VIBRATIONAL-SPECTRA OF ALKALI-METAL (LI, NA AND K) URANATES AND CONSEQUENT ASSIGNMENT OF URANATE ION SITE SYMMETRY

Vibrational (Raman and infrared) spectra of nine alkali metal (lithium , sodium and potassium) uranates have been measured in the infrared ra nge of 4000-250 cm(-1) and the Raman shift range of 1100-50 cm(-1). Th e Raman spectra of sodium and potassium uranates, and lithium polyuran ates are reported for the first time. From these spectra the site symm etries of intrinsic uranate groups are deduced by comparing the number of observed and resolved bands with the number predicted by the vario us site symmetries subgroups possible for each uranate crystal symmetr y. The following could then be assigned: C-2h for Li2UO4; D-2h for alp ha-Na2UO4; D-4h for K2UO4; D-2 for Na2U2O7 and C-2h for K2U2O7. For th e Lithium polyuranates, Li2O . 1.6UO(3), Li2O . 1.75UO(3), Li2U2O7 and Li2U3O10, as their crystal symmetries are not fully known, no definit e conclusions concerning uranate site symmetry could be drawn, except that primitive monoclinic symmetry point groups must be excluded. (C) 1998 Elsevier Science B.V. All rights reserved.