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Precision mapping the topological bands of 2D spin-orbit coupling with microwave spin-injection spectroscopy
摘要： To investigate the band structure is one of the key approaches to study the fundamental properties of a novel material. We report here the precision band mapping of a 2-dimensional (2D) spin-orbit (SO) coupling in an optical lattice. By applying the microwave spin-injection spectroscopy, the band structure and spin-polarization distribution are achieved simultaneously. The band topology is also addressed with observing the band gap close and re-open at the Dirac points. Furthermore, the lattice depth and the Raman coupling strength are precisely calibrated with relative errors in the order of 10?3. Our approach could also be applied for exploring the exotic topological phases with even higher dimensional system.
关键词： Topological band,Microwave spin-injection spectroscopy,Spin polarization,Topological phase transition,2D spin-orbit coupling
更新于2025-09-23 15:23:52
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Suppression of Electrochemically Driven Phase Transition in Nanostructured MoS2 Pseudocapacitors Probed Using Operando X-ray Diffraction
摘要： Pseudocapacitors with non-diffusion-limited charge storage mechanisms allow for fast kinetics that exceed conventional battery materials. It has been demonstrated that nanostructuring conventional battery materials can induce pseudocapacitive behavior. In our previous study, we found that assemblies of metallic 1T MoS2 nanocrystals show faster charge storage compared to the bulk material. Quantitative electrochemistry demonstrated that the current response is capacitive. In this work, we perform a series of operando X-ray diffraction studies upon electrochemical cycling to show that the high capacitive response of metallic 1T MoS2 nanocrystals is due to suppression of the standard first-order phase transition. In bulk MoS2, a phase transition between 1T and triclinic phases (LixMoS2) is observed during lithiation and delithiation in both the galvanostatic traces (as distinctive plateaus) and the X-ray diffraction patterns with the appearance of the additional peaks. MoS2 nanocrystal assemblies, on the other hand, show none of these features. We hypothesize that the reduced MoS2 crystallite size suppresses the first-order phase transition and gives rise to solid solution-like behavior, potentially due to the unfavorable formation of nucleation sites in confined space. Overall, we find that nanostructuring MoS2 suppresses the 1T-Triclinc phase transition and shortens Li-ion diffusion path lengths, allowing MoS2 nanocrystal assemblies to behave as nearly ideal pseudocapacitors.
关键词： intercalation pseudocapacitor,pseudocapacitance,MoS2,phase transition suppression,porous electrodes,nanocrystal assemblies,fast charging
更新于2025-09-23 15:23:52
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Comparative Raman study of two laterally fluorinated LC compounds having different terminal chains
摘要： In this article, we present the Raman study of two laterally fluorinated liquid crystal compounds, namely, C3PP(23F)P-NCS and C3PP(23F)PC3. The two compounds have different terminal groups, one with NCS which is more polar than the other which has an alkyl group. The Raman bands were deconvoluted with Lorentzian profiles to get the values of spectral parameters. The main feature of the work is the temperature-dependent behaviour of the spectra profiles of the C–H bending mode, C–F stretching modes and aromatic C–C stretching mode in the vicinity of the phase transitions. The effect on the charge distribution over different bonds of the molecule and the vibrational energy of the bonds due to the presence of the more polar group on the terminal chain is well observed. The contrasting behaviours of the spectral profiles at the Cr–N and N–I transitions were also observed which we have ascribed to some pre-transitional effect associated with the breaking of the orientational order near the N–I transition. Density functional theory using B3LYP exchange correlation with the 6-31G (d,p) basis set was also used to generate a theoretical spectra which were found to be matching with the experimental spectra.
关键词： laterally fluorinated liquid crystals,isothiocyanato (NCS) compound,phase transition,Raman study
更新于2025-09-23 15:23:52
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Ferroelastic phase transition in Cu <sub/>6</sub> PS <sub/>5</sub> Br <sub/>1-x</sub> Cl <sub/>x</sub> mixed crystals
摘要： Cu6PS5Br1-xClx mixed crystals were grown by chemical vapour transport. Optical absorption edge and optical polarization measurements were performed in the temperature range 77–320 K. The in?uence of anionic Br→Cl substitution on the phase transitions in Cu6PS5Br1-xClx mixed crystals is studied. Compositional dependence of the ferroelastic phase transition temperature for Cu6PS5Br1-xClx mixed crystals is obtained. The variation of optical parameters at ferroelastic phase transition is analyzed.
关键词： absorption edge,optical parameters,phase transition,mixed crystals,Ferroelastic
更新于2025-09-23 15:23:52
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Structure and multiferroic properties of ternary (1?x)(0.8BiFeO3-0.2BaTiO3)-xK0.5Na0.5NbO3 (0?≤?x?≤?0.5) solid solutions
摘要： The ternary (1?x)(0.8BiFeO3-0.2BaTiO3)-xK0.5Na0.5NbO3 (0 ≤ x ≤ 0.5) solid solutions have been successfully synthesized by a solid-state reaction route. X-ray diffraction and Rietveld refinement studies reveal the phase transition from the rhombohedral and tetragonal phases to the single tetragonal phase with x increasing. The average grain size decreases initially and then increases as x increases, whereas the remnant magnetization shows an opposite trend and reaches the maximum value of ~2.09 emu/g at x = 0.3. An enhanced remnant polarization of ~8.6 μC/cm2 appears at x = 0.3 due to the structure distortion and the decrement of defects. Moreover, the remanent polarization and the relative permittivity reach the maximum value of ~20.14 μC/cm2 (10 Hz) and ~644 (1 kHz) at x = 0.5, respectively, and the corresponding dielectric loss decreases to the lowest value of ~0.022 (1 kHz). These results indicate that the properties of ternary BFO-BTO-KNN solid solutions can be modulated by adjusting the K0.5Na0.5NbO3 content to adapt to different application needs.
关键词： Microstructure,Dielectric loss,Phase transition,Multiferroic properties
更新于2025-09-23 15:22:29
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Structural and thermoelectric properties of copper sulphide powders
摘要： Over the past few years, Cu-based materials have been intensively studied focusing on their structural and thermoelectric properties. In this work, copper sulphide powders were synthesized by the sol-gel method. The chemical composition and the morphological properties of the obtained samples were analyzed by X-ray diffraction, differential thermal analysis, and scanning electron microscopy. It is shown that the decomposition from one phase to another can be obtained by annealing. The electrical resistivity and the crystallite size were found to be strongly affected by the phase transition. Thermoelectric analyses showed that the digenite phase exhibits the highest power factor at room temperature. The Seebeck coefficient of the compound Cu1.8S shows a pronounced peak at the γ–β transition temperature. This behavior was statistically explained in terms of a dramatic increase in the disorder in the atoms-carriers ensemble.
关键词： thermoelectricity,copper sulphide,annealing temperature,phase transition
更新于2025-09-23 15:22:29
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Peculiarities of the dielectric properties of ternary 0.5(Y0.1Zr0.9O2) – 0.5(0.6SrTiO3 – 0.4BiScO3) ceramic system
摘要： Ceramic samples of ternary 0.5(Y0.1Zr0.9O2) – 0.5(0.6SrTiO3 – 0.4BiScO3) system consisting of individual Y0.1Zr0.9O2 and 0.6SrTiO3 – 0.4BiScO3 subsystems were synthesized via solid-state processing techniques. By XRD analysis, a coexistence of tetragonal P42/nmc phase related to the Y0.1Zr0.9O2 subsystem, and cubic Pm m3? and tetragonal P4mm phases associated with the 0.6SrTiO3 – 0.4BiScO3 subsystem was found. A deviation of real composition from nominal one for both Y0.1Zr0.9O2 and SrTiO3 – BiScO3 subsystems due to Sc substituting for Zr in the Y0.1Zr0.9O2 subsystem and, vice versa, Zr substituting for Sc in the SrTiO3 – BiScO3 subsystem was also observed. Peculiarities of the dielectric properties related to both di?use ferroelectric phase transition and dielectric relaxation processes were found and analyzed in comparison with the dielectric properties of two-component 0.6SrTiO3 – 0.4BiScO3 system. It was found that the di?use phase transition in ternary system, ?rstly, shifts to lower temperatures and, secondly, has a less degree of di?useness as compared to two-component system. Such kind of behavior could be attributed to a di?erence of ionic radii of ions Zr4+ and Sc3+. Dielectric relaxation processes associated with the O2- ions migration were observed within temperature 500–800 K for both ternary and two-component systems. Two dielectric relaxation processes related to the Y0.1Zr0.9O2 and 0.6SrTiO3 – 0.4BiScO3 subsystems were found in ternary system, whereas one dielectric relaxation process was observed in two-component system. The activation energies for the dielectric relaxation processes were estimated as ~ 1.3 eV and ~ 0.9 eV for Y0.1Zr0.9O2 and 0.6SrTiO3 – 0.4BiScO3 subsystems, respectively, for ternary system, and ~ 0.75 eV for two-component system.
关键词： Dielectric relaxation process,Two-component ceramic system,Y0.1Zr0.9O2 and 0.6SrTiO3 – 0.4BiScO3 subsystems,Ternary ceramic system,Di?use phase transition
更新于2025-09-23 15:22:29
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Room-temperature multiferroic and magnetodielectric properties of SrTiO3/NiFe2O4 composite ceramics
摘要： Various xNiFe2O4 ? (1-x)SrTiO3 (x = 0.04, 0.05, 0.1, 0.2) composite ceramics were prepared using sol–gel method and two-step calcination. The composite ceramics possessed no impurities and exhibited obvious magnetic properties (22.8 emu/g at x = 0.2). The magnetic second phase imposed strain effects on the SrTiO3 matrix to induce ferroelectricity. Strain values of (001) and (110) crystal planes were ~2.9% and ~1.3%. The tetragonal phase transition was evident in the Raman spectra. The remanent and maximum polarizations were 1.4 and 15.8 μC/cm2, respectively, in ceramic with 10 mol.% NiFe2O4. The dielectric permittivity was tuned with 1.6% change rate at 50 kHz and 10000 Oe.
关键词： Phase transition,Ferroelectricity,Strains,SrTiO3,Magnetodielectric
更新于2025-09-23 15:22:29
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Microscopy and Spectroscopy Study of Nanostructural Phase Transformation from β-MoO3 to Mo under UHV – MBE Conditions
摘要： We report a simple reduction of molybdenum oxide (β-MoO3) grown on reconstructed Si(100) by thermal annealing in ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). By increasing the substrate temperature during deposition or the annealing temperature after growth, the morphologies of as-deposited structures were found to vary from nanoribbons (NRs) of β-MoO3 to nanoparticles (NPs) of Mo. The change in morphologies have been associated with a structural transition from β-MoO3 to MoO2 at 400 °C and MoO2 to Mo at 750 °C. The in-situ X-ray photoelectron spectroscopy (XPS) measurements revealed a shift of the Mo 3d peaks towards lower binding energies, representing the reduction in Mo oxidation states until a pure Mo 3d peak at 750°C was observed. The ex-situ KPFM measurements showed a decrease in the local work function (Φ) (from ≈ 5.27 ± 0.05 eV to ≈ 4.83 ± 0.05 eV) with increasing substrate temperature. A gradual reduction of the band gap from ≈ 3.32 eV for β-MoO3 NRs to zero band gap for Mo NPs is also observed during the annealing up to 750 °C.
关键词： in-situ XPS,KPFM,molecular beam epitaxy (MBE),Mo nanoparticles,β-MoO3 nanoribbons,phase transition
更新于2025-09-23 15:22:29
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The phase transition and optical properties of Cr2+-doped ZnSe under high pressure
摘要： The phase transition pressure, electronic structure, optical properties and stability for ZnSe and Cr2+:ZnSe with different doping concentrations were calculated by first-principles calculation based on density-functional theory. The phase transition pressure was calculated by enthalpy-pressure relation. The introduction of dopant (Cr2+) reduces the phase transition pressure, and the phase transition pressure decreases with the increase of doping concentration. The high pressure enhances the degeneracy of Cr-d orbitals. Under the high-pressure conditions, the absorption peak positions of Cr2+:ZnSe have obvious blue-shift. Meanwhile, the stability of structures for ZnSe and Cr2+:ZnSe were further confirmed by defect formation energy and elastic constants.
关键词： Phase transition pressure,Cr2+:ZnSe,First-principles calculation,Optical properties
更新于2025-09-23 15:22:29