  The effects of Ca substitutions on the structure, magnetism and electrical
properties of YCrO3 ceramics are investigated by X-ray diffraction, magnetic
susceptibility and electrical conductivity measurements. The cell volume
decrease occurs through the change from Cr(III) to Cr(IV) as a result of the
charge compensation of the Ca doping. No changes are observed in the
antiferromagnetic transition temperature while strong changes are observed in
the transport measurements due to Ca content. The increase of the electrical
conductivity as well as the decrease of the activation energy are caused by the
formation of the small-polarons localized in the O-Cr-O lattice distortion. The
origin of small-polarons in the undoped sample is different in nature from the
calcium doped. "Local non-centrosymetry" is the source of the small-polaron
formation in undoped sample, while the change from Cr(III) to Cr(IV) through
the charge compensation of Ca(II) in the Y(III) site is the source of
small-polarons formations. The decrease of the average bond length Cr-O as well
as effective moments in the paramagnetic state and the increase of the
electrical conductivity are clear evidence that the Ca doping induces localized
polarons, which in turn, these quasiparticles move from site to site by a
thermally activated process in the doped YCrO3 compound. Here, we also discuss
a possible mechanism of small-polaron injections in YCrO3 matrix.
