Unusual Strain Dependence ofTcand Related Effects for High-Temperature (A−15-Structure) Superconductors: Elastic, Thermal, and Alloy Behavior

The specific heats of ${\mathrm{V}}_3$Ge and ${\mathrm{V}}_3$Si, and the elastic behavior of ${\mathrm{V}}_3$Ge are given. These data are used to calculate the strain dependence of $T_c$ in the preceding paper, and to confirm some of the predictions of that calculation. From measurements of specific heat and elecrical resistance, it is found that $T_c$ for tetragonal ${\mathrm{V}}_3$Si is up to 0.4 °K below that for the cubic state. This result, as well as the strain dependence of the specific-heat discontinuity at $T_c$, are in reasonable agreement with the calculated results obtained in the previous paper. Finally, the dependence of $T_c$ on lattice parameter for ${\mathrm{V}}_3$Si, ${\mathrm{V}}_3$Ge, and ${\mathrm{V}}_3$Ga, predicted in the previous paper, is compared with the results for ${\mathrm{V}}_3$X alloys. The remarkable agreement obtained in this comparison indicates that the chemical changes on alloying are relatively unimportant in establishing the large changes in $T_c$.