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Title: Co-Substitution Tuned Multifunctionality In Lanthanum Orthoferrite
Authors: Rai, A. P.
Keywords: Physics
Issue Date: 2018
Publisher: IIT Patna
Series/Report no.: TH-85;
Abstract: Effect of co-substitution on structural, optical, dielectric, magnetic and electrical properties in LaFeO3 by mono/divalent cations at La3+ and multivalent Mn at Fe3+ lattice have been analyzed. XRD studies confirmed single phase nanocrystalline powder which was corroborated subsequently by electron microscopy. Structural parameters calculated by Rietveld refinement and vibrational spectrum analysis (Raman/FTIR) confirmed the presence of Jahn-Teller distortion and compressive strain in the system on co-substitution of LaFeO3. It clearly indicated presence of strong Fe/Mn-O stretching band shifting upward and bending Fe/Mn-O-Fe/Mn mode shifting downward on cosubstitution in LaFeO3. Magnetic property measured at room temperature indicated typical weak ferromagnetic response with substantial improvement in magnetic parameters (Ms, Mr, Hc) on cosubstitution. Interestingly, divalent co-substitution (Ca/Mn) exhibits higher coercivity and lower remnant / saturation magnetization as compared to mono valent (Li/Na) co-substitution in LaFeO3. Presence of temperature dependent poly dispersive (non-Debye) dielectric relaxation with distribution of relaxation time is observed Temperature dependent relative permittivity exhibits dielectric anomaly at relatively lower temperature accompanied by a maxima indicating possibility of ferroelectric phase transition. Transition temperature decreases with increasing concentration of co-substituents. It may be assigned to weakening of dipolar order due to displacive changes in structure under the influence of co-substituents. Substantial enhancement in electrical conductivity, on co-substitution, is attributed to change in the oxidation state of Mn3+, due to release of additional free charge carriers in the crystal lattice. Electrical transport occurs due to polaron hopping. Band gap lowering on co-substitution is also noticed. It is noted that monovalent cations of smaller ionic size possess highest conductivity among the co-substituted LaFeO3. Application feasibility as an electrode in energy storage device has also been explored. A capacity fading (14 %) was noted after 1000 cycles.
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