Brent Fultz received his undergraduate degree from MIT, and his Ph.D. from U. C. Berkeley in 1982. He was a Presidential Young Investigator, and he received an IBM Faculty Development Award and a Jacob Wallenberg Scholarship. He won the 2010 TMS EMPMD Distinguished Scientist Award and the 2016 William Hume-Rothery Award of TMS. He was elected Fellow of the Neutron Scattering Society of America in 2016, full member of the Society of Sigma Xi in 2017, Fellow of the American Physical Society in 2017, Fellow of TMS in 2018, "Outstanding Referee" of the American Physical Society in 2019, and received the 2022 service and leadership award of the Neutron Scattering Society of America. He serves on review boards of the Advanced Photon Source and the Spallation Neutron Source. He consulted for an electronics testing company, Everett Charles Technologies, for the Defense Science Board, was a member of the Science Advisory Board of Actium Materials, Contour Energy, and the Materials Project. Fultz has authored or co-authored over 400 publications, including two textbooks that are in their second and fourth editions with Cambridge and Springer publishers. He supervised 50 Ph.D. theses at Caltech.

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Brent Fultz and Jim Howe authored a graduate-level textbook on diffraction and microscopy of materials (now in its fourth English edition). Fultz authored a second graduate-level textbook on phase transitions in materials that unifies concepts from materials science and condensed-matter physics.

X-ray and neutron scattering are two of the most important methods for studying materials, and the U.S. community of scattering scientists now has access to remarkably powerful and precise synchrotrons and neutron sources. These require innovative hardware and software for new studies of materials. Brent Fultz was the Principal Investigator for building the ARCS spectrometer at the Spallation Neutron Source, in operation since 2007. Scientific computing offers opportunities for doing new science with neutron scattering experiments, and he was the Principal Investigator of the software development project, Distributed Data Analysis for Neutron Scattering Experiments, DANSE.

Understanding Vibrations, Entropy and Free Energy

Our group studies phonons, which are quantized vibrations in crystals. These vibrations create many arrangements of atoms, giving entropy. From the entropy and its dependence on temperature and pressure, we can obtain the phonon contribution to the free energy. The phonon entropy dominates the total entropy of most solids, and is a key quantity for understanding material stability.

We have measured and calculated the phonon entropies of different materials, and how they change with temperature and pressure. At high temperatures, phonons begin to interact with each other and with the electrons and spins of metals, creating complex effects that we work to unravel. Two instruments that we use to measure phonons are: 1) Inelastic neutron scattering, one of the most powerful ways to map out phonon spectra and magnetic excitations, and 2) High-resolution inelastic X-ray scattering, which lets us study vibrations in small specimens at megabar pressures inside diamond anvil cells.

Modern ab initio simulations -- especially finite temperature density functional theory and molecular dynamics -- allow us to calculate the phonon and electron states. From these simulations, sometimes combined with experimental data, we can predict thermophysical properties, such as thermal expansion and changes in elastic constants with temperature. This was our approach to explaining the Invar effect in 2023 as a delicate balance between vibrational and magnetic excitations. Today, we are pursuing the general physics of phonon entropy in magnetic materials.

New neutron spectrometers, such as ARCS at the SNS, are orders of magnitude more efficient at measuring phonons and have enabled us to discover new phenomena in phonon physics. Ongoing work includes characterizing phonon second harmonic generation, intermodulation phonon sidebands, and high-frequency phonon noise in anharmonic materials.

Energy Conversion Materials

We have studied materials that store lithium, sodium, and hydrogen. Using nuclear resonant scattering at high pressure with samples in diamond anvil cells, we measured how atoms distort when electrons hop between ions. This distortion, known as the "activation volume," helps explain how many battery cathode materials conduct electricity through small polaron hopping.

Recently, we have been studying magnetocaloric materials that serve as refrigerants in magnetic refrigerators, with a focus on the mechanisms of energy losses during magnetic transitions.

Brief descriptions of recent research results are given in the Fultz Group site.