PSI - Issue 23

Atsushi Kubo et al. / Procedia Structural Integrity 23 (2019) 372–377 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Phase transition is induced to high-pressure (metastable) phases such as rocksalt and unbuckled wurtzite structures [Sarasamak et al. (2008)], shown in Fig. 4. Phase transition to rocksalt structure is observed in the cases of  2110  -tension to wurtzite and  110  -tension to zincblende phases for all materials. Phase transition to unbuckled wurtzite structure [also referred to as hexagonal boron nitride (h-BN) structure] is most clearly found in  1100  -tension to wurtzite-AlN, while SiC does not undergo this type of transition under the same deformation mode. The latter category (phase transition) involves a considerable decrease in  c because a more favorable path for unstable deformation to a metastable phase is newly opened by a complex multiaxial loading condition. In wurtzite GaN and wurtzite-AlN, two types of phase transition are possible (Fig. 4) according to the loading direction. However, even for these materials, no phase transition was observed under  0001  -tension. This is simply because the loading direction is exactly along chemical bonds; only bond stretching to breaking is allowed, while there is no room for bond bending to occur.

(a-ii) 3C-SiC

(a-iii) 4H-SiC

(a-i) 2H-SiC

(c) zincblende-AlN

(b) zincblende-GaN

Fig. 2. Tensile stress-strain relationships under uniaxial tensile strain  along various crystal orientations without transverse stress  t for (a) SiC [(i) 2H, (ii) 3C, (iii) 4H], (b) zincblende-GaN and (c) zincblende-AlN.