State of the Art and Prospects in Metal-Organic Framework-Derived Microwave Absorption Materials

Microwave has been widely used in many fields,including communication,medical treatment and military industry;however,the corresponding generated radiations have been novel hazardous sources of pollution threating human’s daily life.Therefore,designing high-performance microwave absorption materials(MAMs)has become an indispensable requirement.Recently,metal-organic frameworks(MOFs)have been considered as one of the most ideal precursor candidates of MAMs because of their tunable structure,high porosity and large specific surface area.Usually,MOF-derived MAMs exhibit excellent electrical conductivity,good magnetism and sufficient defects and interfaces,providing obvious merits in both impedance matching and microwave loss.In this review,the recent research progresses on MOF-derived MAMs were profoundly reviewed,including the categories of MOFs and MOF composites precursors,design principles,preparation methods and the relationship between mechanisms of microwave absorption and microstructures of MAMs.Finally,the current challenges and prospects for future opportunities of MOF-derived MAMs are also discussed.

Microscopic origin and relevant grain size effect of discontinuous grain growth in BaTiO_(3)-based ferroelectric ceramics

Barium titanate[BaTiO_(3)(BT)]-based ceramics are typical ferroelectric materials.Here,the discontinuous grain growth(DGG)and relevant grain size effect are deeply studied.An obvious DGG phenomenon is observed in a paradigmatic Zr^(4+)-doped BT-based ceramic,with grains growing from∼2.2–6.6 to∼121.8–198.4μm discontinuously near 1320℃.It is found that fine grains can get together and grow into large ones with liquid phase surrounding them above eutectic temperature.Then the grain boundary density(D g)is quantitatively studied and shows a first-order reciprocal relationship with grain size,and the grain size effect is dependent on D g.Fine grains lead to high D g,and then cause fine domains and pseudocubic-like phase structure because of the interrupted long-range ferroelectric orders by grain boundary.High D g also causes the diffusion phase transition and low Curie dielectric peak due to the distribution of phase transition temperature induced by internal stress.Local domain switching experiments reveal that the polarization orientation is more difficult near the grain boundary,implying that the grain boundary inhibition dominates the process of polarization orientation in fine-grain ceramics,which leads to low polarization but a high coercive field.However,large-grain ceramics exhibit easy domain switching and high&similar ferroelectricity.This work reveals that the grain boundary effect dominates the grain size effect in fine-grain ceramics,and expands current knowledge on DGG and grain size effect in polycrystalline materials.

Enhanced ferro-/piezoelectric properties of tape-casting-derived Er^(3+)-doped Ba_(0.85)Ca_(0.15)Ti_(0.9)Zr_(0.1O3) optoelectronic thick films

Er^(3+)-doped Ba_(0.85)Ca_(0.15)Ti_(0.9)Zr_(0.1O3)(xEr-BCTZ,x=0,0.005,0.01,0.015)multifunctional thick films were prepared by the tape-casting method,using sol-gel-derived nano-sized powders as the matrix material.The surface morphologies,photoluminescence,and electrical properties were investigated.Dense microstructures with pure perovskite structure were obtained in the thick films.By doping an appropriate amount of Er^(3+),the samples exhibit superior up-conversion photoluminescence performance and simultaneously enhanced electrical performances.In addition,relatively higher texture fractions(with the largest value of 83.5%)were realized through introducing plate-like BaTiO_(3) templates to make the thick film grow by the[001]_(c) orientation.And the ferro-/piezoelectric properties of the thick films were further improved,showing potential in the applications of micro-optoelectronic devices.

Strain and illumination triggered regulations of up-conversion luminescence in Er-doped Bi_(0.5)Na_(0.5)TiO_(3)-BaTiO_(3)/Mica flexible multifunctional thin films

External stimuli induced effective regulations of luminescent material are of significant interest in the development of smart optical devices.Here,by simply doping with Er^(3+) in the 0.94Bi_(0.5)Na_(0.5)TiO_(3)-0.06BaTiO_(3)(BNTBT)ferroelectric host,using the bendable mica substrate,and exerting mechanical strain(bending)or light illumination(via photochromic reaction),the all-inorganic,highly-transparent and flexible Er-doped BNTBT/Mica luminescent-ferroelectric thin films were designed and fabricated,displaying strain-induced dramatically elevation of up-conversion photoluminescence(PL)intensity,suppression of PL concentration quenching,outstanding endurance and durability,convenient illuminationmediated PL quenching.And the strain-induced structural changes and local lattice distortions of the thin films were further explored through theoretical calculations and Raman measurement.Our results can supply the guidance of designing other luminescent-ferroelectric materials with controlled PL properties via easy mechanical/photo stimuli for expanding the application of multifunctional wearable memory devices.

Eu-doped K_(0.5)Na_(0.5)NbO_(3)-(Ba,Sr)TiO_(3):A novel lead-free luminescent ferroelectric transparent ceramic with reversible photochromism

Photochromic(PC)luminescent ferroelectric materials have aroused great interest because of their potential applications in optical information memories,optical switches and bio-imaging.However,those materials are basically opaque.In this work,we prepared a PC luminescent K_(0.5)Na_(0.5)NbO_(3)-(Ba,Sr)TiO_(3)-based ferroelectric transparent ceramic by modifying with Eu^(3+),Ba^(2+,)Ti^(4+)and Sr^(2+),which not only have good optical transmittances(-60%at 900 nm),moderate ferroelectric properties and down-conversion photo-luminescence(PL)properties,but also exhibit reversible PC behavior.After the illumination by xenon lamp,the colors of the ceramics change from pale green to gray,and then reversibly recover to their initial state via thermal stimulus(200℃for 10 min).Interestingly,both the optical transmittances and PL intensities can be effectively tailored by controlling the PC reaction process.The results suggest that the ferroelectric transparent ceramics are promising for the modulation of photoenergy and the design of optoelectronic devices.

Sustainable shape memory polymers based on epoxidized natural rubber cured by zinc ferulate via oxa-Michael reaction

Although various shape memory polymers(SMPs)or diverse applications have been widely reported,the SMPs based on rubbers have been rarely realized due to the low triggering temperature of rubbers.In another aspect,the SMPs based on sustainable substances are highly desired for the growing shortage in fossil resources.In the present study,we accordingly developed the sustainable SMPs with tunable triggering temperature,based on natural rubber(NR)and ferulic acid(FA)as the raw materials.Specifically,the SMPs are based on a crosslinked network of epoxidized natural rubber(ENR)crosslinked by in situ formed zinc ferulate(ZDF)via oxa-Michael reaction.The excellent shape memory effect(SME)is found in these SMPs,as evidenced by the high fixity/recovery ratio and the tunable triggering temperature.With the incorpora-tion of natural halloysite nanotubes(HNTs),the stress and recovery rate of the SMPs are found to be tunable,which widens the application of this kind of SMPs.The combination of adoption of sustainable raw materials,and the excellent and tunable SME makes these SMPs potentially useful in many applications,such as various actuators and heat-shrinkable package materials.

Hospital Strain and COVID-19 Fatality—England,April 2020–March 2022

Summary What is already known about this topic?During the coronavirus disease 2019(COVID-19)pandemic,tremendous efforts have been made in countries to suppress epidemic peaks and strengthen hospital services to avoid hospital strain and ultimately reduce the risk of death from COVID-19.However,there is limited empirical evidence that hospital strain increases COVID-19 deaths.

Characteristics and Containment of 74 Imported COVID-19 Outbreaks: Experiences, Lessons, and Implications — China, 2020–2021

What is already known about this topic?After the initial coronavirus disease 2019(COVID-19)outbreak in Wuhan,China,the outbreaks during the dynamic-zero policy period in the mainland of China have not been systematically documented.What is added by this report?We summarized the characteristics of 74 imported COVID-19 outbreaks between March 19,2020 and December 31,2021.All outbreaks of early severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)variants were successfully contained with the aid of nucleic acid testing,modern communication technologies,and non-pharmacological interventions.What are the implications for public health practice?These findings provide us with confidence for the containment of future emerging infectious diseases alike at early stages to prevent pandemics or to win time to gain experience,develop vaccines and drugs,vaccinate people,and wait for the possible lessening of the virus’pathogenicity.