Structural changes in pressure induced superconducting BaFe$_{2}$As$_{2}$: Similarities to chemical doping

We have determined the crystal structure of BaFe$_{2}$As$_{2}$ as a function of temperature (4$-$150 K) and pressure (0$-$6 GPa) using neutron powder diffraction. The structural features important to superconductivity, namely suppression of the T$-$O phase transition and reduction in the As$-$Fe$-$As bond angle and Fe$-$Fe distance, show exactly the same behaviour under pressure up to the optimal T$_{C}$ value, as found in chemically doped samples. This result suggests that chemical doping and pressure have similar effects on the electronic degrees of freedom in this family of iron pnictide superconductors.