Structure and Thermoelectric Characterization of Ba₈Al₁₄Si₃₁

Abstract

A molten Al flux method was used to grow single crystals of the type I clathrate compound Ba8Al14Si31. Single-crystal neutron diffraction data for Ba8Al14Si31 were collected at room temperature using the SCD instrument at the Intense Pulsed Neutron Source, Argonne National Laboratory. Single-crystal neutron diffraction of Ba8Al14Si31 confirms that the Al partially occupies all of the framework sites (R1 = 0.0435, wR2 = 0.0687). Stoichiometry was determined by electron microprobe analysis, density measurements, and neutron diffraction analysis. Solid-state (27)Al NMR provides additional evidence for site preferences within the framework. This phase is best described as a framework-deficient solid solution Ba8Al14Si31, with the general formula, Ba(8)Al(x)Si(42-3/4x)[](4-1/4x) ([] indicates lattice defects). DSC measurements and powder X-ray diffraction data indicate that this is a congruently melting phase at 1416 K. Temperature-dependent resistivity reveals metallic behavior. The negative Seebeck coefficient indicates transport processes dominated by electrons as carriers.

Universal Relation between Guest Free Space and Lattice Thermal Conductivity Reduction by Anharmonic Rattling in Type-I Clathrates

“…36 The data of κ L at 150 K in type-I clathrates 4,5,27,28,[37][38][39][40][41] are plotted vs. R cag e in Fig. 7(a).…”

Electrochemical Cycling of Sodium‐Filled Silicon Clathrate

“…Silicon with a clathrate or cage-like structure has been recently investigated as a potential anode, with both theoretical [9] and experimental verification by Langer et al [10] that lithiation is feasible. Since prior studies on silicon clathrates have focused predominately on their superconducting [11][12][13][14][15][16][17][18] and thermoelectric [19][20][21][22][23][24] properties, this is a potentially new and exciting application for this class of materials. Type-I clathrates of the form M 8 Si 46 , where M is a guest atom intercalated into the structure, are made of two pentagonal dodecahedra (Si 20 ) cages and six tetrakaidecahedra (Si 24 cages) per unit cell and crystallize in the Pm " 3n space group (Figure 1 a).…”

Cs8−xSi46: A Type‐I Clathrate with Expanded Silicon Framework

“…[17a,b] The radius of Cs atoms was estimated to be too large for both types of cages in the Si 46 framework and, therefore, the formation of the clathrate-II silicide Cs~7Si 136 is attributed to the preferential occupation of the largest Si 28 cages in this atomic arrangement. [15] However, the synthesis of Ba 8Àx Si 46 at high-pressure high-temperature conditions [11] or the ternary phase Ba 7.5 Al 13 Si 29 [18] indicate that a clathrate-I framework can host atoms as large as Ba inside the E 20 or E 24 cages. Nevertheless, the preparation of a clathrate-I silicide with Cs remained a challenge since Cs atoms require even more volume than Ba atoms.…”