Superconductivity of MgB₂in the BCS framework with emphasis on extrinsic effects on critical temperature

Abstract

The discovery of superconductivity in MgB2 with an unusually high TC of 39 K interested material scientists all over the world. Many of its superconducting properties, including an experimentally observed double energy gap, differ significantly with those of conventional LTS and HTS. Many scientists proposed exotic and unconventional mechanisms to explain the superconductivity in MgB2, but after more than 5 years it is now accepted that MgB2 is a BCS type superconductor with exceptionally high TC. In this review we discuss qualitatively the origin of superconductivity in MgB2 based on both experimental and theoretical results. The variation of TC of MgB2 with various processes, such as irradiation of high energy ions, doping and external pressure, etc., is discussed and reviewed. TC of MgB2 decreases upon irradiation, by applying external pressure and by most of the doping. The reduction of density of states at the Fermi level, increased band scattering and changes in the phonon frequencies are the main factors which reduce the TC under these conditions.

Structural and thermodynamic properties of compounds in the Mg–B–C system from first-principles calculations

“…In a system with a volume, V, at temperature, T, the Helmholtz free energy F(V,T) per atom [12][13][14] can be approximated as FðV; TÞ ¼ E c ðVÞ þ F ph ðV; TÞ þ F el ðV; TÞ; (1) where, in the framework of first-principles calculations, E c is the 0-K static total energy, F ph the vibrational free energy of the lattice atoms, and F el the thermal electronic contribution. Nowadays the 0-K static total energy, E c , can be calculated routinely when the structure and lattice parameter of the compound are known.…”

“…Doping is an important method to improve the technical performance of the MgB 2 superconductor [1], which was discovered in 2001 [2] to have a critical transition temperature of 39 K. For example, doping carbon into MgB 2 can dramatically increase upper critical magnetic field at the cost of lowering T c [3] In the Mg-B-C system, there are six binary compounds (MgC 2 , Mg 2 C 3 , MgB 2 , MgB 4 , MgB 7 , and B 4 C) and one ternary compound (MgB 2 C 2 ) reported in the literature [4][5][6][7]. However, there are very limited thermochemical data for these compounds, especially for MgB 2 C 2 .…”

Influence of nanoparticle doping on electronic properties of MgB2bulk samples

“…Superconducting-and normal-state properties of MgB 2 were found to be strongly influenced by its multiband-band electronic structure -that can be approximated by one quasi-2D σ band and one 3D π band with different energy gaps -and the consequent intraband and interband scattering mechanisms [1][2][3][4]. Doping with different elements or compounds [2,3,5] is the most promising solution for a controlled disorder introduction inside MgB 2 that, affecting both intraband and interband scattering processes, changes its superconducting and normal-state properties and allows the production of more and more competitive material.…”

“…Superconducting-and normal-state properties of MgB 2 were found to be strongly influenced by its multiband-band electronic structure -that can be approximated by one quasi-2D σ band and one 3D π band with different energy gaps -and the consequent intraband and interband scattering mechanisms [1][2][3][4]. Doping with different elements or compounds [2,3,5] is the most promising solution for a controlled disorder introduction inside MgB 2 that, affecting both intraband and interband scattering processes, changes its superconducting and normal-state properties and allows the production of more and more competitive material. The best results in the enhancement of critical parameters such as the upper critical field (B c2 ) and the critical current density (J c ) as well as in the reduction of the material intrinsic anisotropy were obtained with pure carbon [6][7][8][9][10][11][12] as well as with organic (carbohydrates [13][14][15]) and carbonaceous inorganic compound (SiC, B 4 C [9,10,[16][17][18]) doping but also additions of different metallic elements were successfully attempted [19][20][21][22][23][24].…”

Superconductivity of Ca2InN with a layered structure embedding an anionic indium chain array

“…The obtained  and  values were 4.24 mJ/mol K 2 and 1.39 mJ/mol K 4 ) was 2.85 mJ/mol K. The Debye temperature (Θ D ) is estimated as 322 K by using:…”