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, such as Los Angeles, experience more heating than surrounding rural areas, leading to detrimental effects to human health and the environment. “Cool” pigments painted on infrastructure in urban heat islands have the advantage of displaying pleasing colors while also reflecting away much of the sun’s heat. We are interested in developing cool pigments using both conventional furnace synthesis and rapid microwave-assisted synthesis (described below), and understanding their near-IR reflectance properties. We will exploit selection rules for electronic transitions (which often result in color) by choosing crystal structures with noncentrosymmetric metal centers and varying the transition metal identity to tune color.