旋磁铁氧体材料的微波烧结及在环行器中的应用研究

对微波烧结旋磁铁氧体材料进行了初步实验,检测和分析了烧成的材料和由其制成的环行器的主要技术参数,并与传统烧结材料进行了对比.结果表明,微波烧结旋磁铁氧体材料介电损耗较低,用其制作的环行器满足设计要求,损耗减小.该烧结方法具有一定的优越性.     

An Investigation Demonstrating the Feasibility of Microwave Sintering of Base-Metal-Electrode Multilayer Capacitors

A microwave sintering technique has been developed for base-metal electrode (BME) multilayer ceramic capacitors (MLCCs). Commercial green chips of size 0603 MLC with nickel electrodes were sintered in a microwave field. With a specially designed susceptor/insulation package to optimize coupling and uniformity of heating, a number of sintering experiments were conducted in the temperature range of 1200 to 1250∘C in a multimode microwave cavity operating at 2.45 GHz under a partially reducing atmosphere. Microstructure of the microwave processed MLCCs was investigated with both SEM and TEM techniques. The dielectric properties of the microwave sintered MLCCs were measured and compared with those sintered using conventional process at 1320∘C and lower pO₂’s ≈ 10^{− 9} atms. The results demonstrate that nickel electrodes remain metallic after microwave sintering even though the pO₂’s were relatively high and would thermodynamically favor NiO. The microwave sintered samples showed a dense, fine and uniform microstructure. The properties of the microwave-sintered samples were comparable to the conventionally sintered samples. The microwave processing was found to have enhanced sintering kinetics of the BME MLCCs, lowering sintering temperature by about 100∘C and also the processing time by about 90%.     

Dielectric properties of Bi2O3–ZnO–Ta2O5 ceramics sintered by microwave

Here we report dielectric studies carried out on a Bi₂Zn_2/3Ta_4/3O₇ (abbreviated as β-BZT) composition. The material was synthesized by conventional ceramic method and microwave sintering processing. The dielectric properties were studied as a function of frequency and temperature. Dielectric constant of Bi₂Zn_2/3Ta_4/3O₇ ceramics prepared from microwave is slightly smaller than that of the conventional sintered ones. The dissipation factor and temperature coefficient of dielectric constant are low for microwave-sintered samples. Microwave sintering of Bi₂Zn_2/3Ta_4/3O₇ ceramics led to higher densification and the fine microstructure in much shorter time duration compared to conventional procedures, improved microstructure and dielectric properties. To achieve the same densification, it requires 4 h of soaking at the same temperature in conventional sintering process. Microwave sintering method may lead to energy savings because of rapid kinetics of synthesis.     

Phase compositions and microwave dielectric properties of MgTiO<Subscript>3</Subscript>-based ceramics obtained by reaction-sintering method

MgTiO₃-based microwave dielectric ceramics were prepared successfully by reaction sintering method. The X-ray diffraction patterns of the sintered samples revealed a major phase of MgTiO₃-based and CaTiO₃ phases, accompanied with Mg₂TiO₄ or MgTi₂O₅ determined by the sintering temperature and time. The microwave dielectric properties had a strong dependence of sintering condition due to the different phase compositions and the microstructure characteristics. The ceramics sintered at 1360 °C for 4 h exhibited good microwave dielectric properties: a dielectric constant of 20.3, a high quality factor of 48,723 GHz (at 9GHz), and a temperature coefficient of resonant frequency of ?1.8 ppm/^oC. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the MgTiO₃-based ceramics for microwave applications.     

Microwave Hydrothermally Synthesized Nanocrystalline Co-Zn Ferrites

Co-Zn ferrite nano-powder was synthesized using the Microwave- Hydrothermal (M-H) method. The powder was characterized using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and Fourier Transform Infrared spectroscopy (FT-IR). The densification of nanoferrites was done using two methods: a) conventional and b) microwave sintering. Electrical and magnetic properties of the sintered samples were measured at room temperature. Electrical properties such as dielectric constant (?'), dissipation factor (D), initial permeability (μ_i) and quality factor (Q) were measured over a wide frequency range (10 kHz to 1 MHz). The Curie temperature has been determined from the permeability versus temperature plots. It was found that the enhanced electrical and magnetic properties were observed for microwave sintered samples.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

Effect of microwave sintering on structural, morphological and dielectric properties of Ba(FeNb)0.5O3 ceramics

Polycrystalline Ba(FeNb)_0.5O₃/BFN ceramics were sintered conventionally and in a microwave (MW) furnace, respectively. Conventional and microwave sintering temperatures were same with different soaking times. Microwave sintering of BFN ceramics showed enhanced grain growth with improved dielectric properties. Highest dielectric constant (~29,913 at 1 kHz) at room temperature (RT) was observed in BFN ceramics sintered in MW furnace for 30 min. At RT, a non-Debye type of dielectric relaxation was observed in both conventionally and MW sintered BFN ceramics. The observed giant dielectric constant of conventionally and MW sintered BFN ceramics was attributed to intrinsic (space charge polarization) and extrinsic (Maxwell-Wagner type polarization) effects, respectively.     

Investigation on structural and electrical properties of BZT ceramics synthesized at low temperature

Abstract

Due to environmental concerns, lead free ceramics such as KNN- NBT and BT have growing interest in applications such as actuators and sensors. Among them Barium Zirconate Titanate (BZT) has become most attractive because it is derived from two perovskite lattice i.e. Barium Titanate (BaTiO₃) and Barium Zirconate (BaZrO₃). It has been reported that Zirconium substitution in titanium lattice enhances the material properties. In the present paper BZT was prepared using solid state route. By adding a mixture of Li₂CO₃ as a sintering aid, the sample could be sintered at 1150?°C having around 94% of the theoretical density. Prepared samples were then subjected to XRD analysis. X-ray diffraction revealed the formation of single phase material. It is observed that the electrical properties of such low-temperature sintered samples are comparable with BZT samples prepared via conventional sintering at a high temperature. It is also observed that the curie temperature shift towards room temperature for a samples sintered at low temperature.     

Synthesis and characterization of novel Ca2Zn4Ti15O36 microwave ceramics derived from sol-gel powder

A novel microwave dielectric ceramics with composition of Ca₂Zn₄Ti₁₅O₃₆ (CZT) have been synthesized at different sintering temperatures, using citrate sol-gel derived powder. The sintering behavior and the phase identification of the powders were evaluated using differential thermal analysis-thermo gravimetric analysis and X-ray powder diffraction analysis techniques. The phase of CZT can be observed in the powder calcined at 900 °C. The single-phase of CZT, however, can only be obtained at sintering temperature of 1,000 °C or above. The single-phase CZT ceramics can be sintered into dense at 1,100 °C, exhibiting excellent microwave dielectric properties of ? _r?=?48.1, Q?×?f?=?27,000 GHz, and τ _f?=?+53.5 ppm/°C. The effects of sintering temperature on the density, microstructure, and dielectric properties of the sintered ceramics were investigated. The mechanism responsible for the change of dielectric properties with sintering temperature was also discussed.     

Thermal and dielectric properties of glass-ceramics sintered based on diopside and anorthite composition

To develop a low dielectric constant of LTCC substrate, we studied the effect of the sintering and crystallization behavior on the dielectric properties of a sintered body by mixing a CaO–Al₂O₃–SiO₂ frit and a CaO–MgO–SiO₂ frit for a low dielectric constant of LTCC substrates. In this work, the two glass frits were mixed at different proportions and sintered at 860~920°C. After sintering at 900^oC for 1h, the glass frits crystallized into diopside and anorthite. The sintered bodies exhibited dielectric properties, ? _r?=?6~8.6 at 1 GHz, which is an essential condition for a substrate in microwave devices. The results suggest that the glass-ceramic can be applied to low dielectric LTCC materials in the electronics packaging industry.     

微波烧结Ni-Zn铁氧体软磁材料的初步研究

采用微波高温烧结炉对Ni-Zn铁氧体软磁材料进行公斤级烧结工艺研究.结果表明,运用微波烧结可以实现Ni-Zn铁氧体材料烧结过程中的快速升温,短时保温,不仅大大降低能源消耗,缩短工艺周期,而且提高了Ni-Zn铁氧体软磁材料物理及机械性能.     

Fabrication and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 from co-precipitation method

High dielectric Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were firstly prepared by co-precipitation method at low temperature. X-ray diffraction results revealed that pure phase of NBCTO was achieved by calcination at 950 °C for 2 h. Thermo-gravimetric analysis on a dried NBCTO precursor was carried out to study the thermal decomposition process. The microstructure and dielectric properties of NBCTO ceramics sintered at different temperatures were investigated. The results indicate that the sintering temperature has a sensitive influence on the microstructure and dielectric properties. Higher sintering temperature gave rise to increased dielectric constant and dielectric loss of NBCTO samples, and the sample sintered at 975 °C for 8 h exhibits high dielectric constant of 8.3?×?10³ and low dielectric loss of 0.069 at 10 kHz. The dielectric properties were further discussed by the impedance spectroscopy.     

La2O3–B2O3–TiO2 Glass/BaO–Nd2O3–TiO2 ceramic for high quality factor low temperature co-fired ceramic dielectric

A conventional BaO–Nd₂O₃–TiO₂ ceramic of microwave dielectric material was added to rare-earth derived borate glasses (La₂O₃–B₂O₃–TiO₂) for use as LTCC (low temperature co-fired ceramic) materials. The sintering behavior, phase evaluation, and microwave dielectric properties were investigated. It was found that increasing the sintering temperature from 750 to 850 °C led to increases in shrinkage and microwave dielectric properties (≈15 for ?_r , >10,000 GHz for Q*f₀ and >94 ppm/ °C for τ _f at 7–8 GHz for resonant frequency). The results suggest that a composite with suitable additives for τ _f could feasibly be developed as a material for LTCC applications.     

Low-temperature sintering and microwave dielectric properties of ZnTiO3-based LTCC materials

The low-temperature sintered microwave dielectric ceramics with composition of ZnTiO₃-0.25TiO₂ were prepared by adding a small amount of low-melting compounds CuO-V₂O₅-Bi₂O₃ (CVB). The phase relationship and dielectric properties as a function of sintering temperature and the additional amount were studied. It is demonstrated that the addition of low-melting CVB can suppress the formation of Zn₂TiO₄ at low temperature, but decrease the decomposition temperature of ZnTiO₃. The sintering temperature has a significant effect on the stability of ZnTiO₃ and dielectric properties of sintered ceramics. CVB addition can promote the densification of ceramics through liquid-phase sintering. The dense 2wt% CVB-doped ZnTiO₃-0.25TiO₂ ceramics prepared at 850 °C have excellent dielectric properties of ??=?30, Q×f?=?32,000 GHz, and τ _f ?=?+12 ppm/ °C.     

Enhancement of dielectric properties by optimization of sintering condition in tungsten–bronze structured Ba5SmTi3Nb7O30 ferroelectric ceramics

In this work, polycrystalline Ba₅SmTi₃Nb₇O₃₀ tungsten–bronze structured ferroelectric ceramics were synthesized by solid-state reaction technique at different sintering temperatures and durations. The X-ray diffractograms reveal the formation of the compounds in orthorhombic crystal system. The density of the compound is observed to increase with increase in sintering temperature and duration. Scanning electron microscopy (SEM) has been used for the microstructural investigation. Detailed dielectric properties of the compounds have been studied as a function of frequency and temperature. The variations of dielectric constant $\left( {\varepsilon \prime _r } \right)$ with temperature show that the compounds undergo a diffuse type ferro-paraelectric phase transition. The dielectric constant is found to increase with the increasing sintering temperature and duration. In all the samples, the variation of dielectric loss (tan δ) with temperature is observed to be almost constant initially but it increases as temperature is increased and a peak is observed only when the material is sintered at higher temperature for longer duration. The frequency dependence of dielectric constant and loss shows a decreasing trend up to nearly 10 kHz and beyond this frequency there is almost no variation. Also, the diffusivities of the samples have been calculated and it is found to increase with increasing sintering temperature and duration.     

Structural,Mechanical and Dielectric Properties of Microwave-Assisted High-Energy Ball Milling Synthesis of Hydroxyapatite

Abstract

In the present work, the effect of high-energy ball milling (HEBM) of starting precursors of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂)/HA system on the processing temperature, morphological, mechanical, and electrical properties are highlighted. Calcination and sintering of HA system were carried out in microwave furnace. XRD study confirmed the evolution of HA phase and EDX analysis confirmed Ca/P ratio ～1.65. Grain size of HA samples, synthesized by using microwave-assisted HEBM technique was found to be in the order of 54–75?nm. Enhanced dielectric and mechanical properties were obtained in HA samples.     

The effect of sintering atmosphere on V2O5 substituted BiNbO4 microwave ceramics

In multiplayer passive devices, low sintering temperature dielectric materials were needed to co-fire with low melting point inner electrode such as copper or silver, a major problem of base metal electrode (BME) was that the devices must be fired under low oxygen partial pressure atmosphere to protect Cu from oxidation. In this paper, dielectric properties of Bi(V_xNb_1?x)O₄ (x?=?0.001, 0.004, 0.008, 0.016, 0.048) microwave ceramics sintered under air and N₂ atmosphere have been investigated. The densification temperature sintered in different atmosphere decreased from 1010 to 830°C with the amount of V₂O₅ increasing from 0.001 to 0.048. Due to the increasing vacancy defects, the density of ceramics sintered in N₂ was smaller than that sintered in air. The ceramics sintered under N₂ have similar dielectric constant, and its Qf values are higher while x?<?0.016.     

Effect of B2O3 Nano-Coating on the Sintering Behaviors and Electrical Microwave Properties of Ba(Nd2 − x Sm x )Ti4O12 Ceramics

Ba(Nd_0.8Sm_0.2)₂Ti₄O₁₂ ceramics prepared by conventional solid-state sintering have a dielectric constant of about 80 and a nearly zero temperature coefficient of resonant frequency; however, the sintering temperature is above 1350_C. Doping with B₂O₃ (up to 5 wt%) promotes the densification and dielectric properties of BNST ceramics. It is found that coating BNST powder with thin B₂O₃ layer of about 180 nm reduces the sintering temperature to below 1020_C. The effects of B₂O₃ nano-coating on the dielectric microwave properties and the microstructures of BNST ceramics are investigated. Ninety-six percent of theoretical densities is obtained for specimens coated with 2 wt% B₂O₃ sintered at 960_C and the samples exhibit significant (002) preferred orientation and columnar structure.     

Effect of the firing temperatures on the phase formation,microstructure and electrical properties of BaTi0.91 Sn0.09O3 ceramics synthesized via the solid state combustion method

Abstract

BaTi_0.91Sn_0.09O₃ (BTS) ceramics were synthesized by the solid state combustion method with glycine as the reducting agent and metal nitrates as the oxidants. The calcination and sintering temperatures were in the range of 1200?°C–1300?°C and 1300?°C–1450?°C, respectively, for 2?h. Pure perovskite powders were obtained from the samples calcined at ≥1275?°C for 2?h. The crystal size calculated by Scherrer equation was in the range of 22–30?nm. XRD results of the sintered ceramics showed the coexistence of the tetragonal (T) and orthorhombic (O) phases in all samples, and were confirmed by Rietveld refinement. The grain sizes increased from 9.04 to 29.83 µm when the sintering temperatures increased from 1300?°C–1450?°C for 2?h. The highest density (5.95?g?cm^?3), large piezoelectric strain (d₃₃* = 830?pm/V) and best dielectric constant (ε_r = 14841) were obtained from the sample sintered at 1350?°C for 2?h. This study clearly demonstrates the potential of the solid state combustion method for producing high density and good dielectric properties in BTS ceramics.     

微波烧结高磁导率Mn-Zn铁氧体材料的研究

介绍了利用微波烧结技术小批量生产高磁导率Mn-Zn铁氧体的烧结工艺与设备.结果表明,微波加热方式不但大大优于传统加热方式,且利用微波烧结技术烧结的高磁导率Mn-Zn铁氧体材料的各项性能均达到或超过传统烧结方式的产品.