Yung-Fu Hsu

High-resolution characterization of the precipitation behavior of an Al–Zn–Mg–Cu alloy

The metastable particles in an Al–Zn–Mg–Cu alloy have been examined at atomic-resolution using high-angle annular dark field (HAADF) imaging. In under-aged conditions, thin η′ plates were formed with a thickness of seven atomic planes parallel to the {111}Al planes. The five inner planes of the η′ phase appear to be alternatively enriched in Mg and Zn, with two outer planes forming distinct Zn-rich interfacial planes. Similar Zn-rich interfacial enrichment has also been identified for the η phase, which is a minimum 11-plane thick structure. In rare instances, particles less than seven planes were found indicating a very early preference for seven-layer particle formation. Throughout the aging, the plate thickness appears constant, while the plate radius increases and no particles between 7 and 11 planes were observed. Based on the HAADF contrast, our observations do not support the η′ models previously set forth by other authors. Clear structural similarities between η′ and η were observed, suggesting that drawing distinctions between η′ and η phases may not be necessary or useful.

Effects of additives on the microstructure and dielectric properties of Ba 2 Ti 9 O 20 microwave ceramic

Preparation of dense and phase-pure Ba 2 Ti 9 O 2 0 is generally difficult to achieve using a solid-state reaction, due to the presence of several thermodynamically stable compounds in the vicinity of the desired composition. This work investigated the effects of various additives (TiO 2 , MnO, and ZrO 2 ) on the densification, microstructural evolution, phase stability, and dielectric properties of Ba 2 Ti 9 O 2 0 . Ceramics with theoretical density of ≥95% were achieved in all cases after sintering at 1300 °C. A pure Ba 2 Ti 9 O 2 0 phase was obtained by treating the material with TiO 2 additions (≤5.6 wt.%) and sintering at temperatures ranging between 1200 and 1350 °C. Ba 2 Ti 9 O 2 0 is a nonstoichiometric compound that can accommodate an excess amount of TiO 2 . As the temperature was increased, pure Ba 2 Ti 9 O 2 0 partially decomposed and formed a mixture of BaTi 4 O 9 and Ba 2 Ti 9 O 2 0 . The ceramic with excess TiO 2 sintered at 1390 °C possessed a higher permittivity and a lower quality factor due to the larger grain size and lower density. For ceramic with the addition of ZrO 2 (≤6 wt.%), pure Ba 2 Ti 9 O 2 0 phase was obtained after sintering between 1200 and 1390 °C, and the quality factor was improved. The decomposition temperature of the Ba 2 Ti 9 O 2 0 phase was greater than 1390 °C. For sintering temperatures ≥ 1350 °C, the extent of Ba 2 Ti 9 O 2 0 phase decreased with MnO additions. As the MnO content reached 0.5 wt.%, only BaTi 4 O 9 and TiO 2 phases existed, suggesting a decrease in the decomposition temperature of Ba 2 Ti 9 O 2 0 with the addition of MnO. The microwave properties of the ceramics degraded significantly at the sintering temperature of 1390 °C.

Effects of Additives on the Densification and Microwave Dielectric Properties of Binary CaO–B2O3–SiO2 Glass

Glass systems, consisting of binary CaO–B2O3–SiO2 (CBS) glass (referred to as glass AB) and various amounts of Li2CO3, TiO2, and Al2O3 additives, were prepared in this study. The effects of the additives on the densification and microwave dielectric properties of binary CBS glass were investigated. Binary glass AB was not densified until the sintering temperature reached 875 °C; however, with the addition of 1 wt % Li2CO3 (referred to as glass L1), the glass achieved a maximum density at 825 °C. The resultant glass-ceramics contained a major phase quartz, SiO2, and a minor phase, CaB2O4, and had a dielectric constant (er) varying from 4.10 to 4.23 and a minimum tan δ of 0.0015, as frequency increased from 4.3 to 18.6 GHz. For glass L1 with further addition of the ceramic filler Al2O3 (up to 30 wt %), the maximum densification was reached at 775 °C and the formation of CaB2O3 and SiO2 crystallites was suppressed. Both er and tan δ increased with the Al2O3 content of the glass-ceramics. Further addition of the crystallization agent TiO2 (up to 5 wt %) to glass L1 slightly reduced the sintering temperature to 800 °C. The X-ray diffraction (XRD) intensities of the quartz SiO2 and CaB2O4 crystallites as well as the er and tan δ values of the resultant glass-ceramic increased with the amount of TiO2 added.

Electrical conductivity and thermal expansion coefficient of internal phases occurring in multilayer ceramic structures

The electrical conductivity and thermal expansion coefficients of interfacial phases, PdPbO2, PdBi2O4, Pd(Pb), and Pd3Pb, have been studied. The interfacial reactions form low conductivity products, which result in discontinuity of the internal electrode. Besides, due to the volume change associated with the interfacial phase formation and wide variation in thermal expansions, physical defects may occur at the electrode–ceramic interfaces during processing.

Effects of Li + and Mg 2+ Dopants on the Magnetic Properties of Ni–Zn Ferrites

Ni_0.5-0.5xZn_0.5-0.5xMg_xFe₂O₄ and Ni_0.4Zn_0.6-2xLi_xFe_2+xO₄ ferrites (x = 0.05, 0.10, and 0.15) were prepared and examined. Both systems after sintering showed a pure spinel phase and a uniform grain size and the lattice constants declined slightly as the amount of the Mg²⁺ and Li⁺ dopants increased. The average grain sizes of the Ni_0.5-0.5xZn_0.5-0.5xMg_xFe₂O₄ ferrites appeared to show little variation (ranging from 4.22 to 4.55 gm), while those of the Li⁺-doped Ni-Zn ferrites were dramatically reduced from 5.95 to 1.40 gm corresponding to the escalation in the x values from 0 to 0.15. In terms of the magnetic properties evaluated, the Ni_0.475Zn_0.475Mg_0.05Fe₂O₄ and Ni_0.4Zn_0.4Li_0.10Fe_2.10O₄ ferrites demonstrated the best performance. The Ni_0.475Zn_0.475Mg_0.05Fe₂O₄ ferrite reported a saturation magnetization of 76.9 emu/g, an initial permeability of 611.3, and a quality factor of 16.3, while the Ni_0.4Zn_0.4Li_0.10Fe_2.10O₄ ferrite presented a saturation magnetization of 82.3 emu/g, an initial permeability of 191.3, and a quality factor of 64.3. The former is marked with a high permeability and the latter a high quality factor. These properties make them exceptionally promising for high-frequency applications.

The effects of boron dopant on the thermal stability, semiconductor characteristic and wear resistance of diamond films

Abstract In this study, the thermal stability, semiconductor characteristics and wear resistance of boron-doped diamond films deposited using the hot-filament chemical vapour deposition process are characterised and discussed. The crystal quality of the as-grown diamond films becomes more disordered as the CH4 concentration increases to 4% during deposition and the evaporation temperature of the boron source reaches 850 °C. The carrier concentration is not proportional to the boron content in the diamond films because part of the boron atoms present as clusters, which do not contribute to the hole carriers. The resistivity of the diamond film is inversely proportional to the magnitude of the carrier concentration, falling in the range of 1.38 × 10−1–2.26 × 10−3 Ω⋅cm. The onset oxidation temperature of the diamond films, correlating to the crystal quality of the diamond films and ranging from 714 to 967 °C, indicates that the incorporation of boron atoms improves the thermal stability of diamond films in air by as much as 250 °C. The wear rate of the diamond films varies from 2.05 × 10−6 to 17.84 × 10−6 mm3/Nm. An increase in boron incorporation and a rise in the p2 carbon content degrade the wear resistance of the diamond films. Of all the samples prepared, the diamond film deposited at 1% CH4 and associated with a boron source heated at 750 °C is characterised by a nearly pure sp3 bonding of the diamond and demonstrates an electrical resistivity of 1.31 × 10−2 Ω⋅cm, an oxidation temperature of 956 °C and a wear rate of 3.39 × 10−6 mm3/Nm. The diamond film, possessing an improved electrical resistivity and a high oxidation temperature combined with an acceptable wear rate, displays a great potential in the production of wear-resistant coatings, MEMS devices, AFM probes and biomedical sensors.