Hyperfine Interactions 77(1993)29-42 29 M issbauer study on M1 and M2 sites of Fe 2+ in natural hypersthene under dynamic crystal field potential approach T.P. Sinha 1, D. Das z and M. Bhattacharya 1 1Solid State and Molecular Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhan Nagar, Calcutta 700064, India 2Department of Solid State Physics, Indian Association for the Cultivation of Science, Calcutta 700032, India Received 2 April 1992; accepted 14 July 1992 57Fe M6ssbauer spectra of hypersthene, a natural silicate mineral belonging to the orthopyroxene group, have been taken over the temperature range 77-292 K. At temperatures above 77 K,/they show asymmetric quadrupole peaks. This asymmetry 2+ 6 5 arises from the overlappigg of two quadrupoledoublets from Fe (3d, D) ions in two different sites (MI and M2). The quadrupolesplitting, isomer shift and their temperature dependence are appreciablydifferent for Fe~-+ ions in the two sites. The Fez+quadrupole splitting in the M1 site decreases linearly with temperature, which can be explained quite satisfactorily by using a very simple model of the orbit-lattice interaction. 1. Introduction The MOssbauer effect has been widely used to study the electronic states of Fe 2+13+ ions in solids, particularly minerals. The information about the electronic charge distribution is obtained from the study of nuclear quadrupole splitting and isomer shift, while the study of the magnetic hyperfine spectrum fumishes the information about the spin ordering. The temperature dependence of the quadrupole splitting of Fe 2÷ in inorganic [1-3], organometaltic [4,5] and biological [6,7] systems can be consistently explained only when the effect of orbit-lattice interaction (or vibronic coupling) is included. This also indicates the inadequacy of the static crystal field approach. It is therefore desirable that more Fe 2+ systems of different types are examined to assess the importance of orbit-lattice interaction on quadrupole splitting. This may help us to m3derstand the importance of structural symmetry, Debye energy, electronic charge distribution and other physical parameters of the crystal related to the electron-phonon coupling in insulators. There are a number of natural minerals containing small amounts of Fe 2÷ ions which may be amenable to MOssbauer investigation from the above viewpoint; hence the present work was undertaken. © J.C. Baltzer AG, Science Publishers