Horiuchi Sachio, Ishibashi Shoji
Research Institute for Advanced Electronics and Photonics (RIAEP), National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8565 Japan.
Research Center for Computational Design of Advanced Functional Materials (CD-FMat), National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba 305-8568 Japan.
Chem Sci. 2021 Oct 6;12(42):14198-14206. doi: 10.1039/d1sc02729h. eCollection 2021 Nov 3.
Dielectrics that undergo electric-field-induced phase changes are promising for use as high-power electrical energy storage materials and transducers. We demonstrate the stepwise on/off switching of large polarization in a series of dielectrics by flipping their antipolar or canted electric dipoles proton transfer and inducing simultaneous geometric changes in their π-conjugation system. Among antiferroelectric organic molecular crystals, the largest-magnitude polarization jump was obtained as 18 μC cm through revisited measurements of squaric acid (SQA) crystals with improved dielectric strength. The second-best polarization jump of 15.1 μC cm was achieved with a newly discovered antiferroelectric, furan-3,4-dicarboxylic acid. The field-induced dielectric phase changes show rich variations in their mechanisms. The quadruple polarization hysteresis loop observed for a 3-(4-chlorophenyl)propiolic acid crystal was caused by a two-step phase transition with moderate polarization jumps. The ferroelectric 2-phenylmalondialdehyde single crystal having canted dipoles behaved as an amphoteric dielectric, exhibiting a single or double polarization hysteresis loop depending on the direction of the external field. The magnitude of a series of observed polarizations was consistently reproduced within the simplest sublattice model by the density functional theory calculations of dipole moments flipping over a hydrogen-bonded chain or sheet (sublattice) irrespective of compounds. This finding guarantees a tool that will deepen our understanding of the microscopic phase-change mechanisms and accelerate the materials design and exploration for improving energy-storage performance. The excellent energy-storage performance of SQA was demonstrated by both a high recoverable energy-storage density of 3.3 J cm and a nearly ideal efficiency (90%). Because of the low crystal density, the corresponding energy density per mass (1.75 J g) exceeded those derived from the highest values (∼8-11 J cm) reported for several bulk antiferroelectric ceramics , without modification to relaxor forms.
经历电场诱导相变的电介质有望用作高功率电能存储材料和换能器。我们通过翻转反极或倾斜电偶极、质子转移并在其π共轭体系中诱导同时发生的几何变化，证明了一系列电介质中大幅极化的逐步开启/关闭切换。在反铁电有机分子晶体中，通过对具有提高的介电强度的方酸（SQA）晶体进行重新测量，获得了最大幅度的极化跃变，为18 μC/cm²。新发现的反铁电体呋喃-3,4-二甲酸实现了第二大极化跃变，为15.1 μC/cm²。场诱导的介电相变在其机制上表现出丰富的变化。在3-(4-氯苯基)丙炔酸晶体中观察到的四重极化滞后回线是由具有适度极化跃变的两步相变引起的。具有倾斜偶极的铁电2-苯基丙二醛单晶表现为两性电介质，根据外部场的方向表现出单极化或双极化滞后回线。通过对氢键链或片（亚晶格）上偶极矩翻转的密度泛函理论计算，在最简单的亚晶格模型中一致地再现了一系列观察到的极化幅度，而与化合物无关。这一发现保证了一种工具，将加深我们对微观相变机制的理解，并加速材料设计和探索以提高储能性能。SQA优异的储能性能通过3.3 J/cm³的高可恢复储能密度和近乎理想的效率（90%）得到证明。由于晶体密度低，相应的单位质量能量密度（1.75 J/g）超过了几种块状反铁电陶瓷报道的最高值（约8 - 11 J/cm³），且无需转变为弛豫形式。
