Role of oxygen nonstoichiometry and the reduction process on the local structure ofNd2−xCexCuO4±δ

Abstract

We report Raman and crystal-field infrared transmission studies of ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ single crystals. ${\mathrm{Nd}}^{3+}$ crystal-field excitations from the ground state to excited multiplets are detected. While the ${\mathrm{Nd}}^{3+}$ regular site is almost not perturbed by $\mathrm{Ce}$-doping and oxygen nonstoichiometry, oxygen vacancies in $\mathrm{O}(1)$ and $\mathrm{O}(2)$ sites, as well as apical oxygen, are detected. The type of oxygen vacancies created is found to be $\mathrm{Ce}$-doping dependent, with the reduction of the optimally doped samples involving only ${\mathrm{CuO}}_{2}$ plane $\mathrm{O}(1)$ oxygen vacancies. In contrast to the widespread belief, the apical oxygen is not removed by the reduction of as-grown samples.