Structure and physical properties of the new telluride BaAg2Te2 and its quaternary variants BaCu delta Ag2-delta Te2

摘要

The new materials BaCu delta Ag2-delta Te2 (0 <=delta <= 2) were prepared from the elements at 800 degrees C in evacuated silica tubes. BaAg2Te2 crystallizes in the alpha-BaCu2S2 type, space group Pnma, with lattice parameters a = 10.8897(3) angstrom, b = 4.6084(1) angstrom, c = 11.8134(3) angstrom (Z = 4). The structure consists of a three-dimensional network of vertex- and edge-condensed AgTe4 tetrahedra, which includes the Ba2+ cations in linear channels running along the short b-axis. Half of the Ag atoms participate in an Ag atom zigzag chain extended parallel to the channels. BaAg2Te2 is a p-type semiconductor with large Seebeck coefficient. Within the series BaCu delta Ag2-delta Te2, the electrical conductivity increases and the Seebeck coefficient decreases strongly with increasing Cu content. (C) 2008 Elsevier Inc. All rights reserved.