Sánchez Martín Josu, Pellicer-Porres Julio, Turnbull Robin, Díaz-Anichtchenko Daniel, Anzellini Simone, Liang Akun, Popescu Catalin, Bettinelli Marco, Rodríguez-Hernández Plácida, Muñoz Alfonso, Errandonea Daniel
Departamento de Física Aplicada-ICMUV, Universidad de Valencia, Dr. Moliner 50, 46100 Valencia, Burjassot, Spain.
Centre for Science at Extreme Conditions and School of Physics and Astronomy, University of Edinburgh, EH9 3FD Edinburgh, UK.
Dalton Trans. 2024 Jul 9;53(27):11490-11499. doi: 10.1039/d4dt01321b.
This study presents evidence that lead metavanadate, PbVO, is a material with zero-linear compressibility, which maintains its crystal size in one crystallographic direction even under external pressures of up to 20 GPa. The orthorhombic polymorph of PbVO (space group ) was studied up to 20 GPa using synchrotron powder X-ray diffraction, Raman spectroscopy, and density-functional theory simulations to investigate its structural and vibrational evolution under compression. Up to this pressure we find no evidence of any structural phase transitions by any diagnostic technique, however, a progressive transformation of the coordination polyhedron of vanadium atoms is revealed which results in the zero-linear compressibility. High-pressure Raman experiments enabled the identification and symmetry assignation of all 54 zone-centre Raman-active modes as well as the calculation of their respective pressure coefficients. Three independent high-pressure powder X-ray diffraction experiments were performed using different pressure-transmitting media (Ne, 4 : 1 methanol-ethanol mixture, and silicone oil). The results show a high anisotropic behaviour in the linear compressibility of the crystallographic axes. The PbVO bulk modulus of 86.1(9) GPa was determined using a third-order Birch-Murnaghan equation of state. The experimental results are supported by density-functional theory calculations, which provide vibrational patterns, unit-cell parameters, and atomic positions. These calculations also reveal that, unlike MgVO and ZnVO, the band gap of PbVO closes with pressure at a rate of -54 meV GPa due to the contribution of the Pb 6s orbital to the top of the valence band.
本研究表明，偏钒酸铅（PbVO）是一种具有零线性压缩性的材料，即使在高达20 GPa的外部压力下，它在一个晶体学方向上仍能保持其晶体尺寸。利用同步辐射粉末X射线衍射、拉曼光谱和密度泛函理论模拟，对PbVO的正交多晶型（空间群）进行了高达20 GPa的研究，以探究其在压缩下的结构和振动演化。在该压力以下，我们通过任何诊断技术均未发现任何结构相变的证据，然而，揭示了钒原子配位多面体的渐进转变，这导致了零线性压缩性。高压拉曼实验能够识别和确定所有54个区中心拉曼活性模式的对称性，并计算它们各自的压力系数。使用不同的压力传递介质（Ne、4∶1的甲醇-乙醇混合物和硅油）进行了三次独立的高压粉末X射线衍射实验。结果表明，晶体学轴的线性压缩性表现出高度的各向异性行为。使用三阶Birch-Murnaghan状态方程确定了PbVO的体模量为86.1(9) GPa。实验结果得到了密度泛函理论计算的支持，该计算提供了振动模式、晶胞参数和原子位置。这些计算还表明，与MgVO和ZnVO不同，由于Pb 6s轨道对价带顶部的贡献，PbVO的带隙随压力以-54 meV/GPa的速率关闭。
