Young-Geun Lee

FABRICATION AND ELECTRICAL PROPERTIES OF PZT-PVDF 0–3 TYPE COMPOSITE FILM

ABSTRACT A film speaker was fabricated with 0–3 type piezoelectric composite. The 0–3 type composite was developed to incorporate the advantages of both ceramic and polymer. The pastes of PZT-PVDF composite were made with various mixing ratio. The paste was printed by conventional screen-printing method on ITO (Indium Tin Oxide) bottom electrode which was deposited on PET (polyethylene terephthalate) polymer film. The prepared composite film was about 80 μm in thickness. After printing the top-electrode of silver-paste, 4 kV/mm of DC field was applied at 120°C for an hour to align the electric dipole in the 0–3 composite film. The piezoelectric charge constant of d33 was increased with increasing the PZT weight percent. The maximum value was 24 pC/N at 70 wt% of PZT. But the piezoelectric voltage constant of g33 had the maximum value about 32 mV · m/N at 65 wt% of PZT. The SPL (Sound Pressure Level) of the speaker fabricated with the 65:35 composite film was tested at various driving voltages of 1 ∼ 100Vrms. The SPL was saturated at the driving voltage of 70Vrms and the value was about 68 dB at 1 kHz.

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

Phase Transformation and Thermoelectric Properties of Fe 0.92 Mn 0.08 Si 2 Prepared by Mechanical Alloying

In an attempt to enhance phase transformation and homogenization of Mn-doped , mechanical alloying of elemental powders was applied. Cold pressing and sintering in vacuum were carried out to produce a dense microstructure, and then isothermal annealing was employed to induce a phase transformation to the -semiconductor. Phase transitions in this alloy system during the process were investigated by using XRD, EDS and SEM. As-milled powders after 100 h of milling were shown to be metastable state. As-sintered iron silicides consisted of untransformed mixture of -and -FeSi phases. -phase transformation was induced by subsequent isothermal annealing at , and near single phase of -was obtained after 24 h of annealing. Thermoelectric properties in terms of Seebeck coefficient, and electrical conductivity were evaluated and correlated with phase transformation. Seebeck coefficient electrical resistivity and hardness increased with increasing annealing time due to phase transformation.