About

James M. LeBeau is the Kyocera Professor of Materials Science and Engineering at MIT. His research develops scanning transmission electron microscopy techniques to connect the atomic structure and chemistry of defects and interfaces with material properties relevant to quantum computing, energy storage, power electronics, dielectrics, and optical applications. His goal is to make electron microscopy more quantitative and reproducible while maintaining the creative elements of scientific inquiry. Professor LeBeau earned a BS in materials science and engineering from Rensselaer Polytechnic Institute in 2006 and a PhD in materials from the University of California, Santa Barbara, in 2010. He joined North Carolina State University as a faculty member in January 2011 and came to MIT as a visiting professor in 2018. He has published more than 90 papers and holds a US patent. His notable contributions include extending the commercial viability of fuel cells by reactivating poisoned metal oxide surfaces and creating high-quality thin films of chalcogenide perovskites for semiconductor applications. His work has been recognized with awards such as the 2020 Burton Medal from the Microscopy Society of America and the 2019 Presidential Early Career Award for Scientists and Engineers from the US Department of Defense.

Research topics

• Materials science
• Chemistry
• Nanotechnology
• Metallurgy
• Optoelectronics
• Engineering physics
• Crystallography
• Physics
• Geology
• Mathematics
• Chemical physics
• Engineering
• Composite material
• Thermodynamics
• Chemical engineering
• Condensed matter physics
• Optics

Selected publications

• Emergence of unconventional magnetic order in strain-engineered RuO2/TiO2 superlattices

  arXiv (Cornell University) · 2026-01-15

  preprintOpen access

  The spin ordering in RuO2 remains a highly debated topic, owing to its elusive nature, with reports ranging from a nonmagnetic ground state to signatures of unconventional magnetic order. Here we provide the first unambiguous, and direct evidence of unconventional magnetism in epitaxial, fully strained RuO2/TiO2 superlattices on TiO2 (110) substrate grown by hybrid molecular beam epitaxy. Polarized neutron reflectometry reveals a finite magnetic moment localized within the compressively strained RuO2 layers, consistent with predictions obtained from first-principles calculations. Complementary density functional theory and X-ray photoemission spectroscopy show that epitaxial strain drives the Ru 4d states toward the Fermi level, triggering a Stoner-type instability that stabilizes non-compensated magnetic order. These unique results reveal that RuO2 exhibits unconventional magnetic states under epitaxial strain, which are not accessible in bulk and establish strain engineering as a powerful route to uncover and control magnetic phases in RuO2 and related oxides.

  PublisherDOI

• Electrochemical corrosion accompanies dendrite growth in solid electrolytes

  Nature · 2026-03-25 · 1 citations

  article
  PublisherDOI

• Unleashing the Electromechanical Response of Ferroelastic Domain Reorganization in Mixed‐Phase Tetragonal Ferroelectric Multilayers (Adv. Mater. 19/2026)

  Advanced Materials · 2026-04-01

  article

  Large Strains from Small Materials In their Research Article (DOI: 10.1002/adma.202518417), Lane W. Martin and co-authors overcome substrate-induced limitations in the electromechanical response of thin films. By producing multilayer heterostructures based on domain-engineered ferroelectrics like PbZr0.2Ti0.8O3 it is possible to produce enhanced piezoelectric coefficients and maximum electromechanical strains that surpass the performance of bulk piezoceramics even in sub-100-nm films.

  PublisherDOI

• Anion Ordering and Phase Stability Govern Optical Band Gaps in BaZr(S,Se)3

  arXiv (Cornell University) · 2026-04-15

  articleOpen access

  Chalcogenide perovskites have emerged as promising lead free materials for photovoltaic and thermoelectric applications. Among them, BaZrS3 has attracted particular attention due to its thermal and chemical stability, favorable optoelectronic properties, and low thermal conductivity. Here, we combine molecular dynamics and Monte Carlo simulations based on machine learned interatomic potentials with scanning transmission electron microscopy to investigate mixing thermodynamics and phase stability in the BaZr(S,Se)3 system. We identify an unusual ordered structure that persists at room temperature, most prominently at 33% S, where S and Se atoms form alternating layers within the crystal. Free energy calculations yield the temperature composition phase diagram, including a nonperovskite delta phase in the Se rich limit and a perovskite phase in the S rich limit, separated by a broad two phase region. Analysis of the dielectric function and the absorption coefficient demonstrates that composition, crystal structure, and anion ordering jointly control the optical band gap. Selenium alloying enables tuning between approximately 1.6 and 1.9eV, while anion ordering within a given composition reduces the gap by about 0.12eV. Lastly, variations between structural polymorphs give rise to band gap differences of up to 0.4eV.

  PublisherOA PDF

• Emergence of unconventional magnetic order in strain-engineered RuO2/TiO2 superlattices

  ArXiv.org · 2026-01-15

  articleOpen access

  The spin ordering in RuO2 remains a highly debated topic, owing to its elusive nature, with reports ranging from a nonmagnetic ground state to signatures of unconventional magnetic order. Here we provide the first unambiguous, and direct evidence of unconventional magnetism in epitaxial, fully strained RuO2/TiO2 superlattices on TiO2 (110) substrate grown by hybrid molecular beam epitaxy. Polarized neutron reflectometry reveals a finite magnetic moment localized within the compressively strained RuO2 layers, consistent with predictions obtained from first-principles calculations. Complementary density functional theory and X-ray photoemission spectroscopy show that epitaxial strain drives the Ru 4d states toward the Fermi level, triggering a Stoner-type instability that stabilizes non-compensated magnetic order. These unique results reveal that RuO2 exhibits unconventional magnetic states under epitaxial strain, which are not accessible in bulk and establish strain engineering as a powerful route to uncover and control magnetic phases in RuO2 and related oxides.

  PublisherOA PDF

• Anion Ordering and Phase Stability Govern Optical Band Gaps in BaZr(S,Se)3

  arXiv (Cornell University) · 2026-04-15

  preprintOpen access

  Chalcogenide perovskites have emerged as promising lead free materials for photovoltaic and thermoelectric applications. Among them, BaZrS3 has attracted particular attention due to its thermal and chemical stability, favorable optoelectronic properties, and low thermal conductivity. Here, we combine molecular dynamics and Monte Carlo simulations based on machine learned interatomic potentials with scanning transmission electron microscopy to investigate mixing thermodynamics and phase stability in the BaZr(S,Se)3 system. We identify an unusual ordered structure that persists at room temperature, most prominently at 33% S, where S and Se atoms form alternating layers within the crystal. Free energy calculations yield the temperature composition phase diagram, including a nonperovskite delta phase in the Se rich limit and a perovskite phase in the S rich limit, separated by a broad two phase region. Analysis of the dielectric function and the absorption coefficient demonstrates that composition, crystal structure, and anion ordering jointly control the optical band gap. Selenium alloying enables tuning between approximately 1.6 and 1.9eV, while anion ordering within a given composition reduces the gap by about 0.12eV. Lastly, variations between structural polymorphs give rise to band gap differences of up to 0.4eV.

  PublisherDOI

• phaser: a unified and extensible framework for fast electron ptychography

  npj Computational Materials · 2026-01-17 · 1 citations

  articleOpen accessSenior author

  We present phaser, an open-source Python package that provides a unified interface to both conventional and autodifferentiation-based ptychographic algorithms. Features such as mixed-state probe, probe position correction, and multislice ptychography make experimental reconstructions practical and robust. Reconstructions are specified in a declarative format and can be run from a command line, Jupyter notebook, or web interface. Multiple computational backends are supported to provide maximum flexibility. We report reconstruction success for a variety of experimental datasets, and detail the effects of regularization on convergence and reconstruction quality. Reconstruction speed is benchmarked for single-slice and multislice reconstructions and compared to state-of-the-art packages. The software promises to speed the application and development of ptychographic methods for materials science.

  PublisherDOI

• Unleashing the Electromechanical Response of Ferroelastic Domain Reorganization in Mixed‐Phase Tetragonal Ferroelectric Multilayers

  Advanced Materials · 2026-01-08 · 1 citations

  article

  ABSTRACT There is considerable interest in thin‐film electromechanical materials due to the prospect for device miniaturization for an array of applications. The electromechanical response of thin films, however, is generally limited by substrate clamping and electrical breakdown. This work designs thin‐film piezoceramics with sub‐100‐nm thickness that address the limitations of clamping and breakdown strength and, as a result, produces films that rival or surpass their bulk piezoceramics counterparts in terms of performance. In the tetragonal ferroelectric PbZr 0.2 Ti 0.8 O 3 , strain‐induced mixtures of in‐ and out‐of‐plane oriented domain structures are leveraged to achieve the ferroelastic interconversion of in‐plane‐polarized a domains to out‐of‐plane‐polarized c domains, opening a pathway to enhanced electromechanical response (1.25%, = 170 pm/V). Operando second harmonic generation and scanning transmission electron microscopy studies confirm the a ‐to‐ c ferroelastic conversion, and establish the switching from a 1 / a 2 to c / a superdomains as the underlying mechanism for the large response. In turn, PbZr 0.2 Ti 0.8 O 3 /0.68PbMg 1/3 Nb 2/3 O 3 ‐0.32PbTiO 3 /PbZr 0.2 Ti 0.8 O 3 trilayers are fabricated to improve the electrical‐breakdown strength while maintaining the domain‐structure interconversion, resulting in the enhancement of the electromechanical strain to 2.1%. Overall, by combining domain‐structure optimization and multilayer‐heterostructure design, remarkable electromechanical response can be achieved even in sub‐100‐nm thin films normally subject to clamping effects.

  PublisherDOI

• Microstructural and preliminary optical and microwave characterization of erbium-doped CaMoO4 thin films

  APL Materials · 2025-10-01

  articleOpen access

  This work explores erbium-doped calcium molybdate (Er:CaMoO4) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the ∼1.5 μm Er3+ 4f–4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction, and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO4 formation that can be in situ doped with Er (typically 2–100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology, while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO4 films. We perform preliminary optical and microwave characterization on the suspected Y1–Z1 transition of 2 ppm, 200 nm epitaxial Er:CaMoO4 annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.

  PublisherDOI

• Tuning Relaxor-Antiferroelectric Order in (1 – <i>x</i>)PbMg_1/3Nb_2/3O₃-(<i>x</i>)PbZrO₃ Thin Films

  ACS Nano · 2025-08-07

  article

  Relaxor antiferroelectrics offer potential advantages such as enhanced energy-storage capacity and improved electromechanical properties over antiferroelectrics or relaxors alone. The fundamental nature of and mechanisms leading to these enhanced properties, however, are understudied. Here, epitaxial thin films of the relaxor-antiferroelectric (1 – x)PbMg1/3Nb2/3O3-(x)PbZrO3 (1 ≥ x ≥ 0.86) are studied to understand the evolution of the crystal and domain structure and dielectric and polarization properties. X-ray diffraction and scanning transmission electron microscopy studies show a structural transition with increasing PbMg1/3Nb2/3O3 content, from an orthorhombic (Pbam) antiferroelectric phase (x = 1) to an intermediate state of coexisting phases (x = 0.96–0.92) characterized by relaxor-like regions in the antipolar ground state that grows into a rhombohedral (R3m) relaxor phase (x = 0.86, with more randomly arranged dipoles). This transition corresponds to increasing dielectric response and reducing polarization-electric field hysteresis. These relaxor-antiferroelectric films also have 1.5–1.8-times larger electrical breakdown fields than PbZrO3, resulting in enhanced maximum electromechanical strains (as large as 1.6% and ∼60% larger) and energy-storage density (∼86% larger) and efficiency (∼33% larger) as compared to PbZrO3. Overall, this study elucidates the fundamental nature of thin-film relaxor antiferroelectrics in terms of their macro- and nanostructures, and corresponding evolution of electrical, electromechanical, and other properties.

  PublisherDOI

Recent grants

• CAREER: Understanding polar surfaces and interfaces using ultra-high resolution electron microscopy and spectroscopy

  NSF · $500k · 2014–2020

• MRI: Acquisition of a Transmission Electron Microscope for In-situ Studies of Soft and Hard Matter

  NSF · $1.4M · 2017–2019

• MRI: Acquisition of a Next Generation Nanofabrication Dual-beam Platform

  NSF · $699k · 2021–2023

Frequent coauthors

• Susanne Stemmer

  University of California, Santa Barbara

  74 shared

• Abinash Kumar

  Oak Ridge National Laboratory

  72 shared

• Everett D. Grimley

  North Carolina State University

  48 shared

• Xiahan Sang

  Wuhan University of Technology

  42 shared

• J. Houston Dycus

  Eurofins (United States)

  38 shared

• Michael Xu

  28 shared

• Scott D. Findlay

  27 shared

• Matthew J. Cabral

  Carnegie Mellon University

  26 shared

Labs

• The LeBeau GroupPI

Education

• Ph.D., Materials Science and Engineering

  Massachusetts Institute of Technology

  1990

• M.S., Materials Science and Engineering

  Massachusetts Institute of Technology

  1986

• B.S., Materials Science and Engineering

  University of California, Santa Barbara

  1984

Awards & honors

• 2020 Burton Medal, Microscopy Society of America
• 2019 Presidential Early Career Award for Scientists and Engi…
• 2014 Young Investigator Award, Air Force Office of Scientifi…
• 2014 Faculty Early Career Development Award, National Scienc…
• 2013 Kurt F. J. Heinrich Award, Microanalysis Society