Characterisation of amorphous state of REE2Fe2+Be2Si2O10 by spectroscopic methods.

This paper presents 57Fe Moessbauer spectroscopy, electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), X-ray diffraction (XRD), gamma-ray spectroscopy and dielectric permitivity spectroscopy studies of fully metamict gadolinite REE2Fe2+Be2Si2O10 from Ytterby (Sweden). X-ray and electron diffraction patterns of the sample show complete lack of long range order (LRO). 57Fe Moessbauer spectroscopy of the sample revealed only Fe3+ ions definitely located in octahedral coordinations, similar to thye crystalline structure of gadolinite. The EPR resonance spectrum is complete and its features corespond to Gd3+ and Mn2+ centers. The Gd3+ centers show low-symmetry of local crystal field and may be characterized by distribution of spin-Hamiltonian parameters such as: g-factor and fine-structure parameters. The temperature dependence of utensity proves that a fraction of gadolinium ions interact by superexchange type mechanism and reveals that these exchange interactions are of the antiferromagnetic type Mn2+ centers and the character of Mn2+ EPR spectra indicate that this spectra are atributed to isolated manganium ions. The AC conductivity exhibits thermally activated behavior above 420 K whereas the dielectric constant shows a step-like anomaly near 230 K.