Small polaron conduction in lead modified lanthanum ferrite ceramics

• Published in: Journal of alloys and compounds 2015-07, Vol.638, p.334-343
• Main Authors: Bhargav, K.K., Ram, S., Majumder, S.B.
• Format: Article
• Language: English
• Subjects: Auto-combustion; Ceramics; Dielectric and impedance spectroscopy; Dielectric constant; Ferrite; Grain boundaries; Lanthanum; Lead (metal); Maxima; Orthoferrites; Polaron conduction; Polarons
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.02.186

•La0.8Pb0.2FeO3 (εr∼30,000) shows higher dielectric constant than LaFeO3 (∼14,000).•Lower A-site dopant content, the dielectric maxima shift to higher temperature.•The frequency dependence of εr and tanδ vs. temperature exhibit CDC like behavior.•Rg and Rgb of Pb modified LaFeO3 follow small polaron hopping conduction model. In the present work we have illustrated the physics of the electrical characteristics of nanocrystalline La1−xPbxFeO3, (0⩽x⩽0.2) powder prepared using auto-combustion synthesis. The effect of lead doping on the dielectric, impedance and ac conductivity characteristics of lanthanum ferrite has systematically been investigated. The synthesized powders were phase pure and crystallized into centro-symmetric Pnma space group. As compared to pure LaFeO3 ceramics (dielectric constant∼14,000), the dielectric constant is grossly increased (∼30,000) in Pb doped LaFeO3. The temperature dependence of dielectric constant of 10.0 at.% Pb doped LaFeO3 exhibits dielectric maxima similar to that observed in ferroelectric ceramics with non-centrosymmetric point group. For La0.8Pb0.2FeO3 ceramics, the frequency dependence of the dielectric constant and loss tangent at various temperatures (300–450K) exhibit typical colossal dielectric constant (CDC) like behavior. From the impedance spectroscopy we have estimated the grain and grain boundary resistance and capacitance of Pb doped LaFeO3 that follow a small polaron hopping conduction model. Long range movement of the charge carriers govern the CDC behavior.