LOCAL ORDER IN CONCENTRATED AQUEOUS-SOLUTIONS OF YTTRIUM CHLORIDE ANDBROMIDE

X-ray diffraction patterns of equimolecular concentrated aqueous solut ions of yttrium chloride and bromide have been investigated from s = 0 .4 Angstrom(-1) up to s = 15 Angstrom(-1). An assumed coordination of eight water molecules around each yttrium cation, at a distance of 2.3 6 Angstrom, reproduces the intensity at high s values in agreement wit h the values obtained by some of the present authors from EXAFS experi ments. Narrow interference maxima at s = (4 pi sin theta)/lambda simil ar or equal to 0.9 Angstrom(-1) may be interpreted as the existence of a local order of the hydrated yttrium cations surrounded by anions an d free water molecules. Structural models with and without close packi ng of the hydrated cations were built to simulate that local order.