Zero thermal expansion in NiPt(CN)6

Nowadays, an increasing number of scientists attach more importance to zero thermal expansion (ZTE) materials which are uncommon yet highly significant in the field of solid-state materials. The key to explore new ZTE compounds is to understand the mechanism, while it remains unclear. Here, we utilize density functional theory calculations to elucidate the mechanisms of NiPt(CN)₆. A joint study of bond nature, atomic mean-square displacements, phonon dispersion curves, Grüneisen parameters, and phonon vibrations to systematically analyze the ZTE mechanisms. The results suggest that the transverse vibrations of the –C≡N− groups are instrumental, particularly due to the involvement of the N atoms and the nature of the Ni–N and Pt–C bonds. Phonon modes with negative Grüneisen parameters at low frequencies play the mainly role to balance the positive thermal expansion from others frequency zone modes to obtain the ZTE behavior. This work demonstrates that NiPt(CN)₆ maintains substantial similarities with its trivalent-trivalent analogues, further enhancing our comprehension of NTE properties within open-framework structure.