Study of the superconducting properties of the new intermetallic compound Zr1-xNb(x)B(2)

摘要

In this paper we report on the synthesis and the structural, electrical, magnetic and thermal analysis for the new material Zr1-xNbxB2 (0.01 <= x <= 0.05). A superconducting transition was observed for all x values studied, despite the non-superconducting matrix ZrB2, which indicates that the superconducting state is induced by the presence of Nb. The results show that the critical temperature increases with Nb content, reaching its maximum (T-c = 8.1 K) for x = 0.04. From the specific heat data we find a Sommerfeld constant of gamma = 1.6 mJ molK(-2) and a Debye temperature of theta(D) = 615.5 K. Unconventional behaviors are observed in specific heat dependence with temperature and in H-c1(T) diagram. These behaviors are investigated in C-e/T versus T curve, where an upturn appears for T < 2.3 K, and in ln (C-e/gamma T-c) versusT(c)/T dependence, which shows a clear deviation from BCS theory for low temperatures. Also, contrary to the conventional theories we found a positive curvature for temperatures near T-c in the lower critical field, besides an upturn around 2.3 K. We suggest that these behaviors possibly arise from multiband superconductivity in Zr0.96Nb0.04B2.