Superconducting materials are materials with properties of zero resistance and repulsive magnetic field lines at a certain low temperature. Twenty-eight elements and thousands of alloys and compounds have been found to be superconductors. Superconducting materials can be divided into element materials, alloy materials, compound materials and superconducting ceramics according to their chemical composition.
1. Element materials
There are 28 elements with superconductivity under normal pressure, among which Nb has the highest Tc (9.26k). The main practical applications of electricians are niobium and lead (Pb, Tc=7.201K), which have been used to manufacture superconducting ac power cables, high-q resonators and so on.
2. Alloy materials
Superconducting elements can improve the overall properties of superconducting materials by adding some other elements as alloy composition. For example, the first application of niobium zirconium alloy (nb-75zr), its Tc is 10.8k, Hc is 8.7 t. Subsequently, niobium titanium alloy was developed. Although Tc was slightly lower, Hc was much higher and could carry a larger current in a given magnetic field. Its performance is nb-33ti, Tc= 9.3k, Hc = 11.0 t. Nb-60ti, Tc= 9.3k, Hc=12 t (4.2k). At present niobium titanium alloy is the main superconducting magnet material used in 7 ~ 8 special magnetic field. The properties of nb-60ti-4ta were further improved by adding tantalum ternary alloy, Tc = 9.9k and Hc= 12.4t (4.2k). The performance of nb-70ti-5ta is, Tc= 9.8k, Hc= 12.8t.
3. Compound materials
Superconducting elements often have excellent superconducting properties when combined with other elements. In the case of Nb3Sn, which has been widely used, Tc= 18.1k and Hc= 24.5t. Other important superconducting compounds are V3Ga, Tc= 16.8k, Hc=24 ts. Nb3Al, Tc= 18.8k, Hc=30 t.
4. Superconducting ceramics
In the early 1980s, miller and bednaulz began to notice that certain oxide ceramic materials might be superconductive. Their team tested some materials and found Tc=35K superconductivity in lanthanum-barium copper-oxide in 1986. In 1987, scientists from China, the United States, Japan and other countries found in barium-yttrium copper oxide that Tc in the liquid nitrogen temperature region has superconductivity, making superconducting ceramics become a promising superconducting material.
