Experimental and theoretical study of the vibrational properties of diaspore (a-AlOOH)
Résumé
Vibrational properties of diaspore, a-AlOOH, have been re-investigated using room-temperature singlecrystal Raman spectroscopy and low-temperature powder infrared (IR) transmission spectroscopy. First-principles harmonic calculations based on density functional theory provide a convincing assignment of the major Raman peaks and infrared absorption bands. The large width of the Raman band related to OH stretching modes is ascribed to mode-mode anharmonic coupling due to medium-strength H-bonding. Additional broadening in the powder IR spectrum arises from depolarization effects in powder particles. The temperature dependence of the IR spectrum provides a further insight into the anharmonic properties of diaspore. Based on their frequency and temperature behavior, narrow absorption features at *2,000 cm-1 and anti-resonance at *2,966 cm-1 in the IR spectrum are interpreted as overtones of fundamental bending bands.