Synthesis,sintering, and thermoelectric properties of Co1-xMxO (M = Na, 0 ≤ x ≤ 0.07; M = Ag, 0 ≤ x ≤ 0.05)

The structural and thermoelectric properties of Na- and Ag-substituted CoO dense ceramics have been investigated. X-ray diffraction shows that pure phase and Ag/CoO composites have been obtained for Na-doped and Ag-doped CoO, respectively. Raman spectroscopy shows an effect of Na dopants on the lattice disorder of CoO. The chemical composition, element distribution, and valence states of the samples have been characterized by Auger electron microscopy and X-ray photoelectron spectroscopy. Substitution of Co by 5 at. % Na enhances the power factor to 250 μW m⁻¹ K^-2 at 1000 K, similar to that of Ca₃Co₄O₉. The corresponding thermal conductivity is also reduced to 3.55 W.m⁻¹ K⁻¹ at 1000 K. Consequently, Co_0.95Na_0.05O exhibits the best thermoelectric figure of merit (ZT), which is 0.07 at 1000 K. On the other hand, the substitution of Ag into CoO leads to the formation of CoO/Ag composites and deteriorates ZT values.     

Structural,magnetic and magnetocaloric properties of CoFe2−xMoxO4 (0.0≤x≤0.3) ferrites

We have investigated structural, magnetic and magnetocaloric properties of CoFe_2-xMo_xO₄ (0.0≤x≤0.3) ferrites. Polycrystalline samples were prepared by the sol gel method and characterized by the powder X-ray diffraction and scanning electron microscopy. X-ray diffraction patterns show that all samples have a cubic spinel structure and the lattice parameter, a, decreases monotonically with increase in Mo concentration. Scanning electron micrographs indicate that most of the particles are in the range of 400–850 nm size. Magnetic measurements, performed by using a cryogen free vibrating sample magnetometer, show that these samples are soft ferromagnets in the measured temperature range. The saturation magnetization, M_s, values of Mo-doped samples are larger than the parent compound with a maximum value of ~106 emu/g for x=0.2 sample. The magnetic entropy change (−ΔS) increases with increase in applied magnetic field and shows a peak in the vicinity of blocking temperature. A maximum value of 0.56 J kg⁻¹ K⁻¹ at 5 T field has been observed for x=0.2 sample.     

Sr1-xLaxFe12O19 (0.0≤x≤0.5) hexaferrites: Synthesis,characterizations, hyperfine interactions and magneto-optical properties

A simple sol-gel auto combustion process was used to synthesize La³⁺ substituted M-type strontium hexaferrite, Sr_1-xLa_xFe_12-xO₁₉ (0.0≤x≤ 0.5). Structural, magnetic, and optical behavior as a function of La³⁺ substitutions were investigated by Fourier transformed infrared spectroscopy (FT-IR). X-ray powder diffraction (XRD). Scanning electron microscopy (SEM), Mössbauer spectroscopy, vibrating sample magnetometer (VSM), and Diffuse reflectance spectroscopy (DRS). XRD data showed single phase magnetoplumbite structure and Rietveld analysis confirmed P6₃/mmc space group for all the series. The average crystallite size was found to be in the range of 43.2–48.4 nm. The variation in line width, isomer shift, quadrupole splitting, relative area and hyperfine magnetic field values have been determined from ⁵⁷Fe Mössbauer spectroscopy data. The fittings accounted for the Fe²⁺/Fe³⁺ charge compensation mechanism at the 2a site due to replacement of Sr²⁺ by La³⁺. The saturation magnetization (σ_s) decreases from 57,21 to 63,23 emu/g and remnant magnetization (σ_r) decreases from 35.6 emu/g to 28.7 emu/g with increasing La substitution. The decrement is sharper at coercive field (H_c) from maximum value of 5325 to minimum 1825 Oe. Demagnetizing factor (N) is 3 times more for the x=0.3, 0.4, and 0.5. However all samples exhibit ferromagnetic behavior at room temperature. Magnetic anisotropy of Hexaferrites was detected as uniaxial and effective anisotropy constants (K_eff) were between 5.93×10⁵ and 4.76×10⁵ Ergs/g. The high magnitudes of anisotropy fields (H_a) in the range of 13863–15574 Oe reveal that all hexaferrites are magnetic hard materials. Tauc plots were applied to extrapolate the direct optical energy band gap (E_g) of hexaferrites. The E_g values decreased from 1.83 to 1.34 eV with increasing La content.     

钙钛矿锰氧化物(La_(1-x)Nd_x)_(0.5)Ca_(0.5)MnO_3(0≤x≤1)的结构,磁性和电输运性质

系统研究了(La1-xNdx)0.5Ca0.5MnO3(x=0,0.2,0.4,0.6,0.8,1.0)系列样品的结构、磁性质和电输运性质。研究表明,所有样品的结构都为钙钛矿正交结构(空间群Pbnm),随着掺杂浓度x的增大,样品的晶格参数a,b,c和晶胞体积V都呈减小的趋势;磁性质的研究表明所有样品在低温下均出现电荷有序态,且电荷有序转变温度随着Nd3+的掺杂浓度x的增加而升高;除了Nd0.5Ca0.5MnO3(x=1.0)外,其它样品均出现顺磁-铁磁转变,其转变温度(即居里温度)随着Nd3+的掺杂浓度x的增加而降低;(0.2≤x≤0.8)样品的铁磁态均出现在电荷有序温度以下,表现出再入型(reentrant)铁磁态性质;电输运性质的研究表明,所有样品的电阻率随温度的升高而下降,表现为绝缘体性质。     

Sintering behavior,phase evolution and microwave dielectric properties of thermally stable Li2O-3MgO-mTiO2 ceramics (1≤m≤6)

Li₂O-3MgO-mTiO₂ (1≤m≤6) ceramics were prepared by the solid state reaction method. X-ray diffraction, energy dispersive spectrometer and scanning electron microscopy techniques were used to investigate the phase composition and crystal structure. With increasing m values, the phase structures of ceramics changed as: (Li₂Mg₃TiO₆, m=1)→(Li₂Mg₃Ti₄O₁₂ and Mg₂TiO₄, m=2,3)→(Li₂Mg₃Ti₄O₁₂, m=4)→(Li₂Mg₃Ti₄O₁₂, MgTiO₃ and Li₂MgTi₃O₈, m=5)→(Li₂Mg₃Ti₄O₁₂, MgTiO₃, Li₂MgTi₃O₈ and MgTi₂O₅, m=6). The optimized sintering temperature was lowered from 1275 °C to 1050 °C. When m=5, Li₂O-3MgO-5TiO₂ ceramics showed good microwave dielectric properties at a wide sintering temperature range of 1000–1200 °C, and the best microwave dielectric properties of Q×f=71,726 GHz, ε_r=21.9 and τ_f=−20.9 ppm/°C were obtained at a relatively low sintering temperature of 1050 °C.     

(ZrO2)n(1≤n≤5)团簇的结构及其光谱特征

应用密度泛函理论方法计算了各种可能的(ZrO2)n(1≤n≤5)团簇结构,同时模拟了对应团簇结构的红外光谱.氧化锆团簇中,锆氧原子间最大程度的交互连接是最稳定的结构.团簇的红外光谱表明:600～700 cm-1附近的峰对应着氧化锆团簇的Zr-O-Zr-O四元环振动,800 cm-1附近的峰对应着氧化锆团簇的Zr-O-Zr-O-Zr-O六元环振动,大于900 cm-1的峰对应着氧化锆团簇的自由氧原子的Zr-O振动.实验分析与理论计算结果表明:500 cm-1附近较强的特征振动峰对应着四方氧化锆的特征振动.     

Influence of Ce addition on the structural,magnetic, and magnetocaloric properties in La0.7−xCexSr0.3MnO3 (0≤x≤0.3) ceramic compound

We report improvement in the magnetocaloric properties of Ce-doped lanthanum manganites. Polycrystalline La_0.7−xCe_xSr_0.30MnO₃ (0≤x≥0.3) samples were prepared using the conventional solid-state reaction method with phase purity and structure confirmed using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order ferromagnetic transition in parent sample and as well as in doped sample with Curie temperature decreasing progressively with increasing Ce-concentration from ~370 K for x=0.0 to 310 K for x=0.30. Magnetic entropy change (ΔS_M) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field dependent magnetization curves. A large ΔS_M associated with the ferromagnetic–paramagnetic transition in La_0.7−xCe_xSr_0.30MnO₃ samples has been observed. The value of ΔS_M was found to increase with Ce-doping up to x=0.15 and the highest value of 2.12 J kg⁻¹ K⁻¹ (at ΔH=2 T) was observed for La_0.55Ce_0.15Sr_0.30MnO₃ sample near the Curie temperature of 356 K. Also, improved relative cooling power of ~122 J kg⁻¹ was observed for the same sample. Due to the large magnetic entropy change and high Curie temperature, the La_0.55Ce_0.15Sr_0.30MnO₃ sample is suggested to be used as potential magnetic refrigerants for magnetic refrigeration technology above room temperature.     

Influence of La addition on the structural,magnetic and magnetocaloric properties in Sr2−xLaxFeMoO6 (0≤x≤0.3) double perovskite

We report the effect of carrier doping via partial substitution of La³⁺ for Sr²⁺ on the structural, magnetic and magnetocaloric properties of Sr₂FeMoO₆ double perovskite. Polycrystalline Sr_2−xLa_xFeMoO₆ (x=0.0, 0.1, 0.2, 0.3) samples were prepared using the conventional solid state reaction method. Using the X-ray diffraction (XRD) analysis it was established that all the samples crystallized in a tetragonal structure with I4/mmm space group. An increase in the La doping lead to an increase in the lattice parameter ‘a’ and the volume of the unit cell. The lattice parameter ‘c’ however remained unchanged. The temperature variation in magnetization and Arrott analysis suggested a second order of ferromagnetic phase transition in all samples with Curie temperature, T_C increasing from 358 K for x=0.0–365 K for x=0.3. A gradual increase in magnetization was also observed with the increasing La content up to x=0.2. The magnetic entropy change was calculated from the measurement of isothermal magnetization versus magnetic field at different temperatures. The tunability of magnetization and T_C simply by adjusting the concentration of La and synthesis conditions makes Sr₂FeMoO₆ an attractive material for magnetic refrigeration at desired temperature.     

Li_(1-x)Ti_xFePO_4(0≤x≤0.02)制备表征及电化学性能研究

采用固相工艺制备了具有锂位掺杂的磷酸铁锂正极材料Li1-xTixFePO4(0≤x≤0.02),并将该材料与相同条件下制备的LiFePO4/C材料进行晶体结构、表面形貌、容量性能以及倍率性能比较。通过比较发现,Li1-xTixFePO4和LiFePO4/C均具有橄榄石结构,且粒径大小均在2～4μm。电化学性能测试结果表明,Li1-xTixFePO4比LiFePO4/C具有更加优异的容量性能和倍率性能。     

Dielectric relaxation and magnetic resonance in microwave absorption performance of CoxFe3-xO4 (0≤x≤1) nanocrystals

Cobalt ferrites (Co_xFe_3-xO₄, 0 ≤ x ≤ 1) may possess large magnetocrystalline anisotropy and coercivity at certain cobalt/iron (Co/Fe) ratios, while further explorations on their microwave absorption mechanisms are not adequate so far. In this study, a series of Co_xFe_3–xO₄ nanocrystals were synthesized by a developed oxidation-precipitation method, and a combination of dielectric relaxation and magnetic resonance was revealed in electromagnetic studies. Dielectric relaxation peaks were originated from orientation polarization and affected by oxygen vacancy densities. Magnetic resonance peaks were shifted to higher frequency due to the increased magnetocrystalline anisotropy at higher Co/Fe ratios. The excellent microwave absorption performance of as-prepared Co_xFe_3–xO₄ were also obtained, which should be attributed to the electromagnetic matching of dielectric relaxation and magnetic resonance at higher frequency ranges.     

Origin of anomalous octahedral distortions and collapse of magnetic ordering in Nd1−xSrxFeO3 (0≤x≤0.5)

The effects of strontium doping on the structural properties and magnetic ordering of Nd_1?xSr_xFeO₃ orthoferrite system have been studied by employing macroscopic and microscopic structural techniques like X-ray diffraction, scanning electron microscopy and ⁵⁷Fe Mössbauer spectroscopy. X-ray diffraction confirmed that single phase materials have been synthesized. It has been observed that orthorhombic distortion, density and porosity have decreased; whereas, grain size, tolerance factor and symmetry have increased with increase in the strontium concentration. Mössbauer results showed an increase in the Fe⁴⁺/Fe³⁺ ratio, sagging and local octahedral distortions while decrease in the magnetic ordering with increase in the strontium content. The origin behind anomalous octahedral distortions in this system has been attributed to the decrease in the oxidation state and mismatch in the ionic radii of A-site cations and increase in the concentration of Fe⁴⁺, due to Sr²⁺ doping at Nd³⁺ sites. The collapse of magnetic ordering has been ascribed to the weakening of super-exchange interactions, dilution of strong long range magnetic sub-lattice of high spin Fe³⁺ (five unpaired electrons) by relatively lower spin of high spin Fe⁴⁺ (four unpaired electrons) and increase in the spin–spin relaxation frequency.     

Thermoelectric properties of copper-deficient Cu2-xSe (0.05 ≤ x ≤ 0.25) binary compounds

Recently, many novel superionic thermoelectric materials have been discovered along the concept of “phonon-liquid electron-crystal” (PLEC). Among them, Cu_2-xSe-based liquid-like materials are typical examples. In this study, a series of copper-deficient Cu_2-xSe (0.05 ≤ x ≤ 0.25) materials were synthesized and used to study the role of Cu vacancies on the electrical and thermal transport properties. The X-ray photoelectron spectroscopy (XPS) measurements suggest that the valence states of Cu and Se are independent on the Cu/Se atomic ratio. With increasing the content of Cu vacancies, the hole concentration is monotonously increased, leading to the improved electrical conductivity and reduced Seebeck coefficient. Based on the single parabolic band model analysis, it is found that changing the content of Cu vacancies does not obviously modify the material's electronic band structure and effective mass. Due to the presence of highly mobile Cu ions inside the crystal structure, the lattice thermal conductivities of all Cu_2-xSe (0.05 ≤ x ≤ 0.25) materials are very low with values around 0.39 W m⁻¹ K⁻¹ at 500 K. Because of the significantly reduced Seebeck coefficient and increased electronic thermal conductivity, the thermoelectric figure of merit zTs are decreased when increasing x from 0.05 to 0.25. At 750 K, a maximum zT of 0.46 is obtained in Cu_1.95Se among all Cu_2-xSe (0.05 ≤ x ≤ 0.25) materials.     

Syntheses,magnetic properties,and reactivity of dinuclear oxovanadium (IV) and copper (II) complexes with (μ-diphenylphosphinato)-bridges

Novel dinuclear oxovanadium (IV) complexes having the formula [(VO)₂(dpp)₃(bpy)₂]NO₃·2H₂O (1), [(VO)₂(dpp)₃(phen)₂]-NO₃·H₂O (2), [(VO)₂(bmp)₃(bpy)₂]NO₃·H₂O (3), and [(VO)₂(bmp)₃(phen)₂]NO₃·H₂O (4), and copper (II) complexes having the formula [Cu₂(bmp)₂(phen)₂](NO₃)₂·MeOH·H₂O (5), and [Cu₂(bmp)₂(bpy)₂](NO₃)₂ (6) (where Hdpp=diphenylphosphinic acid, Hbmp=bis(4-methoxyphenyl)phosphinic acid, bpy=2,2^′-bipyridine, and phen=1,10-phenanthroline) with (μ-phosphinato)-bridges, 1–6, have been prepared and characterized. Crystal structure of complex 2 reveals that two vanadium ions are linked by tris(μ-phosphinato)-bridges. The magnetic susceptibility data for 1–3, and 6 conform to the usual dimer equation with −2J values of 16–24 cm⁻¹, indicating a weak antiferromagnetic interaction between vanadium(IV) ions.The oxidation of cinnamyl alcohol was studied using complexes 1–6 as catalyst and molecular oxygen as an oxidant. In the presence of complex 3 as a catalyst, cinnamyl alcohol was oxidized to cinnamaldehyde 61% yield in 7 h. Consequently, complex 3 activates oxygen, and then alcohol was quite efficiently oxidized by activated oxygen.     

Li1-xTixFePO4(O≤x≤0.02)制备表征及电化学性能研究

采用固相工艺制备了具有锂位掺杂的磷酸铁锂正极材料Li1-xTixFePO4(0≤x≤0.02),并将该材料与相同条件下制备的LiFePO4/C材料进行晶体结构、表面形貌、容量性能以及倍率性能比较.通过比较发现,Li1-xTixFePO4和LiFePOJC均具有橄榄石结构,且粒径大小均在2～4 μn.电化学性能测试结果表明,Li1-xTixFePO4比LiFePO4/C具有更加优异的容量性能和倍率性能.     

混合导体透氢膜SrCe_(0.95-x)Zr_xTm_(0.05)O_(3-δ)(0≤x≤0.40)的制备及其性能研究(英文)

Zr-substituted,Tm-doped SrCeO3(SrCe0.95-xZrxTm0.05O3-δ,0≤x≤0.40)were synthesized via citrate complexing method,and the membranes of SrCe0.95-xZrxTm0.05O3-δwere prepared by pressing followed by sintering. X-ray diffraction(XRD)was used to characterize the phase structure of sintered membrane.The microstructure of the sintered membranes was studied by scanning electron microscopy(SEM).Protonic and electronic conductivities were measured under different circumstance.Hydrogen permeation through the SrCe0.75Zr0.20Tm0.05O3-δmembranes was carried out using gas permeation setup.Hydrogen permeation fluxes( 2H J)of the SrCe0.75Zr0.20Tm0.05O3-δ membrane reach up to 0.042 ml·min -1 ·cm-2 at H 2 partial pressure of 0.4×10 5 Pa at 900°C.The hydrogen permea- tion fluxes( 2H J)obtained in this paper are slightly lower than that of SrCe0.95Tm0.05O3-δon the same orders,and Zr doping can increase chemical stability of the SrCe0.75Zr0.20Tm0.05O3-δmembranes.     

Crystal structure,magnetic and electric properties of highly coercive ferrites Sr1 − x Sm x Fe12 − x Zn x O19 (0 ≤ x ≤ 0.4)

The samples of highly coercive ferrites Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ (0 ≤ x ≤ 0.4) with the structure of magnetoplumbite have been obtained by the solid-phase method. It has been determined that the samples Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ are single-phase at x ≤ 0.2 and contain the impurity phases of α-Fe₂O₃, SmFeO₃, and ZnFe₂O₄ at x ≥ 0.3. In the magnetic fields up to 14 T, the specific magnetization has been measured and the values of coercive force (_σ H _c ) have been determined at 5 and 300 K. It has been shown that semiconductor electroconductivity of single-phase samples Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ gradually decreases with the increase in the degree of substitution of x from 0 to 0.2.     

Ceramic pigments from CoxNi3-xP2O8 (0 ≤ x ≤ 3) solid solutions

Co_xNi_3-xP₂O₈ (0 ≤ x ≤ 3) solid solutions were synthesized via the chemical co-precipitation method. Variation of unit cell parameters and interatomic distances indicated that these solid solutions with the Ni₃P₂O₈ structure are stable between 800 and 1200 °C in compositions with 0 ≤ x ≤ 1.5 and between 800 and 1000 °C when (0 ≤ x ≤ 3). When (2.5 ≤ x ≤ 3.0), the solid solutions lead to the Co₃P₂O₈ structure, being stable between 800 and 1000 °C.The yellow colour of the Ni₃P₂O₈ compound changes to pink or red when Co(II) ions are incorporated in the structure as Ni₃P₂O₈ solid solutions are formed. Bands corresponding to second and third electronic transitions of the Co(II) ions in octahedral coordination appear in the 450–600 nm in the UV-V spectra, and they are responsible of the observed changes in the colour. Absorbance in the visible spectra was also obtained from enamelled samples but a new band at 650 nm with considerable absorbance when x > 1.0 increased the blue amount, and colour of the enamelled samples was yellowish brown, brown, green and blue.     

Synthesis and characterization of a high near infrared reflectance yellow pigment SbxWO3 (x ≤ 0.14)

In this work, a novel yellow near-infrared (NIR) reflective pigment based on the formula of Sb_xWO₃ was developed by high temperature solid-state method at 700–900 °C. The formation of Sb_xWO₃ was confirmed by XRD analysis, and the synthesized pigments are orthorhombic phase with high near infrared reflectivity (84.69%–87.28%). The acid/alkali resistance studies reveal that the color difference ΔE * of the pigments before and after soaking was less than 5, and the as prepared pigments are chemically stable under the atrocious weather. In addition, the synthetic pigments are bright yellowish green (L* = 92.1–92.9, a* = -4.9–4.1, b* = 35.0–37.0). In the heat insulation performance test, the indoor temperature with the Sb_xWO₃ heat insulation coating is 3.1 °C lower than that without heat insulation coating. In summary, the as prepared Sb_xWO₃ pigment has the advantages of high solar reflectivity and less toxic elements, making this new environmentally friendly energy-saving yellow pigment used as a colorant for building exterior coating formulations to reduce heat accumulation and cooling energy consumption.     

Synthesis,spectral, structural,Hirshfeld surface and DFT studies on bis(N-(4-fluorobenzyl)-N-(2-phenylethyl)dithiocarbamato-S,S′)zinc(II) and its use for the preparation of ZnS and ZnO nanoparticles

Two new complexes, bis(N-(2-phenylethyl)-N-(4-fluorobenzyl)dithiocarbamato-S,S′)zinc(II) (1) and bis(N-(2-phenylethyl)-N-(4-chlorobenzyl)dithiocarbamato-S,S′)zinc(II) (2), have been synthesized and characterized by various physicochemical techniques. Structure of 1 has been determined by single crystal X-ray diffraction. Complex 1 is a dimer. Zinc atom is four coordinated with a distorted tetrahedral environment. Geometry optimization, geometrical parameters, molecular electrostatic potential (MEPs) and frontier molecular orbital analysis of dimeric and monomeric structures of 1 have been carried out by DFT methods and compared with the experimental X-ray diffraction data. The noncovalent interactions in the complex 1 have been analyzed using Hirshfeld surface analysis. 1 and 2 have been used as single source precursors for the preparation of zinc sulfide and zinc oxide nanoparticles. As-prepared zinc sulfides and zinc oxides have been characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM), UV–vis absorption, photoluminence and energy dispersive X-ray spectroscopy (EDS). X-ray diffraction study reveals that zinc sulfides and zinc oxides are composed of rhombohedral and hexagonal phases, respectively. Photocatalytic activities of zinc sulfides and zinc oxides were evaluated by degradation of rhodamine B in aqueous solution under UV light irradiation. The results demonstrated the capability of zinc sulfides and zinc oxides as photocatalyst under UV irradiation to degrade the dye.