Abstract
The oxygen deficient and formally Ni1+-Ni2+ mixed-valence La2−x SrxNiO4−δ system has been studied by means of neutron diffraction. It is found that, for the described synthesis procedure, there exists a critical Sr concentration x c ≈ 0.135 separating the stability regions of two different crystallographic phases. For small Sr doping (x < x c), La2−x Sr xNiO 4−δ samples have basically the same structure as stoichiometric La2NiO4, undergoing similar phase transitions. For x > x c, the partial ordering of the oxygen vacancies produces a change of the crystallographic symmetry (from Bmab to Immm) and prevents the two structural phase transitions observed in the x < x c region. In contrast to the behavior observed in hole-doped nickelates, the local fluctuations of the oxygen content produce lattice microstrains, the presence of which is clearly detected by the strong broadening of a family of Bragg reflections. A simple statistical model has been used to quantitatively characterize the microstrain distribution, supposed to be gaussian, from the observed (hkl) -dependence of the reflection broadening.
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Medarde, M., Rodríguez-Carvajal, J. Oxygen vacancy ordering in La2− x SrxNiO4 − δ (0 ≤ ≤ 0.5): the crystal structure and defects investigated by neutron diffraction. Z. Phys. B 102, 307–315 (1997). https://doi.org/10.1007/s002570050293
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DOI: https://doi.org/10.1007/s002570050293