Browsing by Author "Huang, C.-C."

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Effect of lithium fluoride on thermal stability of proton-conducting Ba(Zr0.8-xCexY0.2)O2.9 ceramics
(2010) Tu, Chi-Shun; Huang, C.-C.; Lee, S.-C.; Chien, R. R.; Schmidt, V. Hugo; Tsai, Chih-Long
In-situ X-ray diffraction (XRD) and micro-Raman scattering have been used to study the thermal stability of lithium fluoride (LiF)-added (7% weight ratio) Ba(Zr0.8−xCexY0.2)O2.9 (BZCY: x = 0.1 and 0.2) proton-conducting ceramic powders as a function of temperature in 1 atm of flowing CO2. This work reveals that LiF-addition can reduce the thermal stability of Ba(Zr0.8−xCexY0.2)O2.9 in CO2 and cause decomposition to BaCO3, and possibly Ba3Ce2(CO3)5F2 (or CeCO3F), and Y2O3-like compound after exposure to CO2 from high temperatures. LiF-related compounds can be removed after calcining (or sintering) in air above 1200 °C, but a minor amount of a Y2O3-like compound could remain after calcining at 1400 °C in air.
Synthesis and characterization of proton-conducting Ba(Zr0.8-xCexY0.2)O2.9 ceramics
(2010) Chien, R. R.; Tu, S.-S.; Schmidt, V. Hugo; Lee, S.-C.; Huang, C.-C.
X-ray diffraction and micro-Raman scattering have been used to characterize the effects of glycine-to-nitrate (G/N) and zirconium-to-cerium (Zr/Ce) molar ratios on structural properties of proton-conducting Ba(Zr0.8 − xCexY0.2)O2.9 (BZCY) ceramic powders fabricated by using the glycine–nitrate combustion method. Particle sizes of as-synthesized and calcined BZCY powders are estimated by using the Scherrer's formula, and are sensitive to G/N and Zr/Ce ratios. A simple cubic perovskite phase is observed for calcined Ba(Zr0.7Ce0.1Y0.2)O2.9 powders fabricated with G/N ratios of 1/3–3/4. Calcined BZCY (x = 0.0–0.8) powders fabricated with G/N = 1/2 exhibit a single-phase structure and a structural transformation from cubic to possibly rhombohedral for Zr/Ce ≤ 2/6. Particle sizes of as-synthesized and calcined BZCY (x = 0.0–0.8) powders fabricated with G/N = 1/2 vary in the ranges of 5–15 and 34–42 nm, respectively. In-situ temperature-dependent linear shrinkage measurement reveals that smaller-particle BZCY powder can reach densification at a considerable lower temperature.
Temperature-dependent structures of proton-conducting Ba(Zr0.8-xCexY0.2)O2.9 ceramics by Raman scattering and x-ray diffraction
(2012) Tu, Chi-Shun; Chien, R. R.; Schmidt, V. Hugo; Lee, S.-C.; Huang, C.-C.
In situ temperature-dependent micro-Raman scattering and x-ray diffraction have been performed to study atomic vibration, lattice parameter and structural transition of proton-conducting Ba(Zr0.8−xCexY 0.2)O2.9 (BZCY) ceramics (x = 0.0–0.8) synthesized by the glycine–nitrate combustion process. The Raman vibrations have been identified and their frequencies increase with decreasing x as the heavier Ce4+ ions are replaced by Zr4+ ions. The main Raman vibrations of Ba(Ce0.8Y 0.2)O2.9 appear near 305, 332, 352, 440 and 635 cm−1. The X–O ( X=Ce, Zr, Y) stretching modes are sensitive to the variation of Ce/Zr ratio. A rhombohedral–cubic structural transition was observed for x = 0.5–0.8, in which the transition shifts toward higher temperature as cerium increases, except for Ba(Ce0.8Y 0.2)O2.9. A minor monoclinic phase possibly coexists in the rhombohedral matrix for x = 0.5–0.8. The lower-cerium BZCYs (x = 0.0–0.4) ceramics do not exhibit any transition in the region of 20–900 °C, indicating a cubic phase at and above room temperature.
Thermal stability of Ba(Zr0.8-xCexY0.2)O2.9 ceramics in carbon dioxide
(2009) Tu, Chi-Shun; Chien, R.R.; Schmidt, V. Hugo; Lee, S.-C.; Huang, C.-C.; Tsai, Chih-Long
In situx-ray diffraction spectra (25–1000 °C) have been measured as a function of temperature for proton-conducting Ba(Zr0.8−xCexY0.2)O2.9 (x=0.0–0.4)ceramics in CO2 atmosphere. Atomic vibrations before and after exposure to CO2 were obtained by using the micro-Raman scattering (150–1600 cm−1). Ba(Zr0.8Y0.2)O2.9 and Ba(Zr0.6Ce0.2Y0.2)O2.9 reveal a promising thermal stability in CO2 without apparent decomposition up to 1000 °C. However, Ba(Zr0.5Ce0.3Y0.2)O2.9 and Ba(Zr0.4Ce0.4Y0.2)O2.9 exhibit thermally stable below 550 °C and then proceed an obvious chemical decomposition of BaCO3 and Zr0.8−xCexY0.2O2 above 550 °C, which were clearly evidenced by the Raman vibrations of 1057 and 466 cm−1, respectively. A first-order orthorhombic-hexagonal structure transition was confirmed in BaCO3 in the region of 810–850 °C upon heating. This study suggests that the Ba(Zr0.8−xCexY0.2)O2.9ceramics with x≤0.2 are promising candidates for proton-conducting applications in CO2-containing environment.