Synthesis and Structural and Physical Properties of New Semiconducting Quaternary Tellurides: Ba<sub>4</sub>Ag<sub>3.95</sub>Ge<sub>2</sub>Te<sub>9</sub> and Ba<sub>4</sub>Cu<sub>3.71</sub>Ge<sub>2</sub>Te<sub>9</sub>
收藏资源简介：
Two quaternary tellurides, Ba4Ag3.95Ge2Te9 and Ba4Cu3.71Ge2Te9, were prepared in evacuated silica tubes at 750 °C. Both tellurides crystallize in space group Pbam, with lattice parameters of a = 8.6835(3) Å, b = 13.6421(4) Å, c = 10.2612(3) Å, and V = 1215.55(7) Å3 (Z = 2) for Ba4Ag3.95Ge2Te9 and a = 8.6464(2) Å, b = 13.5305(4) Å, c = 10.0810(3) Å, and V = 1179.38(6) Å3 (Z = 2) for Ba4Cu3.71Ge2Te9. These structures are comprised of planar Ag4/Cu4 clusters and dimeric Ge2Te6 units, which are interconnected through Te atoms into a three-dimensional structure. Several split sites in the case of Ba4Cu3.71Ge2Te9 are reflected in additional, different clusters, including a linear Cu3 unit. The covalent Ag−Te/Ge−Te network surrounds a one-dimensional linear channel running along the c direction, encompassing the Ba atoms. Electronic structure calculations and transport property measurements show that these two compounds are p-type semiconductors with calculated band gaps of 0.24 eV for the Ag compound and 1.0 eV for the Cu compound.
