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An extended high pressure-temperature phase diagram of
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Image of FIG. 1.
FIG. 1.

Synchrotron XRD pattern of the cubic phase of collected at 0.8 GPa and room temperature with the results of Rietveld analysis. The peak positions marked as “a” (green) correspond to that of and those marked as “b” (pink) are of NaCl.

Image of FIG. 2.
FIG. 2.

Selected XRD patterns of : (a) the cubic (3.4 GPa), tetragonal (6.5 GPa), and orthorhombic (9 GPa) phases at room temperature (b) at various temperatures and 6.5 GPa. Between 323 and 373 K, tetragonal to cubic phase transition occurs. Peaks marked as are of NaCl, which was used to determine pressure in the experiment.

Image of FIG. 3.
FIG. 3.

Pressure dependence of the unit cell volume (circles) for the high-pressure phase of cubic during compression at room temperature and at 573 K fitted with third order Birch–Murnaghan EOS (line) in comparison with the data reported by Kumar and Cornelius (Ref. 4) (asterisks).

Image of FIG. 4.
FIG. 4.

phase diagram of investigated through DAC technique using combined XRD and Raman spectroscopic measurements (circles) including the results of low temperature study of Sundqvist and Andersson (Ref. 6) (asterisks). The phase regions marked as C, T, O, and M are cubic, tetragonal, orthorhombic, and monoclinic respectively. The “?” mark implies that the structure is not confirmed.

Image of FIG. 5.
FIG. 5.

Selected Raman spectra of (a) at different pressures, and the spectrum marked as “?” corresponds to the appearance of a new phase, and (b) at 9.5 GPa and at various temperatures in comparison with a spectrum at 3 GPa. The peak marked as is due to impurities of diamond in DAC.

Image of FIG. 6.
FIG. 6.

Some selected Raman spectra of (a) during compression in the range of 14–30.4 GPa, (b) at 14 GPa and various temperatures, and (c) during decompression.

Image of FIG. 7.
FIG. 7.

The Raman shift vs pressure obtained by peak fitting of B–H stretching modes at each pressure (a) during compression and (b) decompression. Pressures that correspond to phase transition are marked with grid lines parallel to the axis.


Generic image for table
Table I.

The observed B–H stretching Raman modes in (sh—shoulder) for different phases of .

Generic image for table
Table II.

The pressure derivative of Raman shift for at different pressure ranges.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: An extended high pressure-temperature phase diagram of NaBH4