Pressure evolution of the phonon modes and force constants of Tb₃Al₅O₁₂ and Lu₃Al₅O₁₂

Abstract

The pressure evolution of the Raman modes of Tb3Al5O12 and Lu3Al5O12 has been measured at room temperature and analyzed theoretically with the rigid ion model. Satisfactory agreement between experiment and theory has been found. The extracted pressure variation of the bond bending and bond stretching force constants shows that the compressibility of the various polyhedra types increases with increasing cation coordination, indicating that the dodecahedra play an important role in the compressibility of the garnet structure. Finally, an estimation of the pressure coefficients for the transverse optical infrared active mode frequencies is given.

Structural, elastic and vibrational properties of nanocrystalline lutetium gallium garnet under high pressure

“…In particular, the study of their elastic properties and mechanical stability under pressure is an interesting subject that can provide important information concerning the study of their structural transformations via the stability criteria. 9,10 Recently, the pressure evolution of the vibrational properties of Y 3 Ga 5 O 12 (YGG), which is also isostructural to LuGG, has been studied both through experiments and first principles simulations; 11 furthermore, the elastic properties of this garnet under pressure have been analyzed by means of ab initio methods. The application of pressure allows the variation of the interatomic distances and bonds, and to obtain the structure dependence of the f-electron states in RE 3+ ions.…”

“…In the literature, few papers report the vibrational properties of garnets, most of them devoted to the rare earth aluminum garnets (RE 3 Al 5 O 12 ) such as Lu 3 Al 5 O 12 (LuAG), which is isostructural to LuGG. 9,10 Recently, the pressure evolution of the vibrational properties of Y 3 Ga 5 O 12 (YGG), which is also isostructural to LuGG, has been studied both through experiments and first principles simulations; 11 furthermore, the elastic properties of this garnet under pressure have been analyzed by means of ab initio methods. 12 Now we are interested in studying similar effects in our system, to evaluate the modifications related to the possible effect of the ''chemical pressure'' related to size effects when changing Y with a Lu atom.…”