A Molecular Ferroelectric Thin Film of Imidazolium Perchlorate That Shows Superior Electromechanical Coupling

Molecular ferroelectric thin films are highly desirable for their easy and environmentally friendly processing, light weight, and mechanical flexibility. A thin film of imidazolium perchlorate processed from aqueous solution is an excellent molecular ferroelectric with high spontaneous polarization, high Curie temperature, low coercivity, and superior electromechanical coupling. These attributes make it a molecular alternative to perovskite ferroelectric films in sensing, actuation, data storage, electro‐optics, and molecular/flexible electronics.     

Halide Double Perovskite Ferroelectrics

Halide double perovskites have recently emerged as a promising environmentally friendly optoelectronic and photovoltaic material for their inherent thermodynamic stability, high defect tolerance, and appropriate band gaps. However, to date, no ferroelectric material based on halide double perovskites has been discovered. Herein, by hetero‐substitution of lead and cation intercalation of n‐propylamine, the first halide double perovskite ferroelectric, (n‐propylammonium)₂CsAgBiBr₇ ( 1 ), is reported and it exhibits distinct ferroelectricity with a notable saturation polarization of about 1.5 μC cm^?2. More importantly, single‐crystal photodetectors of 1 exhibit extraordinary performance with containing high on/off ratios of about 10⁴, fast response rates of 141 μs, and detectivity as high as 5.3×10¹¹ Jones. This finding opens a new way to design high‐performance perovskite ferroelectrics, and provides a viable approach in the search for stable and lead‐free optoelectronic materials as an alternative to the lead‐containing system.     

3D-to-2D Dimensional Reduction for Exploiting a Multilayered Perovskite Ferroelectric toward Polarized-Light Detection in the Solar-Blind Ultraviolet Region

Polarized-light detection in solar-blind ultraviolet region is indispensable for optoelectronic applications, whereas new 2D candidates targeted at solar-blind UV range remain extremely scarce. 2D hybrid perovskite ferroelectrics that combine polarization and semiconducting properties are of increasing interest. Here, using the 3D-to-2D dimensional reduction of CH₃NH₃PbCl₃, we designed a multilayered hybrid perovskite ferroelectric, (CH₃CH₂NH₃)₂(CH₃NH₃)₂Pb₃Cl₁₀, which shows spontaneous polarization and a high Curie temperature (390 K) comparable with that of BaTiO₃ (393 K). The wide band gap (ca. 3.35 eV) and anisotropic absorbance stemming from its intrinsic 2D motif, greatly favor its polarization-sensitive activity in UV region. The device displays excellent polarization-sensitive behavior under 266 nm, along with a large dichroic ratio (ca. 1.38) and high on/off current ratio (ca. 2.3×10³).     

Sr2Bi4Ti5O18的压致结构相变

 使用4∶1的甲醇-乙醇混合液作传压介质，利用金刚石对顶砧装置（DAC），研究了层状铁电体Sr₂Bi₄Ti₅O₁₈的在位高压拉曼光谱和压致结构相变（0～27 GPa）。发现在8.31 GPa，Sr₂Bi₄Ti₅O₁₈经历了一次结构相交。在23.13 GPa以上，Sr₂Bi₄Ti₅O₁₈似乎出现了压致非晶相交的先兆。并使用内模方法对Sr₂Bi₄Ti₅O₁₈的内模进行了指认。     

Computational studies on magnetism and ferroelectricity

Magnetics, ferroelectrics, and multiferroics have attracted great attentions because they are not only extremely important for investigating fundamental physics, but also have important applications in information technology. Here, recent computational studies on magnetism and ferroelectricity are reviewed. We first give a brief introduction to magnets, ferroelectrics, and multiferroics. Then, theoretical models and corresponding computational methods for investigating these materials are presented. In particular, a new method for computing the linear magnetoelectric coupling tensor without applying an external field in the first principle calculations is proposed for the first time. The functionalities of our home-made Property Analysis and Simulation Package for materials (PASP) and its applications in the field of magnetism and ferroelectricity are discussed. Finally, we summarize this review and give a perspective on possible directions of future computational studies on magnetism and ferroelectricity.     

Ferroelectricity from iron valence ordering in rare earth ferrites?

The possibility of multiferroicity arising from charge ordering in LuFe₂O₄ and structurally related rare earth ferrites is reviewed. Recent experimental work on macroscopic indications of ferroelectricity and microscopic determination of coupled spin and charge order indicates that this scenario does not hold. Understanding the origin of the experimentally observed charge and spin order will require further theoretical work. Other aspects of recent research in these materials, such as geometrical frustration effects, possible electric‐field‐induced transitions, or orbital order are also briefly treated.

     

Proton radiation damage in SrTiO3 thin film by computer simulation

Perovskite ferroelectrics (FEs) have high endurance to radiation. Strontium titanate (STO) (SrTiO₃) is a kind of perovskite FE with a large dielectric constant, which has attracted a good deal of attention due to its excellent dielectric, photoelectric and optical properties. The proton radiation damage in STO thin films is investigated by computer simulations in this work. The threshold displacement energy is an important input parameter for Monte Carlo simulation based on a binary collision approximation model, so we first use molecular dynamics to calculate the averaged threshold displacement energy of Sr, O and Ti atom. The calculated values are 67, 50 and 136 eV, which are obviously larger than default value (25 eV) in the Stopping and Range of Ions in Matter (SRIM) code. The results of the SRIM simulation demonstrate the dependency of vacancy number and position distribution on the proton's energy and the angle of incidence.     

Strain at junctions in multidomain configurations

This article deals with the determination of multidomain configurations in ferroics taking into account the elastic compatibility of the neighbouring domains. The proposed method is based on transformation matrices, which describe the spacial relationship of two crystal lattice bases for coherent domain pairs. The matrices are calculated using the symmetry operations between domains and lattice parameters. The principle point of this method is the comparison of the product of transformation matrices and the unity matrix. For example, by using this method it was shown that the junction of three and five orientation domains is strained whereas the encounter of four domains is strain free in three different ferroelastic perovskite phases. The derived allowed four-domain configurations are confirmed by experimental data.