Enhanced magnetic,ferroelectric, and photocatalytic properties of (1-x)BiFeO3-xBaTiO3 (0.0 ≤ x ≤ 0.4) powders

The magnetic, ferroelectric, and photocatalytic properties of (1-x)BiFeO₃-xBaTiO₃ (0.0 ≤ x ≤ 0.4) powders synthesized by sol-gel method have been investigated. X-ray diffractometry confirms that the phase of the samples changed from rhombohedral to cubic with the increase in BaTiO₃ content. The grain size decreases and the particle shape becomes homogeneous with the introduction of BaTiO₃. BaTiO₃ substitution enhances the multiferroic properties of the ceramics and the maximum remnant magnetization (0.261 emu/g) and remnant polarization (20 μC/cm²) have acquired in 0.8BiFeO₃-0.2BaTiO₃ and 0.7BiFeO₃-0.3BaTiO₃, respectively. The absorbance in ultraviolet and visible light regions is improved obviously for powder with x = 0.3. The energy band gap of the samples decreases from 2.06 eV to 1.57 eV with the introduction of BaTiO₃, indicating that the excitation rate of photogenerated electron-hole pairs is improved. The highest methylene blue degradation efficiency of ~62% within 3 h under the visible light is achieved in the 0.7BiFeO₃-0.3BaTiO₃ which can be attributed to its suitable energy band gap and large remnant polarization.     

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.     

Design and characterization of novel manganite perovskites Ba1-xBixTi1-xMnxO3 (0≤x≤0.2)

Polycrystalline manganite powders of Ba_1-xBi_xTi_1-xMn_xO₃ (x = 0, x = 0.1 and x = 0.2) were synthesized by the conventional solid-state reaction process. Their crystal structure, morphological, optical, dielectric and electrical properties were investigated. X-ray diffraction of the prepared samples was made at room temperature and confirmed the formation of a perovskite phase. Structural refinement, using the Rietveld method, revealed a tetragonal P4mm phase of pure BTO and a tetragonal P4/mmm phase with the presence of vacancies for both doped samples (x = 0.1 and x = 0.2). Scanning electron microscopy indicated that the perovskite samples had a grain size smaller than 1 μm. From UV–vis–NIR spectra, we found that the band gap reduces from 3.29 eV to 1.48 eV with the increase of Bi and Mn amounts, resulting in a shift of the absorption wavelength region toward the visible range. Dielectric analysis was conducted in a wide range of temperatures at different frequencies. Phase transitions were identified from thermal dielectric results, showing that the samples exhibited a non-relaxor behavior. The structural transformation from tetragonal to cubic structure corresponding to the transition from ferroelectric phase to paraelectric phase was observed in the dielectric properties investigation. The complex impedance spectroscopy indicated the presence of grain and grain boundary effects in the conduction mechanism. Electrical analysis showed that doping with Bi and Mn enhanced the DC conductivity. Furthermore, the DC conductivity temperature dependence confirmed that the studied samples present a semiconductor behavior. The activation energies of grain and grain boundaries depended on the amount of incorporated Bi and Mn. The activation energy of grain varied between 0.54 and 0.87 eV suggesting that the DC electrical conductivity is governed by ionized oxygen vacancies. The activation energy of grain boundaries varied between 0.85 and 0.58 eV.     

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.     

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.     

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.     

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.     

The effect of Gd3+ and Ti4+ co-doping on the thermal radiation performance of (Sm1-xGdx)2(Hf1-xTix)2O7 (0 ≤ x ≤ 0.2) ceramic coatings

In this study, the (Sm_1-xGd_x)₂(Hf_1-xTi_x)₂O₇ (0 ≤ x ≤ 0.2) ceramic coatings were fabricated by atmospheric plasma spraying. The chemical compositions, morphologies and thermo-optical properties of the samples were systemically investigated. It can be found that the infrared emissivity of (Sm_1-xGd_x)₂(Hf_1-xTi_x)₂O₇ ceramic coatings at the wavelength range of 0.76–15 μm increased with the increasing content of Gd³⁺ and Ti⁴⁺. The (Sm_0.8Gd_0.2)₂(Hf_0.8Ti_0.2)₂O₇ ceramic coating exhibited the highest infrared emissivity among the coatings, which was 0.773 and 0.816 at room temperature and 1400 °C, respectively. The mechanism of the increasing infrared emissivity was attributed to the Gd³⁺ and Ti⁴⁺ co-doping can improve the free carrier concentration and the frequency and mode of the lattice vibration. Moreover, the (Sm_0.8Gd_0.2)₂(Hf_0.8Ti_0.2)₂O₇ ceramic coating possessed good thermal resistance, which did not show obvious change in the phase, surface morphology and infrared emissivity after 60 h calcination at 1400 °C.     

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。     

Transport properties of p-type Ca3-xLnxCo4O9-Ag (Ln = Lu,Yb; 0.1≤x≤0.2) oxides

Thermoelectric transport properties of p-type Ca_3-xLn_xCo₄O₉/yAg oxides (Ln = Lu & Yb; 0.1 ≤ x ≤ 0.2; 0.05 ≤ y ≤ 0.1) synthesized by sol-gel methodology were investigated in this paper. The structural analyses (SEM, XRD and TEM) confirmed the presence of two phases, viz, Ca_3-xLn_xCo₄O₉ and Ag-metallic phases. The contribution of rare earth doping in one hand and presence of Ag as secondary phase on the other hand were studied. The resistivity measurements indicated the reduction of electrical resistance at the grain boundary leading to an overall decrease in electrical resistivity with increasing Ag-concentration. The enhancement of Seebeck coefficient is attributed to the substitution of Ln³⁺ at Ca²⁺ sites that in turn reduces hole concentration through formation Co³⁺ for charge concentration counter balance in Ca_3-xLn_xCo₄O₉/yAg matrix. The tuning of electrical transport properties through Ca_3-xLn_xCo₄O₉ and Ag-metallic bi-phasic formation resulted high power factor of 582 μW m⁻¹ K⁻² for Ca_2.8Ln_0.2Co₄O₉/0.05Ag and 548 μW m⁻¹ K⁻² for Ca_2.8Yb_0.2Co₄O₉/0.05Ag at 950 K highlighting its potential application on small scale energy harvesting to power sensor and wireless sensor network where requirement of power is in the milliwatt range.     

LaCr1-xFexO3 (0≤x≤0.7): A novel NTC ceramic with high stability

Perovskite-phase LaCr_1-xFe_xO₃ (0 ≤ x ≤ 0.7) ceramics were fabricated by two-step sintering of powders synthesized by conventional solid-state reaction. XRD patterns reveals that the ceramics are single-phased LaCr_1-xFe_xO₃ solid solution at lower Fe contents, but form a biphasic mixture of LaCrO₃-LaFeO₃ at higher Fe contents. SEM analysis indicates that Fe doping causes a reduction in porosity, and a corresponding increase in density. The effects of Fe doping on electrical properties have also been investigated. The electrical resistivity ρ_25°C decreases initially and then increases within a wide range of 634.4–83915.9 Ω·cm with increasing Fe content, whereas B varies within a relatively narrow range of 3651−4301 K. Such combination enables it to be a potential candidate for NTC thermistors. An investigation of elevated-temperature aging behavior shows that the resistance shifts at 25 °C were less than 0.65 % after annealing at 125 °C in air for 1000 h, revealing that the material exhibits excellent stability.     

Electrochemical performance of NixCo1-xMoO4 (0 ≤ x ≤ 1) nanowire anodes for lithium-ion batteries

Ni _x Co_1-x MoO₄ (0 ≤ x ≤ 1) nanowire electrodes for lithium-ion rechargeable batteries have been synthesized via a hydrothermal method, followed by thermal post-annealing at 500°C for 2 h. The chemical composition of the nanowires was varied, and their morphological features and crystalline structures were characterized using field-emission scanning electron microscopy and X-ray powder diffraction. The reversible capacity of NiMoO₄ and Ni_0.75Co_0.25MoO₄ nanowire electrodes was larger (≈520 mA h/g after 20 cycles at a rate of 196 mA/g) than that of the other nanowires. This enhanced electrochemical performance of Ni _x Co_1-x MoO₄ nanowires with high Ni content was ascribed to their larger surface area and efficient electron transport path facilitated by their one-dimensional nanostructure.     

Influence of TiO2 doping on thermo-optical properties of pyrochlore Sm2(Zr1–xTix)2O7 (0≤x≤0.15) ceramics

Sm₂(Zr_1–xTi_x)₂O₇ (0≤x≤0.15) ceramics have been fabricated by pressureless-sintering method at 1973 K for 10 h in air. The influence of TiO₂ doping on microstructure and thermo-optical properties of Sm₂(Zr_1–xTi_x)₂O₇ ceramics is investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The partial substitution of Ti⁴⁺ for Zr⁴⁺ results in a significant increase in emissivity at low wavelengths contrasted with undoped Sm₂Zr₂O₇. Sm₂(Zr_0.85Ti_0.15)₂O₇ ceramic exhibits a high emissivity of above 0.70 at 1073 K in a wavelength range of 3–16 µm, where the highest value at this temperature is more than 0.90 especially in the wavelength range of 9–14 µm. FT-IR spectra and optical absorption spectra unveil the mechanisms of enhanced emissivity in Sm₂(Zr_1–xTi_x)₂O₇ (0.05≤x≤0.15) ceramics in the intermediate infrared range, especially at the wavelengths of 3–8 µm, due to Ti⁴⁺ ion substitution for Zr⁴⁺ ion.     

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.     

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.     

掺杂少量Sm时La0.67-xSmxSr0.33MnO3(0.00≤x≤0.30)的磁电性质

通过测量样品的磁化强度-温度(M-T)曲线、电阻率-温度(ρ-T)曲线及磁电阻(magnetoresistance)-温度(MR-T)曲线,研究了Sm掺杂(x=0.00,0.10,0.20,0.30)对La0.67-xSrmxSr0.33MnO3磁电性质的影响.发现在铁磁相主要是单磁子散射起作用,表现为金属型导电,可用公式ρ=ρ0+AT2拟合,其中ρ为温度T时的电阻率;ρ0为0 K时的电阻率;A为常数.顺磁相的输运机制主要是小极化子跃迁起作用,可以用公式ρ=BTexp·(Ea/kBT)拟合,其中Ea为激活能;kB为Bolzman常数;B为常数.在相变温区是顺磁相的小极化子与铁磁相的单磁子2种输运性质共存.     

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.     

(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.     

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。