SYMMETRY CHANGE AT THE FCC DISTORTED-FCC PHASE-TRANSITION OF LANTHANIDES UNDER PRESSURE

The crystal structure of the distorted-fcc high-pressure phase of the rare-earth elements is discussed in connection with the Landau theory of phase transition. From x-ray-diffraction spectra the irreducible representation EuL is found to drive the (almost) continuous transition fcc→distorted fcc. Using just symmetry arguments four structures induced by EuL are compatible with the x-ray-diffraction pattern; but only one (space group Cmmm, Z=8) can have a continuous transition to fcc. © 1994 The American Physical Society.