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 Pm3̄n, 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.