The structure of the trihydride GdH3

The unit cell parameters of the trihydride GdH3, (Pearson symbol hP24, spac e group P3cl, HoH3 type) were determined employing Guinier powder diffracti on patterns. The structure of the interstitial compound GdH3, is formed by departing from a hexagonal close-packed substructure of gadolinium and by f illing its tetrahedral and triangular atomic positions with hydrogen atoms. The occupation of interstitial atomic positions in the hexagonal close-pac ked structure causes lattice dilatation associated with a significant chang e of the axial ratio cia. In the intermediate phases of the binary system G d-H, the interatomic distance between gadolinium and hydrogen atoms, d(Gd-H ) decreases with increasing hydrogen content; the shortest d(Gd-H) distance was observed to occur in GdH3 A set of powder diffraction data was obtaine d for GdH3. (C) 2000 Elsevier Science S.A. All rights reserved.