Free-growth morphology of crystalline grains was observed within the sealed cavities of sintered 0.7Pb(Zn0.2Ni0.8)(1/3)Nb2/3O3-0.3PbTiO(3) (PZNNT) ceramics. The perfect two-dimensional (2D) and three-dimensional (3D) morphologies reflect the growth mechanism of relaxor-PbTiO3 single crystals. We propose that the growth of concentric layers on six {1 0 0} faces contributes to the evolution of the 3D pseudo-cubic morphology, and the 3D morphology inversely constrains the lateral spreading of such layers at edges and corners of the pseudo-cube. The mechanism may help reveal the formation of the quasi-cubic morphology of relaxor-PbTiO3 single crystals reported previously. (c) 2005 Elsevier B.V. All rights reserved.