Local structure modulation of the low La-doped layered strontium manganite Sr₄Mn₃O₁₀ studied by transmission electron microscopy and electron energy-loss spectroscopy

Transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) have been used to characterize the structure and microstructure of the low La-doped layered manganite La _x Sr_4−x Mn₃O₁₀ (x ≤ 0.15). The structure of the perfect phase has been identified as an n = 3 layered structure of the hexagonal series by electron diffraction (ED), high-resolution electron microscopy (HRTEM) together with numerical image simulations. The presence of local superstructure modulation associated with La ordering in the compounds was revealed by electron diffraction and high-resolution electron microscopy. Electron diffraction data indicate that this superstructure modulation is two-dimensional, and the modulation plane lies in the ac plane. The two primary modulation vectors are \( q_{1} = (1/4)a^{*} \) and \( q_{2} = (1/2)c^{*} . \) In addition, another type of modulated structure associated with periodic lattice distortion was occasionally visible in the La_0.15Sr_3.85Mn₃O₁₀ phase. Energy-loss spectroscopy data indicate that the periodic lattice distortion is led by ordered oxygen deficiency.