Chang-Shan Yang

Reversible Phase Transition with Ultralarge Dielectric Relaxation Behaviors in Succinimide Lithium(I) Hybrids

Dielectric relaxations have widely applied on high permittivity capacitors, dielectric switches, ferroelectrics, pyroelectrics, and electrical insulating materials. However, few investigations of large dielectric relaxation behaviors on organic-inorganic hybrid materials have been documented before. Here we present a novel two-dimensional succinimide lithium(I) hybrid compound, [Li(PDD)2ClO4]n, 1, (PDD = 2,5-pyrrolidinedione = succinimide) which shows reversible phase transition behavior in the vicinity of 228 K accompanied by an unusual symmetry breaking from I41/amd to C2/c. X-ray single crystal diffractions analysis indicates the twist motion of pyrrolidine heterocycles, and order-disorder motion of ClO4- anions triggered the reversible phase transition. By means of an intuitive crystallographic model (rattling ion model), we further illustrated the mechanism of the interesting reversible phase transition. Particularly, 1 shows ultralarge dielectric relaxation behavior in the vicinity of the phase transition by its dielectric constant dependence on temperatures and frequencies as well as its Cole-Cole relation.

A novel co-crystallization molecular ferroelectric induced by the ordering of sulphate anions and hydrogen atoms

Molecular ferroelectrics based on co-crystallization complexes have been very seldom reported before. Here we present the interesting case of the co-crystallization copper complex [EG]·[Cu(phen)2·SO4], 1 (EG = ethylene glycol, phen = 1,10-phenanthroline), which displays a reversible paraelectric–ferroelectric phase transition at 272 K. 1 undergoes symmetry breaking from C2/c to Cc at around 272 K which is triggered by the disorder–order transition of sulphate anions and hydrogen bonds. The real component of the dielectric constant versus temperature shows very large maxima for dielectric anomalies, corresponding to the phase transition. The activation energy is about 84.2 kJ mol−1, which can be calculated using the Arrhenius equation τ = τ0 exp(Ea/kBT) in a graph of dielectric loss changes with temperature at different frequencies. The measurement of ferroelectric properties shows a maximum spontaneous polarization (Ps) of ca. 3.18 μC cm−2 with a coercive field (Ec) of 1.2 kV cm−1. The phase transition sequence of 1 was further verified by differential scanning calorimetry (DSC) with one heat anomaly peak observed at around 272 K.