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RRJOMS | Volume 5 | Issue 4 | July, 2017
July 27-29, 2017 Vancouver, Canada
10
th
International Conference on
Emerging Materials and Nanotechnology
Crystal growth of Na-Si clathrates by the flux method
Haruhiko Morito
Tohoku University, Japan
Introduction:
Si clathrate compounds have been widely studied due to their unique open-framework structures of Si
polyhedrons. Two types of Si clathrates encapsulating Na atoms have been known: type I (Na
8
Si
46
) and type II (Na
x
Si
136
, 0 < x
≤ 24). These Na-Si clathrates have been generally synthesized by thermal decomposition of a Na-Si binary compound, Na
4
Si
4
,
at 673–823 K under high-vacuum conditions (< 10
−2
Pa), and the obtained samples were in the form of powder with a particle
size in the micrometer range.
Purpose:
The purpose of this study is the crystal growth of the type I and type II Na-Si clathrates by using a Na-Sn flux.
Experiment:
The starting material of a mixture of Na, Na4Si4, and Na15Sn4 was prepared by heating Na, Si, and Sn (molar
ratio, Na/Si/Sn = 6:2:1) at 1173 K in Ar atmosphere. The mixture was heated at 673–873 K for 6–24 hours in the container with
a temperature gradient. After heating, air-sensitive compounds in the samples, such as Na-Sn compounds, were reacted with
ethanol, and the water-soluble reactants were removed by washing with water. Sn present in the products or formed by the
ethanol treatment was removed by dissolution in a dilute nitric acid aqueous solution.
Results:
The single crystals of type I clathrate were crystallized due to the evaporation of Na from the Na-Sn-Si solution at
673–773 K. Most of the single crystals had sizes of several hundred micrometers to 1 mm, and the maximum size reached to
about 3 mm. Heating the starting mixture at 823–873 K resulted in the crystal growth of the type II clathrate. The single crystals
having {111} habit planes grew up to about 2 mm in size.
Biography
Haruhiko Morito has his expertise in Material Science and Engineering. The main objective of his research is to develop an emerging material which has a new
function and new physical properties. In particular, he has developed new functional ceramics containing alkali metals. He has also developed a new crystal growth
process based on the binary phase diagram of sodium and silicon. He has synthesized various silicon-based materials by the sodium flux method.
morito@imr.tohoku.ac.jpHaruhiko Morito, Res. Rev. J Mat. Sci. 2017
DOI: 10.4172/2321-6212-C1-002