Transport and magnetic properties of Pr1-xCaxCrO3 (x = 0.0–0.5): effect of t2g orbital degeneracy on the thermoelectric power

Abstract

We report on the resistivity (ρ), thermoelectric power (S for Seebeck) and magnetic measurements of the series Pr1-xCaxCrO3 (x=0.0–0.5). These orthochromites exhibit a T independent, large and positive S, from 100 K to 700 K which follows the Cr4+ concentration. Upon Ca2+ for Pr3+ substitution, a concomitant decrease of the resistivity and S values is found. The evolution of S as a function of hole concentration (Cr4+) can be nicely fitted by the modified Heikes formula which takes into account the orbital degeneracy associated to Cr3+/Cr4+. This is in good agreement with the model previously calculated by Marsh and Parris, in the case of weak magnetic coupling [Phys. Rev. B 54, 7720 (1996)]. The magnetic susceptibility measurements support the assumption of a weak magnetic coupling since the antiferromagnetic ordering TN values are found to be lower than 250 K. For Pr0.7Ca0.3CrO3, the power factor PF= S2/ρ measured at 700 K is equal to 1.9×10-4 W m-1K-2. The present system, chemically stable in air up to T > 1000 °C, is promising for thermoelectric application at very high temperature.