Neutron powder diffraction study of the magnetoelectric relaxor Pb(Fe2/3W1/3)O3

The structural properties of complex perovskite lead iron tungstate, Pb(Fe2/3W1/3)O3 (PFW) which belongs to a class off disordered magnetoelectrics has been studied by neutron powder diffraction. Rietveld refinement of neutron powder diffraction data collected at different temperatures, between 10 and 700 K, have been carried out in order to extract structural information. The long-range structure of PFW is a cubic one (space group Pm 3 ¯ m) within the whole temperature interval. The PFW sample demonstrated very low thermal expansion at lower temperatures. The iron and tungsten ions were found to be disordered over the perovskite B-sites. Pb cations show a position disorder shifting from their high-symmetry positions along the [1 1 1] direction. Furthermore, in order to obtain a good agreement with experiment at low temperatures, below TN, it was necessary to assign non-zero magnetic moments to the iron ions, these being in a co-linear antiferromagnetic arrangement in accordance with the antiferroelectric properties of PFW. The magnetic structure can be described with a doubling of the unit cell axes. The factors governing the observed nuclear and magnetic structures of PFW are discussed and compared with those of other quaternary iron-containing perovskites.