Huang Yingying, Zhu Liuyuan, Li Hanlin, Fang Haiping, Chen Ruoyang, Sheng Shiqi
School of Physics, East China University of Science and Technology, Shanghai, 200237, China.
Department of Physics, Zhejiang Normal University, 321004, Jinhua, China.
Phys Chem Chem Phys. 2024 Nov 7;26(43):27783-27790. doi: 10.1039/d4cp02543a.
Crystal materials can exhibit novel properties under high pressure, which are completely different from properties under ambient conditions. Water ice has an exceptionally rich phase diagram with at least 20 known crystalline ice phases from experiments, where the high-pressure ice X and ice XVIII behave as an ionic state and a superionic state, respectively. Thus, the ice structures stabilized under high pressure are very likely to possess other novel properties. Herein, we constructed a sequence of hypothetical high-pressure ices whose structures were generated according to the topological frameworks of common metal oxides. Based on density functional theory calculations, the pressure-induced phase transition sequence is in order that the known AgO-3̄ structure (ice X) transformed into a previously undiscovered TiO_brookite- structure at a pressure of 300 GPa, followed by a transition to a new NaO-3 structure at a pressure of 2120 GPa. Hitherto unreported NaO-3 ice with a cubic structure is in the ionic state, where the oxygen atoms in NaO-3 have a face-centered cubic (fcc) sublattice, and the coordination number of H atoms increases to 3. These two structures are dynamically stable according to phonon spectrum analysis and remain stable at temperature of 100 K based on molecular dynamics (AIMD) simulations. More importantly, the NaO-3 ice exhibits novel metallic properties with a closing band gap above a pressure of 2600 GPa, owing to the electron orbital coupling of oxygen atoms in close proximity induced by pressure.
晶体材料在高压下可展现出与常压条件下截然不同的新奇特性。水冰具有极为丰富的相图，实验已发现至少20种已知的结晶冰相，其中高压下的冰X和冰XVIII分别呈现离子态和超离子态。因此，高压下稳定存在的冰结构极有可能具备其他新奇特性。在此，我们构建了一系列假设的高压冰，其结构是根据常见金属氧化物的拓扑框架生成的。基于密度泛函理论计算，压力诱导的相变顺序为：已知的AgO-3̄结构（冰X）在300 GPa压力下转变为先前未发现的TiO-板钛矿结构，随后在2120 GPa压力下转变为新的NaO-3结构。迄今未报道的具有立方结构的NaO-3冰处于离子态，其中NaO-3中的氧原子具有面心立方（fcc）子晶格，H原子的配位数增加到3。根据声子谱分析，这两种结构是动态稳定的，并且基于分子动力学（AIMD）模拟在100 K温度下保持稳定。更重要的是，由于压力诱导相邻氧原子的电子轨道耦合，NaO-3冰在压力高于2600 GPa时呈现出具有闭合带隙的新奇金属特性。
