Single-phase synthesis of α_II-VOPO₄ has been achieved by meticulous control of the seed formation and water vapor. The solid solution (V_1–xNb_x)OPO₄ (0.1 ≤ x < 1.0) (α_II-VOPO₄/MoOPO₄-type structure) has been obtained by solution combustion synthesis. It is thermodynamically stable only for x ≥ 0.8; for smaller x values, equilibration leads to β-VOPO₄ and (V_0.2Nb_0.8)OPO₄. With increasing niobium content, the a-axis of the tetragonal unit cell increases, while the c-axis decreases. Calculated model structures (density functional theory (DFT) using CRYSTAL17, PW1PW hybrid functional, and D3 dispersion correction) suggest that the dopant Nb⁵⁺ cations lead to less distorted [(V^V ≡ O)O₄O] octahedra in their vicinity. The experimental vibrational (IR, Raman) and electronic ultraviolet/visible (UV/vis) spectra show considerable variation with composition, perfectly reflecting the calculated dopant effects. These results suggest that within the solid solution [(V^V ≡ O)O₄O] and [(Nb^V ≡ O)O₄O] polyhedra are present as in the boundary phases in addition to just one type of geometrically slightly modified [(V^V ≡ O)O₄O] and [(Nb^V ≡ O)O₄O] groups. The continuous variation of lattice parameters with x is related to the concentration of these four types of polyhedra. Reversible reduction (hydrogen) and reoxidation (air) of (V_1–xNb_x)OPO₄ are possible at 400 °C. Thus, (V_0.5^VNb_0.5^V)OPO₄ yields (V_0.5^IIINb^V)O_0.5PO₄, which decomposes at 800 °C in a sealed ampule to V^IIIPO₄ and Nb^VOPO₄.

中文翻译：

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固溶体 （V1–xNbx）OPO4 （0.1 ≤ x < 1.0）：一项结合实验和理论的研究，旨在了解取代对结构、键合和催化行为的影响


α II-VOPO₄ 的单相合成是通过对种子形成和水蒸气的精细控制来实现的。固溶体 （V_1–xNb_x）OPO₄ （0.1 ≤ x < 1.0） （α II-VOPO ₄/MoOPO₄ 型结构）是通过固溶体燃烧合成获得的。它仅在 x ≥ 0.8 范围内具有热力学稳定性;对于较小的 x 值，平衡导致 β-VOPO₄ 和 （V_0.2Nb_0.8）OPO₄。随着铌含量的增加，四方晶胞的 a 轴增加，而 c 轴减小。计算的模型结构（使用 CRYSTAL17、PW1PW 杂化泛函和 D3 色散校正的密度泛函理论 （DFT））表明，掺杂剂 Nb⁵⁺ 阳离子导致它们附近 [（V^{V ≡} O）O₄O] 八面体的扭曲较小。实验振动（IR、Raman）和电子紫外/可见光 （UV/vis） 光谱显示出相当大的成分变化，完美地反映了计算出的掺杂剂效应。这些结果表明，在固溶体中，除了一种几何略有改性的 [（V、^V、≡≡ O_）O、4O]、O、4_O]和 [（Nb ≡^V、≡ O）O、_{4 O]}基团外，还存在与边界相一样的多面体。晶格参数随 x 的连续变化与这四种多面体的浓度有关。 （V_1–xNb_x）OPO₄ 的可逆还原（氢气）和再氧化（空气）在 400 °C 下是可能的。 因此，（V_0.5^VNb_0.5^V）OPO₄ 产生 （V_0.5^IIINb^V）O_0.5PO₄，它在 800 °C 的密封安瓿瓶中分解为 V^IIIPO₄ 和 Nb^VOPO₄。