Superconductivity of various borides: The role of stretched c-parameter

Authors

Monika Mudgel, National Physical Laboratory India
V P. Awana, National Physical Laboratory, New Delhi
H Kishan, National Physical Laboratory, New Delhi, India
I Felner, Hebrew University of Jerusalem
Gustavo A. Alvarez, University of WollongongFollow
G L. Bhalla, National Physical Laboratory, New Delhi, India

RIS ID

32374

Publication Details

Mudgel, M., Awana, V. P., Kishan, H., Felner, I., Alvarez, G. A. & Bhalla, g. v. (2009). Superconductivity of various borides: The role of stretched c-parameter. Journal of Applied Physics, 105 (7), 07E313-1-07E313-3.

Abstract

The superconductivity of MgB₂, AlB₂, NbB_2+x, and TaB_2+x is intercompared. The stretched c-lattice parameter (c = 3.52 Å) of MgB₂ in comparison to NbB_2.4 (c = 3.32 Å) and AlB₂ (c = 3.25 Å) decides empirically the population of their π and σ bands and as a result their transition temperature T_c values, respectively, at 39 and 9.5 K for the first two and no superconductivity for the later. The nonstoichiometry induces an increase in c parameter with Boron excess both in NbB_2+x and TaB_2+x. Magnetization (M-T) and resistivity measurements (ρ-T) in case of niobium boride samples show the absence of superconductivity in stoichiometric NbB₂ sample (c = 3.26 Å) while a clear diamagnetic signal and a ρ = 0 transition for boron excess NbB_2+x samples. On the other hand, superconductivity is not achieved in TaB_2+x case. The probable reason behind is the comparatively lesser or insufficient stretching of c parameter.