Specific features in the behavior of electrical resistivity of the pine biocarbon preform/copper composite

The electrical resistivity $\rho(T)$ of the novel type of composites prepared by infiltrating melted copper in vacuum in empty sap channels of white pine high-porosity biocarbon preforms has been measured in the temperature range 5–300 K. Biocarbon preforms have been prepared by pyrolysis of tree wood in an argon flow at two carbonization temperatures, 1000 and 2400$^\circ$C. The electrical resistivity of the composites has been found to vary relatively weakly with temperature and to pass through a characteristic minimum near 40–50 K, which can be ascribed to iron and manganese impurities penetrating into copper from the carbon preform when liquid copper is infiltrated into it. It has been shown that the electrical resistivity $\rho(T)$ of the composites is governed primarily by the specific microstructure of the preform, which is made up of parallel channels with an average diameter of about 50 $\mu$m interrupted by systems of thin capillaries. The small cross section of the copper-filled capillaries accounts for these regions providing the major contribution to the electrical resistivity of the composites. An increase in the wood carbonization temperature brings about a noticeable increase in the effective capillary cross section and a decrease in the electrical resistivity $\rho(T)$ of the composite.