Static and dynamic Jahn-Teller effect in the alkali metal fulleride salts A(4)C(60) (A = K, Rb, Cs)

Klupp, Gyöngyi and Kamarás, Katalin and Nemes, N. M. (2006) Static and dynamic Jahn-Teller effect in the alkali metal fulleride salts A(4)C(60) (A = K, Rb, Cs). PHYSICAL REVIEW B CONDENSED MATTER AND MATERIALS PHYSICS, 73 (8). Paper-085415. ISSN 1098-0121

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Abstract

We report the temperature dependent mid- and near-infrared spectra of K4C60, Rb4C60, and Cs4C60. The splitting of the vibrational and electronic transitions indicates a molecular symmetry change of C-60(4-) which brings the fulleride anion from D-2h to either a D-3d or a D-5d distortion. In contrast to Cs4C60, low temperature neutron diffraction measurements did not reveal a structural phase transition in either K4C60 and Rb4C60. This proves that the molecular transition is driven by the molecular Jahn-Teller effect, which overrides the distorting potential field of the surrounding cations at high temperature. In K4C60 and Rb4C60 we suggest a transition from a static to a dynamic Jahn-Teller state without changing the average structure. We studied the librations of these two fullerides by temperature dependent inelastic neutron scattering and conclude that both pseudorotation and jump reorientation are present in the dynamic Jahn-Teller state.

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