Tantalum is the only element of Group 5 in the periodic table that lacks any experimental reports on the existence of reduced crystalline oxide between the pentoxide (Ta2O5) and the dioxide (TaO2). We computationally predict the existence of a novel tantalum oxide with Ta4O9 stoichiometry, which lies at the midpoint between Ta2O5 and TaO2. The ground-state Ta4O9 structure was found through simulated annealing based on a cluster expansion model, which is trained using 186 density functional theory calculations. The newfound Ta4O9 material has space group number 10 (P2/m), and it can be viewed as an oxygen-deficient λ-Ta2O5 structure in which oxygen vacancies aggregate pair-wise in nearest-neighbor sites. Tad–Tad bonds fill the spatial void of the oxygen vacancies, keeping the system non-magnetic and non-metallic. The synthesis of the new Ta4O9 crystal is deemed feasible through a controlled reduction of λ-Ta2O5. The reported Ta4O9 has the potential to open new avenues in catalysis and resistive switching device applications where the reduced tantalum oxides are broadly employed.

中文翻译：

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使用基于第一性原理的簇扩展计算预测结晶 Ta4O9 相

钽是元素周期表中唯一没有关于在五氧化物 (Ta2O5) 和二氧化物 (TaO2) 之间存在还原结晶氧化物的实验报告的第 5 族元素。我们通过计算预测存在具有 Ta4O9 化学计量的新型氧化钽，它位于 Ta2O5 和 TaO2 之间的中点。基态 Ta4O9 结构是通过基于簇扩展模型的模拟退火发现的，该模型使用 186 次密度泛函理论计算进行训练。新发现的 Ta4O9 材料的空间群数为 10 (P2/m)，可以将其视为缺氧的 λ-Ta2O5 结构，其中氧空位在最近邻位点成对聚集。Tad-Tad 键填充氧空位的空间空隙，使系统保持非磁性和非金属性。通过控制 λ-Ta2O5 的还原，合成新的 Ta4O9 晶体被认为是可行的。报道的 Ta4O9 有可能为广泛使用还原钽氧化物的催化和电阻开关器件应用开辟新的途径。