Spectroscopic Study of Al3+-Substituted Strontium Hexaferrite

The substituted Y type hexaferrites (where ？=？2, 4, 6, 10) are prepared by standard ceramic technique. The infrared absorption spectra of the prepared compounds are studied in the range 400？cm？1 to 4600？cm？1. These spectra are used to locate the vibrational ranges due to substituted cations with the nearest oxygen layers and also to understand the band positions attributed to the lattice sites. The absorption regions found around 460？cm？1 and 600？cm？1 are the common features of all spinel ferrites. Both X-ray and IR spectroscopic studies in these ferrites do not detect the presence of Fe2+. Also with increase in aluminium substitution, the higher frequency bands start disappearing. This may be due to reduced vibrations of trivalent cations Fe–O bonds at both octahedral and tetrahedral sites which in turn affect Fe3+–O2？–Fe3+ superexchange interactions present in the structure. 1. Introduction Infrared spectroscopy is the most powerful technique for the chemical identification of crystal structure. It provides useful information about the structure of molecules without tiresome evaluation methods, which are applied in other usual methods of structural analysis such as X-ray diffraction and neutron diffraction. With the absorption of infrared radiations, the molecules of the chemical substance vibrate at many rates of vibration, giving rise to close packed absorption bands. Thus such infrared spectra give the vibrational behavior of the crystal structure. It is interesting to note here that till date much less effort has been taken in studying the vibrational spectrum of the ferrites. In that, most of the work is concentrated on spinel ferrites [1–3]. Infrared spectral analysis has been carried out for several ferrites by Waldron in 1955, who reported two absorption bands within the wave numbers 200–800？cm？1, which are attributed to the tetrahedral and octahedral complexes of the spinel structure. Cr substituted Ni spinel ferrite is also studied [4] and authors attributed the existence of fine structure to the Jahn-Teller effect. Gd3+ substituted Cd-Ca spinel ferrite [5] and Nd3+ substituted Zn-Mg spinel ferrite [6] are also studied by using infrared absorption spectroscopy. Thus it is clear that as far as the hexaferrite is concerned, no previous infrared studies of these materials were found in the literature with the exception of the reflection spectrum of Ba2-Y type [7], Sr2-Y with divalent substitution [8], and absorption spectra of Ba-M type ferrite [9]. In the present paper, the results regarding the infrared absorption spectral analysis of four