Polycrystalline ferrites, , (where and ), were prepared by using ceramic method. Single phase cubic structure was confirmed by X-ray diffractometer. The lattice parameter “a” was found to increase with increasing ion substitution. IR spectra of the samples were recorded from 200 to 1000？cm？1. The two primary bands corresponding to tetrahedral and octahedral were observed at about 575？cm？1 and 370？cm？1, respectively. Elastic properties of these mixed ferrites were estimated as a function of composition. Young's modulus , rigidity modulus , bulk modulus , Debye temperature ( ), and mean sound velocity ( ) were calculated from the transverse ( ) and longitudinal ( ) wave velocities. The variation of elastic moduli with composition was interpreted in terms of binding forces between the atoms of spinel lattice. AC conductivity and dielectric properties of the samples were measured at room temperature over 100？Hz–1？MHz. The electrical conduction mechanism could be explained with the electron hopping model. Frequency exponential factor was calculated and it was found between 0.4 and 0.8. 1. Introduction Polycrystalline ferrites have very important structural, magnetic, electrical, and dielectric properties that are dependent on various factors, such as method of preparation, substitution of cations, and microstructure [1, 2]. Introduction of a relatively small amount of foreign ions can change the properties of ferrites [3]. It can provide us with information for obtaining a high-quality ferrite for particular applications. Modification in electric and magnetic properties of lithium ferrites by substitution of different ions has been extensively studied [4–6]. Infrared spectroscopy was used to determine the local symmetry of crystalline and noncrystalline solids and to study the ordering phenomenon in ferrites [6]. IR absorption bands mainly appear due to the vibrations of oxygen ions with cations at various frequencies. The frequencies depend upon cation masses, lattice parameter, and cation-oxygen bonding, and so forth. [7]. Ultrasonic pulse transmission (UPT) is a very common technique for studying elastic constants. However, a new technique based on infrared spectroscopy has been developed by Modi et al. [8] for studying the elastic properties of spinel and garnet ferrites. The elastic constants are of much importance because they reveal the nature of binding forces in solids and help to understand thermal properties of the solids [9]. Elastic properties of spinel ferrites have not been studied so systematically as their magnetic and electrical properties.
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