Study On Processing And Properties Of Bismuth Layered Structure BaBi₄ Ti₄O₁₅ Piezoelectric Ceramics

As the strengthen of human awareness for environmental protection, the investigation and development to the lead-free piezoelectric ceramics become an urgent issue with large social and economic significances due to the damage to human and the environment in the process of the production and use of traditional PZT ceramics. Bismuth layer lead-free piezoelectric ceramics is considered to be one of the most promising materials in the field of the lead-free piezoelectric ceramics because of its characteristics such as high Curie temperature, large anisotropy of electromechanical coupling coefficient, high mechanical quality factor, the time stability of resonant frequency and good temperature stability. The relatively poor piezoelectric properties of piezoelectric ceramics with bismuth layered structure can be improved by doping, heat treatment and other measures.In this thesis, with BaBi₄Ti₄O₁₅ (m = 4) bismuth layer structure ceramics as the study object, its process of powder preparation, polarization conditions and dielectric as well as properties were investigated. As a result, the optimum ingredient is Bi excess of 10%; pressure of 100MPa, pretreatment temperature of 750°C, and the sintering temperature of 1020°C are the best preparation process parameters; 30°C, 1.5 kV / mm and 5min are the optimum polarization temperature, polarization voltage and polarization time for polarization process, respectively. The piezoelectric constant of pure BaBi₄Ti₄O₁₅ ceramic d₃₃ = 4.4pC / N under this conditions.After A-substituted by Mn, Mg, Sr, La elements, the ceramic crystalline phase grain of BaBi₄Ti₄O₁₅ is uniform sheet structure with low porosity. Doped ceramic samples have been formed layered perovskite structure and the introduction of trace elements does not breach the layer structure of the ceramic. However, XRD characteristic diffraction peaks of ceramic powder shift slightly because of the differences in ionic radius. When the doping content of Mn is 0.04, the maximum relative dielectric constant (ε_r = 764.26 (1KHz)) and smaller dielectric loss( tanδ= 0.006647 (1KHz)) are obtained, while Mn of 0.06 brings the maximum piezoelectric constant (d₃₃ = 9.5pC / N). When the doping content of Mg is 0.02, larger relative dielectric constant(ε_r = 228.52 (1KHz)) is achieved, and Mg of 0.04 leads to the maximum piezoelectric constant (d₃₃ = 5.5pC / N). When the doping content of Sr is 0.02, larger the relative dielectric constant(ε_r = 260.16 (1KHz)) is obtained, while Sr of 0.04 and 0.06 brings the maximum piezoelectric constant d₃₃ = 7.9pC / N. When the doping content of La is 0.08, the maximum relative dielectric constant of ceramic(ε_r = 318.20 (1KHz)) and the maximum piezoelectric constant is 9.3pC / N .Perovskite phase of layered structure is formed in the complex ceramic structure without other miscellaneous phases such as pyrochlore. Grains mainly is in layer-based, grains show a better development with the increase of the doping content, and the gap between the grains reduces. In series of (1-X) BaBi₄Ti₄O₁₅-XMnBi₄Ti₄O₁₅ ceramic, when X is 0.6, the maximum relative dielectric constant is 823.16 (1KHz), and when X is 0.4, tanδ= 0.0066 (1KHz), piezoelectric constant is up to 8.3 pC / N; in series of (1-X) BaBi₄Ti₄O₁₅-X MgBi₄Ti₄O₁₅ ceramic, when X is 0.4, the maximum relative dielectric constant is 551.88 (1KHz), and when X is 0.2 , the maximum piezoelectric constant is 7.6 pC / N; in series of (1-X) BaBi₄Ti₄O₁₅-XSrBi₄Ti₄O₁₅ ceramic, when X is 0.6 , the maximum relative dielectric constant is 224.28 (1KHz), and when X is 0.2 , the maximum piezoelectric constant is 7.0 pC / N.By Vickers hardness test, it is found that the hardness of BaBi₄Ti₄O₁₅ ceramic is 2.8GPa, the Vickers hardness is 3.82GPa when the doping content of Mn element is 0.08; the Vickers hardness is 5.74 GPa when the doping content of Mg element is 0.06; the highest Vickers hardness of ceramics is 2.58GPa When the introducing amount of Sr is 0.06; the Vickers hardness of ceramic is 3.3GPa when the doping content of La element is 0.08. For the complex structural ceramics: Vickers hardness of the 0.2BaBi₄Ti₄O₁₅-0.8MnBi₄Ti₄O₁₅ ceramic samples is up to 4.03GPa; the highest Vickers hardness of 0.8BaBi₄Ti₄O₁₅-0.2MgBi₄Ti₄O₁₅ ceramics is 1.45GPa; the highest Vickers hardness of 0.8BaBi₄Ti₄O₁₅-0.2SrBi₄Ti₄O₁₅ ceramic samples is 4.27 GPa.