ИСТИНА

As was first noticed in Ref. [1], hydrogen uptake by palladium and many of its fcc alloys is accompanied by a similar, non-linear volume expansion ΔVa(x) (see the left figure below). Our previous X-ray investigation of Pd and its alloys with 6 and 20 at.% Au loaded with hydrogen at pressures up to 7.4 GPa and an elevated temperature of 600 °C showed that the ΔVa(x) dependences for the resulting homogeneous and stress-free solid solutions were linear and coincided with each other [2] (the blue line on the right figure). The equal slopes of all three ΔVa(x) dependences were rather unexpected in view of the different H-Pd and H-Au interactions and significant increase in the volume of Pd doped with Au, which reached +0.44 Å3/metal atom in the alloy with 20 at.% Au. In the present work, we carried out a similar X-ray investigation of stress-free solid hydrogen solutions in fcc Pd-Cu alloys with 10 and 25 at.% Cu prepared under the same T = 600 °C and P ≤ 7.4 GPa. Alloying Pd with Cu significantly decreases its atomic volume, the effect reaching –0.64 Å3/metal atom in the alloy with 25 at.% Cu. As seen from the right figure, the replacement of Au by Cu retained the linearity of the ΔVa(x) dependences and did not noticeably change their slope. The work was partly supported by the Program “Physics of Fundamental Interactions and Nuclear Technologies” of the Russian Academy of Sciences. [1] B. Baranowski et al., J. Phys. F: Metal Phys. 1 (1971) 258. [2] V.E. Antonov et al., MH2016, Abstracts, p. 33, https://mh2016.ch/program/.