Electronic structure and transport properties of Ba2Cd2Pn3 (Pn = As and Sb): An efficient materials for energy conversion

The full potential method within the recently modified Becke-Johnson potential explore that the Ba2Cd2Pn3 (Pn = As and Sb) compounds are narrow band gap semiconductors of about 0.49 and 0.32 eV, which confute the finding of the previous TB-LMTO-ASA calculation that Ba2Cd2Sb3 is a poor metal. It has been found that there are subtle difference in band desperations of the two compounds, resulting in significant influence on the electronic and transport properties, taking into account the size and the electro-negativity differences between As and Sb atoms. Calculation show that there exists a strong hybridization between the orbitals which may lead to form covalent bonding which is more favorable for the transport of the carriers than ionic one. The electronic structure, the anisotropy and the inter-atomic interactions are further analyzed by calculating the valence electronic charge density distribution in two crystallographic planes. The semi-classical Boltzmann theory as incorporated in BoltzTraP code was used to calculate the transport properties of Ba2Cd2As3 and Ba2Cd2Sb3 at different temperatures and chemical potentials to ascertain the influence of temperatures and substituting As by Sb on the transport properties. The carries mobility decreases with increasing the temperature also with increasing the carriers concentration. We have observed that substituting As by Sb lead to increase the carries mobility of Ba2Cd2Sb3 along the whole temperature interval and the carries concentration range. It has been found that Ba2Cd2As3 exhibit higher carriers concentration, electronic electrical conductivity and Seebeck coefficient than that of Ba2Cd2Sb3 along the investigated temperature range. The highest value of Seebeck coefficient occurs at 300 K, which show good agreement with the experimental data. The power factor increases linearly with increasing the temperature and Ba2Cd2As3 exhibit a bit higher power factor than that of Ba2Cd2Sb3 up to 500 K. Above this temperature both compounds are alternating. Based on the results our finding that the Ba2Cd2Pn3 (Pn = As and Sb) compounds are efficient materials for energy conversion.