Effect of ammonium fluoride doping on the ice III to ice IX phase transition.
Effect of ammonium fluoride doping on the ice III to ice IX phase transition.
复制标题
氟化铵掺杂对冰 III 到冰 IX 相变的影响。
DOI：
10.1063/5.0032485
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发表时间：
2021
影响因子：
4.4
通讯作者：
C. Salzmann
中科院分区：
文献类型：
--
作者：
Z. Sharif;J. Shephard;B. Slater;C. Bull;Martin Hart;C. Salzmann
冰III是冰的氢无序相，在约0.2和0.35 GPa之间稳定。冷却后，它在冰II的稳定区域内转变为氢有序的对应物冰IX。在这里，氟化铵掺杂对这种相变的影响进行了研究，其次是第一次与原位中子衍射。的a和c晶格常数被发现分别扩大和收缩，氢订购后，产生一个整体的负体积变化。有趣的是，在晶格常数的各向异性持续冰IX完全形成时，观察到负的热膨胀。类似于同构热液岩和β-锂辉石，负热膨胀可以通过a-b平面内的扭转应变的积累来解释，因为结构内的螺旋“弹簧”在加热时膨胀。加热时的相变的可逆性被证明。如在衍射和拉曼光谱中看到的，氟化铵掺杂诱导额外的残留氢在冰IX的障碍，并建议是一种化学方式的“激发”的配置冰规则的歧管。与冰VIII相比，冰IX中掺杂剂诱导的氢无序较小，这表明冰IX中接近基态的可接近构型态的密度较高。这项研究强调了掺杂剂对探索水的相图的重要性，并支持了冰的高度复杂的固态化学。
Ice III is a hydrogen-disordered phase of ice that is stable between about 0.2 and 0.35 GPa. Upon cooling, it transforms to its hydrogen-ordered counterpart ice IX within the stability region of ice II. Here, the effect of ammonium fluoride doping on this phase transition is investigated, which is followed for the first time with in situ neutron diffraction. The a and c lattice constants are found to expand and contract, respectively, upon hydrogen ordering, yielding an overall negative volume change. Interestingly, the anisotropy in the lattice constants persists when ice IX is fully formed, and negative thermal expansion is observed. Analogous to the isostructural keatite and β-spodumenes, the negative thermal expansion can be explained through the buildup of torsional strain within the a-b plane as the helical "springs" within the structure expand upon heating. The reversibility of the phase transition was demonstrated upon heating. As seen in diffraction and Raman spectroscopy, the ammonium fluoride doping induces additional residual hydrogen disorder in ice IX and is suggested to be a chemical way for the "excitation" of the configurational ice-rules manifold. Compared to ice VIII, the dopant-induced hydrogen disorder in ice IX is smaller, which suggests a higher density of accessible configurational states close to the ground state in ice IX. This study highlights the importance of dopants for exploring the water's phase diagram and underpins the highly complex solid-state chemistry of ice.