Microstructure of La_1-XCa_xMnO₃ studied by transmission electron microscopy

Microstructures of La_1-xCa_xMnO₃ compounds (x = 1/3 and 0.5) prepared with and without intermediate grinding were studied using transmission electron microscopy. A high density of antiphase boundaries (APBs) with displacement vector 1/2〈111〉, indexed in orthorhombic unit cell, has been observed in bulk samples with no or minimum intermediate grinding. The nature of this APB is analyzed and found to be due to the symmetry breaking introduced by the tilting of MnO₆ octahedra relative to the ideal perovskite structure. Samples prepared using two intermediate grinds do not show these defects indicating that the microstructure can be controlled through synthesis routes. The effect of domain boundaries on the colossal magnetoresistance effect is discussed.