Most of the crystalline materials seldom show a well-defined dielectric loss peak due to domination of dc conductivity contribution, but effects of loss peaks are seen at high frequencies. Ac electrical data of nano-crystalline Mn0.5Zn0.5Fe2O4 synthesised by chemical co-precipitation method show such behaviour. Properly combined and formulated conduction and dielectric relaxation functions are required for such materials. Cole-Cole type relaxation function in the combined conduction and dielectric process is formulated for complex resistivity ρ(ω), complex permittivity ε(ω), complex conductivity σ(ω) and complex electric modulus M(ω). Conduction and dielectric relaxation are linked to Jonscher's idea of 'pinned dipole' and 'free dipole' to understand the relaxation dynamics. The physical parameters of 'pinned dipole' and 'free dipole' formalism are unique for all representations like ρ(ω), ε(ω), σ(ω) and M(ω). 'Pinned dipole' relaxation time τc related to conduction process and 'free dipole' relaxation time τd related to dielectric process show Arrhenius behaviour with the same activation energy. Correlation of dc conductivity σc with τc and τd indicates the coupled dynamics of 'pinned dipole' and 'free dipole'. Time-temperature scaling of conduction and dielectric relaxation reveals that the mechanism of coupled dynamics of 'pinned dipole' and 'free dipole' is temperature independent. Hopping of charge carriers with dynamics of disordered cation distribution of host matrix generates a coupled conduction and dielectric relaxation in Mn0.5Zn0.5Fe2O4.
Bibliographical noteFunding Information:
Authors thank Central Instrumentation Facility, Pondicherry University for the dielectric spectroscopy measurements and CSIR project 03(1279)/13/EMR-II for financial support. One of the authors (N.S.K.K.) acknowledges DST-PURSE SR/S9/Z-23/2010/36 for the financial support as project assistant.
- Hopping conduction
- Impedance/dielectric spectroscopy
- Non-Debye dispersion