| The PbNb2O6-based piezoelectric ceramics were studied as a main research object in this thesis. Lead metaniobate (PbNb2O6, PN) is a tungsten bronze-structured ferroelectric. PN-based ceramics are widely used in science and technology as one of the high-temperature piezoelectric ceramics. In this dissertation, the doping of Sr2+ and W6+ ions into PN-based piezoelectric ceramics were studied. In order to obtain PN-based ceramics with high Curie temperature and improved piezoelectric activity. A conventional ceramic fabrication method was employed to prepare the PN-based lead ceramics. The properties of phase structure, microstructure, dielectric, piezoelectric and ferroelectric properties were investigated.(Pbi-xSrx)Nb1.96Tio.os06 with 2 wt% excess PbO (x=0,0.02,0.04,0.06,0.08) piezoelectric ceramics with high Curie temperature were fabricated via the conventional solid state reaction method. Effects of Sr2+ amount on crystallite structure, microstructure, dielectric, piezoelectric and ferroelectric properties were studied. The substitution of Sr2+ ions for Pb2+ ions is effective to lower sintering temperatures. X-ray diffraction patterns indicate that all ceramics form a single orthorhombic ferroelectric phase. SEM and density results indicate that the doping of Sr2+ ions facilitates improving densification of the ceramics. Grain size and lattice parameters of the ceramics vary with the change in the Sr2+ contents. Both Curie temperature and maximum dielectric constant change with increasing the Sr2+ amount. The dielectric constant data were also studied using the Curie-Weiss law and modified Curie-Weiss law. The ceramic with x=0.04 possesses excellent piezoelectric and dielectric properties, presenting a high potential to be used in high-temperature applications as piezoelectric transducers.Pb0.95-xBa0.05(Nb1-xWx)206with 2 wt% excess PbO and 0.25 wt% TiO2(x=0,0.025, 0.05,0.075,0.1)piezoelectric ceramics with high Curie temperature were prepared via the conventional solid state reaction method. Effects of the doping of W6+ ions on the crystallite structure, microstructure, dielectric and piezoelectric properties were studied in detail. SEM and density results indicate that the doping of W6+ ions improves the densification of the ceramics.X-ray diffraction patterns indicate that all ceramics form the single orthorhombic ferroelectric phase. The lattice parameters and grain size vary with the increasing of the W6+ contents. All ceramics exhibit the typical characteristic in ferroelectrics with normal ferroelectric-paraelectric phase transition at Curie temperature. Both Curie temperature and maximum dielectric constant are related to the W6+ amounts. The ceramic with x=0.075 possesses the high piezoelectric constant (d33, 108pC/N), low mechanical quality factor (Qm,29), low dielectric loss (tanδ,0.006), and high Curie temperature (Tc,448℃). The values of d33 and Kp do not show obvious drop when the annealing temperatures are≤400℃. From room temperature to 400℃, the d33 value is still higher than 96pC/N and only lowered by about 11%. It reveals that the obtained PBNW/0.075 ceramic is very stable to thermal annealing, and can be potentially used in high temperature piezoelectric applications.In order to satisfy the needs of high-temperature piezoelectric transducers of petroleum logging. PBNW/0.075 (Φ28.55mm×3.5mm) lead ceramics were prepared via the solid state reaction method. PBNW/0.075 ceramics exhibit a single phase of tungsten bronze structure at 1210℃,1230℃ and 1250℃, indicating that PBNW/0.075 ceramic possesses a wide sintering range. SEM results show that the sintering temperatures can affect grain size obviously. Grains cannot grow completely at relatively lower sintering temperature, but melt at relatively higher sintering temperature. The PBNW/0.075 ceramic shows fine grains with almost no pores and cracks on the surface,corresponding to the high density at the best sintering temperature. The values of dielectric constant remain nearly unchanged from room temperature up to about 400℃, exhibiting excellent high-temperature stability for the application of transducers. The Tc values are about 450℃. The effects of diameter and thickness of the samples on radial resonant frequency have been studied. The results show that the radial resonant frequency of sample is inversely proportional to its diameter and thickness. The ceramic with x=0.075 possesses the average piezoelectric constant (d33,75pC/N), low mechanical quality factor (Qm,24), high dielectric loss (tanδ,0.01), and planar electromechanical coupling factor (Kp,0.24). The piezoelectric constant increases to 85pC/N as the ceramics cool rapidly under the poling electric field during the poling experiment.
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