BaFe(2)AS(2) has been studied by high-pressure energy dispersive X-ray diffraction. The compression mechanism was found to be highly anisotropic, and a tetragonal to orthorhombic phase transition was observed at about 17 GPa. The length of the a- and c-axes of the tetragonal phase is reduced by 2 and 11, respectively, at the transition pressure. Furthermore, an increase in compressibility was observed at about 1 GPa. The zero-pressure bulk modulus was determined to be B-0 = 71(4) GPa using experimental data points in the pressure range from 1 to 16.5 GPa. The experimental results are supported by electronic structure calculations within the extended Huckel approximation. (C) 2009 Elsevier Ltd. All rights reserved.
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