phase-tetragonal ferroelectric phase transition around room temperature and tetragonal ferroelectric phase-cubic paraelectric phase transition around the Curie temperature(85 ℃). The poled 0.5 mol% Mn-doped 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30 Pb Ti O3(PIMNT-Mn) single crystals also experience successive ferroelectric phase transitions from rhombohedral ferroelectric phase-monoclinic ferroelectric phase, monoclinic ferroelectric phase-tetragonal ferroelectric phase and tetragonal ferroelectric phase-cubic paraelectric phase at 130 ℃, 148 ℃ and the Curie temperature(183 ℃), respectively. The dielectric-temperature curves, the temperature dependence of d?/d T, phase degree ?, resonant frequencies f and S-E curves at different temperatures further confirm the occurrence of ferroelectric phase transitions.Based on the analysis of the phase structure and electrical properties, the superior feroelectric properties of BCZT-based ceramics are closely related to the coexistence of orthorhombic and tetragonal ferroelectric phases around room temperature. The BCZT-based ceramics possess ultrahigh piezoelectric properties, which can be comparable with the PZT-based ceramics. The BCZT-based ceramics show a promising future as lead-free ceramics for the piezoelectric applications.