Viscoelastic Properties of Crystals

TL;DR

This paper investigates the fundamental viscoelastic differences between fluids and crystals, revealing that crystals do not have infinite zero-frequency shear viscosity and differ from glasses in their viscosity properties.

Contribution

It challenges the common assumption that crystals have infinite shear viscosity and clarifies the viscoelastic distinctions between fluids, crystals, and glasses.

Findings

Crystals do not have infinite zero-frequency shear viscosity.

Crystals have higher viscosity than liquids but lower than glasses.

Shear modulus is zero for fluids, but not necessarily for crystals.

Abstract

We examine the question of whether fluids and crystals are differentiated on the basis of their zero frequency shear moduli or their limiting zero frequency shear viscosity. We show that while fluids, in contrast with crystals, do have a zero value for their shear modulus, in contradiction to a widespread presumption, a crystal does not have an infinite or exceedingly large value for its limiting zero frequency shear viscosity. In fact, while the limiting shear viscosity of a crystal is much larger than that of the liquid from which it is formed, its viscosity is much less than that of the corresponding glass that may form assuming the liquid is a good enough glass former.