Preparation of Tl-2212 and -1223 superconductor thin films and their microwave properties

Abstract Tl 2 Ba 2 CaCu 2 O y (Tl-2212) and Tl(Ba,Sr) 2 Ca 2 Cu 3 O y (Tl-1223) superconductor thin films have been prepared on CeO 2 buffered sapphire substrate by an ex situ process namely, amorphous phase epitaxy (APE) method. In the case of Tl-1223, an amorphous layer of TlSr 2 CaCu 2 O y (TlSr-1212) was deposited on top of CeO 2 layer to avoid chemical reaction between Tl-1223, containing Ba, and CeO 2 layers. All films are epitaxial with smooth surface and excellent crystallinity. Superconducting transition temperatures ( T c ) of Tl-2212 and 1223 are around 95 and 104 K, respectively. Critical current density ( J c ) at 77 K measured on 5×5 mm films by inductive technique is as high as 2 MA/cm 2 . Surface resistance R s of Tl-2212 films measured by a dielectric resonator technique at 38 GHz is comparable to the best YBCO films.