The Effect of Shear Deformation on C-N Structure under Pressure up to 80 GPa

Abstract

We studythe effect of shear deformation on graphitic g-C3N4 under pressures of up to 80 GPa at room temperature. g-C3N4 samples are transformed from initial amorphous flakes into onion-like structures, in which the nitrogen content in the quenched samples decreases with increasing pressure (from 42% in the initial conditions to 1% at 80 GPa). The concentration of the sp2 bonds also decreases from 1 (the initial sample) to 0.62 with increasing pressure to 80 GPa. This transformation of the sample is due to the fact that in the pressure range of 55–115 GPa, the equilibrium phase is not a diamond, but instead, carbon onions cross-linked by sp3 bonds, which are denser than diamonds. The results of our study show that the presence of nitrogen in sp3-bonded structures at pressures of higher than 55 GPa reduces the density and, accordingly, carbon structures without nitrogen become thermodynamically favorable.

Synthesis of Ultra‐Incompressible and Recoverable Carbon Nitrides Featuring CN4 Tetrahedra

“…Various experimental techniques were employed, in particular chemical (CVD) and physical (PVD) vapor depositions, [27] solvothermal methods, [9] and static and dynamic high-pressure methods. [3,7,8,10,13,15,17,28,29] In spite of these extensive studies, there is but a single report on the formation of a fully saturated sp 3 -hybridized carbon nitride, namely the CN compound, obtained in a diamond anvil cell laser-heated to 7000 K above 55 GPa. [3] The structure was proposed based on the match of the observed powder diffraction peaks with those of the theoretically predicted 𝛽-InS type CN compound.…”

“…[ 2 ] These predictions sparked an enormous interest and resulted in numerous experimental and theoretical investigations. [ 3–26 ] It was suggested that the initially considered β‐Si 3 N 4 ‐type C 3 N 4 [ 1 ] is thermodynamically unfavorable compared to other CN compounds. [ 4,23 ] Three possible stoichiometries, CN, C 3 N 4, and CN 2 , were proposed for stable carbon nitrides, all featuring 3D polymeric structures in which C and N atoms are fourfold‐ and threefold‐coordinated, respectively.…”