Does the 8-N bonding rule break down in As₂Se₃ glass?

¹ Department of Physics, Graduate School of Science and Technology, Kumamoto University Kumamoto, 860-8555, Japan
² Department of Chemistry, Physical Chemistry, Philipps University of Marburg - 35032 Marburg, Germany, EU
³ Institut Néel, Centre National de la Recherche Scientifique/Université Joseph Fourier (CNRS/UJF) 38042 Grenoble Cedex 9, France, EU
⁴ Research and Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8) Hyogo 679-5198, Japan

Received: 1 May 2013
Accepted: 13 June 2013

Abstract

The coordination numbers in As₂Se₃ glass were determined by a combination of anomalous X-ray scattering experiments, reverse Monte Carlo modeling, and ab initio molecular dynamics simulations. We found that the well-known “8-N bonding rule” proposed by Mott breaks down around the As atoms, exceeding the rule by 7–26%. An experimental prediction based on mean-field theory agrees with the present experimental and theoretical results. The fourfold coordinated As atoms likely form As-As wrong bond chains rather than ethan-like configurations, which is identified as the origin for the breakdown of the “8-N bonding rule”.