On the role of disorder produced by manganese vacancy at the B site on the structural and magnetic properties of La0.67Ba0.33Mn1-xO3 nanocrystalline

Single-phase perovskite-type manganese oxides La0.67Ba0.33Mn1−xO3 with x = 0.00-0.08 have been prepared by the modified sol-gel method (Pechini) and the influence of the vacancy concentration in the B-site on their structures and magnetic properties has systematically been investigated. The structural elucidation of the synthesized materials was carried out by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. Rietveld analysis of fitted and observed X-ray diffraction patterns exhibited the single-phase nature of all the studied materials, which crystallize in R3¯c space group. The average crystallite size was found to be around 56 nm. FTIR spectra present the prominent absorption peak of the in-phase stretching mode (B2g mode) rising from the vibration of MnO bond length. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing B-site vacancy concentration. All the samples undergo a ferro-to paramagnetic transition, at temperatures that vary from 335 to 216 K as the manganese vacancy increases. As follows from the results of structural and magnetic analyses, creating a vacancy at the Mn site (increase of chemical disorder) induces the formation of Mn4+ ions, which results in the decrease of unit cell volume and leads to a shortage of 3d electrons of the transition metal.