Band gap evolution and 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-principle calculations [Phys. Rev. B 89, 235105 (2014)]. 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/C2 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.