Ordered phase transformation and Cu doping effects in room-temperature ferromagnetic Sr₃YCo₄O_10.5+

Sr₃YCo₄O_10.5+ (314-SYCO), with an unusual ordered structure and a high Curie temperature (T ≈ 335 K), is attracting increasing attention. Herein, to improve the electrical performance of 314-SYCO, Cu-doped Sr₃YCo_4- Cu O_10.5+ (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 Sr₃YCo_4- Cu O_10.5+ . 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 was approximately 321 K for x = 0. The magnetisation and T decreased with increasing Cu content, and a G-type antiferromagnetic-to-ferromagnetic phase transition occurred due to the spin state change for some Co³⁺ 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.