Dynamic Local Distortions in Ferroelectrics

TL;DR

This paper uses molecular-dynamics simulations to reveal dynamic chain-like structures in ferroelectrics, explaining phase transitions and phonon behavior through a first-principles effective Hamiltonian.

Contribution

It demonstrates that real-space chains explain both displacive and order-disorder aspects of ferroelectric phase transitions, validated by simulations.

Findings

Preformed dynamic chain-like structures exist in paraelectric phase.

Simulations reproduce the correct ferroelectric phase sequence.

First-principles Hamiltonian captures microscopic fluctuations.

Abstract

Molecular-dynamics simulations of KNbO$_3$ reveal preformed dynamic chain-like structures, present even in the paraelectric phase, that are related to the softening of phonon branches over large regions of the Brillouin zone. The phase sequence of ferroelectric transitions is correctly reproduced, showing that the first-principles effective Hamiltonian used in the simulations captures the essential behavior of the microscopic fluctuations driving the transitions. Real space chains provide a framework for understanding both the displacive and order-disorder characteristics of these phase transitions.