Gadolinium Gallium Garnet (Gd₃Ga₅O₁₂ - GGG) crystals serve as a lasing host material for various dopants.  It has been shown that GGG:Yb laser crystals, showing laser action at a wavelength of about 1 μm, can be diode pumped. GGG crystals can be easily grown using various methods including a very convenient for research the micro-pulling down method.

GGG crystallises in Ia3d space group. Rare-earth ions in these crystals substitute Ga³⁺  at dodecahedral positions. The point symmetry of this site is D₂. Luminescence studies at high hydrostatic pressure indicate a possibility of change of the point symmetry at this site even to O_h at pressure of about 10 GPa and a return to D₂ at higher pressures. However, in the earlier experimental diffraction studies the first phase transition is observed only at much higher pressure of about 80 GPa. This intriguing behavior of site symmetry change can be observed when splitting of so called R­-level (⁴F_3/2) of Nd³⁺ ions is removed by applying pressure of about 10 GPa to GGG crystals. This phenomenon can occur only if Nd³⁺ ions are located at sites with O_h symmetry [1].

            In this work we report high-pressure X-ray diffraction study for GGG performed at room temperature in diamond-anvil cell. In the experiment, hydrostatic conditions were well preserved at least up to 10 GPa. The measured pressure dependence of lattice parameter is compared with theoretical ab initio calculations and earlier theoretical estimations of bulk modulus and its pressure derivative for GGG crystals, reported in Refs [2,3]. The experimental bulk modulus was derived from the diffraction data using the EOSFIT program assuming the 3rd order Birch-Murnaghan equation of state. Our results confirm earlier theoretical estimations that the GGG crystal exhibits the smallest bulk modulus among a few other garnets containing both Gd and Ga ions. Moreover, the theory shows that at certain pressure the Ga at dodecahedral site – O distances are equal, which is a prerequisite for increase of the symmetry of this site.

 Acknowledgements: The work was partially supported by a grant from the Polish Ministry of Science and Education for the years 2006–2009.

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