New substituted gallium garnets containing trivalent lanthanum on dodecahedral crystallographic sites

A number of new garnet compounds containing trivalent lanthanum on dodecahedral sites have been prepared. Incorporation of La3+ into dodecahedral crystallographic sites was achieved by means of expansion of the crystal lattice of gallium garnet by substitution for Ga3+ on the octahedral sites. It is shown that substitution of trivalent scandium in the octahedral sites of gallium garnet expands its lattice and enlarges dodecahedral holes enough to allow relatively large La3+ ions to fill the dodecahedral sites almost completely. It has been found that small rare earth ions such as Lu3+, Yb3+, and Tm3+ may also be used instead of Sc3+ to prepare the lanthanum-containing garnets. It has been observed that such substituted compounds are not strictly stoichiometric according to the formula {La3} [R2](Ga3)O12, where R may be Sc3+, Lu3+, Yb3+ or Tm3+, but they rather follow the formula {La3−yRy}[R2](Ga3)O12 with the value of y increasing with ionic radius of R. The minimum values of y needed in order to obtain single-phase materials were determined.