Computer simulation of a quadrupolar glass

Abstract

A model of solid solutions of has been studied by Monte Carlo techniques over a wide range of temperatures for various concentrations x. The results are discussed in terms of a recently presented discrete-state model for cubic orientational glasses. Comparison is made to experiment. At temperatures smaller than the fcc - Pa3 transition temperature of the pure model system, the following phases were found. For x > 0.9, the Pa3 structure turns out to be stable. At x = 0.9, the Pa3 structure is stable, as is a frozen-in orientational disordered phase, which has a local ferroelastic type of ordering. At x = 0.7, indications of two-step relaxation can be observed, indicating a primary and a secondary relaxation. The local order is ferroelastic but the disorder is no longer frozen in. For smaller concentrations, 0.1 < x < 0.5, neighbouring molecules remain parallel but the relaxation is clearly a one-step process. When translation - rotation coupling is suppressed by keeping the atoms and molecules fixed to their lattice sites, the Pa3 structure remains stable even at concentrations as low as x = 0.5.