Pathway models for fast ion conductors by combination of bond valence and reverse Monte Carlo methods Stefan Adams a, * , Jan Swenson b a GZG Abt. Kristallographie, Universita ¨t Go ¨ttingen, Goldschmidtstr. 1, D-37077, Go ¨ttingen, Germany b Department of Applied Physics, Chalmers University of Technology, S-41296, Go ¨teborg, Sweden Accepted 14 February 2002 Abstract Both the bond-valence (BV) method and the reverse Monte Carlo (RMC) method have proven to be useful tools for the investigation of the interplay between the microscopic structure and the transport properties in solid electrolytes. A combination of these two approaches opened a way for a deeper understanding of ion transport, especially in amorphous solid electrolytes, where the lack of reliable structural information so far have impeded minute atomistic descriptions of transport mechanisms. In this paper, we discuss both the abilities and limitations of this new approach. Special emphasis is put on the requirements for the consistent determination of bond-valence parameters that as necessary reflect the bond softness. For a variety of Ag + ion conducting glasses, we find, using bond softness sensitive bond-valence parameters, pathways for ion transport in the reverse Monte Carlo produced structural models of the glasses. From the volume fraction of these pathways, we are able to predict both the absolute value and the activation energy of the ionic conductivity. Simulations of ion transport as random walks within the bond-valence pathway network shed further light on the transport process and provide a complementary way to predict the conductivity from structural models. D 2002 Elsevier Science B.V. All rights reserved. PACS: 61.43.Fs Glasses; 66.30.Hs Self-diffusion and ionic conduction in nonmetals; 66.30.Dn Theory of diffusion and ionic conduction in solids Keywords: Structure conductivity correlation; Reverse Monte Carlo method; Bond valence; Ion conducting glasses; Fast ion conductors 1. Introduction The concept of bond valence has been proposed in 1970 by Donnay and Allmann [1] as a generalization of Pauling’s electrostatic valence principle into empir- ical relationships between length and strength of individual chemical bonds. Due to its simplicity and the availability of bond-valence parameters for almost every atom pair (from structure data of reference compounds compiled in crystal structure databases; see, e.g., Refs. [2–5]), bond-valence (BV) calcula- tions nowadays are widely used in crystal chemical considerations. In earlier studies, we have demonstra- ted that the BV approach can be effectively utilized to study the interplay between structure and ionic con- ductivity of solid electrolytes [6,7]. While for crystalline solid electrolytes the ion transport processes may be traced back to a few fundamental mechanisms, a generally accepted model 0167-2738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-2738(02)00423-X * Corresponding author. Tel.: +49-551-393898; fax: +49-551- 399521. E-mail address: sadams@gwdg.de (S. Adams). www.elsevier.com/locate/ssi Solid State Ionics 154 – 155 (2002) 151 – 159