RESUMO
A systematic investigation on the thermodynamic properties of La-based ternary intermetallic superconductors crystallizing in a U(3)Ni(4)Si(4)-type structure is presented. The U(3)Ni(4)Si(4)-type structure consists of a characteristic intergrowth of periodic BaAl(4) (ThCr(2)Si(2))- and AlB(2)-type segments. Pristine low temperature specific heat data for recently discovered members La(3)Ni(4)Si(4) and La(3)Ni(4)Ge(4) with T(c)s of 1.0 and 0.7 K, respectively, are presented as well as La(3)Pd(4)Ge(4) with the highest T(c) of 2.5 K in the U(3)Ni(4)Si(4)-type group. Owing to the higher T(c)s of U(3)Ni(4)Si(4)-type superconductors than the related ThCr(2)Si(2)-type compounds, comparisons are drawn in our investigations of the ternary intermetallics of LaPd(2)Ge(2), LaNi(2)Si(2), and LaNi(2)Ge(2) having a ThCr(2)Si(2)-type structure. Our investigations of the thermodynamic properties show that La(3)Ni(4)Si(4) and La(3)Ni(4)Ge(4) have higher values of γ(n), N(E(F)), and Θ(D) than La(3)Pd(4)Ge(4). The same trend was found in ThCr(2)Si(2)-type compounds of LaPd(2)Ge(2), LaNi(2)Si(2), and LaNi(2)Ge(2). It turns out that the difference in T(c) between La(3)Pd(4)Ge(4), La(3)Ni(4)Si(4), and La(3)Ni(4)Ge(4), as well as the relatively higher T(c) of the U(3)Ni(4)Si(4)-type superconductors than of the related ThCr(2)Si(2)-type compounds, are largely due to the strength of electron-phonon coupling.
