Large electric field-induced strain and piezoelectric responses of lead-free Bi0.5(Na0.80K0.20)0.5TiO3-Ba(Ti0.90Sn0.10)O3 ceramics near morphotropic phase boundary (original) (raw)

PZT-based ceramics have been the dominant piezoelectric material for a half century. They are widely used in various applications such as actuators, sensors and ultrasonic transducers. [1] The compositions near the morphotropic phase boundary (MPB) in PZT-based ceramics have attracted great attention because of their excellent electromechanical properties. [2] However, with the potential for regulations (RoHS/WEEE) that may restrict the use of hazardous substances in electronic devices, intensive efforts have been devoted to search for lead-free piezoelectric materials to serve as a substitute for PZT-based ceramics. In searching for high-performance lead-free piezoelectric ceramics, the MPB between two end members with different crystal structures has been one of the main strategies. Within the MPB region, maximum polarization values are attainable which leads to enhanced electrical properties. [2] Much attention has been paid to BNT-based solid solutions [3-7] Lead-free piezoelectric ceramics with compositions belonging to family of compositions (1-x)Bi0.5(Na0.80K0.20)0.5TiO3-xBa(Ti0.90Sn0.10)O3 or (1-x) BNKT-xBTS (when x = 0.05-0.15 mol fraction) near the morphotropic phase boundary (MPB) were fabricated by a conventional mixed oxide method. Sintered samples had relative densities greater than 98% of their theoretical values. X-ray diffraction data revealed that the MPB region consisted of coexisting rhombohedral and tetragonal phases in the BNKT-BTS system was identified over the entire compositional range. A large electric field-induced strain (Smax) of 0.36% and a normalized strain coefficient (d * 33) of 649 pm/V were observed in the BNKT-0.05BTS sample. The sample close to the MPB composition (BNKT-0.11BTS) exhibited the maximum dielectric constant (εr = 1770), temperature of maximum permittivity (Tm = 333C°) and lowfield piezoelectric coefficient (d33 = 227 pC/N), along with reasonable ferroelectric properties (Pr = 20.6 mC/cm 2 , Rsq = 0.88) and strain properties (d * 33 = 445 pm/V and Smax = 0.24%).