Features of the rhombohedral-to-orthorhombic structural phase transition in La_1-xSr_xMnO₃

The R3̄c-to-Pbnm structural phase transition in La_1-xSr_xMnO₃, Which is characterized by changes in the rotational displacement of the MnO₆ octahedra and in the crystal system, has been investigated by transmission electron microscopy. The experimental data indicate that the former change results in the appearance of thé antiphase boundary and the latter produces the (110) and (112) twin structures. In addition, the structural phase transition can be reproduced on the basis of the Landau theory, in which a normal structure and an order parameter are, respectively, assumed to be the Pm3m structure and normal coordinates of the rotational displacements.