Research | M-cube | Washington University in St. Louis

Traditional materials discovery through trial and error can be costly and time consuming. We aim to accelerate this process by using fundamental structure-property relationships to understand why certain materials work well, allowing targeted improvements to desired properties.

Several aspects of perovskites are shown. A hybrid organic-inorganic perovskite with an organic molecule at the A site. A perovskite with a polar distortion due to displacement of the B site. A perovskite with mixed occupancy at an anion site due to substitution. An example of octahedral tilting in perovskites. A perovskite with layered A-site ordering. A perovskite with rock salt B-site ordering.

Each of these degrees of freedom affects the perovskite’s properties

Our work is focused on functional materials such as catalysts and semiconductors, especially those required for emerging renewable energy technologies. We use density functional theory (DFT) and other computational techniques to predict materials which we expect to be useful, and we have several ongoing collaborations with experimental scientists who synthesize the materials we predict. A second thrust is to characterize the atomic and electronic structure of the synthesized materials for further optimization of properties. We use some of the most powerful electron microscopes—located at Oak Ridge National Laboratory—to perform the characterization experiments.

Please see our Publications page for recent examples of this process of rational design and optimization of materials with tailored properties. The following are some of the areas where we currently pursue this combined theoretical and experimental approach:

1. Platinum-group-metal-free and transition-metal dichalcogenide catalysts for renewable energy reactions

2. Ga₂O₃-based semiconductors for high-power and high-frequency electronics

3. Mixed-anion perovskites with multiple co-existing functionalities

4. Ionic conductors for fuel cells and advanced combustion cycles

5. Perovskite-based high-performance semiconductors

6. Multi-principal element alloys for high-temperature structural applications

M-cube Research Projects

Perovskite oxides with multiple functionalities, such as ferroelectric and magnetic ordering, are valuable in modern electronic devices. However, each functionality comes with its own unique constraints on the crystal structure and composition, and these constraints are not always compatible. Can we use fluorine substitution as an additional degree of freedom to allow these multiple orderings to co-exist in the same material?

Ga₂O₃ is a good material for high-power electronics because it has a large electronic band gap. The polar ε-Ga₂O₃ phase is especially interesting because it offers the chance to create a tunable 2-dimentional electron gas (2DEG) at the interface of ε-Ga₂O₃ with a non-polar material. However, the ε phase is not the ground state. To use ε-Ga₂O₃ in devices, we must first find a suitable growth substrate which has the correct lattice size mismatch to stabilize the desired ε phase relative to the unwanted β phase.

Alloys with many principal elements can be more stable at high temperatures than conventional binary or ternary alloys, due to their high entropy of mixing. We are collaborating with the Flores Research Group to design new high-entropy alloys for high-temperature structural applications using a combination of atomistic phase-diagram calculations, additive manufacturing and atomic scale characterization.

Polymer electrolyte membrane fuel cells (PEMFCs), are expected to be the central technology for renewable energy generation in vehicles in the future. However, the biggest bottleneck is the cost and durability of the catalyst for oxygen reduction reaction. To tackle this issue, we are developing Pt-free active sites on corrosion-resistant supports in collaboration with the Ramani Lab.