On the compressibility of BaFe2As2

BaFe2As2 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 B0=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 Hückel approximation.