A5016373269- Magnetic and transport properties of perovskites and related materials
- Electronic and Structural Properties of Oxides
- Advanced Condensed Matter Physics
- Advanced Thermoelectric Materials and Devices
- ZnO doping and properties
- Copper-based nanomaterials and applications
- Thermal Expansion and Ionic Conductivity
- Magnetic Properties of Alloys
- Ferroelectric and Piezoelectric Materials
- Metal Extraction and Bioleaching
- Transition Metal Oxide Nanomaterials
- Physics of Superconductivity and Magnetism
- Metallurgical Processes and Thermodynamics
- Thermal properties of materials
- Minerals Flotation and Separation Techniques
- Rare-earth and actinide compounds
- Advancements in Solid Oxide Fuel Cells
University of Minnesota System
2025
University of Minnesota
2020-2024
Abstract Despite their highly anisotropic complex-oxidic nature, certain delafossite compounds ( e.g ., PdCoO 2 , PtCoO ) are the most conductive oxides known, for reasons that remain poorly understood. Their room-temperature conductivity can exceed of Au, while low-temperature electronic mean-free-paths reach an astonishing 20 μm. It is widely accepted these materials must be ultrapure to achieve this, although methods growth (which produce only small crystals) not typically capable such....
Solid-state control of the thermal conductivity materials is exceptional interest for novel devices such as diodes and switches. Here, we demonstrate ability to continuously tune nanoscale films La0.5Sr0.5CoO3-δ (LSCO) by a factor over 5, via room-temperature electrolyte-gate-induced non-volatile topotactic phase transformation from perovskite (with δ ≈ 0.1) an oxygen-vacancy-ordered brownmillerite = 0.5), accompanied metal-insulator transition. Combining time-domain thermoreflectance...
Perovskite cobaltites have emerged as archetypes for electrochemical control of materials properties in electrolyte-gate devices. Voltage-driven redox cycling can be performed between fully oxygenated perovskite and oxygen-vacancy-ordered brownmillerite phases, enabling exceptional modulation the crystal structure, electronic transport, thermal magnetism, optical properties. The vast majority studies, however, focused heavily on end points. In contrast, here we focus hysteresis reversibility...
Much recent attention has focused on the voltage-driven reversible topotactic transformation between ferromagnetic metallic perovskite (P) SrCoO3-δ and oxygen-vacancy-ordered antiferromagnetic insulating brownmillerite (BM) SrCoO2.5. This is emerging as a paradigmatic example of power electrochemical gating (using, e.g., ionic liquids/gels), wide modulation electronic, magnetic, optical properties generating clear application potential. SrCoO3 films are challenging with respect to stability,...
Tensile-strained $\mathrm{LaCo}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ thin films are ferromagnetic, in sharp contrast to the zero-spin bulk, although no clear consensus has emerged as origin of this phenomenon. While magnetism been heavily studied, relatively little attention paid electronic transport, due insulating nature strain-stabilized ferromagnetic state. Here, structure, magnetism, and transport studied epitaxial (10--22-nm thick) on various substrates (from 1.4%...
Cobalt oxides have long been understood to display intriguing phenomena known as spin-state crossovers, where the cobalt ion spin changes vs. temperature, pressure, etc. A very different situation was recently uncovered in praseodymium-containing oxides, a first-order coupled spin-state/structural/metal-insulator transition occurs, driven by remarkable praseodymium valence transition. Such transitions, particularly when triggering and metal-insulator offer highly appealing functionality, but...
CdO has drawn much recent interest as a high-room-temperature-mobility oxide semiconductor with exciting potential for mid-infrared photonics and plasmonics. Wide-range modulation of carrier density in is both fundamental reasons (to explore transport mechanisms single samples) applications (in tunable photonic devices). Here, we thus apply ion-gel-based electrolyte gating to ultrathin epitaxial CdO(001) films, using transport, x-ray diffraction, atomic force microscopy deduce reversible...
Electrolyte-based transistors utilizing ionic liquids/gels have been highly successful in the study of charge-density-controlled phenomena, particularly oxides. Experimental probes beyond transport played a significant role, despite challenges to their application electric double-layer transistors. Here, we demonstrate synchrotron soft X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) as operando charge state magnetism ion-gel-gated ferromagnetic perovskite films....
Pr-based cobaltites exhibit extraordinary phenomena where abrupt valence shifts trigger coupled structural/spin-state/metal-insulator transitions. Recent work achieved strain control of these in thin films, with epitaxial compression even stabilizing room-temperature Here, we study the thickness dependence effects model system compressively strained...
Pr-containing perovskite cobaltites exhibit unusual valence transitions, coupled to coincident structural, spin-state, and metal-insulator transitions. Heteroepitaxial strain was recently used control these phenomena in the model ${({\mathrm{Pr}}_{1\ensuremath{-}y}{\mathrm{Y}}_{y})}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Co}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ system, stabilizing a nonmagnetic insulating phase under compression (with room-temperature...
Metallic delafossite materials (e.g., $\mathrm{PdCo}{\mathrm{O}}_{2}, \mathrm{PtCo}{\mathrm{O}}_{2}$), have attracted much recent attention due to record-high oxide conductivities, the origins of which remain unclear. Relatively little has been paid their related thermal properties, however. We address this here via wide temperature range experimental studies crystal structure, expansion, and specific heat single-crystal $\mathrm{PdCo}{\mathrm{O}}_{2}$, combined with density-functional...
Solid-state control of the thermal conductivity materials is exceptional interest for novel devices such as diodes and switches. Here, we demonstrate ability to continuously tune nanoscale films $\rm La_{0.5}Sr_{0.5}CoO_{3-δ}$ (LSCO) by a factor over 5, via room-temperature electrolyte-gate-induced non-volatile topotactic phase transformation from perovskite (with $δ\approx 0.1$) an oxygen-vacancy-ordered brownmillerite $δ=0.5$), accompanied metal-insulator transition. Combining time-domain...
Cobalt oxides have long been understood to display intriguing phenomena known as spin-state crossovers, where the cobalt ion spin changes vs. temperature, pressure, etc. A very different situation was recently uncovered in praseodymium-containing oxides, a first-order coupled spin-state/structural/metal-insulator transition occurs, driven by remarkable praseodymium valence transition. Such transitions, particularly when triggering and metal-insulator offer highly appealing functionality, but...