Mechanism Research of phase Transformation Effects Acted on the conductivity Property of Chromic Lanthanum Doped with Calcium

The mechanism of phase transformation process acting on the electrical conductivity of lanthanum chromite doped with calcium was studied. The electrical conductivity data of lanthanum chromite doped with calciumsuggest that, the active energy of carriers is different in high temperature zone (above 500 degrees C) and low temperature zone (below 300 degrees C). Based on the data of CTE and DSC, it is found that the phase transformation from orthorhombic structure (Pnma) to rhombohedral stucture (R3C) occurrs at the temperature of 300-500 degrees C. Based on the XRD of samples at different temperatures, with revieltd refine treament, the lattice parameters and the bond length of Cr-Cr, O-O and La-O were calculated. The phase transition process may lead to the increasement of bond length and decrease of the activation energy of electrics and vacancies of two carriers,which enhance the electrical concductivity consequently.