Electronic conductivity in the Pr1-xSrxCo1-yMnyO3-δ system

The effect of Mn substitution for Co and of Sr doping for Pr on the electronic conductivity of Pr1-xSr1-yCo1-yMnyO3-delta (x = 0.3, 0.5, 0 less than or equal to y less than or equal to 1) was investigated. All oxides have an orthorhombic GdFeO3-type structure (space group Pbnm), as determined by XRD. The pseudo-cubic lattice constant increases with increasing Mn content. The electrical conductivity was measured in the temperature range from 100 to 800 degrees C in air. The substitutionally-mixed compositions exhibit a semiconducting behavior, where the small polaron hopping conductivity model applies. The normalized conductivity shows a sharp decrease when y increases in the range 0 < y < 0.4, and it reaches a minimum in the range 0.4 < y < 0.6. The small polaron is trapped at the energetically lower Mn sites, and the slow transition rate to a neighboring Co site dominates the hopping process. At higher y values, the hopping proceeds among adjacent Mn sites, and as a result, an increase of conductivity is observed. The calculated activation energy values agree with the above mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.