Solid State Communications 146 (2008) 65–68 www.elsevier.com/locate/ssc Raman scattering and X-ray diffraction study in Cu 2 GeSe 3 G. Marcano a , C. Rinc ´ on a,∗ , G. Mar´ ın a , G.E. Delgado b , A.J. Mora b , J.L. Herrera-P´ erez c , J.G. Mendoza-Alvarez d , P. Rodr´ ıguez d a Centro de Estudios de Semiconductores, Departamento de F´ ısica, Facultad de Ciencias, Universidad de Los Andes, M´ erida, Venezuela b Laboratorio de Cristalograf´ ıa, Departamento de Qu´ ımica, Facultad de Ciencias, Universidad de Los Andes, M´ erida, Venezuela c CICATA-IPN, M´ exico DF 11500, Mexico d Cinvestav-IPN, Departamento de F´ ısica, M´ exico DF 07000, Mexico Received 12 December 2007; received in revised form 24 December 2007; accepted 17 January 2008 by D.J. Lockwood Available online 25 January 2008 Abstract A combined study of X-ray diffraction data and micro-Raman scattering of Cu 2 GeSe 3 is presented. From the analysis of the X-ray data it is confirmed that this compound crystallizes in an orthorhombic cell, space group Imm2. From Raman spectra, optical modes are identified and their possible symmetry assignments are suggested. Peaks at 212, 266 and 300 cm −1 , tentatively assigned to B 2 modes, agree well with those reported from infrared reflectivity. The most strong peak at 189 cm −1 which is only Raman active is assigned to one of the two A 2 modes. Lines at 135, 235 and 254 cm −1 are attributed to A 1 or B 1 modes. The highest phonon frequency band, observed at 385 cm −1 , probably comprises the remaining A 2 mode and an overtone from the strong line at 189 cm −1 . c  2008 Elsevier Ltd. All rights reserved. PACS: 78.30.-j; 78.40.Fy Keywords: A. Semiconductors; D. Optical properties; D. Raman scattering; E. Elastic light scattering 1. Introduction The ternary compound Cu 2 GeSe 3 belongs to the family of diamond-like semiconductors with general composition A I 2 –B IV –C VI 3 where A I = Cu or Ag, B VI = Ge or Sn, and C VI = S, Se or Te. This is one of the two possible families of the three-fold normal derivatives of the A II B VI binary compounds [1]. These materials have received considerable attention recently for acousto-optic applications due to their low band gaps, low melting points, high mean atomic weights and high refractive indices. Some studies on single crystals [2–4] and nano-crystals [5–7] of these materials have been reported. Among them, Cu 2 GeSe 3 is of considerable interest [8–12]. However, very little work on its physical properties appears in the literature. Only recently, analysis of the temperature dependence of its electrical and optical properties has been reported [10,11]. ∗ Corresponding author. Tel.: +58 0274 2401323; fax: +58 0274 2401286. E-mail address: crincon@ula.ve (C. Rinc ´ on). Lattice vibrations in Cu 2 GeSe 3 have been studied by infrared reflectivity (IR) spectra [13]. From the analysis of these spectra, the parameters of four vibrational modes were determined. However, study of Raman scattering which could give more complete information related to vibrational modes of Cu 2 GeSe 3 has not appeared in the literature. Hence, the lattice dynamics of this compound remain unclear. In addition, different crystal structure types for Cu 2 GeSe 3 have been reported by several authors. Earlier X-ray powder analysis by Rivet [14] and Hann [15] indicated that it crystallizes in cubic and tetragonal chalcopyrite structures, respectively, whereas Parth´ e and Gar´ ın [16], on the basis of single-crystal analysis, found Cu 2 GeSe 3 to be orthorhombic. More recently, it has been suggested that this compound crystallizes in a triclinic structure [17]. For these reasons, in the present communication, a combined study of X-ray diffraction data and micro-Raman scattering of this compound is presented. From the analysis of the experimental X-ray powder data, the crystal structure is obtained and refined. From Raman spectra, the 0038-1098/$ - see front matter c  2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2008.01.018