skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Mechanisms of Hysteresis and Reversibility across the Voltage-Driven Perovskite–Brownmillerite Transformation in Electrolyte-Gated Ultrathin La 0.5 Sr 0.5 CoO 3−δ
Title: Mechanisms of Hysteresis and Reversibility across the Voltage-Driven Perovskite–Brownmillerite Transformation in Electrolyte-Gated Ultrathin La 0.5 Sr 0.5 CoO 3−δ
ABSTRACT: Perovskite cobaltites have emerged as archetypes for electrochemical control of materials properties in electrolytegate devices. Voltage-driven redox cycling can be performed between fully oxygenated perovskite and oxygen-vacancy-ordered brownmillerite phases, enabling exceptional modulation of the crystal structure, electronic transport, thermal transport, magnetism, and optical properties. The vast majority of studies, however, have focused heavily on the perovskite and brownmillerite end points. In contrast, here we focus on hysteresis and reversibility across the entire perovskite ↔ brownmillerite topotactic transformation, combining gate-voltage hysteresis loops, minor hysteresis loops, quantitative operando synchrotron X-ray diffraction, and temperature-dependent (magneto)transport, on ion-gel-gated ultrathin (10-unit-cell) epitaxial La0.5Sr0.5CoO3−δ films. Gate-voltage hysteresis loops combined with operando diffraction reveal a wealth of new mechanistic findings, including asymmetric redox kinetics due to differing oxygen diffusivities in the two phases, nonmonotonic transformation rates due to the first-order nature of the transformation, and limits on reversibility due to first-cycle structural degradation. Minor loops additionally enable the first rational design of an optimal gate-voltage cycle. Combining this knowledge, we demonstrate state-of-the-art nonvolatile cycling of electronic and magnetic properties, encompassing >105 transport ON/OFF ratios at room temperature, and reversible metal−insulator−metal and ferromagnet−nonferromagnet−ferromagnet cycling, all at 10-unit-cell thickness with high room-temperature stability. This paves the way for future work to establish the ultimate cycling frequency and endurance of such devices. KEYWORDS: electrolyte gating, magnetoionics, complex oxides, perovskite−brownmillerite transformation, hysteresis, reversibility  more » « less
Award ID(s):
2011401
PAR ID:
10506577
Author(s) / Creator(s):
; ; ; ; ; ; ;
Publisher / Repository:
ACS
Date Published:
Journal Name:
ACS Applied Materials & Interfaces
Volume:
16
Issue:
15
ISSN:
1944-8244
Page Range / eLocation ID:
19184 to 19197
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Nature Communications)
    Abstract Solid-state control of the thermal conductivity of materials is of exceptional interest for novel devices such as thermal diodes and switches. Here, we demonstrate the ability tocontinuouslytune the thermal conductivity of nanoscale films of La0.5Sr0.5CoO3-δ(LSCO) by a factor of over 5, via a room-temperature electrolyte-gate-induced non-volatile topotactic phase transformation from perovskite (withδ≈ 0.1) to an oxygen-vacancy-ordered brownmillerite phase (withδ= 0.5), accompanied by a metal-insulator transition. Combining time-domain thermoreflectance and electronic transport measurements, model analyses based on molecular dynamics and Boltzmann transport equation, and structural characterization by X-ray diffraction, we uncover and deconvolve the effects of these transitions on heat carriers, including electrons and lattice vibrations. The wide-range continuous tunability of LSCO thermal conductivity enabled by low-voltage (below 4 V) room-temperature electrolyte gating opens the door to non-volatile dynamic control of thermal transport in perovskite-based functional materials, for thermal regulation and management in device applications. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; (, Journal of Materials Chemistry C)
    null (Ed.)
    A systematic study of (1− x )Pb(Fe 0.5 Nb 0.5 )O 3 – x BiFeO 3 ( x = 0–0.5) was performed by combining dielectric and electromechanical measurements with structural and microstructural characterization in order to investigate the strengthening of the relaxor properties when adding BiFeO 3 into Pb(Fe 0.5 Nb 0.5 )O 3 and forming a solid solution. Pb(Fe 0.5 Nb 0.5 )O 3 crystalizes in monoclinic symmetry exhibiting ferroelectric-like polarization versus electric field ( P–E ) hysteresis loop and sub-micron-sized ferroelectric domains. Adding BiFeO 3 to Pb(Fe 0.5 Nb 0.5 )O 3 favors a pseudocubic phase and a gradual strengthening of the relaxor behavior of the prepared ceramics. This is indicated by a broadening of the peak in temperature-dependent permittivity, narrowing of P–E hysteresis loops and decreasing size of ferroelectric domains resulting in polar nanodomains for x = 0.20 composition. The relaxor behavior was additionally confirmed by Vogel–Fulcher analysis. For the x ≥ 0.30 compositions, broad high-temperature anomalies are observed in dielectric permittivity versus temperature measurements in addition to the frequency-dispersive peak located close to room temperature. These samples also exhibit pinched P–E hysteresis loops. The observed pinching is most probably related to the reorganization of polar nanoregions under the electric field as shown by synchrotron X-ray diffraction measurements as well as by piezo-response force microscopy analysis, while in part affected by the presence of charged point defects and anti-ferroelectric order, as indicated from rapid cooling experiments and high-resolution transmission electron microscopy, respectively. 
    more » « less
  3. ; ; ; ; ; (, Advanced Optical Materials)
    Abstract Materials with tunable infrared refractive index changes have enabled active metasurfaces for novel control of optical circuits, thermal radiation, and more. Ion‐gel‐gated epitaxial films of the perovskite cobaltite La1−xSrxCoO3−δ(LSCO) with 0.00 ≤x≤ 0.70 offer a new route to significant, voltage‐tuned, nonvolatile refractive index modulation for infrared active metasurfaces, shown here through Kramers–Kronig‐consistent dispersion models, structural and electronic transport characterization, and electromagnetic simulations before and after electrochemical reduction. As‐grown perovskite films are high‐index insulators forx< 0.18 but lossy metals forx> 0.18, due to a percolation insulator‐metal transition. Positive‐voltage gating of LSCO transistors withx> 0.18 reveals a metal‐insulator transition from the metallic perovskite phase to a high‐index (n> 2.5), low‐loss insulating phase, accompanied by a perovskite to oxygen‐vacancy‐ordered brownmillerite transformation at highx. Atx< 0.18, despite nominally insulating character, the LSCO films undergo remarkable refractive index changes to another lower‐index, lower‐loss insulating perovskite state with Δn >0.6. In simulations of plasmonic metasurfaces, these metal‐insulator and insulator‐insulator transitions support significant, varied mid‐infrared reflectance modulation, thus framing electrochemically gated LSCO as a diverse library of room‐temperature phase‐change materials for applications including dynamic thermal imaging, camouflage, and optical memories. 
    more » « less
  4. ; ; ; ; ; (, APL Materials)
    Epitaxial cobaltites have emerged as exemplary materials for electrochemical gating, in large part due to their topotactic perovskite (P) ↔ brownmillerite (BM) transformations. SrCoO3−δ, for example, can be cycled between metallic ferromagnetic P SrCoO3 and insulating BM SrCoO2.5, realizing exceptional modulation of electronic, thermal, and optical properties. It is often presumed that such cycling also generates ferromagnetic–antiferromagnetic (F-AF) modulation due to the G-type AF order in bulk SrCoO2.5. Little is understood about magnetism in thin-film BM SrCoO2.5, however, meaning that the true magnetic property modulation is unclear. We address this here through a neutron diffraction study of BM La1−xSrxCoO2.5 films at x = 0.5 and 1.0. Lightly compressively strained SrCoO2.5 films are shown to retain G-type AF order, albeit with suppressed Néel temperature (∼340 K). Of high interest for AF spintronics, room-temperature F–AF cycling is thus possible across the SrCoO3-δ P ↔ BM transformation. At x = 0.5, however, BM La0.5Sr0.5CoO2.5 films are found to exhibit no detectable G-type AF order but instead weak F order (Curie temperature ∼115 K), unveiling a La0.5Sr0.5CoO3−δ phase diagram with two distinct F phases. These results thus uncover new, unanticipated magnetic phase behavior in these materials, in addition to being directly relevant to cobaltite-based magnetoionics. 
    more » « less
  5. ; ; ; ; ; ; ; ; (, Journal of Materials Chemistry A)
    null (Ed.)
    Methylammonium lead iodide (MAPbI 3 ) is an important light-harvesting semiconducting material for solar-cell devices. We investigate the effect of long thermal annealing in an inert atmosphere of compacted MAPbI 3 perovskite powders. The microstructure morphology of the MAPbI 3 annealed samples reveals a well-defined grain boundary morphology. The voids and neck-connecting grains are observed throughout the samples, indicating a well-sintered process due to mass diffusion transfer through the grain boundary. The long 40 h thermal annealing at T = 522 K ( k B T = 45 meV) causes a significant shift in the structural phase transition, stabilizing the low-electrical conductivity and high-efficiency cubic structure at room temperature. The complete disordered orientation of MA cations maximizes the entropy of the system, which, in turn, increases the Pb–I–Pb angle close to 180°. The MA rotation barrier and entropy analysis determined through DFT calculations suggest that the configurational entropy is a function of the annealing time. The disordered organic molecules are quenched and become kinetically trapped in the cubic phase down to room temperature. We propose a new phase diagram for this important system combining different structural phases as a function of temperature with annealing time for MAPbI 3 . The absence of the coexistence of different structural phases, leading to thermal hysteresis, can significantly improve the electrical properties of the solar cell devices. Through an entropy-driven stabilization phenomenon, we offer an alternative path for improving the maintenance, toughness, and efficiency of the optoelectronic devices by removing the microstructural stress brought by the structural phase transformation within the solar cell working temperature range. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email