Микроскопическое описание механизма перехода между политипами 2H и 4H карбида кремния

Abstract—The mechanism of displacement of one close-packed SiC layer from one minimum position to another on the example of SiC polytype transition 2 H → 4 H has been studied by ab initio methods. It has been shown that the intermediate state with monoclinic symmetry Cm greatly facilitates this displacement breaking it into two stages. Initially, the Si atom chiefly moves, only then—mainly the C atom. In this case, the Si–C bond is significantly tilted in comparison with the initial position, which allows the reducing of the compression of the SiC bonds in the ( $$11\bar {2}0$$ ) plane. Two transition states of this process, which also possess the Cm symmetry, have been computed. It has been found that the height of the activation barrier of the process of moving the close-packed layer of SiC from one position to another is equal to 1.8 eV. The energy profile of this movement has been calculated.

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Пути политипных превращений в карбиде кремния

Физика твердого тела ◽

10.21883/ftt.2019.08.47967.452 ◽

2019 ◽

Vol 61 (8) ◽

pp. 1443

Author(s):

С.А. Кукушкин ◽

А.В. Осипов

Keyword(s):

Silicon Carbide ◽

Ab Initio ◽

Activation Barrier ◽

Initial Position ◽

Ab Initio Methods ◽

Monoclinic Symmetry ◽

Trigonal Symmetry ◽

Energy Profiles ◽

Intermediate States ◽

Short Time

In this work, two main polytypic transformations in silicon carbide, namely, 2H→6H and 3C→6H, were studied using ab initio methods. It is shown that intermediate states with trigonal symmetry P3m1 and monoclinic symmetry Cm greatly simplify the movement of close-packed layers during such transitions, breaking them up into separate stages. It was found that the two polytypic transformations occur quite differently. During the 2H→6H transition, the displaceable bonds are noticeably tilted compared to the initial position, which makes it possible to reduce the compression of SiC bonds in the (112 ̅0) plane. The 3C→6H transition takes place through the formation of auxiliary Si – Si and C – C bonds that live for a short time and help the tightly packed layers exchange places. As a result, the activation barrier for the conversion of 2H→6H (1.7 eV/atom) is significantly less than the activation barrier for the conversion of 3C→6H (3.6 eV/atom), which means that the second transition must occur at temperatures of 750-800 ℃ higher than the first one. The energy profiles of these polytypic transformations, as well as the geometry of all intermediate and transitional phases, are calculated. It is shown that all transition states have monoclinic symmetry.

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Efficient determination and characterization of transition states using ab-initio methods

Chemical Physics Letters ◽

10.1016/0009-2614(77)80099-7 ◽

1977 ◽

Vol 45 (3) ◽

pp. 595-602 ◽

Cited By ~ 217

Author(s):

Andrew Komornicki ◽

Kazuhiro Ishida ◽

Keiji Morokuma ◽

Robert Ditchfield ◽

Morgan Conrad

Keyword(s):

Ab Initio ◽

Transition States ◽

Ab Initio Methods

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An ab initio study of 1,5-suprafacial shifts in 5-substituted 1,3-cyclopentadienes

Canadian Journal of Chemistry ◽

10.1139/v05-141 ◽

2005 ◽

Vol 83 (9) ◽

pp. 1299-1305 ◽

Cited By ~ 4

Author(s):

Cory C Pye ◽

Raymond A Poirier

Keyword(s):

Ab Initio ◽

Activation Barrier ◽

Computational Study ◽

Transition States ◽

Ab Initio Study ◽

Group 14 ◽

Carbon Framework

A computational study of the degenerate 1,5-suprafacial migration of the 5-substituted cyclopentadienes is presented. The substituents considered are the Group 1417 elements of the second through fifth periods, saturated by hydrogens as needed to fulfill normal valence requirements. The geometry of most transition states are remarkably similar in the carbon framework. The activation barrier to migration was shown to correlate well with a dimensionless "stretching" parameter, especially at the MP2 level.Key words: 5-substituted 1,3-cyclopentadiene, 1,2-haptotropic shift, 1,5-suprafacial shift, ab initio, transition states.

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