We wish to use NIMROD to study the distribution and nature of defect sites in the high-thermal-stability metal-organic framework UiO-66. For the most part, defect structures in MOFs are either assumed not to exist, or even if their presence is acknowledged there is no attempt made to understand what they actually look like and how they affect material properties. We are proposing to use the wide-Q range possible on NIMROD to collect total scattering data that will allow us to characterise defects in UiO-66 and also to understand their correlations on a medium-range length scale. We have also discovered that the material exhibits isotropic negative thermal expansion that is many times stronger than classic materials such as ZrW2O8; there are indications that defects are implicated in this behaviour.