Terahertz time-domain spectroscopy(THz-TDS)is an effective nondestructive and noninvasive tool for investigating sulfur-containing pigments.Combined with Raman spectroscopy and vibrational mode analysis,it is signific...Terahertz time-domain spectroscopy(THz-TDS)is an effective nondestructive and noninvasive tool for investigating sulfur-containing pigments.Combined with Raman spectroscopy and vibrational mode analysis,it is significant for artifact identification and conservation.In this work,the terahertz absorption spectra of pararealgar(As_(4)S_(4))and orpiment(As_(2)S_(3))samples mixed with polytetrafluoroethylene(PTFE)are characterized in a range from 0.2 THz to 2.2 THz,and their distinctive peaks are observed,respectively.Meanwhile,qualitative analysis is also implemented by using Raman spectroscopy as a complementary technique.The lattice vibrations are simulated by using solid-state density functional theory(ss-DFT),illustrating different characteristic absorption peaks for specific crystalline structures and dynamic properties.This work provides a reliable database of sulfur-containing pigments for using the THz technology to actually analyze and diagnose cultural relics.展开更多
We present a variational density-functional perturbation theory (DFPT) to investigate the lattice dynamics and vibra- tional properties of single crystal bismuth telluride material. The phonon dispersion curves and ...We present a variational density-functional perturbation theory (DFPT) to investigate the lattice dynamics and vibra- tional properties of single crystal bismuth telluride material. The phonon dispersion curves and phonon density of states (DOS) of the material were obtained. The phonon dispersions are divided into two fields by a phonon gap. In the lower field, atomic vibrations of both Bi and Te contribute to the DOS. In the higher field, most contributions come from Te atoms. The calculated Born effective charges and dielectric constants reveal a great anisotropy in the crystal. The largest Born effective charge generates a significant dynamic charge transferring along the c axis. By DFPT calculation, the greatest LO-TO splitting takes place in the infrared phonon modes and reaches 1.7 THz in the Brillouin zone center. The Raman spectra and peaks corresponding to respective atomic vibration modes were found to be in good agreement with the experimental data.展开更多
It is shown that the traditional explanation of the free electron properties, such as mean free electron path, drift mobility, and the relaxation time, by lattice vibrations, is not valid for real free randomly moving...It is shown that the traditional explanation of the free electron properties, such as mean free electron path, drift mobility, and the relaxation time, by lattice vibrations, is not valid for real free randomly moving (RM) electrons in materials with degenerate electron gas. It is shown that the effective density of the free RM electrons in elemental metals is completely determined by density-of-states at the Fermi surface and by absolute temperature. The study has shown that the lattice vibrations excite not only the free RM electrons but also produce the same number of weakly screened ions (so-named electronic defects), which cause the scattering of the free RM electrons and related electron kinetic characteristics.展开更多
We review lattice vibrational modes in atomically thin two-dimensional (2D) layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismu...We review lattice vibrational modes in atomically thin two-dimensional (2D) layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between "layers", while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials (MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus), including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories: phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.展开更多
Non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3)(-0.04=x≤0.04,NMS)ceramics were fabricated via a conventional solid-state reaction method.Crystal structures and morphologies were investigated by Xray diffraction(...Non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3)(-0.04=x≤0.04,NMS)ceramics were fabricated via a conventional solid-state reaction method.Crystal structures and morphologies were investigated by Xray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The main crystalline phase is monoclinic Nd(Mg_(1/2)Sn_(1/2))O_(3) with a double perovskite structure(P21/n space group)for the NMS system proved by XRD.The sample at x=0.01 has the best crystallinity and evenly distributed crystal grains observed by SEM.The optimum performances(ε_(r)=19.87,Q×f=41840 GHz,f=12.05 GHz)are obtained at x=0.01.Lattice vibrational modes of the Raman spectra were assigned and illustrated,in detail.The dielectric properties obtained by fitting infrared reflectance spectra with the help of four-parameter semi-quantum model are consistent with the calculated values by microscopic polarization and damping coefficients.The reverse translational vibration of the NdeMgO_(6),the F_(5u)^((5)) mode,provides the greatest contribution to the dielectric response.The relationships between crystal structures and dielectric properties were mainly established using lattice vibrational modes as a media.展开更多
In this paper, modified two-dimensional peri- odic lattice materials with local resonance phononic band gaps are designed and investigated. The design concept is to introduce some auxiliary structures into conventiona...In this paper, modified two-dimensional peri- odic lattice materials with local resonance phononic band gaps are designed and investigated. The design concept is to introduce some auxiliary structures into conventional pe- riodic lattice materials. Elastic wave propagation in this kind of modified two-dimensional lattice materials is studied us- ing a combination of Bloch's theorem with finite element method. The calculated frequency band structures of illus- trative modified square lattice materials reveal the existence of frequency band gaps in the low frequency region due to the introduction of the auxiliary structures. The mechanism underlying the occurrence of these frequency band gaps is thoroughly discussed and natural resonances of the auxiliary structures are validated to be the origin. The effect of geo- metric parameters of the auxiliary structures on the width of the local resonance phononic band gaps is explored. Finally, a conceptual broadband vibration-insulating structure based on the modified lattice materials is designed and its capabil- ity is demonstrated. The present work is anticipated to be useful in designing structures which can insulate mechanical vibrations within desired frequency ranges.展开更多
Sr_(2)MgWO_(6)(SMW)is a typical perovskite oxide compound,but there has been little research on the effects of processing on its dielectric properties.In this work,SMW ceramics were prepared by solid-state synthesis w...Sr_(2)MgWO_(6)(SMW)is a typical perovskite oxide compound,but there has been little research on the effects of processing on its dielectric properties.In this work,SMW ceramics were prepared by solid-state synthesis with sintering at 1450℃,1475℃,1500℃and 1525℃,respectively.XRD results confirmed that the samples possessed double perovskite structure(Fm-3m).The Raman and FTIR spectra were used to study the lattice vibrational modes.The FPSQ model was used to obtain the fitting curves of the FTIR spectra and derive the intrinsic properties of the material that were found to be in agreement with the measured data.The structure-property relationships were successfully established based on the Raman mode results.The optimal sintering temperature of SMW ceramics was identified as 1475℃due to the excellent performances characteristics(ε_(r)=16.97,Q×f=23,872 GHz,τ_(f)=-35.38 ppm/℃)obtained at this temperature.This study explored the relationships among the crystal structures,lattice vibrational characteristics and dielectric properties of SMW ceramics,so as to further understand their dielectric response mechanism and lay a solid theoretical foundation for the development of microwave ceramics.展开更多
Lattice vibration modes of LuVO4 and Nd:LuVO4 crystals were calculated by using space group theory,and polarized Raman spectra were recorded with four different geometrical scattering configurations at room temperatu...Lattice vibration modes of LuVO4 and Nd:LuVO4 crystals were calculated by using space group theory,and polarized Raman spectra were recorded with four different geometrical scattering configurations at room temperature to test the theoretical prediction and assign the normal vibrations of these crystals.The measured specific heats at 293.15 K were 0.368,0.378 and 0.363 J/(g·K) for LuVO4,2 at.% and 3 at.% Nd:LuVO4,respectively.The thermal diffusivities of Nd:LuVO4 crystals were obtained in the temperature range of 303.15-563.15 K.The calculated thermal conductivity was 5.149(4.579) W/(m·K) along the [001]([100]) direction for 2 at.% Nd:LuVO4 at 303.15 K,and 5.059(4.225) W/(m·K) for 3 at.% Nd:LuVO4.展开更多
As for CaZrO_(3)(CZ)ceramic,the reported dielectric property values,especially dielectric constants,were much different from 23 to 32,which is reliable and credible?Without precise property data,CZ can’t be further d...As for CaZrO_(3)(CZ)ceramic,the reported dielectric property values,especially dielectric constants,were much different from 23 to 32,which is reliable and credible?Without precise property data,CZ can’t be further developed and utilized accurately.Herein,CZ ceramic was fabricated by a traditional two-step sintering process,then simulated and calculated the dielectric properties precisely at a microscopic polarization angle using the lattice vibrational spectra and the Clausius-Mossotti(C-M)as well as damping equations.The Raman and Fourier transform far-infrared modes were analyzed and used to predict the intrinsic properties,which were consistent well with the values calculated from C-M and damping equations.The intrinsic permittivity,after precise prediction,is about 20,which is reliable and credible.As for the dielectric loss,the value of about 6×10^(-4)was obtained after precise calculation,which is similar to other results.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61805129 and 11874245)the National Key Research and Development Program of China(Grant No.2021YFB3200100)the Yungang Special Fund of Shanxi Datong University,China(Grant No.2020YGZX005)。
文摘Terahertz time-domain spectroscopy(THz-TDS)is an effective nondestructive and noninvasive tool for investigating sulfur-containing pigments.Combined with Raman spectroscopy and vibrational mode analysis,it is significant for artifact identification and conservation.In this work,the terahertz absorption spectra of pararealgar(As_(4)S_(4))and orpiment(As_(2)S_(3))samples mixed with polytetrafluoroethylene(PTFE)are characterized in a range from 0.2 THz to 2.2 THz,and their distinctive peaks are observed,respectively.Meanwhile,qualitative analysis is also implemented by using Raman spectroscopy as a complementary technique.The lattice vibrations are simulated by using solid-state density functional theory(ss-DFT),illustrating different characteristic absorption peaks for specific crystalline structures and dynamic properties.This work provides a reliable database of sulfur-containing pigments for using the THz technology to actually analyze and diagnose cultural relics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.50971101 and 51074127)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)of China(Grant No.SKLSP201010)
文摘We present a variational density-functional perturbation theory (DFPT) to investigate the lattice dynamics and vibra- tional properties of single crystal bismuth telluride material. The phonon dispersion curves and phonon density of states (DOS) of the material were obtained. The phonon dispersions are divided into two fields by a phonon gap. In the lower field, atomic vibrations of both Bi and Te contribute to the DOS. In the higher field, most contributions come from Te atoms. The calculated Born effective charges and dielectric constants reveal a great anisotropy in the crystal. The largest Born effective charge generates a significant dynamic charge transferring along the c axis. By DFPT calculation, the greatest LO-TO splitting takes place in the infrared phonon modes and reaches 1.7 THz in the Brillouin zone center. The Raman spectra and peaks corresponding to respective atomic vibration modes were found to be in good agreement with the experimental data.
文摘It is shown that the traditional explanation of the free electron properties, such as mean free electron path, drift mobility, and the relaxation time, by lattice vibrations, is not valid for real free randomly moving (RM) electrons in materials with degenerate electron gas. It is shown that the effective density of the free RM electrons in elemental metals is completely determined by density-of-states at the Fermi surface and by absolute temperature. The study has shown that the lattice vibrations excite not only the free RM electrons but also produce the same number of weakly screened ions (so-named electronic defects), which cause the scattering of the free RM electrons and related electron kinetic characteristics.
基金Q. H. X. gratefully thanks Singapore National Research Foundation via a Fellowship grant (No. NRF-RF2009-06) and an Investigatorship grant (No. NRF-NRFI2015-03), Ministry of Education via a tier2 grant (No. MOE2012-T2-2-086) and a tier1 grant (No. 2013-T1-002-232). S. Y. Q. and X. Luo gratefully acknowledge the Singapore National Research Foun- dation (NRF) for funding under the NRF Fellowship (No. NRF-NRFF2013-07). Z. J. gratefully thanks National Natural Science Foundation of China (Nos. 11574305 and 51527901) and financial support from the National 1000 Talent Plan of China via a Young Project. The computations were performed on the cluster of NUS Graphene Research Centre. S. Y. Q. and X. Luo acknowledge the National Research Foundation, Prime Minister's Office, Singapore, under its Medium Sized Centre Programme.
文摘We review lattice vibrational modes in atomically thin two-dimensional (2D) layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between "layers", while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials (MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus), including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories: phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.
基金supported by National Natural Science Foundation of China(Grant 11874240)Guangxi Information Materials Key Laboratory Open Research Fund(171007-K)+3 种基金State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(No.KF201811)the Opening Project of Key Laboratory of Inorganic Functional Materials and Devices,Chinese Academy of Sciences(Grant No.KLIFMD201803)the Natural Science Foundation of Shandong Province,China(No.ZR2016EMM21)Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents(No.2016RCJJ002).
文摘Non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3)(-0.04=x≤0.04,NMS)ceramics were fabricated via a conventional solid-state reaction method.Crystal structures and morphologies were investigated by Xray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The main crystalline phase is monoclinic Nd(Mg_(1/2)Sn_(1/2))O_(3) with a double perovskite structure(P21/n space group)for the NMS system proved by XRD.The sample at x=0.01 has the best crystallinity and evenly distributed crystal grains observed by SEM.The optimum performances(ε_(r)=19.87,Q×f=41840 GHz,f=12.05 GHz)are obtained at x=0.01.Lattice vibrational modes of the Raman spectra were assigned and illustrated,in detail.The dielectric properties obtained by fitting infrared reflectance spectra with the help of four-parameter semi-quantum model are consistent with the calculated values by microscopic polarization and damping coefficients.The reverse translational vibration of the NdeMgO_(6),the F_(5u)^((5)) mode,provides the greatest contribution to the dielectric response.The relationships between crystal structures and dielectric properties were mainly established using lattice vibrational modes as a media.
基金supported by the National Natural Science Foundation of China (90916007)
文摘In this paper, modified two-dimensional peri- odic lattice materials with local resonance phononic band gaps are designed and investigated. The design concept is to introduce some auxiliary structures into conventional pe- riodic lattice materials. Elastic wave propagation in this kind of modified two-dimensional lattice materials is studied us- ing a combination of Bloch's theorem with finite element method. The calculated frequency band structures of illus- trative modified square lattice materials reveal the existence of frequency band gaps in the low frequency region due to the introduction of the auxiliary structures. The mechanism underlying the occurrence of these frequency band gaps is thoroughly discussed and natural resonances of the auxiliary structures are validated to be the origin. The effect of geo- metric parameters of the auxiliary structures on the width of the local resonance phononic band gaps is explored. Finally, a conceptual broadband vibration-insulating structure based on the modified lattice materials is designed and its capabil- ity is demonstrated. The present work is anticipated to be useful in designing structures which can insulate mechanical vibrations within desired frequency ranges.
基金supported by National Natural Science Foundation of China(Grant 11874240)Shandong Provincial Key Research and Development Program,China(No.2019GGX101060).
文摘Sr_(2)MgWO_(6)(SMW)is a typical perovskite oxide compound,but there has been little research on the effects of processing on its dielectric properties.In this work,SMW ceramics were prepared by solid-state synthesis with sintering at 1450℃,1475℃,1500℃and 1525℃,respectively.XRD results confirmed that the samples possessed double perovskite structure(Fm-3m).The Raman and FTIR spectra were used to study the lattice vibrational modes.The FPSQ model was used to obtain the fitting curves of the FTIR spectra and derive the intrinsic properties of the material that were found to be in agreement with the measured data.The structure-property relationships were successfully established based on the Raman mode results.The optimal sintering temperature of SMW ceramics was identified as 1475℃due to the excellent performances characteristics(ε_(r)=16.97,Q×f=23,872 GHz,τ_(f)=-35.38 ppm/℃)obtained at this temperature.This study explored the relationships among the crystal structures,lattice vibrational characteristics and dielectric properties of SMW ceramics,so as to further understand their dielectric response mechanism and lay a solid theoretical foundation for the development of microwave ceramics.
基金supported by the State Key Research Development Program of China(2010CB833103)National Natural Science Foundation of China(50721002)
文摘Lattice vibration modes of LuVO4 and Nd:LuVO4 crystals were calculated by using space group theory,and polarized Raman spectra were recorded with four different geometrical scattering configurations at room temperature to test the theoretical prediction and assign the normal vibrations of these crystals.The measured specific heats at 293.15 K were 0.368,0.378 and 0.363 J/(g·K) for LuVO4,2 at.% and 3 at.% Nd:LuVO4,respectively.The thermal diffusivities of Nd:LuVO4 crystals were obtained in the temperature range of 303.15-563.15 K.The calculated thermal conductivity was 5.149(4.579) W/(m·K) along the [001]([100]) direction for 2 at.% Nd:LuVO4 at 303.15 K,and 5.059(4.225) W/(m·K) for 3 at.% Nd:LuVO4.
基金the National Natural Science Foundation of China(51641206)Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents(Grant No.2016RCJJ002)the Opening Project of State Key Laboratory of High Performance Ceramics and Superfine Microstructure(Grant No.SKL201503SIC).
文摘As for CaZrO_(3)(CZ)ceramic,the reported dielectric property values,especially dielectric constants,were much different from 23 to 32,which is reliable and credible?Without precise property data,CZ can’t be further developed and utilized accurately.Herein,CZ ceramic was fabricated by a traditional two-step sintering process,then simulated and calculated the dielectric properties precisely at a microscopic polarization angle using the lattice vibrational spectra and the Clausius-Mossotti(C-M)as well as damping equations.The Raman and Fourier transform far-infrared modes were analyzed and used to predict the intrinsic properties,which were consistent well with the values calculated from C-M and damping equations.The intrinsic permittivity,after precise prediction,is about 20,which is reliable and credible.As for the dielectric loss,the value of about 6×10^(-4)was obtained after precise calculation,which is similar to other results.