Structural, optical and electrical properties of ZnO/Zn2GeO4 porous-like thin film and wires

Zinc oxide/zinc germanium oxide (ZnO/Zn₂GeO₄) porous-like thin film and wires has been fabricated by simple thermal evaporation method at temperature about 1120 °C for 2.5 h. The structural and optical properties of the porous-like-thin film and wires have been investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. Metal semiconductor metal (MSM) photodetector structure was used to evaluate the electrical characteristics by using current-voltage (I-V) measurements. Room temperature photoluminescence spectrum of the sample shows one prominent ultraviolet peak at 378 nm and a shoulder at 370 nm. In addition, broad visible blue emission peak at wavelength 480 nm and green emission peak at 500 nm are also observed. Strong photoelectric properties of the MSM in the UV demonstrated that the porous-like-thin film and wires contribute to its photosensitivity and therefore making ZnO/Zn₂GeO₄ wires potential photodetector in the shorter wavelength applications.     

Magnetic and dielectric properties of alkaline earth Ca and Ba ions co-doped BiFeO3 nanoparticles

Ca²⁺ and Ba²⁺ ions co-doped BiFeO₃ nanoparticles, Bi_0.8Ca_0.2−xBa_xFeO₃ (x=0-0.20), were prepared by a sol-gel method. The phase structure, grain size, dielectric and magnetic properties of the prepared samples were investigated. The results showed that the lattice structure of the nanoparticles transformed from rhombohedral (x=0) to orthorhombic (x=0.07-0.19) and then to tetragonal (x=0.20) with x increased. The dielectric properties of the nanoparticles were affected by the properties of the substitutional ions as well as the crystalline structure of the samples. The magnetic properties of the nanoparticles were greatly improved and the T_N of the nanoparticles was obviously increased. All the Ca²⁺ and Ba²⁺ ions co-doped BiFeO₃ nanoparticles presented the high ratio of M_r/M from 0.527 to 0.571 and large coercivity from 4.335 to 5.163 KOe.     

Synthesis,structural and electrical properties of Ti modified Bi2Sn2O7 pyrochlore

Polycrystalline ceramic samples of Bi₂Sn_2−xTi_xO₇ (x=0.00, 0.2, 0.4, 0.6 and 0.8) have been synthesized by standard high temperature solid state reaction method. The effect of homovalent cation (titanium) substitution on the Sn-site on the structural and electrical properties of the pure Bi₂Sn₂O₇ ceramic have been studied by X-ray diffraction followed by SEM, dielectric and dc conductivity studies. The structural analysis indicates that the increase of titanium contents do not lead to any secondary phase. The frequency and temperature dependent dielectric studies have been carried out. It is found that the Ti doping reduces the material particle size. The size of the particles are strongly influenced by the addition of titanium to the system. The substitution of Ti for Sn ions affected the degree of disorder and modified the dielectric properties leading to more resistive ceramic compounds. The activation energies of all the compounds were calculated using the relation σ=σ₀exp(−Ea/kT).     

Synthesis and photoluminescence properties of Sm-doped CaWO4 nanoparticles

The Sm³⁺-doped CaWO₄ nanoparticles were synthesized by hydrothermal method. The room temperature photoluminescence (PL) spectra of Sm³⁺-doped CaWO₄ nanoparticles doped with different Sm³⁺ concentrations under 405 nm excitation have been investigated. The PL spectra showed four strong emission peaks at 460, 571, 609, and 653 nm. The first emission peak at 460 nm could be due to a structural defect of the lattice, an oxygen-deficient WO₃ complex. The other three emissions at 571, 609, and 653 nm were due to the f-f forbidden transitions of the 4f electrons of Sm³⁺, corresponding to ⁴G_5/2→⁶H_5/2 (571 nm), ⁶H_7/2 (609 nm), and ⁶H_9/2 (653 nm), respectively. In addition, the optimum Sm³⁺ concentration in CaWO₄ nanoparticles for optical emission was determined to be 1.0%. The Sm³⁺⁴G_5/2→⁶H_7/2 (609 nm) emission intensity of Sm³⁺-doped CaWO₄ nanoparticles significantly increased with the increase of Sm³⁺ concentration, and showed a maximum when Sm³⁺ doping content was 1.0%. If Sm³⁺ concentration continued to increase, namely more than 1.0%, the Sm³⁺⁴G_5/2→⁶H_7/2 emission intensity would decrease. The present materials might be a promising phosphor for white-light LED applications.     

Effect of Mg doping on the electrical properties of SnO2 nanoparticles

Sol-gel derived Mg doped tin oxide (Sn_1−xMg_xO₂) nanocrystals were synthesized with x ranging between 0.5 and 7 at. %. Characteristic single phase tetragonal structure of pure and doped samples was obtained and doping saturation was inferred by X-ray diffraction analysis. Structural, morphological and phase informations were obtained by high resolution transmission electron microscope, field emission scanning electron microscope and X-ray photoelectron spectroscopy respectively whereas bonding information was obtained from Fourier transformed infrared spectroscopy. Measurement of different electrical parameters with frequency (200 Hz-10⁵ Hz) has been carried out at room temperature. Ultrahigh dielectric constant and metallic AC conductivity were observed for undoped tin oxide and the profiles reflected highly sensitive changes in the atomic and interfacial polarizability generated by doping concentrations. Relaxation spectra of tangent loss of any sample did not show any loss peak within the frequency range. Both the grain and grain boundary contributions are observed to increase as the doping concentration increased. Results of first principle calculation based on density functional theory indicated effective Fermi level (E_F) suppression due to Mg doping which is responsible for the experimentally observed conductivity variation. AC conductivity was found to depend strongly on the doping concentration and the defect chemistry of the compound. Mg doped SnO₂ may find applications as a low loss dielectric and high density energy storage material.     

Precipitate synthesis of BaMoO4 and BaWO4 nanoparticles at room temperature and their photoluminescence properties

The uniform BaMoO₄ and BaWO₄ nanoparticles (NPs) have been successfully synthesized by solution route – the direct precipitation of Ba(NO₃)₂ and Na₂MO₄ (M = Mo and W) in ethylene glycol under 24 h stirring. The XRD patterns and SEM images proved that the products were tetragonal structured BaMoO₄ and BaWO₄ with uniform round nanoparticles. Shape, average particle size and particle-size distribution of products were analyzed by TEM – showing the round nanoparticles with the average size of 31.52 ± 4.65 nm for BaMoO₄, and 59.77 ± 9.61 nm for BaWO₄. The room temperature photoluminescence (PL) indicated that the products have strong blue emission centered at 441 nm – excited with 280 nm wavelength for BaMoO₄ NPs, and strong violet emission centered 378 nm – excited with 344 nm wavelength for BaWO₄ NPs. These PL behaviors attributed the existence of intrinsic transitions in the [MO₄]^2-$[{\text{MO}}_4{]}^{2-}$ (M = Mo and W) tetrahedrons of their crystal lattices.     

Influence of Lu2O3 on electrical and microstructural properties of CaCu3Ti4O12 ceramics

In this work, the influence of Lu₂O₃ doped on the dielectric and electrical properties of CaCu₃Ti₄O₁₂ was reported. Lu₂O₃-doped CCTO was prepared by a conventional solid state technique using CuO, TiO₂, and CaCO₃ as starting materials. The samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM); dielectric measurements were measured in the 10² Hz–10⁷ Hz frequency range at room temperature; and the nonlinear behavior of all samples was measured. The doping of Lu₂O₃ resulted in an increase in the dielectric constant of CCTO, but decreased the stability of the frequency dependence. Increasing concentrations of Lu₂O₃ resulted in decreasing nonlinear coefficients.     

Effects of vanadium doping on structure and electrical properties of SrBi4Ti4O15 thin films

The effects of vanadium(V) doping into SrBi₄Ti₄O₁₅ (SBTi) thin films on the structure, ferroelectric, leakage current, dielectric, and fatigue properties have been studied. X-ray diffraction result showed that the crystal structure of the SBTi thin films with and without vanadium is the same. Enhanced ferroelectricity was observed in the V-doped SrBi₄Ti₄O₁₅ (SrBi_4−x/3Ti_4−xV_xO₁₅, SBTiV-x (x = 0.03, 0.06, and 0.09)) thin films compared to the pure SrBi₄Ti₄O₁₅ thin film. The values of remnant polarization (2P_r) and coercive field (2E_c) of the SBTiV-0.09 thin film capacitor were 40.9 μC/cm² and 105.6 kV/cm at an applied electric field of 187.5 kV/cm, respectively. The 2P_r value is over five times larger than that of the pure SBTi thin film capacitor. At 100 kHz, the values of dielectric constant and dielectric loss were 449 and 0.04, and 214 and 0.06 for the SBTiV-0.09 and the pure SBTi thin film capacitors, respectively. The leakage current density of the SBTiV-0.09 thin film capacitor measured at 100 kV/cm was 6.8 × 10⁻⁹ A/cm², which is more than two and a half orders of magnitude lower than that of the pure SBTi thin film capacitor. Furthermore, the SBTiV-0.09 thin film exhibited good fatigue endurance up to 10¹⁰ switching cycles. The improved electrical properties may be related to the reduction of internal defects such as bismuth and oxygen vacancies with changes in the grain size by doping of vanadium into SBTi.     

Optical and electrical properties of single Sb2Se3 nanorod

In this report, methods of solvothermal synthesis of Sb₂Se₃ nanorods from a single-source precursor Sb[Se₂P(O ⁱPr)₂]₃ were demonstrated. The synthesized Sb₂Se₃ nanorods were expected to have new optical and electrical properties. With the electron beam (E-beam) lithography and focus ion beam (FIB) techniques, we achieved immobilization and positioning of a single Sb₂Se₃ nanorod on a patterned template. By using the confocal Raman microscope and two-point-contact electrical measurement methods, we obtained optical and electrical characteristics from a single Sb₂Se₃ nanorod.     

The electrical properties of dielectric stacks of SiO2 and Al2O3 prepared by atomic layer deposition method

We produced dielectric stacks composed of ALD SiO₂ and ALD Al₂O₃, such as SiO₂/Al₂O₃, Al₂O₃/SiO₂, and SiO₂/Al₂O₃/SiO₂, and measured the leakage currents through the stacks in comparison with those of the single oxide layers. SiO₂/Al₂O₃ shows lowest leakage current for negative bias region below 6.4 V, and Al₂O₃/SiO₂ showed highest current under negative biases below 4.5 V. Two distinct electron conduction regimes are observed for Al₂O₃ and SiO₂/Al₂O₃. Poole-Frenkel emission is dominant at the high-voltage regime for both dielectrics, whereas the direct tunneling through the dielectric is dominant at the low-voltage regime. The calculated transition voltage between two regimes for SiO₂ (6.5 nm)/Al₂O₃ (12.6 nm) is −6.4 V, which agrees well with the experimental observation (−6.1 V). For the same EOT of entire dielectric stack, the transition voltage between two regimes decreases with thinner SiO₂ layer.     

Physical, electrical and dielectric properties of Ca-substituted strontium hexaferrite (SrFe12O19) nanoparticles synthesized by co-precipitation method

Calcium substituted strontium hexaferrite Ca_xSr_1−xFe₁₂O₁₉ (x=0.0−0.6) nanoparticles are synthesized by chemical co-precipitation method. The synthesized samples are characterized by Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy, Transmission Electron Microscopy, DC electrical resistivity and dielectric measurements. FTIR data of uncalcined sample shows that nitrate ions are present which disappeared on calcination at 920 °C. The XRD data shows that a single hexagonal magnetoplumbite phase is formed in samples in which the calcium content, x, is ≤0.20. However, a nonmagnetic phase (α-Fe₂O₃) in addition to the hexagonal phase is also present in samples with x>0.20. The average crystallite size is found between 17 and 29 nm. The DC electrical resistivity increases with increase of calcium content up to level of x=0.2 but decreased on further addition of calcium. The enhanced resistivity of the calcium doped material has potential applications in microwave devices. The variations of dielectric constant and dielectric loss angle are explained on the basis of Maxwell-Wagner and Koops models.     

Effect of nickel doping on structural, optical and electrical properties of TiO2 nanoparticles by sol-gel method

Nickel-doped anatase TiO₂ nanoparticles have been prepared by sol-gel method. The X-ray powder diffraction study reveals that all the prepared samples have pure anatase phase tetragonal system. The average crystallite size of the prepared sample is 14 nm, when found through transmission electron microscope. A strong frequency dependence of both dielectric constant (?′) and dielectric loss (tan δ) were observed for various dopant levels at room temperature in the frequency range of 42 Hz to 5 MHz. At low frequency, the piling up of mobile charge carriers at the grain boundary produces interfacial polarization giving rise to high dielectric constant. The asymmetric shape of frequency dependence of the dielectric loss for the primary relaxation process is observed for each concentration. From the ac conductivity studies, the reduction in conductivity may arise due to the decreasing particle with the increase in Ni-dopant level.     

CaCu3Ti4O12陶瓷的微观结构和电学性能

利用传统的固相反应工艺，在不同的烧结温度下制备了一系列的CaCu₃Ti₄O₁₂陶瓷样品，考察了其微观结构以及介电和复阻抗方面的电学性质.研究发现这些样品在微观结构方面可分为三种类型，高介电性与微观结构有着密切的关联性.室温下，样品的低频介电常数随陶瓷晶粒尺寸的增大而提高.随着测试温度的升高，不同微观结构类型的样品呈现出不同的电学性质的变化，但其中也存在着一些相同的特征.高温下，介电频谱呈现出一个低频介电响应和两个类Debye型弛豫色散，复阻抗谱呈现出三个Cole-Cole半圆弧.将实验上观测到的电学性质的起因归于陶瓷多晶微结构中的晶畴、晶界和晶粒内的缺陷. 关键词： 3Ti₄O₁₂')" href="#">CaCu₃Ti₄O₁₂ 微观结构 电学性质     

Effect of La substitution on conductivity and dielectric properties of Bi1−xLaxFeO3 ceramics: An impedance spectroscopy analysis

Bismuth ferrite (BFO) and La-substituted BFO with composition Bi_1−xLa_xFeO₃ (x=0.05, 0.1 and 0.15) (BLFO_x=0.05-0.15) ceramics were prepared using the solid state reaction route. A structural phase transition from rhombohedral phase to triclinic phase was observed for BLFO_x=0.05-0.15 ceramics. Modulus spectroscopy reveals the deviation of dielectric behavior from ideal Debye characteristics and the dependence of conductivity on ion hopping in BFO and BLFO_x=0.05-0.15 ceramics. The conductivity of the BFO ceramics decreases for La content of 5 mol%, followed by a subsequent increase with 10 and 15 mol% of lanthanum doping. The typical values of the activation energies at high temperature reveal the contribution of short range movement of doubly ionized oxygen vacancies to the conduction process in BFO and BLFO_x=0.05 ceramics. Both short range and long range motion of oxygen vacancies are responsible for large conductivity in BLFO_{x=0.1 and 0.15} ceramics.     

复合层状Bi7Ti4NbO21铁电陶瓷的结构与介电和压电性能研究

制备了Bi₇Ti₄NbO_{21，Bi4Ti3O12及Nb掺杂Bi4Ti3O12(Nb-Bi4Ti3O12)层状结构铁电陶瓷材料.结合Nb-Bi 4Ti3O12的介电温谱和 退极化实验结果，研究了Bi7Ti4NbO21的晶体结构 对其介电、压电性能的影响 .高分辨透射电镜结果表明，在Bi7Ti4NbO21中， 沿着c轴方向，(Bi2Ti3O10)^2-和(BiTiNbO7)^2-两个类钙钛矿层分别 与(Bi2O2)²⁺层叠加堆积而成.这种晶体结构决定了Bi7Ti4NbO21的 介电温谱在668℃和845℃出现介 电双峰.结合极化样品的退化实验分析，说明材料在这两个温度附近发生了铁电—铁电相变 、铁电—顺电相变，分别是(Bi2Ti3O10)^{2-< /sup>和(BiTiNbO7)2-层状 结构发生微观结构相变的结果.在退极化过程中，由于受热时钙钛矿层内空位引起的缺陷偶 极子的定向排列受到破坏，引起材料部分退极化，表现为300℃热处理后Bi7Ti 4NbO 21的压电活性降低了10%，显示了室温下材料的压电性能来源于自发极化的固有电 偶极子和缺陷偶极子的共同贡献.}}     

Crystal structure,dielectric and piezoelectric properties of Ta/W codoped Bi3TiNbO9 Aurivillius phase ceramics

Aurivillius phase Bi₃Ti_1−xTa_xNb_1−xW_xO₁₂ high temperature piezoceramics were prepared by a conventional solid state reaction method. The crystal structure, dielectric, electrical conduction and piezoelectric properties were systematically studied. Pure or modified Bi₃TiNbO₉ ceramics revealed the presence of only two-layered Aurivillius phase, indicating that Ta/W doping entered into the B-site of pseudo-perovskite structure and formed solid solutions. The Curie temperature had a strong reliance on the structural distortion. Furthermore, Ta/W dopants act as a donor doping, decrease the number of oxygen vacancies and facilitate the domain wall motion. As a result, Ta/W modifications significantly increase the DC resistivity and piezoelectric properties. Bi₃Ti_0.98Ta_0.02Nb_0.98W_0.02O₁₂ ceramics possess the optimum d₃₃ value (∼12.5 pC/N) together with a high T_C point (∼893 °C). Moreover, the resonance–antiresonance spectra demonstrate that the Ta/W-BTN ceramics are indeed piezoelectric in nature at 600 °C. The d₃₃ value of BTTNW-2 ceramic remains ∼12.2 pC/N after annealing at 700 °C. These factors suggest that the BTTNW-based ceramic is a promising candidate for ultra-high temperature sensor applications.     

β-Si3N4电子结构和光学性质的第一性原理研究

采用基于密度泛函的平面波赝势方法(PWP)和广义梯度近似(GGA)，计算了β相氮化硅(β-Si₃N₄)的电子结构和光学性质，得到的晶格常数、能带结构等均与实验结果较好符合.进一步还研究了β-Si₃N₄的光吸收系数以及禁带宽度随外压力的变化规律，为β-Si₃N₄材料在高压条件下的应用提供了理论参考. 关键词： β相氮化硅 电子结构 能带结构 光学性质     

Magnetic and electrical properties of bulk BaTiO3+MgFe2O4 composite

BaTiO₃+MgFe₂O₄ material system was synthesized by hybrid chemical process using chlorides and nitrates of barium, titanium, iron, and magnesium. Magnetic properties of the composite samples measured as a function of annealing conditions indicated soft magnetic behavior. Saturation specific magnetization from 8 21 emu/g was observed for samples annealed at temperature between 950 and 1150 °C. Variation of specific saturation magnetization with respect to annealing temperature was related with the distribution of Fe cations in the tetrahedral and octahedral sites of MgFe₂O₄. Electrical properties of the samples annealed at different temperatures were measured to analyze the coexistence of ferroelectric phase. Dielectric constant varying from 15 to 200 with respect to frequency was observed for samples annealed from 950 to 1150 °C.     

Mo掺杂SrBi4Ti4O15陶瓷的铁电介电性能

用传统的固相烧结工艺，制备了钼掺杂铁电陶瓷样品SrBi₄Ti₄O₁₅(SBTi)铁电陶瓷SrBi_4-2x/3Ti_4-xMo_xO₁₅(x=0.00，0.003，0.012，0.03，0.06，0.09).X射线衍射的结果表明，样品均为单一的层状钙钛矿结构相，Mo掺杂未改变SBTi的晶体结构.通过扫描电子显微镜观测发现，样品晶粒为片状，随掺杂量的增加，晶粒逐 关键词： 4Ti₄O₁₅')" href="#">SrBi₄Ti₄O₁₅ Mo掺杂 剩余极化 居里温度     

Synthesis and properties of Au-Fe3O4 and Ag-Fe3O4 heterodimeric nanoparticles

Monodisperse Au-Fe 3 O 4 heterodimeric nanoparticles (NPs) were prepared by injecting precursors into a hot reaction solution.The size of Au and Fe 3 O 4 particles can be controlled by changing the injection temperature.UV-Vis spectra show that the surface plasma resonance band of Au-Fe 3 O 4 heterodimeric NPs was evidently red-shifted compared with the resonance band of Au NPs of similar size.The as-prepared heterodimeric Au-Fe 3 O 4 NPs exhibited superparamagnetic properties at room temperature.The Ag-Fe 3 O 4 heterodimeric NPs were also prepared by this synthetic method simply using AgNO 3 as precursor instead of HAuCl 4.It is indicated that the reported method can be readily extended to the synthesis of other noble metal conjugated heterodimeric NPs.