Thermoelectric and Thermomagnetic Effects in Slightly Radiation-Damaged Graphite

Thermoelectric and thermomagnetic properties have been investigated of a single crystal graphite irradiated with fast neutrons of a total dose of 3×10 16 nvt, and after subsequently annealed at 250°C and 1400°C. The Seebeck coefficients ( S ) of the post-irradiated as well as the 250°C-annealed crystals are wholly positive at temperatures ( T ) between 300 K and 4.2 K, while the characteristic phonon drag anomaly still survives in the S vs T diagram, consisting of positive and negative components located around 25 K and 40 K respectively. Annealing at 1400°C, whereby the radiation-induced vacancies have mostly been recovered, makes the S vs T curve not much different from that of the unirradiated graphite, except for the doublet structure of the phonon drag dip. The presence of a magnetic field enhances the thermoelectricity in positive and/or negative direction. The Nernst-Ettingshausen coefficient measured at 6 kOe is also accompanied by the phonon drag anomaly having the doublet structure.