Electrical conductivity and seebeck coefficient of divalent-metal-doped YCrO3

The substitution of divalent metal ions for Y(+3) in YCrO3 results in a charge compensating transition of Cr(+3) to Cr(+4) and the formation of small polarons as charge carriers. The experimentally measured electrical conductivity, σ, and Seebeck coefficient, S, exhibit behavior consistent with a theoretical model developed for small polaron transport in these narrow-band semiconductors. The small polaron transport is a thermally-activated process with a measured activation energy, E, of about 0.18 to 0.25 eV in these materials. Both σ and S increase with temperature and show a near linear dependence on dopant concentration and a strong dependence on dopant (ionic) size. Analysis of the results in terms of the model indicates that Ca is much more effective in polaron formation than any of the other dopants in YCrO3; this is due to the similar ionic size of Ca(+2) and Y(+3) which minimizes the lattice distortion from substitution