Ferroelectric domain structures and their morphology evolution in the Bi- and Zn-modified (Pb0.985Bi0.01)(Ni1/4Zn1/12Nb2/3)(x)(Zr sigma Ti1-sigma)(1-x)O-3 piezoelectric ceramics (0.20 <= x <= 0.60 and 0.10 <=sigma <= 0.60) are investigated as a function of the relaxor Pb(Ni1/3Nb2/3)O-3 content and the Zr/(Zr+Ti) ratio (sigma) by transmission electron microscopy and selected area electron diffraction, and followed by a complete analysis of the nature of the domain walls based on the predicated twinning planes for the formation of domains in these piezoelectric ceramic systems. A systematic variation in the domain morphology was observed as the compositions move from the ferroelectric tetragonal (F-T) to pseudocubic (F-pc) phases, and then to the rhombohedral (F-R) phase. Wedged-shaped domains with misoriented {110} domain walls and mixed with herringbone-like configuration are the main features of the ferroelectric domains in the F-T and F-pc phases, whereas in the compositions near the morphotropic phase boundary (MPB) between the F-pc and F-R phases, the characteristic feature of the ferroelectric domains is an intricate domain structure exhibiting a fluctuating mottled contrast. However, the domain boundaries in the F-R phase exhibit a wavy character. The domain feature for the compositions at/near the MPB between the F-T and F-R phases with high property coefficients is a 90 degrees domain texture mixed with an intricate domain structure. The different domain configurations observed in the F-T and F-R phases are due to their different accommodations of local elastic strain fields. The piezoelectric soft behavior and a normal-relaxor ferroelectric behavior transition observed in this piezoelectric ceramic system are closely related to the above domain morphology evolution as increasing the PNN content or the Zr/(Zr+Ti) ratio.