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5.1 Preparation of Bi-Sr-Ca-Cu-O Systems

The Bi₂Sr₂Ca_n-1Cu_nO_2n+4 superconductor series was first discovered in 1988.¹¹²  Of the three main phases, the Bi₂Sr₂CaCu₂O_8±x is the most studied phase since it is the easiest to produce in single phase.  While Bi₂Sr₂CaCu₂O_8±x can be produced in a variety of methods,^113-116 the simple solid-state reaction of stoichiometric amounts of metal oxides and carbonates was used for most experiments.  Table 5.1 gives an example of the precursors used to produce the superconductor.  These powders are mechanically mixed in an alumina or agate mortar and pestle with a small amount of acetone until the mixture is homogenous and the acetone has evaporated.  The sample is then heated to 850-865 ^oC for ~36 hours with intermediate grinding before being pressed into pellets.  After sintering the pellets for 6-12 hours, the samples were slow cooled in air at 60^oC/hr.  Other cooling rates were studied as seen in Table 5.2, but slow cooling in air was the method typically used.  The crystal structure of Bi₂Sr₂CaCu₂O_8±x is shown is Illustration 5.1.

Table 5.2:      Cooling methods used to anneal samples of Bi₂Sr₂CaCu₂O_8±x.