Origin of negative thermal expansion phenomenon in solids

We show that the negative thermal expansion (NTE) phenomenon originates from the existence of high pressure, small volume phases with higher entropy, with their configurations present in the stable phase matrix through thermal fluctuations, thus exists. Consequently, it extends the platform for designing structures with desired thermal expansion properties whether positive, negative, or zero. The theory is validated for a range of pure elements and compounds and utilized to provide insights to the NTE phenomenon in Fe3Pt and ZrW2O8.