The structural symmetry of epitaxial Tl-2201 films

Tl2-xBa2CuO6 (Tl-2201) films with a thallium content of 1.85 and 2.04 were prepared on single crystal LaAlO3 and SrTiO3 substrates using a multi-step procedure involving laser ablation. The films were c-axis oriented and epit axial. The structural symmetry of the films was studied by performing X-ray phi -scans. For a film with a thallium content of 1.85, a phi scan of the (1,1,10) reflection showed four peaks while a 2 theta scan of the same refl ection exhibited single peak structure. This shows that the film is epitaxi al and tetragonal. A film with a thallium content of 2.04 was also found to be epitaxial. In t his case a 2 theta scan of the corresponding reflection showed that it exhi bited a double peak structure. This indicates an orthorhombic splitting of the reflection into (2,0,10) and (0,2,10). The phi scan also revealed a sma ll deviation from tetragonal symmetry supporting the conclusion that this f ilm is orthorhombic.