Single crystal of the 1223/1234 intergrowth phase Hg1.44Re0.5Ba4Ca5Cu7O20:structure and properties

A single crystal of Hg1.44Re0.5Ba4Ca5Cu7O20 (HgRe-2457) has been grown with a gas-phase high pressure technique at 10 kbar. X-ray single-crystal struc ture analysis showed that the crystal is composed of alternating blocks of 1223 and 1234 units. Until now, intergrowth structures in the Hg based seri es have only been observed in a small submicron scale or as a defect. Rheni um substitutes 25% of mercury and forms short bonds of 1.98 Angstrom to oxy gen atoms. They coordinate Re octahedrally and are shifted off their ideal positions to (0.36, 0.36, z). The bond lengths are in the range of pure 122 3 or 1234 compounds. The stacking sequence is disturbed by double or triple layers of 1223 or 1234, like...3-4-3-4-4-3-4-3.... This feature is visible in Fourier maps and included in the refinement. The transition temperature of this 2457 crystal is 83 K. (C) 1999 Published by Elsevier Science B.V. All rights reserved.