Showing papers by "Yuji Hiruma published in 2012"

Lead‐Free Piezoelectric Ceramic Based on (Bi1/2Na1/2)TiO3‐(Bi1/2K1/2)TiO3‐BaTiO3 Solid Solution

Abstract: Piezoelectric properties of a solid solution based on three components of bismuth sodium titanate, (Bi 1/2 Na 1/2 )TiO 3 (BNT), bismuth potassium titanate, (Bi 1/2 K 1/2 )TiO 3 (BKT), and barium titanate, BaTiO 3 (BT), that is, x(Bi 1/2 Na 1/2 )TiO 3 -y(B 1/2 K 1/2 )TiO 3 -zBaTiO 3 [abbreviate as BNBKy:z(x); x+y+z=l] are studied as a lead-free piezoelectric material. High piezoelectric properties in lead-free piezoelectric ceramics were obtained near the MPB composition, and the highest electromechanical coupling factor, k 33 and k p , and piezoelectric constant, d 33 , were 0.58 and 0.36 for BNBK2:1(0.89) and 181 pC/N for BNBK2:1(0.88). Nevertheless, the depolarization temperature, T d , shifts to lower temperature around the MPB compositions, and T d 's of BNBK2:1(0.88-0.90) are about 100 °C. On the tetragonal side, the T d shift to higher temperature with increasing the lattice anisotropy, cla. In this study, the T d higher than 200 °C was obtained in the range of x ≤ 0.78, that is, the k 33 and d 33 for BNBK2.1(0.78) were 0.45 and 128 pC/N, respectively.

Fabrication of Dense KNbO$_{3}$ Ceramics Derived from KHCO$_{3}$ as a Starting Material

Abstract: Potassium niobate-based ceramics, K(1+x)NbO3 (KN-10000x, x = 0–0.001), were fabricated using KHCO3 powder as a starting material to improve their reproducibility. The KN-7.2 ceramics all had high relative density ratios exceeding 96% and resistivities of above 1012 Ωcm. Additionally, many KN-7.2 ceramics were prepared under different levels of humidity of about ~70% in the weighing process. The relative density ratios of all the KN-7.2 ceramics were similar, showing the excellent reproducibility obtained using KHCO3 powder as a starting material. The electromechanical coupling factor k33 and piezoelectric strain constant d33 of the KN-7.2 ceramics were 0.50 and 90 pC/N, respectively.