Anomalous electrical resistivity and defects inA−15compounds

Abstract

The temperature dependence of the electrical resistivity $\rho$ of Nb-Ge, ${\mathrm{V}}_3$Si, ${\mathrm{V}}_3$Ge, and Nb is reported for a variety of samples produced with differing chemical composition (for Nb-Ge), preparation conditions, and with varying amounts of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$-induced defects. The great susceptibility of the $A-15$ structure to defect formation and its profound effects on the physical behavior are shown. The resistance-ratio-$T_c$ correlation previously reported for Nb-Ge is found in ${\mathrm{V}}_3$Si and ${\mathrm{V}}_3$Ge. Residual resistivities increase far more rapidly with ${}_{}{}^4{}_{}{}^{}\mathrm{He}$-induced defects in the $A-15\text{'}\mathrm{s}$ than in Nb, and at least for ${\mathrm{Nb}}_3$Ge, saturate at the highly disordered state where the minimum $T_c$ occurs. Decreasing $T_c$, no matter how achieved, is accompanied by not only the loss of the Woodard and Cody anomaly in $\rho \mathrm{}\left(T\right)\mathrm{}$ but the loss of almost all the thermal resistivity (electron-phonon interaction) as well. The temperature dependence and the magnitude of $\rho$ are compared with predictions and other published values and some unexpected correlations with $T_c$ are found. The data indicate a defect with universal behavior in the $A-15\text{'}\mathrm{s}$, and of considerable consequence to the superconducting and normal-state behavior.