Electrical Properties of Crystalline 3D-Polymeric C60 Fullerites Obtained by HPHT Treatment

The crystalline 3D-polymeric C60 with different lattice parameters and densities in the range of 2.3–2.65 g·cm−1 were obtained by high-pressure-high-temperature treatment at P=11.5–13 GPa, T=670–950K.. Their d.c. electrical conductivity investigated for the first time at temperatures 30–350K. Variable range hopping mechanism dominates in all samples up to room temperature. Within the Mott-Davis approximation an increase by a factor of 1010÷1012 was found in the density of states close to the Fermi level at T > 80 K in two samples, indicating an electronic phase transition. The temperature activated conductivity was observed in samples with densities 2.45 – 2.65 g·cm−1. The evaluated bandgap value is in the range of 0.27 – 0.54 eV.