Hydrogen ordering in rare-earth intermetallic (Er, Tb)Fe2 compounds with giant spontaneous magnetostriction

X-ray diffraction studies of rare-earth intermetallic Er_{1 ? x} Tb _x Fe₂ compounds (with 0 ≤ x ≤ 0.6) and their hydrides were performed at room temperature. As the terbium content (x) in Er_{1 ? x} Tb _x Fe₂ increases, the sign of the magnetostriction constant λ₁₁₁ was shown to alternate from positive to negative. The lattice parameters, amount of incorporated hydrogen, and sizes of interstices were found to increase with increasing terbium content. The sizes of interstices accessible for occupation with hydrogen atoms were calculated for all alloys and their hydrides. Spontaneous anisotropic magnetostriction related to the rare-earth atoms was found to make no determining contribution to the resulting crystal lattice distortion caused by the incorporation of hydrogen atoms.