Specific features of the electrical properties in partially graphitized porous biocarbons of beech wood

The electrical and galvanomagnetic properties of partially graphitized highly porous bioC(Ni) biocarbon matrices produced by pyrolysis (carbonization) of beech wood at temperatures $T_{\mathrm{carb}}$ = 850–1600$^\circ$C in the presence of a Ni-containing catalyst have been studied in comparison with their microstructural features. The temperature dependences of the resistivity, the magnetoresistance, and the Hall coefficient have been measured in the temperature range of 4.2–300 K in magnetic fields to 28 kOe. It has been shown that an additional graphite phase introduction into samples with $T_{\mathrm{carb}}\ge$ 1000$^\circ$C results in an increase in the carrier mobility by a factor of 2–3, whereas the carrier (hole) concentration remains within $\sim$ 10$^{20}$ cm$^{-3}$, as in biocarbons obtained without catalyst. An analysis of experimental data has demonstrated that the features of the conductivity and magnetoresistance of these samples are described by quantum corrections related to their structural features, i.e., the formation of a globular graphite phase of nano- and submicrometer sizes in the amorphous matrix. The quantum corrections to the conductivity decrease with increasing carbonization temperature, which indicates an increase in the degree of structure ordering and is in good agreement with microstructural data.