Abstract Lower deuterides of Zr 3 FeD x ( x =1.3, 2.5 and 5.0) were obtained by desorption of deuterium from Zr 3 FeD 6.7 and were studied by means of powder X-ray and neutron diffraction. Their metal sublattices are of the Re 3 B-type (space group Cmcm ; a =3.3261(4)–3.4524(1); b =11.2333(5)–11.317(1); c =8.999(1)–9.4746(4) A for x =1.3–5.0), and are hence mainly unchanged with respect to the initial intermetallic Zr 3 Fe and the “highest” deuteride Zr 3 FeD 6.7 . A gradual expansion of the orthorhombic unit cells accompanies the increase in D content. There appears to exist a broad solid solution phase, and the volume increase is in the range 4.8( x =1.3)–14.2%( x =5.0) relative to Zr 3 Fe. The expansion is anisotropic, for low x mainly located in the bc plane, for larger x in the ac plane. Rietveld refinements of the high resolution powder neutron diffraction data show that the initially occupied four types of interstices in Zr 3 FeD 6.7 , i.e. Zr 3 Fe 2 , Zr 3 Fe and two non-equivalent Zr 4 sites, are depopulated in a step-wise manner on desorption at increasing temperatures. On decreasing the D content, deuterium is first removed from interstices having iron atoms in their surroundings (Zr 3 Fe 2 and Zr 3 Fe sites), whereas the occupancy of the Zr 4 tetrahedra remains complete. In the “lower” deuterides, Zr 3 FeD 2.5 and Zr 3 FeD 1.3 , these tetrahedra become differently occupied. The reduced stability of one of these sites correlates with having an unfavourable smaller size. On going from Zr 3 FeD 6.7 to Zr 3 FeD 5.0 the originally completely ordered hydrogen sublattice with all D–D distances exceeding 2.0 A becomes partially disordered. The partially filled Zr 3 Fe interstices (50% occupancy) become closer on average (in Zr 3 FeD 5.0 : 1.54 A), which must be understood in terms of significant short range order. The metal–deuterium distances decrease gradually with decreasing D/Zr 3 Fe ratio, being shorter than those of Zr 3 FeD 6.7 : Zr–D=2.058(5)–2.204(7) A; Fe–D=1.713(4)–1.7914(3) A (at 293 K). There are no indications for either D ordering or for magnetic long range order in the powder neutron diffraction data of Zr 3 FeD 5.0 at 7 K.