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.