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A new avenue to relaxor-like ferroelectric behaviour found by probing the structure and dynamics of [NH3NH2]Mg(HCO2)3
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2023-06-14 , DOI: 10.1039/d3tc00480e Thomas J. Hitchings 1 , Helen M. Wickins 2 , George U. L. Peat 2 , Paul Hodgkinson 2 , Anant Kumar Srivastava 1 , Teng Lu 3 , Yun Liu 3 , Ross O. Piltz 4 , Franz Demmel 5 , Anthony E. Phillips 6 , Paul J. Saines 1
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2023-06-14 , DOI: 10.1039/d3tc00480e Thomas J. Hitchings 1 , Helen M. Wickins 2 , George U. L. Peat 2 , Paul Hodgkinson 2 , Anant Kumar Srivastava 1 , Teng Lu 3 , Yun Liu 3 , Ross O. Piltz 4 , Franz Demmel 5 , Anthony E. Phillips 6 , Paul J. Saines 1
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The field of relaxor ferroelectrics has long been dominated by ceramic oxide materials exhibiting large polarisations with temperature and frequency dependence. Intriguingly, the dense metal–organic framework (MOF) [NH3NH2]Mg(HCO2)3 was reported as one of the first coordination frameworks to exhibit relaxor-like properties. This work clarifies the origin of these relaxor-like properties through re-examining its unusual phase transition using neutron single crystal diffraction, along with solid-state NMR, quasielastic neutron scattering and dielectric spectroscopy studies. This reveals that the phase transition is caused by the partial reorientation of NH3NH2 within the pores of the framework, from lying in the planes of the channel at lower temperatures to along the channel direction above the transition temperature. The transition occurs via a dynamic process such that the NH3NH2 cations can slowly interconvert between parallel and perpendicular orientations, with an estimated activation energy of 50 kJ mol−1. Furthermore these studies are consistent with proton hopping between the hydrazinium cations oriented along the channel direction via a proton site intermediate. This study suggests the ferroelectric properties of [NH3NH2]Mg(HCO2)3 are likely driven by a hydrogen bonding mechanism. The relaxor behaviour is proposed to be the result of polar regions, which likely fluctuate due to increased cation dynamics at high temperature. The combination of cation reorientation and proton hopping fully describes this material's relaxor-like behaviour, suggesting a route to the future design of non-oxide-based relaxor ferroelectrics.
中文翻译：
通过探测 [NH3NH2]Mg(HCO2)3 的结构和动力学发现了类弛豫铁电行为的新途径
弛豫铁电体领域长期以来一直由陶瓷氧化物材料主导，这些陶瓷氧化物材料表现出与温度和频率相关的大极化。有趣的是，致密金属有机骨架（MOF）[NH 3 NH 2 ]Mg(HCO 2 ) 3被报道为第一个表现出类似弛豫特性的配位骨架之一。这项工作通过使用中子单晶衍射以及固态核磁共振、准弹性中子散射和介电谱研究重新检查其不寻常的相变，澄清了这些类似弛豫特性的起源。这表明相变是由NH 3 NH 2的部分重新取向引起的在框架的孔隙内，从位于较低温度下的通道平面到高于转变温度的沿通道方向。该转变通过动态过程发生，使得NH 3 NH 2阳离子可以在平行和垂直方向之间缓慢相互转换，估计活化能为50 kJ mol -1。此外，这些研究与通过质子位点中间体沿通道方向定向的肼阳离子之间的质子跳跃一致。这项研究表明[NH 3 NH 2 ]Mg(HCO 2 ) 3具有铁电性质可能是由氢键机制驱动的。弛豫行为被认为是极区的结果，极区可能由于高温下阳离子动力学的增加而波动。阳离子重新取向和质子跳跃的结合充分描述了这种材料的类弛豫行为，为非氧化物基弛豫铁电体的未来设计提供了一条途径。
更新日期：2023-06-14
中文翻译：
通过探测 [NH3NH2]Mg(HCO2)3 的结构和动力学发现了类弛豫铁电行为的新途径
弛豫铁电体领域长期以来一直由陶瓷氧化物材料主导，这些陶瓷氧化物材料表现出与温度和频率相关的大极化。有趣的是，致密金属有机骨架（MOF）[NH 3 NH 2 ]Mg(HCO 2 ) 3被报道为第一个表现出类似弛豫特性的配位骨架之一。这项工作通过使用中子单晶衍射以及固态核磁共振、准弹性中子散射和介电谱研究重新检查其不寻常的相变，澄清了这些类似弛豫特性的起源。这表明相变是由NH 3 NH 2的部分重新取向引起的在框架的孔隙内，从位于较低温度下的通道平面到高于转变温度的沿通道方向。该转变通过动态过程发生，使得NH 3 NH 2阳离子可以在平行和垂直方向之间缓慢相互转换，估计活化能为50 kJ mol -1。此外，这些研究与通过质子位点中间体沿通道方向定向的肼阳离子之间的质子跳跃一致。这项研究表明[NH 3 NH 2 ]Mg(HCO 2 ) 3具有铁电性质可能是由氢键机制驱动的。弛豫行为被认为是极区的结果，极区可能由于高温下阳离子动力学的增加而波动。阳离子重新取向和质子跳跃的结合充分描述了这种材料的类弛豫行为，为非氧化物基弛豫铁电体的未来设计提供了一条途径。
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