When carbon impurities trigger the synthesis of alpha boron at high pressure and high temperature. (1st May 2023)

• Record Type: Journal Article
• Authors: Chakraborti, Amrita; Cho, Yeonsoo; Sjakste, Jelena; Baptiste, Benoit; Henry, Laura; Guignot, Nicolas; Le Godec, Yann; Vast, Nathalie
• Is Part Of: Acta materialia. Volume 249(2023)
• Publication Date: 2023-05-01
• Subjects: Alpha boron -- High pressure high temperature synthesis -- Boron phase diagram -- Carbon impurities; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2023.118820
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: The role of carbon in the formation of α boron at high pressure and high temperature (HPHT) has been investigated by combining HPHT experiments and density functional theory (DFT) calculations. Starting from β rhombohedral or amorphous boron and amorphous carbon at 5 GPa, the α boron phase has been repeatedly observed between 1373 K and 2273 K, at temperatures that are much higher than those reported in the phase diagram of boron. The DFT investigation of the effect of carbon insertion into the α rhombohedral boron atomic structure on the formation enthalpy, volume and optical properties shows that the (B11 C) substituted icosahedron defect accounts for the slight volume contraction observed in α boron, is compatible with the observed red colour of α boron crystals, and consistently has a very low formation energy. Our calculations turn out to provide a calibration means to evaluate the concentration of carbon in our samples. Finally, the synthesis temperature is found to be an easy means to control the carbon concentration on demand. Graphical abstract: Highlights: Formation of α boron from other boron phases treated with amorphous carbon at HPHT. Modelling of carbon insertion into the atomic structure of α boron accounts for the observed physical properties. Carbon impurities trigger the synthesis of α boron.