Hydrogen ordering in fcc solid solution in rare-earth metal hydrides

It is find in consequence of neutronographic investigation into the CeDsub(2.26) and CeDsub(2.43) ordered phases and analysis of known experimental data that in the MeDsub(2+x) (Me = La, Ce, Pr, 0 < x <0.5) system in the temperature range from room temperature to 90 K there are two types of Me4X and Me2X superstructures (space groups of 14/mmm and 141 md, correspondingly) stable to the formation of antiphase domains. General properties of the superstructures are the tetragonal symmetry of an elementary cell (a--a0 and c approximately 2a0), existence of a static wave of atom displacements from ideal posititions of the initial fcc lattice and formation of vacancies in the tetrahedrical hydrogen sublattice (approximatly 3%)