Solid State Ionics 121 (1999) 189–192 XANES and EXAFS at Mo K-edge in (AgI) (Ag MoO ) 1 2x 2 4 x glasses and crystals a a ,b c, c c * F. Rocca , A. Kuzmin , P. Mustarelli , C. Tomasi , A. Magistris a CEFSA-Centro CNR-ITC di Fisica degli Stati Aggregati, Via Sommarive 14, I-38050 Povo ( Trento), Italy b Institute of Solid State Physics, Kengaraga Street 8, LV -1063 Riga, Latvia c CSTE-CNR and Department of Physical Chemistry, University of Pavia, Via Taramelli 16, I-27100 Pavia, Italy Received 13 November 1998; accepted 4 December 1998 Abstract (AgI) (Ag MoO ) glasses and crystals have been studied by X-ray absorption spectroscopy at the Mo K-edge. All the 12x 2 4 x ˚ measured samples contain isolated [MoO ] tetrahedra with R(Mo–O) 5 1.78560.008 A and mean square relative 4 2 2 ˚ displacement (MSRD) s 5 0.004360.0013 A , which are unchanged upon insertion of AgI. The glasses have a quite similar environment around molybdenum, which resembles that of the crystal (AgI) (Ag MoO ) with x 5 0.33. The x 2 4 x presence of AgI modifies the local environment around molybdenum already in the second coordination shell.  1999 Published by Elsevier Science B.V. All rights reserved. Keywords: EXAFS; XANES; Glasses; Molybdates; AgI 1. Introduction et al. [1,2], while the equilibrium phase diagram over the whole composition range was determined by our | The pseudobinary glasses with composition group [3]. The eutectic was found at T 1808C for 5 | (AgI) (Ag MoO ) belong to fast ion conducting x 0.25, whereas a peritectic was observed at 5 12x 2 4 x | (FIC) glasses which can be used as electrolytes in 2408C, for x 0.5 which corresponds to the forma- 5 solid state electrochemical devices like batteries and tion of (AgI) (Ag MoO ) (1:1 composition) 0.5 2 4 0.5 sensors. Such an application is favoured by the high compound. 22 21 21 values (of the order of 10 ohm cm ) of We have recently revisited by DSC and X-ray conductivity displayed by silver-based glasses at diffraction the devitrification and the approach to- room temperature. wards stability [4]: a metastable crystalline com- The (AgI) (Ag MoO ) glasses can be prepared pound with composition (AgI) (Ag MoO ) 12x 2 4 x 0.67 2 4 0.33 in the range 0.2 , x # 0.4. Their structural, transport nucleates at | 1108C over the entire composition and thermal properties were early studied by Minami range. In the present work, we present an X-ray absorp- * tion spectroscopy study of the local environment Corresponding author. Tel.: 1 39-0382-507-776. E-mail address: mustarelli@matsci.unipv.it (P. Mustarelli) modifications around molybdenum ions in the 0167-2738 / 99 / $ – see front matter  1999 Published by Elsevier Science B.V. All rights reserved. PII: S0167-2738(98)00546-3