The effect of Nb2O5 dopant on the structural and magnetic properties of MnZn-ferrites

In the present work, the role of Nb2O5 additions on the structural and electromagnetic properties of MnZn-ferrites has been investigated. Nb2O5 additions at a concentration of about 200 ppm are found to lower the losses by almost 17%. At higher concentrations Nb2O5 segregates at the grain boundaries, promotes grain growth and affects negatively the microstructure development. At concentrations up to 200ppm, where a gradual improvement of the magnetic properties is observed, Nb2O5 is found to precipitate together with CaO homogeneously along the grain boundaries and participates in the formation of glassy phases. Those phases act as buffers between the grains, smoothening the transition from one grain to the other. Moreover they also reduce Zn-evaporation at the grain boundary area. Both effects are in favour of low electromagnetic power losses and of high relative magnetic permeabilities. (C) 2002 Elsevier Science B.V. All rights reserved.