Structural properties and Raman spectroscopy of rhombohedral La1−xNaxMnO3 (0.075 ≤ x ≤ 0.15)

The present work reports Rietveld refinement of X-ray powder diffraction, Raman study of La1−xNaxMnO3 (x = 0.075, 0.125, 0.15) manganites and low temperature Raman of La0.925Na0.075MnO3. All Raman active phonon modes predicted by the group theory were observed. The A1g mode is substantially shifted with increasing Na substitution. The shifting is attributed to the fact that the variation of 〈rA〉 caused an internal pressure in the lattice. A change in the frequency of Eg modes is also observed. We have analyzed the frequencies and widths of the observed Raman modes as a function of temperature for La0.925Na0.075MnO3. The sample shows a drastic change in Raman spectra and frequency shift between 300 K and 100 K, which attributed to magnetic ordering experience by the sample at low temperature. We observed the splitting of the rotational modes at 100 K that probably caused by the large orthorhombic distortion found in doped rhombohedral manganites.

► XRD patterns of Na-doped LaMnO3 are indexed by R3¯c rhombohedral lattice.
► Shifting of A1g mode with enhanced Na doping is attributed to an increase of 〈rA〉.
► Eg mode shift is associated with Mn–O and O–Mn–O vibrations.
► Splitting of rotational A1g at T = 100 K is due to large orthorhombic distortion.
► Hardening of A1g phonon mode correlated with the increase of internal pressure.