Convergent-beam electron diffraction study of the low-temperature ferromagnetic insulator phase of La_1-xSr_xMnO₃ (x = 0.11, 0.12)

The low-temperature ferromagnetic insulator (FMI) phase of La_1-xSr_xMnO₃ (x = 0.11.0.12) was investigated by convergent-beam electron diffraction (CBED) together with selected-area electron diffraction (SAED). We have revealed that the FMI phase belongs to the triclinic space group P1̄, and has a unit cell of ∼2a_c x 46_c x 4c_c, where a_c, b_c, c_c are lattice parameters in the pseudocubic perovskite notation. These findings indicate that the FMI phase is neither the re-entrant phase of the high temperature phase (∼√2a_c x 2√2b_c x 2c_c) as reported by Kawano et al. nor the polaron-ordering phase with a unit cell of (∼2a_c x 2b_c x 4c_c) as proposed by Yamada et al.