Papers by Author: Cheng Fu Yang

Abstract: 0.65(K_0.5Bi_0.5)TiO₃–0.35BaTiO₃ (0.65 KBT-0.35 BT3) ceramic was synthesized using a conventional calcination process (CC-process), and using a two-step calcination process that combined hydrothermal and CC processes (HT-CC-process). The effects of these two different calcination processes on the physical and dielectric properties of 0.65 KBT-0.35 BT3 ceramics were recorded and analyzed. When the CC-process was used, secondary phases—namely, BaBi₄Ti₄O₁₅, K₂TiO₃, and K₄Ti₃O₈—were observed in the XRD patterns of 0.65 KBT-0.35 BT3 ceramics. When the HT-CC-process was used, only the (K_0.5Bi_0.5)TiO₃ (or (K_0.5Bi_0.5, Ba)TiO₃) phase was observed in the XRD patterns, with no secondary phases. Due to the secondary phases, the CC-process 0.65 KBT-0.35 BT3 ceramic had lower dielectric peaks and broader temperature-dielectric constant curve than the 0.65 KBT-0.35 BT3 ceramic synthesized using the HT-CC-process.

Abstract: A method is proposed to improve both the gamma-ray radiation-and thermal stress-induced degradations of springback characteristics in Invar alloy. Invar foil was first subjected to a 30 kGy-irradiation followed by 60 cycles of hot-then-cold (radiation+hot-then-cold) treatments. It was found that both the radiation-and thermal stress-induced springback degradations in Invar foil tended to be stabilized after 5 cycles of radiation+hot-then-cold treatments. XRD analyses showed no difference between controls and experimental samples, thus excluding the possibility of structural or phase transformations. The weak bonds inside the foil possibly rearranged and recovered during the radiation+hot-then-cold processes, resulting in radiation-and thermal stress-hard springback behaviors.

Abstract: Sr0.4Ba0.6Nb1.85Ta0.15O6 (SBNT) ceramic was used as a target and SBNT thin films were deposited at room temperature. After deposition, the SBN thin films were annealed in conventional furnace (CFA) and in an oxygen atmosphere for 1h by changing the temperature from 700oC to 900oC. The thicknesses of the SBN thin films were calculated by SEM and they were about 450nm independent on the annealing temperature. From the XRD patterns, the as-deposited SBNT thin films displayed amorphous phase, whereas as CFA-treatment was used, the SBNT thin films displayed smooth surfaces. The grain sizes also increased with increasing CFA-treated temperature. In addition, the remanent polarization and saturation polarization increased and coercive field decreased with increasing CFA-treated temperature. Finally, the lnJ-E1/2 curves of the SBNT thin films was developed to find that the linear variations of leakage current densities correspond either to the Schottky emission mechanism or to the Poole-Frenkel emission mechanism.

Abstract: In this paper, we report the characterization of springback degradation of an Invar sheet with a combination of gamma-ray irradiation and repeated hot-then-cold stresses. The springback factor value of fresh Invar without radiation shows a linear increase with the number of hot-then-cold stress cycles. Continuous springback degradations are observed as the number of hot-then-cold stress cycles reaches 100. When the Invar sheet is subjected to gamma-ray irradiation, the springback factor is greater than that of the repeated hot-then-cold stressed samples. After applying the repeated hot-then-cold stresses to the post-irradiated Invar sheets, the springback factors are first restored to the value of fresh Invar, and then revert to an increasing trend. Our previous X-ray diffraction (XRD) analysis excluded the crystalline structural changes in the post-irradiated Invar. It is believed that the radiation-induced defects, which are closely related to the springback degradation, are possibly annealed during the first 20 hot-then-cold stress cycles. These cycles ultimately dominate the springback behavior of the stressed Invar sheets.

Abstract: In this paper, we report a new phenomenon observed in the gamma-ray radiation-induced hydrophobic effects on an Invar surface: When the Invar alloy is subjected to different doses of gamma-ray irradiation, the contact angle increases with the radiation dose. Invar samples with exposed to a higher dose appear more hydrophobic, but this tendency disappears following post-irradiation etching. The contact angles of the irradiated and etched Invar samples can be restored back to a stable value with small deviation after 30 min of annealing at 150°C. X-ray diffraction (XRD) analysis found no crystalline structural changes. High resolution field emission scanning microscope (FE-SEM) analyses showed that irradiation might induce crack-like surfaces which could be removed at higher radiation dose in the following acid etchings. It is believed that the chemical bonds of Invar oxide on the surface were broken by the gamma-ray irradiation, thus raising the likelihood of binding with free ions in the air and resulting in the exclusion of the hydrophilic OH bonds, leaving a hydrophobic post-irradiation Invar surface.

Abstract: Perovskite-based (1-x) (Na_0.5Bi_0.5)TiO₃-x NaNbO₃ [(1-x) NBT-x NN, x = 0.1, 0.2, 0.3 and 0.4] ceramics were sintered at 1080°C. Dielectric characteristics, crystalline structures, and Raman investigations were carried out on (1-x) (Na_0.5Bi_0.5)TiO₃-x NaNbO₃ ceramics. X-ray diffraction (XRD) patterns showed that NaNbO₃ ceramic would form a solid solution with (Na_0.5Bi_0.5)TiO₃ ceramic, and and unknown or second phases were not observable as well. NaNbO₃ ceramic diffused into the crystalline structure of (Na_0.5Bi_0.5)TiO₃ ceramic and (1-x) NBT_-x NN ceramics still revealed a rhombohedral structure. The temperature-dielectric constant curves showed that as NN content increased, the temperature to reveal the maximum dielectric constant (T_m) was raised, the depolarization temperature (T_d) was shifted to lower value, and the dielectric constant at Tm and the loss tangent at T_d gradually decreased. The Raman bands at 770 and 830 cm^-1 were attributed to the existence of the oxygen vacancies. In this study, the relaxor-type ferroelectric properties of NBT ceramic had been improved as NN ceramic was added.

Abstract: “GfE Coating Materials Company” had developed a novel AZOY transparent conducting oxide (TCO) material that used ZnO as raw material and contained a small amount of Y2O3 and Al2O3. In this study, the AZOY material developed by GfE company is used as the based TCO material and we will develop the influences of substrate temperatures on the characteristics of AZOY TCO films by RF sputtering method, under optimal O2/argon ratio and depositing pressure. After deposition, the sheet resistance of AZOY films is measured with a four point probe, and surface morphology and cross-sections are studied using a field emission scanning electron microscope (FESEM). And finally, the UV-Vis spectrophotometer is used to find the transmittance of AZOY TCO films.

Abstract: W-TiO2 (W, tungsten) dual-layer thin films are deposited by RF magnetron sputtering onto glass substrates and annealed at 150oC~400oC for 4hrs. The crystal structure, morphology, and trans- mittance of annealed W-TiO2 dual-layer thin films are investigated by X-ray diffraction, FESEM, and UV-Vis spectrometer, respectively. The annealing temperatures have large effect on the properties of W-TiO2 dual-layer thin films. The band gap energy values of W-TiO2 dual-layer thin films are evaluated from (h)1/2 versus energy plots. The energy gap for un-annealed W-TiO2 dual-layer thin film is 3.16 eV. As the annealing temperature increases from 150oC to 400oC, the energy gap decreases from 3.16 eV to 3.10 eV.

Abstract: In this study, ferroelectric thin films of SrBi2Ta2O9 (SBT) or bilayered SrBi2Ta2O9/ Ba(Zr0.1Ti0.9)O3 (SBT/BZT) are successfully deposited on Si substrate under the optimal RF magnetron sputtering conditions, and their electrical and ferroelectric characteristics are discussed. Ferroelectric thin films are deposited on Si substrate under the RF power of 80 W, chamber pressure of 10 mTorr, substrate temperature of 550oC, and different oxygen concentrations. The surface morphology of deposited thin films is observed from the FESEM images, and the memory windows and leakage current of the Al/SBT/BZT/Si (MFS) structure are measured by an impendence phase analyzer and a semiconductor parameter analyzer, respectively. The memory window, capacitance and leakage current density of MFS structures under different oxygen concentrations are also reported. We find that the memory window of bilayered SBT/BZT structure shows larger than one of single layer SBT structure.

Abstract: Perovskite Ba(Zr0.1Ti0.9)O3 (BZ1T9) ferroelectric thin films well deposited on ITO/glass substrates for applications in system-on-panel (SOP) devices are produced and investigated. The sputtering parameters of as-deposited BZ1T9 thin films were rf power of 160 W, chamber pressure of 10 mTorr, substrate temperature of 550oC, and an oxygen concentration of 40%. From the SEM cross- sectional observation, the deposition rate were about 2.5 nm/min. Additionally, the maximum dielectric constant and leakage current density of annealed BZT films under the rapid temperature annealing would be increased, as the temperature increased to 6500C. Further, the maximum remnant polarization and coercive field of BZT films were found and calculated from the p-E curves.