Superconductivity of lanthanum intermetallic compounds with the Cu 3Au structure

Abstract

Studies have been made of the crystal structure, metallurgical properties, and superconducting critical temperature of intermetallic compounds of lanthanum of the composition La X 3, where X is tin, lead, thallium, and indium. These compounds are all congruently melting and single crystals of the indium and tin compounds have been prepared. X-ray measurements on carefully electropolished surfaces indicate that these compounds have the ordered Cu 3Au crystal structure. The tin, lead, and thallium compounds were found to be superconducting with critical temperatures of 6·45, 4·05, and 1·57°K, respectively. The indium compound was not superconducting above 1°K. The critical temperatures do not appear to be related to interatomic spacing in the compounds but rather seem to depend upon the valence of the element at the X sites. The compounds of lead and tin (quadrivalent elements) have the higher T c 's. The compounds of thallium and indium (trivalent elements) have the lower T c 's.