Man-Soon Yoon

Effect of synthesizing method on the properties of LiFePO4/C composite for rechargeable lithium-ion batteries

Olivine-type LiFePO4/C cathode materials are fabricated with FePO4 powders that are pre-synthesized by two different processes from iron chloride solution. Process I is a modified precipitation method which is implemented by the pH control of a solution using NH4OH to form FePO4 precipitates at room temperature. Process II is a conventional precipitation method, of which H3PO4 (85%) solution is gradually added to a FeCl3 solution during the process to maintain a designated mole ratio. The solution is subsequently aged at 90°C in a water bath until FePO4 precipitates appear. In order to synthesize LiFePO4/C composites, each batch of FePO4 powders is then mixed with pre-milled lithium carbonate and glucose (8 wt. %) as a carbon source in a ball-mill. The structural characteristics of both LiFePO4/C composites fabricated using iron phospates from two different routes have been examined employing XRD and SEM. The modified precipitation process is considered to be a relatively simple and effective process for the preparation of LiFePO4/C composites owing to their excellent electrochemical properties and rate capabilities.

Dependence of material properties on piezoelectric microspeakers with AlN thin film

This paper reports the dependence of residual stress on the piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film deposited onto Mo/Ti electrode. This successful achievement is followed by using a compressively stressed silicon nitride film as a supporting diaphragm and high quality AlN thin film with compressive residual stress (less than -100 MPa). The sound pressure level (SPL) is relatively small when we use a tensile stressed silicon nitride film, the SPL of the fabricated microspeakers that have compressively stressed composite diaphragm shows more than 60 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with 20 Vpeak-to-peak sinusoidal input biases and 10 mm distances from the fabricated microspeakers to the reference microphone. The packaging structure enhances the low frequency characteristics significantly.

Effect of high-energy milling process on microstructure and piezoelectric/dielectric properties of 0.99Pb(Zr0.53Ti0.47)O3-0.01BiYO3 ceramic for piezoelectric energy harvesting devices

A piezoelectric ceramic, 0.99Pb(Zr0.53Ti0.47)O3-0.01BiYO3 [PZT-BY], was fabricated via high-energy milling (HEM) and conventional ball milling methods. The HEM process improved the reaction activity and homogeneity of the materials used throughout the process and reduced the calcination temperature by 150°C compared with the conventional process. The effects of the HEM process on the microstructure, dielectric, and piezoelectric properties of the PZT-BY ceramic were systematically investigated. The modified method using HEM resulted in a high d33 of 315 pC/N and kp of 63%, with a low K33T of 684, whereas the conventional process had values of 280 pC/N, 56%, and 748 respectively. In addition, piezoelectric voltage constant (g33), and transduction coefficient (d33 × g33) have also been evaluated. The large (d33 × g33) of 16,568 × 10−15 m2/N indicates that the PZT-BY ceramic fabricated by the HEM process is a good candidate material for energy harvesting devices.

Synthesis of Li excess LiFePO4/C using iron chloride extracted from steel scrap pickling

Olivine-type Li rich Li1+xFePO4/C composites are synthesized by a solid state reaction process using premilled Li2CO3 and pre-synthesized amorphous FePO4·xH2O powders. The amorphous FePO4·xH2O powders are prepared from an industrial waste liquid (by-product), a FeCl3 (38%) solution, via a precipitation process. In addition, lithium carbonate is pre-milled using a high energy nano mill to control particle sizes and shape differences for enhancing the reaction activity in the starting materials. The main purpose of this study is to investigate the effect of excess Li on the electrochemical properties of LiFePO4 cathode materials. The pre-synthesized FePO4 powders are mixed with pre-milled lithium carbonate and glucose (8 wt%) using a ball-mill process. The structural characteristics of the Li1+xFePO4/C composites are examined by XRD and SEM. To investigate the effect of excess Li content on the electrochemical properties in Li1+xFePO4/C composites, a Li[LiPF6 (Ethylene carbonate + Dimethyl carbonate)] Li1+xFePO4/C model cell is used. It is demonstrated that the 1% Li rich Li/[Li1.01FePO4/C] cell exhibits the best electrochemical performance and delivers an initial discharge capacity of 161 mAhg−1, which is 25 mAhg−1 higher than that of the Li/[LiFePO4/C] cell.

Low Temperature Sintering of PNN-PZT Ceramics and Its Electrical Properties

To fabricate a multi-layered piezoelectrics/electrodes structure, the piezoelectrics should be sintered at the temperature lower than to use the silver electrode, which is cheaper than the electrodes containing noble metals such as Pd and Pt. Therefore, in this study, we modified the composition of -based material as to lower the sintering temperature and to improve the piezoelectric properties. Small amount of , , and were also added to lower the sintering temperature of the ceramic. The prepared raw powders were mixed by using a ball mill for 24 hours. And then the mixed powders were calcinated for 2 hours at . The calcinated powders were again crushed with the ball mill for 72 hours. The final powders were pressed for making the shape of disk. The disk-type samples were sintered at temperature range of . The crystal phases of the sintered specimens were perovskite structure without secondary phases. All of the measured electrical properties such as electromechanical coupling coefficients (), mechanical quality factors (), and piezoelectric charge constants () were decreased with decreasing the sintering temperatures. The electrical properties measured at the sample sintered at were 54% of , 503 of , and 390 pC/N of , respectively. These properties were considered to be fairly good for the application of multi-layered piezoelectric generators or actuators.

CHARACTERISTICS OF BaTiO3-PVDF 0-3 COMPOSITE FILM FOR INORGANIC ELECTRO-LUMINESCENCE DEVICE

ABSTRACT In order to increase the brightness, the relative dielectric constant of the dielectric layer inserted between rear electrode and phosphor layer should be high. We manufactured BaTiO3-PVDF 0-3 type composite film for the application of the dielectric layer in the high brightness inorganic electro-luminescence (EL) device. The pastes for the BaTiO3-PVDF composite film were made with various mixing ratio by using 3-roll milling mixer. The pastes were coated on the phosphor layer by screen-printing method. The phosphor layer was also coated on a substrate by using the same screen-printing system. The substrate is an indium tin oxide (ITO) film deposited on PET (polyethylene terephthalate) polymer film. The others of rear electrode and insulating layer were also coated by the screen-printing method. Both the relative dielectric constant and the brightness of the fabricated EL device were increased with increasing the weight percent of BaTiO3 dielectric material in the composite films. The brightness was also increased with decreasing the thickness of the dielectric layer. The brightness was enough to be applied to the backlight of the keypad in mobile phones.

The Effect of NiO Addition to the PNN-PZT Piezoelectric Ceramics on Piezoelectric Properties

Perovskite ceramics were synthesized by conventional ceramic processing technique. In order to modify piezoelectric properties for sensor application in this system, NiO addition was considered to provide as an acceptor, which was known to occupy with B site in the structure. The effect of NiO addition up to on the following piezoelectric properties as well as sintering properties was investigated. When NiO added more than , average grain size was decreased and second phase was found to form. Moreover, the second phase caused decrease in relative dielectric constant , electro-mechanical coupling factor , and piezoelectric charge constant , while increasing mechanical quality factor . When NiO was added, density, dielectric properties and piezoelectric properties were abruptly increased.

Effects of Mechanically Activated Milling and Calcination Process on the Phase Stability and Particle Morphology of Monoclinic Zirconia Synthesized by Hydrolysis of ZrOCl 2 Solution

The purpose of this paper was to investigate the effect of a high-energy milling (HEM) process on the particle morphology and the correlation between a thermal treatment and tetragonal/monoclinic nanostructured zirconia powders obtained by a precipitation process. To eliminate chloride residue ions from hydrous zirconia, a modified washing method was used. It was found that the used washing method was effective in removing the chloride from the precipitated gel. In order to investigate the effect of a pre-milling process on the particle morphology of the precipitate, dried Zr(OH)4 was milled using a HEM machine with distilled water. The particle size of the Zr(OH)4 powder exposed to HEM reduced to 100~150 nm, whereas that of fresh Zr(OH)4 powder without a pre-milling process had a large and irregular size of 100 nm~1.5 μm. Additionally, modified heat treatment process was proposed to achieve nano-sized zirconia having a pure monoclinic phase. It was evident that two-step calcining process was effective in perfectly eliminating the tetragonal phase, having a small average particle of ~100 nm with good uniformity compared to the sample calcined by a single-step process, showing a large average particle size of ~300 nm with an irregular particle shape and a broad particle size distribution. The modified method is considered to be a promising process for nano-sized zirconia having a fully monoclinic phase.

BCTZ Addition on the Microstructure, Piezoelectric/Dielectric Properties and Phase Transition of NKLN-AS Piezoelectric Ceramics

Presently, the most promising family of lead-free piezoelectric ceramics is based on (KNN). Lithium, silver and antimony co-doped KNN ceramics show high piezoelectric properties at room temperature, but often suffer from abnormal grain growth. In the present work, the component, which has relaxor ferroelectric characteristics, was doped to suppress the abnormal grain growth. To investigate this effect, Lead-Free [KNLN-AS-xBCTZ] piezoelectric ceramics were synthesized by ball mill and nanosized-milling processes in lead-Free in order to suppress the abnormal grain growth. The nanosized milling process of calcined powders enhanced the sintering density. The phase structure, microstructure, and ferroelectric and piezoelectric properties of the KNLN-AS ceramics were systematically investigated. XRD patterns for the doped and undoped samples showed perovskite phase while tetragonality was increased with increasing BCZT content, which increase was closely related to the decrease of TO-T. Dense and uniform microstructures were observed for all of the doped BCZT ceramics. After the addition of BCTZ, the tetragonal-cubic and orthorhombic-tetragonal phase transitions shifted to lower temperatures compared to those for the pure KNNL-AS. A coexistence of the orthorhombic and tetragonal phases was hence formed in the ceramics with x

Effects of Glass Frit Addition on Microstructures and Dielectric Properties of Sintered BaTiO 3 Ceramics

dielectric ceramics are widely used to multi-layer ceramic capacitor. The powder was synthesized at by using a solid state reaction and grinded by using a high-energy mill. And then, 2.53 wt% glass frit was added to the synthesized powders for lowering the sintering temperature. The mixed powders were sintered at various temperatures of , , . Microstructures of the sintered ceramics were inspected by SEM and crystal structures were analyzed by XRD method. The relative dielectric constant was measured by using a impedance/gain phase analyzer. The synthesized powder had the tetragonal perovskite structure without secondary phase and the particle size was below 200 nm. The relative densities measured at the samples sintered at the temperature above were about 95%. The relative dielectric constant showed maximum value of 2310, which was measured in the specimen sintered at . From these results, we could know that the added glass frit had effects on both lowering the sintering temperature and improving the dielectric property.