SYNTHESIS AND CHARACTERIZATION OF CHARGE-SUBSTITUTED GARNETS YCALNGA5O12 (LN=CE, PR, TB)

A low temperature method is described for the preparation of the new g arnet compounds YCaLnGa5O12 (Ln = Ce, Pr, Tb. In this set of compounds (Ca2+ + Ln4+) replaces 2Y3+ in the parent gallium based garnet Y3Ga5O 12 in order to stabilize as effectively as possible the Ln4+ species i n the eight-coordinate ''A'' site of the garnet structure. Characteriz ation of the oxides by X-ray powder diffraction and thermogravimetric analysis is discussed with regard to the structural relationship of th e substituted compound to the parent material. The tetravalent ions Pr 4+ and Tb4+ exhibit increased thermal stability in reducing conditions as compared to the Ln4+ states in the fluorite (LnO2) and perovskite (BaLnO3) type structures. This result is discussed with reference to t he complex crystal chemistry of these systems.