Mossbauer study of the phase transitions in some iron sulfate and iron chloride compounds

Quadrupole coupling with electric field gradient is a sensitive indicator f or structural phase transitions. Fe-57 Mossbauer spectroscopy provides us w ith quadrupole couplings of Fe-57 nuclei with surrounding electric field gr adients(EFG). We report here about the Mossbauer spectroscopy of K2Fe(SO4)( 2). 2H(2)O, FeCl2. 6H(2)O and [N(CH3)(4)](2)FeCl4. The crystal K2Fe(SO4)(2) . 2H(2)O was recently found to undergo a ferroelectric phase transition at 364 K. The Mossbauer spectrum of this crystal shows only one doublet both i n the paraelectric and ferroelectric phases. The quadrupole splitting shows quite similar temperature dependence to that of order parameter. The deute rated crystal was also investigated by Mossbauer spectroscopy. The crystal FeCl2. 6D(2)O was reported to undergo a phase transition at around 126K. We have measured Mossbauer splittings in FeCl2. 6H(2)O down to 12 K. A double t line is observed at room temperature down to 22K. We have also studied th e crystal [N(CH3)(4)](2)FeCl4 which shows pressure-induced ferroelectricity and incommensurate phase transition.