Electronic structures of PbBi4Te7 and GeBi4Te7 calculated by a first-principle pseudopotential method

Electronic band calculations of PbBi4Te7 and GeBi4Te7 have been done using the density functional theory under the local density approximation. PbBi4Te7, which was assumed to have the crystal structure proposed by Petrov and Imamov, has nearly the same electronic structure as Bi2Te3 other than the Pb4s band near the top of the second highest valence band. Pb introduction into the Bi–Te lattice may cause a decrease in heat conduction through weakening the bond strength between Bi and Te. The DOSs of the modeled structures of PbBi4Te7 proposed by Zhukova and Zaslavskii [Soviet Phys Crystallogr 16 (1971) 796] (Pb7Bi27Te48, Pb7Bi28Te48 and Pb8Bi27Te48) show the closure of the band gap though the Fermi levels are located near the dent in the DOS curve. The structural data of Agaev et al. [Soviet Phys Crystallogr 13 (1968) 44] for GeBi4Te7 can hardly be acceptable from the predicted DOS curve and energetic point of view.