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Phase transition-induced lamellar domain structures together with the phase transition process in Ca [( Mg 1/3 Ta 2/3)0.9 Ti 0.1] O 3 complex perovskite ceramics have been investigated by high-resolution transmission electron microscopy. As the orthorhombic and monoclinic structures coexist in the present ceramics and even in a single grain, groups of lamellar domains have been observed and analyzed in the three characteristic zone axes of the parent cubic perovskite structure: 〈100〉, 〈110〉, and 〈111〉. zone axes. The antiparallel displacement of A-site cations, in-phase, and antiphase oxygen octahedra tilting and B-site 1:2 cation ordering cause superstructure reflections to destroy the symmetry of the parent cubic structure and subsequently induce domain structures. Groups of (010), (100) reflection twin domains and 90° rotation domains along the [100], [010], and [001] directions in the 〈100〉 and 〈110〉 zone axes are refined to be caused by the loss of reflection planes and fourfold rotation symmetry, whereas the loss of threefold rotoinversion and gain of twofold rotation symmetry lead to 120° and 180° rotation domains in the [111] zone axis. Rhombohedral inline image m and tetragonal 4/mmm structures are revealed to act as the bridging intermediate phase to make the first-order phase transitions from the parent cubic m inline image m structure to the orthorhombic mmm structure and monoclinic 2/m structure without group-subgroup relations continuous and diffusionless, and thus could occur via second order to form domain structures.