Pressure Dependence of the Superconducting Transition Temperature of Vanadium and Niobium

The pressure dependence of the superconducting transition temperature $T_c$ of vanadium ($\frac{\partial T_c}{\partial P}=11\mathrm{}\pm 3\times {10}^{-6\mathrm{}}$ °K ${\mathrm{bar}}^{-1\mathrm{}}$) and niobium ($\frac{\partial T_c}{\partial P}=0\mathrm{}\pm 3\times {10}^{-6\mathrm{}}$ °K ${\mathrm{bar}}^{-1\mathrm{}}$) has been studied up to a maximum pressure of 10 kbar. The observed values are compared with values calculated from calorimetric and thermal-expansion data. A possible explanation of the observed variation in the sign of the pressure dependence of $T_c$ in the transition-metal superconductors is offered.