Study of temperature dependent atomic correlations in MgB2

We have studied temperature evolution of the local as well as the average crystal structure of MgB2 using real-space atomic pair distribution function (PDF) measured by high resolution neutron powder diffraction in a wide temperature range of T=10-600 K. We find small positive correlation factors for the B-B and B-Mg pairs, determined by mean-square displacements (MSD) and the mean-square relative displacements (MSRD). We analyze the PDF using both Einstein and force constant models finding a good agreement between the experimental data and the two models. This indicates that B and Mg atomic correlations are not sensitive to the details of phonon dispersion.