STRUCTURE AND MAGNETIC-PROPERTIES OF THE TERNARY COMPOUND COPPER IRONTELLURIDE

Initial measurements made by X-ray diffraction on polycrystalline samp les indicated that stoichiometric CuFeTe2 did not show single phase be haviour, but that samples with composition Cu1.13Fe1.22Te2 (CFT) were single phase. Neutron diffraction measurements were made on a sample o f CFT at Various temperatures in the range 4.2-300 K using a neutron w avelength of 0.15525 nm. Analysis of the resulting data showed that CF T has a defect Cu2Sb-type structure with space group P4/nmm and lattic e parameters a = 0.39850 and c = 0.60920 nm at room temperature. It wa s shown that the 2a(0 0 0) sites are occupied by Cu and Fe and 2c(0 1/ 2 z) sites by Te, while the excess Cu and Fe occupy 2c'(0 1/2 z') site s, which are 10-15% filled. However, no ordering of the Cu and Fe on e ither type of site could be detected. Also, no extra magnetic lines we re observed at any temperature, indicating that no ordered magnetic st ructure was observed. Measurements of magnetic susceptibility as a fun ction of temperature on CFT samples showed the presence of a spin-glas s transition in the range 60-80 K. The spin-glass behaviour is attribu ted to the effects of Fe atoms in the 2c' sites which cause frustratio n in the Fe atoms on the 2a sites, Any local variation of the density of 2c' Fe atoms would result in a corresponding variation of the spin- glass transition temperature, as observed. (C) 1998 Elsevier Science B .V. All rights reserved.