Radtke G, Klotz S, Lazzeri M, Loubeyre P, Krisch M, Bossak A
Sorbonne Université, CNRS UMR 7590, MNHN, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), 4 place Jussieu, CEDEX 05, 75252 Paris, France.
CEA, DAM, DIF, 91297 Arpajon Cedex, France and Université Paris-Saclay, CEA, Laboratoire Matière en Conditions Extrêmes, 91680 Bruyères le Châtel, France.
Phys Rev Lett. 2024 Feb 2;132(5):056102. doi: 10.1103/PhysRevLett.132.056102.
The phonon dispersion of ice VII and that of its proton-ordered analog ice VIII are investigated through a combination of inelastic x-ray scattering (IXS) measurements and first-principles calculations of the oxygen sublattice dynamic structure factor. Particular attention is devoted to hydrogen-disorder in ice VII, addressed theoretically through a statistical ensemble of fictitious ordered supercell configurations. Similar phonon densities of states are found in both phases but are significantly less structured in the case of ice VII. Our data further show that, despite a full proton disorder, the acoustic phonon branches in this phase clearly inherit the periodicity of its body-centered cubic oxygen lattice. The calculations predict, however, the presence of gap openings in the one-atom phonon dispersion. These predictions are supported by revisiting the analysis of previous single-crystal IXS measurements along the longitudinal [111] branch of ice VII.
通过非弹性X射线散射（IXS）测量与氧亚晶格动态结构因子的第一性原理计算相结合的方法，研究了冰VII及其质子有序类似物冰VIII的声子色散。特别关注冰VII中的氢无序，通过虚拟有序超晶胞构型的统计系综进行理论处理。在两个相中发现了相似的声子态密度，但在冰VII的情况下结构明显较少。我们的数据进一步表明，尽管存在完全的质子无序，但该相中声学声子分支明显继承了其体心立方氧晶格的周期性。然而，计算预测在单原子声子色散中存在能隙开口。通过重新分析先前沿冰VII的纵向[111]分支的单晶IXS测量结果，这些预测得到了支持。
