Ionic conductivity (Ag + ) in AgGeSe glasses M.A. Uren ˜a * , A.A. Piarristeguy, M. Fontana, B. Arcondo Laboratorio de So ´lidos Amorfos, Departamento de Fı ´sica, Facultad de Ingenierı ´a, Universidad de Buenos Aires. Paseo Colo ´n 850, (1063) Buenos Aires, Argentina Received 20 November 2003; received in revised form 2 July 2004; accepted 13 September 2004 Abstract Ag x (Ge 0.25 Se 0.75 ) 100x (10Vx V25 at.%) ionic conductor glasses, prepared by a melt-quenching method, are investigated by impedance spectroscopy in the frequency range 5 Hz–2 MHz at different temperatures T from room temperature to 363 K. The conductivity of the glasses r was obtained as a function of the silver concentration and the temperature. The temperature dependence of the ionic conductivity follows an Arrhenius type equation r=(r 0 /T)d exp(E r /kT). The activation energy of the ionic conductivity E r and the preexponential term r 0 were calculated. It was found that the room temperature conductivity increases by a factor of about 10 with increasing silver content (1.32 10 5 S cm 1 at x =10 and 1.09 10 4 S cm 1 at x =25), while the activation energy decreases from 0.367 to 0.339 eV. The diffusion coefficient of the Ag + ions was estimated. In addition, a model proposed by Elliott was applied to determine the activation energy of conductivity in the high-modifier-content region. The results are discussed in connection with structural aspects and with those published in the literature related to other chalcogenide and chalcohalide systems. D 2004 Elsevier B.V. All rights reserved. PACS: Ionic conduction solids 66.30.D Keywords: AgGeSe; Chalcogenide glasses; Fast ionic conductors; Ag + ; Impedance spectroscopy 1. Introduction Chalcogenide glasses have been studied exhaustively due to their electric properties [1,2]. In particular, some of these systems with metals in their composition are able to behave like fast ionic conductors. The interest in these glasses has increased in recent years because of the potential application of these materials as solid electrolytes in new devices (i.e., solid-state microbatteries) [3,4]. In general, the conductivity of the chalcogenide glasses increases significantly with the increase in the metal content from 10 16 –10 14 (insulator materials) to values larger than 10 7 S cm 1 , behaving as fast-ionic-conducting materials (where the electronic conductivity is many orders lower than the ionic one). In some cases, this colossal change in the conductivity occurs in a limited concen- trations range, indicating a percolation transition [5–8]. The AgGeSe [9], AgGeS and AgGeSeSb [5] glassy systems present an abrupt variation of the Ag + ionic conductivity with the concentration. Although the chemical nature of these systems is similar, different behaviors of the Ag + conduction in these glasses are reported: (a) the conductivity in the AgGeSe system is about two or three orders larger than in the AgGeS system in the fast-ionic- conducting region [5], (b) the conductivity regime changes in the selenium system at a higher Ag concentration than in the sulphur system [9]. In this work, we study the conductivity of Ag x (Ge 0.25 Se 0.75 ) 100x glasses with x =10, 15, 20 and 25 at.% and its dependence on the temperature and the composition. We calculate the activation energies and observe a power law dependence of conductivity on the carriers content. The results are compared with those of other chalcogenide and chalcohalide systems and connected to the glass structure. 0167-2738/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2004.09.008 * Corresponding author. Tel.: +54 11 4343 0092ext.279; fax: +54 11 4331 1852. E-mail addresses: murena@fi.uba.ar (M.A. Uren ˜a)8 apiarri@fi.uba.ar (A.A. Piarristeguy). Solid State Ionics 176 (2005) 505 – 512 www.elsevier.com/locate/ssi