Zinc-blende to rocksalt transition in SiC in a laser-heated diamond-anvil cell

Abstract

We explore the stability of the ambient pressure zinc-blende polymorph (B3) structure of silicon carbide (SiC) at high pressures and temperatures where it transforms to the rock-salt (B1) structure. We find that the transition occurs ~40 GPa lower than previously measured when heated to moderately high temperatures. A lower transition pressure is consistent with the transition pressures predicted in numerous ab initio computations. We find a large volume decrease across the transition of ~17%, with the volume drop increasing at higher formation pressures, suggesting this transition is volume driven yielding a nearly pressure-independent Clapeyron slope. Such a dramatic density increase occurring at pressure is important to consider in applications where SiC is exposed to extreme conditions, such as in industrial applications or planetary interiors.

High-Pressure, High-Temperature Behavior of Silicon Carbide: A Review

“…Both experimental and computational work indicates that the volume of SiC drops between 15% and 20% across the transition. Such a large density increase has implications for the role of SiC deep in planetary interiors as has been discussed by several studies [24,27,43]. A compilation of the transition parameters from computations and experiments is presented in Table 1, while a summary of the P-T transition conditions, with a focus on experimental work, can be found in Figure 3.…”

“…Impurities may also play a role in the expressed polytypes as has been observed in ambient pressure experiments [13]. In reported static experiments at high-pressures the starting polytype structure remains throughout pressure loading and unloading [22,23], at least up to the conditions of the transition to the rocksalt structure [20,24,25]. See Figure 2 for a compilation of experimental data on the stability of common polytypes at pressure.…”

“…DAC studies find that 15R remains under compression to at least 35 GPa at 300 K [22], 3C remains stable to 105 GPa at 300 K and 6H remains stable to 95 GPa at 300 K before transition to a dense, high-pressure rocksalt structure [25]. LHDAC experiments find that both 6H and 3C remain in experiments covering conditions of~10-80 GPa and~3000 K (shown in blue) before transition to the rocksalt structure [18,23,24,27,28]. Shock experiments up to 25 GPa and~2000 K find an increase in the proportion of rhombohedral and cubic phases at high P-T and a decrease in hexagonal phases [16].…”

“…It was first predicted for the 3C-SiC system by [30] and first observed experimentally by [25] during room temperature compression of SiC in a static diamond-anvil cell (DAC). Since these early results, many computational studies have worked to better understand the transition conditions [31][32][33][34][35][36][37][38] and several experimental studies have further observed the transition using both laser-heated diamond-anvil cells (LHDAC) and shockwave experiments [20,21,24,27,28,39,40]. Calculations also predict the transition to the rocksalt structure from the 6H polytype as well [33,36,41].…”

“…Bars extending from shock studies (blue triangle [20], blue square [21]) indicate the likely high sample temperature. Open symbols represent the low pressure B3 structure (open circle [24], open triangles [27]) while solid symbols indicate the appearance or stability of the B1 structure in (LH) DAC experiments (solid circles [24], solid triangles [27], solid thick diamond [25], solid thin diamonds [28]). Computations considering the hysteresis across the transition are plotted in red crosses [44], while the range of most transition temperatures found in computational studies is shown by the red bar.…”