Neutron and X-Ray Diffraction Studies of Nonstoichiometric Metal Hydrides

Abstract

The zirconium-deuterium system in addition to α-Zr consists of three deuteride phases: γ, δ, and ε. Each phase exists over a wide range of compositions. The γ phase is tetragonal. The δ phase is cubic (CaF2-type). The ε phase is tetragonal. Its lattice constants vary with composition as it approaches stoichiometry of ZrD2. The unit cell contains 4ZrD2 with atoms in similar positions as in the δ phase. The γ phase retains its structure over long periods of time at room temperature. The δ + ε region has a finite width. The sizes of interstitial octahedral and tetrahedral voids in α-Zr are calculated and shown to be larger or smaller, respectively, than those of tetrahedral sites actually occupied by deuterium atoms in the deuterides to permit interstitial solid solution.