Effect of vanadium doping on the semiconducting properties of La/sub 0.67/Ca/sub 0.33/MnO/sub 3/ ceramics

Manganites perovskite compound exhibit the transition of semiconducting to metallic conductivity at T/sub P/ and the magnetic properties observed in the /spl chi/'-temperature curves show transition from paramagnetic to ferromagnetic at T/sub C/. The coexistence of T/sub C/ and T/sub P/ are due to the double exchange interaction of two electrons in Mn/sup 3+/-O/sup 2-/-Mn/sup 4+/ and Mn/sup 4+/-O/sup 2-/-Mn/sup 3+/ configuration which brings the system below T/sub C/ into a metallic state. Hence it is observed that the Curie temperature T/sub C/ is closely related to the sharp decrease in the electrical resistivity of the samples. However, both transition temperatures shift to lower temperature as vanadium doping increases indicating the loss of ferromagnetic order and transport properties. As for the transport properties the semiconductor model ln(/spl sigma/)/spl sim/(E/sub a//kT) was used to explain the conduction mechanism of perovskite manganites above T/sub P/. It was concluded that the total conductivity, /spl sigma//sub tot/, consists of the intrinsic and the extrinsic components, such that /spl sigma//sub tot/=/spl sigma//sub int/+/spl sigma//sub ext/. The total activation energy increases initially from 0.150 eV to maximum value of 0.228 eV at x=0.01 and decreases to 0.1 eV at the composition of x=0.30.