Michael Walden

Prediction of Ferroic Properties in Epitaxial BiXO3 Systems via Density-Functional Theory


Michael Walden is a fifth-year Ph.D. student in the Functional Ceramics Group. He is advised by Geoff Brennecka and co-advised by Cristian Ciobanu. Walden began his studies at Mines in 2016 after finishing his B.S. in Ceramic Engineering at Missouri S&T. He has been active in the American Ceramics Society since 2015 and received several recognitions therein, including the Du-Co Ceramics Scholarship. Walden has served on the ACerS President’s Council of Student Advisors (PCSA) since 2017 and currently serves as the Chair of that Council. Michael maintains a strong commitment to working with undergraduates with interest in ceramics, assisting with the Mines Keramos chapter, managing the Furnace Lab, and teaching slip-casting to sophomore students each year. Following his academic studies, Walden plans to work in the field of ceramics R&D, either at the national lab or industrial levels, for several years. His ultimate goal is to return to academia to teach and conduct research in a ceramics engineering program.


Prediction of Ferroic Properties in Epitaxial BiXO3 Systems via Density-Functional Theory

This project uses density-functional theory to model the structural, magnetic and electronic properties of the bismuth-based perovskite oxides. The BiFeO3 (BFO) and BiCrO3 (BCO) systems are the archetypical candidates in this system of phases, and are perovskite ferroelectrics which exhibit antiferromagnetic order. The coexisting ferroic properties in these magnetoelectric systems may be tuned using epitaxial strain, opening up a much broader set of properties in these systems. The context of epitaxial thin films makes this diverse material space directly relevant to current ferroelectric and ferromagnetic material applications.

Our calculations utilizing the VASP code incorporate the local spin-density approximation for all structural and electronic calculations, accounting for the magnetic coupling of B-site cations via a superexchange mechanism, supplemented by a Hubbard (+U) style correction to improve validity of DFT at local resolution. The supercells modeled accommodate the full space of compositional and magnetic ordering feasible in the appropriate antiferromagnetic BXO space. This includes consideration of many different chemical phases which may be stabilized using epitaxial strain, such as monoclinic or tetragonal for BiFeO3 and monoclinic or orthorhombic for BiCrO3, as well as the full range of first-neighboring antiferromagnetic order (A-, C-, F-, G-Type) possible in these pseudo-perovskite systems. Our results are consistent with prior experimental predictions, including for instance the confirmation of a super-tetragonal phase of BFO beyond ~4.2% compressive epitaxial strain, but explore new territory in predicting the stable chemical, magnetic, and dielectric properties of BXO systems under epitaxial strain well beyond what is captured in existing literature. Our calculations bear great utility both in the practical context of predicting the nominally expected properties of a BXO system of a particular composition deposited in a particular epitaxial strain context, but also seek to establish a theoretic basis connecting a particular B-site occupation and coordination environment to the general multiferroic properties which may be thereby stabilized.