Berlin 2018 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 11: Ferroelectric Domain Walls I (joint session KFM/TT)

TT 11.7: Hauptvortrag

Montag, 12. März 2018, 11:30–12:00, EMH 225

Understanding the dielectric enhancement from domain walls in conventional and relaxor ferroelectrics — •Andrew Rappe — University of Pennsylvania, Philadelphia, PA, USA

The dielectric properties of ferroelectric materials are a key driver of smart materials applications. In this talk, two key aspects of anomalous dielectric enhancement will be analyzed: domain walls and relaxor ferroelectrics. A comprehensive theoretical viewpoint will be sketched that unifies these aspects, based on multi-scale materials modeling.

Incorporating quenched Coulombic disorder in ferroelectrics disrupts and changes the character of this transition; instead of a sharp transition in a small temperature range, these oxide alloys exhibit “relaxed” transitions over 100-200 K and are called “relaxor ferroelectrics.” I will describe how a first-principles based multi-scale model can reveal the dynamic and statically correlated motions of ions that lead to relaxor behavior, and I will discuss their promise for next-generation piezoelectric and dielectric material systems, with emphasis on the emergent stabilization of a high density of low-angle domain walls.

I will also present molecular dynamics simulations of 90 degree domain walls (separating domains with orthogonal polarization directions) in the ferroelectric material PbTiO₃ to provide microscopic insights that enable the construction of a simple, universal, nucleation-and-growth-based analytical model that quantifies the dynamics of many types of domain walls in various ferroelectrics. This new model illuminates domain wall influence on the dielectric responses of conventional and relaxor ferroelectrics.