CRYSTALLOGRAPHIC PROPERTIES OF I 2 –Fe–IV–Vi 4 MAGNETIC SEMICONDUCTOR COMPOUNDS M. Quintero 1 *, A. Barreto 1 , P. Grima 1 , R. Tovar 1 , E. Quintero 1 , G. Sa ´nchez Porras 1 , J. Ruiz 1 , J.C. Woolley 2 , G. Lamarche 2 , and A-M. Lamarche 2 1 Centro de Estudios de Semiconductores, Departamento de Fı ´sica, Facultad de Ciencias, Universidad de Los Andes, Me ´rida 5101, Venezuela 2 Ottawa-Carleton Institute for Physics, University of Ottawa, Ottawa, Ontario, K1N 6N5 Canada (Refereed) (Received March 1, 1999; Accepted March 3, 1999) ABSTRACT X-ray powder diffraction measurements were made at room temperature on sixteen polycrystalline samples of I 2 –Fe–IV–VI 4 (I: Cu, Ag; IV: Si, Ge, Sn, Pb; VI: Se, Te) magnetic semiconductor compounds. The diffraction patterns were analyzed to determine values of lattice parameter for each compound. The results showed that Cu 2 FeSiSe 4 , Cu 2 FeGeSe 4 and Cu 2 FeSnSe 4 have the tetragonal stannite structure (I4 ¯ 2m), while the rest of the materials have an orthorhombic superstructure of wurtzite which is known as wurzt-stannite (Pmn2 1 ). It was found that, when the values of the effective parameter a e = (V/N) 1/3 are plotted against the molecular weight W of the materials, the tetragonal and orthorhombic compounds lie on different straight lines. In addition, differential thermal analysis (DTA) measurements were made, and the peaks on the DTA cooling curves were used to determine values corre- sponding to the melting temperature for the compounds. © 2000 Elsevier Science Ltd KEYWORDS: A. semiconductors, A. magnetic materials, C. X-ray diffrac- tion, D. crystal structure *To whom correspondence should be addressed. Materials Research Bulletin, Vol. 34, Nos. 14/15, pp. 2263–2270, 1999 Copyright © 2000 Elsevier Science Ltd Printed in the USA. All rights reserved 0025-5408/99/$–see front matter PII S0025-5408(00)00166-5 2263