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arXiv · 1705.08712

Unusual coexistence of negative/positive charge-transfer in mixed-valence Na$_x$Ca$_{1-x}$Cr$_2$O$_4$

M. Taguchi·H. Yamaoka·Y. Yamamoto·H. Sakurai·N. Tsujii·M. Sawada·H. Daimon·K. Shimada·J. Mizuki
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Abstract

We have investigated the electronic structure of Na$_x$Ca$_{1-x}$Cr$_2$O$_4$ using x-ray absorption spectroscopy together with Anderson impurity model calculations with full multiplets. We show Na$_x$Ca$_{1-x}$Cr$_2$O$_4$ taking a novel mixed-valence electronic state in which the positive charge-transfer (CT) and the negative self-doped states coexist. While CaCr$_2$O$_4$ (one end member) exhibits a typical CT nature with strong covalent character, Na substitution causes a self-doped state with an oxygen hole. In NaCr$_2$O$_4$ (the other end member), positive CT and negative self-doped states coexist with equal weight. This unusual electronic state is in sharp contrast to the conventional mixed-valence description, in which the ground state can be described by the mixture of Cr$^{3+}$ ($3d^3$) and Cr$^{4+}$ ($3d^2$).

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M. Taguchi, H. Yamaoka, Y. Yamamoto, H. Sakurai, N. Tsujii, M. Sawada, H. Daimon, K. Shimada, J. Mizuki. 2017-05-24. Unusual coexistence of negative/positive charge-transfer in mixed-valence Na$_x$Ca$_{1-x}$Cr$_2$O$_4$. https://doi.org/10.1103/physrevb.96.245113

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