The measurements of the electrical resistivity and the low temperature heat capacity in the superconducting (La1-yMy)3S4 compounds with M = vacancy, Sc, Y, Ce, Lu, and Th were made in zero field and in magnetic fields up to 16 and 10 T, respectively. The optimum superconducting properties appear in the cubic La0.97Th0.03S1.333, which has ∼10% higher Tc and about a threefold higher Hc2(0) than the hypothetical values in the tetragonal LaS1.333. The relationship between Hc2(0) and Tc (i.e. Hc2(0) = C0Tc, where C0 = 1.96 and 1.32 T/K for the cubic and tetragonal phases, respectively ) is found in a series of La1-yMySx compounds. The high Hc2(0) values for the cubic compounds originate in the anomalously large values of the residual resistivity, which may reflect the instability of the cubic lattice.
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