Huang Yanping, Huang Xiaoli, Zhao Zhonglong, Li Wenbo, Jiang Shuqing, Duan Defang, Bao Kuo, Zhou Qiang, Liu Bingbing, Cui Tian
State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, People's Republic of China.
J Chem Phys. 2014 Jun 28;140(24):244507. doi: 10.1063/1.4884819.
A detailed high-pressure study on NH3BH3 has been carried out using in situ synchrotron X-ray diffraction (XRD) and Raman scattering with a diamond anvil cell up to 20 and 33 GPa, respectively. The Rietveld refinement based on the XRD pattern and analysis of Raman data indicate two first-order phase transitions from the ambient pressure I4 mm structure (α-NH3BH3) to a high pressure Cmc21 phase (β-NH3BH3) at 2.14 GPa, and further into a monoclinic P21 (Z = 2) phase (γ-NH3BH3) at 9.67 GPa. Fitting the measured volumetric compression data to the third order Birch-Murnaghan equation of state reveals a bulk modulus of B0 = 9.9 ± 0.5 and 17.0 ± 3.0 GPa (with fixed B0 (') = 4) for the β-NH3BH3 below and above 5 GPa, respectively. Still, with the splitting of the NBH rock mode in Raman experiment, it is concluded that a second-order isostructural phase transition occurs at 5 GPa. By analyzing the dihydrogen bonding framework, the origin of the isostructural phase transition is attributed to the number of dihydrogen bondings per molecule in the Cmc21 phase increasing from 12 to 14 at 5 GPa.
利用金刚石对顶砧分别在高达20吉帕和33吉帕的压力下进行原位同步辐射X射线衍射（XRD）和拉曼散射，对氨硼烷（NH₃BH₃）开展了详细的高压研究。基于XRD图谱的Rietveld精修和拉曼数据分析表明，在2.14吉帕时，发生了从常压下的I4mm结构（α-NH₃BH₃）到高压Cmc21相（β-NH₃BH₃）的两个一级相变，在9.67吉帕时进一步转变为单斜P21（Z = 2）相（γ-NH₃BH₃）。将测量的体积压缩数据拟合到三阶Birch-Murnaghan状态方程，结果显示，对于β-NH₃BH₃，在5吉帕以下和以上时，体模量分别为B0 = 9.9 ± 0.5吉帕和17.0 ± 3.0吉帕（固定B0(') = 4）。不过，根据拉曼实验中NBH摇摆模式的分裂，得出在5吉帕时发生了二级同结构相变的结论。通过分析双氢键框架，同结构相变的起源归因于在5吉帕时，Cmc21相每个分子的双氢键数量从12增加到14。
