Pressure-dependent properties of SiC polytypes

Abstract

We present a first-principles study on the pressure-dependent properties of cubic and hexagonal polytypes of silicon carbide ͑SiC͒. Our calculations have been performed within density-functional perturbation theory, using the plane-wave pseudopotential approach. The stability of several high-pressure SiC phases is discussed in terms of the ionicity and metallicity of the Si-C bonds. Furthermore, we investigate pressure dependence of the zone-center frequencies, of the Born effective charges, and of the static and high-frequency dielectric constants for 3C, 2H, and 4H polytypes of SiC. Whereas the structural and electronic properties of the cubic and hexagonal polytypes are very similar, remarkable pressure-induced differences are found for the dynamical and dielectric properties. The unusual behavior of the transverse effective charge recently observed experimentally for 6H SiC is discussed. ͓S0163-1829͑96͒02119-4͔

Apparent Scarcity of Low-Density Polymorphs of Inorganic Solids

“…Figure 2 shows the resulting relative energies of the different polymorphs for the different TBSs plotted against their relative molecular volume (V m =V m wurtzite ) and allows for three clear observations. First on a methodological note, in all cases the wurtzite and zincblende polymorphs and the 4H and 6H polytypes lie lowest in energy and their order of stability follows that found by calorimetry [28,29] and, where experimental data is currently unavailable, by previous theoretical work [30][31][32]. Second, for all TBSs studied we find a dense spectrum of polymorphs that are approximately evenly spaced over a wide range of relative molecular volumes, reaching up to relative molecular volumes at least 20% larger than that of wurtzite.…”

Mechanically induced stiffening, thermally driven softening, and brittle nature of SiC

“…Previous high pressure experimental [3,4] and theoretical [5][6][7][8][9][10][11][12][13][14][15] research of SiC infers cubic (3C), hexagonal (6H), and rhombohedral (15R) structures. Energy-dispersive X-ray diffraction with a diamond anvil cell shows a structural transition from zinc blende (ZB, B3) to rock salt (RS, B1) at 100 GPa with a volume collapse of about 20.3% [3].…”

“…Structural and thermal stability as well as high pressure behavior of 3C SiC has been described by ab initio [5][6][7][8][9][10][11][12] and molecular dynamics simulations [1316]. The ab initio density functional calculation with the local density approximation (LDA) retraces the transition from zinc blende to rock salt at around 60 GPa [4][5][6][7].…”

“…The ab initio density functional calculation with the local density approximation (LDA) retraces the transition from zinc blende to rock salt at around 60 GPa [4][5][6][7]. Following the Perdew-Wang generalized gradient approximation (GGA) for the exchange correlation potential and the Troullier-Martins pseudopotentials, the transition pressure of about 63 GPa is predicted [810].…”

“…Details of method of calculations are earlier reported [19]. [4] 66±5 [5,6] 63 [8,9,10] 100 [13] 90 [15] 66.6 [7] 100 [11] 75.4 [14] Volume collapse (%)…”