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295 results on '"Saez-Puche R"'

6. Importance of tetrahedral coordination for high-valent transition metal oxides: YCrO$_4$ as a model system

Author

Tsirlin, A. A., Rabie, M. G., Efimenko, A., Hu, Z., Saez-Puche, R., and Tjeng, L. H.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract

We have investigated the electronic structure of the high oxidation state material YCrO$_4$ within the framework of the Zaanen-Sawatzky-Allen phase diagram. While Cr$^{4+}$-based compounds like SrCrO$_3$/CaCrO$_3$ and CrO$_2$ can be classified as small-gap or metallic negative-charge-transfer systems, we find using photoelectron spectroscopy that YCrO$_4$ is a robust insulator despite the fact that its Cr ions have an even higher formal valence state of 5+. We reveal using band structure calculations that the tetrahedral coordination of the Cr$^{5+}$ ions in YCrO$_4$ plays a decisive role, namely to diminish the bonding of the Cr $3d$ states with the top of the O $2p$ valence band. This finding not only explains why the charge-transfer energy remains effectively positive and the material stable, but also opens up a new route to create doped carriers with symmetries different from those of other transition-metal ions., Comment: 6 pages, 6 figures

Published
2014
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45. Synthesis, structural characterization and magnetic properties of RCrO4 oxides, R=Nd, Sm, Eu and Lu

Author

Jimenez-Melero, Enrique, Isasi, J., and Saez-Puche, R.

Subjects
Exchange and superexchange, Ceramics and Composites, Magnetically ordered materials, ResearchInstitutes_Networks_Beacons/03/02, Chemical synthesis, Magnetic measurements, Condensed Matter Physics, Advanced materials, X-ray diffraction
Abstract

This paper reports the specific conditions used in the preparation of RCrO4 oxides, R=Nd, Sm, Eu and Lu, the structural determination, and the study of their magnetic behaviour. The structure of these compounds has been refined from X-ray powder diffraction by the Rietveld method, assigning the zircon type, space group I41/amd. A linear decrease has been observed in the lattice parameters from NdCrO4 to LuCrO4, according to the lanthanide contraction. Magnetic susceptibility measurements reveal the existence of an antiferromagnetic ordering in which both Cr5+ and R3+ sublattices are involved. In the case of NdCrO4, the estimated Neel temperature appears to be lower than 2 K; for the remaining oxides, it is 14.9 K, 15.9 K and 9.9 K for Sm, Eu and Lu, respectively. A superexchange mechanism has been proposed to explain such a magnetic behaviour. The pathways through which these interactions take place have also been analysed, taking into account the structural features that these oxides present. The Cr5+ plays an important role as a promoter of these interactions in the R3+ sublattice.

Published
2000

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