非静水压环境对U<sub>3</sub>O<sub>8</sub>高压拉曼声子行为的影响

doi:10.3964/j.issn.1000-0593(2025)01-0059-07

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摘要：八氧化三铀（U₃O₈）是动力学和热力学最稳定的铀氧化物。研究U₃O₈的高压相稳定性和高压声子行为对其在核工业、催化剂等领域的应用具有重要参考价值。由于铀原子（[Rn]5f³6d¹7s²）和氧原子（[He]2s²2p⁴）核外电子结构存在显著差异，因此很难通过同步辐射X射线衍射技术探测高压下铀氧化合物中U—O 键合的细微变化。然而拉曼光谱对高压下U—O键合变化非常敏感，它能揭示物质在高压下包括键合或者化学计量等方面的重要信息。目前对U₃O₈高压结构相变的研究通常聚焦于静水压环境，而非静水压环境对U₃O₈高压相变的影响尚未得到深入研究。该研究基于金刚石对顶砧的高压拉曼散射技术探究了静水压和非静水压环境对正交α-U₃O₈高压相变与声子行为的影响。研究表明，静水压（8.1 GPa）和非静水压（8.2 GPa）条件下α-U₃O₈高压相变起始压力很接近。但由于非静水压环境中样品内的微区偏应力较大，因此非静水压环境中U₃O₈高压相变结束压力（16.4 GPa）比静水压环境中相应压力（18.5 GPa）约低2~3个GPa。同时本文给出了两对比实验中主拉曼模的一阶压力系数与Mode-Grüneisen参数γ。对比分析可知，高压相变前静水压条件下各主模零压下的一阶压力系数绝对值|dω/dP|几乎均大于非静水压条件下的相应值，这表明相变前非静水压环境中各拉曼模对压力响应不明显；一旦高压相变开始，由于较大微区偏应力的存在极大程度增强了铀氧原子外层电子的耦合作用，故相变后非静水压下压力系数绝对值显著增大。零压下B⁽⁶⁾₂模的γ值最小，因此对外部扰动有更积极的响应。此外室温加压时A⁽³⁾₂和A⁽⁴⁾₂模（代表沿a轴氧原子的振动）的一阶压力系数通常小于B⁽⁴⁾₂和B⁽⁶⁾₂模（代表bc面内氧原子的位移），这表明α-U₃O₈高压相变前a轴比b、c轴更难被压缩。该工作深入探究了静水压和非静水压环境对α-U₃O₈高压相变的影响，为了解α-U₃O₈高压相稳定性和晶格动力学行为提供了重要参考。

关键词：U₃O₈；高压拉曼光谱；高压相变；非静水压

Abstract：The triuranium octoxide (U₃O₈) exhibits exceptional kinetic and thermodynamic stability among various uranium oxides. The study of the high-pressure phase stability and high-pressure phonon behaviour of U₃O₈ is an important reference for its application in the nuclear industry, catalysts, and other fields. Due to the complexity of the electron structure outside the nucleus of the uranium atoms ([Rn]5f³6d¹7s²), compared to the oxygen atoms ([He]2s²2p⁴), significant differences exist between their electron configurations. Therefore, synchrotron X-ray diffraction makes it difficult to detect subtle changes in U—O bonding for uranium oxides under high pressure. However, Raman spectroscopy is highly sensitive to changes in U—O bonding at high pressure, and it can reveal some important information about substances at high pressure, including bonding or stoichiometry. To date, the investigations on the high-pressure structural phase transition for U₃O₈ have typically focused on exploring its evolution in hydrostatic environments. However, a deep investigation of the effects of non-hydrostatic environments on the high-pressure phase transition of U₃O₈ has not been conducted yet. In this work, the effects of hydrostatic and non-hydrostatic environments on the high-pressure phase transition and phonon behaviour for orthorhombic α-U₃O₈ have been investigated using a high-pressure Raman scattering technique based on the diamond anvil cell. Our results show that initialization transition pressures of α-U₃O₈ under hydrostatic (8.1 GPa) and non-hydrostatic (8.2 GPa) conditions are very close. However, the significant micro zonation bias stress present within the sample in the non-hydrostatic environments leads to the completion transition pressure (16.4 GPa) being approximately 2 to 3 GPa lower compared to the corresponding values in the hydrostatic environments (18.5 GPa). The first-order pressure coefficients and mode-Grüneisen parameters γ of the main Raman modes in two comparison experiments were given. The results show that before the high-pressure phase transition, the absolute values of the zero-pressure first-order pressure coefficients |dω/dP| for the main Raman modes under the hydrostatic environments are generally greater than those under the non-hydrostatic environments, which indicates that the Raman modes exhibit an insignificant response to the pressure under the non-hydrostatic environments. However, the absolute values of the first-order pressure coefficients under the non-hydrostatic environments are significantly larger once the high-pressure phase transition begins. This may be caused by significant micro zonation bias stress that greatly strengthens the mutual coupling between the outer electrons of the uranium-oxygen atoms. The B⁽⁶⁾₂ mode exhibits the smallest γ value at zero pressure, indicating a more positive response to external perturbations. Moreover, the first-order pressure coefficients of the A⁽³⁾₂ and A⁽⁴⁾₂ modes (representing the vibrations of the oxygen atoms along the a-axis) are typically smaller than those of the B⁽⁴⁾₂ and B⁽⁶⁾₂ modes (representing the displacements of the oxygen atoms in the bc-plane) when pressurized at room temperature, suggesting that the a-axis is less sensitive to pressure than the b-axis and c-axis before the high-pressure phase transition for α-U₃O₈. The effect of hydrostatic and non-hydrostatic environments on the high-pressure phase transition for α-U₃O₈ was investigated deeply for the first time in this work, which offered valuable insights into the high-pressure phase stability and lattice dynamics behavior of α-U₃O₈.

Key words：U₃O₈; High-pressure Raman spectroscopy; High-pressure phase transition; Non-hydrostatic pressure

收稿日期: 2024-03-31 修订日期: 2024-04-29

中图分类号:

O433.4

基金资助: 国家自然科学基金项目（12374013，U2030107），中央高校基本科研业务费专项资金（2020SCUNL107）资助

通讯作者: 雷力 E-mail: lei@scu.edu.cn

作者简介: 王艺佳，女，1999年生，四川大学原子与分子物理研究所硕士研究生 e-mail: wyj18835734561@163.com

引用本文:

王艺佳，吴彬彬，刘静仪，房雷鸣，刘本琼，雷力. 非静水压环境对U₃O₈高压拉曼声子行为的影响[J]. 光谱学与光谱分析, 2025, 45(01): 59-65.
WANG Yi-jia, WU Bin-bin, LIU Jing-yi, FANG Lei-ming, LIU Ben-qiong, LEI Li. The Effect of Non-Hydrostatic Pressure Environments on the High-Pressure Raman Phonons for U₃O₈. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(01): 59-65.

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