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Issue 19, 2018
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Crossover of thermal expansion from positive to negative by removing the excess fluorines in cubic ReO3-type TiZrF7−x

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Abstract

We report the crossover of the coefficient of thermal expansion (CTE) from positive to negative by withdrawing the excess fluorines in ReO3-type TiZrF7−x (x = 0, 0.5 and 1) compounds. The average volumetric CTE between 300 K and 623 K changes from 8.07 ppm K−1 for x = 0, to 0.66 ppm K−1 for x = 0.5 and finally to −6.09 ppm K−1 for x = 1. After withdrawing the excess fluorines, the lattice expands and the edge-sharing polyhedra partially transform to corner-sharing ones, which enhances the transverse vibrations of fluorines and thus accounts for the crossover of CTE. Moreover, these compounds are narrow-gap semiconductors with the energy gap decreasing with x. NTE may also be achievable in other fluorine-excess cubic fluorides by removing the excess fluorines, which opens up a new avenue for exploring the NTE in fluorides.

Graphical abstract: Crossover of thermal expansion from positive to negative by removing the excess fluorines in cubic ReO3-type TiZrF7−x

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Publication details

The article was received on 25 Oct 2017, accepted on 25 Mar 2018 and first published on 27 Mar 2018


Article type: Paper
DOI: 10.1039/C7TC04875K
Citation: J. Mater. Chem. C, 2018,6, 5148-5152
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    Crossover of thermal expansion from positive to negative by removing the excess fluorines in cubic ReO3-type TiZrF7−x

    C. Yang, Y. Zhang, J. Bai, B. Qu, P. Tong, M. Wang, J. Lin, R. Zhang, H. Tong, Y. Wu, W. Song and Y. Sun, J. Mater. Chem. C, 2018, 6, 5148
    DOI: 10.1039/C7TC04875K

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