TY - JOUR
T1 - AC conductivity and dielectric response of polycrystalline and amorphous C70
AU - Gómez-Aguilar, Ramón
AU - Ortiz-López, Jaime
N1 - Funding Information:
One of us (J.O.L.) gratefully acknowledges partial support from CONACYT (Mexico) grants F143-19201 and F-596-E9404, to CGPI-IPN for support to Projects 20010558 and 20020911, and to COFAA-IPN for a SIBE fellowship.
PY - 2004/11
Y1 - 2004/11
N2 - The AC conductivity and dielectric constant of polycrystalline and amorphous C samples were measured in the 75-300 K temperature range and in the 100 Hz to 1MHz frequency range. For polycrystalline samples, we observe effects caused by O2 intercalation due to prolonged exposure to ambient air. The conductivity σ of these samples around 300 K depends on the measuring frequency v as a σ ∼ vn with n ≈ 0.88, implying a strong reduction of DC conductivity to less than 10-12 S/cm. The dielectric constant of polycrystalline samples shows an anomaly at 285 K which is interpreted as due to the transition from its intermediate rhombohedral phase into its monoclinic low-temperature phase. In contrast with the polycrystalline samples, the amorphous C70 samples prepared by sublimation do not contain interstitial 02, their conductivity at 300 K is of about 10-6 S/cm, is independent of frequency, and is well described by the hopping mechanism (Davis-Mott T1/4 law) in the 200-300 K range. All evidence of phase transitions disappears in the amorphous samples.
AB - The AC conductivity and dielectric constant of polycrystalline and amorphous C samples were measured in the 75-300 K temperature range and in the 100 Hz to 1MHz frequency range. For polycrystalline samples, we observe effects caused by O2 intercalation due to prolonged exposure to ambient air. The conductivity σ of these samples around 300 K depends on the measuring frequency v as a σ ∼ vn with n ≈ 0.88, implying a strong reduction of DC conductivity to less than 10-12 S/cm. The dielectric constant of polycrystalline samples shows an anomaly at 285 K which is interpreted as due to the transition from its intermediate rhombohedral phase into its monoclinic low-temperature phase. In contrast with the polycrystalline samples, the amorphous C70 samples prepared by sublimation do not contain interstitial 02, their conductivity at 300 K is of about 10-6 S/cm, is independent of frequency, and is well described by the hopping mechanism (Davis-Mott T1/4 law) in the 200-300 K range. All evidence of phase transitions disappears in the amorphous samples.
KW - Conductivity
KW - Dielectric permittivity
KW - Fullerenes
UR - http://www.scopus.com/inward/record.url?scp=10044251400&partnerID=8YFLogxK
U2 - 10.1081/FST-200032874
DO - 10.1081/FST-200032874
M3 - Artículo
SN - 1536-383X
VL - 12
SP - 731
EP - 744
JO - Fullerenes Nanotubes and Carbon Nanostructures
JF - Fullerenes Nanotubes and Carbon Nanostructures
IS - 4
ER -