Chen-Ti Hu

Domain structure study of SrBi2Ta2O9 ferroelectric thin films by scanning capacitance microscopy

Scanning capacitance microscopy was used to image the polarization-induced microstructural patterns of sol-gel derivative SrBi2Ta2O9 (SBT) thin films. A sharp image contrast was induced between the nanosized domains owing to the various polarities, so that the domain structure in the SBT thin film was clearly revealed. As a result, the switched and unswitched regions could be unequivocally identified. This investigation also confirms that the reversal polarization process of a ferroelectric domain is much easier inside a large grain than in a small grain.

Modification on the electron field emission properties of diamond films: The effect of bias voltage applied in situ

In this work, we have systematically examined the effect of bias voltage applied in situ on the characteristics of diamond films. Raman spectroscopic and scanning electron microscopic examinations indicate that the applied positive bias voltage changes the thin films’ morphology and the Raman spectroscopy insignificantly, but markedly lowers their effective work function (Φe) and turn-on field (E0). The enhancement of the field emission properties of these films is assumed to result from the introduction of impurity and surface states. By contrast, the negative bias voltage applied during a chemical vapor deposition process leads to pronounced modification of the morphology of diamond films due to an etching effect. Such a process results in a fine granular structure for the diamond films, significantly improving their field emission behavior via the enhancement of field concentration effect.

Effect of sintering process on microstructure characteristics of Ba(Mg1/3Ta2/3)O3 ceramics and their microwave dielectric properties

Abstract Microstructure of Ba(Mg1/3Ta2/3)O3, BMT, materials were examined using transmission electron microscopy. Selected area electron diffractions imply that the ordering of Mg2+ and Nb5+ cations transforms the BMT materials from cubic symmetry to P 3 m1 symmetry, which induces the formation of polar domains in BMT grains. Large grains contain wavy polar domain boundaries, dislocations and even the dislocation networks, which are detrimental to the microwave dielectric properties. Presumably, induction of abundant defects in association with large BMT grains is the prime factor degrading the microwave dielectric properties of the BMT materials, when they were sintered at too high temperature.

Defect structure and electron field-emission properties of boron-doped diamond films

The correlation between electron field-emission properties of diamond films prepared by the chemical vapor deposition (CVD) process and the defect structure induced by boron doping was examined. Secondary ion mass spectroscopic analysis indicates that the solubility limit of boron in diamond is (B3+)2=5×1021 cm−3, whereas the infrared absorption (IR) spectroscopic analysis reveals that the largest boron concentration that can be incorporated as substitutional dopants is only one tenth of the solubility limit, (B3+)d=5×1020 cm−3. Including boron species higher than this concentration induces large strain and atomic defects, which are inferred by the distorted Raman resonance peak, noisy IR spectra, and twinned microstructure for diamond. Presumably, the presence of atomic defects, which behave as electron traps, is the mechanism deteriorating the electron field-emission properties of CVD diamonds.

Influence of Zr-doping on the microstructure and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 materials

The effect of Zr-species addition on the microwave dielectric properties of Ba(Mg 1/3 Ta 2/3 )O 3 , BMT materials was examined. The sintering behavior and the microwave dielectric properties of the BMT materials varies with the routes by which the Zr-species were incorporated. Two-step process leads to pronounced improvement, whereas single-step process results in markedly degradation on microwave Q-factor for the materials. SEM and X-ray diffraction analyses reveal that the main factor, resulting in deleterious effect due to addition of Zr-species via single-step process, in the induction on the formation of secondary phase, which is turn, is owing to the slow reaction kinetics of ZrO 2 and BaCO I for the formation of BaZrO 3 perovskite phase.

dc thermal plasma synthesis and properties of zinc oxide nanorods

In this research, a dc thermal plasma reactor was used to produce ZnO nanorods with a diameter of about 30nm and a length of 100–200nm. In the photocatalytic study, visible light absorption of the ZnO nanorods was achieved by doping up to a few thousands ppm of nitrogen. The nitrogen-doped ZnO nanorods under the visible light radiation exhibited excellent antimicrobial ability. UV-visible spectroscopy of the N-doped ZnO nanorods annealed in a reductive atmosphere revealed a strong absorption of near-IR light starting at around 1μm, which is attributed to the effect of plasmon resonance. Room-temperature photoluminescence spectroscopy of the N-doped ZnO nanorods showed an UV emission peak at 380nm, a green emission peak at 520nm, and a weak near-IR emission peak at 760nm. The UV emission was assigned to the near band-edge emission, while the green and the near-IR emissions corresponded to the deep-level emission from different defects. In addition, we found that photoluminescent characteristic of the ZnO n...

Effect of Y2O3/MgO Co-doping on the electrical properties of base-metal-electroded BaTiO3 materials

Effect of MgO and Y 2 O 3 additions on modifying the dielectric constant-temperature (K-T curve) properties of the base-metal-electroded BaTiO 3 materials was systematically studied. The absolute value of (ΔC/C) -55 C and (ΔC/C) 125-C can be reduced, i.e., be moved upward, by incorporating large enough concentration of MgO and Y 2 O 3 additives into the BaTiO 3 , such that the K-T characteristics of the materials meet the X7R specification. The Y 2 O 3 doping is more effective than the MgO doping in moving the (ΔC/C) -55 C and (ΔC/C) 125 C upward, which can be attributed to the fact that Y 2 O 3 species addition flattens the K-T curves without shifting the Curie point of the materials. However, the proportion of Y 2 O 3 incorporated into the materials should exceed the solubility of the BaTiO 3 materials such that the Y 2 O 3 species can reside at the grain boundary region, forming a core-shell microstructure.

Influence of CaO addition on the electrical properties of BaTiO3 ceramics

The microstructure and electrical properties of calcium‐modified barium titanate ceramics of compositions (Ba1−xCax)TiO3 have been investigated. From the influence of the CaO content and stoichiometry on the said characteristics of the materials, it is concluded that the cationic ratio, α=(Ba+Ca)/Ti, is the predominant factor affecting the resistance of materials against the reducing sintering atmosphere. The electrical properties, including resistivity and dielectric dispersion, can be completely preserved when the sintering atmosphere is switched from air to H2 /N2 , but only for samples with values of α greater than unity. The formation of a hexagonal BaTiO3−δ phase, which consumes the oxygen vacancies, is presumed to be the factor that improves the resistance of these materials against the reducing sintering atmosphere.

V-shaped positive temperature coefficient of resistivity (PTCR) characteristics of microwave-sintered (Sr0.4Pb0.6)TiO3

Abstract The resistivity-temperature (ϱ-T) characteristics of the (Sr0.4Pb0.6)TiO3 materials prepared by the microwave sintering process were examined. The resistivities varied insignificantly with sintering temperature (1000–1100 °C) and soaking time (10–30 min), but increased markedly as the cooling rate reduced or as the heat-treatment temperature increased. The Curie temperature was not altered by the cooling rate control process but was shifted from Tc = 302 to 210 °C when the as-sintered samples were post-heat-treated at 1100 °C for 1 h. The high Curie temperature of the as-sintered samples was proposed to result from the core-shell structure of the grains. The ‘shell’, which contained Pb-rich perovskite of composition (Sr0.29Pb0.71)TiO3, was homogenized with the ‘core’ during heat treatment such that the Curie temperature approached Tc = 210 °C, as the composition of the ‘shell’ reduced to the designed value, (Sr0.4Pb0.6)TiO3.

DOUBLE CRITICAL TEMPERATURE CHARACTERISTICS OF SEMICONDUCTING (BA0.7PB0.3)TIO3 MATERIALS PREPARED BY MICROWAVE SINTERING

In this work, we obtain (Ba0.7Pb0.3)TiO3 materials possessing double critical temperature Tc in resistivity–temperature (ρ–T) behavior by microwave sintering at 1050–1080 °C for 5 min. The cooling‐rate control and postannealing processes modify the relative magnitudes of low‐ and high‐Tc resistivity jumps without altering the Tc values. The donor Ed and trap Es levels of those materials are estimated to be Ed≂0.05–0.07 eV and Es≂1.07–1.32 eV. According to experimental results the voltage sensitivity and transient responsivity of the current passing through double‐Tc materials are observed to be superior to those of single‐Tc materials prepared by the conventional furnace sintering method. Also, the double‐Tc characteristics are attributed to the dual phases with a core‐shell structure. Moreover, the change in the relative proportion of the two phases accounts for the influence of post‐heat treatment processes on the materials’ ρ–T behavior.