TY - JOUR
T1 - Resistivity and E.S.R. studies of graphite HOPG/fluorine intercalation compounds
AU - Vaknin, D.
AU - Palchan, I.
AU - Davidov, D.
AU - Selig, H.
AU - Moses, D.
PY - 1986/12
Y1 - 1986/12
N2 - We present conductivity and e.s.r. studies of graphite HOPG/fluorine intercalation compounds. The in-plane resistivity, ρ{variant}a, was measured as a function of fluorine concentration and temperature using a contactless technique. The c-axis resistivity, ρ{variant}c, was measured as a function of temperature and hydrostatic pressure using the four-contact technique. The main features of our results can be summarized as follows: 1. (1) The conductivity along the planes increases initially with fluorine concentration and reaches a maximum conductivity of σa/σ0 ≅ 11 (σ0 is the in-plane conductivity of HOPG). Above a concentration of x = 0.18 in C1 - xFx the conductivity, σa, dramatically decreases. 2. (2) ρ{variant}a is 'metallic' for concentrations x < 0.2 and can be fitted to the equation: ρ{variant}a = A + BT + CT2. For x = 0.25, the in-plane resistivity is significantly larger and temperature independent. 3. (3) The c-axis resistivity, ρ{variant}c, versus temperature exhibits a clear maximum for x < 0.2 but is anomalously large and almost temperature independent for x = 0.25. We suggest that carrier localization due to structural deformation and consequent changes in the band structure are responsible for the limiting conductivity. However, a percolation mechanism and domain-wall formation might also play an important role. The maximum in c-axis resistivity is attributed to a cross-over between two mechanisms of conduction: 'tunneling' or 'conducting path' mechanisms at low temperatures, but a hopping mechanism at high temperatures. The activation energy for hopping is extracted, as well as its pressure dependence. Finally, we provide a critical analysis of previous interpretations of carrier spin resonance in GICs. We have critically checked the theory of Dyson by measuring the A/B ratio, ρ{variant}a and ρ{variant}c versus temperatures on the same samples. We demonstrate that extracting bulk resistivities from the e.s.r. lineshape may not be justified.
AB - We present conductivity and e.s.r. studies of graphite HOPG/fluorine intercalation compounds. The in-plane resistivity, ρ{variant}a, was measured as a function of fluorine concentration and temperature using a contactless technique. The c-axis resistivity, ρ{variant}c, was measured as a function of temperature and hydrostatic pressure using the four-contact technique. The main features of our results can be summarized as follows: 1. (1) The conductivity along the planes increases initially with fluorine concentration and reaches a maximum conductivity of σa/σ0 ≅ 11 (σ0 is the in-plane conductivity of HOPG). Above a concentration of x = 0.18 in C1 - xFx the conductivity, σa, dramatically decreases. 2. (2) ρ{variant}a is 'metallic' for concentrations x < 0.2 and can be fitted to the equation: ρ{variant}a = A + BT + CT2. For x = 0.25, the in-plane resistivity is significantly larger and temperature independent. 3. (3) The c-axis resistivity, ρ{variant}c, versus temperature exhibits a clear maximum for x < 0.2 but is anomalously large and almost temperature independent for x = 0.25. We suggest that carrier localization due to structural deformation and consequent changes in the band structure are responsible for the limiting conductivity. However, a percolation mechanism and domain-wall formation might also play an important role. The maximum in c-axis resistivity is attributed to a cross-over between two mechanisms of conduction: 'tunneling' or 'conducting path' mechanisms at low temperatures, but a hopping mechanism at high temperatures. The activation energy for hopping is extracted, as well as its pressure dependence. Finally, we provide a critical analysis of previous interpretations of carrier spin resonance in GICs. We have critically checked the theory of Dyson by measuring the A/B ratio, ρ{variant}a and ρ{variant}c versus temperatures on the same samples. We demonstrate that extracting bulk resistivities from the e.s.r. lineshape may not be justified.
UR - http://www.scopus.com/inward/record.url?scp=0022877730&partnerID=8YFLogxK
U2 - 10.1016/0379-6779(86)90172-4
DO - 10.1016/0379-6779(86)90172-4
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AN - SCOPUS:0022877730
SN - 0379-6779
VL - 16
SP - 349
EP - 365
JO - Synthetic Metals
JF - Synthetic Metals
IS - 3
ER -