Superconductivity in Ternary Rare Earth Transition Metal Silicides and Germanides with the Sc sub 5 Co sub 4 Si sub 10 -Type Structure

摘要

Low temperature heat capacity measurements indicate the presence of a complicated phonon density of states in these structurally complex compounds. A better description of the phonon spectrum of the high-T/sub c/ materials, Sc sub 5 Rh sub 4 Si sub 10 , Sc sub 5 Ir sub 4 Si sub 10 , and Y sub 5 Os sub 4 Ge sub 10 , is presented and discussed. The large values of delta C/ gamma /sub n/T/sub c/ and the electron-phonon coupling constant for these high T/sub c/ compounds indicate that they are strong-coupled superconductors. Dc electrical resistivity measurements on these compounds show resistivity behaviors deviating from those exhibited by simple metals. The rho(T) data for Y sub 5 Ir sub 4 Si sub 10 , Lu sub 5 Rh sub 4 Si sub 10 , Lu sub 5 Ir sub 4 Si sub 10 , and Y sub 5 Os sub 4 Ge sub 10 , indicate anomalies. Static molar magnetic susceptibility measurements performed on these compounds indicate a small effective magnetic moment of 0.26 mu /sub B/ on the Co atom and anomalous behaviors in the Lu sub 5 Rh sub 4 Si sub 10 , Lu sub 5 Ir sub 4 Si sub 10 , Y sub 5 Ir sub 4 Si sub 10 , Lu sub 5 Ir sub 4 Ge sub 10 , and Y sub 5 Rh sub 4 Ge sub 10 data. The formation of a charge- or spin-density wave may be causing the anomalous behaviors in both resistivity and susceptibility. Upper critical magnetic field measurements were performed on Sc sub 5 Co sub 4 Si sub 10 , Sc sub 5 Rh sub 4 Si sub 10 , Sc sub 5 Ir sub 4 Si sub 10 , Lu sub 5 Rh sub 4 Si sub 10 , Lu sub 5 Ir sub 4 Si sub 10 , and Y sub 5 Os sub 4 Ge sub 10 . Y sub 5 Os sub 4 Ge sub 10 exhibits very high values for (-dH/sub c2//dT)/sub Tc/ = 10.2 kOe/K and H/sub c2/(0) = 60.4 kOe. Comparing the value of (-dH/sub c2//dT)/sub Tc/ gained from the fit of the data to the WHH theory to the calculated (-dH/sub c2//dT)/sub Tc/ yields various degrees of agreement for these compounds. There seems to be little or no Pauli limiting and the spin-orbit effect appears to be negligible. (ERA citation 11:051432)