Phase transformation and slow relaxation in fluosilicates : Mössbauer study

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Abstract
The phase transformation P3ml → P21/C occurring in Fe, Mg, Mn fluosilicates has been characterized by the following observations : (i) removal of the axial symmetry of the electric field gradient, (ii) sharp variation of the asymmetrical shape of the quadrupole spectra of powdered samples, (iii) no noticeable variation of the quadrupole splitting (Mn-Fls excepted). The asymmetry parameter of the gradient has been measured with a Mg-fluosilicate single crystal in a 120 kOe magnetic field. The asymmetry of the quadrupole spectra has been used to determine the transition temperatures. By applying a magnetic field to a Fe-fluosilicate single crystal held at 40 K, we obtained experimental evidence for the presence of slow electronic relaxation which is responsible for the asymmetrical shape of the quadrupole spectra