High-pressure synthesis and crystal structures of B2Sr3(Y,Sr)2Cu3O12 and B2Sr3(Ho,Sr)2Cu3O12

Two new layered oxyborates B2Sr3.2Y1.8Cu3O12 and BSr3.11 Ho1.89Cu3O12 have been synthesized at 6 GPa using a belt-type apparatus. These compounds could be described as intergrowth between B-1201 and B-1212 phases. The crystal structure of B2Sr3.11Ho1.89Cu3O12 has been determined using single crystal X-ray data. It was refined to R1 (I > 2sigma(I)) = 0.0456, wR2(all data) 0.1044 with F-2 data. B2Sr3.2Y1.8Cu3O12 and B2Sr3.11Ho1.89Cu3O12 crystallize in the space group P4/mmm (no. 123), Z = 1 with a = 3.852(1) Angstrom, c = 17.770(6) Angstrom and a = 3.8516(4) Angstrom, c = 17.764(2) respectively. A weak superstructure with a(s) = aroot2, b(s) = broot2, c(s) = c was deduced from an electron diffraction pattern for B2Sr3.11Ho1.89Cu3O12 probably due to local ordering of the triangular BO3 groups although such ordering was not revealed from single crystal X-ray data. (C) 2003 Elsevier B.V. All rights reserved.