Co-substitution tailored dielectric relaxation and electrical conduction in lanthanum orthoferrite

Effect of co-substitution on structural, dielectric and electrical conduction property of LaFeO₃ is reported. Partial co-substitution of La by Na and Fe by Mn has been observed to cause substantial modification in structural property including lattice distortion in LaFeO_3. Evidence of Jahn teller distortion has been noticed in Raman analysis due to presence of Mn³⁺ Jahn teller active ion at Fe lattice site. Raman analysis also indicated Fe–O–Fe bond weakening in LaFeO₃ on co-substitution. Dielectric response provides evidence of temperature dependent polydispersive relaxations contributed by combined effect of dipolar and space charge relaxations. Temperature response of dielectric parameter (ε_r and tan δ) provided indication of phase transition that is similar to found in ferroelectric materials. The dielectric relaxations are studied in the framework of complex impedance and electrical modulus spectrum. The electrical response comprises both grain and grain boundary contribution in the reported polycrystalline sample and it seems consistent with brick layer model of electrical equivalent circuit. It is evident from the activation energy estimation from modulus and conductivity plot that the small polarons hoping are the key factor in both dielectric ordering as well as electrical conduction mechanism in co-substituted LaFeO₃.