SYNTHESIS, STRUCTURES AND PROPERTIES OF CUBIC R(3)IN AND R(3)INZ PHASES (R=Y, LA, Z=B, C, N, O) - THE EFFECT OF INTERSTITIAL-Z ON THE SUPERCONDUCTIVITY OF LA3IN

Samples of La3In, Y3InCx and La(3)InZ(x) for 0.3 less than or equal to x less than or equal to 1.5, Z = C and O, La3InBx for 0.7 less than o r equal to x less than or equal to 1.5, and La3InN were synthesized in welded Ta containers by powder sintering, fusion and annealing techni ques. Y3In and La3Ga could not be obtained. All of the R(3)InZ(x) exam ples were single phase between x approximate to 0.3-0.5 and x approxim ate to 1.0 and had the inverse perovskite structure (stuffed Cu3Au). S ingle crystal refinements for Y3InC and La3InN confirmed the type and stoichiometry (<Pm(3)over bar m>, a = 4.9023(7) Angstrom, 5.102(1) Ang strom, and R(F)/R(w) = 1.1/1.3%, 2.2/2.4% respectively). Magnetic susc eptibilities measured for both normal and superconducting states showe d T-c approximate to 10 K and 10(chi RT)(4) approximate to 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 Y3InC, La3In C and La3InN parallels their 10(chi RT)(4) values of less than or equa l to 2 emu mol(-1); the temperature dependencies of chi for these were also notably less than for the superconductors. These last phases are also more brittle. Extended Huckel band calculations indicated apprec iable In and B (La-In and La-B) contributions at E(F) for La3InB. Ther eafter, the La-Z bonding states rapidly fall in energy as does the amo unt of La-In bonding at E(F), the last returning somewhat with the ele ctron-richest oxygen interstitial. The decrease in T-c with increasing x in La3InCx parallels a decrease in densities-of-states at E(F).