Na-Ga-Si type-I clathrate single crystals grown via Na evaporation using Na-Ga and Na-Ga-Sn fluxes.

Single crystals of a Na-Ga-Si clathrate, Na 8 Ga 5.70 Si 40.30 , of size 2.9 mm were grown via the evaporation of Na from a Na-Ga-Si melt with the molar ratio of Na : Ga : Si = 4 : 1 : 2 at 773 K for 21 h under an Ar atmosphere. The crystal structure was analyzed using X-ray diffraction with the model of the type-I clathrate (cubic, a = 10.3266(2) Å, space group Pm 3̄ n , no. 223). By adding Sn to a Na-Ga-Si melt (Na : Ga : Si : Sn = 6 : 1 : 2 : 1), single crystals of Na 8 Ga x Si 46- x ( x = 4.94-5.52, a = 10.3020(2)-10.3210(3) Å), with the maximum size of 3.7 mm, were obtained via Na evaporation at 723-873 K. The electrical resistivities of Na 8 Ga 5.70 Si 40.30 and Na 8 Ga 4.94 Si 41.06 were 1.40 and 0.72 mΩ cm, respectively, at 300 K, and metallic temperature dependences of the resistivities were observed. In the Si L 2,3 soft X-ray emission spectrum of Na 8 Ga 5.70 Si 40.30 , a weak peak originating from the lowest conduction band in the undoped Si 46 was observed at an emission energy of 98 eV.