Strain enhancement in lead-free Bi _0.5 (Na _0.78 K _0.22 ) _0.5 TiO ₃ ceramics by CaZrO ₃ substitution

The effects of CaZrO ₃ substitution on the crystal structure, electric field–induced strain, and piezoelectric properties of Bi _0.5 (Na _0.78 K _0.22 ) _0.5 TiO ₃ ceramics have been investigated. The CaZrO ₃ substitution resulted in a transition from ferroelectric tetragonal to pseudocubic symmetry with relaxor characteristics, leading to degradations in the piezoelectric coupling coefficient, electromechanical quality factor, and piezoelectric coefficient d ₃₃ . However, the electric field–induced strain was significantly enhanced by the CaZrO ₃ -induced phase transition and reached a highest value of S _max / E _max = 617 pm/V when CaZrO ₃ content reached 3 mol%. The result supports a prediction that a large strain at the ferroelectric–relaxor transition region can be observed when the tolerance factor of the Bi-perovskite is decreased by the substitution of ABO ₃ -type modifiers.