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Green Synthesis Approach for Nano sized CoFe2O4 through Aloe Vera Mediated Sol-gel Auto Combustion Method for High Frequency Devices
摘要： Nanosized CoFe2O4 was synthesized by Aloe vera-mediated sol-gel auto-combustion method. The yielded nanoparticles were characterised by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) to investigate the phase formation and morphology of the obtained powders. FTIR, XRD and Raman spectra revealed the formation of single phase CoFe2O4. FESEM micrographs showed the formation of some bud like structure and the particle size obtained is around 50-65?nm. Investigation of magnetic properties viz. saturation magnetization (Ms), remenant magnetization (Mr) and coercivity (Hc) were studied from the M-H loop and were found to be 72.23 emu/gm, 31.29 emu/gm, 1519 Oe respectively. In addition, the massive dielectric constant, low dielectric loss, and AC conductivity of the CoFe2O4 nanoparticles were dependent on the frequency (100 Hz-1 MHz), method of preparation and grain size. Room temperature ferroelectric measurement reveals a partially unsaturated P-E loop due to the high coercive field and influence of leakage current.
关键词： Aloe vera plant extract,magnetism,nanostructured materials,Dielectric properties,sol-gel auto combustion
更新于2025-09-23 15:21:21
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Structural and dielectric properties of PLD grown BST thin films
摘要： Thin films of Barium Strontium Titanate (BaSrTiO3, BST) have been deposited on platinised silicon substrate using pulsed laser deposition (PLD) technique. The effect of growth pressure and temperature during the film deposition on the crystallization and dielectric behaviour of the BST films has been studied. The effect of plume dynamics due to variation in deposition parameters present inside the deposition chamber has also been investigated. The dielectric constant of the BST thin film deposited under variable deposition pressures increases with increase in deposition temperature at a frequency of 1 MHz. The BST thin film deposited at 1.33 × 10?4 bar and 800 °C substrate temperature exhibits high dielectric constant (≈475) with 65% tunability which can be efficiently exploited for the realization of tunable resonators and filters.
关键词： Barium Strontium Titanate,BST,PLD,tunability,dielectric properties
更新于2025-09-23 15:21:21
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Structural, electrical, dielectric properties and conduction mechanism of sol-gel prepared Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 compound
摘要： A detailed investigation of structural, electrical and dielectric properties of Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 manganite prepared by the sol-gel method was undertaken. The Rietveld refinement of X-ray diffraction pattern reveals that this compound is indexed in the orthorhombic structure with Pbnm space group. Structural properties are also analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy at room temperature. DC conductivity (σDC) data show the presence of a semiconductor-metal transition at TSM=360K. σDC is described by small polaron hopping model at high temperatures and variable range hopping model at low temperatures. AC conductivity results follow the universal Jonscher's power law at relatively low temperatures and Drude's model at high temperatures. The impedance plots display the contribution of both intra- and inter-granular contributions. Dielectric measurements exhibit highly remarkable dielectric permittivities useful in electronic devices. Dielectric losses are shown to be governed by the DC conduction mechanism and described by the Giuntini theory.
关键词： Electrical properties,Dielectric properties,Metal-semiconductor transition,Impedance spectroscopy
更新于2025-09-23 15:21:01
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The effect of Yb3+ ion substitution on dielectric and microstructural properties of Y3Al5O12 ceramics
摘要： The electrical and dielectric properties of Y3Al5O12 (yttrium aluminum garnet, YAG) ceramics are investigated in detail. YAG:(Yb)x (0.01 ≤ x ≤ 0.09) was synthesized by a solid state reaction and characterized by X-ray powder diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The electrical and dielectric properties have been intensively studied under certain bias voltages up to a frequency of 10 MHz. These properties are dependent on the substitution rates, independent of the bias voltages. The experimental result shows that Yb3+ ion substitution into YAG ceramics significantly influences the conductivity, dielectric constant, and lossy mechanisms, which is probably owing to the 3d-Al ions and 4f-Yb ions incorporated at different positions of structural symmetries in Y3?xYbxAl5O12 (0.00 ≤ x ≤ 0.09) ceramics.
关键词： ceramics,Yb3+ ion substitution,Y3Al5O12,dielectric properties,microstructural properties
更新于2025-09-23 15:21:01
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Design and Optimization Methodology of Coplanar Waveguide Test Structures for Dielectric Characterization of Thin Films
摘要： This paper describes an accurate design method of coplanar waveguide (CPW) test structures on characterizing dielectric properties of thin films with arbitrary thickness. Current CPW measurement method has difficulty in providing accurate dielectric properties of films with extremely small thickness. To address this issue, an optimized algorithm is presented to generate proper geometric parameters of CPW test structures for films with different thickness. To validate the accuracy of the proposed design methodology, various test cases of CPW structures with different dimensions have been designed and implemented, the extracted dielectric properties (e.g., dielectric constant and loss tangent) from the S-parameters of the different test cases are compared to the benchmark results simulated by accurate electromagnetic tool Ansys HFSS. It demonstrates the efficacy of the proposed optimized method on quickly producing correct dimensions of CPW test lines for accurate properties characterization of thin films.
关键词： Dielectric properties,Thin film,Coplanar waveguide test structure,Optimization method
更新于2025-09-23 15:21:01
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Structure stability, bond characteristics and microwave dielectric properties of co-substituted NdNbO4 ceramics
摘要： Structure-property relationship of co-substituted (Mg2+1/4Mo6+3/4)5+, (Al3+1/3Mo6+2/3)5+, (Si4+1/2Mo6+1/2)5+, (Zr4+1/2Mo6+1/2)5+ for Nb5+ in NdNbO4 ceramics was investigated systematically. The remarkable differences in dielectric properties of each composition originated from their bond characteristics and structure stability. The elongated/compressed bonds have an effect on the cell volume and polarization. And the average bond covalency of Nb-O bond was responsible for the development of permittivity. Q×f values and the total lattice energy went up to maximum when (Si0.5Mo0.5) occupied Nb-site. Variations of lattice energy together with Nb-O bond energy suggest that a more stable structure was obtained through co-substitution. The optimal microwave dielectric properties is: εr=18.97, Q×f=49466GHz, τf=7.34 ppm/℃ for NdNb0.97(Si0.5Mo0.5)0.03O4, sintered at 1250℃.
关键词： bond characteristics,Rietveld refinement,NdNbO4,microwave dielectric properties
更新于2025-09-23 15:21:01
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Effect of the occupation of Ba and Ti sites on the structural, optical and dielectric properties of Sm-doped BaTiO3 ceramics
摘要： Sm-doped BaTiO3 powders have been synthesized with the help of the sol gel process. X-ray diffraction (XRD) patterns of the obtained powders, heat treated at a relatively low temperature (750 °C/3 h), revealed their crystallization in the pure perovskite structure without the presence of secondary phases. The occupation of the Ba and Ti sites by Sm in the BaTiO3 lattice and the evolution of the crystalline parameters as functions of the dopant content have been discussed based on XRD and Raman results. Dielectric measurements performed on the samples revealed a strong increasing diffuse character of the ferro-to-paraelectric phase transition with increasing Sm content. Moreover, the behavior of the permittivity as a function of frequency indicates that the samples are approaching their resonance frequency. The study of the conductivity showed the existence of a weak positive temperature coefficient of resistivity (PTCR) effect.
关键词： Sm-doped BaTiO3,dielectric properties,PTCR effect,perovskite structure,sol gel process
更新于2025-09-23 15:21:01
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Dielectric Measurements of Polymer Composite Based on CdS Quantum Dots in Low Density Polyethylene at Microwave Frequencies
摘要： CdS nanoparticles (NPs) as quantum dots (QDs) added into low density polyethylene (LDPE) can significantly change the MW dielectric properties of the composites. Introducing into the matrix of low density polyethylene CdS QDs increase the dielectric constant of more than twice. CdS QDs with concentration of 5 wt % to 20 wt % were prepared by the method of high-speed thermal decomposition. The size of CdS nanoparticles ranged from 2 nm to 7 nm. Experimental samples based on polymer-based nanocomposite in the form of thick films with a thickness of 80 to 100 microns were prepared by thermocompression. Complex dielectric permittivity of thick film samples was measured by T/R method from 2 to 8 GHz at room temperature (25°C). For samples with 20 wt % CdS NPs size effect was found. The change of dielectric properties of polymer composite materials is associated with the size of QDs. The dielectric constant and dielectric loss increases with decreasing size of the quantum dots. It is shown that the highest mean value of the dielectric constant and dielectric loss at a frequency range of 5 GHz to 8 GHz for cadmium sulfide nanoparticles with size of 4 nm were 12 and 189 dB/m, respectively. For QDs with ones of 6 nm average dielectric constant and dielectric loss were 5.8 and 134 dB/m, respectively. The effective dielectric constant and dielectric losses in the microwave range can be changed by CdS QDs of different sizes what consequently increases the possibility of using polymer nanocomposites as core elements of the microwave band-pass filters for various purposes.
关键词： quantum dot,cadmium sulfide,polymer composite,filled polymer,MW dielectric properties,low density polyethylene,composites
更新于2025-09-23 15:19:57
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Effects of substrate-controlled-orientation on the electrical performance of sputtered BaTiO <sub/>3</sub> thin films
摘要： In this work, the relationships between bottom electrode/substrate configuration, crystalline microstructure, and electrical performances of BaTiO3 (BTO) thin films were investigated. The films were fabricated via RF magnetron sputtering on (Sr0.5La0.5)CoO3 (LSCO) buffered (110)-, (111)-SrTiO3 (STO) and SrRuO3 (SRO) buffered (110)-, (111)-MgO (MGO) substrates. The x-ray diffractometer results show that the LSCO/STO substrate resulted in films with high-quality epitaxial orientation, whereas the SRO/MGO substrate resulted in films having a strong (110) texture. The electrode/substrate configurations were designed to control the crystalline microstructure, which in turn affects the electrical performances of the films. The electrical performances were studied by employing a metal/ferroelectric/metal model. The J-V characteristics show obvious asymmetry with bias, which is mainly due to the varying transport state of oxygen vacancies. BTO films grown on LSCO/STO substrates exhibit large dielectric frequency dispersion, while those grown on SRO/MGO substrates display a nearly frequency independent response. All electrical parameters of these films were strongly affected by the polarization-tilting angle and the preferred orientation degree. Epitaxial and textured (110)-oriented films show higher permittivity but lower loss tangent, free-carrier concentration, built-in voltage, and leakage current density as compared to the epitaxial (111)-oriented film.
关键词： dielectric properties,electrical performance,substrate-controlled-orientation,BaTiO3 thin films,RF magnetron sputtering
更新于2025-09-23 15:19:57
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Epitaxial growth and in-plane dielectric properties of DyMnO <sub/>3</sub> by pulsed-laser deposition
摘要： Perovskite manganites DyMnO3 thin film was grown epitaxially on LaAlO3 (110) substrate by using pulsed-laser deposition (PLD) technique. The film showed perfectly orthorhombic crystallization and was well-aligned with the substrates. The in-plane dielectric properties of DyMnO3 film were measured as functions of temperature (80–300 K) and frequency (120–100 kHz) by using parallel-plate interdigital electrodes (IDEs). Distinct transitions can be observed in the complex permittivity and loss tangent and the respective peaks shifted to higher temperatures as the measuring frequency increased. By the Arrhenius plots, the determined activation energy of the thermally activated dielectric relaxations was about 0.20 eV. According to the relationship of the real and imaginary parts of the complex permittivity, the in-plane dielectric properties of epitaxial DyMnO3 thin film can be described as the universal dielectric response (UDR) behavior.
关键词： DyMnO3 thin film,orthorhombic,Dielectric properties,interdigital electrodes
更新于2025-09-23 15:19:57