| 1. |
- Yao, Mingguang, et al.
(författare)
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Effect of high pressure on electrical transport in the Li4C60 fulleride polymer from 100 to 400 K
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:15, s. 155441-155448
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Tidskriftsartikel (refereegranskat)abstract
- In situ resistance measurements have been carried out on Li4C60 under pressures up to 2 GPa at temperatures from below 100 to 400 K. In agreement with recent reports we find an Arrhenius law behavior for the conductivity, which can be interpreted in terms of Li+ ionic conduction with an activation energy near 225 meV. The activation energy decreases with increasing pressure at an initial rate of about −11%/GPa and the room-temperature conductivity increases by a factor of about 6 from 0.1 to 2 GPa. We also observe conductivity terms with a lower excitation energy, most probably associated with conduction by electrons excited from defect-induced states in the main band gap. We discuss this conduction behavior in the context of recent measurements on both Li4C60 and other alkali-metal intercalated phases such as Rb4C60, Na2C60, and Na4C60. After heating to 400 K at 2 GPa the conduction behavior changes drastically, manifested by a change in the slopes of R versus T curves signifying newly created gap states. Postexperimental characterization by Raman spectroscopy and x-ray diffraction indicate the loss of Li especially from the grain surfaces. Finally, high-pressure Raman studies suggest a possible metallization transition above 9 GPa.
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| 2. |
- Yao, Mingguang, et al.
(författare)
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Laser-induced transformation of Li4C60 and Na4C60 polymers into metallic monomeric fulleride phases
- 2010
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 489:1-3, s. 64-68
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that laser irradiation on the narrow-gap insulator Li4C60 and Na4C60 polymers results in metallic monomeric structures, having the same Raman features as metallic fcc K3C60 and Rb3C60, with orientationally disordered C3-60 anions stable at ambient conditions. The Raman Ag(2) mode indicates that a single phase was obtained. Additionally, a monomeric A4C60-type phase (A = K, Rb) is observed in Na4C60 after irradiation. The electron–phonon coupling constants derived from Raman modes of C3-60 fullerides is found to be higher than that of C3-60 fullerides, agreeing with the trend found in heavy alkali fullerides. We propose possible structures of the metallic phases.
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| 3. |
- Yao, Mingguang, et al.
(författare)
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Reversible nano-scale phase separation of Rb4C60 under pressure
- 2010
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Ingår i: Journal of physics: conference series. - Bristol : Institute of Physics (IOP). ; , s. 012020-
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Konferensbidrag (refereegranskat)abstract
- The alkali fulleride Rb4C60 has been investigated by studies of the resistance and by Raman spectroscopy under pressures up to 2 GPa and 13 GPa, respectively. Our data show a reversible phase separation into metallic Rb3C60 and Rb6C60 at pressures above 1 GPa. The reversibility indicates that the phase separation primarily occurs on the nanometer length scale. The data explain several puzzling results reported in the recent literature.
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