Structural modulation, hole distribution, and hole-ordered structure of the incommensurate composite crystal(Sr2Cu2

Abstract

Modulated structure of incommensurate composite crystal (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 , ''Sr 14 Cu 24 O 41 ,'' has been investigated by single-crystal x-ray-diffraction method using centrosymmetric (3ϩ1)-dimensional superspace group. In (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 , displacive modulation of O atom in the CuO 2 chain is fairly large. Considering the modulation of bond angles, it has been found that the Cu-O bond in the CuO 2 chain is tilting toward the Cu 2 O 3 ladder in order that the O atom in the chain plays as apical oxygen for the CuO 4 square in the ladder. The bond-valence sum ͑BVS͒ method has been applied to investigate the hole distribution in the modulated structure of (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 . It is indicated that the valence of Cu atom in the Cu 2 O 3 ladder is ϩ2.04, where about 0.03 holes are certainly transferred from the CuO 2 chain through the modulated O atom in the CuO 2 . The BVS calculation has demonstrated that almost all of the holes are prepared in the CuO 2 chain by the large modulation of the Cu-O bond. Cu atoms in the modulated CuO 2 chain have been proved to form hole-ordered structure with next-nearest-neighbor Cu 2ϩ ions separated by Cu 3ϩ ion on the Zhang-Rice singlet site. The periodicity of the hole-ordered structure is five times of the average CuO 2 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 CuO 2 plane has been obtained by the BVS calculation. Furthermore, the two-dimensional configuration of the spin dimers has been successfully derived from the holeordered structure in the CuO 2 plane. It has been concluded that the valences of Cu atoms both in the Cu 2 O 3 ladder and in the CuO 2 chain are well controlled by the modulated O atom in the CuO 2 chain.

Phonon Energy Gaps in the Charged Incommensurate Planes of the Spin-LadderSr14Cu24O41Compound by Raman and Infrared Spectroscopy

“…1. The energy scale and the relative frequencies of the Raman and IR1 modes can be understood qualitatively by taking into account the c-axis incommensurability between the chain and ladder unit cells, c ch /c ld 0.699, in accordance with recent x-ray studies [26,27] which demonstrated that consideration of the super space group is mandatory. We assign n, m and q to the corresponding atomic mass density, unit-cell mass and charge respectively.…”

Influence of doping on the Hall coefficient inSr14−xCaxCu24OTafra1, Korin-Hamzić2, Basletić3 et al. 2008Phys. Rev. BSelf Cite11051View full textAdd to dashboardCite

“…are found in the ladders for x = 0 and 1.1 for the x = 12 compound. Also, Gotoh et al 13 performed an x-ray diffraction study on Sr 14 Cu 24 O 41 crystals. The bond-valence sum calculation based on their data has indicated that only 0.5 holes per f.u.…”

Structure analysis of mutually incommensurate composite crystal (Ca0.5Y0.5)0.80CuO2

“…type, Fuji Photo Film Co. Ltd.) was used to detect the weak satellite reflections of composite structure of (Ca 0.5 Y 0.5 ) 0.8+δ CuO 2 . We have taken the c-axis as the mutually incommensurate direction in accord with the structure determination of (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 , "Sr 14 Cu 24 O 41 " in the (Sr 2−x Ca x Cu 2 O 3 ) 0.7+δ CuO 2 series [5]. The X-ray diffraction data of both substructures were collected together with common reflections at room temperature using Rigaku AFC5 diffractometer (Mo K␣ radiation).…”

“…It is known that some compounds of them form composite crystals with mutually incommensurate substructures. In the (Sr 2−x (Ca, La, Y) x Cu 2 O 3 ) 0.7+δ CuO 2 , "Sr 14−x (Ca, La, Y) x Cu 24 O 41 " series, the CuO 2 chain in the CuO 2 substructure shows unique structural modulations and acts as hole reservoir of the two-legged Cu 2 O 3 ladder in the Sr 2−x (Ca, La, Y) x Cu 2 O 3 substructure [5]. By the use of polycrystalline sample [6], on the other hand, it has been preliminarily revealed that so-called Ca 2+x Y 2−x Cu 5 O 10 series [7] 0925-8388/$ -see front matter © 2005 Elsevier B.V. All rights reserved.…”