Theoretical study on anomalous thermal expansion of two AB2-type compounds

Anomalous thermal expansion, or other words, negative thermal expansion (NTE), resulting from the lattice contraction upon temperature increasing, has been an enduring topic for material science and engineering. The variation of a lattice go with the temperature is straightly originated from its electronic structures and is inseparable from those physical properties. In the past several decades, many efforts have been made to searching new series of NTE compounds or control the thermal expansion performance in order to supply various demands of different extreme applications. These development of new NTE systems also dependences on the theoretical studies. Here, we carried out theoretical calculation on CrB₂ and FeZr₂ with anisotropic negative thermal expansion. Intriguingly, theoretical calculations reveal that the binding of either Cr-Cr pair or Fe-Fe pair is relatively small. The results reveal that the origin of NTE is the ordered magnetic state during the increasing of temperature. The localized electrons would prevent the lattice parameters increase with heating, which shows macroscopic NTE phenomenon.