Predicted Formation of Superconducting Platinum-Hydride Crystals under Pressure in the Presence of Molecular Hydrogen

Noble metals adopt close-packed structures at ambient pressure and rarely undergo structural transformation at high pressures. Platinum (Pt) is normally considered to be unreactive and is therefore not expected to form hydrides under pressure. We predict that platinum hydride (PtH) has a lower enthalpy than its constituents solid Pt and molecular hydrogen at pressures above 21.5 GPa. PtH transforms to a hexagonal close-packed or face-centered cubic (fcc) structure between 70 and 80 GPa. Linear response calculations indicate that PtH is a superconductor at these pressures with a critical temperature of about 10–25 K. These findings help to shed light on recent observations of pressure-induced metallization and superconductivity in hydrogen-rich materials. We show that the formation of fcc noble metal hydrides under pressure is common and examine the possibility of superconductivity in these materials.

Figure 1

Comparison of the enthalpies of $\mathrm{Pt}+\frac{1}{2}{\mathrm{H}}_2$ and the tetragonal and fcc phases of PtH.

Figure 2

Superconducting transition temperature $T_c$ of PtH as a function of pressure. Filled squares and hollow hexagons show values of $T_c$ for the fcc and hcp structures, respectively, with the higher $T_c$ value at each pressure corresponding to the choice ${\mu }^{*}=0.10$ and the lower $T_c$ value to the choice ${\mu }^{*}=0.13$. The inset displays the evolution with pressure of the electron-phonon coupling parameter $\lambda$ and the asymptotic phonon momentum ${\Omega }_{\log }$ (see the Supplemental Material [22]). The fcc phase is dynamically unstable below 77 GPa and the hcp phase is dynamically unstable below 100 GPa.

Figure 3

Spectral function ${\alpha }^{2}F$ (red shaded areas), the integral of the spectral function up to frequency $\omega$ (${\int }_0^{\omega }{\alpha }^{2}F({\omega }^{\prime })/{\omega }^{\prime }d{\omega }^{\prime }$) (red line), and the phonon density of states (solid black line) as a function of frequency at selected pressures for (a) fcc PtH and (b) hcp PtH.

Figure 4

Maximum $T_c$ (calculated at the onset of dynamical stability of the fcc phase) for the metal hydrides RhH, PdH, AgH, IrH, PtH, and AuH. Note that the corresponding elemental metals in their fcc form all possess either extremely small $T_c$ (Rh and Ir) or are not superconducting at all (Pd, Ag, Pt, and Au).