High-pressure neutron diffraction study of BaFe<Subscript>2</Subscript>As<Subscript>2</Subscript>

The crystal structure of BaFe<Subscript>2</Subscript>As<Subscript>2</Subscript> was studied by high-pressure neutron powder diffraction in the pressure range from ambient to 6.5 GPa as well as in the temperature range from 12 K to 293 K at 4.4 GPa and no pressure or temperature induced phase changes were observed. The compression mechanism of BaFe<Subscript>2</Subscript>As<Subscript>2</Subscript> was found to be anisotropic as the a- and c-axes are reduced by 2.49 and 3.66%, respectively at 6.5 GPa. Within the FeAs layers the Fe-As and Fe-Fe bonds decrease by 2.49 and 3.66%, respectively. The Ba-As distance decreases by 3.70% while the As-As inter-atomic distance along the c-axis exhibits a complex pressure dependence. The bulk modulus B <Subscript>0</Subscript> and its pressure derivative B <Subscript>0</Subscript>' were determined to be B <Subscript>0</Subscript>=59(2) GPa and B <Subscript>0</Subscript>'=6.1(7) at ambient temperature. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010