Fabrication of Dy2Ho2Er2Tm2Yb2O15 high-entropy oxide: Comparative microstructural characterization

Novel Dy₂Ho₂Er₂Tm₂Yb₂O₁₅ high-entropy oxide successfully synthesized via conventional sintering. • Single-phase cubic bixbyite structure (Ia-3) formed across all sintering conditions. • Higher sintering time/temperature promoted grain growth, strain relaxation and homogeneity. • Bandgap narrowed to 4.45 eV due to high-entropy induced lattice distortion. characters). • Promising photoluminescence properties indicating potential photocatalytic activity. A bixbyite-structured rare-earth high-entropy oxide with the composition Yb₂Tm₂Er₂Dy₂Ho₂O₁₅ was synthesized by a conventional compaction–sintering route. The effects of sintering temperature and time on phase formation, microstructure, chemical homogeneity, and optical properties were systematically investigated. XRD confirmed the formation of a cubic bixbyite structure with the space group $\mathit{Ia}\bar{3}$ , while Williamson–Hall analysis indicated improved crystallinity and strain relaxation with increasing sintering severity. SEM/TEM observations and EDS mapping revealed progressive grain growth, densification, and homogeneous distribution of the constituent rare-earth elements. XPS results confirmed the predominance of trivalent rare-earth cations and a stable oxygen environment, with no major chemical-state changes after sintering. UV–Vis analysis showed a band gap of 4.45 eV, which is lower than those of the individual constituent oxides, suggesting that lattice distortion and compositional complexity influence the electronic structure. PL results further indicated reduced electron–hole recombination in the UV region. Overall, the results demonstrate that conventional compaction and sintering can produce chemically homogeneous bixbyite-type rare-earth HEOs with tunable microstructural and optical characteristics.