Superconductivity at 17 K in yttrium metal under nearly hydrostatic pressures up to 89 GPa

In an experiment in a diamond anvil cell utilizing helium pressure medium, yttrium metal displays a superconducting transition temperature which increases monotonically from T-c similar or equal to 3.5 K at 30 GPa to 17 K at 89.3 GPa, one of the highest transition temperatures for any elemental superconductor. The pressure dependence of T-c differs substantially from that observed in previous studies under quasihydrostatic pressure to 30 GPa. Remarkably, the dependence of T-c on relative volume V/V-o is nearly linear over the entire pressure range above 33 GPa, implying that higher values of T-c are likely at higher pressures. For the trivalent metals Sc, Y, La, and Lu, there appears to be some correlation between T-c and the ratio r(a)/r(c) of the Wigner-Seitz radius to the ion core radius.