AUTHOR=Ren Lingqi , Zhang Xiaodong , Du Xiaoli , Wang Jianlu , Yu Lan 

TITLE=Ordered phase transformation and Cu doping effects in room-temperature ferromagnetic Sr3YCo4O10.5+δ

JOURNAL=Frontiers in Chemistry

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.1073946

DOI=10.3389/fchem.2022.1073946

ISSN=2296-2646

ABSTRACT=<p>Sr<sub>3</sub>YCo<sub>4</sub>O<sub>10.5+<italic>δ</italic></sub> (314-SYCO), with an unusual ordered structure and a high Curie temperature (<italic>T<sub>c</sub></italic> ≈ 335 K), is attracting increasing attention. Herein, to improve the electrical performance of 314-SYCO, Cu-doped Sr<sub>3</sub>YCo<sub>4−<italic>x</italic></sub>Cu<sub><italic>x</italic></sub>O<sub>10.5+<italic>δ</italic></sub> (<italic>x</italic> = 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 <italic>x</italic> = 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<sub>3</sub>YCo<sub>4−<italic>x</italic></sub>Cu<sub><italic>x</italic></sub>O<sub>10.5+<italic>δ</italic></sub>. This phase was formed with a mass gain of ∼0.8% and heat released at ∼1,042°<italic>C</italic>. 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 <italic>T<sub>c</sub></italic> was approximately 321 K for <italic>x</italic> = 0. The magnetisation and <italic>T<sub>c</sub></italic> decreased with increasing Cu content, and a <italic>G</italic>-type antiferromagnetic-to-ferromagnetic phase transition occurred due to the spin state change for some Co<sup>3+</sup> 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.</p>