The synthesis, crystal structure, and physical properties (magnetization, resistivity, heat capacity) in combination with theoretical calculations of the electronic structure and phonon properties are reported for intermetallic compounds LiPd2X (X=Si, Ge, and Sn). LeBail refinement of powder x-ray diffraction data confirms that all compounds belong to the Heusler family (space group Fm-3m, No. 225). The lattice parameter increases with atomic size of X, and its value varies from a=5.9059(4)Å for LiPd2Si and a=6.0082(3)Å for LiPd2Ge, to a=6.2644(1)Å for LiPd2Sn. The first compound, LiPd2Si, has apparently not been previously reported. All measured quantities demonstrate that LiPd2Ge exhibits superconductivity below Tc=1.96K and the normal- and superconducting-state data indicate that it is a weak-strength type-I superconductor (C/γTc=1.38) with electron-phonon coupling constant λe-p=(0.53-0.56). LiPd2Si and LiPd2Sn are not superconducting above 1.68 K. The experimental observations are supported by theoretical calculations which show that LiPd2Ge has the highest computed λe-p and Tc of the group. A strong softening of the acoustic phonon mode is calculated, and in the case of X=Ge and Sn, imaginary phonon frequencies were computed. The soft mode is most pronounced in the case of LiPd2Ge, which suggests its correlation with superconductivity.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics