New garnet compounds with trivalent rare-earth ions on both dodecahedral and octahedral sites

This study deals with preparation of garnets of the type {Nd _{3- y}R _y}[R _xGa _{2- x}](Ga ₃)O ₁₂, in which R is Lu, Yb, Tm, Er, Ho, or Dy. It has been found that the placement of large rare-earth ions such as Nd ³⁺ on the dodecahedral sites opens up the lattice so that small rare-earth ions may enter the octahedral sites. For the case of R = Lu single-phase {Nd ₃}[Lu ₂]Ga ₃O ₁₂ (i.e., y = 0, x = 2) has been prepared. Calculations indicate that similar compounds of Yb and perhaps Tm have also been prepared, though impure. To prepare single-phase Yb and Tm compounds with x = 2, it is necessary simultaneously to place determined minimum amounts of R in the dodecahedral positions. This minimum required value of y increases with increasing radius of R. Many single-phase garnet solid solutions have also been prepared; the region in which pure garnets occur is indicated in a ternary diagram.