paper

Unusual coexistence of negative/positive charge-transfer in mixed-valence Na $_{x}$ Ca $_{1 - x}$ Cr $_{2}$ O $_{4}$

arXiv:1705.08712 · doi:10.1103/PhysRevB.96.245113

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 $^{3 +}$ ( $3 d^{3}$ ) and Cr $^{4 +}$ ( $3 d^{2}$ ).

5 pages, 5 figures

Unusual coexistence of negative/positive charge-transfer in mixed-valence Nax​Ca1−x​Cr2​O4​

Abstract

Unusual coexistence of negative/positive charge-transfer in mixed-valence Na $_{x}$ Ca $_{1 - x}$ Cr $_{2}$ O $_{4}$