Germanium selenide glass structures studied by 77 Se solid state NMR and mass spectroscopy Bruno Bureau a, * , Johann Troles a , Marie Le Floch a , Pierre Gu enot b , Fr  ed eric Smektala a , Jacques Lucas a a Laboratoire des Verres et Ceramiques, UMR-CNRS 6512, Universit e de Rennes 1, Campus de Beaulieu, 35042 Rennes cedex, France b Centre R egional de Mesures Physiques de lÕOuest, Universit e de Rennes 1, Campus de Beaulieu, 35042 Rennes cedex, France Received 1 July 2002; received in revised form 9 September 2002 Abstract Some resolved solid state 77 Se NMR spectra are presented in the Ge x Se 1x glass family at ambient temperature. Two types of line positions are exhibited related to the presence or absence of Ge atoms as first neighbours around one Se atom. The relative intensity measurements of both lines are carried out via deconvolution of the spectra. It appears that a scenario involving a selenium clustering process has to be considered rather than a structural model based on GeSe 4 tetrahedra homogeneously distributed among the network. This result is supported by mass spectroscopy experiments that demonstrate the presence of Se 6 rings in the glass. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 76.60.k; 76.60.Cq; 61.72.Hh; 61.43.Fs 1. Introduction Due to their potential application in infrared optics, germanium chalcogenide Ge x Se 1x glasses have been intensively investigated during the past decades. In the past 10 years X-ray [1,2], neutrons scattering [3,4], EXAFS [5] and Raman [6,7] techniques have been used to investigate the Ge x Se 1x or Ge x S 1x structures which are expected to be very similar. These previous studies have led to the description of short range order as con- trolled by a chemical ordering process which de- pends on heteropolar bonds. Thus, the Ge atoms are coordinated to four Se neighbors constituting slightly distorted GeSe 4 tetrahedrons whereas the Se atoms have a twofold coordination with Se or Ge as first neighbors with an environment de- pending on the x value. Obviously, the number of Se–Se bonds is expected to increase when x de- creases. Concerning the longer range order, two descriptions directly related to the way the tetra- hedra are spread over the network are in compe- tition for the Se-enriched glasses (x < 0:33). The first model, called Ôchain crossing modelÕ, is the more intuitive and simpler one [6–8]. It consists of * Corresponding author. Tel.: +33-2 23 23 65 73; fax: +33-2 23 23 56 11. E-mail address: bruno.bureau@univ-rennes1.fr (B. Bureau). 0022-3093/03/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0022-3093(02)01911-7 Journal of Non-Crystalline Solids 319 (2003) 145–153 www.elsevier.com/locate/jnoncrysol