Time and composition dependence of the spectral shape of the X-ray Ce L III absorption in the R 2− xCe xCuO 4− δ superconductors

• Published in: Materials letters Vol. 16; no. 5; pp. 265 - 269
• Main Authors: Finkelstein, L.D., Efremova, N.N., Postnikov, A.V., Kurmaev, E.Z., Babushkina, N.A., Balakrishnan, G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1993
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/0167-577X(93)90188-4

X-ray absorption Ce L III spectra in electron superconductors PNd 2− x Ce x CuO 4− δ and Pr 2− x Ce x CuO 4− δ with perovskite-like T′ structure have been obtained. The spectral shape of freshly prepared samples is similar to that of Ce L III in cubic perovskite BaCeO 3, but not to Ce L III in CeO 2, in contrast to what has previously been published. The changes of the spectral shape with time have been detected and thought to be due to the degradation of the samples. The spectrum of the most degraded sample is similar to the spectra of CeO 2 and Ce(OH) 4. It is found that the compositions most stable towards degradation are those which exhibit maximal T c values. It is supposed that at values of x corresponding to 0.15 in Nd-Ce-Cu-O and 0.14 in Pr-Ce-Cu-O, Ce atoms are ordered, and perovskite-like structure acquires the highest thermodynamical stability. LMTO band structure calculations of fictitious ordered compound Nd 3CeCu 2O 8 in the T′ structure were performed, and Ce 5d partial density of states compared to the Ce L III spectrum. All the main features of the Ce L III spectrum are explained. The valence state of Ce is close to Ce 4+, similarly to that in CeO 2 and BaCeO 3.