Guo-hua Chen

Guilin University of Electronic Technology, Ling-ch’uan, Guangxi Zhuangzu Zizhiqu, China

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Publications (40)81.34 Total impact

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    ABSTRACT: Thick-film thermistor with negative temperature coefficient (NTC), low room-temperature resistivity and modest thermistor constant was screen-printed on the alumina substrate by the combination of with Ba0.5Bi0.5Fe0.9Sn0.1O3. The electrical properties of the thick films were characterized by a digital multimeter, a Keithley 2400 and an impedance analyzer. The results show that with the Ba0.5Bi0.5Fe0.9Sn0.1O3 content increasing from 0.05 to 0.25, the values of room-temperature resistivity, thermistor constant and peak voltage of the thick films increases and are in the ranges of 1.47-26.5 O-cm, 678-1345 K and 18.9-47.0 V, respectively. The corresponding current at the peak voltage of the thick films decreases and is in the range of 40-240 mA. The impedance spectroscopy measurement demonstrates that the as-prepared thick films show the abnormal electrical heterogeneous microstructure, consisting of high-resistive grains and less resistive grain boundary regions. It can be concluded that the addition of Ba0.5Bi0.5Fe0.9Sn0.1O3 into improves the thermistor behavior and but also deteriorates the current characteristics.
    No preview · Article · Dec 2015 · Transactions of Nonferrous Metals Society of China
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    ABSTRACT: (1 − x)(Sr0.4Na0.3La0.3)TiO3–xLnAlO3 (Ln = Sm, Nd) (0.25 ≤ x ≤ 0.4) ceramics were prepared through the conventional solid-state route. The X-ray patterns revealed that a single phase with perovskite-like structure was obtained in the range of 0.25 ≤ x ≤ 0.4 for the specimens with SmAlO3. However, a small amount of second phase was detected in the specimens with NdAlO3 at x = 0.4 when the sintering temperature was 1520 °C. The dielectric constant (ɛr) linearly decreased with an increasing of LnAlO3 content due to the smaller dielectric polarizability of LnAlO3 than that of (Sr0.4Na0.3La0.3)TiO3. The quality factor (Q·f) was strongly depended on microstructures of these ceramics. And the temperature coefficient of the resonant frequency (τf) shifted to near zero and negative direction with a rise of x, which resulted from the decrease in atomic bond length. Moreover, the effects of different sintering conditions on dielectric properties were studied for the (1 − x)(Sr0.4Na0.3La0.3)TiO3–xNdAlO3 (x = 0.4) ceramics sintered at 1580 °C. The excellent microwave dielectric properties with a near-zero τf ∼ 1.2 ppm/°C, ɛr ∼ 45.2 and Q·f ∼ 38,000 GHz (at 5.01 GHz) could be obtained for x = 0.4 after being sintered at 1580 °C for 4 h.
    No preview · Article · Jul 2015 · Journal of the European Ceramic Society
  • Guo-hua Chen · Ji-le Li · Xi Chen · Xiao-ling Kang · Chang-lai Yuan
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    ABSTRACT: ZnO based varistor ceramics were prepared by a solid state reaction route, and the phase composition, microstructure and electrical properties were also investigated by XRD, SEM, a V-I source/measure unit and impedance spectroscopy. Results show that all the samples consist of mainly ZnO grains and secondary phases including Bi2O3, Zn7Sb2O12, Y2O3, Nd-rich and Y-containing Bi-rich phases. With the increase of sintering temperature, the number of grain boundaries and varistor voltage per grain boundary decreases, and the breakdown field (E1mA) decreases from 556.4 to 319.4 V/mm. The nonlinear coefficient value (α) is in the range of 60-70, the leakage current density values (JL) of all the varistor ceramics are
    No preview · Article · Apr 2015 · Journal of Materials Science Materials in Electronics
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    ABSTRACT: Dense ceramic samples in the (1−x) BiVO4−xLi0.5Sm0.5WO4 (0.05 ≤ x ≤ 0.1) system are prepared using the solid-state reaction process. A single solid–solution phase with monoclinic structure formed through the entire compositions and the unit cell volume increases linearly with x. When x = 0.07, the composition of 0.93BiVO4–0.07 Li0.5Sm0.5WO4 readily sintered at 750 °C has excellent microwave properties with a high permittivity of 73.9, and a Q × f value of 9054 GHz and a near-zero temperature coefficient of −1.61 ppm/°C. The ceramics have applications for microwave devices requiring ultra-low sintering temperatures.
    No preview · Article · Feb 2015 · Journal of Materials Science
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    ABSTRACT: Low firing temperature 0.2Ca0.8Sr0.2TiO3–0.8Li0.5Sm0.5TiO3 (CST–LST) ceramics by BaCu (B2O5) addition and TiO2 dopant were prepared via the conventional solid-state ceramic route, and the sintering, phase evolution, microstructure, and dielectric properties were investigated. Addition of BaCu (B2O5) lowered the firing temperature about 300 °C. The CST–LST ceramics with 5 wt% BaCu(B2O5) sintered at 950 °C exhibited single phase perovskite structure, together with the optimum microwave dielectric properties of ϵr = 66.7, Q × f = 3222 GHz, τf = −21.3 ppm/°C. Adding TiO2 improved the microwave properties. Typically, the CST–LST + 5 wt% BaCu(B2O5) + 1.5 wt% TiO2 sintered at 950 °C showed ϵr = 71.6, Q × f = 3441 GHz, τf = −10.8 ppm/°C. The high permittivity and low temperatures of the ceramics were ideal for the development of low cost ultra-small dielectric loaded antenna. Compatibility with Ag electrode indicated that this material was suitable for low temperature co-fired ceramics.
    No preview · Article · Jan 2015 · Materials Research Bulletin
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    ABSTRACT: (1-x)SrTiO(3-)xCa(0.4)Sm(0.4)TiO(3) (0.6 <= x <= 0.9) ceramics are prepared through the conventional solid-state route. Powders are calcined at 1200 degrees C and sintered at 1400-1500 degrees C. High density, CaTiO3-like perovskite structures are obtained in the range 0.6 <= x <= 0.9. The phase purity, microstructures and microwave dielectric properties are investigated. With an increase of Ca0.4Sm0.4TiO3 content, the dielectric constant (epsilon(r)) decreases, which is dependent on the difference of ionic polarizability between Ca0.4Sm0.4TiO3 and SrTiO3. The product of dielectric Q value and resonant frequency (Q.f) increases up to x = 0.8, and then decreases due to the abnormal grain growth. The variation of temperature coefficient of resonant frequency (tau(f)) with B-site bond valence and tolerance factor (t) is discussed by using the theory of bond valence and the changes of tolerance factor in perovskite structure. The (1-x)SrTiO3-xCa(0.4)Sm(0.4)TiO(3) (0.6 <= x <= 0.9) ceramics show the dielectric properties of epsilon(r) similar to 101.4-142.7, Q.f similar to 1999.5-5986.3 GHz (at 2.8-4 GHz) and tau(f) similar to 359.8-199.6 ppm/degrees C at different sintering temperatures of 1400 -1500 degrees C for 4 h.
    No preview · Article · Dec 2014 · Materials Chemistry and Physics
  • Tao-yong LIU · Guo-hua CHEN · Jun SONG · Chang-lai YUAN
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    ABSTRACT: Glass-ceramic materials of strontium barium niobate system were prepared through a melt-quenching method. The effects of crystallization temperature on the microstructure, dielectric property, breakdown strength and energy storage density of barium strontium niobate glass-ceramics were studied. The crystallization mechanism of the glass-ceramics was discussed and should be one-dimensional interfacial growth. The results indicate that the breakdown strength remarkably increases with the increase of crystallization temperature. The glass-ceramic heat treated at 900 °C was found to possess optimal properties with breakdown strength of 1300 kV/cm and energy storage density of 2.8 J/cm3, which is promising dielectric materials for high energy storage density dielectrics.
    No preview · Article · Mar 2014 · Transactions of Nonferrous Metals Society of China
  • Jun Song · Guo-hua Chen · Chang-lai Yuan · Yun Yang
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    ABSTRACT: Strontium barium niobate-based borate system ferroelectric glass–ceramics with various Sr/Ba ratios were prepared via controlled crystallization method, and the subsequent microstructure, phase evolution, and electrical properties were investigated. The results reveal that increasing Sr/Ba ratio facilitates the formation of uniform dense and fine-grained structure in glass–ceramics and suppresses the crystallization of SBN ferroelectric crystal. The changes in the Sr/Ba ratio dramatically modify the dielectric properties: a high Sr/Ba ratio leads to raised breakdown strength and decreased dielectric constant.
    No preview · Article · Feb 2014 · Materials Letters
  • Guo-hua Chen · Ji-le Li · Yun Yang · Chang-lai Yuan · Chang-rong Zhou
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    ABSTRACT: The Dy2O3-doped ZnO–Bi2O3 based varistor ceramics were prepared by a solid state reaction route, and the microstructure and electrical properties were also investigated. The results show that a multiphase composition exists in all samples. With increasing content of Dy2O3, the average size of ZnO grains decreases and the threshold voltage greatly increases. The nonlinear coefficient of the ceramics is in the range of 4.7–60.2, the threshold voltage is in the range of 364.6–884 V/mm, and the leakage current is between 1.77 μA/cm2 and 159.1 μA/cm2. Typically, the varistor ceramics with 0.60 mol.% Dy2O3 sintered at 1050 °C exhibit excellent electrical properties with the threshold voltage of 872.5 V/mm, the nonlinear coefficient of 60.2 and the leakage current of 5.46 μA/cm2. The results show doping Dy2O3 is a promising route for the production of the higher threshold voltage of ZnO–Bi2O3 based varistor ceramics.
    No preview · Article · Feb 2014 · Materials Research Bulletin
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    ABSTRACT: Negative temperature coefficient thermistor ceramics based on Yn(Ba0.8Bi0.2)1-n Fe0.9Sn0.1O3 were fabricated by conventional solid-state reaction techniques. Phases, microstructures, resistance-temperature curves and impedance characteristics of thermistor ceramics were characterized by X-ray diffraction, scanning electron microscope, resistance-temperature tester and ac impedance analyzer, respectively. Yn(Ba0.8Bi0.2)1-n Fe0.9Sn0.1O3 thermistor ceramics with pseudo-cubic perovskite structure show average grain size of ~1.0 μm and the decreasing lattice parameter a with increase of Y content. Room-temperature resistivity, thermistor constant and activation energy of thermistor ceramics are in the range of 2.17-9.17 MΩ·cm, 6757-7171 K and 0.583-0.618 eV, respectively. When n=0.02 and 0.04, the ceramic resistance is mainly attributed to the contribution of grain boundaries, grains and grain shells. Among them, the resistance value of grain is the highest one. However, for the ceramics with n=0.06 and 0.08, the total resistance of thermistor ceramics is ascribed to the contribution of grain boundaries, domain walls and domains, and the domain regions show the larger resistance value than that of the other two elements. In the limited measured temperature range, all of grain boundaries, grain shells, grains, domain walls and domains show negative temperature coefficient thermistor behavior.
    No preview · Article · Jan 2014 · Journal of Inorganic Materials
  • Guo-hua Chen · Ji-le Li · Chang-lai Yuan · Yun Yang
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    ABSTRACT: ZnO-based varistor ceramics with various amounts of CaSiO3 have been prepared by the conventional solid-state reaction route, and the phase composition, microstructure and electrical properties have been investigated by XRD, SEM, a V–I source/measure unit and impedance spectroscopy (IS). The XRD analyses show the presence of primary phase ZnO and some minor secondary phases. The electrical properties analysis results show that the nonlinear coefficient of the varistor ceramics is in the range of 14.9–30.9, the breakdown voltage in the range of 57.0–168.8 V/mm, and the leakage current in the range of 1.1–31.5 μA/cm2. A schematic model for the electrical microstructure of ZnO-based varistor ceramics is proposed with an equivalent circuit of R a (R g C g )(R gbC gb) by IS.
    No preview · Article · Jan 2014 · Journal of Materials Science
  • Guo-hua Chen · Chang-lai Yuan · Chang-rong Zhou · Yun Yang
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    ABSTRACT: High permittivity 0.4Ca0.6Sm0.8/3TiO3-0.6 (Li0.5Nd0.5) TiO3 ceramics with low firing temperature by BaCu(B2O5) addition were prepared and the ceramic sintering behavior, phase purity, microstructure and microwave dielectric properties were investigated. Addition of BaCu(B2O5) can effectively lower the firing temperature by about 200 °C. The 0.4Ca0.6Sm0.8/3TiO3-0.6 (Li0.5Nd0.5) TiO3 ceramics with 3 wt% BaCu(B2O5) sintered at 1100 °C exhibit good microwave dielectric properties with a permittivity of 96.3, a Qf value of 3133.3 GHz, and a temperature coefficient of resonant frequency of −19.5 ppm/°C, which is suitable for dielectric loaded antenna applications.
    No preview · Article · Dec 2013 · Ceramics International
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    ABSTRACT: The effects of Li2O-MgO-B2O3 (LMB) glass additive on the sintering characteristics, phase purity, microstructure, and microwave dielectric properties of Li2MgTi3O8 ceramics were investigated. The experimental results demonstrate that the addition of LMB glass effectively lowers the sintering temperature of Li2MgTi3O8 ceramic from 1025 °C to 875 °C and induces no obvious degradation of the microwave dielectric properties. Typically, the 1.5% LMB glass-added Li2MgTi3O8 ceramic sintered at 875 °C for 4 h shows excellent microwave dielectric properties of Q×f=45403 GHz, εr=25.9 and τf≈0 °C−1. The dielectric ceramic exhibits stability against the reaction with the Ag electrode, which indicates that the ceramics could be applied in multilayer microwave devices requiring low firing temperatures.
    No preview · Article · Nov 2013 · Transactions of Nonferrous Metals Society of China
  • Guo-Hua Chen · Ji-Le Li · Chang-Lai Yuan · Yun Yang
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    ABSTRACT: ZnO-based varistor ceramics doped with fixed Y2O3 and different Sm2O3 have been prepared by the conventional solid-state reaction route, and the phase composition, microstructure and electrical properties have been investigated by XRD, SEM and a V–I source/measure unit. The XRD analyses show the presence of primary phase ZnO and some minor secondary phases. Doping appropriate contents of Sm2O3 decrease the leakage current and enhance nonlinearity characteristics of ZnO-based varistor ceramics markedly. The varistor ceramics with 0.25 mol% Sm2O3 sintered at 1,125 °C for 1 h exhibit reasonable electrical properties with the breakdown field of 446.4 V/mm, the nonlinear coefficient of 65.8 and the leakage current of 2.36 μA/cm2. The results illustrate that doping Y2O3 and Sm2O3 may be a promising route for the production of ZnO-based varistor ceramics with good electrical properties.
    No preview · Article · Oct 2013 · Journal of Materials Science Materials in Electronics
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    ABSTRACT: Glass-ceramic materials of the SrO-BaO-Nb2O5-B2O3-SiO2 system added with various amounts of BaF2 have been prepared by conventional melting and heat treated crystallization method. The effect of BaF2 addition on crystallization kinetics has been explored for dielectric applications. The addition of BaF2 to the glass-ceramics decreases the activation energy of crystallization and enhances the dielectric constant as well as breakdown strength remarkably. Glass-ceramic with a dielectric constant of 63.4, breakdown strength of 1120 kV/mm and energy storage density of 3.52 J/cm(3) could be achieved. A new electrode structure could effectively improve the electrical properties, and energy storage density could be increased from 3.52 J/cm(3) to 4.82 J/cm(3), which is promising in high energy storage density dielectrics.
    No preview · Article · Oct 2013 · Journal of Non-Crystalline Solids
  • Guo-hua Chen · Hua-rui Xu · Chang-lai Yuan
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    ABSTRACT: Li2Ti1−x(Zn1/3Nb2/3)xO3 (0≤x≤0.5) ceramics were prepared by a solid state ceramic route, and the phase purity, microstructure, and microwave dielectric properties were investigated. The XRD results suggest the formation of solid solutions for all studied compositions (0≤x≤5). The dielectric properties are strongly dependent on the compositions, the densifications and the microstructures of the samples. The Q×f value increases with x up to x=0.2 and then decreases with the further increase of x. The best microwave dielectric properties of εr=20.5, Q×f =75,257 GHz, and τf =15.4 ppm/°C could be obtained when x=0.2.
    No preview · Article · Jul 2013 · Ceramics International
  • Tao-yong Liu · Guo-hua Chen · Jun Song · Chang-lai Yuan
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    ABSTRACT: Glass-ceramic materials of the SrOBaONb2O5B2O3SiO2 system, with various amounts of CeO2 added, have been prepared by conventional melt casting followed by controlled crystallization. The effect of CeO2 addition on crystallization kinetics has been explored for dielectric applications. The addition of CeO2 to the glass-ceramics decreases the activation energy of crystallization and enhances the dielectric constant as well as breakdown strength remarkably. Glass-ceramic with a dielectric constant of 49, breakdown strength of 1250 kV/mm and energy storage density of 3.39 J/cm3 could be achieved, so this is promising in high energy storage density dielectrics.
    No preview · Article · Jul 2013 · Ceramics International
  • Li Ji-le · Guo-hua Chen · Chang-lai Yuan
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    ABSTRACT: ZnO-based varistor ceramics doped with Nd2O3 and Y2O3 have been prepared by the conventional ceramics method. The phase composition, microstructure and electrical properties of the ceramics have been investigated by XRD, SEM and a V–I source/measure unit. The XRD and EDS analyses show the presence of ZnO, Bi2O3, Zn7Sb2O12, Y2O3, Nd-rich phase and Y-containing Bi-rich phase. The electrical properties analyzed show that the nonlinear coefficient of the varistor ceramics is in the range of 4.4–70.2, the threshold voltage is in the range of 247.1–1288.8 V/mm, and the leakage current is in the range of 1.51–214.6 μA/cm2. The 0.25 mol% Nd2O3 added varistor ceramics with 0.10 mol%Y2O3 sintered at 1050 °C exhibits excellent electrical properties with the high threshold voltage of 556.4 V/mm, the nonlinear coefficient of 61 and the leakage current of 1.55 μA/cm2. The results illustrate that doping Nd2O3 and Y2O3 in ZnO-based varistor ceramics may be a very promising route for the production of the higher threshold voltage and the nonlinear coefficient of ZnO-based varistor ceramics.
    No preview · Article · Apr 2013 · Ceramics International
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    ABSTRACT: Lead-free (0.996-x)KNN-0.004BM-Xls (x=0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06) ceramics were prepared by the traditional ceramic sintering processing. The effect of LS content on the microstructure and piezoelectric properties of KNN-BM lead-free ceramics was investigated. The results show that the ceramics have a single orthorhombic phase structure when x≤0.02, a co-existed phases orthorhombic and tetragonal phases structure at 0.03≤x≤0.05, and a single tetragonal phase structure at x=0.06. The morphotropic phase boundary (MPB) for the ceramics is identified in the composition range of 0.03≤x≤0.05. With increasing the LS content, both d33 and kp of the ceramics firstly increase and then decrease. At x=0.05, d33 and kp reach their maximum values which are 230 pC/N and 0.42, respectively. The To-t and Tc of the ceramics shift to the low temperature with the increasing of the LS content. The To-t and Tc of the ceramics are 455 and 215°C at x=0, 385 and 150°C at x=0.02, 370 and 75°C at x=0.06, respectively.
    No preview · Article · Mar 2013 · Journal of Inorganic Materials
  • Guo-hua Chen · Mei-zhen Hou · Yun Yang
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    ABSTRACT: The effects of Li2O–MgO–B2O3 (LMB) frit on the sintering characteristic, phase purity, microstructure and microwave dielectric properties of Li2TiO3 ceramics were investigated. The results show that a single-phase Li2TiO3 is formed and no secondary phase is formed. Addition of LMB frit can lower the sintering temperature of the ceramics by about 400 °C without deteriorating the microwave dielectric properties. Typically, the sample with 5 wt% LMB frit sintered at 850 °C shows good microwave dielectric properties with a permittivity of 21.4, a Q×f value of 64,100 GHz, and a temperature coefficient of resonant frequency of 26.9 ppm/°C.
    No preview · Article · Dec 2012 · Materials Letters