Preparation of porous barium titanate ceramics and enhancement of piezoelectric sensitivity

Porous piezoelectric ceramic shows some advantages, such as high hydrostatic figure of merit, low acoustic impedance, and excellent piezoelectric sensitivity, compared with its compact counterpart. These merits make it used widely in various electronic devices, such as underwater acoustic transducer, ultrasonic transducer, and sensor. Currently, the researches of porous piezoelectric ceramics mainly focus on the Pb(Zr, Ti)O₃ ceramic, which is harmful to environment and human health. In this paper, the lead-free porous barium titanate (BaTiO₃) ceramic doped with dextrin is prepared by using the conventional solid-state method. The effects of sintered temperature and dextrin content on the structure, porosity, and morphology of the pores are studied experimentally and theoretically. Also, the relationship between porosity and dielectric, piezoelectricity, electro-mechanical coupling factor, acoustic impedance, and hydrostatic figure of merit are explored. The X-ray diffraction pattern shows that the lattice constants of ceramic are not affected by dextrin. The BaTiO₃ ceramic demonstrates single perovskite structure with P4mm space group. The SEM micrograph reveals that the porous ceramic has three-dimensional open pores with the size of 1−7 <inline-formula><tex-math id="M2">\begin{document}${\text{μ}}{\rm m}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181790_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181790_M2.png"/></alternatives></inline-formula>. Sintering temperature plays a key role in porosity in the BaTiO₃ ceramic. The porosity of ceramic gradually declines with sintered temperature increasing from 1250 to 1300 °C. The max porosity of up to 58% is obtained in 10% dextrin-doped BaTiO₃ ceramic sintered at 1250 °C. The porosity of 5% dextrin-doped ceramic is smaller than that of the undoped one when the sintering temperature is 1250 °C or 1280 °C, indicating that a small amount of dextrin is beneficial to the densification of BaTiO₃ ceramic. Both the dielectric and piezoelectric property gradually decrease with dextrin content increasing. For the BaTiO₃ ceramic, high sintering temperature contributes to better dielectric and piezoelectric property than low temperature. Here, the ceramic with 10% of dextrin sintered at 1250 °C exhibits the highest hydrostatic figure of merit (8376 × 10^–15 Pa^–1) and the lowest acoustic impedance (~ 2.84 Mrayls). The binding force between grains is also obviously enhanced in the ceramic sintered at 1280 °C, which is very helpful for their mechanical strength improvement. The excellent properties of the BaTiO₃ ceramic doped with dextrin indicate its potential applications in sensor and hydrophone.