Integrated XRD spectra of pure Cu at 7.3 GPa (bottom panel); Cu2H along with remaining Cu at 21.1 GPa (middle panel); the fully converted Cu2H along with reflections from excess H2 at 27 GPa (upper panel). Tick marks indicate calculated peak positions of Cu (blue) in the bottom panel, Cu (top row, blue), and Cu2H (bottom row, red) in the middle panel and Cu2H (red) in the upper panel. The inset shows the (001) superstructure peak of the layered anti-CdI2 structure of Cu2H. The optical micrograph in the bottom panel shows the sample at 50 GPa.
Equation of state of copper and its hydrides. Blue open triangles denote fcc-Cu, red solid triangles ε-Cu2H, and green diamonds γ-CuH∼0.15. Triangles pointing upwards are data points from compression, triangles pointing downwards are from decompression. For comparison, green circles are data points belonging to γ-CuH∼0.4, taken from Ref. 21 . Dotted and dashed lines are literature equations of state for fcc-Cu and wurtzite-type CuH, respectively (Refs. 13 and 12 ). The solid line is a Vinet-type fit to the observed equation of state of ε-Cu2H. The inset shows the pressure variation of the c/a-ratio for ε-Cu2H.
Ordering of hydrogen (small, blue) and copper (large, copper) atoms showing (a) wurtzite-type CuH (P63/mc space group), (b) anti-CdI2 structure ε-Cu2H ( space group, the displacement of copper atoms is exaggerated), and (c) cubic γ-Cu-H (Fm m space group) (visualised via VESTA 30 ).
Equation of state parameters for Cu, wurtzite-type CuH, and hexagonal Cu2H. The bulk modulus of the chemically obtained CuH is significantly lower than for pure copper, in contrast to Cu2H, where the mechanical properties are unchanged.
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