Structural, optical and dielectric study of Mn doped PrFeO3 ceramics

Polycrystalline bulk samples of PrFe1−xMnxO3 (x = 0.0, 0.1, 0.3, 0.5) were synthesized by solid state reaction method to understand their structural, optical and dielectric properties. X-ray diffraction (XRD) and Raman spectroscopy were investigated to confirm chemical phase and the orthorhombic pbnm structure. As the concentration of Mn increases, the lattice parameter b increases while the lattice parameters a and c/√2 decrease but the change of former is less than later. PrFe1−xMnxO3 exhibits O-type (a < c/√2 < b) orthorhombic pbnm structure upto x = 0.5. From XRD it is also evident that the peaks shift towards higher 2θ values with increase in Mn content indicating the development of strain in the crystal structure possibly due to Jahn-Teller distortion after the incorporation of Mn3+ ions in the parent compound PrFeO3. From the Raman study, the modes exhibit a blue shift with broadening of spectral features in the doped samples. The observed shift in wave number with doping clearly indicates change in the bond lengths of Fe-O/Mn-O as well as their impact on FeO6/MnO6 octahedra. The dielectric constant (ɛ′) and dielectric loss (tan δ) are also studied as a function of frequency and temperature. The dielectric constant and ac conductivity increases with Mn doping. The variation of dielectric properties such as ac conductivity, tan δ and ɛ′ suggests that small polarons contribute to the conduction mechanism. Activation energy (Eσ) and optical band gap (Eg) decreases with the concentration of Mn. The observed higher values of these quantities reveals that there is hopping between Mn3+ to Mn4+ and Fe3+ to Fe2+ at the octahedral sites of the compound. Possible mechanism contributing to these processes has been discussed.