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Home / Academics / Division of Math & Science / Faculty / Christopher Jones / Dissertation / Chapter 1-Section 5.1

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

The Bi2Sr2Can-1CunO2n+4 superconductor series was first discovered in 1988.112 Of the three main phases, the Bi2Sr2CaCu2O8x is the most studied phase since it is the easiest to produce in single phase. While Bi2Sr2CaCu2O8x 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 60oC/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 Bi2Sr2CaCu2O8x is shown is Illustration 5.1.

Precursors

# of moles of Precursors

Mass

Bi2O3

1 mole

9.3192 grams

SrCO3

2 moles

5.3146 grams

CaCO3

1 mole

2.4022 grams

CuO

2 moles

3.1816 grams

Table 5.1: Stoichiometric amounts of metal precursors are used to make the Bi2Sr2CaCu2O8 superconductor.

Cooling

Method

Resistivity

at 25oC

Tc

(onset)

Tc

(zero)

Quenched in liquid nitrogen

1.8 x 104 mW-cm

96 K

48 K

Cooled in flowing O2

1.0 x 104 mW-cm

96 K

67 K

Slow cooled in air

2.3 x 103 mW-cm

73 K

60 K

Table 5.2: Cooling methods used to anneal samples of Bi2Sr2CaCu2O8x.

Crystal structure of Bi2Sr2CaCu2O8±x where the layers contain a) calcium, b) copper-oxide, c) strontium-oxide, and d) bismuth-oxide.

Illustration 5.1: Crystal structure of Bi2Sr2CaCu2O8x where the layers contain a) calcium, b) copper-oxide, c) strontium-oxide, and d) bismuth-oxide.

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Updated on: April 15, 2010 8:26 PM