Crystal Chemical Study of the Rare-Earth Iron Garnets

Crystallographic and preparative data are given for high-purity rare-earth iron garnets (R3Fe2Fe3O12 and R3—xRx′Fe2Fe3O12, where R and R′ are rare earths). Lattice constants are obtained for hypothetical La, Pr, and Nd iron garnets. Maxima have been found for amounts of Pr substitution in Sm, Gd, Y, and Lu iron garnets which in turn lead to a principal maximum lattice constant of 12. 540 Å for any rare-earth iron garnet, in good agreement with 12. 538 Å obtained by Geller, Williams, and Sherwood. The maximum for La substitution in YIG is also given. A plot of lattice constant vs atomic number shows some influence of crystal field on the trivalent rare-earth ions with nonspherical electron configuration superposed on the lanthanide contraction. The importance of the size difference of the dodecahedral rare-earth ions in the praseodymium-substituted rare-earth iron garnets with respect to the maximum attainable lattice constants is shown corroborating observations on the neodymium substituted rare earth iron garnets. A set of relative effective CN (12) trivalent rare earth radii is calculated from the rare-earth iron garnet lattice constants.