Effect of Co~(3+) ion on metal-insulator transition in (La_(0.1)Ca_(0.9)) (Mn_(1-x)Co_x) O_3

摘要

Orthorhombic perovskite-type (La_(0.1)Ca_(0.9))(Mn_(1-x)Co_x)O_3 was synthesized in the range 0.00<=x <=0.08. The Rietveld analysis indicates that the (Mn, Co)-O(1 and 2) distances are independent of the composition (x). Measurements of the electrical resistivity (#rho#) and the Seebeck coefficient (#alpha#) indicate that (La_(0.1)Ca_(0.9))(Mn_(1-x)Co_x)O_3 is an n-type semiconductor at the low temperature. At the high temperature, (La_(0.1)Ca_(0.9))(Mn_(1-x)Co_x)O_3 exhibits a metal-insulator transition in the range 0.0 <=x <=0.04. The metal-insulator transition temperature (T_t) increases with increasing the Co~(3+) ion content, while d#rho#/dT in the metallic region decreases with increasing the Co~(3+) ion content. The variation of E_a and T_t is explained by the difference in the electronegativity between Mn and Co atoms. The variation of d#rho#/dT in the metallic region is explained by the increase in the collective #sigma# bond.