Electron spin resonance study of a-Cr2O3 and Cr2O3·nH2O quasi-spherical nanoparticles

Abstract

The quasi-spherical nanoparticles of hydrated Cr2O3 · nH2O, and crystalline -Cr2O3, have been synthesized by reduction of the first row (3d) transition metal complex of K2Cr2O7. The temperaturedependence of electron spin resonance (ESR) spectrum was studied in terms of g-factor, line width and intensity. ESR of both Cr2O3 · nH2O and -Cr2O3 has been studied at X-band (9.61 GHz) in the temperature range of 292–420K. An anomalous thermal hysteresis was observed in the ESR intensity and linewidth (Hpp of Cr2O3 · nH2O. This study shows that there could be a dominant water loss/gain during the heating-cooling cycles which is influencing the thermal relaxation time of Cr2O3 · nH2O. A similar hysteresis was observed in the differential scanning calorimetry (DSC) data which correlates well with that of ESR indicating possible surface dehydration/rehydration of Cr2O3 ·nH2O nanoparticles during the heating–cooling cycles of ESR measurements.