High thermal insulation properties of A2FeCoO6−δ (A = Ca, Sr)

Abstract

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. Sr₂FeCoO_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 Ca₂FeCoO_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.