(TL,PB,CU)SR-2(TL,PB,CU)(2)CU2O8-DELTA - A NONSUPERCONDUCTING TL-1222-ASTERISK CUPRATE WITH BOTH HEAVY-ATOM SINGLE AND OXYGEN DEPLETED DOUBLE-LAYER MOTIFS

An account is given of the synthesis and structural investigation of a newly discovered tetragonal (Tl, Pb, Cu)Sr-2(Tl, Pb, Cu)(2)Cu2O8-delt a compound (Tl-1222 phase) with both (Tl, Pb, Cu)O single and oxygen depleted (Tl, Pb, Cu)(2)O-x double layer motifs, space group I4/mmm, l attice parameters a = 3.8405(2), c = 29.2536(5) Angstrom, and D-x = 7. 46 g cm(-3). Micaceous and highly reflecting black single crystals of 1 mm x 1 mm X 3-5 mu m size were obtained from a Tl(2)0(3)- and CuO-ri ch partial melt. The as-grown compound is nonsuperconducting. The very thin crystals an extremely liable to bend out of shape. Deterioration could not be observed within the period of a year under ambient condi tions. The complex crystal structure has been solved using single crys tals. We take note of the similarity of the unit cell dimensions to su perconducting (Tl, Cu)(2)Ba-2(Ca, Tl)Cu2O8 (Tl-2212 phase) with TlO do uble rocksalt layers, and compare crystal-chemical details of similar compounds. Apart from the possibility of obtaining superconducting pro perties by suitable doping, the mechanical properties of the new mater ial are very attractive from the point of view of its use as highly sc attering composite layers of an X-ray monochromator. (C) 1998 Elsevier Science B.V. All rights reserved.