Mechanism of small-polaron formation in the biferroic YCrO3 doped with calcium

Abstract

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.

Reversal magnetization, spin reorientation, and exchange bias in YCrO3 doped with praseodymium

“…The internal structural parameters such as the octahedral distortion (∆) and the < Cr − O − Cr > bond angles are affected by the Y/Pr substitution whereas the average < Cr − O > bond lengths are rigid remaining almost constant. This fact is an expected result for Cr +3 in octahedral environment [28,29] Fig. 3 a, b).…”

Investigations on electrical conductivity and dielectric properties of Na doped ZnO synthesized from sol gel method

“…But in the presence of transition metal ions, we speak about electronic conductivity which is governed by the following mechanism [14][15][16]: during doping, defects are created in the band gap and are filling some energy level [17]. Around these levels, the charge carriers are localized and creating a small polaron [18][19][20]. The conduction can take place by transfer of electrons between the localized states [21].…”

Temperature dependent X‐ray diffraction and Raman spectroscopy studies of polycrystalline YCrO3 ceramics across the TC ~ 460 K

“…As can be seen, the Raman intensity of all modes decreases significantly with the increase of temperature, and there are anomalous changes at FE to PE transition temperature. Interestingly, earlier reports on the temperature‐dependent permittivity data for YCO have also reported such anomaly across T C . These anomalies are much more pronounced in line widths versus temperature plot, as depicted in Figure .…”