In this study, we investigate the utility of Ca2FeMnO6-δand Sr2FeMnO6-δas materials with low thermal conductivity, finding potential applications in thermoelectrics, electronics, solar devices, and gas turbines for land and aerospace use. These compounds, characterized as oxygen-deficient perovskites, feature distinct vacancy arrangements. Ca2FeMnO6-δadopts a brownmillerite-type orthorhombic structure with ordered vacancy arrangement, while Sr2FeMnO6-δadopts a perovskite cubic structure with disordered vacancy distribution. Notably, both compounds exhibit remarkably low thermal conductivity, measuring below 0.50 Wm−1K−1. This places them among the materials with the lowest thermal conductivity reported for perovskites. The observed low thermal conductivity is attributed to oxygen vacancies and phonon scattering. Interestingly as SEM images show the smaller grain size, our findings suggest that creating vacancies and lowering the grain size or increasing the grain boundaries play a crucial role in achieving such low thermal conductivity values. This characteristic enhances the potential of these materials for applications where efficient heat dissipation, safety, and equipment longevity are paramount.
more »
« less
SEM Investigation of the Microstructure of Oxygen-Deficient Ca2FeGaO6-δ
This study presents a detailed investigation of the microstructure of the oxygen-deficient perovskite material Ca2FeGaO6-δ using Scanning Electron Microscopy (SEM). The material exhibits significant porosity and irregular grain morphology, with variations in grain size and growth. Unlike conventional perovskite structures, Ca2FeGaO6-δ shows non-uniform grain development, which can be attributed to the presence of oxygen vacancies (δ ). SEM analysis reveals that the irregularities in grain size and shape, coupled with the porous nature of the material, are likely to influence its functional properties. These findings provide valuable insights into the structural features of Ca2FeGaO6-δ , offering a foundation for understanding its potential applications in catalysis, sensors, and other technologies. The study highlights the critical role of microstructural characteristics in determining the material’s performance.
more »
« less
- Award ID(s):
- 1839895
- PAR ID:
- 10649602
- Publisher / Repository:
- Scientific Research Publishing, Inc.
- Date Published:
- Journal Name:
- Journal of Materials Science and Chemical Engineering
- Volume:
- 13
- Issue:
- 01
- ISSN:
- 2327-6045
- Page Range / eLocation ID:
- 1 to 6
- Subject(s) / Keyword(s):
- XRD, Solid-State Reaction, Perovskite Oxides, Oxygen Deficiency, SEM
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
unknown (Ed.)This study introduces a novel oxygen-deficient perovskite, Sr2Fe0.75Co0.75Mn0.5O6-δ, synthesized through a solid-state reaction and thoroughly characterized by Powder XRD, SEM and direct current (DC) electrical conductivity measurements. The material, exhibiting a cubic crystal structure with the Pm3̅m space group, demonstrates intriguing electrical properties. At temperatures ranging from 25 to 400 °C, the material displays semiconductor-type conductivity, transitioning seamlessly to metallic-type conductivity from 400 to 800 °C. The deliberate incorporation of cobalt into the perovskite structure is found to be pivotal, as evidenced by a comparative analysis with its parent compound, Sr2FeMnO6-δ. This investigation reveals a substantial improvement in electrical conductivity, underscoring the significance of the partial substitution of cobalt. The tailored electrical properties of Sr2Fe0.75Co0.75Mn0.5O6-δ position it as a versatile candidate for electronic applications.more » « less
-
Perovskite oxides are gaining significant attention for use in next-generation magnetic and ferroelectric devices due to their exceptional charge transport properties and the opportunity to tune the charge, spin, lattice, and orbital degrees of freedom. Interfaces between perovskite oxides, exemplified by La1−xSrxCoO3−δ/La1−xSrxMnO3−δ (LSCO/LSMO) bilayers, exhibit unconventional magnetic exchange switching behavior, offering a pathway for innovative designs in perovskite oxide-based devices. However, the precise atomic-level stoichiometric compositions and chemophysical properties of these interfaces remain elusive, hindering the establishment of surrogate design principles. We leverage first-principles simulations, evolutionary algorithms, and neural network searches with on-the-fly uncertainty quantification to design deep learning model ensembles to investigate over 50,000 LSCO/LSMO bilayer structures as a function of oxygen deficiency (δ) and strontium concentration (x). Structural analysis of the low-energy interface structures reveals that preferential segregation of oxygen vacancies toward the interfacial La0.7Sr0.3CoO3−δ layers causes distortion of the CoOx polyhedra and the emergence of magnetically active Co2+ ions. At the same time, an increase in the Sr concentration and a decrease in oxygen vacancies in the La0.7Sr0.3MnO3−δ layers tend to retain MnO6 octahedra and promote the formation of Mn4+ ions. Electronic structure analysis reveals that the nonuniform distributions of Sr ions and oxygen vacancies on both sides of the interface can alter the local magnetization at the interface, showing a transition from ferromagnetic (FM) to local antiferromagnetic (AFM) or ferrimagnetic regions. Therefore, the exotic properties of La1−xSrxCoO3−δ/La1−xSrxMnO3−δ are strongly coupled to the presence of hard/soft magnetic layers, as well as the FM to AFM transition at the interface, and can be tuned by changing the Sr concentration and oxygen partial pressure during growth. These insights provide valuable guidance for the precise design of perovskite oxide multilayers, enabling tailoring of their functional properties to meet specific requirements for various device applications.more » « less
-
Materials with low thermal conductivity are essential to providing thermal insulation to many technological systems, such as electronics, thermoelectrics and aerospace devices. Here, we report ultra-low thermal conductivity of two oxide materials. Sr 2 FeCoO 6−δ has a perovskite-type structure with oxygen vacancies. It shows a thermal conductivity of 0.5 W m −1 K −1 , which is lower than those reported for perovskite oxides. The incorporation of calcium to form Ca 2 FeCoO 6−δ , leads to a structural change and the formation of different coordination geometries around the transition metals. This structural transformation results in a remarkable enhancement of the thermal insulation properties, showing the ultra-low thermal conductivity of 0.05 W m −1 K −1 , which is one of the lowest values found among solid materials to date. A comparison to previously reported perovskite oxides, which show significantly inferior thermal insulation compared to our materials, points to the effect of oxygen-vacancies and their ordering on thermal conductivity.more » « less
-
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
An official website of the United States government

