Structural phase transitions in yttrium up to 183 GPa
Edward J. Pace, S. E. Finnegan, C. V. Storm, M.G. Stevenson, M. I. McMahon, Simon G. MacLeod, Evgeny Plekhanov, Nicola Bonini, Cédric Weber
Abstract
Angle-dispersive x-ray powder diffraction experiments have been performed on yttrium metal up to 183 GPa. We find that the recently discovered $oF16$ structure observed in the high-$Z$ trivalent lanthanides is also adopted by yttrium above 106 GPa, pressures where it has a superconducting temperature of $\ensuremath{\sim}20$ 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 $oF16$ structure, after which the compression is that of a ``regular'' metal. Electronic structure calculations of $oF16$-Y confirm its stability over $oF8$ structure seen in Nd and Sm, and provide insight into the nature of the shift of orbital character from $s$ to $d$ under compression.