Piezoelectric and Dielectric Properties of (Bi,Na,K,Ag)TiO3–BaTiO3Lead-Free Piezoelectric Ceramics

Lead-free (1- y )(Bi 0.5 Na 0.49- x K x Ag 0.01 )TiO 3 – y BaTiO 3 ( 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 La 2 O 3 /MnO to BNKAT-BT specimens affected the crystal structure and electrical properties. La 2 O 3 /MnO-added BNKAT-BT-10/100 y (0.02≦ y ≦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.