Hydrostatic Pressure Dependence of the Superconducting and Structural Properties of MgB2

In this paper we report parallel in situ neutron powder diffraction and Tc(P) measurements versus pressure on the same MgB2 sample in a He-gas apparatus to 0.6 GPa; in addition, we present Tc(P) measurements in a helium-loaded diamond-anvil-cell to 20 GPa on the same sample. Our results are compared with those of other groups. The high precision achieved in these measurements allows a quantitative evaluation of the change in Tc as a function of the changes in structure. Our results are consistent with electron-phonon pairing in MgB2.