Malec Leszek M, Gryl Marlena, Stadnicka Katarzyna M
Faculty of Chemistry , Jagiellonian University , Gronostajowa 2 , 30-387 Krakow , Poland.
Inorg Chem. 2018 Apr 16;57(8):4340-4351. doi: 10.1021/acs.inorgchem.7b03161. Epub 2018 Apr 4.
New nontoxic and biocompatible ferroelectric materials are a subject undergoing intense study. One of the most promising research branches is focused on H-bonded organic or hybrid ferroelectrics. The engineering of these materials is based on mimicking the phase transition mechanisms of the well-known inorganic ferroelectrics. In our study, a coupled experimental and theoretical methodology was used for a precise investigation of the ferroelectric phase transition mechanism in ammonium sulfate (AS). A series of single-crystal X-ray diffraction measurements were performed in the temperature range between 273 and 163 K. The detailed inspection of the obtained static structural data, in the above-mentioned temperature range, allowed us to reveal dynamical effects at the ferroelectric phase transition. Accurate analysis of all geometrical features within the obtained crystal structures was carried out. The results were discussed in the view of previously discovered physical properties. X-ray studies were complemented by the use of quantum theory of atoms in molecules calculations and Hirshfeld surface analysis. Valence shell charge concentration analysis allowed us to find the subtle changes between charge density distribution within SO in para- and ferroelectric phases. H-bond interactions, geometrically classified in both AS phases, were all confirmed by the appropriate critical points. The interaction energies were estimated for the structures at 273, 233, 213, 183, and 163 K. Correlation between the geometrical approach and the results of theoretical calculations enabled us to discover the differences in interaction equilibrium between the AS phases. The mechanism of the phase transition originates from the disruption of the vibrational lattice mode between sulfate anions. Our studies resolved the problem, which was under discussion for more than 60 years.
新型无毒且生物相容的铁电材料是一个正在进行深入研究的课题。最有前景的研究分支之一聚焦于氢键有机或混合铁电体。这些材料的工程设计基于模拟著名无机铁电体的相变机制。在我们的研究中，采用了实验与理论相结合的方法来精确研究硫酸铵（AS）中的铁电相变机制。在273至163 K的温度范围内进行了一系列单晶X射线衍射测量。对上述温度范围内获得的静态结构数据进行详细检查，使我们能够揭示铁电相变时的动力学效应。对所得晶体结构中的所有几何特征进行了精确分析。根据先前发现的物理性质对结果进行了讨论。通过使用分子中原子的量子理论计算和 Hirshfeld 表面分析对X射线研究进行了补充。价层电荷浓度分析使我们能够发现顺电相和铁电相中SO内电荷密度分布之间的细微变化。在两个AS相中按几何分类的氢键相互作用均由适当的临界点证实。估算了273、233、213、183和163 K温度下结构的相互作用能。几何方法与理论计算结果之间的相关性使我们能够发现AS相之间相互作用平衡的差异。相变机制源于硫酸根阴离子之间振动晶格模式的破坏。我们的研究解决了一个已经讨论了60多年的问题。
