M�ssbauer effect characterization and thermal transformations of Fe(III) ions co-precipitated with praseodymium trihydroxide

Abstract

Mossbauer studies at+27 and−196° C on 5 wt % Fe(III) ions co-precipitated with praseodymium trihydroxide and subjected to annealing for 24h at 100, 350, 600, 725, 825 and 1100° C are reported. Variations in Mossbauer spectral parameters and the results of thermal analysis, infra-red spectroscopy, electron microscopy and X-ray diffraction (XRD) studies on the samples have been used to follow and to gain insight into the nature of thermal and microstructural processes that occur during phase transitions. In the co-precipitate, Fe ions exist as ferric oxide hydrate gel-like species. In samples annealed at 100° C Fe ions exhibit an increase in dispersion strengthening in the lattice while in samples annealed at 350° C they become somewhat labile due to disruption of lattice planes on dehydroxylation. In samples annealed at 600° C magnetically split sixline Mossbauer spectra are observed, which in agreement with XRD analysis and electron paramagnetic resonance studies indicate the precipitation of PrFeO3 microphases in Pr6O11. Annealing to higher temperatures finally leads to a pronounced agglomeration of iron microphases and the establishment of a better crystallized host lattice.