Mixing unmixables: Unexpected formation of Li-Cs alloys at low pressure

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Science Advances  09 Oct 2015:
Vol. 1, no. 9, e1500669
DOI: 10.1126/sciadv.1500669


  • Fig. 1 Synchrotron x-ray diffraction patterns for a starting mixture of Cs-rich Li-Cs, synthesized at low pressure and at 298 K.

    Obvious changes in x-ray diffraction patterns were observed as a function of pressure. Radiation wavelength is 0.41373 Å.

  • Fig. 2 Synchrotron x-ray diffraction patterns for an approximately equimolar Li-Cs mixture at 298 K (A, left panel) and 498 K (B, right panel) at various pressures.

    Note that x-ray diffraction patterns were recorded for pressure upstroke and downstroke at 298 and 498 K, respectively.

  • Fig. 3 Compression of the cubic Li-Cs alloy.

    (Left panel) Unit cell parameter of the cubic Li-Cs alloy at a function and pressure at two different temperatures, namely, 298 and 498 K. (Right panel) Comparison of the pressure dependence of the average atomic volume in Li-Cs alloys at 298 and 498 K (this work) occupied by Cs in Cs-I (14), Cs-II (15), Cs-III (17), and Cs-IV (16) and Li in Li-I (14) and Li-II (30).

  • Fig. 4 Three-dimensional electron density probability as obtained from an analysis of x-ray diffraction data by the MEM.

    The x-ray data are for the Li-Cs sample at 8 GPa and 298 K. The surface contour value is 3.25 e3.

  • Fig. 5 Results of a Rietveld analysis of the high-temperature/high-pressure (498 K and 5 GPa) x-ray data of the Li-Cs alloy using two different cubic structural models (symbols, observed x-ray diffraction pattern; solid black line, calculated x-ray diffraction pattern; solid blue line, intensity difference).

    (Top) Structural model A. Space group Pm-3m; atomic positions: Cs (0,0,0) and Li (0,1/2,1/2), Li (1/2, 0, 1/2), Li (1/2,1/2,0); lattice parameter = 3.572(4) Å; Rp = 20.1% and Rwp = 17.1%. (Bottom) Structural model B. Space group Pm-3m; atomic positions Cs (0,0,0) and Li (1/2,1/2,1/2); lattice parameter = 3.572(3) Å; Rp = 16.9% and Rwp = 9.18%.

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