The following tables list superconducting properties of elements, compounds, and alloys (“low-temperature superconductors”). The extensive series of cuprates and iron-based compounds (“high-temperature superconductors”) are listed separately in this section. Individual tables are also given here for thin films, elements under high pressures, and for the critical magnetic fields of selected compounds and alloys.
The historically first observed and most distinctive property of a superconductor is its total loss of electrical resistance at some critical temperature Tc, which is characteristic of each material. Figure 1(a) schematically illustrates two possible superconducting transitions. The temperature interval ΔTc over which the transition between the normal and superconducting states takes place may be of the order of as little as 10–5 K or as much as several kelvin, depending on the material. The sharp vertical discontinuity in resistance is indicative of that observed in a single crystal of a pure element. The broad transition suggests the shape seen for materials that are strained or inhomogeneous. Careful testing of the upper resistivity limit for the fully superconducting state has shown it to be less than 4 × 10–23 Ω cm. This is at least 1017 times less resistive than copper at room temperature — comparable to the difference in resistivity between copper and glass.
The defining property of a superconductor, however, that distinguishes it from a notional perfect conductor, is its perfect diamagnetism: a superconducting body expels a magnetic field from its interior. A Type I superconductor expels a magnetic field up to some critical field Bc, whereupon it reverts to the normal state as shown in the B-T phase diagram of Figure 1(b). A Type II superconductor, in contrast, passes from the perfect diamagnetic state to a mixed state at a lower critical field Bc1 before attaining the normal resistive state at an upper critical field Bc2 as shown on the magnetization curve of Figure 1(c). In the mixed state between Bc1 and Bc2, regions of normal material exist within the superconducting matrix, allowing the penetration of quantized magnetic flux through the body. The number of flux lines present increases in proportion to the applied field B until at Bc2 the flux line density has become so large as to drive the entire volume of the superconducting body normal. This gradual penetration of magnetic flux enables the superconductivity to persist to much higher fields than it otherwise would. This property of Type II superconductors has enabled the development, half a century after their discovery, of technologically relevant superconducting materials. Tables 5 and 6 list some of the available critical field data of Type II materials.
The great majority of superconducting materials are Type II. The elements in pure form — with the exception of vanadium, niobium, technetium, and protactinium — as well as a very few precisely stoichiometric and well-annealed compounds, such as TaSi2, Bi2Pt, boron-doped SiC, and SnAs, are Type I.
Metallurgical Aspects
Superconducting properties are very sensitive to the material state, and this sensitivity has been used in a reverse sense to study and specify the detailed state of alloys. The mechanical state, the homogeneity, and the presence of impurity atoms and other electron-scattering centers are all capable of influencing the critical temperature and the current-carrying capability in magnetic fields. This sensitivity underlines a general problem in the tabulation of properties for superconducting materials. The occasional divergent values of the critical temperature or critical fields quoted for a Type II superconductor may lie in the variation in sample preparation. Critical temperatures of materials studied early in the history of superconductivity must be evaluated in light of the probable metallurgical state of the material, as well as the availability of less pure starting elements.
These tables are based on the original work by L. I. Berger and B. W. Roberts and are compiled from a large number of sources spanning the primary literature. Individual references for each datum are too numerous to list. Secondary sources, as listed under the references, have been used to ensure the accuracy and completeness of the work.
FIGURE 1. Physical properties of superconductors. (a) Resistivity vs. temperature for a pure and perfect lattice (solid line); impure and/or imperfect lattice (broken line). (b) Magnetic-field temperature dependence for Type I superconductors. (c) Schematic magnetization curve for Types I and II superconductors.
Symbols in tables: Tc: Critical temperature; Ho: Critical magnetic field in the T = 0 limit; θD: Debye temperature; and γ: Electronic-specific heat.
Element | Tc/K | Bo/mT | θD/K | γ/mJ mol–1K–1 |
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Al | 1.175 ± 0.002 | 10.49 ± 0.03 | 420 | 1.35 |
Am (α) | 0.79 | |||
Am (β) | 1.1 | |||
Be (α) | 0.026 | 1390 | 0.21 | |
Cd | 0.517 ± 0.002 | 2.8 ± 0.1 | 209 | 0.69 |
Ga (α) | 1.083 ± 0.001 | 5.83 ± 0.02 | 325 | 0.60 |
Ga (β) | 5.9, 6.2 | 56 | ||
Ga (γ)* | 7 | 95 | ||
Ga (Δ)* | 7.85 | 81.5 | ||
Hf (α) | 0.128 | 1.27 | 256 | 2.21 |
Hf (β) | 0.506 | |||
Hg (α) | 4.154 ± 0.001 | 41.1 ± 0.2 | 87, 71.9 | 1.81 |
Hg (β) | 3.949 | 33.93 | 93 | 1.37 |
In | 3.4087 ± 0.001 | 28.15 ± 0.2 | 109 | 1.672 |
Ir | 0.1125 ± 0.001 | 1.600 ± 0.005 | 425 | 3.19 |
La (α) | 4.88 ± 0.02 | 80 ± 1 | 151 | 9.8 |
La (β) | 6.00 ± 0.1 | 109.6, 160 | 139 | 11.3 |
Li | 0.0004 | |||
Lu (α) | 0.1 ± 0.03 | 35 ± 5 | 210 | 10.2 |
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