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首页> 外文期刊>Chemistry: A European journal >A Copper-Formate Framework Showing a Simple to Helical Antiferroelectric Transition with Prominent Dielectric Anomalies and Anisotropic Thermal Expansion, and Antiferromagnetism
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A Copper-Formate Framework Showing a Simple to Helical Antiferroelectric Transition with Prominent Dielectric Anomalies and Anisotropic Thermal Expansion, and Antiferromagnetism

机译：铜构架显​​示简单的螺旋反铁电跃迁，具有明显的介电异常和各向异性热膨胀以及反铁磁

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摘要

We present here the compound [NH4][Cu(HCOO) 3], a new member of the [NH4][M(HCOO) 3] family. The JahnTeller Cu2+ ion leads to a distorted 4(9) 6(6) chiral Cu-formate framework. In the low-temperature (LT) orthorhombic phase, the Cu2+ is in an elongated octahedron, and the NH_4 ions in the framework channel are off the channel axis. From 94 to 350 K the NH4- ion gradually approaches the channel axis and the related modulation of the framework and the hydrogen- bond system occurs. The LT phase is simple antiferroelectric (AFE). The material becomes hexagonal above 355 K. In the high-temperature (HT) phase, the Cu2+ octahedron is compressed, and the NH_4 ions are arranged helically along the channel axis. Therefore, the phase transition is one from LT simple AFE to HT helical AFE. The temperature-dependent structure evolution is accompanied by significant thermal and dielectric anomalies and anisotropic thermal expansion, due to the different status of the NH4- ions and the framework modulations, and the structure-property relationship was established based on the extensive variable-temperature single-crystal structures. The material showed long range ordering of antiferromagnetism (AFM), with low dimensional character and a N el temperature of 2.9 K. Therefore, within the material AFE and AFM orderings coexist in the low-temperature region.
机译：我们在这里介绍化合物[NH4] [Cu（HCOO）3]，[NH4] [M（HCOO）3]家族的新成员。 JahnTeller Cu2 +离子导致扭曲的4（9）6（6）手性Cu甲酸酯骨架。在低温（LT）正交晶相中，Cu2 +位于细长的八面体中，框架通道中的NH_4离子不在通道轴上。从94 K到350 K，NH4-离子逐渐接近通道轴，并发生骨架和氢键系统的相关调节。 LT相是简单的反铁电（AFE）。该材料在355 K以上变为六边形。在高温（HT）相中，Cu2 +八面体被压缩，并且NH_4离子沿通道轴螺旋排列。因此，相变是从LT简单AFE到HT螺旋AFE的一种。由于NH4-离子的状态不同和骨架调制不同，与温度相关的结构演化伴随着明显的热和介电异常以及各向异性的热膨胀，并基于广泛的可变温度单分子建立了结构-性质关系。 -晶体结构。该材料显示出反铁磁（AFM）的远距离有序，具有低尺寸特征和2.9 K的Nel温度。因此，在材料内，AFE和AFM在低温区域共存。

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