Thin film growth of the 2122-phase of BCSCO superconductor with high degree of crystalline perfection
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Thin film growth of the 2122-phase of BCSCO superconductor with high degree of crystalline perfection K. K. Raina, S. Narayanan, and R. K. Pandey Center for Electronic Materials, Electrical Engineering Department, Texas A&M University, College Station, Texas 77843-3128 (Received 10 February 1992; accepted 18 May 1992)
Thin films of the 80 K-phase of BiCaSrCu-oxide superconductor having the composition of Bi2Ca105Sr2.iCu2.i9O^ and high degree of crystalline perfection have been grown on c-axis oriented twin free single crystal substrates of NdGaO 3 . This has been achieved by carefully establishing the growth conditions of the liquid phase epitaxy (LPE) experiments. The temperature regime of 850 °C to 830 °C and quenching of the specimens on the termination of the growth period are found to be pertinent for the growth of quasi-single crystalline superconducting BCSCO films on NdGaO 3 substrates. The TEM analysis reveals a single crystalline nature of these films which exhibit 100% reflectivity in infrared regions at liquid nitrogen temperature. I. INTRODUCTION Ever since the discovery of Bi—Ca-Sr—Cu—O (BCSCO) superconducting systems by Maeda et al.,1 there have been numerous reports on the thin film growth of this material. High quality epitaxial films of this superconducting material are of vital importance for a large number of applications. Various techniques such as electron beam deposition,2"5 magnetron sputtering,6"11 molecular beam epitaxy,12"14 and laser ablation15"19 have been widely used for the growth of thin films of BCSCO superconducting material. In contrast there have been only a few reports on the growth of these films by the LPE method.20"24 The main advantage of the LPE process over other thin film techniques, with the exception of laser ablation, is the superior stoichiometric control of the grown layers in the film. This is not possible with other methods due to the different vapor pressures of the individual elements of BCSCO at fixed substrate temperatures. Moreover, because of the nonuniform stoichiometric control with these techniques, the films have to be annealed subsequent to the growth to achieve the 80 K or 110 K phases. The post deposition annealing treatment of the films imposes a severe restriction on the choice of the substrates because of the possibility of diffusion of substrate constituents into the film. This problem of interdiffusion has been observed in the case of NdGaO 3 (in the present work) and LaGaO 3 substrates.24 We report here the optimization of growth conditions in the LPE experiments to produce high quality thin films of the 2122-phase of BCSCO which do not require post annealing to observe superconducting properties. The substrates that have been so far widely used for growing superconducting films are MgO and SrTiO3. Although these substrates have a very good structural stability at higher temperatures, they suffer from a large J. Mater. Res., Vol. 7, No. 9, Sep 1992
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lattice constant mismatch with the 2122 p
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