Hyperfine Interact (2010) 195:191–197 DOI 10.1007/s10751-009-0119-1 Crystallographic and 119 Sn and 155 Gd Mössbauer analyses of Gd 5 Ge 2 (Si 1−x Sn x ) 2 (x = 0.23 and x = 0.40) J. C. P. Campoy · A. O. dos Santos · L. P. Cardoso · A. Paesano Jr · M. T. Raposo · J. D. Fabris Published online: 2 October 2009 © Springer Science + Business Media B.V. 2009 Abstract We report the structural characterization of Gd 5 Ge 2 (Si 1−x Sn x ) 2 (x = 0.23 and x = 0.40) compounds by means of 100 and 298 K-X-ray diffractometry (XRD) and 4 K- 155 Gd and 298 K- 119 Sn Mössbauer spectroscopy. These compounds order ferromagnetically at 218.4 and 172.7 K, respectively. At ∼100 K, it was identified the Gd 5 Si 4 -orthorhombic phase (type I) for both samples. At ∼298 K, it was identified a Gd 5 Si 2 Ge 2 -monoclinic phase, for x = 0.23 and a Sm 5 Sn 4 -orthorhombic phase (type II), for x = 0.40. The Rietveld analysis of XRD data suggests a first order magneto-structural transition at Curie temperature for both compositions. J. C. P. Campoy · L. P. Cardoso Instituto de Física “Gleb Wataghin”, Universidade Estadual de Campinas, 13083-970, Campinas, SP, Brazil A. O. dos Santos CCSST, Universidade Federal do Maranhão, 65900-410, Imperatriz, MA, Brazil A. Paesano Jr Departamento de Física, Centro de Ciências Exatas, Universidade Estadual de Maringá, 87020-900, Maringá, Paraná, Brazil M. T. Raposo (B ) Departamento de Ciências Naturais, Universidade Federal de São João Del Rei, C.P. 110, 36301-160, São João Del Rei, MG, Brazil e-mail: mtraposo@ufsj.edu.br J. D. Fabris Departamento de Química—ICEx, Universidade Federal de Minas Gerais, Campus-Pampulha, 31270-901, Belo Horizonte, MG, Brazil