Effect of ionic-size change of the rare earth ion on the electrical properties of the hole doped double perovskite Gd_(0.95)Sr_(0.05)BaCo_2O_(5.5)

摘要

We report the effect of co-doping Y on the electrical properties of the hole doped double perovskite Gd_(0.95)Sr_(0.05)BaCo_2O_(5.5). New compositions Gd_(0.95-x)Y_xSr_(0.05)BaCo_2O_(5.5) have been successfully synthesized and characterized. A contraction in all three lattice parameters of the orthorhombic unit cell has been observed on Y doping. A reduction in the insulator to metal-like transition temperature (T_(IM)) has been observed upon Y doping from 348K for x=0 to 331K for x=0.2. These observed shifts have been interpreted in terms of the possible mechanisms of the insulator-metal transition. The low temperature electrical resistivity data in the range 300-77K has been fitted to different conduction models. They fit best to a variable range hopping (VRH) model at low temperature below 120K followed by small polaron hopping model (SPH) at intermediate temperature (120-200K). The presence of magnetic polarons in the cobaltite systems has been envisaged recently and this provides further evidence for the same.