Comparison between layering NbSe2 and rod characteristic of MgB2 by investigation of elastic constants

Although the delicate balancing of strong anisotropy, CDW- order “TCDW=33 K” and finally emerging superconductivity at “Tc= 7.2 K” are the most intriguing question in characteristic behavior of NbSe2, but the original... [ view full abstract ]

Although the delicate balancing of strong anisotropy, CDW- order “T_CDW=33 K” and finally emerging superconductivity at “T_c= 7.2 K” are the most intriguing question in characteristic behavior of NbSe₂, but the original mechanism of MgB₂ old superconductor, which has unlike the cuprates a lower anisotropy and larger coherence length of the grain boundary to current flow is still unknown. Since the cause and the mechanism of band- effect of these two original layering- structures on bond- rupturing- atomic positions are unknown, here the stability of crystalline structure of interatomic potential through the elasticity-compressibility is investigated. The investigations are based on the presented different stiffness of two elements of the same column “Be” and “Mg” (table1). Whereas the direction of the semi-metallic bonding of “Be” is the cause of the quasi- two- dimension metallic surface state of Be, the MgB₂ could be formed as rod- and wiring- shape unlike the NbSe₂ which is to be layered. Relative to layering of low T_c=0.7 of BeB_2, as it’s presented by others, high T_c=40 of MgB₂ is decreased by external pressure, while, low T_c=7.2 of NbSe₂ is increased up to critical pressure P_c=10 (GPa) and then decrease. Therefore, the difference between layering character of NbSe₂ and rod-formation character of MgB₂ superconductors could be the intriguing question.

The directional bond formation or a strong anisotropy of different “B-B” length do to smaller- intro- layer to the inter-layer distance of “B-B” could be the cause where we are following characteristic behavior of MgB₂ for the cause of direction rod/wire character.

Insignificancy of T_c=0.7 in BeB₂ is surprisingly in a challenge which could be due to its layering- character- formation as its common feature with NbSe₂. Consequently, in order to clear out the strong difference between the layering of NbSe₂ and domination of rod-character resulted to all about similarity consideration simultaneously the both stability of crystal structure through the cohesive energy c/a(fig1), c_zz(Fig2) and c₃₃(table2) are investigated. The proposed investigations are more evidence on different characteristic behavior of calculated parameters.