Temperature Coefficient Of Dielectric Constant Research Articles

Gd3+ substitution effects, electrical and AC impedance characterizations of Gd/Cr co-doped SrBi4Ti4O15 Aurivillius-phase ceramics

Gd/Cr co-doped SrBi4Ti4O15 (Sr1-xGdxBi4Ti4O15 + 0.2 wt% Cr2O3, x = 0∼0.08) Aurivillius-phase ceramics were prepared by the traditional solid-state reaction process, the influences of Gd3+ doping concentration (x) on the structures and electrical properties of SrBi4Ti4O15 were investigated, as well as the AC impedance characterizations of the ceramics were analyzed. The incorporation of Gd2O3 and Cr2O3 into SrBi4Ti4O15 induced the lattice distortion of its orthorhombic structure. The donor substitution of Gd3+ for Sr2+ at A-site improved the Curie temperature (TC) and decrease the temperature coefficient of dielectric constant (TKε), as well as change the relaxation activation energy (Earel) of SrBi4Ti4O15 through the lattice distortion caused. Between 425 °C and 700 °C, the DC conduction behaviors of the ceramics was found with a transition from the mixed conduction mechanism involved in both the single-ionized oxygen vacancy and the double-ionized one to the single mode dominated by the latter one. Above TC, the imaginary part of modulus (M″) gradually shifts towards higher frequencies with increasing temperature, indicating the emergence of a new dielectric relaxation mode related to the phase transition process of the ceramics. Owing to the co-doping effects of Gd3+ and Cr3+, the optimized composition with x = 0.03 achieved excellent electrical properties (TC = 550 °C and d33 = 30 pC/N) and good thermal stability (TKε = 4.19 × 10−3/°C between RT and 500 °C, and the lose in d33 is only 3.3% after being annealed at 500 °C for 4 h), which make it promising for stable applications below 500 °C in the high-temperature piezoelectric devices.

Structures, dielectric properties and AC impedance characteristics of BiFeO3–BaTiO3 high-temperature lead-free piezoceramics synthesized by the hydrothermal method

Among the lead-free piezoceramics, ([Formula: see text])BiFeO[Formula: see text]BaTiO3 (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature ([Formula: see text]C) and good electromechanical properties. In this work, the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO3 and BaTiO3, and then the mixed powder compacts with the chemical composition of 0.7BF–0.3BT were sintered under pressureless conditions. The influence of the hydrothermal reaction times (12–24[Formula: see text]h) of BiFeO3 on the structures and electric properties of the sintered ceramics was instigated. First, all the samples synthesized with the tetragonal BaTiO3 and BiFeO3 powders were identified with relatively stable dielectric properties. As the hydrothermal reaction time to synthesize BiFeO3 increased, the dielectric properties as well as the temperature stability of the 0.7BiFeO3–0.3BaTiO3 ceramics also improved. At the condition of a hydrothermal reaction time of 24[Formula: see text]h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant ([Formula: see text]C between RT and [Formula: see text]C) and the highest Curie temperature ([Formula: see text]C at 100[Formula: see text]kHz). Moreover, at high temperatures, it exhibits a higher AC impedance than others. The calculating result based on the resistive constant-phase-element model (R-CPE) circuit model showed that the grain boundary of the 0.7BF–0.3BT ceramics contributes more resistance to the conductivity at high temperatures. In summary, the hydrothermal reaction proved to be a useful way that achieves the preparation of single-phase 0.7BF–0.3BT ceramics with improved electrical properties.

Engineering DyCrO3 ceramics toward room-temperature high-κ dielectric applications

The search for a high-κ dielectric material that combines a high dielectric constant (ϵ′) and low dielectric loss is very crucial because of its widespread use in gate dielectrics to avoid the leakage current that arises due to continued miniaturization of present SiO2-based metal-oxide semiconductor field-effect transistor devices. RCrO3 (R is a rare-earth ion) materials have been at the center of interest because of their intriguing ferroelectric and magnetic properties, as well as their room-temperature colossal dielectric constant (CDC) values. Although CDC (ϵ′∼104) in RCrO3 materials is quite common, it is unsuitable for device applications since it is associated with a larger dielectric loss value (tan δ∼7 at 11 kHz). Here we have focused on polycrystalline DyCrO3, prepared using multiple synthesis techniques, and thoroughly investigated the origin and tuning of the various dielectric relaxations that give rise to CDC and large dielectric loss values. A clear understanding of the origin of dielectric relaxations enables us to design a specially synthesized DyCrO3 (SPS-DCO) in which the extrinsic dielectric relaxations driven large dielectric loss values can be completely suppressed and which is found to be associated with optimized high-κ dielectric properties [ϵ′∼130, tan δ∼0.06, and temperature coefficient of dielectric constant (TCϵ) ∼ 2280 ppm/K at 11 kHz, 300 K]. The only remaining intrinsic Debye-type dielectric relaxation in SPS-DCO arises due to electric-field-assisted charge hopping among various valences of Cr (investigated using x-ray photoelectron spectroscopy) that presently limits the lowest attainable loss value.

Correlation between structure and microwave dielectric properties of ordered olivine CaLnGaO4 (Ln = Pr, Yb) ceramics

The microwave dielectric properties of olivine-structured CaLnGaO4 (Ln = Pr, Yb) ceramics with a 1:1 order at the octahedra site were investigated using bond valance, P–V-L chemical bond theory, and Raman spectra. The theoretical permittivity εr(C-M) values are far below the porosity-corrected εr(Corr) values, indicating that the dielectric polarizabilities of CaLnGaO4 (Ln = Pr, Yb) were underestimated, and this phenomenon was mainly influenced by rattling cations. The difference in εr is mainly determined by the ionic polarizability per unit volume (αm/Vm). The τf values of CaLnGaO4 (Ln = Pr, Yb) did not decrease with the decrease of the εr, which was due to the larger positive temperature coefficient of dielectric constant (τε) and the higher coefficient of thermal expansion (αL) of CaPrGaO4 ceramic compared to CaYbGaO4, respectively. The difference in Q × f values between CaPrGaO4 and CaYbGaO4 is mainly due to the strain of chemical bonds and the Raman spectrum.

Research on Ba2Ti9O20-filled polybutadiene composites with near-zero temperature coefficient of dielectric constant by SiO2 addition

Research on Ba2Ti9O20-filled polybutadiene composites with near-zero temperature coefficient of dielectric constant by SiO2 addition

Low temperature co-fired ceramic application of nano SnMo2O8 synthesised via modified combustion technique

In this work, modified combustion synthesis of nano Tin Molybdate and its suitability as low temperature co-fired ceramic (LTCC) material was analyzed. All the XRD peaks of SnMo2O8 were indexed for a perfect cubic structure. The calculated lattice parameter was a = 8.88Å which was well agreeing with that in JCPDS. The average crystalline size determined using Scherrer equation was 32 nm. The sample was sintered in the Microwave furnace at temperature of 800 °C with a soaking time of 20 min at a constant rate of 4 oCmin−1. Sample achieved a maximum density of 98.6% on sintering. SEM micrograph confirms that sample had achieved high degree of densification. Room temperature dielectric constant (εr) and loss factor of the sintered pellet at 5 MHz was 11.99 and 6.40 × 10-3 respectively. The temperature coefficient of dielectric constant was −95.04 ppm/oC. The negative temperature coefficient indicates that this material is ideal for temperature sensitive applications. Nano structured SnMo2O8 prepared by the present technique was an excellent low temperature co-fired ceramic material with good dielectric properties.

Температурно-частотная зависимость диэлектрического отклика в мультиферроике LuFe-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=-

The results of the study of temperature-frequency spectra of the complex dielectric permittivity of the LuFe2O4 multiferroic in the range of temperatures 100 – 400 K and frequencies 20 Hz – 120 MHz are presented. Peculiarities were found in the form of a change in the sign of the temperature coefficient of dielectric constant, as well as in the form of maxima and minima of ac conductivity in the temperature range ~ 150 - 350 K and frequencies ~ 30 - 120 MHz. These features are due to independent resonant mechanisms: coincidence of the frequency of the measuring ac voltage with the frequency of electron hopping during the realization of hopping conduction; the proximity of the period of the measuring signal to the time of formation of the barrier layer at the boundary of contact with the sample; the approximation of the ac frequency of the external field to the frequency of the structural elements of the sample.

Modified BCZN particles filled PTFE composites with high dielectric constant and low loss for microwave substrate applications

The modified 0.7Ba (Co1/3Nb2/3)O3-0.3Ba(Zn1/3Nb2/3)O3 (BCZN) powders filled PTFE composites were synthesized by hot-pressing. The influences of BCZN content on the microstructure, dielectric, thermal, mechanical properties and moisture absorption were investigated systematically. The modified BCZN powders filled PTFE composites exhibited better microstructure and dielectric properties compared with untreated powders. Various mathematic models were utilized to predict the dielectric constant of different composites and the effective medium theory (EMT) showed perfect consistency with the experimental results. The modified BCZN/PTFE composites possess the best comprehensive properties at the powders content of 50 vol% with high dielectric constant (εr) of 7.7, low loss (tanδ) of 0.0014, acceptable temperature coefficient of dielectric constant (τε) of −125.6 ppm/°C and temperature coefficient of resonant frequency (τf) of 29.4 ppm/°C at 7 GHz, low moisture absorption of 0.07% and low coefficient of thermal expansion (CTE) of 33 ppm/°C. All the results show modified BCZN/PTFE composites are the potential materials for microwave substrate applications.

Behavior of Electrical Conductivity and Dielectric Study of Chalcogenide Ag0.5(As40S30Se30)99.5 Glass

Electrical properties of amorphous Ag0.5(As40S30Se30)99.5 alloy have been investigated using complex impedance spectroscopy at different temperatures in the frequency range from 100 Hz to 1 MHz. Direct current (DC) conductivity data follows Arrhenius behavior, while the nature of frequency dependence of alternating current (AC) conductivity follows Jonscher’s power law. Impedance spectra were analyzed by means of an equivalent-circuit model that revealed the presence of a temperature-dependent electrical relaxation phenomenon of the non-Debye type. Different activation energy values of conduction and of the relaxation process were obtained, suggesting different mechanisms of conduction and relaxation. Dielectric properties were analyzed where the real part (e′) and imaginary part (e″) of the dielectric constant were found to decrease with frequency and increase with temperature. The temperature coefficient of dielectric constant (TCP) is evaluated. The analysis of dielectric loss leads to determination of the barrier height Wm which is found to be 0.086 eV.

Synthesis and characterization of PTFE/(NaxLi1-x)0.5Nd0.5TiO3 composites with high dielectric constant and high temperature stability for microwave substrate applications

In the current work, (NaxLi1-x)0.5Nd0.5TiO3 (abbreviated to NLNT100x, x = 0.3,0.4,0.5,0.6,0.7) ceramics were synthesized by solid phase reaction. X-ray diffraction analysis confirmed the successful synthesis of NLNT ceramics. Dielectric measurements of the synthesized ceramics show that the dielectric constant (εr) is increased first as increasing x, then decreased at x > 0.5, meanwhile the temperature coefficient of dielectric constant (τε) varied toward negative direction with the increase of x. Then, composite substrates with high dielectric constants and adjustable τε were fabricated by filling polytetrafluoroethylene (PTFE) with 60 wt% NLNT100x ceramics and using 5 wt% E glass fibers (E-GF) as reinforcement materials. In order to improve the interfacial compatibility of ceramics with PTFE polymer, hydrogen peroxide (H2O2) was used to enhance the hydroxyl group (-OH) on the surface of inert perovskite ceramics, which is conducive for ceramics to further react with silane coupling agent (F8261 in this work). The modified ceramic was homogeneously dispersed in PTFE and composites with excellent dielectric properties were obtained. When x is 0.6, the prepared NLNT/PTFE composite substrate has a dielectric constant (εr) of 10.4, a low dielectric loss (tan δ) of 0.0026, and a near-zero dielectric constant temperature coefficient (τε) of approximately −-0.9 ppm/°C.

Effects of coupling agent on dielectric properties of PTFE based and Li2Mg3TiO6 filled composites

In this study, Li2Mg3TiO6 (LMT) ceramic powders were synthesized by conventional solid state route, optimized using perfluorooctyltriethoxysilane (F8261) and then loaded into polytetrafluoroethylene (PTFE) emulsion. The effects of F8261 on the surface characteristics of LMT particles were investigated by analyzing SEM, XPS and contact angle. After the coating of F8261, the surface energy of LMT was decreased, leading to a more compatible microstructure with PTFE matrix than untreated LMT particles. As a comparison, the untreated and optimized LMT/PTFE composites were fabricated with different content of LMT (ranged from 30 wt % to 70 wt %). As compared to untreated samples, the substrates loaded with F8261 optimized LMT exhibited better properties with higher dielectric constant and lower dielectric loss. Furthermore, the dielectric constant of optimized LMT filled composites matched well with the values calculated by Effective medium theory (EMT). The temperature coefficient of dielectric constant (τε) of the composites were theoretically discussed. Finally, F8261 optimized LMT/PTFE composites performed prominent dielectric properties of εr = 6.17, tan δ = 0.0019 and τε = 123 ppm/°C at high optimized LMT loading of 70 wt %.

Medium dielectric constant and low‐loss PTFE composites filled with MgO‐LiF co‐doped Li2TiO3 particles

ABSTRACTIn this work, we presented a simple strategy to fabricate medium dielectric constant and low‐loss composites for microwave substrate applications. MgO‐LiF co‐doped Li2TiO3 (LT) powders were fabricated by the solid‐state reaction route and modified by perfluorooctyltriethoxysilane (F8261). The LT/polytetrafluoroethylene (PTFE) composites were fabricated by cold pressing and hot treatment. The XPS and contact angle analysis indicated that the fluorinated group was introduced to LT particle successfully. The effects of modified LT powders content on the dielectric, thermal, and mechanical properties of composites were investigated. As the modified LT content increases, the dielectric constant, dielectric loss, and temperature coefficient of dielectric constant (τε) increase while the bending strength and coefficient of thermal expansion (CTE) decrease, which is attributed to the higher dielectric constant of LT ceramic, more pores, stable τε of LT ceramic, interface defects and low CTE of LT ceramic, respectively. The composites with 60 wt % LT exhibit the best microwave dielectric properties: εr = 6.8, tanδ = 0.001, τε = −29.6 ppm °C−1 at 8 GHz and acceptable coefficient of thermal expansion (28.3 ppm °C−1). Therefore, modified LT powders filled PTFE composites are potential materials for high‐frequency microwave substrate applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47980.

Preparation and microwave dielectric properties of BaMoO4–Ba3(VO4)2 ceramic composites

A new low-temperature fired dense (1 – x)BaMoO4–xBa3(VO4)2 (BM–BV) composite ceramics were prepared by a standard solid-state reaction process. The microstructure and phase composition were characterized by scanning electron microscopy and X-ray diffraction analysis. In this system, the consequences explained that BM and BV crystal phases are coexisted perfectly. With the BV addition increase, the er and the Q × f increase first and then decrease, and temperature coefficient of dielectric constant can be adjusted to nearly zero. In particular, the 0.48BM–0.52BV microwave dielectric ceramics sintered at 950 °C for 4 h possesses optimal dielectric performance: er = 11.9, Q × f = 43613 GHz and τf = 0.38 ppm/°C.

Microstructures and properties of glass fiber reinforced PTFE composite substrates with laminated construction

Three kinds of composite substrates have been fabricated by stacking layers of glass fiber cloth (GFC) or glass fiber mat (GFM) impregnated with polytetrafluoroethylene (PTFE). The difference of the three kinds of substrates is the layered structures, composed of simplex GFC or GFM, or GFC and GFM alternately. The effects of glass fiber types and laminated constructions on the physical properties of composite substrates, such as dielectric constant (εr), dielectric loss (tgδ), water absorption, coefficient of thermal expansion (CTE) and microstructures were studied. The PTFE/GFM composites show similar performances with PTFE/GFC composites. The results demonstrate that the dielectric constant (GFM up to 2.23, GFC up to 2.24) and dielectric loss (GFM up to 0.0016, GFC up to 0.0018) are increased with an increase of the number of layers, on the contrary, the temperature coefficient of dielectric constant (τε) of composites has a decreasing tendency (GFM of −121 ppm °C, GFC of −114 ppm °C). At the same time, the water absorption of composites is decreased with an increase of the number of layers, which is almost twice that of other literatures (GFM of 0.019% and GFC of 0.005%). In consideration of low CTEx and CTEy of PTFE/GFC composites and low CTEz of PTFE/GFM composites, composite substrates with PTFE and alternate GFC and GFM were prepared, exhibiting relatively low CTE of 28.64, 30.52, 223.7 ppm C−1 at X, Y, Z directions, which is obviously superior to other substrates of the same type.

Synthesis of nano Lead Tungstate (PbWO4) by Single Step Modified Combustion Process and Characterization for their application as LTCC and Optical Material

NanostructredScheelitePbWO4were synthesized through a single step modified auto-ignition combustion technique. The X-ray diffraction, Fourier transform Raman and infrared spectroscopy studies revealed that the as-prepared samples were phase pure and the average crystallite size was ∼49 nm. PbWO4 crystallizes in tetragonal structure. The particle size and morphology of the sample was studied using transmission electron micrograph. The optical properties of the sample were studied using Ultraviolet-visible and photoluminescence spectra. The samples showed a maximum transmission in the visible regions but poor transmittance in the ultraviolet region. The optical band gap of the samples calculated using the Kubelka-Munk method was 3.87 eV, suggesting their semiconducting behavior. The photoluminescence spectra recorded on the samples showed that nano PbWO4 has visible luminescence. The thermal stability of the sample at elevated temperatures has been studied using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). No substantive weight loss were observed for the samples in the temperature range 50-900oC. The PbWO4 samples were sintered to 98% relative density at very low temperature of 787oC without using any sintering aid. The microstructure of the sintered pellets observed by Scanning Electron Micrograph (SEM) showed that the pellets were well sintered with minimum porosity. The dielectric constant (εr) of the sintered PbWO4 sample was recorded using an LCR meter in the range 50 Hz to 5 MHz and showed a value of 86 at 1 MHz with a loss factor of 10-2. The calculated temperature coefficient of dielectric constant is negative. The low sintering temperature, dielectric constant, low loss factor and negative temperature coefficient make the sample ideal for low temperature co-fired ceramic, electronic substrate materials as well as suitable for various optical applications such as UV filters, transparent films for window layers on solar cells, anti-reflection coatings, scintillators, detectors.

Fabrication of 0.8BaTi4O9-0.2BaZn2Ti4O11 filled and glassfiber reinforced polytetrafluoroethylene composites with near-zero temperature coefficient of dielectric constant

A study on 0.8BaTi4O9-0.2BaZn2Ti4O11 (BZT) filled and glassfiber (GF) reinforced polytetrafluoroethylene (PTFE) was described. The content of GF was 4 wt. %, and the BZT content varied from 26 wt. % to 66 wt. %. BZT complex phase powder was prepared by one synthetic route and modified using perfluorooctyltriethoxysilane (F8261). The microstructure, thermal properties, dielectric properties and temperature coefficient of dielectric constant of the composites were investigated in detail. The results revealed that BZT/GF/PTFE composites hold outstanding dielectric properties and stable thermal properties. Moreover, the specimens exhibited strong hydrophobicity due to the modification of filler using F8261. The BZT/GF filled PTFE composites exhibited reliable dielectric constant (εr = 4.4), acceptable dielectric loss (tan δ = 0.001), low water absorption (0.02%) and a near-zero temperature coefficient of dielectric constant (τε = 1.57 ppm/°C) at filler with contents of 4 wt. % GF and 46 wt. % BZT.

Research on hydrophobicity treatment of aluminum nitride powder and the fabrication and characterization of AlN/PTFE composite substrates

A study on fabrication and characterization of different filler ratios AlN/ PTFE composite substrates was described. Phenyltrimethoxysilane (Z6124) was used to modify AlN ceramic powder. The contents of Z6124 were 0.8, 1.0, 1.2, 1.4, 1.6 wt%, respectively. The infrared spectroscopy, microstructure, contact angle and the pH changes in water of AlN ceramic powder were investigated in detail. The results revealed that 1.0 wt% Z6124 modified AlN ceramic powder exhibited the largest contact angle (θ = 148.4°), obvious coupling agent characteristic peak, and excellent water resistance. Next, 1.0 wt% Z6124 modified AlN powders were used to manufacture AlN/PTFE composites, and the contents of AlN ceramic filler were 25, 30, 35, 40, 45, 50 and 55 wt%, respectively. The effects of AlN ceramic content on the microwave dielectric properties, water absorption and thermal conductivity of AlN/PTFE composite substrates were systematically investigated. When the content of filler was 45 wt%, composite substrates exhibited reliable dielectric constant (er = 3.38), acceptable dielectric loss (tan δ = 0.006) and excellent temperature coefficient of dielectric constant (− 32.6 ppm/°C), lower water absorption (0.056%) and high thermal conductivity (0.957 W/m K).

Evaluation of surface treatment on Li2Mg3SnO6 ceramic powders and the application of Li2Mg3SnO6 powders filled polytetrafluoroethylene composites

In this paper, we studied the properties of polytetrafluoroethylene (PTFE) based and Li2Mg3SnO6 (LMS) filled composites. The LMS powders were synthesized by one synthetic process and modified by C14H19F13O3Si (F8261). The content of modified LMS changed from 26 to 66 wt%. XRD and TEM were employed to investigate the crystal phase of obtained LMS. The analysis of XPS and Contact Angle were conducted to study the surface characteristics of F8261 modified LMS. The morphology, microstructure, dielectric properties of PTFE based composites filled with untreated LMS and modified LMS were investigated in detail. Further, various theoretical models were put forward to discuss the dielectric constant of the composites. At last, the modified LMS filled PTFE composites exhibited reliable dielectric constant (εr = 3.61), acceptable dielectric loss (tan δ = 0.002), stable frequency dependence of dielectric constant and low temperature coefficient of dielectric constant (τε = 9.42 ppm/°C) at filler loading of 46 wt% LMS.

Temperature–stable dielectrics based on Ni–doped Bi2Zn2/3Nb4/3O7 pyrochlore ceramics for low temperature co-fired ceramic

As an admirable candidate of thermostable LTCC materials, Bi2(Zn1-xNix)2/3Nb4/3O7 (0.0 ≤ x ≤ 0.5) ceramics with improved dielectric properties have been prepared via conventional mixed oxide route. Microstructure analysis manifests that the phase transition occurs from monoclinic zirconolite phase (β-BZN) to cubic phase (α-BZN) for Ni doped specimens. The crystal field theory supported the analysis of the initial phase transition processes. From the structure transformation and electrical properties test result, the Ni2+ substituted Zn2+ shows an effective method to restrain the grain growth and improve dielectric constant when sintered at 925 °C. The temperature coefficient of dielectric constant is controlled by phase composition and is found to be −6.4 ppm/°C at the two-phase coexistence region of the doping content x = 0.35. The dielectric properties of ε = 101.2, tanδ = 9.5 × 10−4 are obtained in this component. The features of the Bi2(Zn1-xNix)2/3Nb4/3O7 ceramics make them promising for use in high-frequency applications.

Effects of particle size distribution of silica on properties of PTFE/SiO2 composites

The properties of Polytetrafluoroethylene (PTFE) filled with two kinds of binary mixtures of silica particles with different size distribution (i.e., 2 μm + 15 μm and 5 μm + 15 μm) were investigated at a fixed total filler content of 62 wt.%. The effects of particle size distribution of silica on the properties of PTFE/SiO2 composites were investigated, including density, moisture absorption, dielectric properties (εr, tan δ), coefficient of thermal expansion (CTE) and temperature coefficient of dielectric constant (τε). Scanning electron microscopy results show that small size silica of appropriate content filled the holes between large size silica, contributing to compact microstructure. However, remarkable agglomeration of SiO2 fillers was observed with too much small size silica and resulted in lower density. As the filler was comprised of 31 wt.% 2 μm and 31 wt.% 15 μm SiO2, the composite showed a compact structure with a high density of 2.157 g cm−3. At the same time, optimal properties were obtained for PTFE/SiO2 composite, including excellent dielectric properties (εr ∼ 2.99, tan δ ∼ 0.002), coefficient of thermal expansion of 18.68 ppm C−1, acceptable water absorption of 0.05% and low temperature coefficient of dielectric constant of 11.43 ppm C−1.