Dr. Yingge Du, Senior Materials Scientist and Team Lead for Atomically Precise Materials at Pacific Northwest National Laboratory (PNNL) will give a seminar titled "Harnessing Chromium’s Redox Versatility: Epitaxial Growth and Metastable Phase Engineering in Complex Oxides" to the interested faculty and stendents at Discovery Park.

Abstract

Chromium’s redox versatility enables the engineering of complex oxides with significant scientific and technological impact. In this talk, I will present our work on the epitaxial growth and characterization of Cr-based oxide thin films, showing how Cr’s variable valence – beyond the typical Cr3+ state in perovskites like LaCrO3 – can be harnessed to develop novel phases and functionalities. By employing aliovalent doping, epitaxial strain, and controlled growth conditions, we stabilize different oxidation states that enhance electronic, catalytic, and ion transport properties.

For example, vacancy ordering in Cr-based ABO3 oxides lead to superstructures, including a SrCrO2.8 rhombohedral phase and a brownmillerite-like structure induced by Fe doping. Atomic-resolution STEM and EELS reveal a striking layer-resolved modulation of Cr valence, highlighting its sensitivity to local oxygen coordination. Expanding this approach to high-entropy oxides like La(5B)O3 – incorporating multiple 3d metals (Cr, Mn, Fe, Co, Ni) – we find that chemical potential can be leveraged as a powerful thermodynamic handle to selectively stabilize metastable Cr-rich configurations and promote the formation of non-equilibrium phases within La(5B)O3. This approach opens new pathways to tailor Cr coordination environments and drive emergent functionality in complex oxide systems. In addition to valence tuning, our work reveals strong nanoscale compositional fluctuations in high-entropy oxides, reflecting the complex interplay among competing cationic interactions. These results underscore the central role of Cr’s redox behavior in enabling adaptive, responsive oxide chemistries.

Taken together, these findings provide new strategies for rationally designing metastable structures and tuning functional properties in transition metal oxides via targeted control of chemical potential, valence states, and structural motifs.

Bio

Dr. Yingge Du is a senior materials scientist and team lead for Atomically Precise Materials at Pacific Northwest National Laboratory (PNNL). After earning his Ph.D. from the University of Virginia, he joined PNNL in 2007. With over a decade of research in epitaxial oxide thin films, his work focuses on developing innovative in-situ tools to monitor and control thin-film growth, advancing the understanding of electron and ion transport, and elucidating the structure–stability–property relationships in complex oxide systems. Dr. Du successfully executed a DOE BES Early Career Research Program and now directs a multidisciplinary team – with mentoring responsibilities for staff scientists, postdoctoral researchers, and students – that drives impactful, cross-disciplinary research.