Band gap evolution and a piezoelectric-to-electrostrictive crossover in (1 − x)KNbO3–x(Ba0.5Bi0.5)(Nb0.5Zn0.5)O3 ceramics

The band gap of (1 − x)KNbO3-x(Ba0.5Bi0.5)(Nb0.5Zn0.5)O3 (0 ≤ x ≤ 0.25) ceramics narrows slightly from 3.22 eV for x = 0 to 2.89 eV for x = 0.25, in broad agreement with first-principles calculations [Phys. Rev. B, 2014, 89, 235105]. In addition, an unreported piezoelectric-to-electrostrictive crossover is observed in this compositional range, which is accompanied by a continuous decrease of the maximum electric field-induced strain due to the presence of a non-ferroelectric phase. An electrostriction coefficient of 0.023 m4 C−2 is measured for x = 0.05, whilst no electromechanical response is observed for non-ferroelectric x = 0.25, even under an applied electric field of 80 kV cm−1