Abstract
Materials combining the hardness and strength of diamond with the higher thermal stability of cubic boron nitride (cBN) have broad potential value in science and engineering. Reacting nanodiamond with cBN at moderate pressures and high temperatures provides a pathway to such materials. Here we report the fabrication of Cx-BN nanocomposites, measuring up to 10 mm in longest dimension, by reacting nanodiamond with pre-synthesized cBN in a large-volume press. The nanocomposites consist of randomly-oriented diamond and cBN domains stitched together by sp3-hybridized C-B and C-N bonds, leading to p-type semiconductivity. Dislocations near the sutures accommodate lattice mismatch between diamond and cBN. Nanotwinning within both diamond and cBN domains further contributes to a bulk hardness ~50% higher than sintered cBN. The nanocomposite of C2-BN exhibits p-type semiconductivity with low activation energy and high thermal stability, making it a functional, ultrahard substance.
Highlights
Highly uniform Cx-BN (x = 2, 4, 6, 8) nanocomposites at 7.5 GPa and 2273 K, which consist of randomly oriented, ~50 nm domains of diamond and Cubic boron nitride (cBN) (~250 nm)
The bulk samples, measuring up to 10-mm diameter by 5-mm in height, combine several novel features from recent syntheses in the diamond-cBN system[2,3,18,24]; in particular, the new C2-BN composite possesses nanotwinning in both diamond and cBN domains, which are stitched by sp3-hybridized C-B and C-N bonds along randomly-oriented interfaces
Dislocations accommodate the lattice mismatch between diamond and cBN and, as recently predicted[24], the C2-BN nanocomposite is a p-type semiconductor with low activation energy
Summary
The sintered diamond (sample S6) and Cx-BN materials with high carbon concentration (sample S5) show good n-type conductivity with a low resistivity that can be due to the graphitization under HPHT treatment Both C2-BN and C4-BN nanocomposites synthesized at 2273 K and 7.5 GPa exhibit p-type semiconductivity. The calculated activation energy is 6.21 meV and is similar to hybridized BN-C graphene[30] Since both pure diamond and cBN are good insulators, the p-type semiconductivity of the Cx-BN composite must derive from the sp3-hybridized C-B and some B-B bonds within the sutures of diamond and cBN domains[30,40]. The composite of nanotwinned diamond and cBN in a 2:1 ratio (C2-BN) shows ultrahard properties by Vickers indentation tests, low compressibility, high thermal stability, and p-type semiconductivity - a combination of features that have not previously been found together in pure diamond-like B-C-N materials. The unique combination of properties in C2-BN provides a pathway for fabrication of diamond-based electronics applicable to multifunctional devices operating in extreme environments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
