XRD, HRTEM, magnetic and Moessbauer studies on chemically prepared Fe~(3+)-doped nanoparticles of cerium oxide

摘要

Nanocrystalline samples of Fe-doped cerium oxide (Ce_(0.90)Fe_(0.1)O_2) are prepared by sol-gel method. The precursor materials used for the synthesis are ferric nitrate and cerium nitrate. The as-prepared samples is annealed at different temperatures to obtain the sample with different particle sizes. The crystallographic phases of the nanocrystalline materials have been confirmed by X-ray diffractograms (XRD). The sizes of the nanoparticles estimated from the peaks of the XRD patterns using Debye-Scherrer equation are in the range 6-58 nm. Results extracted from the high-resolution transmission electron microscopy (HRTEM) are in agreement with the findings obtained from XRD. The average magnetic susceptibilities of all the samples with different particle sizes are measured in the temperature range 300-14 K. The average susceptibilities of the samples annealed below ～740 ℃ show paramagnetic behaviour. The susceptibilities of the samples annealed at and above ～740 ℃ sharply decrease at ～240 K and this sharp transition is quite likely due to the anti-parallel alignment of Fe~(3+) spins and is attributed to Morin transition of α-Fe_2O_3. Mossbauer spectra of the samples annealed at and above ～740 ℃ give sextet patterns indicating the presence of exchange interaction among the Fe~(3+) ions of these samples and these sextets are also of typical nature of the α-Fe_2O_3 phase. The Mossbauer spectra of the samples annealed below ～740℃ are doublets which may be attributed to either superparamagnetic and/or paramagnetic type nanoparticles.