Lamellar phase separation and dynamic competition in La _0.23Ca_0.77MnO₃

We report the coexistence of lamellar charge-ordered (CO) and charge-disordered (CD) domains, and their dynamical behavior, in La _0.23Ca_0.77MnO₃. Using high-resolution transmission electron microscopy (TEM), we show that below T_CD ∼ 170 K a CD-monoclinic phase forms within the established CO-orthorhombic matrix. The CD phase has a sheetlike morphology, perpendicular to the q vector of the CO superlattice (a axis of the Pnma structure). For temperatures between 64 and 130 K, both the TEM and resistivity experiments show a dynamic competition between the two phases: at constant T, the CD phase slowly advances over the CO one. This slow dynamics appears to be linked to the magnetic transitions occurring in this compound, suggesting important magnetoelastic effects.