Structural Study on the Copper Oxyhalide Sr-Ca-Cu-O-Cl System
Samples of copper oxyhalide of the Sr-Ca-Cu-O-Cl system have been synthesized using a high pressure synthesis technique. X-ray and electron diffraction analyses and high resolution transmission electron microscopic observation have revealed the formation of a homologous series, 02(n-l)n, in this system. The crystal structure of a nearly single phase (Sr,Ca)3Cu2O4+xCl2-y is determined by x-ray Rietveld refinement. Based on these crystallographic data, a general model is suggested for the 02(n-l)n series. The simulated x-ray diffraction pattern for 0223 by this model shows a rather good agreement with the measured one. Meanwhile, a new phase 0435, which actually was formed by a regular intergrowth of 0212 and 0223, has been observed by TEM, too. Since the intergrowth of 0223 and 0234 has been observedin the local area, a general model for a new homologous series, 04(2n-l)(2n+l) (or [02(n-l)n+02n(n+l)]), is proposed. Some of our samples showed superconductivity in a range of 60–80 K. Considering the present crystal structure, we propose that the carriers are induced by anion substitution in the apical position for this Sr-Ca-Cu-O-Cl system.
KeywordsHomologous Series Apical Position Anion Substitution Half Unit Cell Field Cool Mode
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