Piezoelectric and Dielectric Properties of (Bi,Na,K,Ag)TiO3–BaTiO3 Lead-Free Piezoelectric Ceramics

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Lead-free ($1-y$)(Bi0.5Na0.49-xKxAg0.01)TiO3–$y$BaTiO3 ($x=0$ to 0.1, $y=0$ to 0.04) [abbreviated as BNKAT-BT-100$x$/100$y$] piezoelectric ceramics were fabricated using various amounts of K and Ba substitutions, and their piezoelectric and dielectric properties were investigated. The crystal structure significantly changed with the amount of K substitution. The BNKAT-BT-5/2 specimens exhibited a pseudocubic structure, while the BNKAT-BT-10/2 specimens exhibited a tetragonal structure and provided a larger electrostrain constant ($d_{33}{}^{*}$) than BNKAT-BT-0/2 specimens, which exhibited a rhombohedral structure. The addition of La2O3/MnO to BNKAT-BT specimens affected the crystal structure and electrical properties. La2O3/MnO-added BNKAT-BT-10/100$y$ ($0.02\leqq y\leqq 0.03$) specimens with a pseudocubic structure exhibited $P$–$E$ hysteresis loops different from those that are characteristic of ferroelectric, and provided a peculiar field-induced strain without the residual strain in the butterfly curve and a very large strain constant ($d_{33}{}^{*}$) of 415 pm/V. This may be associated with the field-forced phase transition from the paraelectric phase to the ferroelectric phase.
2009-09-25