A thallium and barium based superconductor, Tl 0 . 8 (CrO 4 ) 0 . 2 Ba 2 CuO 4 . 2 - δ with a T c of 42 K, has been stabilized by partially substituting chromium for thallium. The structure of this new oxychromate has been characterized using electron diffraction, EDS, high-resolution electron microscopy, infrared spectroscopy and X-ray diffraction. It exhibits a 1201-type structure with a P-type lattice and the parameters of the average tetragonal cell are a = 3.8873(1) and c = 9.3435(4) . The presence of chromate groups has been shown from IR. They are located within the intermediate layer of the '1201' structure, Cr sitting in the Tl sites. The HREM investigation evidences the existence of short range ordering between thallium and chromate groups. The ordering mode is compared with that adopted by the '1201' strontium based oxychromate Tl 3 (CrO 4 )Sr 8 Cu 4 O 1 6 .