Synthesis, structures and properties of cubic R 3In and R 3InZ phases (R = Y, La; Z = B, C, N, O) : The effect of interstitial Z on the superconductivity of La 3In

Abstract

Samples of La 3In, Y 3InC x and La 3InZ x for 0.3 ⩽ x ⩽ 1.5 , Z = C and O, La 3InB x for 0.7 ⩽ x ⩽ 1.5, and La 3InN were synthesized in welded Ta containers by powder sintering, fusion and annealing techniques. Y 3In and La 3Ga could not be obtained. All of the R 3InZ x examples were single phase between x ≈ 0.3–0.5 and x ≈ 1.0 and had the inverse perovskite structure (stuffed Cu 3Au). Single crystal refinements for Y 3InC and La 3InN confirmed the type and stoichiometry ( Pm¯3 m, a = 4.9023(7)A˚, 5.102(1)A˚, and R(F)/R w = 1.1/1.3%, 2.2/2.4% respectively). Magnetic susceptibilities measured for both normal and superconducting states showed T c ≈ 10K and 10 4χ RT ≈ 4 emu mol −1 were retained through the B and O series, with some enhancement of density and supercurrent shielding for B and a reduction of both for O. The absence of superconductivity (greater than 2 K) for Y 3InC, La 3InC and La 3InN parallels their 10 4χ RT values of less than or equal to 2 emu mol −1; the temperature dependencies of χ for these were also notably less than for the superconductors. These last phases are also more brittle. Extended Hu¨ckel band calculations indicated appreciable In and B (La In and La B) contributions at E F for La 3InB. Thereafter, the La Z bonding states rapidly fall in energy as does the amount of La In bonding at E F, the last returning somewhat with the electron-richest oxygen interstitial. The decrease in T c with increasing x in La 3InC x parallels a decrease in densities-of-states at E F.