SUPERCONDUCTING TL2BA2CUO6 - THE ORTHORHOMBIC FORM

The structure of an orthorhombic variant of Ti//2Ba//2CuO//6 (Z equals 4), with a superconducting onset at 90 K, has been studied using neutron powder diffractometry at 12 K. The distortion from I4/mmm symmetry, reported in single-crystal X-ray investigations, to Abma is manifested in the T1-O layer. At the temperatures studied, the coordination of TI to oxygen is (2 plus 1 plus 2) square pyramidal rather than octahedral. At lower temperatures, distortion decreases but does not disappear. Despite the orthorhombic symmetry the CuO//2-layers remain flat.