Domain Structures in Perovskite-Type Lanthanum Magnesium Titanate Ceramics

La(Mg_1/2Ti_1/2)O₃ ceramics were prepared using a conventional solid-state reaction route. X-ray diffraction analysis revealed that La(Mg_1/2Ti_1/2)O₃ possesses a distorted perovskite structure consisting of both in-phase and anti-phase tilting accompanied by anti-parallel shifting of La³⁺ cation. Superlattice reflections, indicative of 1:1-type ordering of Mg²⁺ and Ti⁴⁺ cations in the octahedral sites, were observed. The crystal symmetry was deduced to be monoclinic with P 2₁/ n space group (No. 14). Transmission electron microscopy analysis revealed two types of twin domains, classified according to the symmetry elements relating adjacent domains. Twin domains with specific orientations, related by mirror operations along {112} and (110) planes, were identified. La(Mg_1/2Ti_1/2)O₃ exhibited a high density of dislocations that interact with the twin boundaries resulting in incoherent twin interfaces. In addition, two morphologically distinct anti-phase domains were observed resulting from (i) off-center displacement of the La³⁺ cations, and (ii) 1:1 ordering of the B-site sublattice.