Traditional materials discovery through trial and error can be costly and time consuming. We aim to accelerate this process by developing fundamental structure-property-processing relationships to understand why certain materials work well, allowing targeted improvements to desired properties.
Our work is focused on functional materials such as catalysts and semiconductors, especially those required for emerging 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.
Current Research
- Development of alloys and their phase diagrams with an emphasis on high-entropy alloys and compounds — that include three or more alloying elements. We are interested in these materials for:
- High-temperature structural applications: See Zhang et al. (2020), Zhang et al. (2022), Li et al. (2021), Li et al. (2018). We collaborate with the Flores group for the experiments.
- Development of catalysts for various electrochemical reactions: See Cavin et al. (2021), Hemmat et al. (2020), Cho et al. (2021).
- Design and development of ferroelectric semiconductors: The integration of semiconductors with ferroelectrics — materials that have a spontaneous dipole moment that can be reversed with an applied electric field — offers tantalizing prospects for novel devices with applications in efficient information storage and processing, energy generation and storage, sensing, and nanophotonics. For instance, ferroelectric materials display the bulk photovoltaic effect wherein the lack of inversion symmetry and a sizeable spontaneous polarization can generate a large photovoltage, beyond the band gap of the material. Thus, they provide a prospect to design solar cells that can surpass the Shockley-Queisser limit. However, conventional ferroelectrics, such as PbTiO3 and BiFeO3, have wide band gaps and low charge carrier mobility. Therefore, they show poor photoconversion efficiency. Our goal is to design and develop ferroelectric semiconductors with desirable electronic, optical and polar properties and strong cross-coupling between these properties. Examples of recent work on ferroelectric semiconductors: Cho et al. (2018), Hartman et al. (2020).
- Development of quasi-1D chalcogenide perovskites: Hexagonal chalcogenide perovskites have quasi-1D chains of face-shared metal-chalcogen octahedral units. This directional structure manifests in highly anisotropic optical and electronic properties such as giant-optical anisotropy. We also observe the presence of polar distortions, extremely low thermal conductivity, first-order electronic transitions and large optical absorbance in these materials. These emergent phenomena — that are not observed in conventional semiconductors — make chalcogenide perovskites a promising class of functional semiconductors with the potential for achieving strong coupling between electrical, optical and ionic degrees of freedom. We are collaborating with the group of Prof. Jayakanth Ravichandran at USC, and others, to develop atomic-scale structure-property-processing correlations in chalcogenide perovskites and use them to seize control over their functional properties. Examples of recent work include: Zhao et al. (2021), Sun et al. (2021).
Past Research
- Mixed-anion perovskites with multiple co-existing functionalities: Mixing multiple cations has been a successful strategy to tailor the properties of functional ceramics, and even induce new properties. In contrast, mixing on the anion sub-lattice, or anion engineering, has remained largely unexplored. Given the key role anions play in the materials’ structure and property, and owing to the different elemental characteristics of anions, such as charge, ionic radii, electronegativity, and polarizability, anion engineering presents an untapped potential to control the stability and functionality of materials. In the past, we have used anion engineering to design compounds that can efficiently harness solar energy as photovoltaics and photocatalysts (Hartman et al. (2021)), mutliferroics (Hartman et al. (2018)) and enable high-capacity intercalation fluoride-ion batteries (Hartman et al (2021)).
- Perovskite-based high-performance semiconductors: In the past, we have investigated the stability and the defect-tolerance of lead-halide perovskite semiconductors (Thind et al. (2017), Morell et al. (2018), Thind et al. (2019)); and developed new, stable, lead-free perovskite alternatives for use in solar cells and LEDs (Thind et al. (2019)).
We thank NSF, ARO, NASA and DOE for supporting our research.