发表机构
Indian Institute of Science Education and Research Kolkata; National Centre for High-Pressure Studies; IMPMC, Sorbonne Université; Beijing Academy of Quantum Information Sciences; Deutsches Elektronen Synchrotron（印度科学教育研究学院加尔各答分校; 高压研究中心; 巴黎第六大学地球物理学研究所; 北京量子信息科学研究院; 德国电子同步辐射中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
高压实验揭示CaV$_2$O$_6$在1 GPa发生结构相变，钒配位由VO$_5$增至VO$_6$，伴随光致发光猝灭和带隙非单调变化，20 GPa以上出现等对称修饰，并验证了配位变化与光电响应的耦合。
AI 中文摘要
在室温下，对二价偏钒酸盐 CaV$_2$O$_6$ 进行了高达 31 GPa 的高压同步辐射 X 射线衍射、拉曼光谱、光致发光（PL）和紫外-可见吸收测量。环境条件下的 CaV$_2$O$_6$ 结晶为具有中心对称的伪铌铁矿单斜结构（$C2/m$），其中钒原子位于五配位的 VO$_5$ 三角双锥体中。在静水压压缩下，体系在约 1 GPa 开始发生结构相变，转变为低对称性、非中心对称的单斜相（$C2$），该相在 5.2 GPa 以上成为唯一稳定相。这一相变涉及钒配位从 VO$_5$ 双锥体增加到共边扭曲的 VO$_6$ 八面体。高压拉曼散射证实了结构相界，在混合相区域（1.0 - 4.4 GPa）表现出模式软化（$\gamma_3 = -0.42$，$\gamma_9 = -0.46$），并在 5.2 GPa 附近出现模式频率和线宽的尖锐异常。光学测量显示，由于局部多面体畸变引入的非辐射复合路径，光致发光在约 1 GPa 附近完全猝灭，同时间接光学带隙呈现非单调演化。在 20 GPa 以上，多面体畸变和内应变的异常驱动了 $C2$ 相内的等对称结构修饰，表现为体压缩率的改变和光学带隙的稳定化。对姊妹化合物 MgV$_2$O$_6$ 的比较高压带隙测量验证了二价偏钒酸盐中阳离子配位变化与光电响应之间的明确耦合。
英文摘要
High-pressure synchrotron X-ray diffraction, Raman spectroscopy, photoluminescence (PL), and UV-Vis absorption measurements were carried out on the divalent metavanadate CaV$_2$O$_6$ up to 31 GPa at room temperature. Ambient CaV$_2$O$_6$ crystallizes in a centrosymmetric pseudo-brannerite monoclinic structure ($C2/m$), where vanadium atoms reside in fivefold-coordinated VO$_5$ trigonal bipyramids. Under hydrostatic compression, the system undergoes a structural phase transition starting at $\sim$1 GPa to a lower-symmetry, non-centrosymmetric monoclinic phase ($C2$), which becomes the single stable phase above 5.2 GPa. This transition involves an increase in vanadium coordination from VO$_5$ bipyramids to edge-sharing distorted VO$_6$ octahedra. High-pressure Raman scattering corroborates the structural phase boundaries, exhibiting mode softening ($γ_3 = -0.42$, $γ_9 = -0.46$) within the mixed-phase regime (1.0 - 4.4 GPa) and sharp anomalies in mode frequencies and linewidths across 5.2 GPa. The optical measurements show complete PL quenching near 1 GPa due to non-radiative recombination pathways introduced by local polyhedral distortions, alongside a non-monotonic evolution of the indirect optical band gap. Above 20 GPa, an anomaly in polyhedral distortion and internal strain drives an isosymmetric structural modification within the $C2$ phase, marked by an alteration in bulk compressibility and stabilization of the optical gap. Comparative high-pressure band-gap measurements on the sister compound MgV$_2$O$_6$ validate the explicit coupling between cation coordination changes and optoelectronic response in divalent metavanadates.
