Due to the atomic-level centrosymmetric spontaneous polarization,antiferroelectric materials exhibit a sensitively nonlinear capacitive response to plural physic fields(mainly electric field and temperature)in a certa...Due to the atomic-level centrosymmetric spontaneous polarization,antiferroelectric materials exhibit a sensitively nonlinear capacitive response to plural physic fields(mainly electric field and temperature)in a certain range,consequently leading to some superb material properties,e.g.,ripple suppression,elec-trocaloric cooling,and dielectric energy storage.However,there are many cognitive blanks about how this exotic multi-field relationε(E_(DC),T)is influenced and manipulated via microscopic structures in the anti-ferroelectrics.In this work,the classic antiferroelectric ceramics PLZT were selected to see this intelligent effect,based on a quad-parameterizedε(E_(DC))relation on the dependence of T.εrelations were studied under different material compositions,temperature,frequency,AC electric field,and DC electric field,re-vealing lattice/domain structure evolution and the underlying mechanism.The inherent phase stability,introduced random field,and hierarchical hysteresis states were found to co-dominate this multi-field nonlinear relation.This work would not only contribute to future progress in the current applications(ripple suppression/electrocaloric cooling/dielectric energy storage)but imply the possibility of co-sensing temperature and electric potential simply and smartly.展开更多
A series of Sr_(1-1.5x)Lu_(x)TiO_(3)(x=0,0.005,0.01,0.015,and 0.02)ceramics was sintered under an air at-mosphere through the solid-state reaction method.The results show that doping with Lu^(3+)consid-erably enhances...A series of Sr_(1-1.5x)Lu_(x)TiO_(3)(x=0,0.005,0.01,0.015,and 0.02)ceramics was sintered under an air at-mosphere through the solid-state reaction method.The results show that doping with Lu^(3+)consid-erably enhances material permittivity.The ceramic with x=0.01 exhibits a colossal permittivity(CP)of~101000 with a tanδof~0.16 at a frequency of 1 kHz,demonstrating enhanced stability over a wide temperature(30-300℃)and frequency(102-106 Hz)range.Based on the analysis of dielectric relaxation,X-ray photoelectron spectroscopy(XPS),and the universal dielectric response law,the CP effect is primarily due to the formation of defect dipoles,which are correlated with the presence of oxygen vacancies,such as Ti^(3+)-V_(O)^(¨)-Ti^(3+),V_(Sr)″-V_(O)^(¨),LuTi′-V_(O)^(¨)-Ti^(3+),and Lu_(Sr)·-Lu_(Ti)′-V_(O)^(¨)-Ti^(3+).These defect dipoles serve to pin electrons,limiting long-range transitions,and enhancing local po-larization.Doping with Lu^(3+)also induces a secondary Lu_(2)Ti_(2)O_(7)phase,which was characterized by X-ray diffraction(XRD)and energy-dispersive X-ray spectroscopy(EDS).The results generated in this study can inform the development and application of new CP materials based on SrTiO_(3).展开更多
A novel method is introduced to optimize the traditional Skanavi model by decomposing the electric field of molecules into the electric field of ions and quantitatively describing the ionic-scale electric field by the...A novel method is introduced to optimize the traditional Skanavi model by decomposing the electric field of molecules into the electric field of ions and quantitatively describing the ionic-scale electric field by the structural coefficient of the effective electric field.Furthermore,the optimization of the Skanavi model is demonstrated and the ferroelectric phase transition of BaTiO_(3)crystals is revealed by calculating the optical and static permittivities of BaTiO_(3),CaTiO_(3),and SrTiO_(3)crystals and the structure coefficients of the effective electric field of BT crystals after Ti4+displacement.This research compensates for the deficiencies of the traditional Skanavi model and refines the theoretical framework for analyzing dielectric properties in high permittivity materials.展开更多
Wettability has complex effects on the physical properties of reservoir rocks.The wettability of rocks should be characterized accurately to explore and develop oil and gas.Researchers have studied the rock wettabilit...Wettability has complex effects on the physical properties of reservoir rocks.The wettability of rocks should be characterized accurately to explore and develop oil and gas.Researchers have studied the rock wettability by dielectric spectra which contained abundant information.To study the rock wettability from dielectric dispersion,four rock samples with different wettabilities were used to design an experimental measurement flow.The relative dielectric permittivity in the frequency range of 100 Hz-10MHz and nuclear magnetic resonance T_(2)spectra of the samples were obtained.Subsequently,the wettabilities of the rocks were verified by the T_(2)spectra.The dielectric dispersions of the samples under different conditions were analyzed.Furthermore,the simulated-annealing(SA)algorithm was used to invert the wettability and related parameters of the rocks by a dielectric dispersion model.The results indicated that the dielectric permittivity of lipophilic rocks is lower than that of hydrophilic rocks,and that the dielectric permittivity of hydrophilic rocks decreases faster as the frequency increases.The dielectric permittivity in the high-frequency band is associated with the water content.The rock wettability parameters obtained via inversion agreed well with the T_(2)spectra,and the saturation index of the rocks.The errors between the rock permittivity calculated by the inverted parameters and the experimentally measured values were minor,indicating that rock wettability could be accurately characterized using dielectric dispersion data.展开更多
Innovative use of HfO_(2)-based high-dielectric-permittivity materials could enable their integration into few-nanometre-scale devices for storing substantial quantities of electrical charges,which have received wides...Innovative use of HfO_(2)-based high-dielectric-permittivity materials could enable their integration into few-nanometre-scale devices for storing substantial quantities of electrical charges,which have received widespread applications in high-storage-density dynamic random access memory and energy-efficient complementary metal-oxide-semiconductor devices.During bipolar high electric-field cycling in numbers close to dielectric breakdown,the dielectric permittivity suddenly increases by 30 times after oxygen-vacancy ordering and ferroelectric-to-nonferroelectric phase transition of near-edge plasma-treated Hf_(0.5)Zr_(0.5)O_(2) thin-film capacitors.Here we report a much higher dielectric permittivity of 1466 during downscaling of the capacitor into the diameter of 3.85μm when the ferroelectricity suddenly disappears without high-field cycling.The stored charge density is as high as 183μC cm^(−2) at an operating voltage/time of 1.2 V/50 ns at cycle numbers of more than 10^(12) without inducing dielectric breakdown.The study of synchrotron X-ray micro-diffraction patterns show missing of a mixed tetragonal phase.The image of electron energy loss spectroscopy shows the preferred oxygen-vacancy accumulation at the regions near top/bottom electrodes as well as grain boundaries.The ultrahigh dielectric-permittivity material enables high-density integration of extremely scaled logic and memory devices in the future.展开更多
Composites featuring negative permittivity have garnered significant attention for their potential in novel capacitance designs,coil-less electrical inductors,and electromagnetic shielding applications.In this study,w...Composites featuring negative permittivity have garnered significant attention for their potential in novel capacitance designs,coil-less electrical inductors,and electromagnetic shielding applications.In this study,we prepared polyvinylidene fluoride(PVDF)matrix composites filled with ZrO_(2)/C nanoparticles de-rived from metal-organic frameworks(MOFs)via a hot-pressing method.With an increase in the ZrO_(2)/C content to 30 wt.%,electrical percolation was observed,accompanied by a transition mechanism from hopping conduction to metal-like conduction.This enabled the realization of ZrO_(2)/C/PVDF composites with tailorable negative permittivity properties,attributed to the plasmonic oscillation of free electrons in the composites beyond the percolation threshold(30 wt.%).Furthermore,the permittivity transition along to a shift in the electrical behavior of the percolative composites from capacitive to inductive.We explored the regulatory mechanism behind the negative permittivity in this random composite system,and our findings highlight the potential of these tunable negative permittivity media as promising candi-dates for diverse electromagnetic applications.展开更多
Flexible composites with negative permittivity have a very broad development prospect in flexible electronics and wearable devices.Currently,how to control the negative permittivity except for from their intrinsic pro...Flexible composites with negative permittivity have a very broad development prospect in flexible electronics and wearable devices.Currently,how to control the negative permittivity except for from their intrinsic properties of components is still a challenge.In this study,the negative permittivity and frequency dispersion were adjusted by changing the heat treatment temperature.Polyvinylidene fluoride(PVDF)was selected as the flexible matrix and reduced graphene oxide(rGO)as the functional filler to prepare rGO/PVDF membranous composites.The negative permittivity was observed in rGO/PVDF composites film,and the effect of heat treatment temperature on the negative permittivity was further studied.It indicated that a higher heat treatment temperature contributed to the formation of conductive network,so as to obtaining negative permittivity.When the molding temperature was 70℃,the negative permittivity spectrum conformed to the Drude model was only observed in the composites with 35 wt%content of rGO.After the heat treatment temperature reached 180℃,when the content of rGO decreased to 25 wt%,the composites film achieved negative permittivity(~-10),which had a low-frequency dispersion in the test frequency range.The negative permittivity of in composites can be regulated by adjusting the heat treatment temperature,which promotes the application and development of flexible metamaterials in underwater sensing and detection,etc.展开更多
Phonon polaritons(PhPs)exhibit directional in-plane propagation and ultralow losses in van der Waals(vdW)crystals,offering new possibilities for controlling the flow of light at the nanoscale.However,these PhPs,includ...Phonon polaritons(PhPs)exhibit directional in-plane propagation and ultralow losses in van der Waals(vdW)crystals,offering new possibilities for controlling the flow of light at the nanoscale.However,these PhPs,including their directional propagation,are inherently determined by the anisotropic crystal structure of the host materials.Although in-plane anisotropic PhPs can be manipulated by twisting engineering,such as twisting individual vdW slabs,dynamically adjusting their propagation presents a significant challenge.The limited application of the twisted bilayer structure in bare films further restricts its usage.In this study,we present a technique in which anisotropic PhPs supported by bare biaxial vdW slabs can be actively tuned by modifying their local dielectric environment.Excitingly,we predict that the iso-frequency contour of PhPs can be reoriented to enable propagation along forbidden directions when the crystal is placed on a substrate with a moderate negative permittivity.Besides,we systematically investigate the impact of polaritonic coupling on near-field radiative heat transfer(NFRHT)between heterostructures integrated with different substrates that have negative permittivity.Our main findings reveal that through the analysis of dispersion contour and photon transmission coefficient,the excitation and reorientation of the fundamental mode facilitate increased photon tunneling,thereby enhancing heat transfer between heterostructures.Conversely,the annihilation of the fundamental mode hinders heat transfer.Furthermore,we find the enhancement or suppression of radiative energy transport depends on the relative magnitude of the slab thickness and the vacuum gap width.Finally,the effect of negative permittivity substrates on NFRHT along the[001]crystalline direction ofα-MoO3 is considered.The spectral band where the excited fundamental mode resulting from the negative permittivity substrates is shifted to the first Reststrahlen Band(RB 1)ofα-MoO_(3) and is widened,resulting in more significant enhancement of heat flux from RB 1.We anticipate our results will motivate new direction for dynamical tunability of the PhPs in photonic devices.展开更多
The complex permittivity of baijiu varies with frequency,and dielectric spectroscopy has been used to evaluate the quality.To simplify the analysis and reduce the number of the parameters,a dielectric relaxation model...The complex permittivity of baijiu varies with frequency,and dielectric spectroscopy has been used to evaluate the quality.To simplify the analysis and reduce the number of the parameters,a dielectric relaxation model is often used to fit the permittivity data.However,existing fitting methods such as the least squares and particle swarm optimization methods are often computationally complex and require preset initial values.Therefore,a simpler calculation method of the relaxation parameters considering the geometric characteristics of the permittivity spectrum is proposed.It is based on the relationship between the Cole-Cole relaxation parameters and the Cole-Cole diagram,which is fitted by a geometric method.First,the concepts of the Cole-Cole parameters and the diagram are introduced,and then the process of obtaining the parameters from the complex permittivity measurement data is explained.Taking baijiu with 56%alcohol by volume(ABV)as an example,the fitting is better than the least squares method and similar to the particle swarm optimization.This method is then used for the parameter fitting of baijiu with ABV of 42-52%,and the average error is less than 1%,demonstrating its wider applicability.Finally,a prediction model is used for baijiu with 53%ABV,and the error is only 1.51%.Hence,the method can be applied to the measurement of ABV of baijiu.展开更多
The pyrolytic carbon （PyC） coatings were fabricated on A1203 fiber fabrics by the method of chemical vapor deposition （CVD）. The microstructures of A1203 fibers with and without PyC coatings were characterized by ...The pyrolytic carbon （PyC） coatings were fabricated on A1203 fiber fabrics by the method of chemical vapor deposition （CVD）. The microstructures of A1203 fibers with and without PyC coatings were characterized by SEM and Raman spectroscopy. The influence of deposition time of PyC on the DC conductivity （ad） of A1203 filaments and complex permittivity of fabrics at X band （8.2-12.4 GHz） were investigated. The values of Crd and complex permittivity increase with increasing deposition time of PyC. The electron relaxation polarization and conductance loss were supposed to be contributed to the increase of ε＇ and ε＂, respectively. In addition, the reflection loss （RL） of fabrics was calculated. The results show that the microwave absorbing properties of Al2O3 fiber fabrics can be improved by PyC coatings. The best RL results are for 60 min-deposition sample, of which the minimum value is about -40.4 dB at about 9.5 GHz and the absorbing frequency band （AFB） is about 4 GHz.展开更多
Rare earth-based Bi_(0.85)La_(0.15)FeO_(3)(BLFO)and NdMnO_(3)(NMO)particles were synthesised using the solidstate route,and their roles affecting structural,electrical,magnetic properties along with hydroelectric appl...Rare earth-based Bi_(0.85)La_(0.15)FeO_(3)(BLFO)and NdMnO_(3)(NMO)particles were synthesised using the solidstate route,and their roles affecting structural,electrical,magnetic properties along with hydroelectric application in different concentrations i.e.,(1-x)BLFO:xNMO(where x=0,0.10,0.20,0.30 and 1.0)ceramics composites were investigated.X-ray diffraction analyses confirm the pure-phase formation of BLFO:NMO composites,featuring micrometer-scale crystallite sizes.Fourier transform infrared(FT-IR)spectra of BLFO:NMO composites reveal peak shifts with rising NMO content,indicating composite formation.These composites exhibit robust Maxwell-Wagner polarization and a pronounced composition-dependent behavior.The addition of NMO to BLFO results in a rise in dielectric permittivity at lower frequencies,confirming relaxor behavior and indicating success in achieving the transition temperature.Impedance spectroscopy facilitates a clearer understanding of how charge carriers contribute to these composites and the impact of grain/grain boundaries.The saturation magnetization maximum value(i.e.,0.807 emu/g)was attained in 0.7BLFO-0.3NMO.The coercivity decreases with the addition of NMO in BLFO.The results suggest the composite's enhanced suitability for microelectronics and hydropower cells,showing improved hydroelectric cell performance with increased NMO in BLFO,highlighting a notable ion diffusion mechanism.展开更多
This theory proposes an extended model of the electron based on the image of the screened electron in the concept of vacuum polarization of QED. The extended electron consists of a negatively charged core −q0which is ...This theory proposes an extended model of the electron based on the image of the screened electron in the concept of vacuum polarization of QED. The extended electron consists of a negatively charged core −q0which is surrounded by an assembly (an aggregation) of tiny static electric dipoles −q,+q. When subjected to an external field, electromagnetic forces are produced on these point charges to give rise to various properties of the electron. Three major properties of the electron that will be explored in this theory are: 1) the effective electric charge of the electron;2) the mechanism of the spin of the electron;3) the mechanism of radiation of the electron. The investigation of these properties leads to various innovative explanations for the generation of anti-particle, the orbital of the electron, the strong nuclear forces between nucleons … Other topics are also listed in the following content.展开更多
In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal struc...In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal structure,microstructure,and microwave dielectric properties were carried out.Rietveld refinements show that the SrEr_(2)O_(4)ceramics crystallize in the orthorhombic with the space group Pnam.The SrEr_(2)O_(4)ceramic sintered at 1575℃ exhibits the good performance of permittivity(ε_(r))=14.44,quality factor(Q × f)=23271 GHz,and resonant temperature frequency coefficient(τ_(f))=-21.5 ppm/℃,which is attributed to its high lattice energy,packing fraction,and relative density.In addition,to satisfy the requirement of temperature stability for communication devices,near-zero τ_(f) value is obtained by adding CaTiO_(3) at the cost of a small quality factor loss.The SrEr_(2)O_(4)+1.25 wt% CaTiO_(3) composite exhibits decent properties with ε_(r)=18.57,Q×f=19940 GHz,and T_(f)=+3.99 ppm/℃,making it an ideal candidate for microwave band applications.展开更多
基金supported by the National Natural Science Foun-dation of China(Grant Nos.U2002217,11774366 and 52102342).
文摘Due to the atomic-level centrosymmetric spontaneous polarization,antiferroelectric materials exhibit a sensitively nonlinear capacitive response to plural physic fields(mainly electric field and temperature)in a certain range,consequently leading to some superb material properties,e.g.,ripple suppression,elec-trocaloric cooling,and dielectric energy storage.However,there are many cognitive blanks about how this exotic multi-field relationε(E_(DC),T)is influenced and manipulated via microscopic structures in the anti-ferroelectrics.In this work,the classic antiferroelectric ceramics PLZT were selected to see this intelligent effect,based on a quad-parameterizedε(E_(DC))relation on the dependence of T.εrelations were studied under different material compositions,temperature,frequency,AC electric field,and DC electric field,re-vealing lattice/domain structure evolution and the underlying mechanism.The inherent phase stability,introduced random field,and hierarchical hysteresis states were found to co-dominate this multi-field nonlinear relation.This work would not only contribute to future progress in the current applications(ripple suppression/electrocaloric cooling/dielectric energy storage)but imply the possibility of co-sensing temperature and electric potential simply and smartly.
基金Project supported by the fund of the Major Science and Technology Programs of Yunnan Province(202102AB080008)the Science and Technology Program of Yunnan Precious Metal Laboratory(YPML-2022050205,YPML-2022050219)。
文摘A series of Sr_(1-1.5x)Lu_(x)TiO_(3)(x=0,0.005,0.01,0.015,and 0.02)ceramics was sintered under an air at-mosphere through the solid-state reaction method.The results show that doping with Lu^(3+)consid-erably enhances material permittivity.The ceramic with x=0.01 exhibits a colossal permittivity(CP)of~101000 with a tanδof~0.16 at a frequency of 1 kHz,demonstrating enhanced stability over a wide temperature(30-300℃)and frequency(102-106 Hz)range.Based on the analysis of dielectric relaxation,X-ray photoelectron spectroscopy(XPS),and the universal dielectric response law,the CP effect is primarily due to the formation of defect dipoles,which are correlated with the presence of oxygen vacancies,such as Ti^(3+)-V_(O)^(¨)-Ti^(3+),V_(Sr)″-V_(O)^(¨),LuTi′-V_(O)^(¨)-Ti^(3+),and Lu_(Sr)·-Lu_(Ti)′-V_(O)^(¨)-Ti^(3+).These defect dipoles serve to pin electrons,limiting long-range transitions,and enhancing local po-larization.Doping with Lu^(3+)also induces a secondary Lu_(2)Ti_(2)O_(7)phase,which was characterized by X-ray diffraction(XRD)and energy-dispersive X-ray spectroscopy(EDS).The results generated in this study can inform the development and application of new CP materials based on SrTiO_(3).
基金Project supported by the National Natural Science Foundation of China(Grant No.51277138)the Natural Science Basic Research Program of Shaanxi Province of China(Grant No.2021JM-442)the Fund from the Shaanxi Provincial Science and Technology Department for Qin Chuangyuan Scientist+Engineer Team(Grant No.2024QCY-KXJ-194)。
文摘A novel method is introduced to optimize the traditional Skanavi model by decomposing the electric field of molecules into the electric field of ions and quantitatively describing the ionic-scale electric field by the structural coefficient of the effective electric field.Furthermore,the optimization of the Skanavi model is demonstrated and the ferroelectric phase transition of BaTiO_(3)crystals is revealed by calculating the optical and static permittivities of BaTiO_(3),CaTiO_(3),and SrTiO_(3)crystals and the structure coefficients of the effective electric field of BT crystals after Ti4+displacement.This research compensates for the deficiencies of the traditional Skanavi model and refines the theoretical framework for analyzing dielectric properties in high permittivity materials.
基金supported by the Beijing Municipal Natural Science Foundation(1242025)。
文摘Wettability has complex effects on the physical properties of reservoir rocks.The wettability of rocks should be characterized accurately to explore and develop oil and gas.Researchers have studied the rock wettability by dielectric spectra which contained abundant information.To study the rock wettability from dielectric dispersion,four rock samples with different wettabilities were used to design an experimental measurement flow.The relative dielectric permittivity in the frequency range of 100 Hz-10MHz and nuclear magnetic resonance T_(2)spectra of the samples were obtained.Subsequently,the wettabilities of the rocks were verified by the T_(2)spectra.The dielectric dispersions of the samples under different conditions were analyzed.Furthermore,the simulated-annealing(SA)algorithm was used to invert the wettability and related parameters of the rocks by a dielectric dispersion model.The results indicated that the dielectric permittivity of lipophilic rocks is lower than that of hydrophilic rocks,and that the dielectric permittivity of hydrophilic rocks decreases faster as the frequency increases.The dielectric permittivity in the high-frequency band is associated with the water content.The rock wettability parameters obtained via inversion agreed well with the T_(2)spectra,and the saturation index of the rocks.The errors between the rock permittivity calculated by the inverted parameters and the experimentally measured values were minor,indicating that rock wettability could be accurately characterized using dielectric dispersion data.
基金supported by the National Key Basic Research Program of China (2022YFA1402904)Basic Research Project of Shanghai Science and Technology Innovation Action (grant number 24CL2900900)the National Natural Science Foundation of China (grant number 61904034)
文摘Innovative use of HfO_(2)-based high-dielectric-permittivity materials could enable their integration into few-nanometre-scale devices for storing substantial quantities of electrical charges,which have received widespread applications in high-storage-density dynamic random access memory and energy-efficient complementary metal-oxide-semiconductor devices.During bipolar high electric-field cycling in numbers close to dielectric breakdown,the dielectric permittivity suddenly increases by 30 times after oxygen-vacancy ordering and ferroelectric-to-nonferroelectric phase transition of near-edge plasma-treated Hf_(0.5)Zr_(0.5)O_(2) thin-film capacitors.Here we report a much higher dielectric permittivity of 1466 during downscaling of the capacitor into the diameter of 3.85μm when the ferroelectricity suddenly disappears without high-field cycling.The stored charge density is as high as 183μC cm^(−2) at an operating voltage/time of 1.2 V/50 ns at cycle numbers of more than 10^(12) without inducing dielectric breakdown.The study of synchrotron X-ray micro-diffraction patterns show missing of a mixed tetragonal phase.The image of electron energy loss spectroscopy shows the preferred oxygen-vacancy accumulation at the regions near top/bottom electrodes as well as grain boundaries.The ultrahigh dielectric-permittivity material enables high-density integration of extremely scaled logic and memory devices in the future.
基金National Natural Science Foundation of China(No.52272117)National Key Research and Development Program of China(Nos.2022YFB3505104,2022YFB3706604)National Youth Fund(No.52207239).
文摘Composites featuring negative permittivity have garnered significant attention for their potential in novel capacitance designs,coil-less electrical inductors,and electromagnetic shielding applications.In this study,we prepared polyvinylidene fluoride(PVDF)matrix composites filled with ZrO_(2)/C nanoparticles de-rived from metal-organic frameworks(MOFs)via a hot-pressing method.With an increase in the ZrO_(2)/C content to 30 wt.%,electrical percolation was observed,accompanied by a transition mechanism from hopping conduction to metal-like conduction.This enabled the realization of ZrO_(2)/C/PVDF composites with tailorable negative permittivity properties,attributed to the plasmonic oscillation of free electrons in the composites beyond the percolation threshold(30 wt.%).Furthermore,the permittivity transition along to a shift in the electrical behavior of the percolative composites from capacitive to inductive.We explored the regulatory mechanism behind the negative permittivity in this random composite system,and our findings highlight the potential of these tunable negative permittivity media as promising candi-dates for diverse electromagnetic applications.
基金financially supported by the National Natural Science Foundation of China(Nos.52101178 and 52271182)the Natural Science Foundation of Shanghai(No.22ZR1426800)+3 种基金the Young Elite Scientist Sponsorship Program by China Association for Science and Technology(No.YESS20200257)Shanghai Pujiang Program(No.22PJ1411300)the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-07-00-10-E00053)the Natural Science Foundation of Shandong Province(No.ZR2021QE090)。
文摘Flexible composites with negative permittivity have a very broad development prospect in flexible electronics and wearable devices.Currently,how to control the negative permittivity except for from their intrinsic properties of components is still a challenge.In this study,the negative permittivity and frequency dispersion were adjusted by changing the heat treatment temperature.Polyvinylidene fluoride(PVDF)was selected as the flexible matrix and reduced graphene oxide(rGO)as the functional filler to prepare rGO/PVDF membranous composites.The negative permittivity was observed in rGO/PVDF composites film,and the effect of heat treatment temperature on the negative permittivity was further studied.It indicated that a higher heat treatment temperature contributed to the formation of conductive network,so as to obtaining negative permittivity.When the molding temperature was 70℃,the negative permittivity spectrum conformed to the Drude model was only observed in the composites with 35 wt%content of rGO.After the heat treatment temperature reached 180℃,when the content of rGO decreased to 25 wt%,the composites film achieved negative permittivity(~-10),which had a low-frequency dispersion in the test frequency range.The negative permittivity of in composites can be regulated by adjusting the heat treatment temperature,which promotes the application and development of flexible metamaterials in underwater sensing and detection,etc.
基金supported by the National Natural Science Foundation of China(Nos.52106099 and 51576004)the Natural Science Foundation of Shandong Province(No.ZR2022YQ57)the Taishan Scholars Program.
文摘Phonon polaritons(PhPs)exhibit directional in-plane propagation and ultralow losses in van der Waals(vdW)crystals,offering new possibilities for controlling the flow of light at the nanoscale.However,these PhPs,including their directional propagation,are inherently determined by the anisotropic crystal structure of the host materials.Although in-plane anisotropic PhPs can be manipulated by twisting engineering,such as twisting individual vdW slabs,dynamically adjusting their propagation presents a significant challenge.The limited application of the twisted bilayer structure in bare films further restricts its usage.In this study,we present a technique in which anisotropic PhPs supported by bare biaxial vdW slabs can be actively tuned by modifying their local dielectric environment.Excitingly,we predict that the iso-frequency contour of PhPs can be reoriented to enable propagation along forbidden directions when the crystal is placed on a substrate with a moderate negative permittivity.Besides,we systematically investigate the impact of polaritonic coupling on near-field radiative heat transfer(NFRHT)between heterostructures integrated with different substrates that have negative permittivity.Our main findings reveal that through the analysis of dispersion contour and photon transmission coefficient,the excitation and reorientation of the fundamental mode facilitate increased photon tunneling,thereby enhancing heat transfer between heterostructures.Conversely,the annihilation of the fundamental mode hinders heat transfer.Furthermore,we find the enhancement or suppression of radiative energy transport depends on the relative magnitude of the slab thickness and the vacuum gap width.Finally,the effect of negative permittivity substrates on NFRHT along the[001]crystalline direction ofα-MoO3 is considered.The spectral band where the excited fundamental mode resulting from the negative permittivity substrates is shifted to the first Reststrahlen Band(RB 1)ofα-MoO_(3) and is widened,resulting in more significant enhancement of heat flux from RB 1.We anticipate our results will motivate new direction for dynamical tunability of the PhPs in photonic devices.
基金financially supported by the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.SJCX23_0099)。
文摘The complex permittivity of baijiu varies with frequency,and dielectric spectroscopy has been used to evaluate the quality.To simplify the analysis and reduce the number of the parameters,a dielectric relaxation model is often used to fit the permittivity data.However,existing fitting methods such as the least squares and particle swarm optimization methods are often computationally complex and require preset initial values.Therefore,a simpler calculation method of the relaxation parameters considering the geometric characteristics of the permittivity spectrum is proposed.It is based on the relationship between the Cole-Cole relaxation parameters and the Cole-Cole diagram,which is fitted by a geometric method.First,the concepts of the Cole-Cole parameters and the diagram are introduced,and then the process of obtaining the parameters from the complex permittivity measurement data is explained.Taking baijiu with 56%alcohol by volume(ABV)as an example,the fitting is better than the least squares method and similar to the particle swarm optimization.This method is then used for the parameter fitting of baijiu with ABV of 42-52%,and the average error is less than 1%,demonstrating its wider applicability.Finally,a prediction model is used for baijiu with 53%ABV,and the error is only 1.51%.Hence,the method can be applied to the measurement of ABV of baijiu.
基金Project (51072165) supported by the National Natural Science Foundation of ChinaProject (KP200901) supported by the Fund of the State Key Laboratory of Solidification Processing,China
文摘The pyrolytic carbon （PyC） coatings were fabricated on A1203 fiber fabrics by the method of chemical vapor deposition （CVD）. The microstructures of A1203 fibers with and without PyC coatings were characterized by SEM and Raman spectroscopy. The influence of deposition time of PyC on the DC conductivity （ad） of A1203 filaments and complex permittivity of fabrics at X band （8.2-12.4 GHz） were investigated. The values of Crd and complex permittivity increase with increasing deposition time of PyC. The electron relaxation polarization and conductance loss were supposed to be contributed to the increase of ε＇ and ε＂, respectively. In addition, the reflection loss （RL） of fabrics was calculated. The results show that the microwave absorbing properties of Al2O3 fiber fabrics can be improved by PyC coatings. The best RL results are for 60 min-deposition sample, of which the minimum value is about -40.4 dB at about 9.5 GHz and the absorbing frequency band （AFB） is about 4 GHz.
基金Project supported by Research Scheme(03(1427)/18/EMR-Ⅱ),Council of Scientific&Industrial Research CSIR,New Delhi,IndiaUniversity Grants Commission-Department of Atomic Energy Consortium for Scientific Research UGC-DAE CSR-Indore,India。
文摘Rare earth-based Bi_(0.85)La_(0.15)FeO_(3)(BLFO)and NdMnO_(3)(NMO)particles were synthesised using the solidstate route,and their roles affecting structural,electrical,magnetic properties along with hydroelectric application in different concentrations i.e.,(1-x)BLFO:xNMO(where x=0,0.10,0.20,0.30 and 1.0)ceramics composites were investigated.X-ray diffraction analyses confirm the pure-phase formation of BLFO:NMO composites,featuring micrometer-scale crystallite sizes.Fourier transform infrared(FT-IR)spectra of BLFO:NMO composites reveal peak shifts with rising NMO content,indicating composite formation.These composites exhibit robust Maxwell-Wagner polarization and a pronounced composition-dependent behavior.The addition of NMO to BLFO results in a rise in dielectric permittivity at lower frequencies,confirming relaxor behavior and indicating success in achieving the transition temperature.Impedance spectroscopy facilitates a clearer understanding of how charge carriers contribute to these composites and the impact of grain/grain boundaries.The saturation magnetization maximum value(i.e.,0.807 emu/g)was attained in 0.7BLFO-0.3NMO.The coercivity decreases with the addition of NMO in BLFO.The results suggest the composite's enhanced suitability for microelectronics and hydropower cells,showing improved hydroelectric cell performance with increased NMO in BLFO,highlighting a notable ion diffusion mechanism.
文摘This theory proposes an extended model of the electron based on the image of the screened electron in the concept of vacuum polarization of QED. The extended electron consists of a negatively charged core −q0which is surrounded by an assembly (an aggregation) of tiny static electric dipoles −q,+q. When subjected to an external field, electromagnetic forces are produced on these point charges to give rise to various properties of the electron. Three major properties of the electron that will be explored in this theory are: 1) the effective electric charge of the electron;2) the mechanism of the spin of the electron;3) the mechanism of radiation of the electron. The investigation of these properties leads to various innovative explanations for the generation of anti-particle, the orbital of the electron, the strong nuclear forces between nucleons … Other topics are also listed in the following content.
基金Porject supported by National Natural Science Foundation of China (61761015, 11664008)Guangxi Natural Science Foundation(2018GXNSFFA050001, 2024GXNSFDA010060)High-Level Innovation Team and Outstanding Scholar Program of Guangxi Institutes。
文摘In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal structure,microstructure,and microwave dielectric properties were carried out.Rietveld refinements show that the SrEr_(2)O_(4)ceramics crystallize in the orthorhombic with the space group Pnam.The SrEr_(2)O_(4)ceramic sintered at 1575℃ exhibits the good performance of permittivity(ε_(r))=14.44,quality factor(Q × f)=23271 GHz,and resonant temperature frequency coefficient(τ_(f))=-21.5 ppm/℃,which is attributed to its high lattice energy,packing fraction,and relative density.In addition,to satisfy the requirement of temperature stability for communication devices,near-zero τ_(f) value is obtained by adding CaTiO_(3) at the cost of a small quality factor loss.The SrEr_(2)O_(4)+1.25 wt% CaTiO_(3) composite exhibits decent properties with ε_(r)=18.57,Q×f=19940 GHz,and T_(f)=+3.99 ppm/℃,making it an ideal candidate for microwave band applications.
