# Synopsis: Rare pressure

Under very high pressures hydrogen may combine with platinum to produce new structural phases and high-temperature superconductivity.

As a noble metal, platinum is resistant to any change. In particular, it retains its close-packed crystal structure even under extreme conditions, and is commonly used in high-pressure experiments such as those with diamond anvil cells.

Up until recently, platinum was considered to be immune to many types of chemical change as well, including the formation of hydrides. However, recent experiments that combined hydrogen with silicon under high pressure to induce metallization, and possibly high-temperature superconductivity, have led theorists to believe that platinum may respond similarly.

In their paper in Physical Review Letters, Duck Young Kim at the Cavendish Laboratory in Cambridge, England, and colleagues calculate how hydrogen may change the composition and behavior of platinum when the two elements are combined under high pressure. They predict that a tetragonal phase of $\text{PtH}$ forms at around $21.5$ gigapascals ($\text{GPa}$) of pressure, and at around $70$$80\phantom{\rule{0.333em}{0ex}}\text{GPa}$, a face-centered-cubic phase of the same compound will appear. A superconducting state occurs in the latter (but not the tetragonal) phase.

In addition to being of interest to researchers studying high-pressure physics and superconductivity, this work indicates that the formation of face-centered-cubic metal hydrides under pressure is quite common among noble metal hydrides and that several of them can be superconducting. – Sami Mitra

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