EFFECT OF PRESSURE ON THE SUPERCONDUCTING T-C OF LANTHANUM

The effect of pressure on the superconducting transition temperature T -c of La was studied up to 50 CPa. T-c(P) shows a rather complicated v ariation with a discontinuous increase in T-c at about 2.2 GPa due to the first-order phase transition from dhcp to fee structure. At about 5.4 GPa a sharp peak is observed due to the soft-mode phase transition from fee to the distorted fee structure and two broad maxima are foun d within the stability region of the distorted fee structure around 12 and 39 GPa. Some differences between these and previous low-pressure data for metastable fee La are noticed. The results are discussed in c onnection with pressure-induced structural phase transitions found in earlier x-ray-diffraction experiments and band-structure calculations giving evidences for van Hove singularities in the density of states.