2002
DOI: 10.1103/physrevlett.89.195507
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Structural Stability and Phase Transitions inK8Si46Clathrate under High Pressure

Abstract: The structural stability of type-I K8Si46 clathrate has been investigated at high pressure by synchrotron x-ray diffraction. In contrast to that observed in the Na-doped structure-II analogue [A. San-Miguel, Phys. Rev. Lett. 83, 5290 (1999)]], no phase separation into the beta-Sn Si structure was identified at 11 GPa. Instead, K8Si46 is found to undergo a transition to an isostructural positional disordered phase at around 15 GPa. Ab initio phonon band structure calculations reveal a novel phenomenon of phonon… Show more

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Cited by 74 publications
(82 citation statements)
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“…in cell volume and interatomic distances are clearly observed. These results verify that the reduction in cell volume observed in previous experiments on K 8 Si 46 clathrate 13 and Ba 8 Si 46 clathrate 14 is indeed an intrinsic phase transition rather than due to a nonhydrostratic effect. At pressures around 7 GPa, no anomaly in the cell volume, Ba-Si and ͑Si-Si͒ bond distances was observed.…”
Section: Experimental and Theoretical Detailssupporting
confidence: 80%
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“…in cell volume and interatomic distances are clearly observed. These results verify that the reduction in cell volume observed in previous experiments on K 8 Si 46 clathrate 13 and Ba 8 Si 46 clathrate 14 is indeed an intrinsic phase transition rather than due to a nonhydrostratic effect. At pressures around 7 GPa, no anomaly in the cell volume, Ba-Si and ͑Si-Si͒ bond distances was observed.…”
Section: Experimental and Theoretical Detailssupporting
confidence: 80%
“…Ab initio phonon band structure calculations for K 8 Si 46 suggested that K atoms are displaced from the center of the Si 24 cages and are responsible for the transition at 15 GPa. 13 It was speculated that a similar mechanism may be responsible for the Ba 8 Si 46 transition 15 at 7 GPa. The nature of the second isostructural transition at about 15 GPa detected by XRD ͑Ref.…”
Section: Introductionmentioning
confidence: 99%
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“…It should be pointed out that in this reported phase transition induced by pressure, the structure type does not change, while the lattice constant or volume has a discontinuity with pressure resulting from the electronic topological transition, as those of isostructure phase transition observed in osmium [13] , K 8 Si 46 clathrate [14] , α-and β-Ge 3 N 4 [15] , EuO [16] , and so on. In the case of osmium, the changes in the band structure on compression could induce the changes of crystal structure and the maxima in band h 7 below the Fermi energy will pass through the Fermi surface resulting in the collapse of small hole ellipsoid under high pressure, which contributes to the isostructural phase transition.…”
mentioning
confidence: 99%
“…If there is no such phase near the original phase, or if the temperature is so low that the atomic relaxation is too slow, amorphization occurs. In fact, irreversible transformation to amorphous phases was observed in clathrate compounds: Ba 8 Si 46 (at 40 GPa) [37], K 8 Si 46 (32 GPa) [38], and Ba 24 Si 100 (23 GPa) [39]. The amorphization of β-rhombohedral boron can be classified as this category with a higher pressure.…”
Section: Classification Of Phase Transitionsmentioning
confidence: 99%