Most solids expand when heated because atomic vibrations increase with temperature, raising the average spacing between atoms (positive thermal expansion). A smaller but technologically important class of materials shows negative thermal expansion (NTE) and they contract upon heating. NTE materials can be used to engineer components with highly stable dimensions by compensating for unwanted thermal expansion.

Our lab studies NTE in transition‑metal framework oxides such as Zn₂V₂O₇, where contraction can arise from cooperative, low‑energy motions of the framework (for example, rotations and distortions of linked polyhedra) rather than simple bond stretching. We combine variable‑temperature X‑ray diffraction, neutron diffraction, and dilatometry to connect changes in crystal structure and lattice dynamics to the measured thermal expansion response. By comparing element‑substituted compositions and materials prepared under different synthesis conditions, we aim to identify the structural mechanisms that control NTE and translate that understanding into design rules for tunable thermal expansion. This work is supported by the Department of Energy, Office of Science, Basic Energy Sciences (DE-SC0024590).

Urban heat islands like Los Angeles can become significantly warmer than surrounding regions, increasing energy demand and contributing to heat‑related health and environmental impacts. “Cool” pigments offer a practical mitigation strategy which are visually appealing colors that reflect a large fraction of solar energy in the near‑infrared (NIR) region, which is responsible for much of the heat from sunlight.

Our lab develops cool pigments based on transition‑metal oxides. We combine X-ray and neutron diffraction to understand composition and structure and assess phase purity. We quantify performance with diffuse reflectance spectroscopy to understand NIR reflection and CIELAB colorimetry to evaluate visible color alongside NIR reflectance. Guided by electronic‑structure selection rules, we target materials with noncentrosymmetric metal sites and systematically vary the transition‑metal identity to tune color. We use conventional furnace synthesis, rapid microwave‑assisted synthesis, and sol-gel synthesis to affect particle size and morphology toward tuning NIR reflectance.