BaAl4-type derivative structure in superconducting La–Pd–Ge system

There are many ternary intermetallic compounds with BaAl4-type and its derivative structures. LaPd2Ge2 is already known as one of the BaAl4-type superconductors with Tc of 1.12 K. We have synthesized a new intermetallic compound La3Pd4Ge4 with higher Tc of 2.75 K than that of LaPd2Ge2, which had the structure with the insertion of the AlB2-type layer in LaPd2Ge2. A detailed crystal structure analysis of La3Pd4Ge4 was carried out by neutron powder diffraction because it is useful to the analysis of small interplanar spacing. The neutron diffraction study indicates that La3Pd4Ge4 has U3Ni4Si4-type structure with a lower symmetry than that of LaPd2Ge2, and the typical interatomic distances of La3Pd4Ge4 are shorter than those of LaPd2Ge2. The coordination of Pd to three Ge in the AlB2-type layer of La3Pd4Ge4 is characteristic, which is not stabilized in other lanthanide-substituted intermetallics Ln3Pd4Ge4 (Ln = Y, Gd–Yb).