Polymerization of cyanoacetylene under pressure: Formation of carbon nitride polymers and bulk structures

Abstract

High-pressure phase transitions of polar and nonpolar molecular structures of cyanoacetylene (HC 3 N) are studied by using first-principles simulations at constant pressure. In both polar and nonpolar crystals, at pressure ∼20 GPa, the cyanoacetylene molecules are interconnected together and form polyacrylonitrile (PA) polymers. At pressure ∼30 GPa, PA polymers are transformed to polymers with fused pyridine rings (FPR's). The individual geometrical structures of PA and FPR polymers obtained from polar and nonpolar molecular crystals of cyanoacetylene are identical, but their stacking is different. At pressures above 40 GPa, the FPR polymers are interconnected together and new three-dimensional (3D) carbon nitride systems are formed. At ambient pressure, the long-length PA and FPR polymers are metallic, and the created 3D structures are an insulator with energy band gaps around 2.85 eV. The electron transport characteristics of FPR polymers with different lengths are investigated at finite biases by using the nonequilibrium Green's function technique combined with density functional theory (DFT) by connecting the polymers to gold electrodes. The results show that FPR polymers have negative differential resistance behavior. Our time-dependent DFT calculations reveal that FPR polymers can absorb light in the visible region. From our results, it is expected that the FPR polymers will be a good material for optoelectronic applications.

Polymerization of Tetracyanoethylene under Pressure

“…In our recent studies of hydrogen cyanide (H–CN), cyanoacetylene (H–CC–CN), and cyanogen (NC–CN), we simulated the phase transformations of the molecular crystals of the above inorganic molecules successfully under high pressure. Our obtained results showed good agreement with experimental data available in the literature. − Our calculations revealed that, at high pressure, the precursors with cyano groups (CN) are transformed into various heterocyclic CN polymers, layered structures, and solids with interesting electronic, optical, and mechanical properties. − Like the inorganic molecules above, TCNE also has four unsaturated CN (cyano group) bonds and one unsaturated CC bond. These unsaturated bonds might be opened under pressure .…”

Growth and analysis of the tetragonal (ST12) germanium nanowires

“…The PL peak position of the ST12-Ge (0.64 eV) reported here matches well with the theoretically calculated bandgap for ST12-Ge. 7,53 Zhao et al 7 and Malone et al 8 have calculated, by DFT using a hybrid functional approach, the fundamental bandgap of bulk ST12-Ge to be indirect with values of 0.70 and 0.54 eV respectively. However, their calculation also predicted a relatively “weak” indirect bandgap for ST12-Ge, in the sense that the direct bandgap is only ∼20 meV (compared to 140 meV for dc-Ge) larger than the indirect bandgap.…”

Pressure-induced amorphization and reactivity of solid dimethyl acetylene probed by in situ FTIR and Raman spectroscopy

“…At high pressures, polymerization of a molecular solid which contains unsaturated bonds is favored as the produced polymer possesses a reduced volume with saturated networks. In recent years, pressure-induced polymerization has been reported for several molecules such as ethylene [2], cyanogen [3], acetylene [4][5][6], cyanoacetylene [7,8], acrylic acid [9], benzene [10][11][12], styrene [13], etc. In particular, polymerization of molecules with triple bond (e.g.…”