ICT2014 Abstracts

We have grown Mg₂Si bulk crystals by vertical gradient freezing (VGF) method using liquid encapslants. High quality Mg₂Si bulk crystal has difficulty in growing from the melt due to high reactivity of Mg, which sticks to a crucible material. In addition, the vapor pressure of Mg is high and thus it easily causes the deviation from the stoichiometric composition of Mg₂Si during the melt growth at around the melting point of Mg₂Si (1085^oC). Furthermore, the melt growth temperature for Mg₂Si is closed to the boiling point of Mg (1090^oC), which may cause an explosion.

The liquid encapsulant techniques can inhibit the effects of these problems by making the layer of the encapsulant surrounding the crucibles and the crystals. In this study, the crystal growth of Mg₂Si has been performed by VGF method using KCl or KCl–MgCl₂ as a liquid encapsulant material. Mg (99.5%) and Si (4N) powders with Mg/Si molar ratio of 2–2.5 were put into a BN coated SiO₂ or an Al₂O₃ crucible with encapsulant powders with MgCl₂/KCl molar ratio of 0–2. Then, it was pressurized to 500 Torr with Ar gas. The temperature of the electric furnace was elevated up to 1100^oC and kept for 1hour and then fallen to room temperature. When the MgCl₂/KCl molar ratios were above 1 and these encapsulants were dissolved in water after the crystal growth, the grown samples were removed from the crucibles without sticking to the crucible. The samples were characterized by Raman spectroscopy, EDS, XRD and Hall effect measurements. In the Raman spectra, strong peaks can be seen at 256cm^-1, which originate from Mg₂Si. The samples grown at Mg/Si molar ratio of 2 exhibited Mg-poor composition. Any contaminations of the grown samples with K and Cl from encapsulants were not observed. The results of Hall effect measurements are also presented.