Analysis of Zn substitution on structure, optical absorption, magnetization, and high temperature specific heat anomaly of the nano-crystalline LaFeO3.

Nano-crystalline LaFe_1−xZn_xO₃ (0 ≤ x ≤ 0.3) samples synthesized through the sol-gel auto-combustion technique have been studied. X-ray diffraction patterns reveal that all the samples have an orthorhombic crystal structure and exist in a single phase. Bond lengths and bond angles determined using Rietveld refinement change with the concentration, leading to the modification of the parent structure. The change in the structure is reflected in the thermal measurements too. The morphological studies reveal a wide-range of particle size distribution, consisting of nanometer-sized particles to macro-agglomerations. FTIR spectra show two strong active vibrational bands present at 564 cm⁻¹ and 410 cm⁻¹, which are related to the functional groups present in the material. The optical bandgap has been determined and is found to decrease with the increase in the concentration of Zn. Raman spectroscopy rules out the symmetry breaking or any other structural phase transition in the system. The Raman spectra reveal the strain present in the samples on increasing the concentration of Zn doping. The doping of Zn in place of Fe produces distortion mainly in the oxygen bending and stretching vibrations. Specific heat as a function of temperature has been studied and found to be sensitive to magnetic ordering. The Neel temperature decreases from 411 °C to 377 °C with the increase in the Zn concentration, which is concomitant with the Rietveld analysis. The density of our system decreases with Zn doping and leads to the increased value of specific heat. Hysteresis loops indicate that Zn doping increases the magnetic moment and decreases the coercivity. [ABSTRACT FROM AUTHOR]