Binary continuous random networks

TL;DR

This paper investigates the conditions under which idealized continuous-random network models accurately represent disordered materials, revealing that defect density can abruptly change and that defects may be either negligible or fundamental to the structure.

Contribution

It analyzes the role of defects in continuous-random networks, showing that defect density behavior varies sharply with interaction strengths and impacts the idealized model's applicability.

Findings

Defect density in tetrahedral networks jumps from near zero to finite values.

In some materials, defects are only thermodynamic excitations.

In others, defects are essential to the ideal structure.

Abstract

Many properties of disordered materials can be understood by looking at idealized structural models, in which the strain is as small as is possible in the absence of long-range order. For covalent amorphous semiconductors and glasses, such an idealized structural model, the continuous-random network, was introduced 70 years ago by Zachariasen. In this model, each atom is placed in a crystal-like local environment, with perfect coordination and chemical ordering, yet longer-range order is nonexistent. Defects, such as missing or added bonds, or chemical mismatches, however, are not accounted for. In this paper we explore under which conditions the idealized CRN model without defects captures the properties of the material, and under which conditions defects are an inherent part of the idealized model. We find that the density of defects in tetrahedral networks does not vary smoothly with variations in the interaction strengths, but jumps from close-to-zero to a finite density. Consequently, in certain materials, defects do not play a role except for being thermodynamical excitations, whereas in others they are a fundamental ingredient of the ideal structure.