Raman characterization studies of synthetic and natural MgAl2O4 crystals

Abstract

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Vibrational spectroscopy of aluminate spinels at 1 atm and of MgAl2O4 to over 200 kbar

“…No modes were found at 225 and 727 cm-1 as previously on synthetic spinel, see Table 2 ( O'Horo et al 1973;Fraas et al 1973; see also Ishii et al 1982). Broad weak features present in the baseline of the spectra at 445, 525, 610, and 718 cm -1 were confirmed as being intrinsic to the crystal by examining the anti-Stokes spectrum and/or using the 457.9-nm laser line for excitation.…”

“…Fraas et al (1973) found these extra modes and a few additional broad peaks in their synthetic spinels. Fraas et al's synthetic spinels displayed a varying degree of disorder as shown by the broadening and loss of resolution of the fluorescence spectrum.…”

“…This hypothesis will be tested in the next section by comparison of the spectra from our well-ordered sample to those of MgO'3A1203 spinel (Ishii et al 1982), for which the tetrahedral sites contain both Mg and A1 but the octahedral sites contain only A1, and to those of the synthetic spinel which is presumably partially disordered (O'Horo et al 1973; Fraas et al 1973). a Acoustic modes subtracted to give total optic modes b For the internal modes, C combination of v3 and v4.…”

“…3AlzO3, that has TO modes at 685, 569, 494, and 308 cm -1 (Ishii et al 1982). In the Raman spectrum, only 4 modes at 312 (Tag), 407 (Eg), 666 (Tlg), and 767 cm -1 (Alg) were found for a natural spinel (Fraas et al 1973) but additional peaks at 225, 492 (Tlg), and 727 cm-1 (Alg) were found for synthetic samples (Fraas et al 1973 ;O'Horo et al 1973 ;Ishii et al 1982). One possible cause of the discrepancies could be the facility with which the MgAI204 spinel structure disorders at relatively low temperatures (~ 670 ~ C), by exchanging cations between the octahedral and tetrahedral sites (Suzuki and Kumazawa 1980;Wood et al 1986).…”

Luminescence channels of manganese-doped spinel

“…Doping effect of transition metals has also been well studied [10][11][12]. Phonon structure has been clarified by Raman spectroscopy [13] and electronic states of doped transition-metal are also understood through their electron spin resonance (ESR) spectrum [14,15].…”