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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Pressure-induced first-order phase transition in (NH4) 2V3O8 fresnoite: A double coordination change for V4+ and V5+
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Pressure-induced first-order phase transition in (NH4) 2V3O8 fresnoite: A double coordination change for V4+ and V5+

机译：（NH4）2V3O8索氏体中压力诱导的一阶相变：V4 +和V5 +的双配位变化

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摘要

The high-pressure behaviour of (NH4)2V 3O8 with the fresnoite structure (P4bm, Z = 2) has been studied at room temperature with single-crystal X-ray diffraction in diamond anvil cells using laboratory and synchrotron facilities. At ambient conditions, the crystal structure is composed of layers of corner-sharing V 5+O4 tetrahedra and V4+O5 square pyramids separated by layers of the NH4+ cations. At about 3 GPa, there occurs a reversible first-order phase transition to a three-dimensional structure (P4/mbm, Z = 2) built of corner-sharing V 5+O5 trigonal bipyramids and V4+O6 octahedra. The NH4+ cations fill up the interstitial sites in the tunnels formed by the vanadate framework. Up to the phase transition, the a lattice parameter of the low-pressure polymorph does not change while the contraction perpendicular to the stacking of the V3O8 slabs accounts entirely for the bulk compressibility. Above the phase transition, the a lattice parameter slightly expands. The structural features of the high-pressure phase of (NH4)2V3O 8 are compared to those of other vanadium oxides.
机译：使用实验室和同步加速器，在室温下利用金刚石晶体砧室中的单晶X射线衍射研究了具有Fresnoite结构（P4bm，Z = 2）的（NH4）2V 3O8的高压行为。在环境条件下，晶体结构由角共享的V 5 + O4四面体层和V4 + O5四棱锥层组成，并由NH4 +阳离子层隔开。在大约3 GPa处，发生了由角共享V 5 + O5三角双锥和V4 + O6八面体构成的可逆一阶相变到三维结构（P4 / mbm，Z = 2）。 NH4 +阳离子填充了由钒酸盐骨架形成的通道中的间隙位置。直到相变为止，低压多晶型物的晶格参数不会改变，而垂直于V3O8板堆叠的收缩则完全说明了整体可压缩性。在相变以上，晶格参数会略微扩展。将（NH4）2V3O 8高压相的结构特征与其他钒氧化物的结构特征进行了比较。

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