Superconductivity of BCC Zr and Zr-Nb alloys at high pressures

The superconducting transition temperature T _c of bcc Zr is measured at pressures to 64 GPa. The T _c value gradually decreases as pressure is increased. For the Zr-Nb alloys, there are found anomalies in the T _c (P) dependences at rather low pressures. The anomalies are discussed within the available theoretical models. We assume on the basis of the T _c (P) experimental data for the Zr-Nb alloys that the T _c (P) curve for bcc zirconium has a maximum in the metastability region.