Crystal structure and superconductivity in the Th-doped LaPtSi compounds

Abstract

As observed with X-ray powder diffraction, the tetragonal structure of the parent compound LaPtSi, which crystallizes in the LaPtSi-type structure with space group I41md, is retained in (La1−xThx)PtSi up to the solubility limit near x=0.5. By considering the size factor of Hume–Rothery theory of alloy phase formation, it is not marvelous that the extensive solid solutions cannot be fully completed in (La1−xThx)PtSi. We present the room temperature powder X-ray diffraction patterns, the room temperature lattice parameters and the dc magnetic susceptibility between 1.8 and 4.0K for three single phase polycrystalline samples in (La1−xThx)PtSi with x=0, 0.25 and 0.50. The refined lattice parameters show that both the a-axis and the volume of the unit cell v contract clearly, though the c-axis gives a less percentage expansion due to doping with thorium. It is found that the change in Tc with x is similar to the change in the lattice parameter a or v, which indicates that the stiffening of the lattice under pressure has a dominant effect on the decrease in Tc in this system.