Thermoelectric power in crystalline boron

The thermoelecric power of mono-crystalline beta-boron (purity >99.9995%, room-temperature resistivity 5 × MegaOhm cm), measured in the dark, increased from 305 to a maximum of 700 µV/K, and then fell to 650 µV/K, respectively, at T = 190, 345, and 435 K. The observed temperature dependence explained assuming two components in the boron conductivity: a p-type conduction in the valence band, and an n-type conduction of electrons hopping in an impurity band