Structural phase transitions in Sr2Fe2O5 under high pressure

The pressure dependence of the crystal structure of Sr2Fe2O5 has been studi ed at room temperature by angle-dispersive synchrotron X-ray powder diffrac tion and Fe-57 Mossbauer spectroscopy using diamond anvil cell techniques. Between 11 and 14 GPa the low-pressure brownmillerite-type structure with a n equal number of octahedrally and tetrahedrally coordinated Fe3+ sites is transformed into a tetragonal perovskite-like structure, The Mossbauer spec tra of the high-pressure phase reveal two subspectra with an intensity rati o of about 3:1, The Mossbauer parameters are consistent with two five-coord inated Fe3+ sites differing in the degree of structural distortion of the F eO, polyhedra, Laser annealing of the high-pressure phase at 15 GPa induces a transformation from the tetragonal perovskite into an orthorhombic phase that is isostructural with Sr2Mn2O5. This structure consists of a network of corner-sharing FeO, square pyramids. The coordination number of the Sr2 ions has increased from 8 in the brownmillerite structure to 10 in the Sr2 Mn2O5-type phase, (C) 2000 Academic Press.