Fig. 3: Formation of hydrides from fcc phase of the Cantor alloy under compression at elevated temperatures.

Powder XRD data were collected at P02.2, PETRA III using λ = 0.2907 Å (experiment DAC02). Panel (a) shows the variation of V/Z for the for the identified phases formed upon compression, resistive heating and reaction of the Cantor alloy with hydrogen. Note that due to diffraction peak overlap we could not unambiguously resolve unit cell volume of hcp–HEA and hcp–HEH for a number of points. For comparison, we show room temperature (RT) (RT) compressibility similar to our previously published data¹⁵. Unless indicated, error bars for the datapoints are of the same size as the symbols or below. Panel (b) illustrates a heatmap composed from individual experimental diffraction patterns. The most important processes are indicated, including formation of fcc– and hcp–HEH based on Cantor alloy. Transformation of fcc alloy into hcp phase happens over an appreciable range of pressures. In addition, we observe domination of HEH with respect to HEA polymorphs at highest pressures indicated to the right of the panel. Diffraction data suggests relative abundance of fcc–HEH with respect to hcp–HEH.