TEM Analysis of Orientational Domain Evolution Triggered by Structural Phase Transition in Bi0.25Ca0.75MnO3 Ceramics

The structural phase transition and associated orientational domain configurations in perovskite-type BixCa1−xMnO3 ceramics were investigated in this work. A series of BixCa1−xMnO3 solid solutions with x = 0.05, 0.25, 0.33 were synthesized, and Bi0.25Ca0.75MnO3 with moderate orthorhombic lattice distortion was selected as the representative sample for systematic TEM characterization. Upon cooling from high temperature, the material undergoes a symmetry-lowering transition from the cubic phase with Pm3¯m space group to the orthorhombic phase with Pnma space group. Selected-area electron diffraction (SAED) and bright-field TEM observations reveal the formation of multiple orientational domains, including both 90° and 120° configurations, within individual grains. High-resolution TEM (HRTEM) further confirms the coexistence of three distinct domain orientations at the atomic scale, with well-defined lattice fringes and domain boundaries. The reciprocal-space orientational relationships derived from SAED patterns demonstrate that these domains originate from the symmetry breaking of the parent cubic lattice during the phase transition. These findings provide direct crystallographic insight into the domain structures of BCMO, and such microstructural features are essential for revealing the structural stability and intrinsic functional behaviors of BCMO manganites.