Superconductivity is a fascinating phenomenon that has captivated scientists and engineers for over a century. It refers to the property of certain materials to conduct electricity with zero resistance and perfect efficiency when cooled below a critical temperature. This property has led to numerous applications, from powerful magnets in particle accelerators to high-speed trains, medical imaging devices, and power grids. In this article, we will explore the fundamentals of superconductivity, the types of Superconducting Materials, and their current and potential applications.
Superconductivity was first discovered in 1911 by Heike Kamerlingh Onnes, a Dutch physicist, who observed that mercury's electrical resistance disappeared when cooled to very low temperatures. This effect was later found in other metals, alloys, and compounds, leading to the identification of several key features of superconductivity. One of the most important characteristics of superconducting materials is the Meissner effect, which describes their ability to expel magnetic fields from their interior when cooled below the critical temperature. This effect is caused by the formation of Cooper pairs, which are pairs of electrons that interact through phonons, the vibrations of the material's crystal lattice. Cooper pairs have a net spin of zero and can move through the material without experiencing resistance or collisions with other particles. When a magnetic field is applied to a superconductor, it disrupts the formation of Cooper pairs, causing them to break apart and generate eddy currents that produce an opposite magnetic field. As a result, the superconductor repels the external field and creates a shielded region of zero field. The critical temperature (Tc) is another crucial parameter of superconductivity, as it determines the maximum temperature at which the material can exhibit zero resistance. For many years, the highest Tc achieved was around 23 K (-250°C) for niobium-titanium alloys, limiting the practical applications of superconductors to low-temperature environments. However, in 1986, a breakthrough discovery by Georg Bednorz and Alex Müller at IBM led to the discovery of high-temperature superconductivity (HTS) in copper-based oxides, with Tc values exceeding 90 K (-180°C). This finding opened up new possibilities for using superconductors at higher temperatures and stimulated research into the underlying mechanisms of HTS. Superconducting Materials can be classified into two main categories: Type I and Type II superconductors. Type I superconductors are characterized by a single critical field (Hc) at which they transition from the superconducting to the normal state. They have a Meissner state up to Hc and a mixed state above Hc, where magnetic flux penetrates the material in the form of quantized vortices. Type I superconductors are usually made of pure metals, such as mercury, lead, or aluminum, and have low Tc values (<10 K)
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