X-Ray Study of the System Palladium-Hydrogen

A unique grating parameter $a_0=4.017\mathrm{}\mathrm{A}$ results when palladium is charged with hydrogen either electrolytically or from the gas phase, in disagreement with the results of Linde and Borelius. Larger values of $a_0$ are possible, but are not stable at 20°C. A difference in stability between some of the electrolytically charged specimens as compared to those charged from the gas phase is associated with the mechanical state of the micro-crystals in the two cases. The concentration ${\mathrm{Pd}}_2$H is associated with the value $a_0=4.017\mathrm{}$. The $L_{111}$ absorption limit of palladium is changed by the presence of hydrogen which causes a shift of the main edge of 0.87 X.U toward shorter wave-lengths, and the occurrence of a secondary absorption 10 X.U. toward shorter wave-lengths. This is taken to indicate a chemical combination between palladium and hydrogen atoms. The molecule PdH is suggested. Impurities in the palladium affect very markedly its occlusion of hydrogen. The unique value $a_0=4.017\mathrm{}$ does not appear but rather all distensions in the range 3.885 to 4.030 are observed. It is suggested that impurities in the palladium might account for the difference between the results of Yamada and those of McKeehan.