Ferroelectronics Lab

Understanding and utilizing non-volatile properties of materials

Advanced Science Showcases Work on Their Cover Page

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“Chemically-Disordered Transparent Conductive Perovskites With High Crystalline Fidelity,” a publication from July 2025 with strong contributions from Pat Keezer, gains attention this month. A graphical abstract artistically describing the work was used on the cover of volume 12, issue 42 of Advanced Science.

“A pulsed laser generates a high-energy plasma plume that quenches and kinetically arrests a high-symmetry, high-entropy, chemically disordered perovskite thin film on a substrate, yielding a material that is simultaneously conductive and transparent. This cover highlights the power of pulsed laser deposition and fast quenching to realize such phases with high crystalline fidelity.” See Advanced Science for more information.

Orignial Abstract: This manuscript presents a working model linking chemical disorder and transport properties in correlated-electron perovskites with high-entropy formulations and a framework to actively design them. This work demonstrates this new learning in epitaxial Srx(Ti,Cr,Nb,Mo,W)O3 thin films that exhibit exceptional crystalline fidelity despite a diverse chemical formulation where most B-site species are highly misfit with respect to valence and radius. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy confirm a unique combination of chemical disorder and structural perfection in thin and thick epitaxial layers. This combination produces an optical transparency window that surpasses that of the constituent end-members in the UV and IR, while maintaining relatively low electrical resistivity. This work addresses the computational challenges of modeling such systems and investigate short-range ordering using cluster expansion. These results showcase that unusual d-metal combinations access an expanded property design space that is predictable using end-member characteristics and their interactions – though unavailable to them – thus offering performance advances in optical, high-frequency, spintronic, and quantum devices.

Read more at Advanced Science

Intel Awards John T. Heron and lab with Outstanding Researcher Award!

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Once a year, Intel presents an award acknowledging work that makes “a significant impact on future technology” and “celebrates exceptional achievements made through Intel sponcered research.” John T. Heron is among the 10 researchers who have recieved this distinguished award.

“The research team demonstrated ultrafast switching of La-doped BiFeO3 ferroelectric capacitors, developed novel metrologies to measure polarization dynamics at nanoscale, demonstrated modeling frameworks to understand the effect of key physical processes such as domain nucleation, growth, and circuit limits on the switching process, and determined a new regime of energy-delay scaling behavior relevant for computing technologies. Furthermore, the researchers developed novel materials critical for accelerating magneto-electric spin-orbit (MESO) device development to deliver target specifications, such as high entropy perovskite oxides with large spin Hall efficiency and resistivity as well as double perovskite ferromagnet layers epitaxially compatible with La-doped BiFeO3.”

Congratulations to both John and the remainder of the research team who supported this achievement! Read more on Intel’s website if you are interested about this achievement.

New Publication! “Investigating Vibrational Modes in High Entropy Oxides using Electron Energy Loss Spectroscopy”

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Abstract: The quest for novel materials with enhanced properties is ongoing. High entropy oxides (HEOs) have transformed material design by providing a vast compositional space and remarkable property tunability. These are multicomponent systems that consist of five or more cations randomly distributed within a solid solution. Since their discovery in 2015, HEOs have garnered significant attention for their potential applications such as ionic conductors, magnetic materials, ferroelectrics, thermoelectrics, and various other functional materials [1-3]. A notable property observed in HEOs is low thermal conductivity [3]. This is attributed to their enhanced phonon scattering because of the presence of local ionic charge disorder [4]. As the lattice vibrations, i.e. the phonon modes play a crucial in understanding the thermal conductivity of a material, it is necessary to investigate the phonons in HEOs.

The vibrational response of materials can be measured using Fourier Transform Infrared Spectroscopy (FTIR), neutron scattering, or Raman spectroscopy for bulk materials [5]. However, there is a need to probe the phonon modes at the nanoscale resolution to better understand the role of microstructural inhomogeneities or interfaces. With advancements in monochromators and spectrometers, Scanning/Transmission Electron Microscopy combined with Electron Energy Loss Spectroscopy (EELS) has now become an ideal tool for probing the phonon dynamics at the atomic scale. Recently, energy resolution in advanced electron microscopes have improved to 4.2meV, expanding the applications of STEM-EELS to probe phonons, excitons, band gaps, and more [6].

In this study, we utilize ultra-high energy resolution STEM-EELS combined with theoretical calculations to investigate the vibrational modes of the prototypical HEO called J14: (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O, as well as six component HEO thin films (J14+Mn and J14+Cr). These films are grown on MgO substrates using Pulsed Laser Deposition (PLD). Due to the presence of aliovalent cations, local structural variations are observed in J14Mn thin film [7]. Figure 1 shows the phonon spectra of J14Cr HEO in comparison to the MgO substrate, acquired in the dark-field EELS geometry (to probe impact phonon scattering and thus study the localized vibrational response of the system at the atomic scale [8]). The phonon spectrum of J14Cr exhibits a peak around 18 meV, which is not observed in the parent oxide (MgO). Between 40 meV and 70 meV, MgO shows a peak around 48 meV, while J14Cr has a peak around 60 meV, indicating a blue shift compared to the MgO peak. We use FTIR and theoretical analysis to investigate the origin of spectral changes and assign the corresponding phonon modes. This investigation focuses on understanding the influence of composition on the phonon resonances in HEOs. Additionally, the variation in vibrational properties resulting from local structural nuances will also be explored using STEM-EELS data [9].

Read more at Microscopy and Microanalysis

New Publication! “Chemically-Disordered Transparent Conductive Perovskites With High Crystalline Fidelity”

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Abstract: This manuscript presents a working model linking chemical disorder and transport properties in correlated-electron perovskites with high-entropy formulations and a framework to actively design them. This work demonstrates this new learning in epitaxial Srx(Ti,Cr,Nb,Mo,W)O3 thin films that exhibit exceptional crystalline fidelity despite a diverse chemical formulation where most B-site species are highly misfit with respect to valence and radius. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy confirm a unique combination of chemical disorder and structural perfection in thin and thick epitaxial layers. This combination produces an optical transparency window that surpasses that of the constituent end-members in the UV and IR, while maintaining relatively low electrical resistivity. This work addresses the computational challenges of modeling such systems and investigate short-range ordering using cluster expansion. These results showcase that unusual d-metal combinations access an expanded property design space that is predictable using end-member characteristics and their interactions– though unavailable to them– thus offering performance advances in optical, high-frequency, spintronic, and quantum devices.

Read more at Advanced Science

New Publication! ” Local structure maturation in high entropy oxide (Mg,Co,Ni,Cu,Zn)1-x(Cr,Mn)xO thin films”

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Abstract: High entropy oxides (HEOs) have garnered much interest due to their available high degree of tunability. Here, we study the local structure of (MgNiCuCoZn)0.167(MnCr)0.083O, a composition based on the parent HEO (MgNiCuCoZn)0.2O. We synthesized a series of thin films via pulsed laser deposition at incremental oxygen partial pressures. X-ray diffraction shows lattice parameters to decrease with increased pO2 pressures until the onset of phase separation. X-ray absorption fine structure shows that specific atomic species in the composition dictate the global structure of the material as Cr, Co, and Mn shift to energetically favorable coordination with increasing pressure. Transmission electron microscopy analysis on a lower-pressure sample exhibits a rock salt structure, but the higher-pressure sample reveals reflections reminiscent of the spinel structure. In all, these findings give a more complete picture of how (MgNiCuCoZn)0.167(MnCr)0.083O forms with varying initial conditions and advances fundamental knowledge of cation behavior in high entropy oxides.

Full text available at The Journal of the American Ceramic Society

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Ferroelectronics Lab
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T: (734) 763-6914
E: jtheron@umich.edu