Resistance and thermoelectric power of carbon fibers upon changing the conductivity type

Upon being subjected to pulsed current, carbon fiber changes the sign of its thermoelectric power from negative to positive. The conductivity activation energy for the initial $n$-type fiber is 60 meV, and that for a fiber modified to $p$-type is 16 meV. Fabric constituted by carbon fibers with a set of $p$–$n$ junctions does not require switching plates. In vacuum or in an inert atmosphere, carbon fibers withstand heating up to 3500 K, which opens up the possibility for developing thermoelectric generators that operate at high temperature gradients.