Abstract
The possibility to the superconducting state transition at temperatures close to room temperature for nanoscale crystals of bismuth and antimony semimetals, as well as their alloys is discussed. All physical reasoning, as well as the estimates given in the paper, are based on the classical thermodynamics laws, as well as on the quantum theory of superconductivity (BCS theory) conclusions, which is based on the idea of electrons pairing (the Cooper pairs formation) as a result of electron-phonon interaction.It is shown that in nanocrystalline particles internal capillary compressive stresses act, the magnitude of which is sufficient for the transformation of semimetals into metals. This transition is accompanied by a change in the energy spectrum of electrons: non-degenerate semiconductors become metals in which the gas of degenerate electrons is characterized by a low Fermi energy. The latter circumstance causes an increase in the density of electronic states and enhances the electron-phonon interaction in metallized semimetals.As the initial chemical elements from which superconducting compounds can be synthesized under pressure, substances that allow the collectivization of electrons can be used. The most suitable substances for this are elements of the fifth group of the periodic system Bi, Sb, As, graphite, etc. They are characterized by a slight overlap of the valence and conduction zones, which leads, on the one hand, to the fact that they remain high conductors of electricity up to the absolute zero temperature, and on the other hand, they have a significantly lower density of charge carriers compared to metals.In addition, a specific structural state is formed in bismuth and antimony alloys at certain concentrations, which leads to a change in the nature of the phonon spectrum (the number of high-frequency phonons increases), which also enhances the electron-phonon interaction.All these changes in the energy spectrum and structural state of semimetals make it possible for nanocrystals to transition to the superconducting state at a temperature of 300K.
Highlights
It has been reliably established that lowdimensional crystalline particles, the size of which is characterized by an interval of values R≈10–100nm, possess physical properties that are fundamentally different from the properties of their bulk analogues
Nano-sized (10 – 100 nm) crystalline particles of semimetals can spontaneously transform into a "metallized" state under the influence of internal capillary pressure
The energy spectrum of electrons formed under the capillary pressure in these objects is characterized by the appearance of a "gas" of "degenerate" electrons obeying the Fermi – Dirac quantum statistics
Summary
It has been reliably established that lowdimensional crystalline particles, the size of which is characterized by an interval of values R≈10–100nm (nano crystals), possess physical properties that are fundamentally different from the properties of their bulk analogues. Substituting in the formula (7) the numerical values of the constants һ and m, as well as the values of r and (N ∕ V), we have, respectively, for Bi and Sb: Р ≈ Ра and Р ≈ Ра This estimate indicates that the internal capillary pressure acting on semimetal nanocrystals is sufficient for these objects to “metallize” and to realize specific changes in the structure of the electron energy spectrum. If for most ordinary metals that conduct electricity well (Cu, Au, Al, etc.), the Fermi energy is characterized by an interval of values (5 – 10 ) eV, in the case of semimetals with artificially “collectivized” electrons, the average Fermi energy is ≈ 10 –2 eV, i.e. more than two orders of magnitude less This circumstance is the basis for the validity of the assertion that in the objects under discussion the electron pairing constant λ, which is the determining parameter in the BCS quantum theory of superconductivity, is characterized by λ >> 1. The following paragraph of this paper is devoted to the discussion of this possibility
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