Vibrational properties of (Gd1−xYx)3Ga5O12 solid solutions

Abstract

The vibrational properties of the (Gd1−xYx)3Ga5O12 (0≤x≤1) mixed garnet crystals are investigated at normal conditions by Raman and reflectivity infrared (IR)-spectroscopy while the end members of the series have been theoretically investigated by means of a rigid ion model. The IR experimental spectra were analyzed by means of the Kramers–Kronig relations and the Lorentz oscillator model. The obtained results are compared and discussed in detail with the theory, providing useful parameters for estimating and understanding the IR optical properties of mixed garnets. The majority of the expected Raman peaks is resolved and their symmetry assignment has been elucidated. The clear one mode behavior of the observed Raman and IR modes as a function of x confirms the formation of solid solutions, resulting from the replacement of the cations at the dodecahedral lattice sites. A softening of almost all Raman and IR modes is found as the unit cell volume increases (x decreases). Finally, the small dispersion of the Grüneisen parameters γi (ω) indicates that the binding forces are of the same nature and order of magnitude and that the binding strength between the various molecular units is quite comparable.