Effect of local structure on negative thermal expansion

We have recently identified a transition from positive to zero to negative thermal expansion by fluoride doping NbO2F. Anionic control over thermal expansion is a novel approach and the mechanism through which it operates is currently not fully understood. Analysis of local structure through the x-ray pair distribution function (PDF) at different temperatures will allow us to separate the influences of anion order from dynamic distortions, and would help to develop this new field of anionic control of thermal expansion.