  (1-x)PbMg1/3Nb2/3O3-(x)PbSc1/2Nb1/2O3 (PMN-PSN) solid solution crystals have
been grown by the flux method in the whole concentration range. X-ray supercell
reflections due to B-cation ordering were observed for as-grown crystals from
the 0.1 < x < 0.65 compositional range. Though the ordered domains are rather
large (~50 nm) the relaxor-like dielectric behavior is observed for
compositions with x < 0.6. The diffusion of the dielectric permittivity maximum
in as-grown crystals is the lowest at x = 0.6 and increases towards the end
members of solid solution. Such behavior is explained within a Bragg-Williams
approach by employing the random layer model. At x ~ 0.6 the excitation energy
determined from the Vogel-Fulcher relation exhibits a jump which we regard to
changing the kind of the polar regions from PbMg1/3Nb2/3O3 to PbSc1/2Nb1/2O3
related type.
