Weakly faceted cellular patterns versus growth-induced plastic deformation in thin-sample directional solidification of monoclinic biphenyl

TL;DR

This study investigates the conditions leading to growth-induced plastic deformation and weakly faceted patterns in thin-sample directional solidification of biphenyl, revealing the role of thermal stress and cellular instability in pattern formation.

Contribution

It identifies the conditions under which biphenyl crystals exhibit either deformation or weakly faceted growth, highlighting the impact of thermal stress and cellular instability.

Findings

GID is a long-range thermal-stress effect that disappears with cellular structures.

Cellular instability can be triggered early to avoid GID.

Weakly faceted patterns depend on crystal orientation and growth conditions.

Abstract

We present an experimental study of thin-sample directional solidification (T-DS) in impure biphenyl. The plate-like growth shape of the monoclinic biphenyl crystals includes two low-mobility (001) facets and four high-mobility {110} facets. Upon T-DS, biphenyl plates oriented with (001) facets parallel to the sample plane can exhibit either a strong growth-induced plastic deformation (GID), or deformation-free weakly faceted (WF) growth patterns. We determine the respective conditions of appearance of these phenomena. GID is shown to be a long-range thermal-stress effect, which disappears when the growth front has a cellular structure. An early triggering of the cellular instability allowed us to avoid GID and study the dynamics of WF patterns as a function of the orientation of the crystal.