1995 Volume 103 Issue 1202 Pages 1057-1062
Various Ni2+-substituted tetrasilicic micas having high contents of Ni2+, such as KNiMgLi(Si4O10)F2, KNi2Li(Si4O10)F2 and KNi2.5(Si4O10)F2, were synthesized at ca. 900°C through solid-state reaction techniques. Lattice constants a, b, c decreased with increasing Ni2+-substitutions, reflecting the decrease in the ionic radius of Ni2+ against Mg2+. UV-visible spectra of Ni2+-micas were very similar to those of [Ni(H2O)6]2+, This can be explained in terms of the nephelauxetic series F-<H2O<Oa (apical oxygen) as well as the spectrochemical series F-<H2O<Oa. IR spectra showed that the tetrahedral distortion changes with increasing Ni2+-substitutions, i.e., the interatomic distance of Si-Oa lengthens while that of Si-Ob (basal oxygen) shortens. Ni2+-micas exhibited paramagnetism when the Ni2+ content was smaller than 2.0 mol in octahedral sites, however, antiferromagnetism seemed to appear at larger substitutions of 2.5 mol Ni2+ per formula unit.
