High-pressure synthesis and thermodynamic stability of PdH(1 +/-epsilon )up to 8 GPa

Article

关键词: X-RAY-DIFFRACTION;    SOLID-STATE ELECTROLYSIS;    MODERATE TEMPERATURES;    PHASE-SEPARATION;    HYDROGEN;    PD;    PALLADIUM;    SUPERCONDUCTIVITY;    VACANCIES;    EQUATION;   

DOI  :  10.1103/PhysRevB.103.024515

来源: SCIE

【 摘 要 】

Palladium hydride alloys are superconductors and hydrogen storage materials. One synthesis route is compression of Pd to high pressure in a hydrogen-rich environment. Here we report the evolution of the unit cell volume of PdHx synthesized by compressing Pd in a pure H-2 medium to pressures from 0.2 to 8 GPa in a diamond anvil cell at room temperature. The volume of the face-centered cubic unit cell changes nonmonotonically with pressure, increasing upon compression from 0.2 to 1 GPa and decreasing upon compression from 1 to 8 GPa. Volume is reversible upon decompression and is independent of whether the sample was heated to 600 K at low pressure (P < 2 GPa). The x-ray diffraction data show no evidence for a phase transition between 0.2 and 8 GPa. The volume maximum at 1 GPa must be caused by progressive hydrogenation from 0 to 1 GPa. Assuming a pressure-volume-composition equation of state derived from previously published data, the [H]: [Pd] ratio in this study increases to a maximum value of x = 1 +/- 0.02 at 2 +/- 0.5 GPa and remains stable upon further compression to and from 8 GPa. These results add to a mounting body of evidence that PdH1 +/-epsilon , is in thermodynamic equilibrium with pure H-2 at room temperature from 2 GPa to at least 8 GPa. The simplest interpretation is that H atoms occupy all octahedral sites and no tetrahedral sites in face-centered cubic PdH1.0.

【 授权许可】

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