Insight into the structural, elastic and electronic properties of a new orthorhombic 6O-SiC polytype

Abstract

Different polytypes of SiC are described and predicted in literature. Here, we report the first occurrence of an orthorhombic 6O-SiC polytype as rock-forming mineral in the nickel laterite mine of Tiebaghi (New Caledonia). This new class of SiC crystallizes in the space group Cmc21 with 12 atoms per unit cell [a = 3.0778(6) Å, b = 5.335(2) Å, c = 15.1219(6) Å, α = 90°, β = 90°, γ = 120°]. The density of 6O-SiC is about 3.22 g/cm3 and the calculated indirect bandgap at room temperature of 3.56 eV is identical to 6H-SiC. Our results suggest that 6O-SiC is the intermediate state in the wurtzite to rocksalt transformation of 6H-SiC.

Occurrence of SiC and Diamond Polytypes, Chromite and Uranophane in Breccia from Nickel Laterites (New Caledonia): Combined Analyses

“…In the case of 6H-SiC, the experimental characteristic phonon modes are assigned as follow [50]: E 2 (TA) at 151 cm −1 , E 1 (TA) at 240 cm −1 , A 1 (LA) at 504 cm −1 , E 2 (TO) at 762 and 783 cm −1 , E 1 (TO) at 791 cm −1 and A 1 (LO) at 887 and 963 cm −1 , respectively. For SiC in the siliceous breccia, the main Raman peaks were confirmed and matched with Raman-active vibrational modes of orthorhombic SiC structure with Space Group Cmc2 1 [17].…”

“…The structure can be described from SiC4 tetrahedra all sharing their neighbour edges. El Mendili et al [17] showed that 6O-SiC results from the 6H-SiC wurtzite to 3C-SiC rock-salt phase transformation as an intermediate state. The 6O-SiC formation requires at least 4 GPa of pressures and high temperatures 2027-2527 °C.…”

“…The structure can be described from SiC4 tetrahedra all sharing their neighbour edges. El Mendili et al [17] showed that 6O-SiC results from the 6H-SiC For all the SiC polytypes [50], the Raman modes consist of transverse acoustic and optical phonons (TA, TO), longitudinal acoustic and optical phonons (LA, LO) and longitudinal acoustic phonons (LA). In the case of 3C-SiC, only two strong Raman bands are observed, at 972 cm −1 attributed to the longitudinal optical phonon (LO) and at 796 cm −1 attributed to the transverse optical phonon mode (TO).…”

“…None of these minerals and mineral association have been so far described from nickel laterite profiles. Recent studies by El Mendili et al [17] give a detailed description of the 6O-SiC polytype in the siliceous breccia studied here. Its presence in an alteration profile is attributed to a three-stage process: formation in the lower mantle, transport into the upper mantle peridotite by second stage melts, weathering, and preservation in breccia pores.…”

Controlling the electrical resistivity of porous silicon carbide ceramics and their applications: A review

“…SiC is reported to exist as various polytypes [58][59][60] and according to the published literature, SiC has more than 200 polytypes. 59,61 These polytypes have distinct bandgaps and ionisation energies, 3,62 which eventually affects the electrical resistivity of sintered samples.…”