Vujosevic Danilo, Müller Klaus, Roduner Emil
Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
J Phys Chem B. 2006 May 4;110(17):8598-605. doi: 10.1021/jp060502k.
The behavior of ferroelectric and thermodynamic parameters of pyridinium perchlorate (PyClO(4)) was simulated based on experimental NMR data and properties of the individual constituting ions. Dynamic (2)H NMR spectroscopy was used to investigate the order-disorder character of ferroelectricity in PyClO(4). Quadrupole echo and inversion recovery experiments were performed in the range from 140 to 300 K. The spectra can be simulated by a rotational jump motion of the pyridinium cations about their pseudo-C(6) axis. This confirms that the ferroelectricity of this compound below a first-order phase transition at 248 K is primarily due to the ordering of cations along a ferroelectric axis. In an intermediate phase between 248 and 233 K, the cation-anion sublattice displacement mechanism also gives a small positive contribution to ferroelectricity. In the family of the ferroelectric pyridinium salts, the paraelectric-ferroelectric phase transition temperature increases with the size and polarizability of the constituting anions, suggesting that the main interaction for ferroelectric ordering occurs via an indirect superexchange mechanism, whereas in compounds with small anions of low polarizability the direct dipole-dipole interaction dominates and leads to antiferroelectric order.
基于实验核磁共振数据和各组成离子的性质，对高氯酸吡啶鎓（PyClO₄）的铁电行为和热力学参数进行了模拟。采用动态²H核磁共振光谱研究了PyClO₄中铁电的有序-无序特性。在140至300 K范围内进行了四极回波和反转恢复实验。光谱可以通过吡啶鎓阳离子围绕其伪C₆轴的旋转跳跃运动来模拟。这证实了该化合物在248 K的一级相变以下的铁电性主要是由于阳离子沿铁电轴的有序排列。在248至233 K的中间相中，阳离子-阴离子亚晶格位移机制对铁电性也有小的正贡献。在铁电吡啶鎓盐家族中，顺电-铁电相变温度随组成阴离子的大小和极化率增加，这表明铁电有序的主要相互作用是通过间接超交换机制发生的，而在具有低极化率小阴离子的化合物中，直接偶极-偶极相互作用占主导并导致反铁电有序。
