The abnormal electrical and optical properties in Na and Ni codoped BiFeO3 nanoparticles

Bi0.97Na0.03Fe1-xNixO3 (x = 0, 0.005, 0.01, 0.015) nanoparticles are prepared via a sol-gel method. Weak ferromagnetism and exchange bias phenomenon without field cooling are observed in the samples. The oxygen vacancy concentration and leakage current density are increased with increasing the Ni content. However, with the increase of Ni content, the band gap of Bi0.97Na0.03Fe1-xNixO3 nanoparticles first decreases and then increases. To explain the abnormal phenomenon, the interplay of oxygen vacancy donor and hole acceptor is analyzed and a phenomenological qualitative model based on the electronic energy band is proposed. Additionally, the threshold switching behavior appears in Bi0.97Na0.03Fe1-xNixO3 samples with x = 0.01, 0.015 and the effect is qualitatively explained by introducing a conducting channel model based on the high-density mobile charges. (C) 2015 AIP Publishing LLC.