Angle-dispersive x-ray powder diffraction experiments have been performed on yttrium metal up to 183 GPa. We find that the recently discovered oF 16 structure observed in the high-Z trivalent lanthanides is also adopted by yttrium above 106 GPa, pressures where it has a superconducting temperature of ∼20 K. We have also refined both tetragonal and rhombohedral structures against the diffraction data from the preceding "distorted-fcc" phase and we are unable to state categorically which of these is the true structure of this phase. Finally, analysis of yttrium's equation of state reveals a marked change in the compressibility upon adoption of the oF 16 structure, after which the compression is that of a 'regular' metal. Electronic structure calculations of oF 16-Y confirm its stability over oF 8 structure seen in Nd and Sm, and provide insight into the nature of the shift of orbital character from s to d under compression.

Angle-dispersive x-ray powder diffraction experiments have been performed on samarium metal up to 222 GPa. Up to 50 GPa we observe the Sm-type (hR9) → dhcp (hP 4) → fcc (cF 4) → distorted-fcc (hR24) → hP 3 transition sequence reported previously. The structure of the highpressure phase above 93 GPa, previously reported as having a monoclinic structure with space group C2/m, is found to be orthorhombic, space group Fddd, with 8 atoms per unit cell (oF 8 in Pearson notation). This structure is the same as that found in Am, Cm and Cf at high pressures. Analysis of samarium's equation of state reveals marked changes in compressibility in the hP 3 and oF 8 phases, with the compressibility of the oF 8 phase being that of a "regular" metal.

Using synchrotron X-ray diffraction, we show that the long-accepted monoclinic structure of the "collapsed" high-pressure phases reported in seven lanthanide elements (Nd, Tb, Gd, Dy, Ho, Er and (probably) Tm) is incorrect. In Tb, Gd, Dy, Ho, Er and Tm we show that the collapsed phases have a 16-atom orthorhombic structure (oF 16) not previously seen in the elements, while in Nd we show that it has an 8-atom orthorhombic structure (oF 8) previously reported in several actinide elements. oF 16 and oF 8 are members of a new family of layered elemental structures, the discovery of which reveals that the high-pressure structural systematics of the lanthanides, actinides and group 3 elements (Sc and Y) are much more related that previously imagined. Electronic structure calculations of Tb, combined with quantum many body corrections, confirm the experimental observation, and calculate that the collapsed orthorhombic phase is a ferromagnet, nearly degenerate with an anti-ferromagnetic state between 60 and 80 GPa. We find that the magnetic properties of Tb survive to the highest pressures obtained in our experiments (110 GPa). Further calculations of the collapsed phases of Gd and Dy, again using the correct crystal structure, show the former to be a type-A antiferromagnet, while the latter is ferromagnetic.

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Vanadium is reported to undergo a pressure-induced bcc-rhombohedral phase transition at 30-70 GPa, with a transition pressure that is sensitive to the hydrostaticity of the sample environment. However, the experimental evidence for the structure of the high-pressure phase being rhombohedral is surprisingly weak. We have restudied vanadium under pressure to 154 GPa using both polycrystalline and single-crystal samples, and a variety of different pressure transmitting media (PTM). We find that only when using single-crystal samples does one observe a rhombohedral high-pressure phase; the high-pressure diffraction profiles from the polycrystalline samples do not fit a rhombohedral lattice, irrespective of the PTM used. The single-crystal samples reveal two rhombohedral phases, with a continuous transition between them, and distortions from cubic symmetry are much smaller than previously calculated.