The Experts below are selected from a list of 14322 Experts worldwide ranked by ideXlab platform

Di Zhou - One of the best experts on this subject based on the ideXlab platform.

  • Cold sintering of microwave Dielectric Ceramics and devices
    Journal of Materials Research, 2021
    Co-Authors: Dawei Wang, Di Zhou, Juan Jiang, Ge Wang, Kaixin Song, Ian M Reaney
    Abstract:

    Abstract Microwave (MW) Dielectric Ceramics are used in numerous electronic components for modern wireless communication systems, including antennas, resonators, capacitors and filters. However, to date, MW Ceramics are manufactured by an energy-intensive, conventional high-temperature (> 1000 °C) sintering technology and thus cannot be co-sintered with low melting point and base electrodes (Ag, Al, etc., < 1000 °C), nor directly integrated with polymers (< 200 °C). Cold sintering is able to densify Ceramics at < 200 °C via a combination of external pressure and a transient liquid phase, reducing the energy consumed and facilitating greater integration with dissimilar materials. This review outlines the basics of MW Ceramics alongside the mechanism of cold sintering. Recent developments in cold sintering of MW Ceramics, composites and devices are described, emphasizing new materials and progress towards component/device fabrication. Future prospects and critical issues for advancing cold-sintered MW materials and devices, such as unclear mechanism, low Q × f values and poor mechanical properties, are discussed. Graphic abstract

  • Dielectric resonator antennas based on high quality factor mgal2o4 transparent Dielectric Ceramics
    Journal of Materials Chemistry C, 2020
    Co-Authors: Huanhuan Guo, Di Zhou, Jian Zhang, Wenfeng Liu, Hetuo Chen, Haiwen Liu
    Abstract:

    For the first time, a MgAl2O4 transparent ceramic cylindrical Dielectric resonator antenna (DRA) is designed using the fundamental HE11δ modes for slot excitation. The transparent microwave Dielectric ceramic was synthesized using high-purity MgO and γ-Al2O3 powders by aqueous gel-casting combined with cold isostatic pressing, pressure-less sintering and hot isostatic pressing methods. Optimum relative permittivity ∼8.2, Q × f (Q = quality factor = 1/Dielectric loss, f = resonant frequency) ∼110 510 GHz and temperature coefficient of resonant frequency ∼−74.1 ppm °C−1 were obtained. The reflection coefficient, the input impedance, the antenna gain and the radiation pattern of the transparent cylindrical ceramic DRA were examined, and it was observed that the simulation results were in reasonable agreement with the measurement results. It has been found that the proposed transparent cylindrical MgAl2O4 ceramic DRA can provide a higher impedance bandwidth (BW = 735 MHz) and radiation efficiency (95.8%) than a state-of-the-art transparent glass DRA. The proposed configuration can potentially be used for such useful antenna decoration and can be used as a lampshade to integrate these antennas in street and traffic lights without compromising the aesthetics of the city.

  • temperature stable li2ti0 75 mg1 3nb2 3 0 25o3 based microwave Dielectric Ceramics with low sintering temperature and ultra low Dielectric loss for Dielectric resonator antenna applications
    Journal of Materials Chemistry C, 2020
    Co-Authors: Huanhuan Guo, Di Zhou, Lixia Pang, Pengjian Wang, Wenfeng Liu, Qiuping Wang, Charanjeet Singh, S V Trukhanov
    Abstract:

    Microwave Dielectric Ceramics are considered to be one of the key materials of Dielectric resonators/filters and have wide application prospects in fifth generation (5G) mobile communication systems. Here we prepared two kinds of low-sintering temperature and high-performance microwave Dielectric Ceramics with monoclinic rock salt structure by adding a small amount of V2O5 and 0.6CuO–0.4B2O3 sintering aids to Li2Ti0.75(Mg1/3Nb2/3)0.25O3 (LTMN0.25). The sintering temperature of LTMN0.25 Ceramics with 2 wt% V2O5 and 1 wt% 0.6CuO–0.4B2O3 additions could be effectively reduced from 1170 °C to below 910 °C due to the liquid phase effects resulting from the additives. Typically, high performance microwave Dielectric properties can be obtained in the LTMN0.25 + 2 wt% V2O5 ceramic sintered at 910 °C for 2 h, with a er ∼ 20.7, a Q × f ∼ 60 460 GHz and a TCF ∼ +4.3 ppm °C−1. The best Dielectric properties of er ∼ 19.9, a Q × f ∼ 60 950 GHz and a TCF ∼ −6.1 ppm °C−1 were obtained for the samples with 1 wt% 0.6CuO–0.4B2O3 sintered at 870 °C for 2 h. A prototype Dielectric resonator antenna (DRA) was fabricated by LTMN0.25 + 1 wt% 0.6CuO–0.4B2O3 ceramic. The antenna resonated at 10.02 GHz with a bandwidth ∼175 MHz at −10 dB transmission loss (S11). Moreover, the chemical compatibility with Ag powder suggests that the LTMN0.25 + 2 wt% V2O5 and LTMN0.25 + 1 wt% 0.6CuO–0.4B2O3 Ceramics may be suitable candidates for low temperature co-fired ceramic technology applications.

  • high quality factor ultralow sintering temperature li6b4o9 microwave Dielectric Ceramics with ultralow density for antenna substrates
    ACS Sustainable Chemistry & Engineering, 2018
    Co-Authors: Di Zhou, Lixia Pang, Dawei Wang, Zeming Qi, Ian M Reaney
    Abstract:

    Dense Li6B4O9 microwave Dielectric Ceramics were synthesized at low temperature via solid-state reaction using Li2CO3 and LiBO2. Optimum permittivity ∼ 5.95, quality factor ∼ 41 800 GHz and temperature coefficient of resonant frequency ∼ – 72 ppm/°C were obtained in Ceramics sintered at 640 °C with a ultrasmall bulk density ∼2.003 g/cm3 (∼95% relative density, the smallest among all the reported microwave Dielectric Ceramics). Li6B4O9 Ceramics were shown to be chemically compatible with silver electrodes but reacted with aluminum forming Li3AlB2O6 and Li2AlBO4 secondary phases. A prototype patch antenna was fabricated by tape casting and screen printing. The antenna resonated at 4.255 GHz with a bandwidth ∼279 MHz at −10 dB transmission loss (S11) in agreement with simulated results. The Li6B4O9 microwave Dielectric ceramic possesses similar microwave Dielectric properties to the commercial materials but much lower density and could be a good candidate for both antenna substrate and low-temperature cofire...

  • structure property relationships of low sintering temperature scheelite structured 1 x bivo4 xlanbo4 microwave Dielectric Ceramics
    Journal of Materials Chemistry C, 2017
    Co-Authors: Lixia Pang, Di Zhou, Zeming Qi, Ian M Reaney
    Abstract:

    A series of (1 − x)BiVO4–xLaNbO4 (0.0 ≤ x ≤ 1.0) Ceramics were prepared via a solid state reaction method. A scheelite-structured solid solution was formed for x ≤ 0.5 but for x > 0.5, tetragonal scheelite, monoclinic LaNbO4-type and La1/3NbO3 phases co-existed. As x increased from 0 to 0.1, the room temperature crystal structure gradually changed from monoclinic to tetragonal scheelite, associated with a decrease in the ferroelastic phase transition temperature from 255 °C (BiVO4) to room temperature or even below. High sintering temperatures were also found to accelerate this phase transition for compositions with x ≤ 0.08. Temperature independent high quality factor Qf >10000 GHz in a wide temperature range 25–140 °C and high microwave permittivity er ∼76.3 ± 0.5 was obtained for the x = 0.06 ceramic sintered at 800 °C. However, small changes in composition resulted in a change in the sign and magnitude of the temperature coefficient of resonant frequency (TCF) due to the proximity of the ferroelastic transition to room temperature. If TCF can be controlled and tuned through zero, then (1 − x)BiVO4–xLaNbO4 (0.0 ≤ x ≤ 1.0) is a strong candidate for microwave device applications.

Shujun Zhang - One of the best experts on this subject based on the ideXlab platform.

  • grain orientation engineered multilayer ceramic capacitors for energy storage applications
    Nature Materials, 2020
    Co-Authors: Zhonghui Shen, Xianghua Chen, Shuai Yang, Wenlong Zhou, Mingwen Wang, Linghang Wang, Qiangwei Kou, Yingchun Liu, Yunfei Chang, Shujun Zhang
    Abstract:

    Dielectric Ceramics are highly desired for electronic systems owing to their fast discharge speed and excellent fatigue resistance. However, the low energy density resulting from the low breakdown electric field leads to inferior volumetric efficiency, which is the main challenge for practical applications of Dielectric Ceramics. Here, we propose a strategy to increase the breakdown electric field and thus enhance the energy storage density of polycrystalline Ceramics by controlling grain orientation. We fabricated high-quality -textured Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 (NBT-SBT) Ceramics, in which the strain induced by the electric field is substantially lowered, leading to a reduced failure probability and improved Weibull breakdown strength, on the order of 103 MV m−1, an ~65% enhancement compared to their randomly oriented counterparts. The recoverable energy density of -textured NBT-SBT multilayer Ceramics is up to 21.5 J cm−3, outperforming state-of-the-art Dielectric Ceramics. The present research offers a route for designing Dielectric Ceramics with enhanced breakdown strength, which is expected to benefit a wide range of applications of Dielectric Ceramics for which high breakdown strength is required, such as high-voltage capacitors and electrocaloric solid-state cooling devices. The energy density of Dielectric ceramic capacitors is limited by low breakdown fields. Here, by considering the anisotropy of electrostriction in perovskites, it is shown that -textured Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 Ceramics can sustain higher electrical fields and achieve an energy density of 21.5 J cm−3.

  • silver niobate lead free antiferroelectric Ceramics enhancing energy storage density by b site doping
    ACS Applied Materials & Interfaces, 2018
    Co-Authors: Lei Zhao, Qing Liu, Jing Gao, Shujun Zhang
    Abstract:

    Lead-free Dielectric Ceramics with high recoverable energy density are highly desired to sustainably meet the future energy demand. AgNbO3-based lead-free antiferroelectric Ceramics with double ferroelectric hysteresis loops have been proved to be potential candidates for energy storage applications. Enhanced energy storage performance with recoverable energy density of 3.3 J/cm3 and high thermal stability with minimal energy density variation (<10%) over a temperature range of 20–120 °C have been achieved in W-modified AgNbO3 Ceramics. It is revealed that the W6+ cations substitute the B-site Nb5+ and reduce the polarizability of B-site cations, leading to the enhanced antiferroelectricity, which is confirmed by the polarization hysteresis and Dielectric tunability. It is believed that the polarizability of B-site cations plays a dominant role in stabilizing the antiferroelectricity in AgNbO3 system, in addition to the tolerance factor, which opens up a new design approach to achieve stable antiferroelec...

  • defect structure electrical property relationship in mn doped calcium strontium titanate Dielectric Ceramics
    Journal of the American Ceramic Society, 2017
    Co-Authors: Shujun Zhang, Lin Zhang, Michael T Lanagan, Hua Hao, Zhonghua Yao, Juan Xie, Jing Zhou, Minghe Cao
    Abstract:

    Ca0.6Sr0.4TiO3 (CST) Ceramics with different amounts of Mn dopant (0~2.0 mol%) were prepared by solid state reaction method. The electric field and temperature stability of energy storage performance was found to be greatly enhanced with moderate doped level of 0.5 mol%. The Dielectric loss-frequency spectra revealed the existence and evolution of defect dipoles at elevated temperature, which was confirmed directly by electron paramagnetic resonance (EPR) spectra. The response of defect dipoles was characterized by thermally stimulated depolarization current (TSDC), where the activation energy and the concentration evolution of defect dipoles were calculated, with the highest values observed for 0.5% doped samples. The dissociation of defect dipoles and the movement of free Vo.. were analyzed by high temperature impedance spectra analysis, with the activation energy of 1.04~1.60 eV, and 0.5% doped samples also demonstrated the highest Ea. The relationship between microscopic defect structure and macroscopic electrical behavior was established in this work. This article is protected by copyright. All rights reserved.

Xiaohui Wang - One of the best experts on this subject based on the ideXlab platform.

  • high energy density high efficiency and excellent temperature stability of lead free mn doped batio3 bi mg1 2zr1 2 o3 Ceramics sintered in a reducing atmosphere
    Journal of Alloys and Compounds, 2020
    Co-Authors: Chaoqiong Zhu, Ziming Cai, Xiaohui Wang
    Abstract:

    Abstract Dielectric Ceramics capacitors are of great interest duo to the improved energy-storage performance and temperature stability. However, to lower the cost and achieve mass production, the co-sintering of Dielectric Ceramics with base metals (such as Ni, Cu) is a huge challenge, since the co-sintering requires a reducing atmosphere to prevent the oxidization of base metals. Here in this work, the multivalence element Mn is doped into a relaxor ferroelectric ceramic system, i.e. 0.85BaTiO3-0.15Bi(Mg1/2Zr1/2)O3 (BT-BMZ) Ceramics through a conventional solid-state reaction method to realize the reducing atmosphere sintering. Effects of MnCO3 contents (0.05–0.25 wt%) on the energy-storage properties, temperature stabilities and electrical structures of the relaxor-ferroelectric BT-BMZ Ceramics are investigated. The optimal energy-storage performance is found in 0.10 wt% MnCO3 doped BT-BMZ Ceramics, with a high discharge energy density of 1.61 J/cm3 and an ultrahigh energy efficiency of 94.3% under the applied electric field of 230 kV/cm. Further, the variation in energy density is less than 15% over the temperature range from 25 to 140 °C under 120 kV/cm. Additionally, the impedance spectroscopy is used to analyze the insulation mechanism of these reducing-atmosphere-sintered Mn-doped BT-BMZ Ceramics.

  • high temperature lead free bnt based Ceramics with stable energy storage and Dielectric properties
    Journal of Materials Chemistry, 2020
    Co-Authors: Chaoqiong Zhu, Ziming Cai, Bingcheng Luo, Limin Guo, Xiaohui Wang
    Abstract:

    High-temperature Dielectric Ceramics are in urgent demand due to the rapid development of numerous emerging applications. However, producing Dielectric Ceramics with favorable temperature, frequency and electric field stability is still a huge challenge. The construction of multi-phase coexistence material systems is an effective way to obtain stable Dielectric and energy storage properties. In this work, NaNbO3 (NN) modified 0.95Bi0.5Na0.5TiO3–0.05SrZrO3 (BNTSZ) Ceramics ((1 − x)BNTSZ–xNN) are designed to achieve the coexistence of rhombohedral and tetragonal phases. The variation in the Dielectric permittivity of the 0.8BNTSZ–0.2NN ceramic is less than ±15% over the temperature range from −55 °C to 545 °C, which is the reported record-high upper operating temperature, with a high room-temperature Dielectric permittivity of 1170. The 0.8BNTSZ–0.2NN ceramic exhibits excellent frequency and electric field stability as well. Additionally, a large discharge energy density of 3.14 J cm−3 is obtained in the 0.85BNTSZ–0.15NN ceramic with an energy efficiency of 79% at a high temperature of 120 °C under 230 kV cm−1, with the variation in the discharge energy density being less than ±4% in the temperature range from 25 °C to 180 °C under 120 kV cm−1. All these features demonstrate that the (1 − x)BNTSZ–xNN Ceramics are promising candidates for use at extremely high temperature in both Dielectric and energy storage capacitor applications.

  • enhanced energy storage density and high efficiency of lead free catio3 bisco3 linear Dielectric Ceramics
    ACS Applied Materials & Interfaces, 2017
    Co-Authors: Bingcheng Luo, Xiaohui Wang, Enke Tian, Hongzhou Song, Hongxian Wang
    Abstract:

    A novel lead-free (1 – x)CaTiO3-xBiScO3 linear Dielectric ceramic with enhanced energy-storage density was fabricated. With the composition of BiScO3 increasing, the Dielectric constant of (1 – x)CaTiO3-xBiScO3 Ceramics first increased and then decreased after the composition x > 0.1, while the Dielectric loss decreased first and increased. For the composition x = 0.1, the polarization was increased into 12.36 μC/cm2, 4.6 times higher than that of the pure CaTiO3. The energy density of 0.9CaTiO3-0.1BiScO3 ceramic was 1.55 J/cm3 with the energy-storage efficiency of 90.4% at the breakdown strength of 270 kV/cm, and the power density was 1.79 MW/cm3. Comparison with other lead-free Dielectric Ceramics confirmed the superior potential of CaTiO3–BiScO3 Ceramics for the design of Ceramics capacitors for energy-storage applications. First-principles calculations revealed that Sc subsitution of Ti-site induced the atomic displacement of Ti ions in the whole crystal lattice, and lattice expansion was caused by va...

  • improved energy storage properties of fine crystalline batio3 Ceramics by coating powders with al2o3 and sio2
    Journal of the American Ceramic Society, 2015
    Co-Authors: Baibo Liu, Xiaohui Wang, Qiancheng Zhao
    Abstract:

    The multilayer structure of capacitor demands for fine grain size of Dielectric Ceramics in devices, because the thinner layer which needs Ceramics with fine grain size is helpful in enlarging the capacitance. In this paper, the aqueous chemical coating method was utilized to modify the BaTiO3 particles. The fine-crystalline BaTiO3 Ceramics with an average grain size below 200 nm without abnormal grain growth by co-coating Al2O3 and SiO2 has been prepared. The phase composition, microstructures of coated particles and Ceramics, and Dielectric properties were investigated. For samples containing 3 wt% of Al2O3 and 1 wt% of SiO2, the energy storage density is 0.725 J/cm3 and the efficiency of the ceramic samples can keep above 80%. The breakdown strength was improved to about 190 kV/cm.

  • electrical and reliability characteristics of mn doped nano batio3 based Ceramics for ultrathin multilayer ceramic capacitor application
    Journal of Applied Physics, 2012
    Co-Authors: Huiling Gong, Xiaohui Wang, Shaopeng Zhang, Zhibin Tian
    Abstract:

    Nano BaTiO3-based Dielectric Ceramics were prepared by chemical coating approach, which are promising for ultrathin multilayer ceramic capacitor (MLCC) applications. The doping effects of Mn element on the microstructures and Dielectric properties of the Ceramics were investigated. The degradation test and impedance spectroscopy were employed to study the resistance degradation and the conduction mechanism of Mn-doped nano-BaTiO3 ceramic samples. It has been found that the reliability characteristics greatly depended on the Mn-doped content. Moreover, the BaTiO3 ceramic with grain size in nanoscale is more sensitive to the Mn-doped content than that in sub-micron scale. The addition of 0.3 mol. % Mn is beneficial for improving the reliability of the nano BaTiO3-based Ceramics, which is an important parameter for MLCC applications. However, further increasing the addition amount will deteriorate the performance of the ceramic samples.

Lixia Pang - One of the best experts on this subject based on the ideXlab platform.

  • temperature stable li2ti0 75 mg1 3nb2 3 0 25o3 based microwave Dielectric Ceramics with low sintering temperature and ultra low Dielectric loss for Dielectric resonator antenna applications
    Journal of Materials Chemistry C, 2020
    Co-Authors: Huanhuan Guo, Di Zhou, Lixia Pang, Pengjian Wang, Wenfeng Liu, Qiuping Wang, Charanjeet Singh, S V Trukhanov
    Abstract:

    Microwave Dielectric Ceramics are considered to be one of the key materials of Dielectric resonators/filters and have wide application prospects in fifth generation (5G) mobile communication systems. Here we prepared two kinds of low-sintering temperature and high-performance microwave Dielectric Ceramics with monoclinic rock salt structure by adding a small amount of V2O5 and 0.6CuO–0.4B2O3 sintering aids to Li2Ti0.75(Mg1/3Nb2/3)0.25O3 (LTMN0.25). The sintering temperature of LTMN0.25 Ceramics with 2 wt% V2O5 and 1 wt% 0.6CuO–0.4B2O3 additions could be effectively reduced from 1170 °C to below 910 °C due to the liquid phase effects resulting from the additives. Typically, high performance microwave Dielectric properties can be obtained in the LTMN0.25 + 2 wt% V2O5 ceramic sintered at 910 °C for 2 h, with a er ∼ 20.7, a Q × f ∼ 60 460 GHz and a TCF ∼ +4.3 ppm °C−1. The best Dielectric properties of er ∼ 19.9, a Q × f ∼ 60 950 GHz and a TCF ∼ −6.1 ppm °C−1 were obtained for the samples with 1 wt% 0.6CuO–0.4B2O3 sintered at 870 °C for 2 h. A prototype Dielectric resonator antenna (DRA) was fabricated by LTMN0.25 + 1 wt% 0.6CuO–0.4B2O3 ceramic. The antenna resonated at 10.02 GHz with a bandwidth ∼175 MHz at −10 dB transmission loss (S11). Moreover, the chemical compatibility with Ag powder suggests that the LTMN0.25 + 2 wt% V2O5 and LTMN0.25 + 1 wt% 0.6CuO–0.4B2O3 Ceramics may be suitable candidates for low temperature co-fired ceramic technology applications.

  • high quality factor ultralow sintering temperature li6b4o9 microwave Dielectric Ceramics with ultralow density for antenna substrates
    ACS Sustainable Chemistry & Engineering, 2018
    Co-Authors: Di Zhou, Lixia Pang, Dawei Wang, Zeming Qi, Ian M Reaney
    Abstract:

    Dense Li6B4O9 microwave Dielectric Ceramics were synthesized at low temperature via solid-state reaction using Li2CO3 and LiBO2. Optimum permittivity ∼ 5.95, quality factor ∼ 41 800 GHz and temperature coefficient of resonant frequency ∼ – 72 ppm/°C were obtained in Ceramics sintered at 640 °C with a ultrasmall bulk density ∼2.003 g/cm3 (∼95% relative density, the smallest among all the reported microwave Dielectric Ceramics). Li6B4O9 Ceramics were shown to be chemically compatible with silver electrodes but reacted with aluminum forming Li3AlB2O6 and Li2AlBO4 secondary phases. A prototype patch antenna was fabricated by tape casting and screen printing. The antenna resonated at 4.255 GHz with a bandwidth ∼279 MHz at −10 dB transmission loss (S11) in agreement with simulated results. The Li6B4O9 microwave Dielectric ceramic possesses similar microwave Dielectric properties to the commercial materials but much lower density and could be a good candidate for both antenna substrate and low-temperature cofire...

  • structure property relationships of low sintering temperature scheelite structured 1 x bivo4 xlanbo4 microwave Dielectric Ceramics
    Journal of Materials Chemistry C, 2017
    Co-Authors: Lixia Pang, Di Zhou, Zeming Qi, Ian M Reaney
    Abstract:

    A series of (1 − x)BiVO4–xLaNbO4 (0.0 ≤ x ≤ 1.0) Ceramics were prepared via a solid state reaction method. A scheelite-structured solid solution was formed for x ≤ 0.5 but for x > 0.5, tetragonal scheelite, monoclinic LaNbO4-type and La1/3NbO3 phases co-existed. As x increased from 0 to 0.1, the room temperature crystal structure gradually changed from monoclinic to tetragonal scheelite, associated with a decrease in the ferroelastic phase transition temperature from 255 °C (BiVO4) to room temperature or even below. High sintering temperatures were also found to accelerate this phase transition for compositions with x ≤ 0.08. Temperature independent high quality factor Qf >10000 GHz in a wide temperature range 25–140 °C and high microwave permittivity er ∼76.3 ± 0.5 was obtained for the x = 0.06 ceramic sintered at 800 °C. However, small changes in composition resulted in a change in the sign and magnitude of the temperature coefficient of resonant frequency (TCF) due to the proximity of the ferroelastic transition to room temperature. If TCF can be controlled and tuned through zero, then (1 − x)BiVO4–xLaNbO4 (0.0 ≤ x ≤ 1.0) is a strong candidate for microwave device applications.

  • microwave Dielectric Ceramics li2mo4 tio2 m mo w with low sintering temperatures
    Journal of the American Ceramic Society, 2014
    Co-Authors: Di Zhou, Hong Wang, Lixia Pang
    Abstract:

    In this work, novel series of (1 − x)Li2MO4–xTiO2 (M = Mo, W; x = 0.3, 0.4, 0.45, 0.5, 0.6) Ceramics were developed for microwave Dielectric application. They were prepared via the mixed-oxide process and the phase composition, microstructures, sintering behaviors, and microwave Dielectric properties were investigated. The X-ray diffraction (XRD) pattern and scanning electron microscope analysis indicated that the Li2MO4 (M = Mo, W) did not react with rutile TiO2 and a stable two-phase composite system Li2MO4–TiO2 (M = Mo, W) was formed. The XRD pattern of cofired Ceramics revealed that some parts of Li2MoO4 phase and very small part of Li2WO4 phase react with Ag to form Ag2MoO4 phase and Ag2WO4 phase, respectively. At x = 0.45–0.5, temperature stable microwave Dielectric materials with low sintering temperature (700°C–730°C) were obtained: er = 10.6–11.0, Qf = 30 060–32 800 GHz, and temperature coefficient of resonant frequency ~0 ppm/°C.

  • low temperature firing microwave Dielectric Ceramics k0 5ln0 5 moo4 ln nd and sm with low Dielectric loss
    Journal of The European Ceramic Society, 2011
    Co-Authors: Di Zhou, Hong Wang, Jing Guo, Lixia Pang, Gaoqun Zhang, Xi Yao
    Abstract:

    Abstract In the present work, novel low temperature firing microwave Dielectric Ceramics (K0.5Ln0.5)MoO4 (Ln = Nd and Sm) were prepared via the traditional solid state reaction method. A pure monoclinic phase can be formed at a low sintering temperature around 680 °C for both (K0.5Nd0.5)MoO4 and (K0.5Sm0.5)MoO4 Ceramics. The densification temperature for the (K0.5Nd0.5)MoO4 and (K0.5Sm0.5)MoO4 Ceramics are 700 °C and 800 °C for 2 h, respectively. The best microwave Dielectric properties for (K0.5Nd0.5)MoO4 was obtained in ceramic sample sintered at 760 °C for 2 h, with a Dielectric permittivity of 9.8, a Qf about 69,000 GHz and a temperature coefficient of frequency about −62 ppm/°C. The best microwave Dielectric properties for (K0.5Sm0.5)MoO4 was obtained in ceramic sample sintered at 800 °C for 2 h, with a Dielectric permittivity of 9.7, a Qf about 20,000 GHz and a temperature coefficient of frequency about −65 ppm/°C.

Ian M Reaney - One of the best experts on this subject based on the ideXlab platform.

  • Cold sintering of microwave Dielectric Ceramics and devices
    Journal of Materials Research, 2021
    Co-Authors: Dawei Wang, Di Zhou, Juan Jiang, Ge Wang, Kaixin Song, Ian M Reaney
    Abstract:

    Abstract Microwave (MW) Dielectric Ceramics are used in numerous electronic components for modern wireless communication systems, including antennas, resonators, capacitors and filters. However, to date, MW Ceramics are manufactured by an energy-intensive, conventional high-temperature (> 1000 °C) sintering technology and thus cannot be co-sintered with low melting point and base electrodes (Ag, Al, etc., < 1000 °C), nor directly integrated with polymers (< 200 °C). Cold sintering is able to densify Ceramics at < 200 °C via a combination of external pressure and a transient liquid phase, reducing the energy consumed and facilitating greater integration with dissimilar materials. This review outlines the basics of MW Ceramics alongside the mechanism of cold sintering. Recent developments in cold sintering of MW Ceramics, composites and devices are described, emphasizing new materials and progress towards component/device fabrication. Future prospects and critical issues for advancing cold-sintered MW materials and devices, such as unclear mechanism, low Q × f values and poor mechanical properties, are discussed. Graphic abstract

  • high quality factor ultralow sintering temperature li6b4o9 microwave Dielectric Ceramics with ultralow density for antenna substrates
    ACS Sustainable Chemistry & Engineering, 2018
    Co-Authors: Di Zhou, Lixia Pang, Dawei Wang, Zeming Qi, Ian M Reaney
    Abstract:

    Dense Li6B4O9 microwave Dielectric Ceramics were synthesized at low temperature via solid-state reaction using Li2CO3 and LiBO2. Optimum permittivity ∼ 5.95, quality factor ∼ 41 800 GHz and temperature coefficient of resonant frequency ∼ – 72 ppm/°C were obtained in Ceramics sintered at 640 °C with a ultrasmall bulk density ∼2.003 g/cm3 (∼95% relative density, the smallest among all the reported microwave Dielectric Ceramics). Li6B4O9 Ceramics were shown to be chemically compatible with silver electrodes but reacted with aluminum forming Li3AlB2O6 and Li2AlBO4 secondary phases. A prototype patch antenna was fabricated by tape casting and screen printing. The antenna resonated at 4.255 GHz with a bandwidth ∼279 MHz at −10 dB transmission loss (S11) in agreement with simulated results. The Li6B4O9 microwave Dielectric ceramic possesses similar microwave Dielectric properties to the commercial materials but much lower density and could be a good candidate for both antenna substrate and low-temperature cofire...

  • structure property relationships of low sintering temperature scheelite structured 1 x bivo4 xlanbo4 microwave Dielectric Ceramics
    Journal of Materials Chemistry C, 2017
    Co-Authors: Lixia Pang, Di Zhou, Zeming Qi, Ian M Reaney
    Abstract:

    A series of (1 − x)BiVO4–xLaNbO4 (0.0 ≤ x ≤ 1.0) Ceramics were prepared via a solid state reaction method. A scheelite-structured solid solution was formed for x ≤ 0.5 but for x > 0.5, tetragonal scheelite, monoclinic LaNbO4-type and La1/3NbO3 phases co-existed. As x increased from 0 to 0.1, the room temperature crystal structure gradually changed from monoclinic to tetragonal scheelite, associated with a decrease in the ferroelastic phase transition temperature from 255 °C (BiVO4) to room temperature or even below. High sintering temperatures were also found to accelerate this phase transition for compositions with x ≤ 0.08. Temperature independent high quality factor Qf >10000 GHz in a wide temperature range 25–140 °C and high microwave permittivity er ∼76.3 ± 0.5 was obtained for the x = 0.06 ceramic sintered at 800 °C. However, small changes in composition resulted in a change in the sign and magnitude of the temperature coefficient of resonant frequency (TCF) due to the proximity of the ferroelastic transition to room temperature. If TCF can be controlled and tuned through zero, then (1 − x)BiVO4–xLaNbO4 (0.0 ≤ x ≤ 1.0) is a strong candidate for microwave device applications.

  • low loss sr1 xcaxla4ti5o17 microwave Dielectric Ceramics
    Materials Research Bulletin, 2011
    Co-Authors: Yaseen Iqbal, Abdul Manan, Ian M Reaney
    Abstract:

    Abstract Microwave Dielectric Ceramics in the Sr 1− x Ca x La 4 Ti 5 O 17 (0 ≤  x  ≤ 1) composition series were prepared through a solid state mixed oxide route. All the compositions formed single phase Ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1450–1580 °C. Theoretical density and molar volume decreased due to the substitution of Ca 2+ for Sr 2+ which was associated with a decrease in the Dielectric constant ( ɛ r ) and temperature coefficient of resonant frequency ( τ f ) but an increase in quality factor, Qf o . Optimum properties were achieved for Sr 0.4 Ca 0.6 La 4 Ti 5 O 17 which exhibited, ɛ r  ∼ 53.7, Qf o  ∼ 11,532 GHz and τ f  ∼ −1.4 ppm/°C.

  • microwave Dielectric Ceramics for resonators and filters in mobile phone networks
    Journal of the American Ceramic Society, 2006
    Co-Authors: Ian M Reaney, D Iddles
    Abstract:

    Temperature-stable, medium-permittivity Dielectric Ceramics have been used as resonators in filters for microwave (MW) communications for several decades. The growth of the mobile phone market in the 1990s led to extensive research and development in this area. The main driving forces were the greater utilization of available bandwidth, that necessitates extremely low Dielectric loss (high-quality factor), an increase in permittivity so that smaller components could be fabricated, and, as ever in the commercial world, cost reduction. Over the last decade, a clear picture has emerged of the principal factors, that influence MW properties. This article reviews these basic principles and gives examples of where they have been used to control microwave properties and ultimately develop new materials.