Effect of paramagnetic manganese ions doping on frequency and high temperature dependence dielectric response of layered Na_1·9Li_0·1Ti₃O₇ ceramics

Abstract

The manganese doped layered ceramic samples (Na_1·9Li_0·1)Ti₃O₇ : XMn(0·01 ≤ X ≤ 0·1) have been prepared using high temperature solid state reaction. The room temperature electron paramagnetic resonance (EPR) investigations exhibit that at lower percentage of doping the substitution of manganese ions occur as Mn³⁺ at Ti⁴⁺ sites, whereas for higher percentage of doping Mn²⁺ ions occupy the two different interlayer sodium/lithium sites. In both cases, the charge compensation mechanism should operate to maintain the overall charge neutrality of the lattice. The manganese doped derivatives of layered Na_1·9Li_0·1Ti₃O₇ (SLT) ceramics have been investigated through frequency dependence dielectric spectroscopy in this work. The results indicate that the dielectric losses in these ceramics are the collective contribution of electric conduction, dipole orientation and space charge polarization. Smeared peaks in temperature dependence of permittivity plots suggest diffuse nature of high temperature ferroelectric phase transition. The light manganese doping in SLT enhances the dielectric constant. However, manganese doping decreases dielectric loss due to inhibition of domain wall motion, enhances electron-hopping conduction, and impedes the interlayer ionic conduction as well. Manganese doping also gives rise to contraction of interlayer space.