Synthesis and Properties of Co<sup>2+</sup>-Substituted Tetrasilicic Fluorine Micas

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  • IHARA Yoshihiro
    Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University
  • KITAJIMA Kunio
    Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University

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Other Title
  • Co<sup>2+</sup>置換フッ素四ケイ素雲母の合成と性質
  • Co2+チカン フッソ シ ケイソ ウンモ ノ ゴウセイ ト セイシツ

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Various Co2+-substituted tetrasilicic micas having high contents of Co2+, such as KCoMgLi(Si4O10)F2, KCo2Li(Si4O10)F2 and KCo2.5(Si4O10)F2, were synthesized through solid-state reaction techniques at 1000, 800 and 800°C, respectively. Lattice constants a, b increased with increasing Co2+-substitutions, reflecting the increase in the ionic radius of Co2+ against Mg2+, while c decreased due to the flattening of octahedral sheets. Both the micas KCoMgLi(Si4O10)F2 and KCo2Li(Si4O10)F2 exhibited pink color while the mica KCo2.5(Si4O10)F2 turned blue due to the trace amount of tetrahedral Co2+-substitution. Site preference of Co2+ ions depended on formation temperature and composition of micas. UV-visible spectra of Co2+-micas were similar to that of [Co(H2O)6]2+. This can be explained in terms of both the nephelauxetic and spectrochemical series of F-<H2O<Oa (apical oxygen). IR spectra showed that the tetrahedral distortion changes with increasing Co2+-substitutions, i.e., the interatomic distance of Si-Oa lengthens. The Co2+-mica KCoMgLi(Si4O10)F2 showed paramagnetism while the larger Co2+-substituted mica KCo2Li(Si4O10)F2 showed antiferromagnetism. On the other hand, the mica KCo2.5(Si4O10)F2 having the highest Co2+-content exhibited only a weaker magnetic interaction between Co2+ ions, probably due to the local variations of octahedral vacancy and Co2+-occupancy into two octahedral sites M1, M2 and tetrahedral sites.

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