Preparation of Tl2Ba2CaCu2O8 superconducting thin films on sapphire substrates via a two-step chemical deposition process

Single-phase Tl2Ba2CaCu2O8 thin films have been deposited on single-crystal sapphire substrates, (11̄02) orientation, via a two-step chemical deposition process. Ba-Ca-Cu-O precursor films were prepared by spin coating a (Ba-Ca-Cu)-2-ethylhexanoate solution followed by a firing in oxygen at 850 °C. Thallium was incorporated by heating the film in a confined surface configuration with an unfired pellet of Tl2Ba2CaCu2Ox composition at 870 °C for 0.1 h. The resultant films (1 μm thick) were oriented with the c axis normal to the substrate. The structural and chemical composition of the films was monitored by x-ray diffraction, electron microprobe, and energy dispersive x-ray analysis. The superconducting properties were characterized by resistance and mutual inductance versus temperature measurements. Zero resistance temperatures as high as 95 K have been observed.