EPR STUDY OF Fe3+ AND Mn2+ DOPED AMORPHOUS AND CRYSTALLINE ALUMINUM BORATES

Abstract

Amorphous and crystalline aluminum borates prepared by sol–gel method doped with iron and manganese were studied by electron paramagnetic resonance in order to determine the matrix effects on Fe3+ and Mn2+ environments during their consolidation by heat treatment up to 860°C. In amorphous matrices, after heat treatments up to 600°C, the Fe3+ environment is almost unaffected but the vicinity of Mn2+ ions is relatively strongly disordered. In partial crystalline alumina and aluminum borate samples, obtained after heat treatments applied at 860°C, the Fe3+ sites are subjected to completely different crystalline fields, as regards intensity and symmetry. If in crystalline alumina we have both sites typical for α and γ phases in crystalline aluminum borate, the well-known spectrum of Fe3+ in disordered systems seems to be solved, suggesting more than one well-defined site. In the case of manganese-doped samples, only a diminishing of hyperfine resolution with increasing heat treatment temperature is observed as a result of environment distortion by improvement of alumina borate sample crystallinity.