The effects of Ca substitutions on the structure, magnetism and electrical properties of YCrO 3 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 areclear 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 YCrO 3 compound. Here, we also discuss a possible mechanism of small-polaron injections in YCrO 3 matrix.

Crystal structure, thermal and magnetic properties were systematically studied in the Y1-x Prx CrO3 with 0 ≤ x ≤ 0.3 compositions. Magnetic susceptibility and specific heat measurements show an increase of the antiferromagnetic transition temperature (TN ) as Pr is substituted in the Y sites and notable magnetic features are observed below TN . Strong coupling between magnetic and crystalline parameters is observed in a small range of Pr compositions. A small perturbation in the lattice parameters by Pr ion is sufficient to induce a spin reorientation transition followed by magnetization reversal, to finally induce exchange bias effect. The spin reorientation temperature (TSR) is increased from 35 K to 149 K for 0.025 ≤ x ≤ 0.1 compositions. It is found that the Cr spins sublattice rotates continuously from TSR to a new spin configuration a lower temperature. In addition, magnetization reversal is observed at T * ∼ 35 K for x= 0.05 up to T * ∼ 63 K for x = 0.20 composition. The M − H curves show negative exchange bias effect induced by Pr ions, which are observed below of 100 K and being more intense at 5 K. At 10 K, the magnetic contribution of the specific heat, as well as the ZFC magnetization, show the rise of a peak with increasing Pr content. The magnetic anomaly could be associated with the freezing of the Pr magnetic moment randomly distributed at the 4c crystallographic site. A clear correspondence between spin reorientation, magnetization reversal and exchange bias anisotropy with the tilting and octahedral distortion is also discussed.

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