Effect Of Annealing And Atmosphere Sintering On The Structure And Electrical Properties Of Pb - Based Piezoelectric Ceramics

The high temperature piezoelectric ceramics have high Curie temperature, which show excellent electrical properties and can be used in the high temperature environment. In this thesis, the PbNb2O6-based piezoelectric ceramics were studied. Effects of the dopants and annealing on structure, dielectric and piezoelectric properties of the PbNb2O6-based ceramics were studied in detail. The results are as following:(1) Pb0.925Ba0.075Nb2O6-0.5wt%TiO2 (PBN-T) piezoelectric ceramics were prepared via a conventional solid state reaction method. Effects of annealing on structure,dielectric and piezoelectric properties of the PBN-T ceramics were studied in detail. The annealing temperatures and annealing time were chosen as 500～800℃; 12 ～168 h; annealing atmospheres were selected as air without excess Pb2+ source, air with excess Pb2+ source and nitrogen atmosphere with excess Pb2+ source. The results show that the electrical properties of the ceramics are closely related to the annealing parameters. The ceramic annealed in nitrogen atmosphere with excess Pb2+ source at 600℃ for 73 h shows the better property, which has the Curie temperature of 523℃, piezoelectric constant of 85 pC/N at room temperature, and 82 pC/N after annealing at 500℃.(2) Pb0.925Ba0.075Nb2O6-0.5wt%Ti02 (PBN-T) piezoelectric ceramics were prepared via a conventional solid state reaction method. The ceramics were calcined and sintered in air, oxygen and nitrogen, respectively. All ceramics exhibit a single orthorhombic phase. The ceramic sintered in nitrogen shifts the peak position toward a higher diffraction angle compared with that sintered in oxygen or air. Lattice binding shrink sintered in nitrogen. The ceramics have homogeneous polygon-shaped grains, the mean size of grains in the ceramics sintered in nitrogen decreases. The ceramics sintered in oxygen have a higher Curie temperature.The ceramics sintered in nitrogen show lower Curie temperatures and εm, and have broader dielectric peak around the Curie temperature.(3) Pb0.925Ba0.075Nb2O6-0.5wt%MnO2 (PBN-M) piezoelectric ceramics were prepared via a conventional solid state reaction method. Effects of annealing on structure, dielectric and piezoelectric properties of the ceramics were studied in detail. The annealing temperature and annealing time were chosen as 600℃ and 12 h, respectively; the annealing atmospheres were selected as air without excess Pb2+ source, nitrogen with excess Pb2+ source and oxygen atmosphere with excess Pb2+ source. The results show that the electrical properties of the ceramics are closely related to the annealing atmospheres. The ceramic annealed in oxygen atmosphere with excess Pb2+ source at 600℃ for 73 h shows the better electrical properties:lower dielectric loss, εm=10621,Tc=520℃,Kp=0.3328, and Qm=12.(4) Pb0.925Ba0.075Nb2O6-0.5wt%TiO2 (PBN-T) piezoelectric ceramics were prepared via hot-pressing sintering method. Effects of sintering temperature, pressure and sintering time on structure, dielectric and piezoelectric properties of the ceramics were studied in detail.The results show that a longer dwell time cannot improve bulk densities of the ceramics. The value of bulk density depends on pressure value. As the pressure is 1.2 t (16.1 MPa), the bulk density is above 6.40 g/cm3. Compared with the conventional solid state reaction method, the hot-pressing sintering method can enhance densification of the ceramics. The ceramics have heterogeneous grains and pores sintered in vacuum without pressure at 1245℃.The average grain size is 9.3 um. With using hot-pressing sintering at 1255℃, the ceramics show better densification, have less pores and bigger grains. When the pressure value is between 0.8 t (10.7 MPa) and 1.51 (19.4 MPa), the ceramics show fine densification and homogeneous grains.