Abstract
Two-dimensional modulation in synthetic Co-åkermanite, Ca2CoSi2O7, has been precisely studied using synchrotron X-ray diffraction methods in the temperature range between 180 and 523 K to determine the temperature dependence of q (the magnitude of the primary wavevectors of modulation waves). Three kinds of plateau-like regions are observed for q ∼ 2/7, 3/10 and 4/13 in addition to the low-temperature commensurate phase (q = 1/3). Using a simulation method we were able to generate nearly commensurate structures. The most probable structure of incommensurate Co-åkermanite is octagonal arrangements of the bundles along the c-axis, which are composed of four CaO6 arrays and a central array of CoO4 tetrahedra.
Acknowledgements
The authors would like to thank Professor Kazuaki Iishi (Yamaguchi University) for syntheses of the samples, Dr. Yusuke Wakabayashi and Professor Hiroshi Sawa (KEK) for the assistance at the X-ray measurements at beamline BL-4C. The synchrotron radiation experiments were performed at the Photon Factory, KEK, under the approval of PF-program Advisory Committee (Proposal No. 2002G228).