Vacancy effects on Tc in superconducting LaPt1-xSi(0 ≤ x ≤ 0.2)

As revealed in the powder X-ray diffraction and crystallographic data, the parent compound LaPtSi, which crystallizes in the LaPtSi-type structure (14(1)md), admits considerable vacancies up to 20% on the Pt sublattice while still retaining its tetragonal symmetry. The refined lattice parameters show that both the a-axis and the volume of the unit cell v contract clearly, though the c-axis exhibits less percentage change due to the existence of vacancies in the compound. These results are consonant with what one would expect from a chemical pressure effect. Magnetic and heat-capacity measurements demonstrate that the change in T-c, with x is similar to the change in the reduced lattice parameters a and v. It is found that the T-c change rate dT(c)/dx = -9.6 +/- 0.6 K and dT(c)/dv = 1.5 +/- 0.3 K/angstrom(3). (C) 2009 Elsevier B.V. All rights reserved.