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Electrical transport properties of Na2C60 under high pressure

Yao, Mingguang (author)
Université de Lyon, Lab. de Phys. Matière Condenseé et Nanostructures, 69622 Villeurbanne, Lyon, France
Wågberg, Thomas (author)
Umeå universitet,Institutionen för fysik
Sundqvist, Bertil (author)
Umeå universitet,Institutionen för fysik
Université de Lyon, Lab de Phys. Matière Condenseé et Nanostructures, 69622 Villeurbanne, Lyon, France Institutionen för fysik (creator_code:org_t)
2009
2009
English.
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:11, s. 115405-
  • Journal article (peer-reviewed)
Abstract Subject headings
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  • We present direct resistance measurements on Na2C60 under high pressure up to 2 GPa in the temperature range ~90–500 K. We show that fresh, nominally pure Na2C60 exhibits a semiconductor-type conduction behavior at all experimental conditions, with a 1.2 eV band gap and a conduction strongly influenced by defect gap states. Contrary to Rb4C60 and Na4C60, both band gap and gap states have large pressure dependences. In contrast, a Na2C60 sample preserved in an oxygen-free environment for several months shows conduction by another mechanism, variable range 3D hopping. This is consistent with recent findings of nanoscale phase segregation in Na2C60 and can be understood in terms of conduction by intergrain hopping. Heating the sample at 2 GPa leads to a significant change in the resistivity, suggesting a structural transition. By characterizing the sample after the phase transformation with Raman spectroscopy and x-ray diffraction we identify a phase separation of the material into two main structures, linearly polymerized orthorhombic C60 and two-dimensionally polymerized Na4C60.

Subject headings

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)
NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Keyword

electrical resistivity
high pressure
solid-state phase transformations
hopping conduction
narrow band gap semiconductors
phase separation
Raman spectra
segregation
sodium compounds
X-ray diffraction
fulleride polymers
gap states
Condensed matter physics
Kondenserade materiens fysik
fysik
Physics

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Wågberg, Thomas
Sundqvist, Berti ...
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Umeå University

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