Spinel Raman

Fig. 3 Raman spectra of Co/y-Al203 and CoRu/y-Al203 after different pretreatments, CoO, C03O4 (spinel), and CoA1204 (spinel).26 Reprinted from Journal of Catalysis, Vol. 204, J. Jongsomjit, J. Panpranot and J. G. Goodwin, Jr, Co-Support compound formation in alumina-supported cobalt catalysts, pp. 98-109. Copyright (2001), with permission from Elsevier.

The physical mechanisms associated with the phase transition of y-Fe203 nanoparticles induced by laser irradiation have been studied by El MendUi et al., by performing in situ micro-Raman measurements of both as-prepared y-Fe203 nanoparticles (about 4 nm in size) as a function of laser intensity and annealed samples [51]. Raman spectrum for the as-prepared nanoparticles showed the presence of three broad peaks at 350, 500, and 720 cm and magnon mode in the neighborhood of 1,300 cm . Such a Raman spectrum obeys the symmetry rules established for the inverse spinel structure with a tetragonal sublattice distortion,... 

The vAl-O-Al IR band was used to study the effects of the caustic ratio on the structure of sodium aluminate solutions.118 Variable-temperature Raman spectra of the spinel MgAl204 showed a band at 727 cm" 1 for samples annealed above 800°C. This was ascribed to cation disorder in these samples.119 The angular force constant method was used to analyse vibrational modes for MA1204, where M = Mg or Zn.120 Ab initio calculations have been made of vibrational wavenumbers involving the OH group in topaz, Al2Si04(0H)2.121... 

The Raman spectrum of the spinel LiMn204 showed characteristic peaks of this species for the first time.253 Raman spectroscopy was also used to follow structural changes of an LiMn204 electrode on doping with A1 and F.254 The... 

Raman studies have been made on natural and a number of synthetic MgAl204 spinel crystals. Deviations in Raman selection rules in the synthetic crystals can be ascribed to disordering in the Mg-Al sites, and can be useful in characterizing such crystals. 

This was observed to occur at similar temperatures of 800°C. In addition, nanoparticles of hematite prepared via an aqueous precipitation have shown a size and temperature-dependent concentration of spinel defects at the surface. The formation of these defects on hematite was shown to be governed by the thermodynamics of the ly-y phase transition with decreasing particle size [121], Raman spectroscopy has shown that similar defects on the surface of highly efficient anodes prepared by APCVD are important to the performance [13]. 

As discussed elsewhere (28), the IR and Raman spectfa of the Mg Fe j Oj spinels with 0 X 0.66 are all closely similar. However, the vl (R) and v5 (R) modes clearly shift progressively although sUghtly up by increasing x. In parallel, vl (IR) and v2 (IR) shift also slightly... 

The IR spectra of the Mg Zn, FejO are shown in Fig. 3.The skeletal spectrum progressively modifies with shifts up of vl (IR) and v2 (IR) by increasing y, as well as with a decrease in intensity of v3 (IR) that likely shifts also down. These spectra indicate that the change from normal to inverse spinel occurs progressively. IR and Raman spectra (that are frequently more sensitive to cation orderings than XRD) confirm that cation ordering in the inverse spinel MgFe O as well as in the mixed spinels does not occur. 

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