Conspectus Although the first ferroelectric discovered in 1920 is Rochelle salt, a typical molecular ferroelectric, the front-runners that have been extensively studied and widely used in diverse ...applications, such as memory elements, capacitors, sensors, and actuators, are inorganic ferroelectrics with excellent electrical, mechanical, and optical properties. With the increased concerns about the environment, energy, and cost, molecular ferroelectrics are becoming promising supplements for inorganic ferroelectrics. The unique advantages of high structural tunability and homochirality, which are unavailable in their inorganic counterparts, make molecular systems a good platform for manipulating ferroelectricity. Remarkably, based on the Neumann’s principle and the Curie symmetry principle defining the group-to-subgroup relationship, we have found some outstanding high-temperature molecular ferroelectrics, like diisopropylammonium bromide (DIPAB) with a large spontaneous polarization up to 23 μC/cm2 (Fu, D. W.; et al. Science 2013, 339, 425 ). However, their application potential is severely limited by the uniaxial nature, leading to major issues in finding proper substrates for thin-film growth and achieving high thin-film performance. Inspired by the commercialized inorganic ferroelectrics like Pb(Zr, Ti)O3 (PZT), where the multiaxial nature contributes greatly to the optimized ferroelectric and piezoelectric performance, developing high-temperature multiaxial molecular ferroelectrics is an imminent task. In this Account, we review our recent research progress on the targeted design of multiaxial molecular ferroelectrics. We first propose the “quasi-spherical theory”, a phenomenological theory based on the Curie symmetry principle, to modify the spherical cations to a low-symmetric quasi-spherical geometry for acquiring the highly symmetric paraelectric phase and the polar ferroelectric phase of multiaxial ferroelectrics simultaneously. Besides the sizes and weights of the cation and anion, the intermolecular interactions are particularly crucial for decelerating the molecular rotation at low temperature to reasonably induce ferroelectricity. It means that the momentums of the cation and anion should be matched, so we describe the “momentum matching theory”. In particular, introducing homochirality, a superiority of molecular materials over the inorganic ones, was demonstrated as an effective approach to increase the incidence of ferroelectric crystal structures. Thanks to the striking chemical variability and structure–property flexibility of molecular materials, our research efforts outlined in this Account have led to and will further motivate the richness and the application exploration of high-temperature, high-performance multiaxial molecular ferroelectrics, along with the implementation and perfection of the targeted design strategies.
To determine the rupture processes of big earthquakes is a fundamental problem of earthquake studies, which also supports earthquake physics research. Although the joint use of seismic, geodetic and ...seismicity data provides good constraints to determine the fault plane information of inland earthquakes, it is still challenging to unveil non-planar fault planes for oceanic earthquake ruptures. For complicated earthquakes, that ruptured more than one fault plane, a method to stably obtain focal mechanism changes is required to determine the fault plane information precisely. In this study, we analyze the stability and flexibility of multiple seismic methods, i.e. back-projections, multi-point-source inversion and finite fault inversion, to determine the rupture kinematics of big earthquakes, and find the stability spatial-temporal resolution and flexibility to resolve focal mechanisms that are not compatible in each single techniques. A sequential strategy is thus proposed to use back-projection results to pres
3D ABX3 organic–inorganic halide perovskite (OIHP) semiconductors like CH3NH3PbI3 have received great attention because of their various properties for wide applications. However, although a number ...of low‐dimensional lead‐based OIHP ferroelectric semiconductors have been documented, obtaining 3D ABX3 OIHP ferroelectric semiconductors is challenging. Herein, an A‐site cation CH3PH3+ (methylphosphonium, MP) is employed to successfully obtain a lead‐free 3D ABX3 OIHP ferroelectric semiconductor MPSnBr3, which shows clear above‐room‐temperature ferroelectricity and a direct bandgap of 2.62 eV. It is emphasized that MPSnBr3 is a multiaxial molecular ferroelectric with the number of ferroelectric polar axes being as many as 12, which is far more than those of the other OIHP ferroelectric semiconductors and even the classical inorganic perovskite ferroelectric semiconductors BiFeO3 (4 polar axes) and BaTiO3 (3 polar axes). MPSnBr3 is the first MP‐based 3D ABX3 OIHP ferroelectric semiconductor. This finding throws light on the exploration of other excellent 3D ABX3 OIHP ferroelectric semiconductors with great application prospects.
MPSnBr3 (MP = methylphosphonium) is the first MP‐based 3D ABX3 hybrid perovskite ferroelectric semiconductor. MPSnBr3 is lead‐free and shows clear ferroelectricity with the number of ferroelectric polar axes up to 12, much more than that of other hybrid perovskite ferroelectric semiconductors. MPSnBr3 also exhibits a direct bandgap of 2.62 eV.
The Minshan Uplift Zone (MUZ) is located at the eastern margin of the Tibetan Plateau, which is the junction of three tectonic terranes. The observed discrepancy between a high uplifting and low ...shortening rate over the MUZ is attributed to the intrusion of a viscous lower crust. In the last 50 years, several significant earthquakes occurred at the boundaries of the MUZ, that is, the Huya and Mingjiang faults. On 8 August 2017, the Jiuzhaigou earthquake (Mw 6.5) occurred on the northern extension of the Huya fault. We adopt a joint inversion of the interferometric synthetic aperture radar and teleseismic body wave data to investigate the rupture process of this event. The obtained slip model is dominated by left‐lateral strike slips on a subvertical fault presenting significant shallow slip deficit. The rupture initiation is composed of both thrust and strike‐slip mechanisms producing a non‐double‐couple solution. We also resolve a secondary fault branch forming an obtuse angle with the main fault plane at its northern end. These phenomena indicate that the northern Huya fault is a young (less mature) fault system. Focal mechanisms of the regional earthquakes demonstrate that the northern and southern Huya faults present different combinations of strike‐slip and reversed motion. We attribute such discrepancy to the lateral extension of the viscous lower crust, which appears to extrude to the east beyond the northern Huya fault, in comparison with that confined under the MUZ near the southern Huya fault. This conceptual model is also supported by geomorphological and magnetotelluric observations.
Plain Language Summary
Earthquake ruptures are controlled by tectonic loading; thus, researching on the earthquake rupture mechanism reflects the tectonic loading mechanism. The Minshan Uplift Zone is located at the eastern margin of the Tibetan Plateau. It is the junction of three tectonic blocks, which presents fast uplift rate and slow shortening rate. Thus, injection of a soft or viscous lower crust may explain this deformation phenomenon. By investigating the 2017 Jiuzhaigou earthquake and the regional earthquakes near the Minshan Uplift Zone, we found that the eastern margin of the Minshan Uplift Zone, so‐called the Huya fault, is a young fault system, which presents a high complexity of rupture processes. The sense of motion also varies between the northern and southern Huya faults. These phenomena appear to be related to the difference of the lower crust intrusion. The injection of a soft viscous lower crust leads to the uplift of the whole Minshan Uplift Zone. The boundary of the lower crust intrusion controls the earthquake mechanisms occurred on the boundary of the Minshan Uplift Zone.
Key Points
Complicated rupture of the Jiuzhaigou earthquake is discovered
The northern Huya fault is an young fault system
Shape of the viscous lower crust beneath the Minshan Uplift Zone supports its uplift pattern
With the development of the times, the cultivation of students’ comprehensive ability has been widely emphasized, among which the cultivation of music appreciation ability is more and more important. ...The purpose of this paper is to develop a framework for a multi-intelligences music appreciation ‘immersion’ teaching mode, which is based on the teaching reform of the music appreciation course. Our process involved collecting and pre-processing data related to music emotion, extracting music emotion features, and building a model for music emotion appreciation using long and short-term memory networks. The construction of a multi-featured memory network knowledge tracking model involved cross-fertilizing students’ responses to music appreciation difficulty and ability. Through the effect test of the memory network knowledge tracking model and the practical analysis of music appreciation curriculum reform, it can be seen that the average effect of the knowledge tracking model proposed in this paper is higher than that of the traditional knowledge tracking model by 0.15~0.21. The total score of the experimental class’s music appreciation ability is 10.21, while the control class’s score is 7.78, and the experimental class based on the teaching music appreciation curriculum of multiple intelligences is higher than that of the control class by 2.43%. This paper provides a reform direction for the teaching reform of music appreciation courses based on the multiple intelligences music appreciation teaching program, which is of practical significance for the development of music appreciation teaching.
Ferroelectric materials have a variety of technological applications, as transducers, capacitors, sensors, etc. Great interest in molecular ferroelectrics has emerged because of their structural ...flexibility, tunability, and homochirality. However, the discoveries of molecular ferroelectrics are not abundant. The lack of chemical design is the main challenge in realizing new molecular ferroelectrics. Consequently, chemical design approaches, including the ideas of introducing quasi-spherical theory, homochirality, and H/F substitution, have been developed recently. Through these advanced methodologies, a wide range of ferroelectrics were successfully synthesized, changing the blind search into a targeted chemical design. In this Perspective, we aim to provide insight into the fundamental chemistry and physics of molecular ferroelectrics and propose the concept of “ferroelectrochemistry”, concerned with the targeted design and performance optimization of molecular ferroelectrics from the chemical point of view. We start with the basic theories used in the modification of chemical structures for new molecular ferroelectrics, such as the quasi-spherical theory. After that, we focus on the fundamentals of homochirality from the perspective of chemistry and advantages of introducing a homochiral molecule within the scope of ferroelectrics. Further, we explore another design strategy, H/F substitution, as an analogue of the H/D isotope effect. The introduction of a F atom usually does not change the polar point group but may induce a minor structural disruption that enhances physical properties such as Curie temperature and spontaneous polarization. We hope our comprehensive studies on the targeted design and performance optimization strategies for molecular ferroelectrics may build up and enrich the content of ferroelectrochemistry.
With prosperity, decay, and another spring, molecular ferroelectrics have passed a hundred years since Valasek first discovered ferroelectricity in the molecular compound Rochelle salt. Recently, the ...proposal of ferroelectrochemistry has injected new vigor into this century-old research field. It should be highlighted that piezoresponse force microscopy (PFM) technique, as a non-destructive imaging and manipulation method for ferroelectric domains at the nanoscale, can significantly speed up the design rate of molecular ferroelectrics as well as enhance the ferroelectric and piezoelectric performances relying on domain engineering. Herein, we provide a brief review of the contribution of the PFM technique toward assisting the design and performance optimization of molecular ferroelectrics. Relying on the relationship between ferroelectric domains and crystallography, together with other physical characteristics such as domain switching and piezoelectricity, we believe that the PFM technique can be effectively applied to assist the design of high-performance molecular ferroelectrics equipped with multifunctionality, and thereby facilitate their practical utilization in optics, electronics, magnetics, thermotics, and mechanics among others.
Along with the rapid development of ferroelectrochemistry, piezoresponse force microscopy (PFM) with high detection speed and accuracy has become a powerful tool for screening the potential candidates for molecular ferroelectrics.
AbstractSurface soil erosion is one of the most common slope degradation processes. In this study, microbial calcification (MC), a stimulated natural biocementation process, was investigated for its ...feasibility as a sandy-slope surface erosion control method. An artificial model slope at 30° was treated by MC via the surface spraying method at three cementation solution concentrations (0.2, 1.0, and 2.0 M). Simulated rainfall was sprayed on the slope surface at 5 mm/min for 30 min. Results show that MC treatment with 0.2- and 1.0-M cementation solution improves surface erosion resistance in terms of observed erosion pattern with time, soil loss weight and rate, and outflow properties. However, MC treatment with 2.0-M cementation solution does not improve surface erosion resistance. Instead, substantial soil loss is observed under rainfall impact while soil is washed away in cemented aggregates. At the end of the rainfall erosion test, microstructural features of the surface samples were identified by scanning electron microscope (SEM) observation. It is found that the effectiveness of MC for sandy-slope surface erosion control is determined by (1) overall CaCO3 precipitation content, (2) treatment depth, and (3) competence between CaCO3 crystal growth and nucleation process.
This study evaluates the influences of air pollution in China using a recently proposed model—multi‐scale geographically weighted regression (MGWR). First, we review previous research on the ...determinants of air quality. Then, we explain the MGWR model, together with two global models: ordinary least squares (OLS) and OLS containing a spatial lag variable (OLSL) and a commonly used local model: geographically weighted regression (GWR). To detect and account for any variation of the spatial autocorrelation of air pollution over space, we construct two extra local models which we call GWR with lagged dependent variable (GWRL) and MGWR with lagged dependent variable (MGWRL) by including the lagged form of the dependent variable in the GWR model and the MGWR model, respectively. The performances of these six models are comprehensively examined and the MGWR and MGWRL models outperform the two global models as well as the GWR and GWRL models. MGWRL is the most accurate model in terms of replicating the observed air quality index (AQI) values and removing residual dependency. The superiority of the MGWR framework over the GWR framework is demonstrated—GWR can only produce a single optimized bandwidth, while MGWR provides covariate‐specific optimized bandwidths which indicate the different spatial scales that different processes operate.
Topological defects, such as vortices and skyrmions, provide a wealth of splendid possibilities for new nanoscale devices because of their marvelous electronic, magnetic, and mechanical behaviors. ...Recently, great advances have been made in the study of the ferroelectric vortex in conventional perovskite oxides, such as BaTiO3 and BiFeO3. Despite extensive interest, however, no intriguing ferroelectric vortex structures have yet been found in organic–inorganic hybrid perovskites (OIHPs), which are desirable for their mechanical flexibility, ease of fabrication, and low acoustical impedance. We observed the robust vortex–antivortex topological configurations in a two-dimensional (2D) layered OIHP ferroelectric (4,4-DFPD)2PbI4 (4,4-DFPD is 4,4-difluoropiperidinium). This provides future directions for the study of perovskites and makes it a promising alternative for nanoscale ferroelectric devices in medical, micromechanical, and biomechanical applications.
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