(Cu43Zr48Al9)98Y2 amorphous alloy bar was prepared by the arc melting copper mold absorption casting method,and then,the amorphous alloy was annealed at different temperatures for different times.The influence of heat...(Cu43Zr48Al9)98Y2 amorphous alloy bar was prepared by the arc melting copper mold absorption casting method,and then,the amorphous alloy was annealed at different temperatures for different times.The influence of heating rate on thermal expansion and thermal stability was studied by thermomechanical analysis(TMA),and the microstructure evolution of the amorphous alloy during structural relaxation and crystallization was studied by XRD and TEM.Results show that the structural evolution behavior of the(Cu43Zr48Al9)98Y2 amorphous alloy can be divided into five different stages(structural relaxation preparation stage,structural relaxation stage,first crystallization stage,second crystallization stage,and grain growth stage).When the heating rate is 20 K/min,the amorphous alloy has the smallest thermal expansion coefficient and the best thermal stability.The width of the supercooled liquid region is 66.42 K.Samples with different relaxation states were prepared by annealing at the heating rate of 20 K/min.The structural evolution of amorphous alloys with different relaxation states is as follows:amorphous→CuZr2+AlCu2Zr7→CuZr2+AlCu2Zr7+CuZr(B2)+CuZr(M)+Cu10Zr7→CuZr2+AlCu2Zr7+CuZr(B2)+CuZr(M).After annealing at 706 K and 726 K(in the supercooled liquid region)for 1.5 h,the amorphous-nanocrystalline composites were obtained.When the annealing temperature is 706 K,the crystallization process of the sample is as follows:amorphous→Cu10Zr7→Cu10Zr7+CuZr,and for the sample at 726 K,it is as follows:amorphous→CuZr2+AlCu2Zr7+Cu10Zr7→Cu10Zr7+CuZr2→CuZr2+CuZr(B2)+Cu10Zr7.展开更多
The thin ribbons and the bulk cylindrical rods with diameters of 2 mm and 10 mm of the Vit1 metallic glass(MG)were prepared by the single roller melt spinning method and the copper mold injection casting method,respec...The thin ribbons and the bulk cylindrical rods with diameters of 2 mm and 10 mm of the Vit1 metallic glass(MG)were prepared by the single roller melt spinning method and the copper mold injection casting method,respectively.The cooling rates of the samples during melt solidification were evaluated.The glass transition behaviors of three groups of MG samples with different solidification cooling rates were studied by differential scanning calorimetry(DSC)at different heating rates.The effects of melt cooling rate on the glass transition kinetic parameters such as apparent activation energy(E)and fragility parameter(m)of the Vit1 MG were studied using the Kissinger and the Vogel-Fulcher-Tammann(VFT)equations.Additionally,the structural relaxation enthalpy(ΔHrel)of three groups of MG samples was quantitatively analyzed by DSC through multi-step temperature rise and fall measurements.Results show that the melt cooling rate(R)has a significant effect on the glass transition kinetics and the structural relaxation of the Vit1 MG.As R decreases in the order of magnitude,the glass transition temperature(Tg),E,m,andΔHrel of the Vit1 MG gradually decreases.Furthermore,in the range of the experimental cooling rates,E,m,andΔHrel all have an approximately linear relationship with lgR.展开更多
In this review the preparation methods of polymer nanoparticles from chemical microemulsion polymerization to physical methods such as spray-drying,freeze-drying,freeze-extracting,fast evaporation and spreading evapor...In this review the preparation methods of polymer nanoparticles from chemical microemulsion polymerization to physical methods such as spray-drying,freeze-drying,freeze-extracting,fast evaporation and spreading evaporation have been summarized.The influence of nanoconfinement on glass transition temperature(T_(g))variation from significant or slight decrease,no evident T_(g) deviation,to even T_(g) increase,as well as possible explanations of T_(g) deviations were discussed.The influences of nanoconfinement or entanglement on the other properties such as structural relaxation,crystallization in polymer nanoparticle samples were also reviewed in this article.展开更多
We present the specific ab-initio calculations that detail the variations of perovskite BaZrO3 caused by in-plane strain. Specifically, the internal relaxation, which was not captured in the widely used biaxial strain...We present the specific ab-initio calculations that detail the variations of perovskite BaZrO3 caused by in-plane strain. Specifically, the internal relaxation, which was not captured in the widely used biaxial strain model, was included in a complementary manner to lattice relaxation. Density functional theory as well as a hybrid functional method based on a plane wave basis set was employed to calculate the lattice structure, elastic constants, electronic properties and optical properties of perovskite BaZrO3. The lattice parameter c exhibited a clear linear dependence on the imposed in-plane strain, but the Poisson＇s ratio caused by internal relaxation was smaller than the elastic deformation, indicating an ＂inelastic＂ or ＂plastic＂ relaxation manner caused by the introduction of internal relaxation. As a result, the related electronic and optical properties of perovskite BaZrO3 were also strongly affected by the in-plane strain, which revealed an effective way to adjust the properties of perovskite BaZrO3 via internal relaxation.展开更多
Multiple donor-acceptor(D-A) combinations represent a promising category of thermally activated delayed fiuorescence(TADF) materials, offering potential for superior efficiency and stability. However, current systems ...Multiple donor-acceptor(D-A) combinations represent a promising category of thermally activated delayed fiuorescence(TADF) materials, offering potential for superior efficiency and stability. However, current systems are predominantly composed of limited donor groups, primarily carbazole-based derivatives. In this work, we developed a series of D-A type materials incorporating helical π-expanded carbazole(Cz Naph) and 7H-dinaphtho[1,8-bc:1,8-ef]azepine(Az Naph), alongside traditional carbazole, ranging from mono-to tetra-substituted configurations(D_(n)-A). Through systematic investigation of geometric and electronic structures, the number and positioning of multiple donors are confirmed with significant manipulations on charge transfer characteristics and the S_(1) state via steric effects. Density functional theory(DFT) calculations reveal that varying the number of π-extended donors within the acceptor framework produces emission colors from ultraviolet to red, providing a diverse range of emitters. Furthermore, the reduced reorganization energy of S1observed in tetra-substituted Cz and Cz Naph, as well as Mono Az N, indicates lower structural relaxation, highlighting these materials' potential as stable luminescent candidates. This study underscores the importance of diverse composing units in achieving efficient and stable TADF emitters with multiple and hetero-donor configurations.展开更多
The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead...The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead to aggregation-induced emission(AIE).In this work,we investigated ultrafast excited state dynamics of a halogen-substituted model system,i.e.squaryliums NSQ-R(R=H,Cl,Br,I),by using femtosecond spectroscopy and theoretical approach.Fast external reorganization(Ex-re,~3 ps)and slow internal reorganization(In-re,5-20 ps)were observed,while quantitative fitting indicated halogen-substitution leads to a slower non-radiative S1→S0 decay(k_(NR)^(s))and subsequently enhanced fluorescence emitting.By analyzing the extracted k_(NR)^(s)within theoretical framework of non-radiative transition in the strong coupling regime,a plausible AIE mechanism of NSQs was revealed.Our work provides a clear picture on non-radiative dynamics of halogen-substituted squaryliums,which might be useful for future development of organic dyes.展开更多
On approaching the glass transition,the structural relaxation of glass-forming liquids slows down drastically,along with a significant growth of dynamic heterogeneity.Recent studies have achieved substantial advanceme...On approaching the glass transition,the structural relaxation of glass-forming liquids slows down drastically,along with a significant growth of dynamic heterogeneity.Recent studies have achieved substantial advancements in elucidating the quantitative correlations between structural relaxation and dynamic heterogeneity.Here,we present the discovery of a novel dynamic crossover with possibly universal dynamic signatures by investigating the relationship between structural relaxation and dynamic heterogeneity.Specifically,the structural relaxation time at the dynamic crossoverτ_(c)is equal to the time scale for the maximum non-Gaussian parameter,which could serve as a quantitative characterization of dynamic heterogeneity.The degree of dynamic heterogeneity at the crossover is approximately equivalent across all investigated glass-forming liquids,leading to a scaling collapse between structural relaxation and dynamic heterogeneity.Moreover,the mean squared displacement at the structural relaxation time is nearly constant across different temperatures as long as the structural relaxation time does not exceedτ_(c).We further observe that the temperature at the dynamic crossover is lower than the onset temperature of slow dynamics.Our findings thus suggest the existence of a novel dynamic crossover with possibly universal dynamic signatures in glass-forming liquids,which merits in-depth investigations.展开更多
A relationship between thermal effects and relaxation of the high-frequency shear modulus upon heat treatment of bulk Zr48(Cu5/6Ag1/6)44Al8 metallic glass is found.This relationship is attributed to the relaxation of ...A relationship between thermal effects and relaxation of the high-frequency shear modulus upon heat treatment of bulk Zr48(Cu5/6Ag1/6)44Al8 metallic glass is found.This relationship is attributed to the relaxation of a interstitial-type defect system frozen-in from the melt upon glass production.Calorimetric data show that thermal effects occurring on heating include heat release below the glass transition temperature,heat absorption above it and heat release caused by crystallization.The equation derived within the Interstitialcy theory can be used to calculate the shear modulus relaxation using the calorimetric data.The obtained results are used to trace the defect concentration as functions of temperature and thermal prehistory.展开更多
Asynchronous responses of mechanical and magnetic properties to structure relaxation for the Fe71Nb6B23 bulk metallic glass were systematically investigated. It is interesting that this ternary alloy can combinedly ex...Asynchronous responses of mechanical and magnetic properties to structure relaxation for the Fe71Nb6B23 bulk metallic glass were systematically investigated. It is interesting that this ternary alloy can combinedly exhibit outstanding magnetic and mechanical properties, especially good ductility, after optimally annealing in structure relaxation stage for eliminating the internal stress and homogenizing the microstructure. The alloy exhibits low coercive force of 1.6 A/m, high effective permeability of 15 x 10^3, high fracture strength of 4.2 GPa and good plastic strAln of 1.8%. It is also found that responses of mechanical and magnetic properties to structure relaxation are asynchronous. The glass transition and crystallization will greatly deteriorate the magnetic and mechanical properties. Here we propose a physical picture and demonstrate that the primary structure factors determining magnetic and mechanical properties are different. This work will bring a promising material for application and a new perspective to study the effect of annealing-induced structure relaxation on mechanical and magnetic properties.展开更多
To identify the re-arrangement of constituent atoms of an amorphous Mg65Cu25Gd10 alloy happened with annealing, structure relaxation of the alloy was investigated as a function of an- nealing time at 373 K through ext...To identify the re-arrangement of constituent atoms of an amorphous Mg65Cu25Gd10 alloy happened with annealing, structure relaxation of the alloy was investigated as a function of an- nealing time at 373 K through extended X-ray absorption fine structure （EXAFS） analysis procedures. To understand the effect of structure relaxation on strength, compression tests were conducted for both the as-cast and the annealed Mg65Cu25Gd10 samples. It is found that short range order around Cu and Gd atoms exhibits different variation trends with increasing annealing time at 373 K, though the structure of the alloy still remains to be amorphous. Based on the fact that the strength of the alloy first exhibits a reduction and then a recovery with annealing time, it is suggested that the enhancement of short range order around Cu should be responsible for the strength reduction, while the enhancement of short range order around Gd should be responsible for the strength recovery.展开更多
The dramatic temperature-dependence of liquids dynamics has attracted considerable scientific interests and efforts in the past decades, but the physics of which remains elusive. In addition to temperature, some other...The dramatic temperature-dependence of liquids dynamics has attracted considerable scientific interests and efforts in the past decades, but the physics of which remains elusive. In addition to temperature, some other parameters, such as pressure, loading and size, can also tune the liquid dynamics and induce glass transition, which makes the situation more complicated. Here, we performed molecular dynamics simulations for Ni_(50)Zr_(50) bulk liquid and nanodroplet to study the dynamics evolution in the complex multivariate phase space, especially along the isotherm with the change of pressure or droplet size. It is found that the short-time Debye–Waller factor universally determines the long-time relaxation dynamics no matter how the temperature, pressure or size changes. The basic correlation even holds at the local atomic scale. This finding provides general understanding of the microscopic mechanism of dynamic arrest and dynamic heterogeneity.展开更多
The rapid solidification process of Mg7Zn3 alloy was simulated by the molecular dynamics method. The relationship between the local structure and the dynamics during the liquid-glass transition was deeply investigated...The rapid solidification process of Mg7Zn3 alloy was simulated by the molecular dynamics method. The relationship between the local structure and the dynamics during the liquid-glass transition was deeply investigated. It was found that the Mg-centered FK polyhedron and the Zn-centered icosahedron play a critical role in the formation of Mg7Zn3 metallic glass. The self-diffusion coefficients of Mg and Zn atoms deviate from the Arrhenius law near the melting temperature and then satisfy the power law. According to the time correlation functions of mean-square displacement, incoherent intermediate scattering function and non-Gaussian parameter, it was found that the β-relaxation in Mg7Zn3 supercooled liquid becomes more and more evident with decreasing temperature, and the α-relaxation time rapidly increases in the VFT law. Moreover, the smaller Zn atom has a faster relaxation behavior than the Mg atom. Some local atomic structures with short-range order have lower mobility, and they play a critical role in the appearance of cage effect in theβ-relaxation regime. The dynamics deviates from the Arrhenius law just at the temperature as the number of local atomic structures begins to rapidly increase. The dynamic glass transition temperature （Tc） is close to the glass transition point in structure （TgStr）.展开更多
This paper reviews the development of current research in bulk glassy alloys by focusing on the trigger point for the synthesis of the first bulk glassy alloys by the conventional mold casting method. This review cove...This paper reviews the development of current research in bulk glassy alloys by focusing on the trigger point for the synthesis of the first bulk glassy alloys by the conventional mold casting method. This review covers the background, discovery, characteristics, and applications of bulk glassy alloys, as well as recent topics regarding them. Applications of bulk glassy alloys have been expanding, particularly for Fe-based bulk glassy alloys, due to their unique properties, high glass-forming ability, and low cost. In the near future, the engineering importance of bulk glassy alloys is expected to increase steadily, and continuous interest in these novel metallic materials for basic science research is anticipated.展开更多
The structural and electronic properties of bulk and (001) plane of TiC were investigated by the first-principles total-energy pseudopotential method based on density functional theory.The calculated bulk properties i...The structural and electronic properties of bulk and (001) plane of TiC were investigated by the first-principles total-energy pseudopotential method based on density functional theory.The calculated bulk properties indicate that bonding nature in TiC is a combination of ionicity,covalency and metallicity,in which the Ti-C covalent bonding is the predominate one.The calculated results of structural relaxation and surface energy for TiC(001) slab indicate that slab with 7 layers shows bulk-like characteristic interiors,and the changes of slab occur on the outmost three layers,which shows that the relaxation only influences the top three layers.Meanwhile,the strong Ti-C covalent bonding can be found in the distribution of charge density on the (110) and (001) planes.Ti-C covalent bonding is enhanced by the charge depletion and accumulation in the vacuum and the interlayer region between top two atomic layers.展开更多
The structural and electronic properties of TiC（110） surfaces are calculated using the first-principles total-energy plane-wave pseudopotential method based on density functional theory. The calculated results of st...The structural and electronic properties of TiC（110） surfaces are calculated using the first-principles total-energy plane-wave pseudopotential method based on density functional theory. The calculated results of structural relaxation and surface energy for TiC（110） slab indicate that slab with 7 layers shows bulk-like characteristic interiors, and the changes of slab occur on the outmost three layers, which shows that the relaxation only influences the top three layers. Meanwhile, the strong Ti—C covalent bonding can be found in the distribution of charge density on the （100） plane. The interlayer Ti—C chemical bonds are reinforced and the outermost interlayer distance is reduced as a result of the charge depletion in the vacuum and the charge accumulations in the interlayer region between the first and second layers. The surface energy of TiC（110） is calculated to be 3.53 J/m2.展开更多
The compression behaviour of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using in-situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation ...The compression behaviour of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using in-situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The equation of state is determined by fitting the experimental data according to the Birch-Murnaghan equation. It is found that the structure of Ni77P23 amorphous alloy is stable under pressures up to 30.5 GPa. Within the pressure range from zero to the experimental one, the pressure-induced structural relaxation is reversible.展开更多
The XRD, TEM, PAT, Curie temperature and internal friction methods were used to study systematically the embrittlement mechanism of rapidly quenched ( RQ ) nanocrystalline soft magnetic alloy Fe73.5Cu1Nb3Si13.5B9.The ...The XRD, TEM, PAT, Curie temperature and internal friction methods were used to study systematically the embrittlement mechanism of rapidly quenched ( RQ ) nanocrystalline soft magnetic alloy Fe73.5Cu1Nb3Si13.5B9.The test results confirmed that the RQ embrittlement mechanism of amorphous alloy FeCuNbSiB was not related to crystallization but that was related to structural relaxation. Furthermore, the structural relaxation temperature of amorphous alloy FeCuNbSiB was much lower than that of used commonly amorphous alloy Fe78B13Si9. It meant that the RQ embrittlement is easier to happen for nanocrystalline alloy FeCuNbSiB than amorphous alloy Fe-B-Si.展开更多
Different heating treatments with the variation of heating rates,holding temperatures and holding time were used to simulate the LTPS procedure.The experimental results show that the reheating shrinkage rates of glass...Different heating treatments with the variation of heating rates,holding temperatures and holding time were used to simulate the LTPS procedure.The experimental results show that the reheating shrinkage rates of glass substrates are rarely changed with increasing the heating rate,but strongly enhanced by raising the holding temperature and time,which shows that the reheating shrinkage of glass is closely related to heat treatment and structural relaxation.The production process of glass is critical to the reheating shrinkage of glass.展开更多
Based on the analysis of different theory for glass tempering process,the“structural theory”with stress relaxation and structural relaxation effects was selected to investigate the tempering of flat glass quantifica...Based on the analysis of different theory for glass tempering process,the“structural theory”with stress relaxation and structural relaxation effects was selected to investigate the tempering of flat glass quantificationally.The geometrical model with small size and non-homogeneous mesh were considered to build the finite element models according to the characteristics of stress field.The tempering process of flat glass with12 mm thickness was calculated with the verified finite element model.The transient and permanent stress of the central area,edge and corner end of the flat glass are obtained and analyzed.From the calculation results of basic case,the transient tensile stress at the upper surface of the central area,the center point of edge,the edge of edge,the edge of corner were 14.30,18.94,40.76 and 34.75 MPa,respectively.The transient tensile stress at these points were dangerous to promote the glass to break during the tempering.In addition,the point at the diagonal line of symmetry plane in the thickness direction,which is 14 mm from corner,has the maximum permanent tensile stress about 70.01 MPa in the flat glass after tempering.Thus,it is indicated that the corner is the weakest region in the tempered glass.展开更多
GeS4 bulk glasses were prepared by the melt-quench technique and the samples were irradiated by 532-nm linearly polarized light. After the laser treatment, the photo-induced changes of the samples were investigated by...GeS4 bulk glasses were prepared by the melt-quench technique and the samples were irradiated by 532-nm linearly polarized light. After the laser treatment, the photo-induced changes of the samples were investigated by UV-1601 speetrophotometer and optical second-order nonlinear tester. The results show that the transmittance of the samples around 532 nm obviously decreases and Bragg reflector forms, which is due to the production of photon-generated carriers. With the increase of laser pulse energy or the extension of irradiation duration, the Bragg reflector increases and gradually tends to be stable. These can be ascribed to the excitation- capture process of the carriers. After irradiation, the relaxation phenomenon results from the release of part of the absorbed energy in the glass matrix. And the fitting equation of the relaxation process is consistent with a conventional Kohlrausch stretched exponential function. The origin of the second harmonic generation （SHG） is because of the dipole reorientation caused by the photo-induced anisotropy in the glass.展开更多
基金financially supported by the Principal Fund of Xi’an Technological University,China(Grant No.0852-302021407)
文摘(Cu43Zr48Al9)98Y2 amorphous alloy bar was prepared by the arc melting copper mold absorption casting method,and then,the amorphous alloy was annealed at different temperatures for different times.The influence of heating rate on thermal expansion and thermal stability was studied by thermomechanical analysis(TMA),and the microstructure evolution of the amorphous alloy during structural relaxation and crystallization was studied by XRD and TEM.Results show that the structural evolution behavior of the(Cu43Zr48Al9)98Y2 amorphous alloy can be divided into five different stages(structural relaxation preparation stage,structural relaxation stage,first crystallization stage,second crystallization stage,and grain growth stage).When the heating rate is 20 K/min,the amorphous alloy has the smallest thermal expansion coefficient and the best thermal stability.The width of the supercooled liquid region is 66.42 K.Samples with different relaxation states were prepared by annealing at the heating rate of 20 K/min.The structural evolution of amorphous alloys with different relaxation states is as follows:amorphous→CuZr2+AlCu2Zr7→CuZr2+AlCu2Zr7+CuZr(B2)+CuZr(M)+Cu10Zr7→CuZr2+AlCu2Zr7+CuZr(B2)+CuZr(M).After annealing at 706 K and 726 K(in the supercooled liquid region)for 1.5 h,the amorphous-nanocrystalline composites were obtained.When the annealing temperature is 706 K,the crystallization process of the sample is as follows:amorphous→Cu10Zr7→Cu10Zr7+CuZr,and for the sample at 726 K,it is as follows:amorphous→CuZr2+AlCu2Zr7+Cu10Zr7→Cu10Zr7+CuZr2→CuZr2+CuZr(B2)+Cu10Zr7.
基金supported by the National Key Research and Development Program of China(No.2019YFB2006501)。
文摘The thin ribbons and the bulk cylindrical rods with diameters of 2 mm and 10 mm of the Vit1 metallic glass(MG)were prepared by the single roller melt spinning method and the copper mold injection casting method,respectively.The cooling rates of the samples during melt solidification were evaluated.The glass transition behaviors of three groups of MG samples with different solidification cooling rates were studied by differential scanning calorimetry(DSC)at different heating rates.The effects of melt cooling rate on the glass transition kinetic parameters such as apparent activation energy(E)and fragility parameter(m)of the Vit1 MG were studied using the Kissinger and the Vogel-Fulcher-Tammann(VFT)equations.Additionally,the structural relaxation enthalpy(ΔHrel)of three groups of MG samples was quantitatively analyzed by DSC through multi-step temperature rise and fall measurements.Results show that the melt cooling rate(R)has a significant effect on the glass transition kinetics and the structural relaxation of the Vit1 MG.As R decreases in the order of magnitude,the glass transition temperature(Tg),E,m,andΔHrel of the Vit1 MG gradually decreases.Furthermore,in the range of the experimental cooling rates,E,m,andΔHrel all have an approximately linear relationship with lgR.
基金supported by Ph.D.Programs Foundation of Ministry of Education of China(No.20100032110025).
文摘In this review the preparation methods of polymer nanoparticles from chemical microemulsion polymerization to physical methods such as spray-drying,freeze-drying,freeze-extracting,fast evaporation and spreading evaporation have been summarized.The influence of nanoconfinement on glass transition temperature(T_(g))variation from significant or slight decrease,no evident T_(g) deviation,to even T_(g) increase,as well as possible explanations of T_(g) deviations were discussed.The influences of nanoconfinement or entanglement on the other properties such as structural relaxation,crystallization in polymer nanoparticle samples were also reviewed in this article.
基金Funded by the National Natural Science Foundation of China(No.51502179)the Colleges and Universities in Hebei Province Science and Technology Research Project(No.YQ2014033)the Hebei Key Discipline Construction Project(B2012210004 and E2013210038)
文摘We present the specific ab-initio calculations that detail the variations of perovskite BaZrO3 caused by in-plane strain. Specifically, the internal relaxation, which was not captured in the widely used biaxial strain model, was included in a complementary manner to lattice relaxation. Density functional theory as well as a hybrid functional method based on a plane wave basis set was employed to calculate the lattice structure, elastic constants, electronic properties and optical properties of perovskite BaZrO3. The lattice parameter c exhibited a clear linear dependence on the imposed in-plane strain, but the Poisson＇s ratio caused by internal relaxation was smaller than the elastic deformation, indicating an ＂inelastic＂ or ＂plastic＂ relaxation manner caused by the introduction of internal relaxation. As a result, the related electronic and optical properties of perovskite BaZrO3 were also strongly affected by the in-plane strain, which revealed an effective way to adjust the properties of perovskite BaZrO3 via internal relaxation.
基金financially supported by the National Key Research and Development Program of China (No. 2023YFB3608902)the National Natural Science Foundation of China (Nos. 22275003, 12404460)+3 种基金Key-Area Research and Development Program of Guangdong Province (No. 2019B010924003)Development and Reform Commission of Shenzhen Municipality (No. XMHT20220106002)Guangdong Key Laboratory of Flexible Optoelectronic Materials and Devices, the Foundation for Youth Innovative Talents in Higher Education of Guangdong Province (No. 2023KQNCX094)the Guangdong Basic and Applied Basic Research Foundation (No. 2023A1515111072)。
文摘Multiple donor-acceptor(D-A) combinations represent a promising category of thermally activated delayed fiuorescence(TADF) materials, offering potential for superior efficiency and stability. However, current systems are predominantly composed of limited donor groups, primarily carbazole-based derivatives. In this work, we developed a series of D-A type materials incorporating helical π-expanded carbazole(Cz Naph) and 7H-dinaphtho[1,8-bc:1,8-ef]azepine(Az Naph), alongside traditional carbazole, ranging from mono-to tetra-substituted configurations(D_(n)-A). Through systematic investigation of geometric and electronic structures, the number and positioning of multiple donors are confirmed with significant manipulations on charge transfer characteristics and the S_(1) state via steric effects. Density functional theory(DFT) calculations reveal that varying the number of π-extended donors within the acceptor framework produces emission colors from ultraviolet to red, providing a diverse range of emitters. Furthermore, the reduced reorganization energy of S1observed in tetra-substituted Cz and Cz Naph, as well as Mono Az N, indicates lower structural relaxation, highlighting these materials' potential as stable luminescent candidates. This study underscores the importance of diverse composing units in achieving efficient and stable TADF emitters with multiple and hetero-donor configurations.
基金support by the National Key R&D Program of China(Nos.2020YFA0714603 and 2020YFA0714604)。
文摘The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead to aggregation-induced emission(AIE).In this work,we investigated ultrafast excited state dynamics of a halogen-substituted model system,i.e.squaryliums NSQ-R(R=H,Cl,Br,I),by using femtosecond spectroscopy and theoretical approach.Fast external reorganization(Ex-re,~3 ps)and slow internal reorganization(In-re,5-20 ps)were observed,while quantitative fitting indicated halogen-substitution leads to a slower non-radiative S1→S0 decay(k_(NR)^(s))and subsequently enhanced fluorescence emitting.By analyzing the extracted k_(NR)^(s)within theoretical framework of non-radiative transition in the strong coupling regime,a plausible AIE mechanism of NSQs was revealed.Our work provides a clear picture on non-radiative dynamics of halogen-substituted squaryliums,which might be useful for future development of organic dyes.
基金support from the National Natural Science Foundation of China(Grant Nos.12374202 and 12004001)Anhui Projects(Grant Nos.2022AH020009,S020218016,and Z010118169),and Hefei City(Grant No.Z020132009)+3 种基金support from the National Natural Science Foundation of China(Grant Nos.T2325004 and 52161160330)Advanced Materials-National Science and Technology Major Project(Grant No.2024ZD0606900)the Talent Hub for“AI+New Materials”Basic ResearchHefei Advanced Computing Center,Beijing Super Cloud Computing Center,and the High-Performance Computing Platform of Anhui University for providing computing resources.
文摘On approaching the glass transition,the structural relaxation of glass-forming liquids slows down drastically,along with a significant growth of dynamic heterogeneity.Recent studies have achieved substantial advancements in elucidating the quantitative correlations between structural relaxation and dynamic heterogeneity.Here,we present the discovery of a novel dynamic crossover with possibly universal dynamic signatures by investigating the relationship between structural relaxation and dynamic heterogeneity.Specifically,the structural relaxation time at the dynamic crossoverτ_(c)is equal to the time scale for the maximum non-Gaussian parameter,which could serve as a quantitative characterization of dynamic heterogeneity.The degree of dynamic heterogeneity at the crossover is approximately equivalent across all investigated glass-forming liquids,leading to a scaling collapse between structural relaxation and dynamic heterogeneity.Moreover,the mean squared displacement at the structural relaxation time is nearly constant across different temperatures as long as the structural relaxation time does not exceedτ_(c).We further observe that the temperature at the dynamic crossover is lower than the onset temperature of slow dynamics.Our findings thus suggest the existence of a novel dynamic crossover with possibly universal dynamic signatures in glass-forming liquids,which merits in-depth investigations.
基金the National Natural Science Foundation of China(Grant No.51971178)the Astronautics Supporting Technology Foundation of China(Grant No.2019-HT-XG)+2 种基金the Natural Science Foundation of Shaanxi Province,China(Grant No.2019JM-344)the Russian Science Foundation(Grant No.20-62-46003)the Fundamental Research Funds for the Central Universities,China(Grant Nos.3102019ghxm007 and 3102017JC01003).
文摘A relationship between thermal effects and relaxation of the high-frequency shear modulus upon heat treatment of bulk Zr48(Cu5/6Ag1/6)44Al8 metallic glass is found.This relationship is attributed to the relaxation of a interstitial-type defect system frozen-in from the melt upon glass production.Calorimetric data show that thermal effects occurring on heating include heat release below the glass transition temperature,heat absorption above it and heat release caused by crystallization.The equation derived within the Interstitialcy theory can be used to calculate the shear modulus relaxation using the calorimetric data.The obtained results are used to trace the defect concentration as functions of temperature and thermal prehistory.
基金This work was mainly supported by the National Key Research and Development Program of China （Grant Nos. 2016YFB0300501, 2017YFB0t）03t）02）, and the National Natural Science Foundation of China （Grant Nos. 51601206, 51771159）. An- dJng Wang and Chain-tsuan Liu would like to acknowledge lhe support by General Research Fund of Hong Kong under the grant number of City 102013.
文摘Asynchronous responses of mechanical and magnetic properties to structure relaxation for the Fe71Nb6B23 bulk metallic glass were systematically investigated. It is interesting that this ternary alloy can combinedly exhibit outstanding magnetic and mechanical properties, especially good ductility, after optimally annealing in structure relaxation stage for eliminating the internal stress and homogenizing the microstructure. The alloy exhibits low coercive force of 1.6 A/m, high effective permeability of 15 x 10^3, high fracture strength of 4.2 GPa and good plastic strAln of 1.8%. It is also found that responses of mechanical and magnetic properties to structure relaxation are asynchronous. The glass transition and crystallization will greatly deteriorate the magnetic and mechanical properties. Here we propose a physical picture and demonstrate that the primary structure factors determining magnetic and mechanical properties are different. This work will bring a promising material for application and a new perspective to study the effect of annealing-induced structure relaxation on mechanical and magnetic properties.
基金Funded by National ‘863’ Program (No. 2003AA305071)
文摘To identify the re-arrangement of constituent atoms of an amorphous Mg65Cu25Gd10 alloy happened with annealing, structure relaxation of the alloy was investigated as a function of an- nealing time at 373 K through extended X-ray absorption fine structure （EXAFS） analysis procedures. To understand the effect of structure relaxation on strength, compression tests were conducted for both the as-cast and the annealed Mg65Cu25Gd10 samples. It is found that short range order around Cu and Gd atoms exhibits different variation trends with increasing annealing time at 373 K, though the structure of the alloy still remains to be amorphous. Based on the fact that the strength of the alloy first exhibits a reduction and then a recovery with annealing time, it is suggested that the enhancement of short range order around Cu should be responsible for the strength reduction, while the enhancement of short range order around Gd should be responsible for the strength recovery.
基金Project supported by the National Natural Science Foundation of China (Grant No.52031016)。
文摘The dramatic temperature-dependence of liquids dynamics has attracted considerable scientific interests and efforts in the past decades, but the physics of which remains elusive. In addition to temperature, some other parameters, such as pressure, loading and size, can also tune the liquid dynamics and induce glass transition, which makes the situation more complicated. Here, we performed molecular dynamics simulations for Ni_(50)Zr_(50) bulk liquid and nanodroplet to study the dynamics evolution in the complex multivariate phase space, especially along the isotherm with the change of pressure or droplet size. It is found that the short-time Debye–Waller factor universally determines the long-time relaxation dynamics no matter how the temperature, pressure or size changes. The basic correlation even holds at the local atomic scale. This finding provides general understanding of the microscopic mechanism of dynamic arrest and dynamic heterogeneity.
基金Project (51101022) supported by the National Natural Science Foundation of ChinaProject (CHD2012JC096) supported by the Fundamental Research Funds for the Central Universities,China
文摘The rapid solidification process of Mg7Zn3 alloy was simulated by the molecular dynamics method. The relationship between the local structure and the dynamics during the liquid-glass transition was deeply investigated. It was found that the Mg-centered FK polyhedron and the Zn-centered icosahedron play a critical role in the formation of Mg7Zn3 metallic glass. The self-diffusion coefficients of Mg and Zn atoms deviate from the Arrhenius law near the melting temperature and then satisfy the power law. According to the time correlation functions of mean-square displacement, incoherent intermediate scattering function and non-Gaussian parameter, it was found that the β-relaxation in Mg7Zn3 supercooled liquid becomes more and more evident with decreasing temperature, and the α-relaxation time rapidly increases in the VFT law. Moreover, the smaller Zn atom has a faster relaxation behavior than the Mg atom. Some local atomic structures with short-range order have lower mobility, and they play a critical role in the appearance of cage effect in theβ-relaxation regime. The dynamics deviates from the Arrhenius law just at the temperature as the number of local atomic structures begins to rapidly increase. The dynamic glass transition temperature （Tc） is close to the glass transition point in structure （TgStr）.
基金supported by Guangdong Innovative Research Team Program (2009010005)
文摘This paper reviews the development of current research in bulk glassy alloys by focusing on the trigger point for the synthesis of the first bulk glassy alloys by the conventional mold casting method. This review covers the background, discovery, characteristics, and applications of bulk glassy alloys, as well as recent topics regarding them. Applications of bulk glassy alloys have been expanding, particularly for Fe-based bulk glassy alloys, due to their unique properties, high glass-forming ability, and low cost. In the near future, the engineering importance of bulk glassy alloys is expected to increase steadily, and continuous interest in these novel metallic materials for basic science research is anticipated.
基金Project(200802015) supported by Post-doctoral Foundation of Shandong Province,ChinaProject(50625101) supported by the National Natural Science Foundation for Distinguished Young Scholars of China
文摘The structural and electronic properties of bulk and (001) plane of TiC were investigated by the first-principles total-energy pseudopotential method based on density functional theory.The calculated bulk properties indicate that bonding nature in TiC is a combination of ionicity,covalency and metallicity,in which the Ti-C covalent bonding is the predominate one.The calculated results of structural relaxation and surface energy for TiC(001) slab indicate that slab with 7 layers shows bulk-like characteristic interiors,and the changes of slab occur on the outmost three layers,which shows that the relaxation only influences the top three layers.Meanwhile,the strong Ti-C covalent bonding can be found in the distribution of charge density on the (110) and (001) planes.Ti-C covalent bonding is enhanced by the charge depletion and accumulation in the vacuum and the interlayer region between top two atomic layers.
基金Project (200902554) supported by National Post-doctor Foundation, ChinaProject (200802015) supported by the Post-Doctor Foundation of Shandong Province, China
文摘The structural and electronic properties of TiC（110） surfaces are calculated using the first-principles total-energy plane-wave pseudopotential method based on density functional theory. The calculated results of structural relaxation and surface energy for TiC（110） slab indicate that slab with 7 layers shows bulk-like characteristic interiors, and the changes of slab occur on the outmost three layers, which shows that the relaxation only influences the top three layers. Meanwhile, the strong Ti—C covalent bonding can be found in the distribution of charge density on the （100） plane. The interlayer Ti—C chemical bonds are reinforced and the outermost interlayer distance is reduced as a result of the charge depletion in the vacuum and the charge accumulations in the interlayer region between the first and second layers. The surface energy of TiC（110） is calculated to be 3.53 J/m2.
基金Supported by the National Natural Science Foundation of China under Grant No 50325103,Hebei Natural Science Foundation under Grant No 503278and the Scientific Research Foundation for the Returned 0verseas Chinese Scholars, State Education Ministry of China.
文摘The compression behaviour of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using in-situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The equation of state is determined by fitting the experimental data according to the Birch-Murnaghan equation. It is found that the structure of Ni77P23 amorphous alloy is stable under pressures up to 30.5 GPa. Within the pressure range from zero to the experimental one, the pressure-induced structural relaxation is reversible.
基金supported by the National Amorphous and Nanocrystalline Alloy Engineering Research Center in CISRI
文摘The XRD, TEM, PAT, Curie temperature and internal friction methods were used to study systematically the embrittlement mechanism of rapidly quenched ( RQ ) nanocrystalline soft magnetic alloy Fe73.5Cu1Nb3Si13.5B9.The test results confirmed that the RQ embrittlement mechanism of amorphous alloy FeCuNbSiB was not related to crystallization but that was related to structural relaxation. Furthermore, the structural relaxation temperature of amorphous alloy FeCuNbSiB was much lower than that of used commonly amorphous alloy Fe78B13Si9. It meant that the RQ embrittlement is easier to happen for nanocrystalline alloy FeCuNbSiB than amorphous alloy Fe-B-Si.
基金Funded by the National Key R&D Program of China(2017YFB0310201-04)。
文摘Different heating treatments with the variation of heating rates,holding temperatures and holding time were used to simulate the LTPS procedure.The experimental results show that the reheating shrinkage rates of glass substrates are rarely changed with increasing the heating rate,but strongly enhanced by raising the holding temperature and time,which shows that the reheating shrinkage of glass is closely related to heat treatment and structural relaxation.The production process of glass is critical to the reheating shrinkage of glass.
文摘Based on the analysis of different theory for glass tempering process,the“structural theory”with stress relaxation and structural relaxation effects was selected to investigate the tempering of flat glass quantificationally.The geometrical model with small size and non-homogeneous mesh were considered to build the finite element models according to the characteristics of stress field.The tempering process of flat glass with12 mm thickness was calculated with the verified finite element model.The transient and permanent stress of the central area,edge and corner end of the flat glass are obtained and analyzed.From the calculation results of basic case,the transient tensile stress at the upper surface of the central area,the center point of edge,the edge of edge,the edge of corner were 14.30,18.94,40.76 and 34.75 MPa,respectively.The transient tensile stress at these points were dangerous to promote the glass to break during the tempering.In addition,the point at the diagonal line of symmetry plane in the thickness direction,which is 14 mm from corner,has the maximum permanent tensile stress about 70.01 MPa in the flat glass after tempering.Thus,it is indicated that the corner is the weakest region in the tempered glass.
基金Supported by the Natural Science Foundation of Hubei Province(No.2013CFA008)NCET(No.11-0687)
文摘GeS4 bulk glasses were prepared by the melt-quench technique and the samples were irradiated by 532-nm linearly polarized light. After the laser treatment, the photo-induced changes of the samples were investigated by UV-1601 speetrophotometer and optical second-order nonlinear tester. The results show that the transmittance of the samples around 532 nm obviously decreases and Bragg reflector forms, which is due to the production of photon-generated carriers. With the increase of laser pulse energy or the extension of irradiation duration, the Bragg reflector increases and gradually tends to be stable. These can be ascribed to the excitation- capture process of the carriers. After irradiation, the relaxation phenomenon results from the release of part of the absorbed energy in the glass matrix. And the fitting equation of the relaxation process is consistent with a conventional Kohlrausch stretched exponential function. The origin of the second harmonic generation （SHG） is because of the dipole reorientation caused by the photo-induced anisotropy in the glass.
