Centre for Planetary Sciences at UCL/Birkbeck, Gower Street, London WC1E 6BT, United Kingdom.
J Chem Phys. 2009 Oct 21;131(15):154503. doi: 10.1063/1.3245858.
We describe the results of a neutron powder diffraction study of perdeuterated ammonia monohydrate (AMH, ND(3).D(2)O) carried out in the range 102<P<502 MPa at T=180 K using the D2B high-resolution diffractometer at the Institut Laue-Langevin. This paper reports observations of the phase transformation from the low-pressure P2(1)2(1)2(1) phase (AMH I) to the high-pressure Pbca phase (AMH II) at 351 MPa, and measurements which have allowed us to determine the volumetric and axial incompressibilities of both polymorphs. At 180 K, the fitted third order Birch-Murnaghan equation of state of AMH I has parameters, V(0)=248.00(2) A(3), K(0)=7.33(3) GPa with the first pressure derivative of K(0) fixed at the value obtained in ab initio calculations, (partial differentialK(0)/partial differentialP)(T)=K(0)'=5.3; the implied value of the second derivative is therefore (partial differential(2)K(0)/partial differentialP(2))(T)=K(0)"=-0.94(1) GPa(-1). At 351 MPa, we observed that the transition from AMH I to AMH II occurred over a period of 90 min, with an associated reduction in molar volume of 4.6% and an increase in the incompressibility of 19.6%.
我们描述了在 T=180 K 下使用 Institut Laue-Langevin 的 D2B 高分辨率衍射仪对氘代一水合氨（AMH，ND(3).D(2)O）进行的中子粉末衍射研究的结果。该研究在 102<P<502 MPa 的范围内进行。本文报道了在 351 MPa 下从低压 P2(1)2(1)2(1)相（AMH I）到高压 Pbca 相（AMH II）的相变观察结果，以及允许我们确定两种多晶型物的体积和轴向不可压缩性的测量结果。在 180 K 下，拟合的 AMH I 的第三阶 Birch-Murnaghan 状态方程的参数为 V(0)=248.00(2) A(3)，K(0)=7.33(3) GPa，其中 K(0)的第一压力导数固定在从头计算中获得的值，（偏微分 K(0)/偏微分 P）(T)=K(0)'=5.3；因此，二阶导数的隐含值为（偏微分(2)K(0)/偏微分 P(2))(T)=K(0)"=-0.94(1) GPa(-1)。在 351 MPa 下，我们观察到 AMH I 向 AMH II 的转变在 90 分钟内发生，摩尔体积减小了 4.6%，不可压缩性增加了 19.6%。
