Impact of Varying Nb Content on Conventional Superconductivities in Nb-Si Systems

Due to the superior properties of niobium silicon-based alloy materials, we systematically studied the structural stability, electronic properties and the relationship between Nb concentration and superconductivity of binary Nb-Si system under pressures below 40 GPa. We have identified three stable structures Nb5Si3, NbSi2 and Nb3Si, that have been experimentally confirmed under ambient pressure, as well as a new ground state stable structure Nb3Si2 above 37 GPa. Electronic structure calculations reveal that all the compounds are metallic. Furthermore we calculated the superconductivity transition temperatures of Nb3Si, gamma-Nb5Si3, NbSi2, and Nb3Si2 at ambient pressure, finding that the critical temperature is closely related to the Nb-d states at the Fermi level and the vibration of Nb atoms. The calculated result of Nb3Si (TC=17.8 K) is in accordance with experimental observations, and the critical temperatures of gamma-Nb5Si3 and Nb3Si2 are 7.7 K and 3.8 K respectively. In addition, we observed that the phase with a higher superconducting temperature tends to appear in compounds with higher Nb content. This may provide valuable insights into the influence of different structures and chemical compositions on superconducting performance, offering guidance for the design and synthesis of novel superconducting materials.