Single crystal growth and structure analysis of type-I (Na/Sr)-(Ga/Si) quaternary clathrates.

Single crystals of (Na/Sr)-(Ga/Si) quaternary type-I clathrates, Na 8- y Sr y Ga x Si 46- x , were synthesized by evaporating Na from a mixture of Na-Sr-Ga-Si-Sn in a 6 : 0.5 : 1 : 2 : 1 molar ratio at 773 K for 12 h in an Ar atmosphere. Electron-probe microanalysis and single-crystal X-ray diffraction revealed that three crystals from the same product were Na 8- y Sr y Ga x Si 46- x with x and y values of 7.6, 2.96; 8.4, 3.80; and 9.1, 4.08. It was also shown that increasing the Sr and Ga contents increased the electrical resistivity of the crystal from 0.34 to 1.05 mΩ cm at 300 K.