As revealed in the powder X-ray diffraction and crystallographic data, the parent compound LaPtSi, which crystallizes in the LaPtSi-type structure (I41md), admits considerable vacancies up to 20% on the Pt sub-lattice while still retaining its tetragonal symmetry. The refined lattice parameters showed that both the a-axis and the volume of the unit cell v contract clearly, though the c-axis exhibited less percentage change due to the existence of vacancies in the compound. These results were consonant with what one would expect from a chemical pressure effect. Magnetic and heat-capacity measurements demonstrated that the change in Tc with x was similar to the change in the reduced lattice parameters a and v. It was found that the Tc change rate dTc/dx = −9.6K and dTc/dv = 1.5K/Å3.

Vacancy Effects on Tc in Superconducting LaPt1−xSi (0 ≤ x ≤ 0.2). W.H.Lee, H.H.Sung, K.J.Syu, J.Y.Chen: Physica C, 2010, 470[1], S774-5