Mössbauer spectroscopic study of the gadolinium–hydrogen system

Abstract

A study has been carried out of the gadolinium–hydrogen system using ¹⁵⁵Gd sources (from ¹⁵⁵Eu) incorporated in SmF₃ and SmPd₃. Sources were held at 4.2 K and absorbers at various temperatures. Using the ‘single-line’ Sm(¹⁵⁵Eu)Pd₃ source, isomer shifts (in mm s^–1) relative to GdF₃ are: Gd, –0.71 ± 0.02; GdH₂, –0.10 ± 0.02; GdH3, –0.11 ± 0.02 at 4.2 K. The hyperfine magnetic field in GdH₂ is –306 ± 30 kG (for the metal it is –382 ± 10 kG). GdH₃ Is quadrupole split, V_zz=(5.1 ± 0.5)× 10¹⁷ V cm^–2. Isomer-shift data are qualitatively in accord with the anionic model of hydride formation. Electron density at the gadolinium nucleus decreases most markedly with initial addition of hydrogen and little, if any, on going from GdH₂ to GdH₃. The reverse is observed for the hyperfine magnetic field at the gadolinium nucleus. Electric and magnetic effects are discussed in relation to other relevant chemical and physical properties of the system.