Quantum chemistry calculation and transport of Bi/sub 2/Te/sub 3/ and Sb/sub 2/Te/sub 3/

The correlation between composition, structure, chemical bond, and transport of Bi/sub 2/Te/sub 3/ and Sb/sub 2/Te/sub 3/ series is studied with density functional theory and discrete variation method (DFT-DVM). Eight models of Bi/sub 20-x/Sb/sub x/Te/sub 32/ (x=0, 2, 6, 8, 12, 14, 18 and 20) are calculated. The results show that there is less difference in the ionic bond between Te(I)-Bi(Sb) and Te(II)-Bi(Sb), but the covalent bond of Te(I)-Bi(Sb) is stronger than that of Te(II)-Bi(Sb). The interaction between Te(I) and Te(I) in different layers is the weakest and the interaction should be Van Der Waals power. The charge of Sb is lower than that of Bi, and the ionic bond of Te-Sb is weaker than that of Te-Bi. The covalent bond of Te-Sb is also weaker than that of Te-Bi. Therefore, the thermoelectric property may be improved with the adjusting of electrical conductivity and thermal conductivity from changing the composition in the compounds of Bi-Sb-Te. The calculated results are consistent with the experiments.