Journal
MATERIALS TODAY COMMUNICATIONS
Volume 31, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.mtcomm.2022.103275
Keywords
Fullerenes; High-pressure; Crystal structure; X-ray diffraction
Categories
Funding
- JSPS KAKENHI [JP18H04303, JP18K18724, JP19H04590, JP21H01907]
- Izumi Science and Technology Foundation
- Masuya Kinen Kenkyu Shinko Foundation
- Czech Science Foundation [19-21575Y]
- Czech Ministry of Education, Youth and Sports [MATFUN-CZ.02.1.01/0.0/0.0/15_003/0000487]
- Murata Science Foundation
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The pressure-dependent structural properties of the metallofullerene salt Li+@C-60][PF6](-) were studied, and it was found that the structure remains a primitive cubic at both ambient and low temperatures, without any phase transition. The interaction between the endohedral Li+ and the interstitial [PF6](-) unit has little influence on the structure, as indicated by the comparable bulk moduli to other cubic close-packed fullerene solids.
The pressure-dependent structural properties of the metallofullerene salt, Li+@C-60][PF6](-), which has been shown before to adopt a primitive cubic structure at ambient conditions, have been studied by synchrotron X-ray powder diffraction at ambient temperature and at 7 K up to similar to 12 GPa. We find no evidence for a phase transition across the accessed pressure range at either temperature with the structure always remaining strictly primitive cubic (space group Pa (3) over bar). The extracted bulk moduli, K-0 of 17.51(13) GPa and 16.6(2) GPa at 7 K and ambient temperature, respectively are comparable to those of other cubic close-packed fullerene solids implying little influence of the interaction between the endohedral Li+ and the interstitial [PF6](-) unit. Rietveld analysis of the diffraction data shows that the adopted primitive cubic structure incorporates orientationally ordered [Li+@C-60] units - they are rotated anticlockwise by similar to 101 degrees about the three-fold [111] rotation axis. This finding together with the lack of observation of a monomer -> polymer phase transition upon pressurization contrast sharply with the structural behaviour of isostructural pristine C-60 and its intercalated salts, (deely quenched) CsC60 and Na2CsC60, which both incorporate orientationally disordered C60 units and have a tendency to easily polymerize via intermolecular C-C bond formation. Such differences can be understood in terms of the expanded nature of the salt and the steric interactions introduced by the large [PF6](-) unit residing in the octahedral interstices.
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