Chen-Chia Chou

Phase transition and piezoelectric property of (Bi0.5Na0.5)0.94Ba0.06ZryTi1−yO3(y=0–0.04) ceramics

The ceramics with the composition of (Bi0.5Na0.5)0.94Ba0.06ZryTi1−yO3 (BNBZ100yT, in which y=0,0.01,0.02,0.04) were prepared successfully by the solid state reaction method. X-ray diffraction studies revealed the perovskite structure in BNBZ100yT ceramics sintered at 1170°C for 2h in air. The relative densities of the sintered ceramics were around 97%–99%. The temperature dependent dielectric properties of BNB6T and BNB6Z4T ceramics showed their relaxor-like behaviors. Decreases in remnant polarization, coercive field, and disappearance of piezoelectric properties were found by the substitution of 2 and 4mol% Zr4+ for Ti4+ in these ceramics. Electron diffraction patterns taken in a transmission electron microscope demonstrated the existence of cubic crystalline phase in the BNB6Z4T ceramics leading to the disappearance of piezoelectric property. Decrease in grain size was also observed with the substitution of Zr4+ for Ti4+ in BNB6T ceramics.

Low-temperature processing of sol-gel derived La0.5Sr0.5MnO3 buffer electrode and PbZr0.52Ti0.48O3 films using CO2 laser annealing

Fabrication of well-crystallized sol-gel derived (La0.5Sr0.5)MnO3 (LSMO) buffer electrode layers and ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films using a continuous wave CO2 laser annealing technique at a relatively low temperature was studied on a Pt/Ti/SiO2/Si substrate. Resistivity, carrier concentration and Hall mobility of laser-annealed conducting oxide LSMO films were optimized by changing the radiation fluence and the substrate temperature. The minimum resistivity of 1.27×10−4 Ω cm was obtained for LSMO/Pt(Si) films prepared by laser irradiating at a fluence of 533 W/cm2 with a simultaneous substrate heating at a temperature of 300 °C. The laser-annealed PZT films coated on LSMO/Pt(Si) substrate shows enhancement in remanent polarization from 10.1 to 17.3 μC/cm2 as the PZT irradiated with a laser fluence of 433–483 W/cm2. The PZT(483 W/cm2)/LSMO(533 W/cm2)/Pt(Si) films showed a good fatigue resistance after 1×1010 switching cycles with a bipolar electric field of 300 kV/cm, implying the feasi...

Ionic conductivity investigation in samarium and strontium co-doped ceria system

Effects of strontium doping on ionic conductivity of Sm2O3-doped ceria (samarium-doped ceria (SDC)) were investigated. The distribution and average radius of oxygen vacancies by co-doping divalent and trivalent cations were calculated from a hard-sphere model. Experimental results exhibit that the best conductivity for Ce0.78Sm0.2Sr0.02O1.88 (0.061 S cm−1) specimen is twice that of Ce0.8Sm0.2O1.9 (0.0371 S cm−1) at 800 °C. A decrease of 50 °C in the working temperature of SDC was developed by modifying the dopant concentration, average binding energy and ionic radius of the dopant. The results confirm the Sm3+ and Sr2+ co-doped ceria material as a potential electrolyte for intermediate-temperature solid oxide fuel cell applications.

Microstructure of Ba(Mg1/3Ta2/3)O3-BaSnO3 microwave dielectrics

Abstract Ceramics of Ba(Mg 1/3 Ta 2/3 )O 3 -BaSnO 3 (BSMT) are synthesized by a two-stage calcination method. Microstructures are analyzed, using X-ray diffractometry, transmission electron microscopy, Raman spectroscopy, and scanning electron microscopy. The addition of BaSnO 3 reduces the cation ordering of Ba(Mg 1/3 Ta 2/3 )O 3 and its sinterability. Variations in ordered structure with BaSnO 3 content are revealed by the reduction in intensity of the superlattice reflections, the domain size, the c/a ratio, and the shifting and broadening in Raman lines. The relations between microstructure and quality factors of BSMT are discussed. ©

Microwave dielectric properties of glass-ceramic composites for low temperature co-firable ceramics

Abstract The densification behavior and the microwave dielectric properties of RBS–(MgCa)TiO 3 (R: MgO, CaO, SrO or BaO, B: B 2 O 3 and S: SiO 2 ) glass–ceramic composite materials were systemically examined. The BaBS glass materials possess highest dielectric constant ( K ) and quality factor ( Q ) among the RBS glass materials and the BaBS–(Mg,Ca)TiO 3 composites materials also exhibited largest K - and Q -value among the RBS–(Mg,Ca)TiO 3 glass–ceramic composite materials. Comparison on the measured K -( Q -) values from the calculated K -( Q -) composition lines implies that the formation of additional crystalline phase other than (Mg,Ca)TiO 3 materials markedly modifies the Q -value, but is insignificantly altering the K -value for the composite materials.

Pulsed laser deposition of ferroelectric Pb0.6Sr0.4TiO3 thin films on perovskite substrates

Abstract Pulsed laser deposited ferroelectric Pb 0.6 Sr 0.4 TiO 3 (PSrT) thin films have been synthesized using La 0.5 Sr 0.5 CoO 3 (LSCO), La 0.5 Sr 0.5 MnO 3 (LMSO), and donor-doped SrTiO 3 (STO), i.e., (Sr 0.9 La 0.1 )TiO 3 (SLTO) and (Sr 0.9 Y 0.1 )TiO 3 (SYTO) thin films as buffer layers. The crystal structure of the PSrT films is remarkably influenced by the texture characteristics of the buffer layers, and the buffer layers show different tendency to develop low index orientations, and therefore the ferroelectric properties of the PSrT films were varied. In this work, we report the ferroelectric and electric fatigue properties corresponding to film texture and material characteristics obtained in the process using various substrates. It is demonstrated that films with LSCO/Pt and LSMO/Pt show superior ferroelectric properties, suitable for device applications.

Electrical Properties and Microstructures of PbZrTiO3 Thin Films Prepared by Laser Annealing Techniques

PbZrTiO3 (PZT) films with 10 mol% excess lead were prepared by a metal-organic decomposition (MOD) method on a Pt-precoated Si substrate. The deposited films were first pyrolyzed at 400°C for 30 min and then an excimer laser with KrF radiation and a continuous-wave CO2 laser were employed for annealing. The experimental results indicated that the remanent polarization of PZT films for CO2-laser-annealed specimens is seven times higher than that of KrF-laser-annealed ones. Transmission electron microscopic investigations suggest that the upper layer of KrF-laser-annealed PZT films crystallized and films at the bottom layer remained amorphous. The combined series of crystallized and amorphous layers degrades the ferroelectric properties of PZT thin films. In contrast, Transmission electron microscopy investigations reveal more homogenous microstructures and better crystallinity for PZT films annealed using the CO2 laser. CO2 laser annealing improves ferroelectric properties of PZT films and good-quality PZT thin films could be obtained at low temperatures.

Accelerated spheroidization of hypoeutectoid steel by the decomposition of supercooled austenite

A thermal cycling treatment was used to produce a spheroidized structure of hypoeutectoid steel from direct decomposition of supercooled austenite. Scanning electron microscopy and quantitative metallography were employed to study the changing microstructure during the thermal cycling treatment. A conventional spheroidizing annealing was also investigated for comparison. It has been shown that the thermal cycling treatment results in a structure of cementite spheroidites homogeneously distributed in a ferrite matrix within a very short processing time, and the coarsening of cementite particles is controlled by the coupled diffusion of both carbon and iron atoms.

Second Phase and Defect Formation in Bi0.5Na0.5-xKxTiO3 Ceramics

The second phase and defect formation mechanisms of [Bi0.5(Na1-xKx)0.5]TiO3 (BNKT100x) ceramics were investigated using electron microscopy, X-ray photoelectron spectroscopy (XPS), and electrical properties measurement. Experimental results indicated that second phase formation induces Bi-rich regions and compositional inhomogeneity within the matrix owing to the thermodynamic stability of potassium titanate. The Ti valence transition for BNKT ceramics sintered in air might be ascribed to the formation of secondary phase and low oxygen atmosphere, rather than simply attributed to the volatilization of bismuth. Li substitution at the A-site in BNKT ceramics suppresses formation of the second phase and Ti valence transition. Appropriate atmosphere control during material processing, such as sintering at higher oxygen pressure, and post oxidization annealing suppress oxygen vacancies and titanium valence transition, and therefore decrease the leakage current as well as improve electrical properties.

Dielectric and Ferroelectric Properties of Polyvinylidene Fluoride (PVDF)-Pb0.52Zr0.48TiO3 (PZT) Nano Composite Films

Solution cast and spin coating techniques were performed to deposit ferroelectric films of PVDF-PZT on Al 3+-ZnO/polyethylene terephthalate(PET) flexible substrates. The composites with 10wt% PZT in PVDF exhibited higher dielectric permittivity and showed better ferroelectric property, might be due to internal field generated by the nano PZT particles, which favours the orientation of PVDF molecules. Higher remanent polarization and low leakage current were successfully demonstrated by coating PVDF layer on PVDF-PZT composite film. The surface of the obtained PVDF films were smooth with less porosity above PVDF-PZT composite film, enabling a significant decrease in the leakage current of composite thin films.