By analyzing the optical spectra and electron paramagnetic resonance parameter D, the local structure distortion of （NiF6）4- clusters in AMF3 （A=K, Rb; M=Zn, Cd, Ca） and K2ZnF4 series are studied using the complet...By analyzing the optical spectra and electron paramagnetic resonance parameter D, the local structure distortion of （NiF6）4- clusters in AMF3 （A=K, Rb; M=Zn, Cd, Ca） and K2ZnF4 series are studied using the complete energy matrix based on the double spin-orbit coupling parameter model for configuration ions in a tetragonal ligand field. The results indicate that the contribution of ligand to spin-orbit coupling interaction should be considered for our studied systems. Moreover, the relationships between D and the spin-obit coupling coefficients as well as the average parameter and the divergent parameter are discussed.展开更多
ZnO thin films co-doped with A1 and Sb with different concentrations and a fixed molar ratio of AlCl3 to SbCl3 at 1：2, are prepared by a sol-gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-r...ZnO thin films co-doped with A1 and Sb with different concentrations and a fixed molar ratio of AlCl3 to SbCl3 at 1：2, are prepared by a sol-gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al distortion, and the biaxial stresses are 1.03× 10^8. 3.26× 10^8 and Sb are of wurtzite hexagonal ZnO with a very small 5.23 × 10^8, and 6.97× 10^8 Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5 Ω·cm.展开更多
Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgA...Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99.展开更多
The local structure distortion, the spin Hamiltonian （SH） parameters, and the electric fine structure of the ground state for Mn^2＋ （3d^5） ion in ZnO crystals are systematically investigated, where spin-spin （SS...The local structure distortion, the spin Hamiltonian （SH） parameters, and the electric fine structure of the ground state for Mn^2＋ （3d^5） ion in ZnO crystals are systematically investigated, where spin-spin （SS）, spin-other-orbit （SOO） and orbit-orbit （OO） magnetic interactions, besides the well-known spin-orbit （SO） coupling, are taken into account for the first time, by using the complete diagonalization method. The theoretical results of the second-order zerofield splitting （ZFS） parameter D, the fourth-order ZFS parameter （a-F）, the Zeeman g-factors： g// and g⊥, and the energy differences of the ground state： δ1 and δ2 for Mn^2＋ in Mn^2＋： ZnO are in good agreement with experimental measurements when the three O^2- ions below the Mn^2＋ ion rotate by 1.085° away from the [111]-axis. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Mn^2＋ ions in Mn^2＋： ZnO crystals. It is found for Mn^2＋ ions in Mn^2＋： ZnO crystals that although the SO mechanism is the most important one, the contributions to the SH parameters, made by other four mechanisms, i.e. SS, SOO, OO, and SO-SS-SOO-OO mechanisms, are significant and should not be omitted, especially for calculating ZFS parameter D.展开更多
The quantitative relationship between the spin Hamiltonian parameters （D, g｜｜ Ag） and the crystal structure parameters for the Cr3＋-Vzη tetragonal defect centre in a Cr3＋ ：KZnF3 crystal is established by using...The quantitative relationship between the spin Hamiltonian parameters （D, g｜｜ Ag） and the crystal structure parameters for the Cr3＋-Vzη tetragonal defect centre in a Cr3＋ ：KZnF3 crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr3＋-Vzn tetragonal defect centre in the KZnF3 crystal are systematically investigated using the complete diagonalization method. It is found that the Vzn vacancy and the differences in mass, radius and charge between the Cr3＋ and the Zn2＋ ions induce the local lattice distortion of the Cr3＋ centre ions in the KZnF3 crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Ag. We find that the ligand F- ion along I001] and the other five F- ions move towards the central Cr3＋ by distances of A1 = 0.0121 nm and A2 = 0.0026 nm, respectively. Our approach takes into account the spin-rbit interaction as well as the spin-spin, spin other-orbit, and orbit-rbit interactions omitted in the previous studies. It is found that for the Cr3＋ ions in the Cr3＋：KZnF3 crystal, although the spin-rbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin- spin, spin-other-orbit, and orbit-orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting （ZFS） parameter D.展开更多
Na^＋ doped sample Li0.95Na0.05FePO4 was prepared through solid state method. Structure characterization shows Na^＋ is successfully introduced into the LiFePO4 matrix. Scanning electron microscopy shows the particle ...Na^＋ doped sample Li0.95Na0.05FePO4 was prepared through solid state method. Structure characterization shows Na^＋ is successfully introduced into the LiFePO4 matrix. Scanning electron microscopy shows the particle size mainly ranges in 1-3 μm. X-ray diffraction Rietveld refinement demonstrates lattice distortion with an increased cell volume. As one cathode material, it has a discharge capacity of 150 mAh/g at 0.1 C rate. The material exhibits a capacity of 109 and 107 mAh/g at 5 and 7.5 C respectively. When cycled at 1 and 5 C, the material retains 84% （after 1000 cycles） and 86% （after 350 cycles） of the initial discharge capacity respectively indicating excellent structure stability and cycling performance. Na^＋ doping enhances the electrochemical activity especially the cycle performance effectively.展开更多
The electron paramagnetic resonance（EPR） spectra of trigonal Mn^（2＋） centers in Zn（ClO4）2·6（H2O） and Mg（ClO4）2·6（H2O） crystals were studied on the basis of the complete energy matrices for a d^5...The electron paramagnetic resonance（EPR） spectra of trigonal Mn^（2＋） centers in Zn（ClO4）2·6（H2O） and Mg（ClO4）2·6（H2O） crystals were studied on the basis of the complete energy matrices for a d^5 configuration ion in a trigonal ligand field. It was demonstrated that the local lattice structure around a trigonal Mn^（2＋） center has an compressed distortion along the crystalline c3 axis, and when Mn^（2＋） is doped in the Zn（ClO4）2·6（H2O） and Mg（ClO4）2·6（H2O） crystals, there is a similar local distortion. From the EPR calculation, the local lattice structure parameters R=2.183 2 ？, for Zn（ClO4）2·6（H2O）, R=2.130 2 ？, for Mg（ClO4）2·6（H2O） have been determined.展开更多
Cobalt hexacyanoferrate (CoHCF) is a potential cathode for aqueous Na-ion batteries due to its high theoretical specific capacity (170 m Ah g^(-1));however,its lower rate capability and cyclability limit its applicati...Cobalt hexacyanoferrate (CoHCF) is a potential cathode for aqueous Na-ion batteries due to its high theoretical specific capacity (170 m Ah g^(-1));however,its lower rate capability and cyclability limit its applications.Structural distortion at a weak N-coordinated crystal field during cycling disintegrates Co,yielding an irreversible reaction.Different Zn amounts ranging 0–1 were added to the Co site to suppress the structural irreversibility of CoHCF,yielding Co_(1-x)Zn_(x)HCF powder;this Zn (x≤0.09) addition reduced the powder’s dimension because the lower four coordination of Zn–N,not the six coordination of Co–N,limits the powder growth.Simultaneously,a small lattice parameter and interaxial angle (~90°) are obtained,implying that a narrower Co_(1-x)Zn_(x)HCF inner structure is formed to accommodate Na ions.Moreover,the electronic conductivity of Co_(1-x)Zn_(x)HCF gradually increased within 0–0.09 range.A smaller particle size with a high surface area leads to a near-surface-limited redox process,similar to a capacitive reaction.Both the surface-limited reaction and electronic conductivity enhances the reversibility due to the smaller charge transfer resistance at the electrode/electrolyte interface caused by Zn addition.Replacing redox-active Co with non-active Zn amount of 0.07 (Co_(1-x)Zn_(x)HCF) slightly reduces the specific capacity from 127 to 119 mAh g^(-1)at 0.1 A g^(-1)due to the shrunken Co charging sites.Rate performance is enhanced by compromising the capacity and reduced distortion,resulting in 81%retention at a 20-times-faster charging rate.Notably,the Co_(1-x)Zn_(x)HCF sample exhibited the good stability while preserving 74%of the initial capacity at 0.5 A g^(-1)after 200 cycles.展开更多
We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magne...We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_(p)~140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near Tp, i.e.,?L_(c)/L_(c)~0.062%. The structural characterization confines that there is no structure transition below and above T_(p). All these results suggest that the nonmagnetic transition of SrCu_(4-x)P_(2) could be associated with structural distortion.展开更多
X-ray absorption spectra （XAS） at Mn K-edge and Fe K-edge in LaMnl-xFexO3 show that with the increase of Fe substitution the chemical valence of Mn4＋ decreases, while the chemical valence of Fe3＋ remains unchanged...X-ray absorption spectra （XAS） at Mn K-edge and Fe K-edge in LaMnl-xFexO3 show that with the increase of Fe substitution the chemical valence of Mn4＋ decreases, while the chemical valence of Fe3＋ remains unchanged. Structural distortions, such as the rotating and tilting for oxygen octahedron in the unit cell vary with iron content. A phase transition occurs at the Fe content values of 0.2~0.3. The evolutions of rotation and tilting angle of FeO6/MnO6 octahedral may be the vital factors to the structure and magnetism. We believe that the spin configuration of Fe3＋ may vary from the intermediate spin t2g4eg1 （S = 3/2） to the higher spin t2g3eg2 （S = 5/2） near the phase transition.展开更多
Valleytronics is an emergent discipline in condensed matter physics and offers a new way to encode and manipulate information based on the valley degree of freedom in materials. Among the various materials being studi...Valleytronics is an emergent discipline in condensed matter physics and offers a new way to encode and manipulate information based on the valley degree of freedom in materials. Among the various materials being studied, Kekulé distorted graphene has emerged as a promising material for valleytronics applications. Graphene can be artificially distorted to form the Kekulé structures rendering the valley-related interaction. In this work, we review the recent progress of research on Kekulé structures of graphene and focus on the modified electronic bands due to different Kekulé distortions as well as their effects on the transport properties of electrons. We systematically discuss how the valley-related interaction in the Kekulé structures was used to control and affect the valley transport including the valley generation, manipulation, and detection. This article summarizes the current challenges and prospects for further research on Kekulé distorted graphene and its potential applications in valleytronics.展开更多
Manganese oxides have received extensive attention in Oxygen Reduction Reaction(ORR)research.How-ever,the poor electrical conductivity and oxygen adsorption capacity of manganese oxides limit their development,so it i...Manganese oxides have received extensive attention in Oxygen Reduction Reaction(ORR)research.How-ever,the poor electrical conductivity and oxygen adsorption capacity of manganese oxides limit their development,so it is necessary to prepare catalysts with highly active surfaces.We propose a method to introduce an ionically conductive medium and induce structural distortion via thermodynamics,re-sulting in novel peak-splitting highly active structures for enhanced oxygen reduction activity.With the aid of refined structural analysis,High-angle annular dark-field(HAADF-STEM)imaging,and theoretical calculations,it is elucidated that this peak-splitting structure results from thermodynamically induced structural distortions and atomic displacements.The introduction of the ionically conductive medium promotes the formation of Ag-O-Mn conductive bond bridges,which regulate the energy level matching of manganese oxides and oxygen intermediates.The thermodynamically induced structural distortion ex-poses new atomic planes in the material,and the creation of this highly active surface is accompanied by a redistribution of surface charges,which modulates the adsorption of manganese active sites with oxy-gen intermediates and greatly enhances the oxygen reduction activity.Specifically,this Ag-OMS-2 with a novel split structure exhibits excellent activity at 0.836 V,superior to Pt/C kinetics and good stability.The preparation of such highly active structures is instructive for the development of manganese oxides.展开更多
We systematically investigated the structural and superconducting properties of polycrystalline 2H-Li_(x)TaSe_(2)(0.1≤x≤1.0)synthesized via a high-temperature solid-state reaction.Lithium(Li)intercalation induces an...We systematically investigated the structural and superconducting properties of polycrystalline 2H-Li_(x)TaSe_(2)(0.1≤x≤1.0)synthesized via a high-temperature solid-state reaction.Lithium(Li)intercalation induces an expansion along the c-axis and intralayer distortions within the Ta-Se coordination network.The superconducting transition temperature(T_(c))is increased to 2.95 K at x=0.1 driven by the synergistic enhancement of the electronic density of states at the Fermi level,N(EF),and strengthened electron-phonon coupling.With further Li doping,although N(EF)continues to increase,lattice stiffening and pronounced distortions in the Ta-Se coordination polyhedra weaken the electron-phonon interaction,ultimately suppressing superconductivity.These findings highlight the critical role of intralayer structural modulation in governing structure-tunable superconductivity in layered materials.展开更多
The electron paramagnetic spectra of trigonal Mn^(2+) centers in[Co(H_(2)O)_(6)]SiF6,[Co(H_(2)O)_(6)]SnF6,and[Co(H_(2)O)_(6)]PtCl6 crystals were studied on the basis of the complete energy matrices for a d5 configurat...The electron paramagnetic spectra of trigonal Mn^(2+) centers in[Co(H_(2)O)_(6)]SiF6,[Co(H_(2)O)_(6)]SnF6,and[Co(H_(2)O)_(6)]PtCl6 crystals were studied on the basis of the complete energy matrices for a d5 configuration ion in a trigonal ligand field.When Mn^(2+) is doped in the[Co(H_(2)O)_(6)]SiF6,[Co(H_(2)O)_(6)]SnF6,and[Co(H_(2)O)_(6)]PtCl6 crystals crystals,there is a similar local distortion.The experimental results show that the local lattice structure around a trigonal Mn^(2+) center has an elongation distortion along the crystalline C3 axis.From the EPR calculation,the local lattice structure parameters R=2.278A,θ=52.6406? for[Co(H_(2)O)_(6)]SiF6,R=2.280,θ=52.4936° for[Co(H_(2)O)_(6)]SnF6 and R=2.244A,θ=53.0616? for[Co(H_(2)O)_(6)]PtCl6 were determined.展开更多
In this work, hierarchical BiOBr<sub>1<span style="white-space:nowrap;">−x</sub>I<sub>x</sub>/BiOBr heterojunction photocatalyst with a microsphere morphology was synth...In this work, hierarchical BiOBr<sub>1<span style="white-space:nowrap;">−x</sub>I<sub>x</sub>/BiOBr heterojunction photocatalyst with a microsphere morphology was synthesized by a facile solvothermal process. It demonstrated that the local structure of the photocatalysts was highly distorted due to the substitution of bromide ions by iodine ions. The photocatalytic properties were evaluated by the photodecomposition of aqueous phenol solution under visible-light irradiation. The results indicated that all the composite photocatalysts exhibited high photocatalytic activity. In particularly, the BiOBr<sub>1<span style="white-space:nowrap;">−x</sub>I<sub>x</sub>/BiOBr (x = 0.25) sample exhibited over 92% degradation efficiency of phenol within 150 min, which is 24.6 and 3.08 fold enhancement in the photocatalytic activity over the pure phased BiOBr and BiOI, respectively. Moreover, this excellent photocatalytic property can be expanded to other colorless organic contaminants, verifying the common applicability of BiOBr<sub>1<span style="white-space:nowrap;">−x</sub>I<sub>x</sub>/BiOBr (x = 0.25) as an excellent visible-light photocatalyst for organics decomposition. The significant improvement in the photocatalytic activity can be explained by the high efficiency of charge separation due to the enhancement in the internal electric fields and band match that comes from the local structure distortion. This work provides valuable information for the design of highly active photocatalysts toward the environmental remediation.展开更多
Polycrystalline BiFeO3 and rare earth substituted Bio.gRo.lFeO3 （BRFO, R=Y, Ho and Er） compounds were prepared by rapid solid state sintering technique. Structural phase analysis indicated that all the compounds sta...Polycrystalline BiFeO3 and rare earth substituted Bio.gRo.lFeO3 （BRFO, R=Y, Ho and Er） compounds were prepared by rapid solid state sintering technique. Structural phase analysis indicated that all the compounds stabilized in rhombohedral structure （R3c space group） and a small orthorhombic phase fraction was observed in BRFO compounds. From the Raman spectra results, the changes in the phonon frequencies （A1） and line widths suggested lattice distortion in the BRFO compounds as was evidenced in the XRD analysis. Compared to the linear variation of magnetization with magnetic field （M-H） shown by BFO, an obvious M-H loop was observed in BRFO compounds which could be due to the suppression of space modulated spin structure and was explained on the basis of weak ferromagnetism and field induced spin reorientation. UV-Vis spectroscopy evidenced a change in local FeO6 envi- ronment due to shift in the 6Alg→4T2g energy transition band. BRFO compounds with improved remnant magnetization and coercive field are applicable for magnetoelectric devices.展开更多
The crystal structure,magnetization,and spontaneous magnetostriction of ferromagnetic Laves phase Gd Fe2 compound have been investigated.High resolution synchrotron x-ray diffraction（XRD） analysis shows that Gd Fe2 ...The crystal structure,magnetization,and spontaneous magnetostriction of ferromagnetic Laves phase Gd Fe2 compound have been investigated.High resolution synchrotron x-ray diffraction（XRD） analysis shows that Gd Fe2 has a lower cubic symmetry with easy magnetization direction（EMD） along [100] below Curie temperature TC.The replacement of Gd with a small amount of Tb changes the EMD to [111].The Curie temperature decreases while the field dependence of the saturation magnetization（Ms） measured in temperature range 5–300 K varies with increasing Tb concentration.Coercivity Hc increases with increasing Tb concentration and decays exponentially as temperature increases.The anisotropy in Gd Fe2 is so weak that some of the rare-earth substitution plays an important role in determining the easy direction of magnetization in GdFe_2.The calculated magnetostrictive constant λ100 shows a small value of 37×10^（-6）.This value agrees well with experimental data 30×10^（-6）.Under a relatively small magnetic field,GdFe_2 exhibits a V-shaped positive magnetostriction curve.When the field is further increased,the crystal exhibits a negative magnetostriction curve.This phenomenon has been discussed in term of magnetic domain switching.Furthermore,magnetostriction increases with increasing Tb concentration.Our work leads to a simple and unified mesoscopic explanation for magnetostriction in ferromagnets.It may also provide insight for developing novel functional materials.展开更多
To insight into the B-site ordering in RFe_(0.5)Cr_(0.5)O_(3)ceramics,a series of RFe_(0.5)Cr_(0.5)O_(3)ceramics(R=La,Y,Lu)were synthesized by the sol-gel method,and the structural and magnetic properties were systemi...To insight into the B-site ordering in RFe_(0.5)Cr_(0.5)O_(3)ceramics,a series of RFe_(0.5)Cr_(0.5)O_(3)ceramics(R=La,Y,Lu)were synthesized by the sol-gel method,and the structural and magnetic properties were systemically investigated.By using the Rietveld refinement of all samples,it is found that the structural distortion is increased as the R ionic radius decreases,leading to the weakened interactions between Fe/Cr ions.Moreover,the Fe and Cr are arranged in disorder in LaFe_(0.5)Cr_(0.5)O_(3),but partially ordered in YFe_(0.5)Cr_(0.5)O_(3)and LuFe_(0.5)Cr_(0.5)O_(3),showing an increasing trend of the proportion of ordered domains with the decrease of R ionic radius.Through fitting the temperature-dependent magnetizations,it is identified that the magnetization reversal(MR)in disorder LaFe_(0.5)Cr_(0.5)O_(3)is resulted from the competition between the moments of Cr and Fe sublattices.In the partially ordered YFe_(0.5)Cr_(0.5)O_(3)and LuFe_(0.5)Cr_(0.5)O_(3)ceramics,because of the presence of Fe-O-Cr networks in the ordered domains whose moment is antiparallel to that of Fe-O-Fe and Cr-O-Cr in the disordered domains,the compensation temperature T_(comp)of MR is increased by nearly 50 K.These results suggest that the changing of R-site ions could be used very effectively to modify the Fe-O-Cr ordering,apart from the structural distortion,which has a direct effect on the magnetic exchange interactions in RFe_(0.5)Cr_(0.5)O_(3)ceramics.Then at values of composition where ordered domains are expected to be larger in number as compared to disordered domains and with a weaker structural distortion,one can expect a higher transition temperature Tcomp,providing a different view for adjustment of the magnetic properties of RFe_(0.5)Cr_(0.5)O_(3)ceramics for practical applications.展开更多
In this paper, the magnetic and transport properties in ABO3-type perovskite-like manganites as functions of the structure have been discussed from the viewpoints of A- and B-site doping, respectively. For the A-site ...In this paper, the magnetic and transport properties in ABO3-type perovskite-like manganites as functions of the structure have been discussed from the viewpoints of A- and B-site doping, respectively. For the A-site doping, two simple parameters, tolerance factor t and variance of the A-cation radius distribution s, can be used to characterize the magnetic/resistive phase diagram. For the B-site doping, the case is complicated due to the direct action to the center of double exchange. However, the dopant-size-induced local strain effect plays an important role in the physical properties besides the size mismatch between A- and B-site ions.展开更多
To enhance the thermoelectric performance of Cu2GeSe3, a series of Te-alloyed samples Cu2Ge（Se（1-x）Tex）3 are synthesized and investigated in this work. It is found that the lattice thermal conductivity is reduced ...To enhance the thermoelectric performance of Cu2GeSe3, a series of Te-alloyed samples Cu2Ge（Se（1-x）Tex）3 are synthesized and investigated in this work. It is found that the lattice thermal conductivity is reduced drastically for x = 0.1 sample, which may be attributed to the point defects introduced by alloying. However, for samples with x ≥ 0.2, the lattice thermal conductivity increases with increasing x, which is related to a less distorted structure. The structure evolution,together with the change in carrier concentration, also leads to a systemically change in electrical properties. Finally, a z T of 0.55@750 K is obtained for the sample with x = 0.3, about 62% higher than that for the pristine sample.展开更多
文摘By analyzing the optical spectra and electron paramagnetic resonance parameter D, the local structure distortion of （NiF6）4- clusters in AMF3 （A=K, Rb; M=Zn, Cd, Ca） and K2ZnF4 series are studied using the complete energy matrix based on the double spin-orbit coupling parameter model for configuration ions in a tetragonal ligand field. The results indicate that the contribution of ligand to spin-orbit coupling interaction should be considered for our studied systems. Moreover, the relationships between D and the spin-obit coupling coefficients as well as the average parameter and the divergent parameter are discussed.
基金Project supported by the Innovation Foundation of Beijing University of Aeronautics and Astronautics for PhD Graduates, China (Grant No. 292122)the Equipment Research Foundation of China (Grant No. 373974)
文摘ZnO thin films co-doped with A1 and Sb with different concentrations and a fixed molar ratio of AlCl3 to SbCl3 at 1：2, are prepared by a sol-gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al distortion, and the biaxial stresses are 1.03× 10^8. 3.26× 10^8 and Sb are of wurtzite hexagonal ZnO with a very small 5.23 × 10^8, and 6.97× 10^8 Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5 Ω·cm.
基金Project supported by the National Natural Science Foundation of China(Grant No.11675255)the National Key R&D Program of China(Grant No.2016YFA0401503).
文摘Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99.
基金supported by the Science and Technology Foundation of Shaanxi Province,China (Grant No 2006K04-G29)the National Defense Foundation of China (Grant No EP060302)the Key Research Foundation of Baoji University of Arts and Sciences,China (Grant No ZK0842)
文摘The local structure distortion, the spin Hamiltonian （SH） parameters, and the electric fine structure of the ground state for Mn^2＋ （3d^5） ion in ZnO crystals are systematically investigated, where spin-spin （SS）, spin-other-orbit （SOO） and orbit-orbit （OO） magnetic interactions, besides the well-known spin-orbit （SO） coupling, are taken into account for the first time, by using the complete diagonalization method. The theoretical results of the second-order zerofield splitting （ZFS） parameter D, the fourth-order ZFS parameter （a-F）, the Zeeman g-factors： g// and g⊥, and the energy differences of the ground state： δ1 and δ2 for Mn^2＋ in Mn^2＋： ZnO are in good agreement with experimental measurements when the three O^2- ions below the Mn^2＋ ion rotate by 1.085° away from the [111]-axis. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Mn^2＋ ions in Mn^2＋： ZnO crystals. It is found for Mn^2＋ ions in Mn^2＋： ZnO crystals that although the SO mechanism is the most important one, the contributions to the SH parameters, made by other four mechanisms, i.e. SS, SOO, OO, and SO-SS-SOO-OO mechanisms, are significant and should not be omitted, especially for calculating ZFS parameter D.
基金Projects supported by the Natural Science Foundation of Shaanxi Province,China (Grant No.2010JM1015)the Special Scientific Program of the Education Department of Shaanxi Province,China (Grant No.11JK0537)the Baoji University of Arts and Sciences Key Research,China (Grant No.ZK0842)
文摘The quantitative relationship between the spin Hamiltonian parameters （D, g｜｜ Ag） and the crystal structure parameters for the Cr3＋-Vzη tetragonal defect centre in a Cr3＋ ：KZnF3 crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr3＋-Vzn tetragonal defect centre in the KZnF3 crystal are systematically investigated using the complete diagonalization method. It is found that the Vzn vacancy and the differences in mass, radius and charge between the Cr3＋ and the Zn2＋ ions induce the local lattice distortion of the Cr3＋ centre ions in the KZnF3 crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Ag. We find that the ligand F- ion along I001] and the other five F- ions move towards the central Cr3＋ by distances of A1 = 0.0121 nm and A2 = 0.0026 nm, respectively. Our approach takes into account the spin-rbit interaction as well as the spin-spin, spin other-orbit, and orbit-rbit interactions omitted in the previous studies. It is found that for the Cr3＋ ions in the Cr3＋：KZnF3 crystal, although the spin-rbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin- spin, spin-other-orbit, and orbit-orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting （ZFS） parameter D.
基金V. ACKNOWLEDGMENTS The work was supported by the Natural Science Foundation of Anhui province （No.90414178） and USTC-NSRL Association funding （No.KY2060030010）.
文摘Na^＋ doped sample Li0.95Na0.05FePO4 was prepared through solid state method. Structure characterization shows Na^＋ is successfully introduced into the LiFePO4 matrix. Scanning electron microscopy shows the particle size mainly ranges in 1-3 μm. X-ray diffraction Rietveld refinement demonstrates lattice distortion with an increased cell volume. As one cathode material, it has a discharge capacity of 150 mAh/g at 0.1 C rate. The material exhibits a capacity of 109 and 107 mAh/g at 5 and 7.5 C respectively. When cycled at 1 and 5 C, the material retains 84% （after 1000 cycles） and 86% （after 350 cycles） of the initial discharge capacity respectively indicating excellent structure stability and cycling performance. Na^＋ doping enhances the electrochemical activity especially the cycle performance effectively.
基金Funded in Part by the National Natural Science Foundation of China(No.61601384)
文摘The electron paramagnetic resonance（EPR） spectra of trigonal Mn^（2＋） centers in Zn（ClO4）2·6（H2O） and Mg（ClO4）2·6（H2O） crystals were studied on the basis of the complete energy matrices for a d^5 configuration ion in a trigonal ligand field. It was demonstrated that the local lattice structure around a trigonal Mn^（2＋） center has an compressed distortion along the crystalline c3 axis, and when Mn^（2＋） is doped in the Zn（ClO4）2·6（H2O） and Mg（ClO4）2·6（H2O） crystals, there is a similar local distortion. From the EPR calculation, the local lattice structure parameters R=2.183 2 ？, for Zn（ClO4）2·6（H2O）, R=2.130 2 ？, for Mg（ClO4）2·6（H2O） have been determined.
基金supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (Ministry of Science, ICT & Future Planning) (NRF-2020R1F1A1075601, NRF-2021R1A4A2001658)supported by the National Natural Science Foundation of China (51904059)+1 种基金the Fundamental Research Funds for the Central Universities (N182505036, N2002005)the Liao Ning Revitalization Talents Program (XLYC1807123)。
文摘Cobalt hexacyanoferrate (CoHCF) is a potential cathode for aqueous Na-ion batteries due to its high theoretical specific capacity (170 m Ah g^(-1));however,its lower rate capability and cyclability limit its applications.Structural distortion at a weak N-coordinated crystal field during cycling disintegrates Co,yielding an irreversible reaction.Different Zn amounts ranging 0–1 were added to the Co site to suppress the structural irreversibility of CoHCF,yielding Co_(1-x)Zn_(x)HCF powder;this Zn (x≤0.09) addition reduced the powder’s dimension because the lower four coordination of Zn–N,not the six coordination of Co–N,limits the powder growth.Simultaneously,a small lattice parameter and interaxial angle (~90°) are obtained,implying that a narrower Co_(1-x)Zn_(x)HCF inner structure is formed to accommodate Na ions.Moreover,the electronic conductivity of Co_(1-x)Zn_(x)HCF gradually increased within 0–0.09 range.A smaller particle size with a high surface area leads to a near-surface-limited redox process,similar to a capacitive reaction.Both the surface-limited reaction and electronic conductivity enhances the reversibility due to the smaller charge transfer resistance at the electrode/electrolyte interface caused by Zn addition.Replacing redox-active Co with non-active Zn amount of 0.07 (Co_(1-x)Zn_(x)HCF) slightly reduces the specific capacity from 127 to 119 mAh g^(-1)at 0.1 A g^(-1)due to the shrunken Co charging sites.Rate performance is enhanced by compromising the capacity and reduced distortion,resulting in 81%retention at a 20-times-faster charging rate.Notably,the Co_(1-x)Zn_(x)HCF sample exhibited the good stability while preserving 74%of the initial capacity at 0.5 A g^(-1)after 200 cycles.
基金Project supported by the National Key Research and Development Program of China (Grant Nos.2023YFA1607403,2021YFA1600201,and 2022YFA1602603)the Natural Science Foundation of China (Grant Nos.U19A2093,U2032214,and U2032163)+5 种基金the Collaborative Innovation Program of Hefei Science Center,CAS (Grant No.2019HSC-CIP 001)the Youth Innovation Promotion Association of CAS (Grant No.2021117)the Natural Science Foundation of Anhui Province (No.1908085QA15)the HFIPS Director’s Fund (Grant No.YZJJQY202304)the CASHIPS Director’s Fund (Grant No.YZJJ2022QN36)supported by the High Magnetic Field Laboratory of Anhui Province。
文摘We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_(p)~140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near Tp, i.e.,?L_(c)/L_(c)~0.062%. The structural characterization confines that there is no structure transition below and above T_(p). All these results suggest that the nonmagnetic transition of SrCu_(4-x)P_(2) could be associated with structural distortion.
基金Project supported by the State Key Program for Basic Research of China (Grant No.2010CB923404)the National Natural Science Foundation of China (Grant Nos.11274153,11204124,and 51202108)
文摘X-ray absorption spectra （XAS） at Mn K-edge and Fe K-edge in LaMnl-xFexO3 show that with the increase of Fe substitution the chemical valence of Mn4＋ decreases, while the chemical valence of Fe3＋ remains unchanged. Structural distortions, such as the rotating and tilting for oxygen octahedron in the unit cell vary with iron content. A phase transition occurs at the Fe content values of 0.2~0.3. The evolutions of rotation and tilting angle of FeO6/MnO6 octahedral may be the vital factors to the structure and magnetism. We believe that the spin configuration of Fe3＋ may vary from the intermediate spin t2g4eg1 （S = 3/2） to the higher spin t2g3eg2 （S = 5/2） near the phase transition.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12174051 and 12304069)。
文摘Valleytronics is an emergent discipline in condensed matter physics and offers a new way to encode and manipulate information based on the valley degree of freedom in materials. Among the various materials being studied, Kekulé distorted graphene has emerged as a promising material for valleytronics applications. Graphene can be artificially distorted to form the Kekulé structures rendering the valley-related interaction. In this work, we review the recent progress of research on Kekulé structures of graphene and focus on the modified electronic bands due to different Kekulé distortions as well as their effects on the transport properties of electrons. We systematically discuss how the valley-related interaction in the Kekulé structures was used to control and affect the valley transport including the valley generation, manipulation, and detection. This article summarizes the current challenges and prospects for further research on Kekulé distorted graphene and its potential applications in valleytronics.
基金supported by the Hebei Province Higher Edu-cation Scientific Research Project(No.JZX2024029)。
文摘Manganese oxides have received extensive attention in Oxygen Reduction Reaction(ORR)research.How-ever,the poor electrical conductivity and oxygen adsorption capacity of manganese oxides limit their development,so it is necessary to prepare catalysts with highly active surfaces.We propose a method to introduce an ionically conductive medium and induce structural distortion via thermodynamics,re-sulting in novel peak-splitting highly active structures for enhanced oxygen reduction activity.With the aid of refined structural analysis,High-angle annular dark-field(HAADF-STEM)imaging,and theoretical calculations,it is elucidated that this peak-splitting structure results from thermodynamically induced structural distortions and atomic displacements.The introduction of the ionically conductive medium promotes the formation of Ag-O-Mn conductive bond bridges,which regulate the energy level matching of manganese oxides and oxygen intermediates.The thermodynamically induced structural distortion ex-poses new atomic planes in the material,and the creation of this highly active surface is accompanied by a redistribution of surface charges,which modulates the adsorption of manganese active sites with oxy-gen intermediates and greatly enhances the oxygen reduction activity.Specifically,this Ag-OMS-2 with a novel split structure exhibits excellent activity at 0.836 V,superior to Pt/C kinetics and good stability.The preparation of such highly active structures is instructive for the development of manganese oxides.
基金supported by the National Natural Science Foundation of China(Grant Nos.22090042 and 22175018).
文摘We systematically investigated the structural and superconducting properties of polycrystalline 2H-Li_(x)TaSe_(2)(0.1≤x≤1.0)synthesized via a high-temperature solid-state reaction.Lithium(Li)intercalation induces an expansion along the c-axis and intralayer distortions within the Ta-Se coordination network.The superconducting transition temperature(T_(c))is increased to 2.95 K at x=0.1 driven by the synergistic enhancement of the electronic density of states at the Fermi level,N(EF),and strengthened electron-phonon coupling.With further Li doping,although N(EF)continues to increase,lattice stiffening and pronounced distortions in the Ta-Se coordination polyhedra weaken the electron-phonon interaction,ultimately suppressing superconductivity.These findings highlight the critical role of intralayer structural modulation in governing structure-tunable superconductivity in layered materials.
基金Funded by the National Natural Science Foundation of China (Nos. 11804285 and 61601384)。
文摘The electron paramagnetic spectra of trigonal Mn^(2+) centers in[Co(H_(2)O)_(6)]SiF6,[Co(H_(2)O)_(6)]SnF6,and[Co(H_(2)O)_(6)]PtCl6 crystals were studied on the basis of the complete energy matrices for a d5 configuration ion in a trigonal ligand field.When Mn^(2+) is doped in the[Co(H_(2)O)_(6)]SiF6,[Co(H_(2)O)_(6)]SnF6,and[Co(H_(2)O)_(6)]PtCl6 crystals crystals,there is a similar local distortion.The experimental results show that the local lattice structure around a trigonal Mn^(2+) center has an elongation distortion along the crystalline C3 axis.From the EPR calculation,the local lattice structure parameters R=2.278A,θ=52.6406? for[Co(H_(2)O)_(6)]SiF6,R=2.280,θ=52.4936° for[Co(H_(2)O)_(6)]SnF6 and R=2.244A,θ=53.0616? for[Co(H_(2)O)_(6)]PtCl6 were determined.
文摘In this work, hierarchical BiOBr<sub>1<span style="white-space:nowrap;">−x</sub>I<sub>x</sub>/BiOBr heterojunction photocatalyst with a microsphere morphology was synthesized by a facile solvothermal process. It demonstrated that the local structure of the photocatalysts was highly distorted due to the substitution of bromide ions by iodine ions. The photocatalytic properties were evaluated by the photodecomposition of aqueous phenol solution under visible-light irradiation. The results indicated that all the composite photocatalysts exhibited high photocatalytic activity. In particularly, the BiOBr<sub>1<span style="white-space:nowrap;">−x</sub>I<sub>x</sub>/BiOBr (x = 0.25) sample exhibited over 92% degradation efficiency of phenol within 150 min, which is 24.6 and 3.08 fold enhancement in the photocatalytic activity over the pure phased BiOBr and BiOI, respectively. Moreover, this excellent photocatalytic property can be expanded to other colorless organic contaminants, verifying the common applicability of BiOBr<sub>1<span style="white-space:nowrap;">−x</sub>I<sub>x</sub>/BiOBr (x = 0.25) as an excellent visible-light photocatalyst for organics decomposition. The significant improvement in the photocatalytic activity can be explained by the high efficiency of charge separation due to the enhancement in the internal electric fields and band match that comes from the local structure distortion. This work provides valuable information for the design of highly active photocatalysts toward the environmental remediation.
基金supported by Department of Science and Technology (DST),Government of India under Fast Track Scheme (SR/FTP/PS-065/2011)
文摘Polycrystalline BiFeO3 and rare earth substituted Bio.gRo.lFeO3 （BRFO, R=Y, Ho and Er） compounds were prepared by rapid solid state sintering technique. Structural phase analysis indicated that all the compounds stabilized in rhombohedral structure （R3c space group） and a small orthorhombic phase fraction was observed in BRFO compounds. From the Raman spectra results, the changes in the phonon frequencies （A1） and line widths suggested lattice distortion in the BRFO compounds as was evidenced in the XRD analysis. Compared to the linear variation of magnetization with magnetic field （M-H） shown by BFO, an obvious M-H loop was observed in BRFO compounds which could be due to the suppression of space modulated spin structure and was explained on the basis of weak ferromagnetism and field induced spin reorientation. UV-Vis spectroscopy evidenced a change in local FeO6 envi- ronment due to shift in the 6Alg→4T2g energy transition band. BRFO compounds with improved remnant magnetization and coercive field are applicable for magnetoelectric devices.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB619401)
文摘The crystal structure,magnetization,and spontaneous magnetostriction of ferromagnetic Laves phase Gd Fe2 compound have been investigated.High resolution synchrotron x-ray diffraction（XRD） analysis shows that Gd Fe2 has a lower cubic symmetry with easy magnetization direction（EMD） along [100] below Curie temperature TC.The replacement of Gd with a small amount of Tb changes the EMD to [111].The Curie temperature decreases while the field dependence of the saturation magnetization（Ms） measured in temperature range 5–300 K varies with increasing Tb concentration.Coercivity Hc increases with increasing Tb concentration and decays exponentially as temperature increases.The anisotropy in Gd Fe2 is so weak that some of the rare-earth substitution plays an important role in determining the easy direction of magnetization in GdFe_2.The calculated magnetostrictive constant λ100 shows a small value of 37×10^（-6）.This value agrees well with experimental data 30×10^（-6）.Under a relatively small magnetic field,GdFe_2 exhibits a V-shaped positive magnetostriction curve.When the field is further increased,the crystal exhibits a negative magnetostriction curve.This phenomenon has been discussed in term of magnetic domain switching.Furthermore,magnetostriction increases with increasing Tb concentration.Our work leads to a simple and unified mesoscopic explanation for magnetostriction in ferromagnets.It may also provide insight for developing novel functional materials.
基金supported by the Natural Science Foundation of Henan Province,China(Grant Nos.232300420353 and 232300420392)the Key Scientific Research Project of Higher Education of Henan Province(Grant No.24B140001)+2 种基金the Doctor Scientific Research Initiate Fund of Anyang Institute of Technology(Grant No.BSJ2022010)the National Basic Research Program of China(Grant No.2009CB939901)the Henan Provincial Science and Technology Research Project(Grant No.232102241016).
文摘To insight into the B-site ordering in RFe_(0.5)Cr_(0.5)O_(3)ceramics,a series of RFe_(0.5)Cr_(0.5)O_(3)ceramics(R=La,Y,Lu)were synthesized by the sol-gel method,and the structural and magnetic properties were systemically investigated.By using the Rietveld refinement of all samples,it is found that the structural distortion is increased as the R ionic radius decreases,leading to the weakened interactions between Fe/Cr ions.Moreover,the Fe and Cr are arranged in disorder in LaFe_(0.5)Cr_(0.5)O_(3),but partially ordered in YFe_(0.5)Cr_(0.5)O_(3)and LuFe_(0.5)Cr_(0.5)O_(3),showing an increasing trend of the proportion of ordered domains with the decrease of R ionic radius.Through fitting the temperature-dependent magnetizations,it is identified that the magnetization reversal(MR)in disorder LaFe_(0.5)Cr_(0.5)O_(3)is resulted from the competition between the moments of Cr and Fe sublattices.In the partially ordered YFe_(0.5)Cr_(0.5)O_(3)and LuFe_(0.5)Cr_(0.5)O_(3)ceramics,because of the presence of Fe-O-Cr networks in the ordered domains whose moment is antiparallel to that of Fe-O-Fe and Cr-O-Cr in the disordered domains,the compensation temperature T_(comp)of MR is increased by nearly 50 K.These results suggest that the changing of R-site ions could be used very effectively to modify the Fe-O-Cr ordering,apart from the structural distortion,which has a direct effect on the magnetic exchange interactions in RFe_(0.5)Cr_(0.5)O_(3)ceramics.Then at values of composition where ordered domains are expected to be larger in number as compared to disordered domains and with a weaker structural distortion,one can expect a higher transition temperature Tcomp,providing a different view for adjustment of the magnetic properties of RFe_(0.5)Cr_(0.5)O_(3)ceramics for practical applications.
基金This work was supported by MOST of China (G19980613) NSFC (Nos. 29831010 & 20023005)+1 种基金 the Post-Doctoral Foundation of Chinathe Founder Foundation of PKU Corresponding author.
文摘In this paper, the magnetic and transport properties in ABO3-type perovskite-like manganites as functions of the structure have been discussed from the viewpoints of A- and B-site doping, respectively. For the A-site doping, two simple parameters, tolerance factor t and variance of the A-cation radius distribution s, can be used to characterize the magnetic/resistive phase diagram. For the B-site doping, the case is complicated due to the direct action to the center of double exchange. However, the dopant-size-induced local strain effect plays an important role in the physical properties besides the size mismatch between A- and B-site ions.
基金supported by the National Natural Science Foundation of China(Grant Nos.51672270,11674040,and 11404044)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant No.QYZDB-SSW-SLH016)the Project for Fundamental and Frontier Research in Chongqing City(Grant No.CSTC2015JCYJBX0026)
文摘To enhance the thermoelectric performance of Cu2GeSe3, a series of Te-alloyed samples Cu2Ge（Se（1-x）Tex）3 are synthesized and investigated in this work. It is found that the lattice thermal conductivity is reduced drastically for x = 0.1 sample, which may be attributed to the point defects introduced by alloying. However, for samples with x ≥ 0.2, the lattice thermal conductivity increases with increasing x, which is related to a less distorted structure. The structure evolution,together with the change in carrier concentration, also leads to a systemically change in electrical properties. Finally, a z T of 0.55@750 K is obtained for the sample with x = 0.3, about 62% higher than that for the pristine sample.
