In this paper, the elastic wave propagation in a two-dimensional piezoelectric phononic crystal is studied by considering the mechanic-electric coupling. The generalized eigenvalue equation is obtained by the relation...In this paper, the elastic wave propagation in a two-dimensional piezoelectric phononic crystal is studied by considering the mechanic-electric coupling. The generalized eigenvalue equation is obtained by the relation of the mechanic and electric fields as well as the Bloch-Floquet theorem. The band structures of both the in-plane and anti-plane modes are calculated for a rectangular lattice by the planewave expansion method. The effects of the lattice constant ratio and the piezoelectricity with different filling fractions are analyzed. The results show that the largest gap width is not always obtained for a square lattice. In some situations, a rectangular lattice may generate larger gaps. The band gap characteristics are influenced obviously by the piezoelectricity with the larger lattice constant ratios and the filling fractions.展开更多
The latest discovery of a new iron-chalcogenide superconductor AXFe2-ySe2 （A =K, Cs, Rb, and Tl, etc.） has attracted much attention due to a number of its unique characteristics, such as the possible insulating stat...The latest discovery of a new iron-chalcogenide superconductor AXFe2-ySe2 （A =K, Cs, Rb, and Tl, etc.） has attracted much attention due to a number of its unique characteristics, such as the possible insulating state of the parent compound, the existence of Fe-vacancy and its ordering, a new form of magnetic structure and its interplay with superconductivity, and the peculiar electronic structures that are distinct from other Fe-based superconductors. In this paper, we present a brief review on the structural, magnetic and electronic properties of this new superconductor, with an emphasis on the electronic structure and superconducting gap. Issues and future perspectives are discussed at the end of the paper.展开更多
The wave propagation is studied in two-dimensional disordered piezoelectric phononic crystals using the finite-difference time-domain （FDTD） method. For different cases of disorder, the transmission coefficients are...The wave propagation is studied in two-dimensional disordered piezoelectric phononic crystals using the finite-difference time-domain （FDTD） method. For different cases of disorder, the transmission coefficients are calculated. The influences of disorders on band gaps are investigated. The results show that the disorder in the piezoelectric phononic crystals has more significant influences on the band gap in the low frequency regions than in the high frequency ones. The relation between the width of band gap and the direction of position disorder is also discussed. When the position disorder is along the direction perpendicular to the wave transmission, the piezoelectric phononic crystals have wider band gaps at low frequency regions than the case of position disorder being along the wave transmission direction. It can also be found that the effect of. size disorder on band gaps is analogous to that of location disorder. When the perturbation coefficient is big, it has more pronounced effects on the pass bands in the piezoelectric phononic crystals with both size and location disorders than in the piezoelectric phononic crystals with single disorder. In higher frequency regions the piezoelectric effect reduces the transmission coefficients. But for larger disorder degree, the effects of the piezoelectricity will be reduced.展开更多
Band gaps of 2D phononic crystal with orthotropic cylindrical fillers embedded in the isotropic host are studied in this paper. Two kinds of periodic structures, namely, the square lattice and the triangle lattice, ar...Band gaps of 2D phononic crystal with orthotropic cylindrical fillers embedded in the isotropic host are studied in this paper. Two kinds of periodic structures, namely, the square lattice and the triangle lattice, are considered. For anisotropic phononic crystal, band gaps not only depend on the periodic lattice but also the angle between the symmetry axis of orthotropic material and that of the periodic structure. Rotating these cylindrical fillers makes the angle changing continuously; as a result, pass bands and forbidden bands of the phononic crystal are changed. The plane wave expansion method is used to reduce the band gap problem to an eigenvalue problem. The numerical example is given for YBCO/Epoxy composites. The location and the width of band gaps are estimated for different rotating angles. The influence of anisotropy on band gaps is discussed based on numerical results.展开更多
Absolute phononic band gaps can be substantially improved in two-dimensional lattices by using a symmetry reduction approach. In this paper, the propagation of elastic waves in a two-dirnensional hybrid triangular lat...Absolute phononic band gaps can be substantially improved in two-dimensional lattices by using a symmetry reduction approach. In this paper, the propagation of elastic waves in a two-dirnensional hybrid triangular lattice structure consisting of stainless steel cylinders in air is investigated theoretically. The band structure is calculated with the plane wave expansion （PWE） method. The hybrid triangular Bravais lattice is formed by two kinds of triangular lattices. Different from ordinary triangular lattices, the band gap opens at low frequency （between the first and the second bands） regime because of lifting the bands degeneracy at high symmetry points of the Brillouin zone. The location and width of the band gaps can be tuned by the position of the additional rods.展开更多
Two new quaternary sulfides, KSmSiS4 （1） and KYbSiS4 （2）, have been synthesized by high-temperature solid-state reaction. Single,crystal X-ray diffraction analyses indicate that both compounds crystallize in the s...Two new quaternary sulfides, KSmSiS4 （1） and KYbSiS4 （2）, have been synthesized by high-temperature solid-state reaction. Single,crystal X-ray diffraction analyses indicate that both compounds crystallize in the space group P21/m, and the crystal data are as follows： a = 6.426（11）, b = 6.582（11）, c = 8.602（15）A, β= 107.90（13）°, Z = 2, V= 346.2（10） A^3, Dc = 3.317 g/cm^3, F（000） = 318,μ（MoKα） = 10.334 mm^-1, the final R = 0.0559 and wR = 0.1370 for 1; and α= 6.3244（10）, b = 6.5552（10）, c = 8.5701（15）A, β= 108.001（13）°, Z = 2, V = 337.91（9） A^3, De= 3.621 g/cm^3, F（000） = 334, μ（MoKα） = 15.737 mm^-1, the final R = 0.0422 and wR = 0.0960 for 2. The KLnSiS4 （Ln = Sm, Yb） structure consists of corrugated ∞^2 [LnSiS4]^- layers which are formed by edge-sharing LnS8 bicapped trigonal prisms and SiS4 tetrahedra. The K^＋ cations are located in the cavities defined by S2 anions between the ∞^2[LnSiS4]^- layers. Band-gap analyses show that compounds 1 and 2 are semiconductors with optical band-gaps of 2.40 and 2.34 eV, respectively.展开更多
Absolute band gaps of a two-dimensional triangular-lattice photonic crystal are calculated with the finite-difference time-domain method in this paper.Through calculating the photonic band structures of the triangular...Absolute band gaps of a two-dimensional triangular-lattice photonic crystal are calculated with the finite-difference time-domain method in this paper.Through calculating the photonic band structures of the triangular-lattice photonic crystal consisting of Ge rods immersed in air with different shapes,it is found that a large absolute band gap of 0.098 (2c/a) can be obtained for the structures with hollow triangular Ge rods immersed in air,corresponding to 19.8% of the middle frequency.The influence of the different factors on the width of the absolute band gaps is also discussed.展开更多
A folding beam-type piezoelectric phononic crystal model is proposed to isolate vibration. Two piezoelectric bimorphs are joined by two masses as a folding structure to comprise each unit cell of the piezoelectric pho...A folding beam-type piezoelectric phononic crystal model is proposed to isolate vibration. Two piezoelectric bimorphs are joined by two masses as a folding structure to comprise each unit cell of the piezoelectric phononic crystal. Each bimorph is connected independently by a resistive-inductive resonant shunting circuit. The folding structure extends the propagation path of elastic waves, while its structure size remains quite small. Propagation of coupled extension-flexural elastic waves is studied by the classical laminated beam theory and transfer matrix method. The theoretical model is further verified with the finite element method(FEM). The effects of geometrical and circuit parameters on the band gaps are analyzed. With only 4 unit cells, the folding beam-type piezoelectric phononic crystal generates two Bragg band gaps of 369 Hz to1 687 Hz and 2 127 Hz to 4 000 Hz. In addition, between these two Bragg band gaps, a locally resonant band gap is induced by resonant shunting circuits. Appropriate circuit parameters are used to join these two Bragg band gaps by the locally resonant band gap.Thus, a low-frequency and broad band gap of 369 Hz to 4 000 Hz is obtained.展开更多
A new quaternary rare-earth sulfide, Cs0.75（6）Er443（5）In3.32（6）S12 （1）, is discovered by high temperature solid state reactions with a slight excess of CsCI flux. The structure is characterized by single-cryst...A new quaternary rare-earth sulfide, Cs0.75（6）Er443（5）In3.32（6）S12 （1）, is discovered by high temperature solid state reactions with a slight excess of CsCI flux. The structure is characterized by single-crystal X-ray diffraction data, while crystallizes in hexagonal space group P63/m （No. 176） with a = 12.0329（6）, c = 3.8693（5）A, V= 485.18（7） A3, Z = 1, Mr = 1606.57, Dc = 5.499 g/cm3,μ = 25.457 mm-1, F（000） = 752, the final R = 0.0337 and wR = 0.0904 for 328 observed reflections with I 〉 2σ（I）. Its structure features a three-dimensional framework with hexagonal channels that are centered by Cs cations. Such channels are formed by double chains of edge-sharing M（1）S6 （M（1） = Er（1）/In（1）） octahedra and single chains of Er（2）S6 triprism interconnected by corner-sharing. The syntheses, single-crystal analyses, optical band gap and magnetic property are reported.展开更多
对纳米 Ga P粉体 -结晶紫水溶液光催化降解进行了研究。纳米 Ga P粉体在紫外光照射条件下对结晶紫具有光催化降解作用 ;随平均颗粒度的降低 ,纳米 Ga P粉体的光催化活性增加。红外光谱测试结果表明 :进行光催化过程以后 ,纳米 Ga P表面...对纳米 Ga P粉体 -结晶紫水溶液光催化降解进行了研究。纳米 Ga P粉体在紫外光照射条件下对结晶紫具有光催化降解作用 ;随平均颗粒度的降低 ,纳米 Ga P粉体的光催化活性增加。红外光谱测试结果表明 :进行光催化过程以后 ,纳米 Ga P表面存在的几种主要振动模式变化较小或不变 ;拉曼光谱测试结果表明 :纳米 Ga P粉体的横向光学声子模与纵向光学声子模 。展开更多
A novel ternary rare-earth sulfide, CsYb7S（11）, has been successfully synthesized by high-temperature solid-state reaction of an elemental mixture with modified Cs Cl flux. The single-crystal X-ray diffraction data ...A novel ternary rare-earth sulfide, CsYb7S（11）, has been successfully synthesized by high-temperature solid-state reaction of an elemental mixture with modified Cs Cl flux. The single-crystal X-ray diffraction data reveal its orthorhombic symmetry in space group Cmca（no. 64） with a = 15.271（3）, b = 13.414（2）, c = 18.869（3） A°, V = 3865.2（2） A°^3, Z = 8, Mr = 1696.85, Dc = 5.832 g/cm^3, μ = 36.538 mm^-1, F（000） = 5768, the final R = 0.0225 and w R = 0.0517 for 2258 observed reflections with I 〉 2σ（I）, 2.67〈θ〈27.48o, w = 1/[σ^2（Fo^2） ＋（0.0443 P）2 ＋ 8.7453 P], where P =（Fo^2 ＋ 2Fc^2）/3, S = 1.036,（Δρ）max = 1.609 and（Δρ）min = –1.922. The remarkable structural feature is the dual tricapped Cs2@S18 cube closed cavities far apart within the three-dimensional [Yb7S（11）]-covalent bonding matrix. Magnetic susceptibility measurements show that the title compound exhibits temperature-dependent（50～300 K） para-magnetism and obey the Curie-Weiss law. Moreover, the optical gap of 2.03 Ev for CsYb7S11 was deduced from the UV/Vis reflectance spectroscopy and DFT study indicates an indirect band gap with an electronic transfer excitation of S-3p to Yb-5d orbital.展开更多
Triglycine sulfate crystal and potassium bromide doped triglycine sulfate crystals were grown from aqueous solution by slow evaporation method. Energy dispersive X-ray analysis identifies the elements present in the c...Triglycine sulfate crystal and potassium bromide doped triglycine sulfate crystals were grown from aqueous solution by slow evaporation method. Energy dispersive X-ray analysis identifies the elements present in the crystal. The Fourier Transform Infrared spectroscopy has been recorded in the range 400 to 4000 cm-1 and the functional groups of the grown crystals have been identified. The structural studies on the grown crystals were carried out by X-ray diffraction analysis technique and found that the grown crystal crystallizes in monoclinic structure. The lattice cell parameters of pure Triglycine sulfate are a = 9.6010 ?, b = 12.5600 ?, c = 5.4500 ?. Ultraviolet-Visible spectra show that the grown crystals have wide optical transparency in the entire visible region.展开更多
In this paper, we analyze the two-dimensional Boat-shaped structure based on the finite element method. We calculated its energy band structure and vibration transmission properties and found that the structure has ba...In this paper, we analyze the two-dimensional Boat-shaped structure based on the finite element method. We calculated its energy band structure and vibration transmission properties and found that the structure has band gaps at both high and low frequencies. Compared with common traditional two- dimensional phononic crystals, the boat-shaped phononic crystal has the advantage of larger bandgap design and modulation parameter space due to their structural complexity. In order to obtain better bandgap characteristics, we studied the influence of four key parameters, such as the rod length and the angle between the rods, on the bandgap. The results show that: for low frequency band gaps, the width of the band gap can be effectively changed by changing the size of the angle between the rods while rod length greatly affects the bandgap position;for high band gaps, the length of rods has a large effect on the band gap position. These laws have guiding significance for the bandgap regulation of boat-shaped phononic crystal.展开更多
Using the plane-wave expansion method, the spin-wave band structures of two-dimensional magnonic crystals consisting of square arrays of different shape scatterers are calculated numerically, and the effects of rotati...Using the plane-wave expansion method, the spin-wave band structures of two-dimensional magnonic crystals consisting of square arrays of different shape scatterers are calculated numerically, and the effects of rotating rectangle and hexagon scaterers on the gaps are studied, respectively. The results show that the gaps can be substantially opened and tuned by rotating the scatterers. This approach should be helpful in designing magnonic crystals with desired gaps.展开更多
Band gaps of elastic waves in 1-D phononic crystals with imperfect interfaces were studied. By using the transfer matrix method （TMM） and the Bloch wave theory in the periodic structure, the dispersion equation was ...Band gaps of elastic waves in 1-D phononic crystals with imperfect interfaces were studied. By using the transfer matrix method （TMM） and the Bloch wave theory in the periodic structure, the dispersion equation was derived for the periodically lami- nated binary system with imperfect interfaces （the traction vector jumps or the displacement vector jumps）. The dispersion equation was solved numerically and wave band gaps were obtained in the Brillouin zone. Band gaps in the case of imperfect interfaces were compared with that in the case of perfect interfaces. The influence of imperfect interfaces on wave band gaps and some interesting phenomena were discussed.展开更多
The concept and analysis method of photonic crystals and band gaps are introduced into one-dimensional(1D) ordered mesoporous materials. MCM-41 type of materials are treated theoretically as photonic crystals. The for...The concept and analysis method of photonic crystals and band gaps are introduced into one-dimensional(1D) ordered mesoporous materials. MCM-41 type of materials are treated theoretically as photonic crystals. The formation of band gaps is exhibited and confirmed by a calculation of transfer matrix technique. PBG was found around 9-42 nm in soft X-ray region. The photonic band-gap was predicted to be dependent on incident direction, pore size and lattice constant. The mesoporous materials with different pore sizes and different lattice constants have different band-gap widths.展开更多
Theoretical study of the optical properties of one dimensional three component photonic band gap structure, which is composed of three alternating dielectric layers of different refractive indices and thickness in a...Theoretical study of the optical properties of one dimensional three component photonic band gap structure, which is composed of three alternating dielectric layers of different refractive indices and thickness in a unit cell, is performed. This one dimensional photonic band gap structure exhibits the transparency band and forbidden band. We find that there are several mini bands of the allowed transmission to be created within the photonic band gap region of the structure if a defect designed specially is introduced inside the structure. This characteristic is very important for some practical applications.展开更多
Two ternary europium chalcogenides, Eu1-xGa2Te4（x ≈ 0.19）（1） and EuY2Se4（2）, have been synthesized by a facile solid-state route using boron as the reducing reagent. Eu1-xGa2Te4 crystallizes in the tetragonal s...Two ternary europium chalcogenides, Eu1-xGa2Te4（x ≈ 0.19）（1） and EuY2Se4（2）, have been synthesized by a facile solid-state route using boron as the reducing reagent. Eu1-xGa2Te4 crystallizes in the tetragonal space group I4/mcm with a = 8.2880（9）, c = 6.7439（12） A, V = 463.24（13） A^3, and Z = 2. EuY2Se4 crystallizes in the orthorhombic space group Pnma with a = 12.4726（16）, b = 4.1204（6）, c = 14.849（2） A, V = 763.11（19） A^3, and Z = 4. Eu1-xGa2Te4 belongs to the Tl Se-type 3D closed structure, while EuY2Se4 adopts the CaFe2O4-type 3D channel structure. The optical band gap of Eu1-xGa2Te4 is determined to be 0.48 Ev. Electronic structures of 1 and 2 are calculated using TB-LMTO software.展开更多
基金the National Natural Science Foundation of China (10672017 and 10632020)
文摘In this paper, the elastic wave propagation in a two-dimensional piezoelectric phononic crystal is studied by considering the mechanic-electric coupling. The generalized eigenvalue equation is obtained by the relation of the mechanic and electric fields as well as the Bloch-Floquet theorem. The band structures of both the in-plane and anti-plane modes are calculated for a rectangular lattice by the planewave expansion method. The effects of the lattice constant ratio and the piezoelectricity with different filling fractions are analyzed. The results show that the largest gap width is not always obtained for a square lattice. In some situations, a rectangular lattice may generate larger gaps. The band gap characteristics are influenced obviously by the piezoelectricity with the larger lattice constant ratios and the filling fractions.
基金Acknowledgements We would like to thank the collaborations with Shanyu Liu, Xiaowen Jia, Junfeng He, Yingying Peng, Li Yu, Xu Liu, Guodong Liu, Shaolong He, Xiaoli Dong, Jun Zhang, Hangdong Wang, Chiheng Dong, Minghu Fang, J. B. He, D. M. Wang, G. F. Chert, J. G. Guo, X. L. Chen, Xiaoyang Wang, Qinjun Peng, Zhimin Wang, Shenjin Zhang, Feng Yang, Zuyan Xu, and Chuangtian Chen. This work was financially supported by the National Natural Science Foundation of China （Grant No. 10734120） and the State Key Development Program for Basic Research of China （973 program, Grant No. 2011CB921703）.
文摘The latest discovery of a new iron-chalcogenide superconductor AXFe2-ySe2 （A =K, Cs, Rb, and Tl, etc.） has attracted much attention due to a number of its unique characteristics, such as the possible insulating state of the parent compound, the existence of Fe-vacancy and its ordering, a new form of magnetic structure and its interplay with superconductivity, and the peculiar electronic structures that are distinct from other Fe-based superconductors. In this paper, we present a brief review on the structural, magnetic and electronic properties of this new superconductor, with an emphasis on the electronic structure and superconducting gap. Issues and future perspectives are discussed at the end of the paper.
基金supported by the National Natural Science Foundation of China(Nos.10672017 and 10632020).supports provided by the China Postdoctoral Science Foundation,Heilongjiang Province Postdoctoral Science Foundation
文摘The wave propagation is studied in two-dimensional disordered piezoelectric phononic crystals using the finite-difference time-domain （FDTD） method. For different cases of disorder, the transmission coefficients are calculated. The influences of disorders on band gaps are investigated. The results show that the disorder in the piezoelectric phononic crystals has more significant influences on the band gap in the low frequency regions than in the high frequency ones. The relation between the width of band gap and the direction of position disorder is also discussed. When the position disorder is along the direction perpendicular to the wave transmission, the piezoelectric phononic crystals have wider band gaps at low frequency regions than the case of position disorder being along the wave transmission direction. It can also be found that the effect of. size disorder on band gaps is analogous to that of location disorder. When the perturbation coefficient is big, it has more pronounced effects on the pass bands in the piezoelectric phononic crystals with both size and location disorders than in the piezoelectric phononic crystals with single disorder. In higher frequency regions the piezoelectric effect reduces the transmission coefficients. But for larger disorder degree, the effects of the piezoelectricity will be reduced.
基金supported by the National Natural Science Foundation of China (No.10672019)
文摘Band gaps of 2D phononic crystal with orthotropic cylindrical fillers embedded in the isotropic host are studied in this paper. Two kinds of periodic structures, namely, the square lattice and the triangle lattice, are considered. For anisotropic phononic crystal, band gaps not only depend on the periodic lattice but also the angle between the symmetry axis of orthotropic material and that of the periodic structure. Rotating these cylindrical fillers makes the angle changing continuously; as a result, pass bands and forbidden bands of the phononic crystal are changed. The plane wave expansion method is used to reduce the band gap problem to an eigenvalue problem. The numerical example is given for YBCO/Epoxy composites. The location and the width of band gaps are estimated for different rotating angles. The influence of anisotropy on band gaps is discussed based on numerical results.
基金supported by the National Natural Science Foundation of China(No.10632020).
文摘Absolute phononic band gaps can be substantially improved in two-dimensional lattices by using a symmetry reduction approach. In this paper, the propagation of elastic waves in a two-dirnensional hybrid triangular lattice structure consisting of stainless steel cylinders in air is investigated theoretically. The band structure is calculated with the plane wave expansion （PWE） method. The hybrid triangular Bravais lattice is formed by two kinds of triangular lattices. Different from ordinary triangular lattices, the band gap opens at low frequency （between the first and the second bands） regime because of lifting the bands degeneracy at high symmetry points of the Brillouin zone. The location and width of the band gaps can be tuned by the position of the additional rods.
基金supported by the NNSFC (20521101)NSF for Distinguished Young Scientist of China (20425104)+1 种基金NSF of Fujian Province (2007J0173)the Fund of Fujian Key Laboratory of Nanomaterials (2006L2005)
文摘Two new quaternary sulfides, KSmSiS4 （1） and KYbSiS4 （2）, have been synthesized by high-temperature solid-state reaction. Single,crystal X-ray diffraction analyses indicate that both compounds crystallize in the space group P21/m, and the crystal data are as follows： a = 6.426（11）, b = 6.582（11）, c = 8.602（15）A, β= 107.90（13）°, Z = 2, V= 346.2（10） A^3, Dc = 3.317 g/cm^3, F（000） = 318,μ（MoKα） = 10.334 mm^-1, the final R = 0.0559 and wR = 0.1370 for 1; and α= 6.3244（10）, b = 6.5552（10）, c = 8.5701（15）A, β= 108.001（13）°, Z = 2, V = 337.91（9） A^3, De= 3.621 g/cm^3, F（000） = 334, μ（MoKα） = 15.737 mm^-1, the final R = 0.0422 and wR = 0.0960 for 2. The KLnSiS4 （Ln = Sm, Yb） structure consists of corrugated ∞^2 [LnSiS4]^- layers which are formed by edge-sharing LnS8 bicapped trigonal prisms and SiS4 tetrahedra. The K^＋ cations are located in the cavities defined by S2 anions between the ∞^2[LnSiS4]^- layers. Band-gap analyses show that compounds 1 and 2 are semiconductors with optical band-gaps of 2.40 and 2.34 eV, respectively.
基金supported by the National Natural Science Foundation of China (Grant No. 10904176)the National Key Basic Research Special Foundation of China (Grant No. 2006CB921702)+1 种基金the Research Foundation of the State Ethnic Affairs Commission of China (Grant No. 09ZY012)the NMOE Project of China (Grant No. 200911002)
文摘Absolute band gaps of a two-dimensional triangular-lattice photonic crystal are calculated with the finite-difference time-domain method in this paper.Through calculating the photonic band structures of the triangular-lattice photonic crystal consisting of Ge rods immersed in air with different shapes,it is found that a large absolute band gap of 0.098 (2c/a) can be obtained for the structures with hollow triangular Ge rods immersed in air,corresponding to 19.8% of the middle frequency.The influence of the different factors on the width of the absolute band gaps is also discussed.
基金Project supported by the National Natural Science Foundation of China(Nos.11272126,51435006,and 51121002)the Fundamental Research Funds for the Central Universities(Nos.HUST:2016JCTD114 and HUST:2015TS121)
文摘A folding beam-type piezoelectric phononic crystal model is proposed to isolate vibration. Two piezoelectric bimorphs are joined by two masses as a folding structure to comprise each unit cell of the piezoelectric phononic crystal. Each bimorph is connected independently by a resistive-inductive resonant shunting circuit. The folding structure extends the propagation path of elastic waves, while its structure size remains quite small. Propagation of coupled extension-flexural elastic waves is studied by the classical laminated beam theory and transfer matrix method. The theoretical model is further verified with the finite element method(FEM). The effects of geometrical and circuit parameters on the band gaps are analyzed. With only 4 unit cells, the folding beam-type piezoelectric phononic crystal generates two Bragg band gaps of 369 Hz to1 687 Hz and 2 127 Hz to 4 000 Hz. In addition, between these two Bragg band gaps, a locally resonant band gap is induced by resonant shunting circuits. Appropriate circuit parameters are used to join these two Bragg band gaps by the locally resonant band gap.Thus, a low-frequency and broad band gap of 369 Hz to 4 000 Hz is obtained.
基金Supported by the National Natural Science Foundation of China(90922021,20773130,20733003,20803080,20973175)"Knowledge Innovation Program of the Chinese Academy of Sciences"(KJCX2-YW-H20,CXJJ-11-M71)
文摘A new quaternary rare-earth sulfide, Cs0.75（6）Er443（5）In3.32（6）S12 （1）, is discovered by high temperature solid state reactions with a slight excess of CsCI flux. The structure is characterized by single-crystal X-ray diffraction data, while crystallizes in hexagonal space group P63/m （No. 176） with a = 12.0329（6）, c = 3.8693（5）A, V= 485.18（7） A3, Z = 1, Mr = 1606.57, Dc = 5.499 g/cm3,μ = 25.457 mm-1, F（000） = 752, the final R = 0.0337 and wR = 0.0904 for 328 observed reflections with I 〉 2σ（I）. Its structure features a three-dimensional framework with hexagonal channels that are centered by Cs cations. Such channels are formed by double chains of edge-sharing M（1）S6 （M（1） = Er（1）/In（1）） octahedra and single chains of Er（2）S6 triprism interconnected by corner-sharing. The syntheses, single-crystal analyses, optical band gap and magnetic property are reported.
文摘对纳米 Ga P粉体 -结晶紫水溶液光催化降解进行了研究。纳米 Ga P粉体在紫外光照射条件下对结晶紫具有光催化降解作用 ;随平均颗粒度的降低 ,纳米 Ga P粉体的光催化活性增加。红外光谱测试结果表明 :进行光催化过程以后 ,纳米 Ga P表面存在的几种主要振动模式变化较小或不变 ;拉曼光谱测试结果表明 :纳米 Ga P粉体的横向光学声子模与纵向光学声子模 。
基金supported by the National Natural Science Foundation of China(21301175,21233009,21571020 and 91422303)the Natural Science Foundation of Fujian Province(2015J01071)
文摘A novel ternary rare-earth sulfide, CsYb7S（11）, has been successfully synthesized by high-temperature solid-state reaction of an elemental mixture with modified Cs Cl flux. The single-crystal X-ray diffraction data reveal its orthorhombic symmetry in space group Cmca（no. 64） with a = 15.271（3）, b = 13.414（2）, c = 18.869（3） A°, V = 3865.2（2） A°^3, Z = 8, Mr = 1696.85, Dc = 5.832 g/cm^3, μ = 36.538 mm^-1, F（000） = 5768, the final R = 0.0225 and w R = 0.0517 for 2258 observed reflections with I 〉 2σ（I）, 2.67〈θ〈27.48o, w = 1/[σ^2（Fo^2） ＋（0.0443 P）2 ＋ 8.7453 P], where P =（Fo^2 ＋ 2Fc^2）/3, S = 1.036,（Δρ）max = 1.609 and（Δρ）min = –1.922. The remarkable structural feature is the dual tricapped Cs2@S18 cube closed cavities far apart within the three-dimensional [Yb7S（11）]-covalent bonding matrix. Magnetic susceptibility measurements show that the title compound exhibits temperature-dependent（50～300 K） para-magnetism and obey the Curie-Weiss law. Moreover, the optical gap of 2.03 Ev for CsYb7S11 was deduced from the UV/Vis reflectance spectroscopy and DFT study indicates an indirect band gap with an electronic transfer excitation of S-3p to Yb-5d orbital.
文摘Triglycine sulfate crystal and potassium bromide doped triglycine sulfate crystals were grown from aqueous solution by slow evaporation method. Energy dispersive X-ray analysis identifies the elements present in the crystal. The Fourier Transform Infrared spectroscopy has been recorded in the range 400 to 4000 cm-1 and the functional groups of the grown crystals have been identified. The structural studies on the grown crystals were carried out by X-ray diffraction analysis technique and found that the grown crystal crystallizes in monoclinic structure. The lattice cell parameters of pure Triglycine sulfate are a = 9.6010 ?, b = 12.5600 ?, c = 5.4500 ?. Ultraviolet-Visible spectra show that the grown crystals have wide optical transparency in the entire visible region.
文摘In this paper, we analyze the two-dimensional Boat-shaped structure based on the finite element method. We calculated its energy band structure and vibration transmission properties and found that the structure has band gaps at both high and low frequencies. Compared with common traditional two- dimensional phononic crystals, the boat-shaped phononic crystal has the advantage of larger bandgap design and modulation parameter space due to their structural complexity. In order to obtain better bandgap characteristics, we studied the influence of four key parameters, such as the rod length and the angle between the rods, on the bandgap. The results show that: for low frequency band gaps, the width of the band gap can be effectively changed by changing the size of the angle between the rods while rod length greatly affects the bandgap position;for high band gaps, the length of rods has a large effect on the band gap position. These laws have guiding significance for the bandgap regulation of boat-shaped phononic crystal.
基金supported by the National Natural Science Foundation of China(Grant Nos.11264028 and 11072104)the Natural Science Foundation of Inner Mongolia Autonomous Region of China(Grant No.2012MS0114)the School Scientific Research Funds of Inner Mongolia Normal University of China(Grant Nos.2013YJRC007 and 2013ZRYB19)
文摘Using the plane-wave expansion method, the spin-wave band structures of two-dimensional magnonic crystals consisting of square arrays of different shape scatterers are calculated numerically, and the effects of rotating rectangle and hexagon scaterers on the gaps are studied, respectively. The results show that the gaps can be substantially opened and tuned by rotating the scatterers. This approach should be helpful in designing magnonic crystals with desired gaps.
基金supported by the National Natural Science Foundation of China (No.10672019)
文摘Band gaps of elastic waves in 1-D phononic crystals with imperfect interfaces were studied. By using the transfer matrix method （TMM） and the Bloch wave theory in the periodic structure, the dispersion equation was derived for the periodically lami- nated binary system with imperfect interfaces （the traction vector jumps or the displacement vector jumps）. The dispersion equation was solved numerically and wave band gaps were obtained in the Brillouin zone. Band gaps in the case of imperfect interfaces were compared with that in the case of perfect interfaces. The influence of imperfect interfaces on wave band gaps and some interesting phenomena were discussed.
文摘The concept and analysis method of photonic crystals and band gaps are introduced into one-dimensional(1D) ordered mesoporous materials. MCM-41 type of materials are treated theoretically as photonic crystals. The formation of band gaps is exhibited and confirmed by a calculation of transfer matrix technique. PBG was found around 9-42 nm in soft X-ray region. The photonic band-gap was predicted to be dependent on incident direction, pore size and lattice constant. The mesoporous materials with different pore sizes and different lattice constants have different band-gap widths.
文摘Theoretical study of the optical properties of one dimensional three component photonic band gap structure, which is composed of three alternating dielectric layers of different refractive indices and thickness in a unit cell, is performed. This one dimensional photonic band gap structure exhibits the transparency band and forbidden band. We find that there are several mini bands of the allowed transmission to be created within the photonic band gap region of the structure if a defect designed specially is introduced inside the structure. This characteristic is very important for some practical applications.
基金supported by NNSFC(21771159)NSF of Yangzhou(YZ2016122)State Key Lab of Structural Chemistry Fund(20150009)
文摘Two ternary europium chalcogenides, Eu1-xGa2Te4（x ≈ 0.19）（1） and EuY2Se4（2）, have been synthesized by a facile solid-state route using boron as the reducing reagent. Eu1-xGa2Te4 crystallizes in the tetragonal space group I4/mcm with a = 8.2880（9）, c = 6.7439（12） A, V = 463.24（13） A^3, and Z = 2. EuY2Se4 crystallizes in the orthorhombic space group Pnma with a = 12.4726（16）, b = 4.1204（6）, c = 14.849（2） A, V = 763.11（19） A^3, and Z = 4. Eu1-xGa2Te4 belongs to the Tl Se-type 3D closed structure, while EuY2Se4 adopts the CaFe2O4-type 3D channel structure. The optical band gap of Eu1-xGa2Te4 is determined to be 0.48 Ev. Electronic structures of 1 and 2 are calculated using TB-LMTO software.
