Date of Award
Doctor of Philosophy
Physics and Astronomy
A systematic study of the superconducting and normal state properties of some ternary rare earth transition metal silicides and germanides of the Sc(,5)Co(,4)Si(,10)-type is reported in this work. 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(,c) materials, Sc(,5)Rh(,4)Si(,10), Sc(,5)Ir(,4)Si(,10), and Y(,5)Os(,4)Ge(,10), given by a model proposed by Junod et al.('1), is presented and discussed. The large values of (DELTA)C/(gamma)(,n)T(,c) and the electron-phonon coupling constant for these high T(,c) compounds indicate that they are strong-coupled superconductors. Relative to other ternary superconductors, many of these materials have large Debye temperatures. The BSC theory does not seem to afford an adequate description of the supercon- ducting state in these compounds;DC electrical resistivity measurements on these compounds show resistivity behaviors deviating from those exhibited by simple metals. The (rho)(T) data for Y(,5)Ir(,4)Si(,10), Lu(,5)Rh(,4)Si(,10), Lu(,5)Ir(,4)Si(,10), and Y(,5)Os(,4)Ge(,10), indicate the presence of anomalies;Static molar magnetic susceptibility measurements performed on these compounds indicate (1) a small effective magnetic moment of 0.26(mu)(,B) on the Co atom and (2) anomalous behaviors in the Lu(,5)Rh(,4)Si(,10), Lu(,5)Ir(,4)Si(,10), Y(,5)Ir(,4)Si(,10), Lu(,5)Ir(,4)Ge(,10), and Y(,5)Rh(,4)Ge(,10) data. It is suggested that the same mechanism, namely, the forma- tion of a charge- or spin-density wave, is causing the anomalous behaviors in both the resistivity and susceptibility data;Lastly, upper critical magnetic field measurements were performed on Sc(,5)Co(,4)Si(,10), Sc(,5)Rh(,4)Si(,10), Sc(,5)Ir(,4)Si(,10), Lu(,5)Rh(,4)Si(,10), Lu(,5)Ir(,4)Si(,10), and Y(,5)Os(,4)Ge(,10). Relative to the other five samples, Y(,5)Os(,4)Ge(,10) exhibits very high values for (-dH(,c2)/dT)(,Tc) = 10.2 kOe/ K and H(,c2)(0) = 60.4 kOe. Comparing the value of (-dH(,c2)/dT)(,Tc) gained from the fit of the data to the WHH theory to the calculated (-dH(,c2)/dT)(,Tc) yields various degrees of agreement for these com- pounds. Indications are also that (1) there seems to be little or no;Pauli limiting and (2) the spin-orbit effect appears to be negligible in these compounds; *DOE Report IS-T-1215. This work was performed under contract No. W-7405-Eng-82 with the U. S. Department of Energy. ('1)A. Junod, D. Bichsel, and J. Muller, Helv. Phys. Acta 52, 580 (1979).
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Linda Sue Berg
Berg, Linda Sue, "Superconductivity in ternary rare earth transition metal silicides and germanides with the Sc5Co4Si10-type structure " (1986). Retrospective Theses and Dissertations. 8056.