Neutron diffraction study of the relaxor-ferroelectric phase transition in disordered Pb(Sc1/2Nb1/2)O3

The crystal structure of chemically disordered lead scandium niobate, Pb(Sc 1/2 Nb 1/2 )O 3 , is studied by the high-resolution neutron powder diffraction method. The data, collected over the temperature range 2-653 K, are analysed using Rietveld refinement. From 653 K to 378 K, the symmetry of PSN is found to be cubic (space group Pm m ) with positional disorder on the lead and oxygen crystallographic sites. For temperatures close to the ferroelectric phase transition (~378 K), the formation of polar domains in the paraelectric phase is deduced from the observation of the diffuse scattering around Bragg peaks. For the ferroelectric phase, between 368 K and down to 2 K, the symmetry of PSN is determined to be trigonal (with space group R 3 m ) and a positional disorder on the Pb site is evidenced perpendicular to the ferroelectric axis.