The 0.2Pb(Zn1/3Nb2/3)O3-0.8Pb(Zr0.5Ti0.5)O3 (0.2PZN-0.8PZT) ceramic system exhibits excellent piezoelectric properties; however, its high sintering temperature (~1,250°C) causes severe PbO volatilization, increases processing cost, and limits co-firing with low-melting-point electrodes in multilayer devices. In this study, LiBiO2 was introduced as a sintering aid to enable lowtemperature densification of 0.2PZN–0.8PZT ceramics. The optimal composition of x = 0.3 mol% sintered at 1,050°C achieved d33 = 367 pC/N, kp = 0.54, and εT33/ε0 = 1,643. The Curie temperature was also enhanced to 347.8°C, compared with 297.2°C for the reference specimen sintered at 1,250°C. These results demonstrate that LiBiO2 addition enables a 200°C reduction in sintering temperature while maintaining piezoelectric performance and improving thermal stability.
Various process technologies for manufacturing power inductors are under development. The core goal is to increase the mixing ratio of the soft magnetic powder in the epoxy, and to uniformly disperse it in a molding-type power inductor, manufactured by the injection molding method. In this study, we investigated the effect of dispersant and silane on the dispersion of soft magnetic metal powders in epoxy. We added 0.6 wt% of dispersant and 2.0 wt% of silane, and an excellent dispersibility resulted. Under the conditions of 0.3 wt% of dispersant and 0.5 wt% of silane, we added both dispersant and silane together to observe the effect of their interaction on dispersibility. Similarly, the addition of 0.3 wt% of dispersant and 0.1 wt% of silane resulted in a sharp increase in viscosity, considered to be due to the interaction of the dispersant and silane. The addition of 0.1 wt% of dispersant with 0.5 wt% of silane resulted in a sharp rise in viscosity, and sedimentation-height decreased sharply due to the dispersion optimization.
In a Pb-included piezoelectric composition, SryPb1-y[(Zn1/3Nb2/3)x-(Ni1/3Nb2/3)0.2-(Zr0.46Ti0.54)0.8-x]O3 was selected in order to attain high piezoelectric properties. According to the PZN ratio (x) and the amount of Sr doping (y), the crystal structure, microstructure and piezoelectric properties were measured and evaluated. In the case of Sr 4 mol% doping, the piezoelectric properties were the highest for a PZN ratio of 0.1. In this condition, the grain size was larger and the intensity was higher. With the PZN ratio fixed and varying the Sr doping, the piezoelectric properties increased until 10 mol% doping and then decreased for over 12 mol% doping. In the case of x＝0.1 and y＝10 mol%, the best piezoelectric properties were obtained, i.e., d33＝660 pC/N and kp＝68.5%, and these values seem to be related to the grain size and crystal structure.
There is growing interest in power inductors in which metal soft magnetic powder and epoxy resin are combined. In this field, the process technology for increasing the packing density of magnetic particles in an injection molding process is very important. However, little research has been reported in this regard. In order to improve the packing density, we investigated and compared the sedimentation heights of pastes for three types of soft magnetic alloy powders as a function of the mixing ratios and the type of resin used. Experimental results showed that the packing density was the highest (71.74%) when the mixing ratio was 80：16：4 (Sendust：Fe-Si：CIP) according to the particle size using an SE-4125 resin. In addition, the packing density was found to be inversely related to the layer separation distance. As a result, it was confirmed that the dispersion of solid particles in the paste was important for curing; however, the duration of the curing process can greatly affect the packing density of the final composite.
A molding-type power inductor is an inductor that uses a hybrid material that is prepared by mixing a ferrite metal powder coated with an insulating layer and an epoxy resin, which is injected into a coil-embedded mold and heated and cured. The fabrication of molding-type inductors requires various techniques such as for coil formation and insertion, improving the magnetic properties of soft magnetic metal powder, coating an insulating film on the magnetic powder surface, and increasing the packing density by well dispersing the powder in the epoxy resin. Among these aspects, researches on additives that can disperse the metal soft magnetic powder having the greatest performance in the epoxy resin with high charge have not been reported yet. In this study, we investigated the effect of silanes, KBM-303 and KBM-403, and a commercial dispersant on the dispersion of metal soft magnetic powders in epoxy resin. The sedimentation height and viscosity were measured, and it was confirmed that the silane KBM-303 was suitable for dispersion. For this silane, the packing density was as high as about 72.49%. Moreover, when 1.2 wt% of dispersant BYK-103 was added, the packing density was about 80.5%.
Pb(Zr, Ti)O3 (PZT) is a piezoelectric material applied in a typical actuator and has been actively studied. However, in order to overcome the limitations of PZT, piezoelectric ceramics comprising mixed solid solutions of PZT with various relaxer electric materials have been studied. The Pb(Zn1/3Nb2/3)-Pb(Ni1/3Nb2/3)-Pb(Zr, Ti)O3 (PZN-PNN-PZT) piezoelectric ceramic, known to have high piezoelectric constant and electromechanical coupling coefficient, was studied herein. The piezoelectric characteristics with various Zr contents (Zr/Ti ratios), PZN molar ratios, and sintering temperatures were compared. The piezoelectric properties of d33＝580 pC/N and kP＝0.68 were obtained with the 0.1PZN-0.2PNN-0.7PbZr0.46Ti0.54O3 composition sintered at 1,290℃.
We investigated the structure of an ultra-thin insulating board with low thermal conductivity along z-axis, which was based on the idea of void layers created during the glass infiltration process for the zero-shrinkage low-temperature co-fired ceramic (LTCC) technology. An alumina and four glass powders were chosen and prepared as green sheets by the tape casting method. After comparison of the four glass powders, bismuth glass was selected for the experiment. Since there is no notable reactivity between alumina and bismuth glass, alumina was selected as the supporting additive in glass layers. With 2.5 vol% of alumina powder, glass green sheets were prepared and stacked alternately with alumina green sheet to form the ‘alumina/glass (including alumina additive)/alumina’ structure. The stacked green sheets were sintered into an insulating substrate. Scanning electron microscopy revealed that the additive alumina formed supporting bridges in void layers. The depth and number of the stacking layers were varied to examine the insulating property. The lowest thermal conductivity obtained was 0.23 W/mK with a 500-㎛-thick substrate.
With high integration of electronic components, power inductors are also miniaturized. Recently, thick film processes for small size power inductors were developed and commercialized. However, the thick film process to prepare soft magnetic green sheets was not reported enough. In this study, we used Fe-Si magnetic and CIP (carbonyl iron powders) as starting materials to lead to a bimodal particle size distribution in the sheet. We proposed a newly developed ‘Modified slurry preparation process’ to get well dispersed condition even at high solid contents. Using the new process, it was possible to prepare a well dispersed slurry over 70 vol% of solid. BYK-103 was better than BYK-111 as dispersant in this slurry and the optimum amount was 0.6 wt%. The optimized slurry was formed into a sheet by tape casting process and then the sheet was laminated. We conformed that small size powder, large size powder, and epoxy resin were well dispersed in the green sheet.
It is necessary for ferrite sheets to be fabricated with high packing density for excellent electrical properties and high strength. In this study, the relationship between the warpage and the packing density of ferrite green sheet, was investigated with amount variation of organic additives. With 0.4 wt% of dispersant, the packing density was about 48% and warpage appeared 0.5~1.3 ㎜ high. With 1.4 wt% of dispersant, the packing density increased up to 57% and warpage appeared 0.8~2.1 ㎜ high. With high packing density, warpage appeared along the edges of specimen, while with low packing density, deformation appeared over whole specimen inhomogeneously. It is thought that inhomogeneous deformation after sintering came from the inhomogeneity in green sheet prepared with badly dispersed slurry. With good homogeneity in green sheet from well-dispersed slurry, isotropic shrinkage is thought to have occurred along the distance from center to edges of specimen during sintering.
In solid oxide fuel cell system, yttria-stabilized zirconia is generally adopted as the electrolyte, which has high strength and superior oxygen ion conductivity, and the air electrode and the fuel electrode are attached to this. Recently, new structure of ``layered planar SOFC module`` was suggested to solve there liability problem due to the high temperature stability of a sealing agent and a binding material. In this study to materialize the air electrode in a layered planar SOFC module, the LSM ink was coated to form homogeneous electrode in the channel after the ink preparation. As the porosity control agent, PMMA oractive carbon powder was adopted with use of a commercial dispersant in ethanol. The optimal amounts of both the porosity control agents and the dispersant were determined. Four (4) vol% of the dispersant for the LSM-PMMA case and 15 vol% for LSM-carbon powder showed the lowest viscosities respectively to indicate the best dispersed states of the slurries. With PMMA and carbon powder, sintered LSM ink shows the relatively homogeneous distributions of pores and with increases of the agents, the porosities increased in both cases. From this, it can be thought that the amount of the PMMA or carbon powder could be used to control the porosity of the LSM ink.
BaTiO3 nano powder can be synthesized by hydrate salt method at 120℃ in air. Decreasing the thickness of thick film, the nano dielectric particle is needed in electronic ceramics. However, the synthesis of BaTiO3 nano particle at low temperature in air and their mechanism were not reported enough. And ultrasonic treatment can be tried because of low temperature process in air. Therefore, in this study, the BaTiO3 nano powder was synthesised with the synthesis time and ultrasonic treatment at120oC in air. In the synthesis process, the effects of process were evaluated. From the experimental observation, the synthesis mechanism was proposed. The homogeneous BaTiO3 particle was synthesized by KOH salt solution at 120℃ for 1hour. It was conformed that the ultrasonic treatment effected on theincrease of synthesis rate. After cutting the salt powder using FIB, BaTiO3 nano particles observed homogeneously in the cross-section of the salt particle.
Ag paste has been used in the front electrode of the Si-solar cell. It is composed by Ag powder, glass frit, binder, solvent and dispersant. The role of the binder and the solvent is to make a flow and a printing property. However, it was not enough to report the printing properties with the variation of binder in the controled viscosity. In this study, we selected 3 kinds of typical binder which were used as binder for the paste in the industry, such as Ethyl cellulose, Hydroxypropyl cellulose and Acrylic. Ag pastes using these were prepared, controled viscosity and printed on the SiNx coated Si wafer. In the ‘A paste’ used Acrylicbinder, printed hight was highest and ‘H paste’ used Hydroxypropyl cellulose binder was lowest. Because ‘Hpaste’ was high viscosity due to the molecular weight, the solvent was added in the paste to control the viscosity. Therefore, the content of solid was lower in ‘H paste’. The relative pattern width which is related to the spreading of paste was the best in the case of ‘H paste’ and ’EH paste’ at 30℃. It is thought that the optimization of the relative pattern width is possible for a paste by the controling shear thinning phenomenon. In the case of ‘A paste’, though printing hight was best, the pattern width was dependant on the temperature.
CIGS is one of thin film solar cell and has been studied so much, because of the possibility of low price and high efficiency. Until now, co-evaporation and sputtering were typical method to prepare CIGS absorption layer, and a few company commercialized solar cell by these method. However,non-vacuum process which has been studied for long time has not been progressed, though the merit of low price. Especially, aerosol deposition method has not been reported, because it is difficult to prepare a large quantity of various CIGS powder. In this study, CIGS powder was synthesized by mechanochemical method and CIGS absorption layer was deposited by aerosol deposition method. The thickness of the CIGS layer was controlled by the number of deposition and the surface roughness of it was affected by the amount of flow gas. And, also, I-V curve of it appeared metallic property in the case of ‘as deposition’. After heat treatment in Se-rich atmosphere, the electrical property of it changed to a semiconductor. CdS and transparent conduction layer were formed by a typical method on it for solar cell. The efficiency of cell was appeared 0.19%. Though the efficiency was low because of the disharmony in the after-process, it was conformed that CIGS solar cell could be prepared by aerosol deposition.
The front electrode should be used to make solar cell panel so as to collect electron. The front electrode is used by paste type, printed on the Si-solar cell wafer and sintered at about 800℃. The paste is composed Ag powder and glass frit which make the ohmic contact between Ag electrode and n-type semiconductor layer. From the previous study, the Ag electrodes which used two commercial glass frit of Bi-system were so different on the interface resistance. The main composition of them was Bi-Zn-B-Si-O and few additives added in one of them. In this study, glass frit was made with the ratio of Bi2O3 and ZnO on the main composition, and then paste using glass frit was prepared respectively. And, also, the paste using the glass frit added oxide additives were prepared. The change of interface resistance was not large with the ratio of Bi2O3 and ZnO. In the case of G6 glass frit, 78 wt% Bi2O3 addition, the interface resistance was 190 Ω and most low. In the glass frit added oxide, the case of Ca increased over 10 times than it of G6 glass frit on the interface resistance. It was thaught that after sintering, Ca added glass frit was not flowed to the interface between Ag electrode and wafer but was in the Ag electrode.
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Properties of Silicon Solar Cells with Local Back Surface Field Fabricated by Aluminum-Silicon Eutectic Alloy Paste Jae-Wook Choi, Sungeun Park, Soohyun Bae, Seongtak Kim, Se Jin Park, Hyomin Park, Yoonmook Kang, Hae-Seok Lee, Donghwan Kim Current Photovoltaic Research.2016; 4(4): 145. CrossRef
The properties of LTCC green sheets formed by the MLS-22 powder of NEG Inc. were investigated for acrylic binders with different PVB and Tg in the variation of temperature. The elongation of the green sheets showed large variation depending on the temperature, and was rapidly decreased near the Tg of the sheets. With the increase of the ratio of plasticizer/binder (P/B), large elongation of the sheets was observed due to the decrease of the Tg. In the stacking process of the multilayer ceramic, the optimal control of the temperature is highly required depending on the Tg of the binder and the ratio of P/Buniform coating.
According to the composition of LTCC material, though it was thought that bulk defect which was made in forming process effects on the densification during the sintering, it was not reported systemically. In this study, we evaluated crystal structure, 3 point bending strength, hardness and microstructure of the samples by uniaxial pressing and tape casting using the commercial powders of the crystallizing glass and the glass/ceramic composite. In the case of glass/ceramic composite, Viox-001 powder with residual glass in the sintering, 3 point bending strength was similar regardless of forming process due to fill the bulk defect by residual glass. In the case of crystallizing glass, MLS-22, because glass phase was small in the sintering, glass did not fill the pore in the sample by uniaxial pressing process, therefore, the 3 point bending strength of it was 167 MPa. However, the 3 point bending strength of the sample by tape casting was 352 MPa and much higher. Meanwhile, crystal structure and hardness were similar regardless of forming process.
In this study, we have coated the inner surface of YSZ channel using LSM powder ink through depressurization process for making the cathode of a stacked planar-type SOFC module. To coat the surface of YSZ channel uniformly, we tried to find the optimum manufacturing condition for LSM ink. We used four different dispersants (BYK series) and two different solvents (ethanol and DMF) to make the LSM ink. It was revealed that the ink made with the ethanol solvent and the BYK-111 dispersant has the lowest viscosity, relatively low contact angle and most excellent dispersibility. After depressurizing a chamber filled with LSM ink and sintered YSZ channel, we have found that the YSZ channel was uniformly coated with LSM cathode. The LSM ink with 25 vol% BYK-111 showed the most uniform coating.
A layered planer SOFC module was designed from planar-type SOFC. It was prepared by multi-layered ceramic technology. To form the cathode and the anode in the layered structure, reliable channels should be made on the both side of electrolyte perpendicularly. However, monolithic SOFC using multi-layered ceramic technology hasn`t been studied another group, and the warpage of electrolyte in the channel, also, hasn`t been studied, when electrode is printed on the electrolyte. In this study, the channels are prepared with electrode printing, and their warpage are evaluated. In the case of YSZ without electrode, the warpages are nothing in the limit of measurement using optical microscope. The warpage of ``YSZ-NiO printed`` increases than that of ``NiO printed``, and also, the case of ``double electrode printed`` is similar to ``YSZ-NiO printed``. It is thought that, in the printed electrolyte, the warpage is related to the difference of the sintering behavior of each material.
In this study we aims to evaluate the effects of 1/3 mol% Co3O4 addition on the reaction, microstructure development, resultant electrical properties, and especially the bulk trap and grain boundary properties of ZnO-Bi2O3-Sb2O3 (Sb/Bi=2.0, 1.0, and 0.5) system (ZBS). The samples were prepared by conventional ceramic process, and characterized by XRD, density, SEM, I-V, impedance and modulus spectroscopy (IS & MS) measurement. In addition of Co3O4 in ZnO-Bi2O3-Sb2O3 (ZBSCo), the phase development, density, and microstructure were controlled by Sb/Bi ratio. Pyrochlore on cooling was reproduced in all systems. The more homogeneous microstructure was obtained in ZBSCo (Sb/Bi=1.0) system. In ZBSCo, the varistor characteristics were improved drastically (non-linear coefficient α=23∼50) compared to ZBS. Doping of Co3O4 to ZBS seemed to form V*o (0.33 eV) as dominant defect. From IS & MS, especially the grain boundary of Sb/Bi=0.5 system is composed of electrically single barrier (0.93 eV) and somewhat sensitive to ambient oxygen with temperature.
In this study, we investigated the effects of Mn dopant (0.1∼3.0 at% Mn3O4 sintered at 100 0℃ for 1 h in air) on the bulk trap (i.e. defect) and grain boundary properties of ZnO, ZM(0.1∼3.0) using admittance spectroscopy (AS), and impedance-modulus spectroscopy (IS & MS). As a result, three kinds of defect were found below the conduction band edge of ZnO as 0.09∼0.14 eV (attractive coulombic center), 0.22∼25 eV (Zn¨(i)), and 0.32∼0.33 eV (V`o). The oxygen vacancy increased with Mn doping. In ZM, an electrically single grain boundary as double Schottky barrier was formed with 0.82∼1.0 eV of activation energies by IS & MS. We also find out that the barriers of grain boundary of Mn-doped ZnO (α-factor=0.13) were more stabilized and homogenized with temperature compared to pure ZnO.
In this study, we have investigated the effects of Co doping on I-V curves, bulk trap levels and grain boundary characteristics of ZnO-Bi2O3 (ZB) varistor. From I-V characteristics the nonlinear coefficient (a) and the grain boundary resistivity (ρgb) decreased as 32→22 and 18.4→0.6×10(9) Ωcm with sintering temperature (900∼1,300℃), respectively. Admittance spectra and dielectric functions show two bulk traps of zinc interstitial, Zn(i)·· (0.16∼0.18 eV) and oxygen vacancy, Vo· (0.28∼0.33 eV). The barrier of grain boundaries in ZBCo (ZnO-Bi2O3-Co3O4) could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.93 eV at the 460∼580 K to 1.13 eV at the 620∼700 K. It is revealed that Co dopant in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against the ambient temperature.
The sintering, defect and grain boundary characteristics of Bi-based ZnO chip varistor (1,608 mm size) have been investigated to know the possibility of lowering a manufacturing price by using 100 % Ag inner-electrode. The samples were prepared by general multilayer chip varistor process and characterized by shrinkage, SEM, current-voltage (I-V), admittance spectroscopy (AS), impedance and modulus spectroscopy (IS & MS) measurement. There are no problems to make a chip varistor with 100% Ag inner-electrode in the sintering temperature range of 850∼900℃ for 1 h in air. A good varistor characteristics (Vn= 9.3∼15.4 V, a= 23∼24, IL= 1.0∼1.6 μA) were revealed but formed Zn(i)·· (0.209 eV) as dominant defect, and increased the distributional inhomogeneity and the temperature instability in grain boundary barriers.
In this study we aims to examine the effects of 0.5 mol% Cr2O3 addition on the reaction, microstructure development, resultant electrical properties, and especially the bulk trap and interface state levels of ZnO-Bi2O3-Sb2O3 (Sb/Bi=0.5, 1.0, and 2.0) systems (ZBS). The samples were prepared by conventional ceramic process, and characterized by XRD, density, SEM, I-V, impedance and modulus spectroscopy (IS & MS) measurement. The sintering and electrical properties of Cr-doped ZBS (ZBSCr) systems were controlled by Sb/Bi ratio. Pyrochlore (Zn2Bi3Sb3O14) was decomposed more than 100℃ lowered on heating in ZBS (Sb/Bi=1.0) by Cr doping. The densification of ZBSCr (Sb/Bi=0.5) system was retarded to 800℃ by unknown Bi-rich phase produced at 700℃. Pyrochlore on cooling was reproduced in all systems. And Zn7Sb2O12 spinel (α-polymorph) and δ-Bi(2)O(3) phase were formed by Cr doping. In ZBSCr, the varistor characteristics were not improved drastically (non-linear coefficient α=7~12) and independent on microstructure according to Sb/Bi ratio. Doping of Cr2O3 to ZBS seemed to form Zn(i) (0.16 eV) and Vo (0.33 eV) as dominant defects. From IS & MS, especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one (1.1 eV) and electrically inactive intergranular one (0.95 eV) with temperature.
In this study, we have investigated the effects of Mn dopant on the bulk trap levels and grain boundary characteristics of Bi2O3-based ZnO (ZB) varistor using admittance spectroscopy and dielectric functions (such as Z*, Y*, M*, ε*, and tanδ). Admittance spectra and dielectric functions show two bulk traps of Zn(i) (0.20 eV) and Vo (0.29~0.33 eV) in ZnO-Bi2O3-Mn3O4 (ZBM). The barrier of grain boundaries in ZBM could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.79 eV at lower temperature to 1.08 eV at higher temperature. The grain boundary capacitance Cgb was decreased slightly with temperature as 1.3~1.8 nF but resistance Rgb decreased exponentially. The relaxation time distribution can result from the heterogeneity of the barriers constituting the varistor. It is revealed that Mn dopant in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against the ambient temperature.
Sintering and electrical characteristics of ZnO varistor with calcined additive of ZnO–Bi2O3–Cr2O3–Mn3O4 Dong-Hyeon Nam, Young-Woo Heo, Youn-Woo Hong Ceramics International.2026;[Epub] CrossRef
A Study of The Surface Dielectric Barrier Discharge Design Conditions for Generating Negative Air Ions Sang-Moon Shin, Jung-Yoon Kim, Jong-Soo Kim, Jae-Ha Choi, Won-Ho Choi Journal of the Korean Institute of Illuminating and Electrical Installation Engineers.2014; 28(1): 114. CrossRef
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