Thermopower coefficient of pine-wood biocarbon preforms and the biocarbon-preform/copper composites

The thermopower $S(T)$ of the composites prepared by filling empty sap channels in high-porosity biocarbon preforms of white pine wood by melted copper in vacuum and the thermopower $S(T)$ of these preforms have been measured in the temperature range 5–300 K. The biocarbon preforms have been obtained by pyrolysis of pine wood in an argon flow at two carbonization temperatures, 1000 and 2400$^\circ$C. An analysis of the experimental data has demonstrated that the thermopower of the composites is determined by the contribution related to the copper filling the channels of the biocarbon preform and exhibits a characteristic temperature dependence with a deep minimum close to 20 K. This suggests that copper in the preform channels is essentially a Kondo alloy with the iron and manganese impurities entering into it from the carbon preform in the course of infiltration of melted copper.