Single crystal X-ray diffraction study of a mixed-valence gold compound, Cs2AuIAuIIICl6 under high pressures up to 18 GPa: Pressure-induced phase transition coupled with gold valence transition
Single crystal X-ray diffraction study of a mixed-valence gold compound, Cs2AuIAuIIICl6 under high pressures up to 18 GPa: Pressure-induced phase transition coupled with gold valence transition
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混合价金化合物 Cs2AuIAuIIICl6 在高达 18 GPa 的高压下的单晶 X 射线衍射研究：压力诱导相变与金价态转变相结合
DOI：
10.1016/j.jssc.2007.01.037
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发表时间：
2007
影响因子：
3.3
通讯作者：
N. Kojima
中科院分区：
文献类型：
--
作者：
N. Matsushita;H. Ahsbahs;S. Hafner;N. Kojima
我们用氦气作理想的静压传压介质，在高压下对钙钛矿型混价化合物Cs2AuIAuIIICl6进行了单晶X射线衍射研究。在不同的压强下，以合理的精度获得了晶格参数和可变的原子位置参数。在约12.5 GPa处发现了从I4/mmm到Pm3m的结构相变。用四方晶胞表示的晶格参数a_0和c_0得到了关系21/2a_0=c_0，并且由于氯离子从Au离子的中点移位引起的超结构反射hkl(L是奇数)在高于相变的压力下消失。在低压阶段，随着压力的增加，拉长的[AuIIICl6]和压缩的[AuICl6]八面体都平稳地逼近正八面体。在12.5 GPa处的结构相变之上，[AuCl6]八面体的晶体结构是等价的，这表明，伴随着AuI/AuIi混合价态到AuII单价态的价态转变，[AuCl6]八面体发生了从四方到立方的转变。
We performed the single-crystal X-ray diffraction study of a perovskite-type gold mixed-valence compound, Cs2AuIAuIIICl6, under high pressures up to 18GPa by using a diamond-anvil-cell with helium gas as an ideal hydrostatic pressure-transmitting medium. The lattice parameters and the variable atomic positional parameters were obtained with reasonable accuracy at various pressures. A structural phase transition at ca. 12.5GPa from I4/mmm to Pm3m was found. The lattice parameters a0and c0, denoted in the tetragonal cell setting, result in the relationship 21/2a0=c0, and the superstructure reflections hkl (l is odd), caused by the shift of the Cl ions from the midpoint of the Au ions, disappeared at pressures above the phase transition. Both elongated [AuIIICl6] and compressed [AuICl6] octahedra in the low-pressure phase smoothly approach regular octahedra with increasing pressure. Above the structural phase transition at 12.5GPa, all the [AuCl6] octahedra are crystallographically equivalent, which shows that the tetragonal-to-cubic phase transition accompanies the valence transition from the AuI/AuIIImixed-valence state to the AuIIsingle-valence state.