Vibrational properties of the rare earth aluminum garnets

Abstract

In this work we present single crystal infrared (IR) reflectance spectra for the Dy3Al5O12 and Er3Al5O12 compounds, their corresponding optical constants, as well as a discussion concerning the vibrational, dielectric, and elastic properties of various members of the rare earth aluminum garnet family. In the framework of the rigid ion model, the frequencies of the experimentally unresolved infrared active modes, the IR eigenvectors and the partial phonon density of states have been calculated. The role of the different atomic species in the various regions of the IR vibrational spectrum has been elucidated. In particular, it is found that the rare earth ionic mass plays a crucial role in the low frequency IR modes (<200 cm−1), while the high frequency modes are related mainly to the molecular modes of the AlO4 tetrahedral subunit. From the volume dependence of the IR active mode frequencies, their mode Grüneisen parameters are estimated and discussed. Finally, by using a modification of the semiempirical Brout’s formula, the bulk moduli have been determined and are compared to those derived from interatomic potential calculations.