About

Thomas S. Duffy is a Professor of Geosciences and serves as the Chair of the Department of Geosciences at Princeton University. His research program focuses on understanding the large-scale behavior of the Earth and other planets through experimental study of geological materials under extreme conditions of pressure and temperature. He explores crystal structures, phase relations, equations of state, elasticity, and deformation behavior in a wide range of materials at conditions up to and exceeding those at the Earth's center. His main tools include static compression using diamond anvil cells combined with optical spectroscopy and x-ray techniques, as well as dynamic compression generated by gas guns and high-powered lasers, which are used to investigate material properties under these extreme conditions. Duffy's work contributes to the understanding of high-pressure mineral physics, exoplanets, shock compression, and related fields.

Research topics

• Physics
• Materials science
• Composite material
• Geology
• Crystallography
• Astrobiology
• Optoelectronics
• Mechanics
• Medicine
• Chemical physics
• Optics
• Mineralogy
• Chemistry
• Thermodynamics
• Astronomy

Selected publications

• Ultrafast x-ray diffraction of high-pressure phases in dynamically compressed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>TiO</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

  Physical review. B./Physical review. B · 2025-09-17

  articleSenior author

  We investigate the high-pressure polymorphism of Ti⁢O₂ under laser-shock compression from 54(5) to 137(7) GPa using <em>in situ</em> femtosecond x-ray diffraction. Our results provide experimental evidence of the 𝑃⁢𝑐⁢𝑎⁢21-type distorted fluorite structure formed from polycrystalline Ti⁢O₂ dynamically compressed to 54(5) GPa. Upon higher compression, we observe the direct formation of the ninefold coordinated F⁡e₂⁢P-type phase at 68(4) and 78(3) GPa in polycrystalline and [001]-oriented Ti⁢O₂, respectively. This represents an unprecedented 100 GPa reduction in the shock synthesis pressure of the F⁡e₂⁢P-type structure relative to quasihydrostatic loading conditions. On pressure release, the F⁡e₂⁢P-type phase transforms to the α-Pb⁢O₂ structure and, at later times, reverts to rutile. Thus, the rutile →F⁡e₂⁢P and α-Pb⁢O₂→rutile transformations are both observed to occur on nanosecond timescales. Our results highlight the unique ability of high-strain-rate uniaxial compression to synthesize novel high-pressure phases and also indicate the importance of <em>in situ</em> atomic-level probes in developing pressure-temperature phase diagrams.

  PublisherDOI

• Body-Centered-Cubic Phase Transformation in Gold at TPa Pressures

  Physical Review Letters · 2025-09-29 · 1 citations

  article

  In situ x-ray diffraction at both the National Ignition Facility and Omega-EP Laser Facility has been utilized to determine the crystallographic state of ramp and shock-ramp compressed gold up to 1.2 TPa (1 TPa=10 Mbar=10×10^{6} atmospheres). In this Letter, we describe a series of experiments that explore a variety of pressure-temperature states in Au, accessed using tailored laser pulses. We find that the ambient pressure face-centered-cubic phase is stable under ramp compression to pressures of at least 1 TPa where the body-centered-cubic phase is observed simultaneously.

  PublisherDOI

• Sound Velocity and Grüneisen Parameter in Shock‐Melted Silica at Deep Earth Pressures

  Journal of Geophysical Research Solid Earth · 2025-08-27 · 2 citations

  articleOpen accessSenior author

  Abstract Silica is a primary component of rocky planet interiors and its melt properties are important for understanding planetary formation and differentiation, magma oceans, and the deep mantle. Although well understood in the solid state, the high‐pressure behavior of liquid silica is poorly constrained at lower mantle pressures. Using laser interferometry to measure shock wave profiles, we report measured stress‐density states and longitudinal sound speeds in shock‐synthesized stishovite, from fused silica staring material, and across the solid‐liquid phase boundary up to 154 GPa. Our results constrain completion of melt at 80 GPa and show that at pressures relevant to the deep mantles of Earth‐sized, rocky planets, the Grüneisen parameter for liquid silica increases with compression. This finding is consistent with a continuous increase in Si‐O coordination above six for liquid silica at core‐mantle boundary relevant pressures and temperatures.

  PublisherOA PDFDOI

• B1-B2 transition in shock-compressed MgO

  Science Advances · 2024-06-07 · 22 citations

  articleOpen access

  Magnesium oxide (MgO) is a major component of the Earth’s mantle and is expected to play a similar role in the mantles of large rocky exoplanets. At extreme pressures, MgO transitions from the NaCl B 1 crystal structure to a CsCl B 2 structure, which may have implications for exoplanetary deep mantle dynamics. In this study, we constrain the phase diagram of MgO with laser-compression along the shock Hugoniot, with simultaneous measurements of crystal structure, density, pressure, and temperature. We identify the B 1 to B 2 phase transition between 397 and 425 gigapascal (around 9700 kelvin), in agreement with recent theory that accounts for phonon anharmonicity. From 425 to 493 gigapascal, we observe a mixed-phase region of B1 and B2 coexistence. The transformation follows the Watanabe-Tokonami-Morimoto mechanism. Our data are consistent with B 2-liquid coexistence above 500 gigapascal and complete melting at 634 gigapascal. This study bridges the gap between previous theoretical and experimental studies, providing insights into the timescale of this phase transition.

  PublisherOA PDFDOI

• Atomic structure and melting of Ni and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mn>36</mml:mn></mml:msub><mml:mi mathvariant="normal">Ni</mml:mi></mml:math> up to 400 GPa

  Physical review. B./Physical review. B · 2024-06-27 · 7 citations

  articleOpen access

  Iron, nickel, and their alloys are critically important materials for industrial and technological applications due to their unique magnetic properties, strength, and thermal expansion. In this study, lasers were used to compress and heat ${\mathrm{Fe}}_{36}\mathrm{Ni}$ alloy (36 wt% Ni) and pure nickel up to the melting temperature using a combination of shock and ramp compression. The structure was measured using nanosecond in situ x-ray diffraction, and simultaneous velocimetry was used to measure the pressure up to 454 GPa. A mixed face-centered-cubic (fcc) solid--liquid phase in ${\mathrm{Fe}}_{36}\mathrm{Ni}$ at 311 GPa provides experimental evidence that, compared with pure iron, the incorporation of nickel expands the stability field of the fcc phase to the melting curve. At lower temperatures, a mixed fcc and hexagonal-close-packed (hcp) phase is observed in ramp-compressed ${\mathrm{Fe}}_{36}\mathrm{Ni}$ at 278 GPa. At the higher compressions, a structure inconsistent with fcc, hcp, and body-centered cubic is observed. In the case of pure Ni, the fcc phase is stable under ramp compression up to 402 GPa.

  PublisherOA PDFDOI

• Shock Compression of Fluorapatite to 120 GPa

  Journal of Geophysical Research Planets · 2023-01-22 · 1 citations

  articleOpen accessSenior author

  Abstract Apatite is a phosphate mineral relevant to shock metamorphism in planetary materials. Here, we report on the response of natural fluorapatite from Durango, Mexico, under shock wave loading between 14.5 and 119.5 GPa. Wave profile measurements were obtained in plate‐impact experiments conducted on [0001]‐oriented fluorapatite single crystals. To 30 GPa peak stresses, we observed a two‐wave structure indicating an elastic‐inelastic response with elastic wave amplitudes of 10.5–13.1 GPa. Between 39.1 and 62.1 GPa, a complex wave structure was observed involving the propagation of three waves. At and above 73.7 GPa, only a single shock wave was observed. The data above 73.7 GPa provided the following linear shock velocity—particle velocity relationship: U s = 6.5(2) + 0.78(6) u p , (mm/μs). Above 80 GPa, the densities in the shocked state exceed both the extrapolated 300‐K density of fluorapatite and the predicted 300‐K density for a mixture of the high‐pressure assemblage, tuite, and CaF 2 . This result indicates that fluorapatite undergoes a transition to a denser structure under shock loading at these conditions. The shock response of fluorapatite is observed to be similar to that of enstatite but stiffer than quartz and albite at the stresses examined in this work.

  PublisherOA PDFDOI

• The role of calcite mineral elastic moduli in carbonate rock physics

  The Leading Edge · 2023-04-01 · 1 citations

  articleSenior author

  Abstract Rock-physics models for carbonate reservoirs assume that the mineral elastic moduli are known variables. A review of publications reveals a range of values for calcite that are out of date and misleading. We present a robust compilation for future investigations. We subsequently discuss the application of calcite elastic moduli for rock-physics modeling and interpretation of wireline data through a case study data set from an offshore Canada carbonate reservoir. The data set exhibits an offset between the zero-porosity intercept and the calcite elastic moduli values. Our experience indicates that this phenomenon is present in many wireline data sets from carbonate reservoirs around the world. We demonstrate that the data can be reconciled to the mineral elastic moduli through the interpretation of microcracks in the formation (defined by a crack density of 0.06). Understanding the microcrack effect in relatively low-porosity formations is important for the correct calibration of pore microstructure parameters and for fluid-substitution calculations. Results in the case study data set show a relatively high sensitivity to changes in fluid saturation. The sensitivity can be reduced through the use of effective mineral elastic moduli that are derived from the data. We justify the effective mineral elastic moduli as a representation of the mineral moduli plus microcracks. The effective mineral elastic moduli are proposed as a relatively simple method to constrain the fluid substitution calculations in low-porosity formations where microcracks are present.

  PublisherDOI

• Ramp Compression of Germanium Dioxide to Extreme Conditions: Phase Transitions in an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>SiO</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> Analog

  Physical Review X · 2023-09-08 · 2 citations

  articleOpen accessSenior author

  Observation of the crystal structure of GeO${}_{2}$ at pressures of hundreds of gigapascals offers insights into the high-pressure behavior of SiO${}_{2}$, which is expected to exist in the deep interior of large rocky exoplanets.

  PublisherOA PDFDOI

• Development of slurry targets for high repetition-rate XFEL experiments

  arXiv (Cornell University) · 2022-01-12

  preprintOpen access

  Combining an x-ray free electron laser (XFEL) with high power laser drivers enables the study of phase transitions, equation-of-state, grain growth, strength, and transformation pathways as a function of pressure to 100s GPa along different thermodynamic compression paths. Future high-repetition rate laser operation will enable data to be accumulated at &gt;1 Hz which poses a number of experimental challenges including the need to rapidly replenish the target. Here, we present a combined shock-compression and X-ray diffraction study on vol% epoxy(50)-crystalline grains(50) (slurry) targets, which can be fashioned into extruded ribbons for high repetition-rate operation. For shock-loaded NaCl-slurry samples, we observe pressure, density and temperature states within the embedded NaCl grains consistent with observations for shock-compressed single-crystal NaCl.

  PublisherOA PDFDOI

• In situ X-ray diffraction of Al₂O₃ during laser compression and release

  2022-07-11

  preprint
  PublisherDOI

Recent grants

• Single-Crystal X-Ray Diffraction of Minerals to Mbar Pressures

  NSF · $397k · 2012–2016

• Perovskite and post-perovskite in the (Mg,Fe)GeO3 system

  NSF · $360k · 2014–2018

• Elasticity of Mantle Minerals at High Pressures and Temperatures

  NSF · $388k · 2012–2015

• In Situ X-ray Diffraction Study of Phase Transitions in Shock-Compressed Minerals

  NSF · $478k · 2017–2021

• Aluminum- and Iron-rich Perovskites and Post-perovskites and Earth's Deep Lower Mantle

  NSF · $378k · 2009–2013

Frequent coauthors

• S. Speziale

  99 shared

• Atsushi Kubo

  The University of Tokyo

  88 shared

• Lowell Miyagi

  University of Utah

  64 shared

• Sébastien Merkel

  Unité Matériaux et Transformations

  63 shared

• H. R. Wenk

  University of California, Berkeley

  63 shared

• Vitali B. Prakapenka

  University of Chicago

  59 shared

• S. R. Shieh

  49 shared

• Russell J. Hemley

  University of Illinois Chicago

  47 shared

Labs

• High-Pressure Mineral Physics LaboratoryPI

Education

• Ph.D.

  California Institute of Technology

  1992

Awards & honors

• Fellow of the American Physical Society