Modulated structure of incommensurate composite crystal (Sr2Cu2O3)0.70CuO2, “Sr14Cu24O41,” has been investigated by single-crystal x-ray-diffraction method using centrosymmetric (3 + 1)-dimensional superspace group. In (Sr2Cu2O3)0.70CuO2, displacive modulation of O atom in the CuO2 chain is fairly large. Considering the modulation of bond angles, it has been found that the Cu-O bond in the CuO2 chain is tilting toward the Cu2O3 ladder in order that the O atom in the chain plays as apical oxygen for the CuO4 square in the ladder. The bond-valence sum (BVS) method has been applied to investigate the hole distribution in the modulated structure of (Sr2Cu2O3)0.70CuO2. It is indicated that the valence of Cu atom in the Cu2O3 ladder is +2.04, where about 0.03 holes are certainly transferred from the CuO2 chain through the modulated O atom in the CuO2. The BVS calculation has demonstrated that almost all of the holes are prepared in the CuO2 chain by the large modulation of the Cu-O bond. Cu atoms in the modulated CuO2 chain have been proved to form hole-ordered structure with next-nearest-neighbor Cu2+ ions separated by Cu3+ ion on the Zhang-Rice singlet site. The periodicity of the hole-ordered structure is five times of the average CuO2 lattice along the crystallographic c axis, which is compatible with the spin-dimerized state at low temperature. The new model of the two-dimensional hole-ordered structure in the CuO2 plane has been obtained by the BVS calculation. Furthermore, the two-dimensional configuration of the spin dimers has been successfully derived from the hole-ordered structure in the CuO2 plane. It has been concluded that the valences of Cu atoms both in the Cu2O3 ladder and in the CuO2 chain are well controlled by the modulated O atom in the CuO2 chain.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Dec 15 2003|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics