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 Ga Si , of size 2.9 mm were grown 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, = 10.3266(2) Å, space group 3̄ , no. 223). By adding Sn to a Na-Ga-Si melt (Na : Ga : Si : Sn = 6 : 1 : 2 : 1), single crystals of Na Ga Si ( = 4.94-5.52, = 10.3020(2)-10.3210(3) Å), with the maximum size of 3.7 mm, were obtained Na evaporation at 723-873 K. The electrical resistivities of Na Ga Si and Na Ga Si 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 soft X-ray emission spectrum of Na Ga Si , a weak peak originating from the lowest conduction band in the undoped Si was observed at an emission energy of 98 eV.