Dependencies of Piezoelectric and Ferroelectric Properties and Crystal Structure on Synthesis and Sintering Processes in BaTiO₃ Prepared by Hydrothermal and Solid-state Methods

Abstract

In recent years, a development of lead-free piezoelectric ceramics is highly expected from the viewpoint of an environmental load, and BaTiO₃ can be regarded as one of the candidates. In this study, we synthesized BaTiO₃ powders by solid-state and hydrothermal methods, then sintered them by a two-step sintering process in addition to a conventional one. By performing Rietveld analyses using the neutron diffraction data, we examined effects of the preparation process on the crystal structures, and then discussed a relationship between the piezoelectric properties and the crystal structure. From SEM observations, it was found that the two-step sintering made densities of the ceramics slightly higher and suppressed the grain growth compared with the normal sintering, regardless of the powder synthesis process. It was also demonstrated that the two-step sintering enhanced piezoelectric properties in the case of the samples prepared by the solid-state method. One the other hand, a sample synthesized by the hydrothermal process with the two-step sintering exhibited lower T_c, ε_s and d₃₃ due to the size effect. From crystal structure analyses, it was revealed that a change in a tetragonality of the crystals by the sintering process depended considerably on the powder synthesis process.