Preparation and X-ray characterization of superconducting and related Tl₂Ba₂CuO₆ phases

Polycrystalline oxides of the form Tl2Ba2CuO6 have been synthesized by a solid-state reaction technique. Tl2Ba2CuO6 displays a variety of properties, ranging from superconductivity to semiconductivity depending on the preparation conditions. X-ray diffraction analysis showed that a superconducting Tl2Ba2CuO6 phase with Tc∼20K has a body-centered tetragonal structure similar to those of the Tl2Ca1Ba2Cu2O8 and Tl2Ca2Ba2Cu3O10 high Tc superconductors. The tetragonal unit cell dimensions refined from a high quality powder diffraction pattern are a=3.8632(2) A ̊, c=23.160(1) A ̊, and V=345.7(2) A ̊3. The non-superconducting Tl2Ba2CuO6 phase was found to have a face-centered orthorhombic structure with a=5.4451(3) A ̊, b=5.4961(7) A ̊, c=23.152(2) A ̊, and V=692.9(1) A ̊3. © 1988.