Disorder-induced f-electron localization in Nb and Y co-doped CeO2

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We report the effect of the charge compensation on the electronic transport and optical properties of CeO2 co-doped with donor, Nb, and acceptor, Y, ions. As expected, the concentration of Ce3+ decreases with an increase in the Y content in Ce0.992−xNb0.008YxO2, where 0 ≤ x ≤ 0.008. More importantly, random electric fields generated by the Y ions bring additional disorder into the system. As a result, the high-temperature activation energy of conductivity increases significantly from 189 to 430 meV. A similar energy shift in the optical absorption peak centered at 1.3–1.5 eV is attributed to an increase in the energy gap separating the localized f-electrons from the empty Ce 4f band. The results underline the paramount importance of the disorder-induced Anderson localization of the f-electrons in ceria.