Transport properties of g-BC3 and t-BC3 phases

The calculated electronic band structure shows that the g-BC3 phase is a narrow band gap semiconductor constructed from an ABAB,., stacking sequence. Whereas t-BC3 is a metallic phase constructed from a sandwich-like metal-insulator lattice from an alternately stacking sequence of a metallic CBC block and an insulating CCC block. The electronic transport coefficients of the g-BC3 and t-BC3 phases are obtained with the aid of the semi-classical Boltzmann theory and the rigid band model based on density functional theory within the recently modified Becke-Johnson potential (mBJ). The semiconductor phase (g-BC3) exhibits a linearly dependent charge carrier concentration and electrical conductivity with temperature, whereas for the t-BC3 phase the charge carrier concentration is increased with increasing temperature up to 200 K, then a rapid decrease occurs upon increasing the temperature. The electrical conductivity of t-BC3 shows the highest value at 50 K then a rapid decrease occurs upon increasing the temperature up to 250 K, and it stays roughly constant above this temperature. The Seebeck coefficient of the g-BC3 and t-BC3 phases shows that these materials exhibit p-type conduction and the g-BC3 phase exhibits a higher Seebeck coefficient than the t-BC3 phase. The g-BC3 phase exhibits an almost linearly dependent power factor with temperature. Whereas the power factor of the t-BC3 phase shows a very high value at low temperature then drops to the lower value at 200 K. Above this temperature the power factor of t-BC3 becomes zero along the whole temperature range. It has been found that the g-BC3 phase shows a higher power factor than that of the t-BC3 phase. The electronic thermal conductivity of g-BC3 exponentially increases with increasing temperature. It has a zero value at 50 K and the highest value 4.6 x 10(14) (W m(-1) K-1 s(-1)) at 900 K. t-BC3 exhibits linearly dependent electronic thermal conductivity with temperature. At low temperature (50 K) the electronic thermal conductivity of t-BC3 is about 0.15 x 10(16) (W m(-1) K-1 s(-1)) while it has a value of about 2.1 x 10(16) (W m(-1) K-1 s(-1)) at 900 K. It is clear that the g-BC3 phase exhibits lower electronic thermal conductivity than the t-BC3 phase.