Structural and optical characteristics of cadmium doped Ce0.80(Zr0.20-xCdx)O2 (x = 0 - 0.20) ceria: An experimental and density functional theory (DFT) investigations

Abstract

Ceria-based oxides find relevance for wide-range applications e.g. fuel cell technologies, hydrogen production, energy storage and conversion, biosciences, and advanced sensing devices. In the present study, zirconium and cadmium co-doped Ce0.80(Zr0.20-xCdx)O2 (x = 0 - 0.20) oxides were synthesized via sol-gel route and systematically characterized for their structural and optical properties, supported by density functional theory (DFT). X-ray diffraction-cum-Rietveld refinement data confirm fluorite-type cubic structure with space group Fm (Formula presented) m and Z = 4. The lattice parameters (af) lie in the range of ∼5.398 - 5.412 Å for x = 0 - 0.20, and an anomalous behaviour, i.e., expansion-contraction-expansion, is observed with increasing cadmium content (x) with average size in the range of ∼90-150 nm. A clear correlation has been found between the calculated bond length with lattice parameter in Ce0.8(Zr0.20-xCdx)O2 oxides. Density functional theory (DFT) calculations independently validate these structural trends with cadmium (x) substitution. Specifically, the Ce-O bond length was 2.369 Å and upon cadmium substitution at zirconium sites completely, the bond length increases from ∼2.299 Å to ∼2.338 Å. The optical absorption peak at ∼266 nm corresponds to the charge transfer transition between the valence band 2p (O2−) and conduction band 4f (Ce4+) orbitals. An additional peak reveals trapped states between valence and conduction bands. The theoretically calculated band gaps are ∼1.561, 1.417 and 1.202 eV for pure CeO2, Ce0.80Zr0.20O2 and Ce0.8Cd0.20O2 samples, respectively. Raman mode at ∼462 cm−1 attributed to a triple degenerated F2g vibrational symmetry/mode of fluorite-type CeO2 structure. Bands at ∼1119 and 1361 cm−1 further confirm oxygen vacancy and defect-states. These results demonstrate that Zr/Cd co-doping in ceria offers an effective strategy for defect and band gap engineering, making these materials promising for ionic conduction and energy-related applications. © 2026 Elsevier Ltd and Techna Group S.r.l. All rights are reserved, including those for text and data mining, AI training, and similar technologies.