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Solid-State Preparation, Structural Characterization, Physical Properties and Theoretical Studies of a Series of Novel Rare-earth Metal-Chalcogenides with Unprecedented Closed Cavities
摘要： Multinary rare-earth metal-chalcogenides have aroused great concern owing to their special structure characteristics and diverse physical functions. In this work, five novel rare-earth chalcogenides adopt the formula Cs2[RE8InS14] (where RE = Ho–Lu), has been obtained by the elementals mixture in CsCl flux at 1273 K. They are isotype and belong to the orthorhombic Cmca (no. 64) [a = 15.711(7)–15.385(2) ?, b = 22.232(2)–21.786(2) ?, c = 15.483(5)–15.244(2) ?, V = 5408.4(4)–5130.1(7) ?3 and Z = 8], exhibiting a dense 3D [RE8InS14] framework consisting of RES6 octahedron and discrete InS4 tetrahedron. The large closed-cavities Cs4@S26 are far apart embedded within the network along bc-plane, which is discovered for the first time. The band gaps from 2.45 to 2.72 eV for Cs2[RE8InS14] were deduced from the UV?Vis–NIR spectroscopy based on the Kubelka-Munk function. Magnetic test indicates that the Cs2[RE8InS14] (RE = Ho–Yb) compounds possess para-magnetism above 50K. In addition, the solid-state preparation, structural characterization, theoretical studies together with a structure–G/H ratio relationship (G = atomic number of guest metals; H = atomic number of host metals) are also presented.
关键词： crystal structure,solid-state reaction,magnetic properties,large closed cavities,rare-earth metal-chalcogenides
更新于2025-09-10 09:29:36
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Crystal structures of Zn<sub>2</sub>GeO<sub>4</sub> cubic/tetragonal spinel and Zn<sub>2</sub>SiO<sub>4</sub> modified spinel phases
摘要： Crystal structures of the cubic and tetragonal spinel phases of Zn2GeO4 and the modified spinel phase of Zn2SiO4 were refined by Rietveld analysis of synchrotron powder X–ray diffraction data. The Zn2GeO4 cubic spinel phase was found to have an inverse spinel configuration. The Zn2GeO4 tetragonal spinel phase is isostructural to Zn2TiO4, where half of Zn occupies the tetrahedral site, and the remaining Zn and Ge are ordered in two octahedral sites. In the modified spinel phase of Zn2SiO4, Zn occupies the octahedral sites. Independent individual cation–oxygen distances in the Zn2GeO4 tetragonal spinel and Zn2SiO4 modified spinel phases were calculated using the bond valence repartition method, and are in reasonable agreement with the refined structures.
关键词： Crystal structure,Rietveld method,Spinel,Bond valence model,Modified spinel
更新于2025-09-10 09:29:36
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Two new luminescent ternary Cd(II)-MOFs by regulation of aromatic dicarboxylate ligands used as efficient dual-responsive sensors for toxic metal ions in water
摘要： Two new Cd(II) metal-organic frameworks (MOFs) formulated as [Cd(L)(atpa)]n (1) and [Cd(L)(tbta)(H2O)]n (2) [H2atpa = 2-aminoterephthalic acid, H2tbta = tetrabromoterephthalic acid, L = 1,4-bis(benzimidazol-1-yl)-2-butene] were hydrothermally synthesized. 1-2 were characterized by IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. 1 displays a 3D framework with five-fold interpenetrating dia topology. 2 holds a 2D corrugated sql layer. Both MOFs were confirmed to be dual-responsive luminescent sensors (Cu2+ and Cr2O7 2- for 1, Hg2+ and Cr2O7 2- for 2) in water through the luminescence quenching experiments. The detection limits for these species were 1.2 μM (Cu2+) and 0.29 μM (Cr2O7 2-) of 1, 0.043 μM (Hg2+) and 0.13 μM (Cr2O7 2-) of 2, respectively. The luminescence quenching mechanism was investigated.
关键词： Hydrothermal synthesis,Luminescence quenching,Semi-rigidity bis(benzimidazole),Crystal structure,Cadmium(II) MOF
更新于2025-09-10 09:29:36
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Characterization of Er-doped AlN films prepared by RF magnetron sputtering
摘要： Er-doped AlN thin film were deposited on sapphire substrates (0001) by RF magnetron sputtering at different sputtering times. The crystalline structure, surface morphology and electrical properties of the thin films have been investigated. The XRD patterns and the SEM sectional diagram indicate that Er-doped AlN thin films presents the preferred orientation of C axis. The crystalline quality of the films rises first and then decreases with the increase of sputtering time and reaches best at 90 minutes. Piezoelectric coefficient d33 indicates maximum value of 9.53pm/V. Correspondingly, the best surface morphology of thin film was obtained at 90 minutes and the surface roughness reached a minimum of 2.012 nm. In addition, the change of resistance is same with change of the crystalline quality and the resistivity reached a maximum of 4.36*1012Ω?cm at 90minutes.
关键词： piezoelectric properties,Er-doped AlN,crystal structure,resistivity,sputtering time,magnetron sputtering
更新于2025-09-10 09:29:36
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Structure and luminescence properties of Zn3V2O8 yellow phosphor for white light emitting diodes
摘要： Extensive attention has been focused on the development of rare-earth-free phosphors, due to their low cost, good absorption and emission properties. However, the yellow light emitted phosphors with good quantum yield and thermal stability are still urgent. Herein, we successfully prepare the single-phase Zn3V2O8 yellow phosphor through a solid state reaction method. The as-prepared phosphors present a broad absorption band in UV/NUV region, and exhibit an intense broadband emission spectrum under the NUV light excitation at 365 nm. The Zn3V2O8 phosphors also show excellent luminescence performance including strong emission intensity, long PL lifetime, high quantum yield, and good thermal stability. Moreover, this sample obtains a CIE coordinate of (0.364, 0.486) in the yellow light region. Therefore, the Zn3V2O8 phosphors can be considered as a novel yellow light source for w-LED devices.
关键词： Phosphors,Zn3V2O8,Crystal structure,Luminescence mechanism
更新于2025-09-10 09:29:36
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Concurrent Zinc-Blende and Wurtzite Film Formation by Selection of Confined Growth Planes
摘要： Recent research on nanowires (NWs) demonstrated the ability of III-V semiconductors to adopt a different crystallographic phase when they are grown as nanostructures, giving rise to a novel class of materials with unique properties. Controlling the crystal structure however remains difficult and the geometrical constraints of NWs cause integration challenges for advanced devices. Here, we report for the first time on the phase-controlled growth of micron-sized planar InP films by selecting confined growth planes during template-assisted selective epitaxy. We demonstrate this by varying the orientation of predefined templates, which results in concurrent formation of zinc-blende (ZB) and wurtzite (WZ) material exhibiting phase purities of 100% and 97%, respectively. Optical characterization revealed a 70 meV higher band gap and a 2.5x lower lifetime for WZ InP in comparison to its natural ZB phase. Further, a model for the transition of the crystal structure is presented based on the observed growth facets and the bonding configuration of InP surfaces.
关键词： template-assisted selective epitaxy,zinc-blende,crystal structure,indium phosphide,wurtzite
更新于2025-09-10 09:29:36
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Crystal Structure Characterization of Thin Layer Zinc Oxide
摘要： In this research the characterization of the crystal structure of a thin layer of ZnO (zinc oxide) were synthesized by sol - gel method and spin coating deposited on a glass substrate. The samples were divided into three sol concentrations of 0.1, 0.3, 0.5 Molar and two deposition temperature is 350 °C, and 550 °C. UV-Vis. spectrophotometer results showed that in the spectrum of visible light (wavelength range 300-800 nm) has a transmittance value of which increases with increasing concentration and temperature deposition of zinc oxide, otherwise the value of the absorption and the band gap energy decreases with temperature. The transmittances value of the highest and lowest absorption was 93.5% and 0.03 is at a concentration of 0.1 M and zinc oxide deposition temperature of 550 °C, with a value of band gap energy of 2.98 eV. The XRD results showed that the zinc oxide crystal orientation in the field of 013 with a crystal grain size 14.4472 nm. SEM results showed the surface morphology of zinc oxide such as rod-like.
关键词： ZnO,sol-gel method,thin layer,crystal structure,optical properties,spin coating
更新于2025-09-10 09:29:36
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Eu3+-doped Sr2(Al1?xMgx)(Al1?xSi1+x)O7 phosphors: electronic, crystal structures and photoluminescence properties
摘要： The union of chemical compositions substitution and spectral controlling is of importance for the discovery of new materials or the implementation of properties optimization. In this work, we employed an effective strategy to regulate crystal structures by chemical unit co-substitution. We applied this strategy to Eu3+-doped Sr2(Al1?xMgx)(Al1?xSi1+x)O7 (0 ≤ x ≤ 1) solid solution phosphor, which was successfully synthesized by high temperature solid state reaction. The crystal structure remained the same group, P-421m, with controlling chemical compositions. The excitation peaks shifted between 263 and 270 nm and emission peaks shifted between 612 and 614 nm with a decreasing Stocks shift in overall tendency. The shift trend was clarified by Crystal Field Theory. The energy band structure and density of states of Sr2Al2SiO7 and Sr2MgSi2O7 were calculated by Density Functional Theory using the generalized gradient approximation. The band gap was also analyzed by diffuse reflectance spectrum as a contrast. The morphology was characterized by field emission scanning electron microscopy. Furthermore, the photoluminescence color of phosphors could be tuned from yellow to orange.
关键词： crystal structure,chemical unit co-substitution,phosphors,photoluminescence,energy band structure
更新于2025-09-09 09:28:46
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On the thermal conductivity of AgSbTe <sub/>2</sub> and Ag <sub/>0.82</sub> Sb <sub/>1.18</sub> Te <sub/>2.18</sub>
摘要： The temperature dependencies of the thermal conductivity of AgSbTe2 and Ag0.82Sb1.18Te2.18 were studied in the temperature range of 5–320 K. The obtained results are compared with quantitative calculations based on a theoretical model of generalized conductivity of heterogeneous systems. It was shown that a rather low value of thermal conductivity of AgSbTe2 and Ag0.82Sb1.18Te2.18 is associated with the disordering of the crystal structure, as well as phonon scattering by point defects and structural components. The presence of the second phase of Ag2Te leads to an increase in the thermal conductivity of AgSbTe2.
关键词： crystal structure disordering,AgSbTe2,thermal conductivity,Ag0.82Sb1.18Te2.18,phonon scattering
更新于2025-09-09 09:28:46
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Structural transformations and physical properties of (1-x) Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3-x</sub> BaTiO<sub>3</sub> solid solutions near morphotropic phase boundary
摘要： Piezoelectric and other physical properties are significantly enhanced at (or near) a morphotropic phase boundary (MPB) in ferroelectrics. MPB materials have attracted significant attention owing to both fundamental physics as well as the possibility of well-regulated energy and information storage devices which are dominated by lead (Pb)-based materials. Here, we report the crystal structure, Raman spectra, dielectric constant and polarization near the MPB of lead free (1-x) Na0.5Bi0.5TiO3 - x BaTiO3 (NBT - BT) (0.00 ≤ x ≤ 0.10) solid-solution, prepared by sol-gel auto combustion technique and sintered by microwave sintering technique. With the addition of BaTiO3 into Na0.5Bi0.5TiO3, it induces a structural phase transition from R3c (a single phase) to R3c+P4mm (a dual phase) close to x = 0.06 and 0.07 and transform to a high symmetry tetragonal phase P4mm at higher compositions (x = 0.08 to 0.10) as evident from our X-ray Rietveld refinement and Raman spectroscopic results. In the prepared solid solution, an anomalous enhancement of remnant polarization (2Pr0) was observed for x = 0.06 and 0.07, which has been explained based on the existence of the MPB. On the other hand, the value of coercive field EC0 was found to be decreased linearly from x = 0.00 to 0.06; it is constant for higher compositions. Further details of the ferroelectric properties on the electric field poled samples have been studied and compared with the as-grown (unpoled) samples. We perform first-principles calculations based on density functional theory that confirm a structural transition from a rhombohedral to a tetragonal phase under increasing x.
关键词： First-principles calculations,Crystal structure,Morphotropic Phase Boundary,Microwave sintering,Lead-free ferroelectric materials,Electrical properties,NBT-BT solid solution
更新于2025-09-09 09:28:46