X-ray absorption and photoemission electron spectroscopic investigation of crystalline and amorphous barium silicates S. Bender a , R. Franke a , E. Hartmann b , V. Lansmann c , M. Jansen c,d , J. Hormes a,e, * a Physikalisches Institut, Universit€ at Bonn, Nußallee 12, D-53115 Bonn, Germany b Institut f€ ur Oberfl€ achenmodifizierung, Permoserstr. 15, D-04303 Leipzig, Germany c Institut f€ ur Anorganische Chemie, Universit€ at Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany d Max-Planck-Institut f€ ur Festk€ orperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany e Center of Advanced Microstructures and Devices, 6980 Jefferson Highway, Baton Rouge, LA 70806, USA Received 25 May 1999; received in revised form 10 December 2001 Abstract X-ray absorption near edge structure (XANES) measurements at the Si K-edge, X-ray photoelectron spectroscopy oftheSi2pandO1sphotoelectronsandX-rayexcitedAugerelectronspectroscopyoftheSiKLLAugerelectronsare applied in order to investigate the degree of polymerisation (Q n )ofthe(SiO 4 )-polyhedra in barium silicate glasses with differentBaO-contents.Thespectraoftheglasseswith33.3and37.0mol%BaOarecomparedtothoseofthecrystalline reference compounds: low quartz, BaSi 2 O 5 , BaSiO 3 and Ba 2 SiO 4 . The analysis reveals a high average polymerisation between Q 3 and Q 4 in both glasses. The results are supported by calculations of the bound state transitions in Si K-XANES using the multiple scattering Xa method. Ó 2002 Published by Elsevier Science B.V. PACS: 61.43.Fs; 61.10.Ht; 82.80.Pv 1. Introduction Silicate glasses play an important role in in- dustrial applications. Macroscopic properties of the glasses such as hardness and chemical resis- tance can be varied over a large range either by introducing network modifiers such as alkali or earth-alkalimetals[1],orbyreplacingoxygenwith other anions like nitrogen or carbon [2–4]. In contrast to their importance, knowledge of the local structure of these amorphous solids is poor. In silicate glasses the bond lengths, the coordina- tionnumbersandthedegreeofpolymerisationQ n , where n is the number of bridging oxygen atoms per (SiO 4 )-unit, are of special interest. Commonly, local structure sensitive techniques are employed to investigate these parameters in amorphous Journal of Non-Crystalline Solids 298 (2002) 99–108 www.elsevier.com/locate/jnoncrysol * Corresponding author. Tel.: +1-225 338 4665; fax: +1-225 388 6954. E-mail address: hormes@lsu.edu (J. Hormes). 0022-3093/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII:S0022-3093(02)00943-2