Structures and local ferroelectric polarization switching properties of orthorhombic YFeO_3 thin film prepared by a sol–gel method

Orthorhombic YFeO_3 thin film was prepared on La_(0.67)Sr_(0.33)MnO_3/LaAlO_3 substrate by a sol-gel spin-coating method. The structures of the YFeO_3/La_(0.67)Sr_(0.33)MnO_3/LaAlO_3(YFO/LSMO/LAO) sample were detected by x-ray diffraction pattern, Raman spectrometer, scanning electron microscopy, and atomic force microscope. The local ferroelectric polarization switching properties of the orthorhombic YFO film were confirmed by piezoresponse force microscopy(PFM) for the first time. The results show that the YFO film deposited on LSMO/LAO possesses orthorhombic structure,with ultra-fine crystal grains and flat surface. The leakage current of the YFO film is 8.39 × 10^(-4) A·cm^(-2) at 2 V,with its leakage mechanism found to be an ohmic behavior. PFM measurements indicate that the YFO film reveals weak ferroelectricity at room temperature and the local switching behavior of ferroelectric domains has been identified. By local poling experiment, polarization reversal in the orthorhombic YFO film at room temperature was further observed.

Laser-induced Voltage in La_(0.85)Sr_(0.015)MnO_3/Fe Heterostructure

在 Si (100 ) 底层上扔的 La_(0.85 )Sr_(0.015 ) MnO_3/Fe 异种结构被劈啪作响的磁控管准备。在在在在 77 K 的 current-in-plane 几何学 andcurrent-perpendicular-to-plane 几何学之间的电压信号的样品和差别的导致激光的电压被调查。这差别能被归因于不同运输机制。

Lattice Effect on the Transport Properties in Double Doped La_(2/3)(Ca_(1-x)Sr_x)_(1/3)MnO_3 Films

The transport properties in the La2/3（Ca（1-x）Sr（x））1/3MnO3 （x=0.1/3, 2/3） films prepared using the RF magnetron sputtering method were investigated, The effect of the Ca, Sr double-doping at the A position in the La（2/3）A（1/3）MnO3 on the structure of the targets and transport of the films has been studied. With the increase of x, the structures of the targets transform from the rhombohedral phase to the cubic phase; the metal-insulator phase transition temperature （Tp） of the films increases; and the corresponding peak resistivity decreases. All the phenomena can be qualitatively explained by the lattice effect.

Enhanced magneto-electric effect in manganite tricolor superlattice with artificially broken symmetry

The magneto-electric effect in magnetic materials has been widely investigated, but obtaining an enhanced magnetoelectric effect is challenging. In this study, tricolor superlattices composed of manganese oxides-Pr（0.9）Ca（0.1）MnO3,La（0.9）Sr（0.1）MnO3, and La（0.9）Sb（0.1）MnO3-on（001）-oriented Nb：SrTiO3 substrates with broken space-inversion and timereversal symmetries are designed. Regarding the electric polarization in the hysteresis loops of the superlattices at different external magnetic fields, both coercive electric field Ec and remnant polarization intensity Pr clearly show strong magneticfield dependences. At low temperatures（〈 120 K）, a considerable magneto-electric effect in the well-defined tricolor superlattice is observed that is absent in the single compounds. Both maxima of the magneto-electric coupling coefficients ？Ec and ？Pr appear at 30 K. The magnetic dependence of the dielectric constant further supports the magneto-electric effect. Moreover, a dependence of the magneto-electric effect on the periodicity of the superlattices with various structures is observed, which indicates the importance of interfaces. Our experimental results verify previous theoretical results regarding magneto-electric interactions, thereby paving the way for the design and development of novel magneto-electric devices based on manganite ferromagnets.

Research on Depression, Anxiety and Memory of Subhealth after Practicing Jianshenqigong-Wuqinxi

Objective: To study the effect of practicing Jianshenqigong-wuqinxi on subhealth problems including depression, anxiety, and memory loss. Methods: 1) 80 cases with subhealth problem were randomly divided into two groups. 40 cases practicing Jianshenqigong-wuqinxi were used as test group, and the other 40 unpracticing cases were used as control group. 2) The test group was practising Jianshenqigong-wuqinxi one hour in the morning five times per week for three months. 3) Scores of subhealth status such as depression and anxiety were evaluated once every two weeks, while the memory test was performed once a month. 4) Data analysis: SPSS11.0 software was used for statistical analyses. Data were shown in mean ± SEM. Difference was considered significant if the t-test P value is less than 0.05. Results: 1) Scores of subhealth state and depression were significantly lower in test group than those of control group. The beneficial effects of practicing Jianshenqigong-wuqinxi were more obvious for the subjects in the test group who had practiced Jianshenqigong-wuqinxi for two to twelve weeks (P < 0.05). 2) Scores of anxiety test were significantly lower in test group than those of control group after practicing Jianshenqigong-wuqinxi for six to twelve weeks (P < 0.05). 3) Scores of memory were significantly higher in test group than those of control group (P < 0.05). Conclusions: 1) Practicing Jianshenqigong-wuqinxi could promote health in people who have subhealth mental problems. 2) Practicing Jianshenqigong-wuqinxi could relieve depression, anxiety while enhance memory.

Cyclic-acyclic monomers metathesis polymerization to access photodegradable polydicyclopentadiene and polyethylene-like materials

The development of degradable and recyclable polymers is an attractive strategy to tackle the post-consumption pollution issue of commercial plastics.Cyclic-acyclic monomers metathesis polymerization(CAMMP)has been recently reported to produce degradable thermoset,thermoplastic and elastomeric polymers,and their degradability is enabled with addition of various chemicals.In this contribution,we demonstrate that the utilization of diene comonomers containing photodegradable moiety can give access to thermoset and thermoplastic materials bearing photo-degradation capabilities.The copolymerization of a series easily accessible diene comonomers bearing photodegradable ortho-nitrobenzyl moieties with dicyclopentadiene(DCPD)or cyclooctene(COE)leads to the formation of photodegradable p DCPD thermosets and p COE thermoplastic polymers with mechanical properties comparable to their non-degradable counterparts.Most importantly,their photo-degradation properties can be efficiently tuned with the addition of ultraviolet absorber during in-situ polymerization.

Synthesis of Ultra-High-Molecular-Weight Polyethylene by Transition-Metal-Catalyzed Precipitation Polymerization

Ultra-high-molecular-weight polyethylene(UHMWPE)plays an important role in many important fields as engineering plastics.In this contribution,a precipitation polymerization strategy is developed by combination of highly active phosphino-phenolate nickel catalysts with polymer-insoluble solvent(heptane)to access UHMWPE(Mn up to 8.3×10^(6)g mol^(-1))with good product morphology,free-flowing characteristics,and great mechanical properties.Compared with the academically commonly used aromatic solvent(toluene),the utilization of heptane offers simultaneous enhancement in important parameters including activity,polymer molecular weight,and catalyst thermal stability.This system can also generate polar functionalized UHMWPE with molecular weight of up to 1.6×10^(6)g mol^(-1)in the copolymerization of ethylene with polar comonomers.More importantly,this precipitation polymerization strategy is generally applicable to several representative transition metal catalyst systems,leading to UHMWPE synthesis with good product morphology control.

Heterogeneousα-Diimine Nickel Catalysts with Improved Catalytic Performance in Ethylene Polymerization

Heterogenization can improve the thermal tolerance of olefin polymerization catalysts and result in good product morphology con-trol,which are two important parameters for industrial polyethylene production.In this work,α-diimine nickel catalysts bearing-OH or-ONa anchoring groups were designed and prepared.The anchoring groups can enable facile heterogenization of the cata-lysts on silica.The heterogeneous catalysts demonstrated enhanced thermal stabilities,along with high catalytic activity at 120℃(up to 5.5×10^(6)g·PE·mol·Ni^(-1)·h^(-1)).Furthermore,the heterogenization process results in the improvements of many other parame-ters,including polymer morphology control,catalytic activity(up to 1.9×10^(7)g·PE·mol·Ni^(-1)·h^(-1))and polyethylene molecular weight(Mn up to 2.3×10^(6)g·mol^(-1)).More importantly,the structure and properties of the polymer products can be controlled by catalyst structures,polymerization conditions and heterogenization to achieve good mechanical properties and elasticity.

Plasma-enabled synthesis of ordered PtFe alloy nanoparticles encapsulated with ultrathin N-doped carbon shells for efficient methanol electrooxidation

Methanol oxidation reaction(MOR),the key reaction for clean energy generation in fuel cells,is kinetically sluggish and short-lasting because of insufficient catalytic activity and stability of the common Pt-based electrocatalysts.Ordered Pt alloy structures which promise to surmount these issues,are challenging and impractical to fabricate using common high-temperature annealing.To address the urgent need for simple and rapid synthesis methods for such alloys,here we report the versatile plasma-assisted thermal annealing synthesis of a robust electrocatalyst with PtFe alloys supported on N-doped carbon nanotubes(denoted as PtFe@NCNT-P).Benefiting from the reactive plasma-specific effects,the PtFe@NCNT-P electrocatalyst features ultrafine PtFe alloy nanoparticles(mean size~2.88 nm,ordered degree~87.07%)and ultrathin N-doped carbon(NC)shells(0.3–0.7 nm),leading to the excellent catalytic activity and stability toward MOR.The catalyst shows the specific and mass activities of 3.99 mA/cm^(2)and 2,148.5 mA/mg,which are 7.82 and 7.41 times higher than those for commercial Pt/C(0.51 mA/cm^(2),290 mA/mg),and 2.18 and 2.59 times higher compared to the plasma-untreated PtFe@NCNT(1.83 mA/cm2,829.5 mA/mg),respectively.The PtFe@NCNT-P further exhibits extraordinary stability during the long-term chronoamperometry test and 1,000-cycle cyclic voltammetry scanning,much better compared to PtFe@NCNT samples even after the longer thermal annealing.These findings show great potential of the plasma-enabled synthesis of high-performance carbon-supported metallic electrocatalysts for the emerging clean energy technologies.

Dual roles of trifluoroborate in nickel-catalyzed ethylene polymerization:Electronic perturbation and anchoring for heterogenization

Brookhart-typeα-diimine nickel and palladium catalysts have been extensively studied over the past several decades;however,the heterogenization of these metal complexes has received much less attention.In this contribution,we installed a trifluoroborate potassium substituent on anα-diimine framework.The ionic nature of trifluoroborate potassium endowed theα-diimine nickel complex with a strong affinity for the SiO_(2)support,while its electron-donating nature enhanced the catalyst stability and polyethylene molecular weight.In the presence of only 100 equiv.of Et2AlCl cocatalyst,the SiO_(2)-supported catalyst demonstrated significantly better performance than its homogeneous analog during ethylene polymerization,with extremely high activity(1.42–6.53×10^(7)g mol^(−1)h^(−1))and high thermal stability.The heterogeneous system led to the formation of high-molecular-weight polyethylenes(Mn 142,500–732,800 g/mol),narrow polydispersities(2.18–3.00),tunable branching densities(21–64 per 1000 carbon atoms),and great mechanical properties.Moreover,the efficient copolymerization of ethylene with comonomers such as methyl 10-undecenoate,6-chloro-1-hexene or 5-hexenylacetate was achieved.These superior properties enabled by the trifluoroborate potassium moiety may inspire its applications in other polymerization catalyst systems.

α-二亚胺镍和钯催化的乙烯聚合及共聚反应中的位阻和电子协同效应

对于过渡金属配合物类的烯烃聚合催化剂,配体的位阻和电子效应能够显著影响其主要的催化性能.然而,对于位阻和电子效应的同时调节在以往的研究中鲜有涉及.本文报道了一种以协同方式调节配体结构中的电子和位阻效应的策略.含有二苯甲基取代基的α-二亚胺配体中,在苯胺结构的3,4,5-位分别引入三个供电子的甲氧基或三个吸电子的氟取代基.上述甲氧基和氟取代基的引入,不仅能够有效调节配体的电子效应,还能够通过甲氧基或氟取代基与二苯甲基之间的空间排斥作用,有效增加配体的空间位阻.在乙烯聚合中,这种电子和位阻效应的协同作用的引入,能够实现改进镍和钯催化剂的几种重要的催化性能参数,包括催化活性、催化剂稳定性以及所得聚合物的分子量、熔点、支化密度.该位阻和电子效应协同的策略在将来很有可能被用于其他催化领域.

(a-Diimine)palladium catalyzed ethylene polymerization and (co)polymerization with polar comonomers

In this review, a recent development of cationic ?-diimine palladium(II) complexes for ethylene polymerization and copolymerization with polar functionalized comonomers was briefly described. First, the polymerization mechanism for this type of catalysts was discussed. Next, recent advances in ligand design were provided with special focus on the influence of ligand structures on the catalytic polymerization properties. Last, the ethylene homopolymerization and copolymerization with various polar comonomers, especially acrylate and vinyl ethers were summarized.

Synthesis of silicon-functionalized polyolefins by subsequent cobalt-catalyzed dehydrogenative silylation and nickel-catalyzed copolymerization

Metal catalyzed olefin hydrosilylation and metal mediated olefin polymerization are both of great academic and industrial importance. In this article, these two aspects are combined to prepare siliconfunctionalized polyolefin materials. First, pyridine-diimine cobalt-catalyzed dehydrogenative silylations of various terminal olefins with alkylsilanes lead to the formation of a variety of allylsilanes at high yields.Then, the allylsilanes are copolymerized with ethylene using an a-diimine nickel catalyst, leading to the formation of branched polyolefins with high molecular weight and moderate comonomer incorporation.This subsequent catalytic process is an efficient strategy for the synthesis of silicon-functionalized polyolefins using widely available and inexpensive starting materials.

Promoting Ethylene (co)Polymerization in Aliphatic Hydrocarbon Solvents Using tert-Butyl Substituted Nickel Catalysts

In the past few decades,the development of high-performance catalysts has been a key driving force and a center of research efforts in the field of olefin polymerization.However,a major discrepa ncy exists between in dustrial researches which utilize aliphatic hydrocarb on solventsz and academic researches which predominantly focus the catalytic properties in aromatic solvents.In this con-tribution,a novel diaryl-methyl aniline bearing eight tert-butyl groups was prepared and subsequently transformed to four different kinds of imine-type ligands.The corresponding nickel complexes as well as their counterparts derived from diphenyl-methyl aniline without the tert-butyl groups were prepared and investigated in ethylene polymerization.

Influence of chelate ring size on the properties of phosphine-sulfonate palladium catalysts

Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization.This type of catalyst features six-membered chelate ring size,and can enable the copolymerizations of ethylene with a wide variety of polar monomers.In this contribution,we decide to investigate the influence of chelate ring size on the properties of phosphinesulfonate palladium catalysts.As such,a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II)complexes[κ~2-(P,O)-2-(CH_2-PR_1R_2)-4-methylphenyl-sulfonato]Pd(Me)(DMSO)(Pd1,R_1=R_2=Cy,Pd2,R_1=R_2=o-Me O-C_6H_4;Pd3,R_1=Ph,R_2=2-[2,6-(Me O)_2C_6H_3]C_6H_4;DMSO=dimethyl sulfoxide)were designed,prepared and characterized.These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether.However,their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2′.The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.

Magnetocaloric and Colossal Magnetoresistance Effect in Layered Perovskite La_(1.4) Sr_(1.6)Mn_2O_7

Magnetocaloric and colossal magnetoresistance effects of the layered perovskite La 1.4 Sr 1.6 Mn 2 O 7 compound have been studied.A broad peak of magnetic entropy change （-△S M） is found above the Curie temperature （T C =120 K）,which can be associated with the existence of two-dimensional short range ferromagnetic order.Additionally,the curvilinear shape of-△S M for layered perovskite is quite different from that of the Ln 1-x A x MnO 3 probably arising from magnetocrystalline anisotropy.At the same time,a wide peak of colossal magnetoresitance effect near T C is found in the layered provskite La 1.4 Sr 1.6 Mn 2 O 7.

Positional Electronic Effects in Iminopyridine-N-oxide Nickel Catalyzed Ethylene Polymerization

A series of dibenzhydryl-based iminopyridine-N-oxide ligands bearing a range of electron-donating or-withdrawing substituents(OMe,H;and NO_(2))and corresponding nickel pre-catalysts are prepared and characterized.The substituents are installed at different positions on the ligand structure,including 4-position of the pyridine-N-oxide moiety(position X)and 4-position of the aniline moiety(position Y).These nickel pre-catalysts are highly active in ethylene polymerization with the addition of very little amount of aluminum cocatalysts,leading to the formation of polyethylenes with molecular weights of well above one million.Electron-donating substituents make the catalysts sensitive to polymerization temperature.In contrast,the catalysts bearing electron-withdrawing NO_(2) substituents show relatively steady performances at different temperatures.Most importantly,we demonstrate that different substituents and different positions both play important roles in determining the properties of nickel catalysts.This provides an alternative strategy for the future design of high-performance polymerization catalyst.

Ni catalyzed ethylene copolymerization with polar monomers

Introduction of polar comonomers into polyethylene is highly challenging,paving the way to tuning the copolymers'mechanical properties,adhesion/compatibility,and biodegradability.Polar-group tolerant single-site palladium and,more tempting,nickel-based catalysts have demon-strated promising reactivities in the ethylene copolymerization with polar comonomers via coordination/insertion mechanism。

Controlling the Ring-Opening Polymerization Process Using External Stimuli

Through the incorporation of stimuli-responsive units,the properties of ring-opening polymerization catalysts can be efficiently modulated using external stimuli.This article summarizes some of the recently reported strategies that control the ring-opening polymerization of cyclic type monomers,using allosteric,redox,Lewis acid/base,supramolecular,electrochemical and light stimuli.These strategies enable the fine tuning of the polymerization process and the microstructure/composition of the final polymeric products.

Lewis acid/base modulation in β-diiminate zinc-catalyzed switchable ring-opening polymerization of rac-lactide

Two β-diiminate zinc complexes were prepared and found to show high activity and well-controlled catalytic behavior in the ring-opening polymerization of rac-lactide. Coordination of the Lewis acid to the zinc complexes completely terminated the polymerization. The coordinated Lewis acid was easily cleaved by using a Lewis base, so that the polymerization could resume.Thus, switchable polymerization could be realized by the subsequent addition of a Lewis acid and a Lewis base. This work provides a new strategy to control the ring-opening polymerization of rac-lactide.