Polaron conduction mechanism in Nickel ferrite and its rare-earth derivatives

Abstract

NiFe2O4 & NiFe1.925R0.075O4 (R = Lu, Yb & Y) samples conductivity response for alternating current (σac) in the high temperature region (300 K to 570 K), and for direct current conductivity (σdc) response in the temperature range 80 K – 300 K were investigated. For all the investigated samples σac increases with raising frequency owing to transfer of charge carriers at the two octahedral sites containing Fe3＋ or Ni2+. The total σac was observed to follow σ = D + Bωn where the frequency exponent n, initially decreases and then increases following overlapping large polaron model. The behaviour of σac with temperature reveals the semiconducting behaviour of the investigated samples. The Arrhenius plots of σac shows two regions of conductivity suggesting two types of relaxation phenomena. The σdc, also increases with increasing temperature, owing to the raise in the thermally stimulated drift mobility of charge carriers. The decrease in the activation energy with decreasing temperature corresponds to small polaron hopping mechanism.