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The perovskite oxides CaMnO3-δ, Ca0.5Sr0.5MnO3-δ, and SrMnO3-δ were synthesized in air using a solid-state method, and their structural, electrical, and electrocatalytic properties were studied in relation to their oxygen evolution reaction (OER) performance. Iodometric titration showed δ values of 0.05, 0.05, and 0.0, respectively, indicating that Mn is predominantly in the 4+ oxidation state across all materials, consistent with prior reports. Detailed characterization was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), iodometric titration, and variable-temperature conductivity measurements. Four-point probe DC measurements revealed that CaMnO3-δ (δ = 0.05) has a semiconductive behavior over a temperature range from 25 °C to 300 °C, with its highest conductivity attributed to polaron activity. Cyclic voltammetry (CV) in 0.1 M KOH was employed to assess OER catalytic performance, which correlated with room-temperature conductivity. CaMnO3-δ exhibited superior catalytic activity, followed by Ca0.5Sr0.5MnO3-δ and SrMnO3-δ, demonstrating that increased conductivity enhances OER performance. The conductivity trend, CaMnO3-δ > Ca0.5Sr0.5MnO3-δ > SrMnO3-δ, aligns with OER activity, underscoring a direct link between electronic transport properties and catalytic efficiency within this series. 

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. 

CaSrFe0.75Co0.75Mn0.5O6-δ, an oxygen-deficient perovskite, had been reported for its better electrocatalytic properties of oxygen evolution reaction. It is essential to investigate different properties such as the thermal conductivity of such efficient functional materials. The thermal conductivity of CaSrFe0.75Co0.75Mn0.5O6-δ is a critical parameter for understanding its thermal transport properties and potential applications in energy conversion and electronic devices. In this study, the authors present an investigation of the thermal conductivity of CaSrFe0.75Co0.75Mn0.5O6-δ at room temperature for its thermal insulation property study. Experimental measurement was conducted using a state-of-the-art thermal characterization technique, Thermtest thermal conductivity meter. The thermal conductivity of CaSrFe0.75Co0.75Mn0.5O6-δ was found to be 0.724 W/m/K at 25 °C, exhibiting a notable thermal insulation property i.e., low thermal conductivity. 

The crystal structure of CaSrFe0.75Co0.75Mn0.5O6−δ is investigated through neutron diffraction techniques in this study. The material is synthesized using a solid-state synthesis method at a temperature of 1200˚C. Neutron diffraction data is subjected to Rietveld refinement, and a comparative analysis with X-ray diffraction (XRD) data is performed to unravel the structural details of the material. The findings reveal that the synthesized material exhibits a cubic crystal structure with a Pm-3m phase. The neutron diffraction results offer valuable insights into the arrangement of atoms within the lattice, contributing to a comprehensive understanding of the material’s structural properties. This research enhances our knowledge of CaSrFe0.75Co0.75Mn0.5O6−δ, with potential implications for its applications in various technological and scientific domains. 

In this study, we investigate the utility of Ca₂FeMnO_6-δand Sr₂FeMnO_6-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. Ca₂FeMnO_6-δadopts a brownmillerite-type orthorhombic structure with ordered vacancy arrangement, while Sr₂FeMnO_6-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. 

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. 

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.