Microwave synthesis and electrical properties of indium-substituted MnZn ferrites Surender Kumar a *, Tukaram J. Shinde b and Pramod N. Vasambekar c a Department of Physics, Pandit Anant Ram Sanatan Dharam College, Baroh, India; b Department of Physics, KRP Kanya Mahavidyalaya, Islampur, India; c Department of Electronics, Shivaji University, Kolhapur, India (Received 9 June 2014; revised 20 July 2014; accepted 31 July 2014) Nanocrystalline ferrites Mn 0.6 Zn 0.4 In y Fe 2-y O 4 (y D 0, 0.035, 0.070, and 0.100) were prepared by the oxalate co-precipitation technique followed by microwave heating. The X-ray diffraction technique conﬁrmed formation of single-phase spinel ferrites with crystallite size in the range of 1116 nm. Vibrations of metaloxygen bonds at octahedral and tetrahedral sites in the crystal lattice were conﬁrmed by Fourier transform infrared spectra. Morphology was veriﬁed by scanning electron microscopy. The effect of composition on room temperature dielectric permittivity, dielectric loss, and AC conductivity of samples was studied in the frequency range from 20 Hz to 1 MHz. Decrease in dielectric constant and dielectric loss were observed with increasing frequency. AC conductivity peaked in the narrow frequency band centered around 500 KHz was observed. Conductivity at resonance increases with increase in indium concentration. The behavior of nanopowders under the inﬂuence of time- varying signal was analyzed on the basis of MaxwellWagner theory. Keywords: ferrites; co-precipitation; electrical properties 1. Introduction Nanocrystalline materials have attracted considerable attention due to the presence of a large number of atoms at the grain surface compared to coarse-grained polycrystalline counterparts. The fraction of atoms on the surface of grains increases with decreasing grain size. Hence, the interface structure plays an important role in determining the elec- trical properties of nanocrystalline materials.[1] Spinel ferrites are magnetic semiconduc- tors with the general formula AB 2 O 4 , where A is a divalent metal ion and B is iron; however, iron can be partially substituted by other trivalent metal ions. Ferrites crystallize in the face-centered cubic crystal system and belong to the space group Fd 3 m(O 7 h ).[2] Oxygen anions arranged in a cubic close-packed lattice form 64 tetrahedrons and 32 octa- hedrons in a unit cell. The cations occupy 8 of tetrahedral sites (A sites) and 16 of octahe- dral sites (B sites); the conventional unit cell then contains eight of such AB 2 O 4 formula units.[3] The tetrahedral and octahedral sites accommodate various metal cations in order to yield a stable spinel structure. Variation in cation distribution is used to tailor physical properties of spinel ferrites.[4] Polycrystalline spinel ferrites have a wide range of applications due to high electrical resistivity, dielectric constant and permeability, chemical stability, and reasonable cost. [5] They are extensively used in radiofrequency circuits, high-quality ﬁlters, rod *Corresponding author. Email: surender.postbox@gmail.com Ó 2014 Chinese Advanced Materials Society Journal of the Chinese Advanced Materials Society, 2014 http://dx.doi.org/10.1080/22243682.2014.951391 Downloaded by [Surender Kumar] at 08:01 23 September 2014