The structural phase transition of ammonia borane under high pressure

Metallization and superconductivity of NBH12 compounds stabilized by dihydrogen bonds

“…Obviously, the tilt angle of AB(H 2 ) 3 is more extreme than that of pure AB due to the addition of H 2 molecules. The tilt angle of pure AB increases sharply in the range of 10-50 GPa, which may be related to the complex structural phase transition of ammonia borane in this pressure range, 17,18 while the angle increases gently with the pressure in the whole pressure range for AB(H 2 ) 3 , which demonstrates the structural stability of this material. Compared with Cmc2 1 -AB and the AB(H 2 ) 1.5 structure proposed by Yu et al, 21 the tilting becomes much less extreme.…”

“…Compared with P2 1 -AB phase, 17 the distance between the AB layers in P2 1 -AB(H 2 ) 3 is significantly increased due to the insertion of additional H 2 molecules. More specifically, one of the H 2 molecules has a hydrogen atom which is located close to the B atom of the AB.…”

“…2(a)), which has the same space group symmetry as the P2 1 -AB phase. 17 The additional hydrogen atoms obviously affect the rotation of the NH 3 and BH 3 units, and the AB molecules in AB(H 2 ) 3 are in an eclipsed conformation while those in P2 1 -AB are staggered. Moreover, AB molecules in P2 1 -AB(H 2 ) 3 form layers parallel to the (101) surface, and the AB layers are alternately staggered, where hydrogen molecules are located between adjacent AB molecular layers (Fig.…”

“…In order to obtain stable structures of ammonia borane mixed hydrogen, we have implemented the particle swarm optimization algorithm by using CALYPSO code, 22,23 which performs well in hydride structure search. 9,17,24 Here, the structure search investigated a cell containing 1-4 AB molecules with six different AB : H 2 ratios: 1 : 0.5, 1.0, 1.5, 2.0, 2.5, 3.0. Each stoichiometry was searched separately at pressures of 0, 50, 100, 150, 200, 250 GPa, and each search was run for a total of 30 generations, producing 20 structures per generation.…”

“…In addition, the dihydrogen bond also plays an important role in the complex structural phase transitions caused by pressure and/or temperature in ammonia borane. [12][13][14][15][16][17][18] In recent years, some experimental studies [19][20][21] have found that AB can form new crystals with hydrogen molecules under high pressure, and the interaction between AB and H 2 can stabilize this compound under high pressure. The results of high pressure Raman spectra by Chellappa et al 19 showed that NH 3 BH 3 -H 2 mixtures up to 60 GPa exhibit unusual pressure-induced complexation and intermolecular interaction.…”