NEUTRON-DIFFRACTION STUDY OF YMN2DX DEUTERIDES LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-3.4)

The YMn2Dx system was studied by means of neutron powder diffraction a t temperatures above the magnetic transition in the range 1 less than or equal to x less than or equal to 3.4 D per formula unit. The C15 st ructure of the YMn2 intermetallic compound is conserved on deuteration . A linear dependence of the cell parameter on deuterium content x was observed. The position and site occupation of deuterium were determin ed; only the A(2)B(2)-type sites are occupied in this range of concent ration. Analysis of the background shows a diffuse contribution attrib uted to deuterium atom correlations. The site filling and the short-ra nge ordering effect can be explained on the basis of geometrical consi derations.