Crystallographic analysis of orientational domain variants and charge-ordered domains inLa0.33Ca0.67MnO3

Abstract

We present a study on the origin of twinning and antiphase domains and their relationship to charge ordering in ${\mathrm{La}}_{0.33}{\mathrm{Ca}}_{0.67}{\mathrm{MnO}}_{3}.$ The evolution of these orientational and charge-ordered domains is attributed to the reduction of the crystal symmetry due to the cubic to orthorhombic and, at the charge ordering temperature ${T}_{c},$ to low-temperature orthorhombic (LTO) phase transformations. The process was predicted by group theory analysis and observed with transmission electron microscopy. In both orthorhombic phases the orientation domain has six variants with 15 possible domain boundaries which can be classified as two types of reflection twins, the $90\ifmmode^\circ\else\textdegree\fi{}/m{100}$ and the $120\ifmmode^\circ\else\textdegree\fi{}/m{110}$ twins. Two kinds of antiphase domains and their domain interfaces, associated with the loss of translation symmetry, with lattice shifts of ${a}_{\mathrm{co}}/3$ and ${a}_{\mathrm{co}}/2$ also were predicted and observed for the LTO phase. This work suggests that the twin domains, which occur well above ${T}_{c},$ are not caused by charge ordering. However, the antiphase domains, which can account for the observed small ${\mathbf{c}}_{O}$ component of the incommensurate modulation at low temperature, are directly related to charge and orbital ordering in ${\mathrm{La}}_{0.33}{\mathrm{Ca}}_{0.67}{\mathrm{MnO}}_{3}.$ Our study clarifies the widespread misunderstanding of twinning being equivalent to charge ordering in the system.