Pressure- and temperature-induced phase transition in the B–C system

Abstract

A direct transformation from the g-BC1.6 phase to a diamondlike BC1.6 phase was obtained in a diamond-anvil cell at high temperature, 2230±140K, and high pressure, 45GPa. Such a transition has not been observed in the B–C system before. The recovered samples were examined using both synchrotron-based x-ray diffraction and confocal micro-Raman spectroscopy at ambient conditions. The lattice parameter of the diamondlike phase (3.5745Å) is close to that of diamond. The measured visible laser-excited Raman spectra of a diamondlike BC1.6 phase reveal a peak at 1315cm−1 which is attributed to the LO mode. It is also found that the orthorhombic/hexagonal phase was formed under high pressure in the areas where heating was not enough to make transformation in the cubic phase.

Phase transition in BCx system under high-pressure and high-temperature: Synthesis of cubic dense BC3 nanostructured phase

“…The HPHT conditions of the transition of the graphitic BC x phase to another phase are also disputable: phase transitions were detected above 35 GPa in Refs. [16][17][18]21 ; and was not observed in the BC x system (1.6 < x ≤ 3) at pressures of 20 GPa 15 , 19 GPa 17 , and 24 GPa (Ref. 16 and this study).…”

“…[16][17][18]21 ; and was not observed in the BC x system (1.6 < x ≤ 3) at pressures of 20 GPa 15 , 19 GPa 17 , and 24 GPa (Ref. 16 and this study). Contrary to abovementioned results, the authors of Ref.…”

“…Recently, researchers claimed to observe a phase transition from graphitic phase to dl-BC 5 at 24 GPa and temperature of 2200 K, in a BC 5 system 19 . Despite progress in the understanding of the phase transition in BC x materials, such as observations of the phase transitions in BC 1.6 , BC 3 , and BC 5 under high pressure and high temperature [15][16][17][18][19][20][21] , we still do not know many important properties of the obtained phases (e.g.…”

“…% B 15 . To avoid this decomposition, we studied the phase transformation BC x phase in a DAC under pressures higher than 40 GPa for the following reasons: (a) XRD data suggested that at 2230±140 K and high pressure of 45 GPa the graphitic phase transformed into cubic BC 1.6 phase 16 ; and (b) measurements of the Raman scattering of the quenched phases demonstrated that graphitic phases transformed into a dl-BC 3 phase after laser heating of the g-BC 3 phase at 2033 K and 50 GPa 17 (see also Ref. 18 ).…”

Ultimate Metastable Solubility of Boron in Diamond: Synthesis of Superhard DiamondlikeBC5

“…Recent experiments on graphitelike BC 3 showed that at 20 GPa and 2200 K in a multianvil press, the phase decomposes into the mixture of boron-doped diamond ($1:8 at% of boron) and boron carbide [9]. Very recently, phase segregation of graphitelike BC 1:6 into a mixture of diamond, boron carbide, and elemental boron was observed in a diamond anvil cell at 45 GPa and 2230 K [10]. Hence, all previous attempts to synthesize diamondlike B-C phases with boron concentration higher than $2 at% have failed.…”