Structure and superconductivity of the ternary intermetallics of La3Ni4Si4, La3Ni4Ge4, and La3Pd4Si4

Ternary intermetallics of La3Ni4Si4, La3Ni4Ge4, and La3Pd4Si4 have been prepared by arc melting. These compounds take a body-centred lattice with an orthorhombic unit cell. The crystal structure of these compounds is U3Ni4Si4 type with the space group Immm, consisting of the combination of structural units of AlB2-type and BaAl4-type layers, as observed for La3Pd4Ge4. DC magnetization and electrical resistivity measurements indicate that La3Pd4Si4 is a type II superconductor with a critical temperature (Tc) of 2.15 K. The lower critical field Hc1(0) is estimated to be 28 Oe. On the other hand, the upper critical field Hc2(0) estimated by the WHH theory is 2.2 kOe. The coherence length ξ(0) of 38 nm and the penetration depth λ(0) of 376 nm are derived. The other compounds La3Ni4Si4 and La3Ni4Ge4 do not show superconductivity above 1.8 K