While the term "metal" typically refers to an elemental substance, the material recognized for exhibiting the highest critical temperature for superconductivity is not a single elemental metal. Instead, it is a complex ceramic compound.
The superconductor with the highest critical temperature is generally understood to be a material comprising Mercury, Barium, Thallium, and Copper oxide. These components are found in various high-temperature superconducting (HTS) cuprates, which exhibit superconductivity at significantly higher temperatures than elemental metals or conventional alloys.
Understanding Critical Temperature
The critical temperature (Tc) is the specific temperature below which a material transitions into a superconducting state, characterized by zero electrical resistance and the expulsion of magnetic fields (Meissner effect).
- Elemental Metals: Superconductivity in elemental metals typically occurs at very low temperatures, often below 10 Kelvin (K). For example, Niobium (Nb) has the highest critical temperature among all elemental metals, at approximately 9.2 K. Lead (Pb) also superconducts at a relatively low 7.2 K.
- High-Temperature Superconductors (HTS): Materials that achieve superconductivity at significantly higher temperatures, often above 77 K (the boiling point of liquid nitrogen), are classified as high-temperature superconductors. These are predominantly complex ceramic compounds, especially those based on copper oxides (cuprates).
Materials with the Highest Critical Temperatures
The components mentioned—Mercury, Barium, Thallium, and Copper oxide—point to specific families of HTS materials known for their record-setting critical temperatures:
- Mercury-based Cuprates: Superconductors in this family, such as HgBa2Ca2Cu3O8+δ (commonly known as Hg-1223), hold the record for the highest critical temperature at ambient pressure. This material can reach up to 135 K. Under high pressure, its critical temperature can be further elevated, exceeding 160 K. These compounds typically contain Mercury, Barium, Calcium, Copper, and Oxygen.
- Thallium-based Cuprates: Another prominent family includes materials like Tl2Ba2Ca2Cu3O10+δ, which can achieve critical temperatures around 127 K. These compounds are composed of Thallium, Barium, Calcium, Copper, and Oxygen.
These complex oxide compounds, despite not being simple elemental metals, represent the pinnacle of critical temperature achievement in superconducting materials. Their discovery has been pivotal in advancing the field of superconductivity, opening possibilities for practical applications at more accessible temperatures.
