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Issue 23, 2015
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Valence properties of Cu and Ru in titanium-substituted LnCu3Ru4O12+δ (Ln = La, Pr, Nd) investigated by XANES and TGA

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Abstract

In the solid-solution series LayCu3RuxTi4−xO12+δ (0 ≤ x ≤ 4) the Cu and Ru electronic states are highly correlated. With increasing Ru content x the system properties change from a paramagnetic insulator with colossal dielectric constant to a heavy-fermion metal. To further elucidate the occurring phase transitions, the valences of Cu and Ru have been investigated utilizing XANES measurements at the Cu-K and the Ru-K absorption edges. It was found that the Ru oxidation number is close to +4 in all samples, while the Cu valence linearly decreases from +2 for the titanate (x = 0) to +1.6 for the ruthenate (x = 4). Additional thermogravimetric measurements have been used to determine the oxygen content and rather high oxygen excesses up to δ ≈ 0.7 (for x = 0.5) were obtained. The additional oxygen for x < 2 is required to compensate the constant Ru +4 valence. Our findings are in accordance with the reported phase transitions of the magnetic and transport properties. Both the valence shift and the shapes of the absorption edges suggest a change from localized to itinerant character of the Cu electronic states with increasing x, while the Ru electrons remain localized. Analogous results concerning the valences were found for the PryCu3RuxTi4−xO12+δ and NdyCu3RuxTi4−xO12+δ solid-solution series.

Graphical abstract: Valence properties of Cu and Ru in titanium-substituted LnCu3Ru4O12+δ (Ln = La, Pr, Nd) investigated by XANES and TGA

  • This article is part of the themed collection: Perovskites
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Publication details

The article was received on 17 Dec 2014, accepted on 17 Mar 2015 and first published on 17 Mar 2015


Article type: Paper
DOI: 10.1039/C4DT03876B
Citation: Dalton Trans., 2015,44, 10852-10859
  • Open access: Creative Commons BY license
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    Valence properties of Cu and Ru in titanium-substituted LnCu3Ru4O12+δ (Ln = La, Pr, Nd) investigated by XANES and TGA

    S. Riegg, A. Reller, A. Loidl and S. G. Ebbinghaus, Dalton Trans., 2015, 44, 10852
    DOI: 10.1039/C4DT03876B

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