Abstract
Materials that shrink during heating are important for advanced applications. Graphene has shown negative thermal expansion (NTE) up to 1000 K, which drives further research towards new two-dimensional allotropes of carbon to achieve higher performance. In this article, we have shown high NTE for Graphynes having sp-sp connectivity and that are stable at high temperature. The effect of heteroatom substitution in NTE for some graphynes and their periodic trends are also studied. Quasi-harmonic approximation (QHA) calculations show that thermal expansion remains negative at least until 1000 K for some graphynes. The results are in good agreement with ab-initio molecular dynamics (AIMD) simulations. The high NTE in the graphynes is understood based on their rigid unit modes (RUMs).
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