Conduction in Mn substituted Ni-Zn ferrites

摘要

The d.c. electrical resistivity ‘ρ’ and thermoelectric power ‘α’ are studied as a function of temperature for Mn substituted ferrites with general formula Zn0·3Ni0·7+xMnxFe2−2xO4. At lower Mn concentrations, the increase in d.c. resistivity is attributed to the hindering of Verwey mechanism Fe2+⇌ Fe3+due to stable bonds of Mn3++ Fe2+pair. The decrease in resistivity at higher Mn concentrations (i.e. whenx>0·15) is attributed to the formation of Mn3+cluster and Ni2+⇌ Ni3+. The activation energy values show one to one correspondence with resistivity values. The compositional variation of thermoelectric power showsn-type behaviour for the samples withx<0·2 whereasp-type behaviour for the samples withx⩾ 0·2. Thep−ntransition is attributed to the formation of Ni3+, Fe2++ vacancies which act asp-type carriers. The temperature dependences ofα, ρ, and mobility clearly confirm the conduction mechanism to