Lattice Instability of High-Transition-Temperature Superconductors. I. Polycrystalline A − 15 Compounds

摘要: The $A\ensuremath{-}15$ ($\ensuremath{\beta}$-tungsten) structure compounds ${\mathrm{Nb}}_{3}$Sn, ${\mathrm{Nb}}_{3}$Al, ${\mathrm{Nb}}_{3}$Ga, ${\mathrm{V}}_{3}$Si, and ${\mathrm{V}}_{3}$Ga, which are all superconducting above 14\ifmmode^\circ\else\textdegree\fi{}K, have been found to exhibit elastic softening on cooling. anomalous temperature dependence of the moduli disappears in state. This unusual behavior does not occur for isostructural ${\mathrm{V}}_{3}$Ge ${\mathrm{Nb}}_{3}$Ge, comparatively low transition temperatures (${T}_{c}\ensuremath{\sim}5\ensuremath{-}7\ifmmode^\circ\else\textdegree\fi{}$K).