Local structure of a switchable dielectric Prussian blue analogue
Local structure of a switchable dielectric Prussian blue analogue
复制标题
DOI：
10.1039/c7ce01883e
复制
发表时间：
2017-12-28
期刊：
影响因子：
3.1
通讯作者：
Phillips, Anthony E.
中科院分区：
文献类型：
--
作者：
Duncan, Helen D.;Beake, Edward O. R.;Phillips, Anthony E.
普鲁士蓝(氰化物桥联，有序双钙钛矿)类似物六氰化咪唑亚铁酸钾，(C3N2H5)(2)K[Fe(CN)(6)]，含有金属氰化物骨架中的咪唑阳离子。它们在中温和高温阶段可以自由旋转，但在低温阶段冻结为固定方向。因此，中温和低温相之间的相变会导致这种材料的介电常数发生很大变化。然而，详细的阳离子动力学，特别是它们在中温和高温相之间的不同，仍然不清楚。我们在这里报告了对这种材料的过氚样品的总中子散射测量。逆蒙特卡罗模拟显示，与其他任何一种相相比，中温相与金属氰化物骨架的硬化有关。这表明，导致相变的动力学涉及弯曲金属-氰化键的能量惩罚和主客体氢键的好处之间的竞争。我们的结果表明，无序骨架材料具有Bragg散射看不到的重要局域结构，并且这种结构与产生可利用的电学性质的动力学之间存在着至关重要的联系。
The Prussian blue (cyanide-bridged, ordered double perovskite) analogue potassium imidazolium hexacyanoferrate, (C3N2H5)(2)K[Fe(CN)(6)], contains imidazolium cations encapsulated within a metal-cyanide framework. These are free to rotate in the intermediate-and high-temperature phases, but freeze into fixed orientations in the low-temperature phase. The phase transition between intermediate-and lowtemperature phases thus causes a substantial change in this material's dielectric constant. However, the detailed cation dynamics, and in particular how they differ between intermediate-and high-temperature phases, remain unclear. We report here total neutron scattering measurements on a perdeuterated sample of this material. Reverse Monte Carlo modelling reveals that the intermediate-temperature phase is associated with a stiffening of the metal-cyanide framework compared to either of the other phases. This shows that the dynamics responsible for the phase transitions involve competition between the energetic penalty for bending the metal-cyanide links and the benefit of host-guest hydrogen bonding. Our results demonstrate both that disordered framework materials have important local structure that is not visible to Bragg scattering, and that there is a crucial link between this structure and the dynamics that give rise to exploitable electric properties.