title: Pressure-Induced Polymerization of LiN(CN)2.
abstract: The high-pressure behavior of lithium dicyanamide (LiN(CN)2) was studied with in situ Raman and infrared (IR) spectroscopies, and synchrotron angle-dispersive powder X-ray diffraction (PXRD) in a diamond anvil cell (DAC) to 22 GPa. The fundamental vibrational modes associated with molecular units were assigned using a combination of experimental data and density functional perturbation theory. Some low-frequency modes were observed for the first time. On the basis of spectroscopic and diffraction data, we suggest a polymorphic phase transformation at ∼8 GPa, wherein dicyanamide ions remain as discrete molecular species. Above ca. 18 GPa, dicyanamide units polymerize, forming a largely disordered network, and the extent of polymerization may be increased by annealing at elevated temperature. The polymerized product consists of tricyanomelaminate-like groups containing sp2-hybidized carbon-nitrogen bonds and exhibits a visible absorption edge near 540 nm. The product is recoverable to ambient conditions but is not stable in air/moisture.
authors: Derek W
authors: DW
authors: Keefer
authors: Geophysical Laboratory, Carnegie Institution of Washington , 5251 Broad Branch Road NW, Washington, DC, 20015, United States.|Center for High Pressure Science and Technology Advanced Research , 1690 Cailun Road, Bldg #6, Pudong, Shanghai 201203, China.
authors: Huiyang
authors: H
authors: Gou
authors: Chemistry Division, Naval Research Laboratory , 4555 Overlook Avenue, SW, Washington, DC, 20375, United States.
authors: Andrew P
authors: AP
authors: Purdy
authors: Chemistry Division, Naval Research Laboratory , 4555 Overlook Avenue, SW, Washington, DC, 20375, United States.
authors: Albert
authors: A
authors: Epshteyn
authors: Geophysical Laboratory, Carnegie Institution of Washington , 5251 Broad Branch Road NW, Washington, DC, 20015, United States.|Center for High Pressure Science and Technology Advanced Research , 1690 Cailun Road, Bldg #6, Pudong, Shanghai 201203, China.
authors: Duck Young
authors: DY
authors: Kim
authors: John V
authors: JV
authors: Badding
authors: Geophysical Laboratory, Carnegie Institution of Washington , 5251 Broad Branch Road NW, Washington, DC, 20015, United States.
authors: Timothy A
authors: TA
authors: Strobel