Temperature and frequency-dependent dielectric properties of Zn substituted Li–Mg ferrites
Introduction
The dielectric properties of ferrites are dependent upon several factors namely, chemical composition, method of preparation, grain size etc. The ferrites behave as inhomogeneous dielectric materials in which individual high-conducting grains are separated by either air gaps or low-conducting layers. The dielectric constants as high as 105 at low frequencies are observed in case of ferrites. For microwave applications, high resistivity with low dielectric losses are needed.
In the early days, Mg–Zn, Ni–Zn and Mn–Zn ferrites were used for the microwave devices, which were later replaced by garnets having high resistivity and low dielectric losses. But because of low Curie temperature, high stress sensitivity and high costs of garnets, once again the physicists and technologists have returned to ferrites especially Li ferrites which have become important materials for microwave applications because of their low costs, squareness of hysteresis loop along with high Curie temperature and low dielectric losses. Many researchers have studied Li–Cd [1], [2], Li–Zn [3], Li–Mg [4] and Li–Ni [5] ferrites. However, no reports have been found in the literature about Zn substituted Li–Mg ferrites so far. Therefore, in the present communication, we report on the dielectric properties of these ferrites.
Section snippets
Experimental procedure
Zn-substituted Li–Mg ferrites having the general formula LixMg0.4Zn0.6−2xFe2+xO4 (where x=0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3) were prepared by conventional double sintering ceramic method. The presintering of the samples was carried at 873 K for 12 h and the final sintering at 1273 K for 24 h. The single-phase formation of the ferrites was confirmed by X-ray diffraction patterns obtained by using PHILIPS PW-1710 diffractometer with Cu Kα radiation (λ=15.418 nm). The DC resistivity (ρDC) and
Compositional variation of ε′ and ρDC
Fig. 1 shows the variations of dielectric constant and DC resistivity with zinc content. From this figure it is clear that ε′ and ρDC have inverse trend with each other. The DC resistivity initially found to decrease while the dielectric constant found to increase with increase in Zn content up to 0.3. The sample with Zn =0.3 has minimum resistivity ρDC=2.5×105 Ω- cm and maximum dielectric constant ε′=2.6×104. Further, with the addition of Zn beyond 0.3, ρDC found to increase while ε′ found to
Acknowledgements
The authors thank Prof. Rohini C. Ayyer, Microwave Lab, Department of Physics, University of Poona, Pune (India) for extending their helping hands during experimental measurements.
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