Thermal decomposition of ammonia borane at high pressures

摘要

The effects of high pressure (up to 9 GPa) on the thermal decomposition of ammonia borane,BH_3NH_3, were studiedin situby Raman spectroscopy in a diamond anvil cell. In contrast with thethree-step decomposition at ambient pressure, thermolysis under pressure releases almost the entirehydrogen content of the molecule in two distinct steps. The residual of the first decomposition ispolymeric aminoborane, (BH_2NH_2)_x, which is also observed at ambient pressure. The residual afterthe second decomposition is unique to high pressure. Presumably it corresponds to a precursor tohexagonal BN where macromolecular fragments of planar hexagon layers formed by B and N atomsare terminated by H atoms. Increasing pressure increases the temperature of both decompositionsteps. Due to the increased first decomposition temperature it becomes possible to observe a newhigh pressure, high temperature phase of BH3NH3 which may represent melting.