Synthesis and ionic conductivity of novel high charged tetrasilisic type micas

Abstract

The objectives of this study were the synthesis of novel high charged tetrasilisic type micas with the chemical compositions of Na4(MgxLi2(4-x))Si8O20F4 (x = 2, 3 and 4) and the estimation of ionic conductivity of the novel micas. The mica with x = 2 has no vacancies in the octahedral sheets and the ratio Mg2+/Li+ in the octahedral sheets is 2/4 in the chemical formula. The micas with x = 3 and 4 have vacancies in the octahedral sheets and the ratio Mg2+/Li+/vacancy is 3/2/1 and 4/0/2, respectively. The synthesis was tried by firing the mixtures of chemical reagents in sealed container. The obtained materials were characterized using X-ray diffraction analyzer, scanning electron microscopy, Fourier transform infrared spectrometer and 23Na magic angle spinning nuclear magnetic resonance equipment. The novel micas with x = 2, 3 and 4 were formed during cooling after melting the mixtures of the reagents. However, a part of Na+ ions which should be interlayer cations originally entered the vacant sites in the octahedral sheets of the obtained mica with x = 4. The mica with x = 2 showed the highest ionic conductivity and the conductivity was 2.4 × 10−2 S/cm at 600 °C. This resulted from the facts that the mica with x = 2 was actually high charged tetrasilisic type mica of which Na+ ions in the interlayers did not transfer to the octahedral sheets and had many mobile Na+ ions in the interlayers.