Polarity of domain boundaries in nonpolar materials derived from order parameter and layer group symmetry

TL;DR

This paper investigates the electric polarity of domain boundaries in nonpolar crystalline materials using order parameter and layer group symmetry analysis, providing a new approach to understanding their functional properties.

Contribution

It introduces a method combining order parameter and layer group symmetries to determine domain boundary polarity, demonstrated on KSCN and lacunar spinel crystals.

Findings

Layer group symmetry helps identify the maximal symmetry of domain boundaries.

Order parameter analysis clarifies the polarity nature of boundaries.

Method applied successfully to specific crystal examples.

Abstract

Domain boundaries and other twin boundaries in crystalline materials are receiving increasing interest. They can carry unique functional properties, which in many cases are absent in the surrounding bulk material. One such property of domain boundaries can be their electric polarity. Phenomenological insight in the polarity of domain boundaries was so far based either on the knowledge of the order parameter and the form of Landau-Ginzburg free energy functional, or on the knowledge of the symmetry of the domain boundaries. In the present work we show on the concrete examples of potassium thiocyanate (KSCN) and lacunar spinel crystals, that the concept of the primary order-parameter can help to find the layer group describing the maximal possible symmetry of a given domain boundary. Combination of layer group and order parameter symmetries is then employed to clarify the nature of the polarity of domain boundaries.