Effects of structural disordering in the manganite La0.825Ba0.175MnO3

Neutron and X-ray diffraction have been used to study the structural state of polycrystalline samples of the perovskite-like manganite La0.825Ba0.175MnO3 with different concentrations of antisite defects produced by fast-neutron irradiation. It has been established that the concentration of antisite defects depends linearly on the fraction of the sample volume affected by cascades of atom-atom displacements, reaching at high fluences a value equal to 0.0875, which is “limiting” for a given composition. The formation of antisite defects is accompanied by the appearance of significant static uncorrelated ion displacements, which for oxygen ions become greater than their tilting displacements. It has been shown that in this case, the tilting mode ϕ, which forms the rhombohedral structure of the manganite, is not destructed completely, although the magnitude of correlated tilting displacements decreases noticeably.