# Ferroelectric glass of spheroidal dipoles with impurities: Polar nanoregions, response to applied electric field, and ergodicity breakdown

## TL;DR

This study uses molecular dynamics to explore ferroelectric glass behavior in spheroidal dipolar systems with impurities, revealing polar nanoregions, heterogeneity, and nonergodic responses similar to relaxor ferroelectrics.

## Contribution

It introduces a detailed simulation of dipolar glasses with spheroidal particles and impurities, elucidating the formation of polar nanoregions and nonergodic phenomena.

## Key findings

- Formation of polar nanoregions (PNRs) at low temperatures.
- Heterogeneous impurity clustering affects dielectric response.
- Observation of nonergodic polarization and strain behavior.

## Abstract

Using molecular dynamics simulation, we study dipolar glass in crystals composed of slightly spheroidal, polar particles and spherical, apolar impurities between metal walls. We present physical pictures of ferroelectric glass, which have been observed in relaxors, mixed crystals (such as KCN$_x$KBr$_{1-x}$), and polymers. Our systems undergo a diffuse transition in a wide temperature range, where we visualize polar nanoregions (PNRs) surrounded by impurities. In our simulation, the impurities form clusters and their space distribution is heterogeneous. The polarization fluctuations are enhanced at relatively high $T$ depending on the size of the dipole moment. They then form frozen PNRs as $T$ is further lowered into the nonergodic regime. As a result, the dielectric permittivity exhibits the characteristic features of relaxor ferroelectrics. We also examine nonlinear response to cyclic applied electric field and nonergodic response to cyclic temperature changes (ZFC$/$FC), where the polarization and the strain change collectively and heterogeneously. We also study antiferroelectric glass arising from molecular shape asymmetry. We use an Ewald scheme of calculating the dipolar interaction in applied electric field.