STRUCTURE AND PROPERTIES OF 1256 AND 1267 TYPE Hg1-xRexBa2Can-1CunO2n+2+4x+delta SINGLE CRYSTALS

摘要

Single crystals of Hg0.75Re0.22Ba2Ca5Cu6O15 and of Hg1-xRexBa2Ca6Cu7O16+4x+delta have been grown with a gas-phase high pressure technique at 10 kbar. They crystallize in space group P4/mmm with lattice parameters a=3.8542(3) angstroms, c=25.162(3) angstroms (HgRe-1256) and a=3.8514(5) angstroms, c=28.388(7) angstroms (HgRe-1267). They represent the n=6, 7 members of the layered cuprate superconductors of the type HgBa2Can-1CunO2n+2+delta. X-ray single crystal structure analysis showed that Re doping decreases the size of thek-salt block. Rhenium substitutes mercury up to 25% and forms short bonds of 1.86 angstroms to O atoms. They coordinate Re octahedrally and are shifted off their ideal positions to (0.34, 0.34, 0). The crystals contain stacking faults which are included in the refinements. In the HgRe-1267 crystal they are so numerous that they influence the refinement severely. A simulation of the Fourier maps proved that observable maxima in the difference electron density map are in fact due to stacking faults. The transition temperature onset of HgRe-1256 is 100 K and that of HgRe-1267 is assumed to be 84 K. 22 refs.