| Piezoelectric materials can directly realize the conversion between electrical energy and mechanical energy. They have been widely used in machinery manufacturing, electronic communications, military and other fields. Piezoelectric materials played an irreplaceable role in the functional conversion device of force, heat, light, electricity, magnetism fields and showed a broad application prospects. Piezoelectric materials can be divided into crystal, ceramic, polymer and composite materials. Among all these piezoelectric materials, piezoelectric ceramics have been occupying most of the market share of piezoelectric materials owning to their excellent piezoelectric properties, abundance in component regulation as well as the relatively simple fabrication process and low cost.Recently, the operating environment of piezoelectric materials received serious challenges due to the rapid development in the automotive industry, energy industry and aerospace industry, etc. For example, the automobile internal combustion engine efi system required the piezoelectric materials be able to work steadily under the environment temperature of 200℃ even 300℃, the pressure sensor for the detecting of hydraulic parameters in the process of oil exploration, also present a new challenge to piezoelectric materials, as well as the engine vibration testing in the aerospace field required piezoelectric materials work at higher temperatures. Research on high temperature piezoelectric materials and their device applications have received the unprecedented concern and attention.However, the most used commercial piezoelectric materials Pb(Zr,Ti)O3 (abbreviation as PZT) ceramics present a Curie temperature～360℃ due to their composition and structure. For bulk piezoelectric materials, the proper functioning temperature limited to half the Tc because of the depolarization effect caused by thermal activation so that the traditional PZT piezoelectric ceramics cannot be used over 200℃. Therefore, it is an urgent need to search for the piezoelectric materials with the Curie temperature over 400℃ as well as high piezoelectric performance.In 2001, Eitel et.al. reported a new series of Bi(Me)O3-xPbTiO3 piezoelectric ceramic solid solutions, where Me refers to a single cation or a mixture of cations of valence +3,such as Sc, In, Yb.,It had been attracted widely attention of the researchers because that for these systems the MPB composition not only has excellent piezoelectric properties, but also keep the high Curie temperature, especially the BiScO3-xPbTiO3 (BS-PT) ceramics, which have the similar crystal structure with PZT and exhibit an excellent piezoelectric performance (d33=460 pC/N) comparable to the commercial PZT near the MPB region located at PT content 64 mol% vicinity and a high Curie temperature of 450℃. Though the expensive raw material of scandium oxide confines the mass industrial production to some extent, BS-PT piezoelectric ceramics attracted close attention of the widely researchers in the high temperature piezoelectric ceramics field, especially the aspect of the application research in aerospace. In this thesis, we have investigated BS-PT based piezoelectric materials to optimize the electrical performance of BS-PT from two aspects, one is to improve the piezoelectric properties with no drop of the Curie temperature, the other is to reduce the amount of Sc elements, and maintain the high Curie temperature and piezoelectric performance.Based on the recent available research, the single element doping to the optimization of material performance has little effect, but it is an efficient method to achieve the comprehensive regulation of material properties and obtain more excellent electrical properties by the substitution of Sc with proper composite cations and the introduction of a third component into BS-PT to form multicomponent solid solution, this is the first research emphasis of this thesis. In addition, the content of the composite cations and the third component has significant effect on the electrical properties, and it is necessary to study the related mechanism to guide the regulation of material properties in BS-PT based piezoelectric ceramics system, this is the second research emphasis of this thesis. Material preparation should combine with the device applications, in this thesis, a high temperature piezoelectric actuator has been designed and fabricated by the BS-PT piezoelectric ceramics with the optimized performance, this is the third research emphasis. Details are described below:(1) The effect on the phase structure and electrical properties of Pb(Sn1/3/Nb2/3)O3 modified BS-PT piezoelectric ceramics have been systematically studied. The 0.025PSN-BS-xPT and 0.05PSN-BS-xPT have been synthesized by traditional solid-state reaction methods, and the microstructural morphology, phase structure and electrical properties near the MPB region were investigated in detail. For the 0.025PSN-BS-xPT system, the optimal electrical properties were obtained at the MPB x=0.62 with d33=523 pC/N.kp=54.6%, Pr=39.8 μC/cm2,Ec=19.3 kV/cm, strain=0.22%, large-signal d33*=734 pm/V,ε33T=2078, and tanδ=0.055, the Curie temperature also maintains at 418℃; and for the 0.05PSN-BS-xPT system, the optimal electrical properties were obtained at the MPB x=0.61 with d33=555 pC/N.kp=58.9%,Pr=41.2 μC/cm2, =19.8 kV/cm, strain=0.25%, large-signal d33*=833 pm/V,ε33T=2095, and tan δ=0.065, the Curie temperature also maintains at 408℃. By the compare of the 0.025PSN-BS-xPT with the 0.05PSN-BS-xPT system, it can be found that with the increasing of PSN content, the MPB region shifts towards the lower PT content, XRD peaks shift to lower angle resulting in the enlargement of the lattice parameter, and the grain growth is further restrained. The measurement of dielectric temperature spectrum presents that the introduction of PSN results in the diffuse phase transition phenomenon in the materials and decreases the Curie temperature of the ceramic system, and as the increasing of PSN content, the dielectric diffuse degree is enlarged and the Curie temperature further drops down. For the electrical properties, the import of trace amounts PSN optimizes the piezoelectric and ferroelectric properties of BS-PT, and the electrical properties have been further improved with the increasing of PSN content. The PSN-BS-PT ceramics possess excellent piezoelectric performance with the d33 over 520 pC/N and kp over 52%, which are more superior than the commercial PZT, and at the same time the piezoelectric constant d33 can keep over 80% of the value at room temprature when the annealing temperature reaches 300℃. The PSN-BS-PT ceramics completely meet the operating requirements with the temperature of 300℃, much higher than that value of 200℃ for PZT ceramics, showing potential for high temperature piezoelectric application.(2) The phase structure and electrical properties of Pb(Cd1/3Nb2/3)O3 modified BS-PT piezoelectric ceramics near the MPB region have been systematically studied. According to the research experience of the modification in BS-PT with PSN, trace amount of relaxation structure factor Pb(Cd1/3Nb2/3)O3 which possess the high transition temperature was imported into the BS-PT binary solid solution. The 0.05PCN-BS-xPT ceramics are identified as a single-phase perovskite structure and no clearly secondary phases have been detected, indicating that the Pb(Cd1/3Nb2/3)O3 end member with BS-PT solid solutions formed a stable single-phase perovskite structure. The optimum properties were obtained at the MPB region x=0.60 with d33=505 pC/N.kp=55.9%, Pr=39.7μC/cm2,Ec=20.8 kV/cm, Strain=0.23% and the Curie temperature also maintain at 403℃.The measurement of dielectric temperature spectrum presents that the Curie temperature increases linearly and the dielectric diffuse phenomenon reduce with the increasing PT content. All these properties together with the good thermal stability make the 0.05PCN-BS-xPT promising candidates for for high temperature piezoelectric applications.(3)The phase structure and electrical properties of Pb(Mg1/3Nb2/3)O3 modified Bi(Sc3/4In1/4)O3-PbTiO3 piezoelectric ceramics near the MPB region have been systematically studied. Bi(Sc3/4In1/4)O3-PbTiO3 ceramics reduce the content of Sc element to a large extent, and the Curie temperature for the MPB composition keeps 457℃, while the piezoelectric constant d33 significantly decrease to 201 pC/N. Then the trace amount of Pb(Mg1/3Nb2/3)O3 has been introduced into the Bi(Sc3/4In1/4)O3-PbTiO3 ceramics forming 0.02PMN-BSI-xPT ternary solid solution and the optimum properties were obtained at the MPB region (PT content 58 mol%) with d33=403 pC/N. kp=45.1%, Pr=36.4 μC/cm2 and Ec=24.7 kV/cm. And the Curie temperature still maintain 421℃ for the MPB composition resulting in the good thermal stability. Furthermore, the piezoelectric properties were enhanced significantly by the introduction of a small amount of PMN, and the piezoelectric constant d33 is doubled that of the binary Bi(Sc3/4In1/4)O3-PbTiO3 system. Though the piezoelectric performance decline a little in comparison with the BS-PT, the 0.02PMN-BSI-xPT systems lessen the content of Sc element and reduce the production cost, showing potential for the large-scale industrial production.(4) The effect on the phase structure and electrical properties have been systematically studied. xBi(Ni1/2Zr1/2)O3-(1-x-y)BiScO3-yPbTiO3 ternary solid solution have been designed and synthesized by traditional solid-state reaction methods according to the research status of Bi(Ni1/2Zr1/2)O3-PbTiO3 and BiScO3-PbTiO3 system. The room temperature phase diagram has been drawn based on the MPB location of the xBi(Ni1/2Zr1/2)O3-(1-x-y)BiScO3-yPbTiO3 ternary solid solution with different Bi(Ni1/2Zr1/2)O3 content. The microstructural morphology, phase structure and electrical properties of the Bi(Ni1/2Zr1/2)O3 modified BS-PT piezoelectric ceramics were investigated in detail. X-ray diffraction analysis presents that the as-prepared ceramics were of pure perovskite phase indicating that the BNZ end member with BS-PT solid solutions formed a stable single-phase perovskite ternary solid solution. With the increasing of BNZ content, the MPB region shifts towards the lower PT content, XRD peaks shift to higher angle resulting in the decrease of the lattice parameter, and the grain growth is further facilitated. The measurement of dielectric temperature spectrum presents that the introduction of BNZ results in the diffuse phase transition phenomenon and decreases the Curie temperature of the ceramic system. For the MPB composition of 0.025BNZ-BS-PT ceramics, the piezoelectric constant d33 and planar electromechanical coupling factor kp reach 480 pC/N and 58.2% together with the reduction of Sc element and the high temperature 439℃, indicating that the combination property of 0.025BNZ modified BS-PT are superior to the pure BS-PT. With the further increase of BNZ content, the cost cut down in line with the amount of usage for Sc element further reduction, while the piezoelectric performance are still equivalent to that of the BS-PT and the Curie temperature keeps over 410℃. All these properties together with the good thermal stability make the xBi(Ni1/2Zr1/2)O3-(1-x-y)BiScO3-yPbTiO3 ceramics promising candidates for for high temperature piezoelectric applications.(5)A disc-type interdigital electrodes piezoelectric actuator was designed and fabricated based on the 0.05PSN-0.34BS-0.61PT high temperature piezoelectric ceramics.This piezoelectric actuator has a novel and reasonable structure, giving a new idea for the actuator design. The piezoelectric constant J33 is fully utilized by the method of the printing interdigital electrodes on the disc surface, and it is a research highlights to release the accumulated stress by opening a hole at the center of the disk. Through the study of the disc-type interdigital electrodes piezoelectric actuator, it can be found that the displacement is proportional to the drive voltage, but inversely proportional to the electrode spacing in case of the fixed actuator size. At room temperature, the output displacement of the actuator can be over 18 μm with the drive voltage of 200 V/mm, and it reaches 56 μm with the drive voltage rising to 500 V/mm, which is far beyond the piezoelectric actuator with the same size. With the increase of testing temperature the displacement increases firstly, reaching the maxima at 150℃, and then decreases with the testing temperature further increasing. In addition, the value of the displacement at the testing temperature 275℃ is still equivalent to that of room temperature. The disc-type interdigital electrodes piezoelectric actuator completely meet the operating requirements of high temperature piezoelectric application, has an excellent application prospects.In this thesis, it achieves the comprehensive regulation of material properties and obtain more excellent electrical properties by the substitution of Sc with proper composite cations and the introduction of a third component into BS-PT to form multicomponent solid solution, the effect of the content of the composite cations and the third component on the electrical properties have been systematically studied, and related mechanism will guide the regulation of material properties in BS-PT based piezoelectric ceramics system in future.In addition, a disc-type interdigital electrodes piezoelectric actuator was designed and fabricated based on the 0.05PSN-0.34BS-0.61PT high temperature piezoelectric ceramics, realizing the research objectives of material preparation combination with the device applications. |
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