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Determining ethylene group disorder levels in $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br

A. U. B. Wolter·R. Feyerherm·E. Dudzik·S. Süllow·Ch. Strack·M. Lang·D. Schweitzer
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Abstract

We present a detailed structural investigation of the organic superconductor $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br at temperatures $T$ from 9 to 300 K. Anomalies in the $T$ dependence of the lattice parameters are associated with a glass-like transition previously reported at $T_g$ = 77 K. From structure refinements at 9, 100 and 300 K, the orthorhombic crystalline symmetry, space group {\it Pnma}, is established at all temperatures. Further, we extract the $T$ dependence of the occupation factor of the eclipsed conformation of the terminal ethylene groups of the BEDT-TTF molecule. At 300 K, we find 67(2) %, with an increase to 97(3) % at 9 K. We conclude that the glass-like transition is not primarily caused by configurational freezing-out of the ethylene groups.

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A. U. B. Wolter, R. Feyerherm, E. Dudzik, S. Süllow, Ch. Strack, M. Lang, D. Schweitzer. 2006-10-24. Determining ethylene group disorder levels in $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br. https://doi.org/10.1103/physrevb.75.104512

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