Synthesis and structural and physical properties of new semiconducting quaternary tellurides: Ba4Ag3.95Ge2Te9 and Ba4Cu3.71Ge2Te9.
Two quaternary tellurides, Ba(4)Ag(3.95)Ge(2)Te(9) and Ba(4)Cu(3.71)Ge(2)Te(9), were prepared in evacuated silica tubes at 750 degrees C. Both tellurides crystallize in space group Pbam, with lattice parameters of a = 8.6835(3) A, b = 13.6421(4) A, c = 10.2612(3) A, and V = 1215.55(7) A(3) (Z = 2) for Ba(4)Ag(3.95)Ge(2)Te(9) and a = 8.6464(2) A, b = 13.5305(4) A, c = 10.0810(3) A, and V = 1179.38(6) A(3) (Z = 2) for Ba(4)Cu(3.71)Ge(2)Te(9). These structures are comprised of planar Ag(4)/Cu(4) clusters and dimeric Ge(2)Te(6) units, which are interconnected through Te atoms into a three-dimensional structure. Several split sites in the case of Ba(4)Cu(3.71)Ge(2)Te(9) are reflected in additional, different clusters, including a linear Cu(3) 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.
Department of Chemistry, University of Waterloo, Waterloo, ON, Canada N2L 3G1.
Yanjie
Y
Cui
Abdeljalil
A
Assoud
Holger
H
Kleinke