Synthesis of Bi₂Sr₂Ca_nCu_n+1O_x Films by Multilayer Deposition Technique

Abstract

Soon after the discovery of high Tc superconductors in Bi-Sr-Ca-Cu -O systems^l, i.e., 80 K and 110 K phases, it was realized that the 110 K mono phase was extremely difficult to be synthesized by the conventional solid state reaction. Frequent intergrowth of many phases, i.e. Bi₂Sr₂Ca_nCu_n+1O_x (n=0–6) are observed². This suggests that the free energy of these phases has no sharp minimum against the number of CaCu layers sandwitched with two neighboring Bi₂O₂ layers. The sequential deposition technique is one of the most promising methods to obtain non equilibrium or metastable material having layered structure. We have attempted to synthesize the phases with n=0,1,2 or 3. In this paper we shall report on our sequential vapor deposition technique, characterization of the resultant multilayered films by X-ray diffraction and by SEM and finally their superconducting transion.