Ferroelecture | Michele Kotiuga, EPFL, Switzerland
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In this seminar I will present a microscopic picture of paraelectric and ferroelectric phases based on a symmetry-based methodology we recently introduced, designed to identify meaningful structural prototypes for local disorder. These prototypes can then serve as minimal structural models used to faithfully represent these phases in calculations. Importantly, these are local minima of the potential-energy landscape and therefore do not display any structural instability. I will show how one can construct prototypes of paraelectric and ferroelectric phases through a group-subgroup analysis refined with density-functional-theory calculations, first using barium titanate as a test case.
The methodology allows us to systematically explore and identify structural prototypes for the paraelectric phase which accommodate the strong chemical drive towards [111] titanium displacements while maintaining a cubic point symmetry. Furthermore, we show how these could be inferred from symmetry-constrained phonon instabilities of the 5-atom-primitive cell [PRR 4, L012042 (2022)]. I will then show how these results extend across all the perovskite titanates, niobates, and zirconates, as well as the extension to the lower-symmetry ferroelectric phases.
Michele Kotiuga is a postdoctoral fellow in the laboratory of theory and simulation of materials — led by Prof. Nicola Marzari — at the École Polytechnique Fédérale de Lausanne in Switzerland. She has a Ph.D. (2015) in Physics from the University of California, Berkeley — supervised by Prof. Jeffrey Neaton — and has held a postdoctoral position at Rutgers University — in the group of Prof. Karin Rabe — before starting at EPFL. Her research focuses on using first-principles calculations to understand nanoscale physics which leads to fascinating materials properties. Notably, she has investigated near-field electrostatics-based effects in inorganic-organic systems as well as novel phase transitions and ferroelectricity in oxides.
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