Department of Condensed Matter Physics, University of the Basque Country, Bilbao, Spain.
Dalton Trans. 2011 May 7;40(17):4572-7. doi: 10.1039/c1dt10142k. Epub 2011 Mar 31.
The high-pressure behaviour of (NH(4))(2)V(3)O(8) 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+)O(4) tetrahedra and V(4+)O(5) square pyramids separated by layers of the NH(4)(+) 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+)O(5) trigonal bipyramids and V(4+)O(6) octahedra. The NH(4)(+) 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 V(3)O(8) 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 (NH(4))(2)V(3)O(8) are compared to those of other vanadium oxides.
具有 fresnoite 结构（P4bm，Z = 2）的（NH4）2V3O8 的高压行为在室温下使用金刚石砧细胞中的单晶 X 射线衍射进行了研究，使用了实验室和同步辐射设施。在环境条件下，晶体结构由顶角共享的 V(5+)O(4)四面体和 V(4+)O(5)四方锥层组成，由 NH(4)(+)阳离子层隔开。在大约 3 GPa 时，发生了一个可逆的一级相变，形成了一个由顶角共享的 V(5+)O(5)三角双锥和 V(4+)O(6)八面体组成的三维结构（P4/mbm，Z = 2）。NH(4)(+)阳离子填充了由钒酸盐骨架形成的隧道中的间隙位置。在相变之前，低压多晶型物的 a 晶格参数不变，而垂直于 V(3)O(8)片层堆积的收缩完全解释了体压缩性。在相变之上，a 晶格参数略有膨胀。（NH4）2V3O8 的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。
