ALUMINUM-GALLIUM SUBSTITUTION IN YTTRIUM GARNETS INVESTIGATED BY NMR

The aluminium-gallium substitution has been studied in the garnet stru cture of composition Y(3)Al5-xG(x)O(12) (x = 0,1,2,3,5) by a local ato m observation using both of (27)AL MAS and Ga-71 static NMR techniques . Each site has been characterised by the isotropic chemical shift (de lta(iso)) and the quadrupolar interaction tensor (C-Q and eta(Q)) An i mportant lineshape (quadrupolar parameter) evolution has been observed when the gallium substitution increases which translates as site defo rmation, viewed on the whole by atoms with octahedral symmetry. Little electric field gradient variation has been observed for the tetrahedr al site. For YGG (Y3Ga5O12), Ga NMR distinguishes two types of octahed ron. They are differently affected by substitution.