Grain growth, densification and electrical properties of lead-free piezoelectric ceramics from nanocrystalline (Ba_0.85Ca _0.15)(Ti_0.90Zr_0.10)O₃ powder by sol-gel technique

The sintering behavior revealed in the sintering processes of the conventional and a two-step process and electrical properties of the (Ba _0.85Ca_0.15)(Ti_0.90Zr_0.10)O ₃ ceramics from the nanocrystalline powders synthesized by a sol-gel technique were systematically studied. It was found that the sintering process of the (Ba_0.85Ca_0.15)(Ti_0.90Zr _0.10)O₃ ceramics made from nanocrystalline powders was significantly improved, the sintering temperature was reduced markedly from 1,540 to 1,280 °C, as well as a high relative density (>97 %) was obtained in the conventional sintering. Under the two-step sintering conditions, the full densification and the most suppression of grain growth was achieved simultaneously. The (Ba_0.85Ca_0.15)(Ti _0.90Zr_0.10)O₃ ceramics from nanocrystalline powders sintered by the two-step sintering technique (sintered at T ₁ of 1,300 °C for 1 min and T ₂ of 1,150 °C for 20 h) exhibited the optimum average grain size of 700 nm and a high relative density of 98 %. The electrical properties of the (Ba_0.85Ca _0.15)(Ti_0.90Zr_0.10)O₃ ceramics were greatly influenced by the grain size and phase structure formed under the both sintering conditions, with sintering temperature and grain size increased, the electrical properties of the (Ba_0.85Ca_0.15)(Ti _0.90Zr_0.10)O₃ ceramics, which made from nanocrystalline powders, shows an enhancing trend: d ₃₃ ~100 pC/N, k _p ~53.3 % for the specimen sintered at 1,300 °C for 1 min and 1,150 °C for 20 h, d ₃₃ ~310 pC/N, k _p ~53.3 % for the specimen sintered at 1,350 °C for 2 h respectively.