Investigation of the structure of the relaxer ferroelectric Pb(Fe1/2Nb1/2)O-3 by neutron powder diffraction

The complex perovskite lead iron niobate, Pb(Fe1/2Nb1/2)O-3 (PFN), has been studied by neutron powder diffraction. Following collection of diffraction data at 300 K and at 10 K, structural refinements have been carried out by means of the Rietveld method. As expected, a straightforward unit cell of symmetry R3m was obtained for the 300 K structure, with the same symmetry a nd a similar unit cell also obtained at low temperature. Furthermore, in or der to obtain a good agreement with experiment at 10 K, it was necessary to assign non-zero magnetic moments to the iron ions, these being in a collin ear, antiferromagnetic alignment. This magnetic structure can be described with reference to doubled unit cell axes. The factors governing the observe d structures of PFN are discussed by comparison with the related system of Pb(Mg1/3Nb2/3)O-3.