Fabrication And Electrical Properties Of Textured(Ba_0.95Ca_0.05)(Ti_0.94Sn_0.06)O₃ Lead-Free Piezoelectric Ceramics

Because of a series of environmental problems caused by the application of lead-based piezoelectric materials, it is very important and necessary to develop lead-free piezoelectrics. BaTiO3（BT） based lead-free piezoelectric ceramics have the potential to replace lead-based ceramics among the lead-free systems. But the electrical properties of Ba TiO3（BT） based ceramics are much lower than lead-based piezoelectric ceramics. By using the macro-structure-design（texturing ceramics） of lead-free piezoelectric ceramics, the piezoelectric properties of ceramics could be enhanced to comparable to those of piezoelectric single crystals with the same compositions, and the comprehensive electrical properties of the materials can be optimized.Firstly, the(Ba_0.95Ca_0.05)(Ti_0.94Sn_0.06)O₃（BCTS） random ceramics were prepared by the conventional solid state reaction method. CuO was used as a sintering aid to investigate its effect on phase structure and electrical properties of BCTS ceramics. BCTS-xCuO% samples with variety CuO doping radios were fabricated. It was found that the sintering-temperatures were significantly reduced when CuO was added, and the samples became much denser. The ceramics showed superior properties when 0.50 mol% CuO were doped: the piezoelectric coefficient d33 = 516 pC/N, electromechanical coupling coefficient kp = 0.42, mechanical quality factor Qm = 352, the relative permittivity（under 1 kHz）εr = 7639, tanδ = 0.007, relative strain Sm = 0.10% and d33* = 996 pC/N. The herringbone domain patterns became much simpler and their number substantially decreased inceramics with 0.50 mol% CuO. Although CuO-doped BCTS ceramics have superior electrical properties, the phase transition temperature significantly decreased nearly 40 ℃, and the Curie temperature of optimum component ceramics is only 53℃.Secondly, by optimizing the parameters, the highly（00l）-oriented BaBi4Ti4O15 platelept recursor with Aurivillius phase structure was successfully prepared by molten salt synthesis. BaTiO3 platelets were prepared from BaBi4Ti4O15 precursor through topochemical microcrystal conversion. The（h00）-oriented platelet BaTiO3 templates with pure perovskite structure and high-aspect-ratio was successfully synthesized. In addition, the template size is 5-10 μ m in length and 500 nm in thickness, the morphology of BaTiO3 platelets meets the requirements of the textured ceramics.Finally, the [001]c BCTS textured ceramics with texture degree of 69.8% were prepared by using templated grain growth while the platelet BaTiO3 served as template. The properties of BCTS textured ceramics were characterized. Compared with random BCTS ceramics, the TR-O of BCTS textured ceramics became 15 ℃ higher and the Curie temperature Tc became 23 ℃ lower（Tc = 68 ℃）. The electrical properties of BCTS textured ceramics were optimized: the piezoelectric coefficient d33 = 395 pC/N, electromechanical coupling coefficient kp = 0.39, mechanical quality factor Qm = 150, the relative permittivity εr（1 kHz） = 4453, and dielectric loss tanδ = 0.018. The electrical properties of BCTS textured ceramics are obviously optimized compared with random ceramics（d33 = 307 pC/N, kp = 0.35, Qm = 134, εr（1 kHz） = 3073, tanδ = 0.026）. The remanent polarization of BCTS textured ceramics Pr reaches 6.27 μC/cm2,and coercive field Ec is 1.46 kV/cm, which are much better than Pr = 4.92 μC/cm2 and Ec = 2.59 kV/cm for random ceramics. Besides, relative strain Sm =0.24% is much higher than that of random ceramics（0.10%）.This work here laid the foundation for further work on [001]c textured BCTS ceramics with higher texture degree and superior electrical properties.