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Clathrate guest atoms under pressure
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10.1063/1.3099589
/content/aip/journal/jap/105/7/10.1063/1.3099589
http://aip.metastore.ingenta.com/content/aip/journal/jap/105/7/10.1063/1.3099589

Figures

Image of FIG. 1.
FIG. 1.

(a) The clathrate type I structure with polygons showing the two different cages. (b) Close-up of the cages with Wyckoff notation of the host structure atoms. The structure has been overlaid on the structure to illustrate the relative displacement of the atom. The arrows indicate the direction of the displacement.

Image of FIG. 2.
FIG. 2.

The ADPs as a function of temperature for , , and (left to right). Triangles pointing up are , circles are , squares are , and inverted triangles are averaged host structure . The lines represent the Einstein and Debye fits.

Image of FIG. 3.
FIG. 3.

Powder INS spectra for with (diamonds), (triangles), (circles), and (squares). The spectra have been successively offset by 200 counts for clarity.

Image of FIG. 4.
FIG. 4.

The effect of the cage volume on rattler energy and lattice thermal conductivity. The volume goes from smallest to largest for , , , , and . Open circles are rattler energies extracted from the powder INS spectra, whereas Einstein temperatures extracted from x-ray data are shown as x’s. The lines are guides to the eyes. The solid squares are the results from the INS pressure experiment. Triangles are to lattice thermal conductivities at 250 K.

Image of FIG. 5.
FIG. 5.

INS spectra of . Squares indicate data collected at ambient pressure with an aluminum sample holder, circles are for data collected at ambient pressure with the sample loaded into the pressure cell, and triangles are for the sample under an applied pressure of 9 kbars. The spectra have been offset for clarity.

Image of FIG. 6.
FIG. 6.

INS spectra collected as a function of temperature for and . The temperatures of 300, 200, and 100 K are shown with squares, circles, and triangles, respectively. The spectra have been offset for clarity.

Image of FIG. 7.
FIG. 7.

The energy of the first (solid) and second (open) peaks observed by INS as function of temperature. and - and are shown as circles, squares, and diamonds, respectively, and the corresponding fits are shown as dotted, solid, and dashed lines.

Image of FIG. 8.
FIG. 8.

Electrical resistivity as a function of temperature for (diamonds), (triangles), and (circles).

Image of FIG. 9.
FIG. 9.

Seebeck coefficient as a function of temperature for (diamonds), (triangles), and (circles).

Image of FIG. 10.
FIG. 10.

Lattice thermal conductivity as a function of temperature for (diamonds), (triangles), and (circles). The charge carrier contribution has been subtracted from the observed thermal conductivity using Wiedemann–Franz law. For comparison the thermal conductivity for - and is included (Ref. 31).

Image of FIG. 11.
FIG. 11.

The dimensionless thermoelectric figure of merit, , for (diamonds), (triangles), and (circles).

Tables

Generic image for table
Table I.

Selected results from Rietveld refinements of the x-ray powder diffraction data. The structural parameters are as follows: Ba1, and Ba2, , and for the host structure , , and . For further details see supplementary material. The fractional volume and the volume of the large tetrakaidecahedral cage have been calculated according to procedures explained in the supporting material. The rattler energy from the powder INS data is given at room temperature. The scattering length , atomic mass, and atomic radius is listed for in . The corresponding values for Ge are as follows: , , and atomic .

Generic image for table
Table II.

Selected results from refinements of the 300 K single crystal x-ray diffraction data. The guest atoms are refined with the following structural parameters: Ba1, and Ba2, , and host structure atoms with , , and . Details from the refinement of data at other temperatures are given in supplementary materials.

Generic image for table
Table III.

Einstein and Debye temperatures and the disorder parameter obtained from multitemperature single crystal x-ray diffraction data. Literature values are listed for comparison.

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/content/aip/journal/jap/105/7/10.1063/1.3099589
2009-04-06
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Clathrate guest atoms under pressure
http://aip.metastore.ingenta.com/content/aip/journal/jap/105/7/10.1063/1.3099589
10.1063/1.3099589
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