Structure and properties of 1256 and 1267 type Hg1-xRexBa2Can-1CunO2n+2+4x+δ single crystals

Single crystals of Hg0.75Re0.22Ba2Ca5Cu6O15 and of Hg1-xRexBa2Ca6Cu7O16+4x+δ 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) angstrom, c = 25.162(3) angstrom (HgRe-1256) and a = 3.8514(5) angstrom, c = 28.388(7) angstrom (HgRe-1267). They represent the n = 6, 7 members of the layered cuprate superconductors of the type HgBa2Can-1CunO2n+2=δ. X-ray single crystal structure analysis showed that Re doping decreases the size of the rock-salt block. Rhenium substitutes mercury up to 25% and forms short bonds of 1.86 angstrom to oxygen 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