Thallium Based Superconducting Thin Films Synthesized by RF-Sputtering and Ex Situ Thallination
Thallium based superconducting thin films of TlBa2CaCu2O7 (Tl-1212), Tl2Ba2CaCu2O8 (Tl-2212) and Tl2Ba2Ca2Cu3O10 (Tl-2223) of about 100-125 nm in thickness have been prepared on (001) LaAlO3 single crystal substrate using rf-sputtering deposition of Ba2Ca2Cu3O7 precursor films and ex-situ thallination in sealed quartz tube under different atmospheres (oxygen, argon and nitrogen). We have studied phases formation as function of partial pressure of Tl2O which may be adjusted by varying thallium source content TlxBa2Ca2Cu3Oz (x = 1.5, 1.6, 1.7, 1.8, 1.9, 2.0) and atmosphere pressure at ambient temperature (300, 500 mbar). The influence of the temperature and time of thallination (60 min to 1400 min) is also presented. The synthesized films were characterised by optical microscopy, atomic force microscopy AFM, AC susceptibility and XRD measurements. The XRD measurement shows that the obtained films contain several superconducting phases and are strongly c-axis oriented. The properties of the resulting films are critically dependant on the microstructures developed during thallination process. Thallium source content as well as the time of thallination and partial atmosphere pressure at room temperature play an important role in the obtained film’s quality and phase’s purity.
T. Guerfi et al., "Thallium Based Superconducting Thin Films Synthesized by RF-Sputtering and Ex Situ Thallination", Materials Science Forum, Vol. 609, pp. 173-178, 2009