Ordered phase transformation and Cu doping effects in room-temperature ferromagnetic Sr(3)YCo(4)O(10.5+δ )

Sr(3)YCo(4)O(10.5+δ ) (314-SYCO), with an unusual ordered structure and a high Curie temperature (T(c) ≈ 335 K), is attracting increasing attention. Herein, to improve the electrical performance of 314-SYCO, Cu-doped Sr(3)YCo(4−x )Cu( x )O(10.5+δ ) (x = 0–0.8) ceramics were prepared using a solid-state reaction method. Systematic research was conducted on both the ordered phase transformation and the effects of Cu doping on the microstructure, electrical transport characteristics, and magnetic properties. For x = 0–0.4, the (103) and (215) planes were observed and combined with Rietveld refinement results for the X-ray diffraction data, confirming the formation of ordered tetragonal Sr(3)YCo(4−x )Cu( x )O(10.5+δ ). This phase was formed with a mass gain of ∼0.8% and heat released at ∼1,042°C. With increasing Cu content, the concentration of hole carriers also increased, leading to a substantial reduction in electrical resistivity. The electrical resistivity decreased by 92–99% at 300 K. The polycrystalline materials have semiconducting behaviour with a three-dimensional Mott variable-range hopping mechanism. For the magnetic properties, a Hopkinson peak was observed at 319 K, and the T(c) was approximately 321 K for x = 0. The magnetisation and T(c) decreased with increasing Cu content, and a G-type antiferromagnetic-to-ferromagnetic phase transition occurred due to the spin state change for some Co(3+) ions from high/intermediate spin to low/intermediate spin. These results lay the groundwork for refinement of the sintering procedure and doping parameters to enhance the performance of 314-SYCO in the context of current applications such as microwave absorbers and solid oxide fuel cell cathodes.