SITE PREFERENCE OF CATIONS AND STRUCTURAL VARIATION IN Y3FE5-XGAXO12 0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-5) SOLID-SOLUTIONS WITH GARNET STRUCTURE

The crystal structures of Y3Fe5-xGaxO12 (0 less than or equal to x les s than or equal to 5) solid solutions (x = 0.0, 1.0, 1.6, 2.0, 2.5, 3. 0, 3.6, 3.8, 4.6 and 5.0) with garnet structure were refined by single -crystal X-ray diffraction analyses. Site preferences of cations in th e crystal structure were examined in detail. The smaller Ga3+ ion occu pies only the four-coordinated site in the composition range x = 0.0-1 .6 (region I), whereas the larger Fe3+ ion occupies only the six-coord inated site from x = 5.0 to 3.8 (region III). Both cations occupy thes e two sites from x = 1.6 to 3.8 (region II). The tendency for site pre ference of cations changes near x = 1.6 and 3.8. When Ga3+ and Fe3+ oc cupy only the four- (region I) and six-coordinated sites (region III), respectively, the enhancement of the cation-cation interaction can be considered as a result of the geometric restriction due to the variat ion of cation size. The change in tendency for cation site preference is most probably caused by the increased cation-cation interaction. Cr ystal data: cubic, Ia ($) over bar 3d, Z = 8, MoK alpha, lambda = 0.71 069 Angstrom; at x = 0.0: a(0) = 12.375 (1) Angstrom,