Structure and thermoelectric characterization of AxBa8-xAl14Si31 (A = Sr, Eu) single crystals

Single crystals of A(x)Ba(8-x)Al(14)Si(31) (A = Sr, Eu) were grown using a molten Al flux technique. Single-crystal X-ray diffraction confirms that A(x)Ba(8-x)Al(14)Si(31) (A = Sr, Eu) crystallize with the type I clathrate structure, and phase purity was determined with powder X-ray diffraction. Stoichiometry was determined to be Sr0.7Ba7.3Al14Si31 and Eu0.3Ba7.7Al14Si31 by electron microprobe analysis. These A(x)Ba(8-x)Al(14)Si(31) phases can be described as framework-deficient clathrate type I structures with the general formula, A(x)Ba(8-x)Al(y)Si(42-3y/4)[](4-1/4y). DSC measurements indicate that these phases melt congruently at 1413 and 1415 K for Sr0.7Ba7.3Al14Si31 and Eu0.3Ba7.7Al14Si31, respectively. Temperature-dependent resistivity indicates metallic behavior, and the negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity of these phases remains low with Sr0.7Ba7.3Al14Si31 having the lowest values.