A study of nanoporous carbon obtained from ZC powders (Z=Si, Ti, and B)

Nanoporous carbon (NPC) material prepared from polycrystalline powders of SiC, TiC, or B₄C carbides, using different techniques, was studied by means of ESR, Hall and conductance measurements for three groups of each type of sample—control group, and those annealed at T=960 and 1180 °C. It is found, according to Hall measurements, that holes are the majority charge carriers in NPC. The concentration of free carriers is found to be rather high (about 10¹⁹–10²¹ cm⁻³). The ESR spectrum has the so-called ‘Dyson line shape’ with a large signal asymmetry. Two groups of carriers with strongly different electronic and magnetic properties are found. The values of the g-factor and their variability are related to the existence of two different kinds of particles: small carbon nanoclusters (1–3 nm) and large-scale carbon skeleton structural elements (up to 1000 nm) of complex shape, where the holes move along graphite-like sp² bonds. The temperature dependence of the integral intensities shows the existence of two non-separable spin subsystems—charge carriers and localised spins. A role of oxygen atoms in the electronic system of NPC is studied.