Aluminium-gallium substitution in yttrium garnets investigated by NMR

The aluminium-gallium substitution has been studied in the garnet structure of composition Y 3 Al 5-x Ga x O 12 (x = 0,1,2,3,5) by a local atom observation using both of 27 Al MAS and 71 Ga static NMR techniques. Each site has been characterised by the isotropic chemical shift (δ iso ) and the quadrupolar interaction tensor (C Q and η Q ). An important lineshape (quadrupolar parameter) evolution has been observed when the gallium substitution increases which translates as site defonnation, viewed on the whole by atoms with octahedral symmetry. Little electric field gradient variation has been observed for the tetrahedral site. For YGG (Y 3 Ga 5 O 12 ), Ga NMR distinguishes two types of octahedron. They are differently affected by substitution.