Lutetium: High pressure polymorph and compression

The effect of pressure on the lattice parameters of the h.c.p. phase of Lu has been studied up to 230 kbar at 23 ± 3°C by means of X-ray diffraction employing a diamond-anvil cell. The data fitted to the Birch equation yield an isothermal bulk modulus of 460 ± 20 kbar with a pressure derivative of 2.8 ± 0.5. The axial ratio $\text{(}\text{c}\text{a}\text{)}$ decreases nonlinearly with increasing pressure, the decrease being 2.4 per cent at 230 kbar. When the pressure exceeds 230 kbar, Lu transforms reversibly from the h.c.p. phase to the Sm-type structure. The transition occurs with increasing pressure in the range of 230 ± 5 kbar. The lattice parameters of the Sm-type structure at about 231 kbar are a = 3.176 ± 0.006 Å and c = 21.77 ± 0.04 Å, and the volume change is $\text{?0.21}\text{cm}{}^3\text{mole}$ or ?1.6 per cent of the volume of the h.c.p. phase.