Reactions of europium with copper or silver in molten alkali metal/polytelluride fluxes have produced the new polytelluride compounds, Cu0.66EuTe2, KCu2EuTe4, and Na0.2Ag2.8EuTe4. All three compounds are stable in air, and crystallize as red-brown plates in tetragonal space groups. Cu0.66EuTe2 crystallizes in the. space group P4lnmm with a=4.481(2), c= 10.260(3)Å (at 23°C), and Z=2. KCu2EuTe4, and Na0.2Ag2.8EuTe4 are isostructural, and crystallize in the space group P4mm with 0 = 4.4365(6), c= 11.365(2) Å (at 23°C) for KCu2EuTe4, and a = 4.4544(6), c= 11.106(2) A (at 23 °C) for Na0.2Ag2.8EuTe4. Cu0.66EuTe2 adopts the CaMnBi2 structure-type with square antiprismatic europium atoms sandwiched between an anti-PbO type layer of [CuTe]-, and a flat square net of tellurium. The structure of KCu2EuTe4 can be derived from that of Cu0.66EuTe2 by systematically replacing half of the europium atoms in the framework with potassium. Electron diffraction studies on KCu2EuTe4, and Na0.2Ag2.8EuTe4 suggest a la × 7b superlattice, the result of a charge density wave (CDW) distortion in the square Te net of these compounds. KCu2EuTe4 exhibits semimetallic behavior while Na0.2Ag2.8EuTe4 is a p-type semiconductor with a bandgap of 0.24 eV.
ASJC Scopus subject areas
- Materials Chemistry