Structural Phase Transitions In Yttrium Up To 183 Gpa

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 similar to 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.