Study On Hydrothermal Method Synthesis, Structure, Piezoelectric Properties Of (Na_1/2Bi_1/2) TiO₃-based Ceramics

Sodium bismuth titanate, (Na₁/2Bi₁/2)TiO₃(NBT), is a kind of perovskite-type ferroelectric with a relatively large remnant polarization at room temperature and a relatively high Curie temperature(T_c =320℃). For its strong ferroelectrics at room temperature, NBT has been considered to be a promising candidate material for lead-free piezoelectric ceramics. But due to the high coercive field, it's difficult to polarize the NBT ceramic sufficiently. Therefore it can't exhibit the true piezoelectricity performance perfectly. In order to get the high-performance NBT-based ceramics, many scholars have carried on a large amount of research work on the A site, B site and dual sites substitution of the NBT-based ceramics. The chemical preparation methods of the ceramic powder have caused worldwide concern. Among the chemical methods, the hydrothermal method has many unique advantages. In this dissertation, a hydrothermal method had been employed to synthesize the NBT powders and ceramics, the structural characteristics and piezoelectric properties of (1-x)Nai/2Bi)1/2TiO₃-xK₁/2Bi₁/2TiO₃ ((1-x)NBT-xKBT) ceramics also had been investigated.It was found that the property of the Ti precursor contributed greatly to the crystallization of NBT powders. In the experiment, we chosed Ti(OC₄H₉)₄ Bi(NO₃)₃·5H₂O and NaOH as the titanium, bismuth resource and minerlizer respectively. It was ascertained that the hydrothermal temperature of 180℃, synthesis time of 48h, crystallizer concentration of 12M, and the pH values of 12¹3 for precursors are preferred. Through the sintering experiment, we found that the synthesis method contributed greatly to the sintering quality of NBT ceramic. Powders synthesized from hydrothermal method presented good sintering performance. Compared with (Na₁/2Bi₁/2)TiO₃ ceramics made by the conventional solid state reaction method, the specimen made by the hydrothermal synthesis method had superior piezoelectric properties with its piezoelectric constant d₃3 attaining a relatively high value of 82 pC/N.The structural characteristics and piezoelectric properties of (l-x)NBT-xKBTceramics were also investigated. The results showed that hydrothermal method did not change the MPB of the ceramics. Near the MPB, the piezoelectric constant da of (l-x)NBT-xKBT ceramics reach its maximums values. Compared with the solid state reaction method, the specimen made by hydrothermal method had superior piezoelectric and ferroelectric properties.