Wang Li, Wang Jia, Fang Chao, Qiao Yuancun, Li Yuwei
North China Institute of Aerospace Engineering, No. 133 Aimin East Road, Langfang, Hebei 065000, China.
Institute for Interdisciplinary Biomass Functional Materials Studies, Jilin Engineering Normal University, Changchun 130052, China.
J Chem Phys. 2023 Dec 28;159(24). doi: 10.1063/5.0185952.
Tungstates and molybdates possessing the scheelite- and wolframite-type (if present) structures hold a significant functional value. Their high-pressure phase diagrams are very complicated and controversial, and even some parts have not been characterized yet. In this study, we investigate the sequence of pressure driven structural phase transitions up to 100 GPa in these tungstate and molybdate families via first-principles structure predictions. Based on our structural predictions, it is possible for isostructural tungstates and molybdates to exhibit a phase transition sequence that is either similar or identical. Examples of these compounds are CaWO4, CaMoO4, and CdMoO4, in addition to EuWO4 and EuMoO4. However, the phase transition sequences of some tungstates and molybdates, especially those with different divalent cations, display noteworthy variations, revealing the intricate influence of ionic radii and electronic properties on crystal configurations. To obtain a deeper understanding of the high-pressure phase transition behavior of tungstates and molybdates, we analyze the high-pressure phase diagrams of MgWO4, SrWO4, and CaMoO4, representative examples of wolframite-type tungstate, scheelite-type tungstate, and scheelite-type molybdate, respectively, using x-ray powder diffraction. Our x-ray diffraction experiments and structure predictions consistently verify that the orthorhombic Cmca phase is a high-pressure phase of SrWO4. Structural configurations and mechanical properties of these predicted structures are discussed, and electronic properties are given. This study could have important implications for the fields of seismology and geophysics, as well as the utilization of these materials in various capacities, such as photocatalysts, photoanodes, and phosphors.
具有白钨矿型和黑钨矿型（若存在）结构的钨酸盐和钼酸盐具有重要的功能价值。它们的高压相图非常复杂且存在争议，甚至有些部分尚未得到表征。在本研究中，我们通过第一性原理结构预测，研究了这些钨酸盐和钼酸盐家族中高达100 GPa的压力驱动结构相变序列。基于我们的结构预测，同结构的钨酸盐和钼酸盐有可能呈现相似或相同的相变序列。除了EuWO4和EuMoO4外，这些化合物的例子还有CaWO4、CaMoO4和CdMoO4。然而，一些钨酸盐和钼酸盐的相变序列，尤其是那些具有不同二价阳离子的，表现出显著差异，揭示了离子半径和电子性质对晶体构型的复杂影响。为了更深入地了解钨酸盐和钼酸盐的高压相变行为，我们分别使用X射线粉末衍射分析了黑钨矿型钨酸盐、白钨矿型钨酸盐和白钨矿型钼酸盐的代表性例子MgWO4、SrWO4和CaMoO4的高压相图。我们的X射线衍射实验和结构预测一致验证了正交Cmca相是SrWO4的高压相。讨论了这些预测结构的结构构型和力学性能，并给出了电子性质。这项研究可能对地震学和地球物理学领域以及这些材料在光催化剂、光阳极和磷光体等各种应用中的利用具有重要意义。
