Crystallographic properties of I-2-Fe-Iv-Vi(4) magnetic semiconductor compounds

X-ray powder diffraction measurements were made at room temperature on sixt een polycrystalline samples of I-2-Fe-IV-VI4 (I: Cu, Ag; IV: Si, Ge, Sn, Ph ; VI: Se, Te) magnetic semiconductor compounds. The diffraction patterns we re analyzed to determine values of lattice parameter for each compound. The results showed that Cu2FeSiSe4, Cu2FeGeSe4 and Cu2FeSnSe4 have the tetrago nal stannite structure (I (4) over bar 2m), while the rest of the materials have an orthorhombic superstructure of wurtzite which is known as wurzt-st annite (Pmn2(1)). It was found that, when the values of the effective param eter a(e) = (V/N)(1/3) are plotted against the molecular weight W of the ma terials, the tetragonal and orthorhombic compounds lie on different straigh t lines. In addition, differential thermal analysis (DTA) measurements were made, and the peaks on the DTA cooling curves were used to determine value s corresponding to the melting temperature for the compounds. (C) 2000 Else vier Science Ltd.