New rare earth-alkaline earth oxide compounds: Predicted compound formation and new families found

Abstract

The study of crystal chemical relationships between sesquioxides of certain rare earth ions [La, Gd, (Y), Ho, Yb] and the alkaline earth oxides shows that compound formation at two compositions is extensive. The molar ratios of these compositions, alkaline earth oxide to rare earth oxide, are 1:1 and 1:2. There appear to be three different structures at the 1:1 composition. From the similarities of X-ray diffraction patterns obtained, the prepared compounds are grouped as follows: (I) CaY 2O 4 and CaHo 2O 4 (II) CaYb 2O 4, SrGd 2O 4, SrY 2O 4, SrHo 2O 4, and SrYb 2O 4 (III) BaGd 2O 4, BaY 2O 4, BaHo 2O 4, and BaYb 2O 4 Even within one of these structural families, it is probable that there are minor distortions which affect exact space group correspondence. The 1:2 compounds have X-ray diffraction patterns which are even more similar. The compounds CaGd 4O 7, CaY 4O 7, CaHo 4O 7, CaYb 4O 7, and SrGd 4O 7 were prepared. Application of simple field strength calculations in these systems predicts compound formation only between BaO and rare earth oxides possessing trivalent rare earth ions of the smallest radii.