Transport properties of g-BC3 and t-BC3 phases

Abstract

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 × 10¹⁴ (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 × 10¹⁶ (W m⁻¹ K⁻¹ s⁻¹) while it has a value of about 2.1 × 10¹⁶ (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.