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  • Title: Discovering Large Isotropic Negative Thermal Expansion in Framework Compound AgB(CN)4 via the Concept of Average Atomic Volume.
    Author: Gao Q, Wang J, Sanson A, Sun Q, Liang E, Xing X, Chen J.
    Journal: J Am Chem Soc; 2020 Apr 15; 142(15):6935-6939. PubMed ID: 32233466.
    Abstract:
    Exploring isotropic negative thermal expansion (NTE) compounds is interesting, but remains challenging. Here, a new concept of "average atomic volume" is proposed to find new NTE open-framework materials. According to this guidance, two NTE compounds, AgB(CN)4 and CuB(CN)4, have been discovered, of which AgB(CN)4 exhibits a large NTE over a wide temperature range (αv = -40 × 10-6 K-1, 100-600 K). The analysis by extended X-ray absorption fine structure spectroscopy and first-principles calculation indicate that (i) the NTE driving force comes from the transverse vibrations of bridge chain atoms of C and N, corresponding to the low-frequency phonon modes; and (ii) the same transverse vibration direction of C and N atoms is a key factor for the occurrence of strong NTE in AgB(CN)4. The present concept of "average atomic volume" can be a simple parameter to explore new NTE compounds especially in those open-framework materials.
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