Enhanced optical and piezoelectric characteristics of transparent Ni-doped BiFeO3 thin films on a glass substrate

Abstract

Very thin and highly transparent BiFeO₃ films are attractive owing to their potential application as ferroelectric photovoltaic devices. Here, we demonstrate enhancements in optical and piezoelectric properties that occur upon very low levels of Ni doping in solution-processed BiFeO₃ thin films (thickness less than 200 nm). Doping only with 0.5 mol% Ni reduces the optical band gap from 2.83 to 2.78 eV and increases the piezoelectric coefficient from 15.4 to 28.0 pm V⁻¹. These improvements are attributed to changes in the morphotropic phase boundary, oxygen-related defects, and crystallinity, which are driven by the low levels of Ni doping. For example, the increased piezoelectric coefficient upon Ni doping is attributed to a movement toward the morphotropic phase boundary and the enhanced crystallinity of the perovskite phase.