Studies of Mn valence conversion and oxygen vacancies in La1−xCaxMnO3−y using electron energy-loss spectroscopy

Using the white line intensities, electron energy-loss spectroscopy in a transmission electron microscope has been employed to characterize the valence conversion and oxygen vacancies in ${\mathrm{La}}_{\text{1−x}}{\mathrm{Ca}}_x{\mathrm{MnO}}_{\text{3−y}}.$ For a nominal doping composition $\text{x=0.33,}$ the ratio of ${\mathrm{Mn}}^{\mathrm{4+}}$ to ${\mathrm{Mn}}^{\mathrm{3+}}$ is determined to be more than 0.25 but less than 0.5, and the content of oxygen vacancy $y$ is no more than 0.065 (equivalent to 2.2 at. % of the oxygen content). At $y_{\max }\text{=0.065,}$ 60% of the residual charge introduced by Ca doping is balanced by the conversion of ${\mathrm{Mn}}^{\mathrm{3+}}$ to ${\mathrm{Mn}}^{\mathrm{4+}}$ and 40% by oxygen vacancy.