AUTHOR=Ma Chao 

TITLE=Modulation of optical absorption and electrical properties in Mn-Co-Ni-O-based high-entropy thin films

JOURNAL=Frontiers in Materials

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2023.1297318

DOI=10.3389/fmats.2023.1297318

ISSN=2296-8016

ABSTRACT=<p>High-entropy thin films of Mn<sub>0.6</sub>Co<sub>0.6</sub>Ni<sub>0.6</sub>Mg<sub>0.6</sub>Cu<sub>0.6</sub>O<sub>4</sub>, Mn<sub>0.6</sub>Co<sub>0.6</sub>Ni<sub>0.6</sub>Mg<sub>0.6</sub> Zn<sub>0.6</sub>O<sub>4</sub>, and Mn<sub>0.6</sub>Co<sub>0.6</sub>Ni<sub>0.6</sub>Cu<sub>0.6</sub>Zn<sub>0.6</sub>O<sub>4</sub> (MCNMC, MCNMZ, and MCNCZ) with equiatomic proportions were synthesized using chemical solution deposition on silicon substrates. Structural analysis confirmed a consistent face-centered cubic spinel structure, while significant differences in surface morphology were observed. Quantification of the valence states of Mn ions revealed an inverse variation in the concentrations of Mn<sup>4+</sup> and Mn<sup>2+</sup> ions. The heightened infrared light absorption of the MCNMC thin film was assigned to Cu-induced Jahn-Teller distortion and highly polarized Mg-O bonds. All samples exhibited negative temperature coefficient behaviors in their electrical properties. Additionally, the MCNMC thin film demonstrated the lowest resistance due to its denser microstructure, close proximity of Mn<sup>3+</sup>/Mn<sup>4+</sup> ion concentrations, and additional Cu<sup>+</sup>/Cu<sup>2+</sup> ion pairs, enhancing small polaron hopping conductivity. In contrast, the MCNMZ thin film showed moderate resistance but boasted the highest thermal constant (<italic>B</italic><sub><italic>25/50</italic></sub>) of 3768 K, attributed to its distinctive grain chain structure, facilitating carrier transport while introducing migration barriers.</p>