Yee-Shin Chang

Magnetic properties and microstructure of iron-platinum thin films

Abstract The microstructure and magnetic properties of sputtered Fe-Pt thin films were studied as a function of Pt content from 0 to 60 at%. Polycrystalline ferromagnetic films were obtained in the range studied. A mixture of body-centered-cubic and disorder face-centered-cubic (γ) phases was obtained for as-deposited films with less than 22 at% Pt, and a disorder face-entered-cubic (γ) structure was obtained for films with more than 33 at% Pt. By annealing films containing about 33 at% Pt, a coercivity of 13 kOe could be obtained depending on the duration and temperature of annealing. An order faced-centered tetragonal (γ 1 ) phase appeared under suitable treatment in the samples containing 22 to 50 at% of Pt. For films comprising about 60 at% Pt, annealing treatment made the magnetic properties to deteriorate owing to the formation of an antiferromagnetic phase (fcc, Ll 2 -type). X-ray analysis and microstructure observations revealed that the magnetic hardening was caused by changing the ordering from the γ to the γ 1 phase.

Synthesis and characterization of zinc titanate doped with magnesium

Zinc titanate crystals doped with magnesium have been grown by conventional solid state reaction technique using metal oxides. It is shown that they are semiconductors. The characteristics of zinc titanate samples were found to depend on the heating conditions and the amounts of additions. Our studies revealed that magnesium can replace the zinc ion and forms a solid solution in the ZnTiO3 phase. The electrical resistivity of (Zn,Mg)TiO3 varied with sintering temperature, and has a minimum when sintered at 900 8C. Increasing amounts of magnesium will also decrease the resistivity. A V-shaped temperature dependence of resistivity was observed. Furthermore, the dielectric constant increased with sintering temperature and decreased with increasing amounts of magnesium. It also shows a maximum Q factor at a frequency of 8 GHz for the sample of (Zn0.9, Mg0.1)TiO3 sintered at 900 8C. q 2003 Elsevier Ltd. All rights reserved.

The structure and properties of zinc titanate doped with strontium

Abstract Doped and undoped zinc titanate powders were prepared by a conventional solid state reaction technique using metal oxides. The characteristics of zinc titanate samples were found to depend on the heating conditions and the amounts of additions. It is shown that they are semiconductors, and the formation of SrTiO3, α-Zn2TiO4, rutile phase, morphology roughness and open porosity increase with increasing the amounts of doped Sr. The electrical resistivities of doped and undoped zinc titanate reveal a transition from semiconductor behavior to metal-like behavior as the temperature increased. All samples represent the V-type resistivity–temperature characteristic and possess the typical PTCR characteristics above room temperature.

Defects of lithium niobate crystals heavily doped with MgO

Abstract Water-clear LiNbO 3 single crystals containing MgO close to the solubility limit, ∽ 25 mol%, have been successfully grown. Someof the defects which are frequently encountered in the growth of MgO-doped LiNbO 3 single crystals are presented. Precipitates formed for inadequately annealed samples are identified as MgNb 2 O 6 . The distribution coefficient ( K ), which is the ratio of Mg cation content in the crystal to that in the melt, is 1.2 for lightly doped materials. It changes abruptly to K = 0.95 if the MgO content is higher than 7.5 mol%. This is ascribed to the change in the site occupancy characteristics of MgO in LiNbO 3 crystal, viz. the Mg cations incorporated into the A-site in these crystals will first obstruct excess A-site Nb cations when lightly doped and they start to reduce the A-site Li cations when heavily doped.

Characteristics of La0.8Sr0.2Co1−xCuxO3−δ film and its sensing properties for CO gas

Abstract La 0.8 Sr 0.2 Co 1− x Cu x O 3− δ films prepared by using the dipping method have been shown to give a relatively high sensitivity to CO of concentration between 50 and 200 ppm for the temperature between 200 and 350°C. The sensing properties of La 0.8 Sr 0.2 Co 1− x Cu x O 3− δ films are functions of temperature and Cu content. The maximum sensitivity was obtained for films doped with x =0.4 of Cu and operated at the temperature of 250°C. The sensing mechanism is a surface reaction process, which can be thermally activated. The relationship of sensitivity to CO concentration is shown to be linear; while, the electric resistance of the films is shown to be an exponential function of CO concentration. An empirical relationship of R ≈ KC CO α with α =0.0273 can be obtained.

Behavior of PbO in the two-stage sintering of PLZT ceramics

Abstract The role of excess PbO in liquid phase sintering of PLZT ceramics has been studied by a modified two-stage atmosphere sintering method. In the first stage of sintering the results showed that the densification rate of PLZT ceramics is strongly dependent on the amount of excess PbO, and a 13 vol.% liquid is enough to obtain a fully dense PLZT by the particle rearrangement process. The second sintering stage was adopted to remove the liquid phase PbO to achieve transparency. The kinetics of evaporation of PbO in the second stage were also examined. Experimental results verified the formula Pb 1−( 3x 2 ) La x 2 ( Zr y Ti 1−y ) O 3 for the PLZT ceramics; and owing to high sinterability, their relative densities did not decrease through vaporization loss of PbO.

Dielectric relaxation properties of perovskite-pyrochlore biphase ceramics

The structure and dielectric relaxation properties of (1−x)NaNbO3-xBiCrO3(0.1⩽x⩽0.5) composite ceramics with perovskite-pyrochlore biphase were studied. The coexistence of cubic perovskite and a cubic pyrochlore structure was characterized. A lack of mutual solubility between the two phases was observed. Biphase ceramics with x=0.3 exhibited dielectric relaxation behavior with a diffuse-like phase transition. Pyrochlore-rich biphase ceramics with x=0.4 exhibit dielectric relaxor-like behavior. The biphase ceramics have high dielectric constants, because of the reorientation of the dipoles and the formation of barrier layers at the grain boundaries.

Magnetic and electrical properties of perovskite La1−xMnO3−δ films

The polycrystalline La1−xMnO3−δ films were grown on Si substrates by organometallic deposition (MOD) method. Self-grown α-SiO2 was used as buffer layer. The magnetization, electrical resistivity and magnetoresistance of films were investigated at temperatures ranging from 5 to 298 K. All La1−xMnO3−δ films showing insulator–metal (I–M) transitions exhibited semiconductor behavior for T>Tp. Magnetic property was strongly affected by experimental parameters. The MR variations were correlated to microstructure. A low field MR of ∼13% at 2 KOe was observed.

The influence of different remelting conditions on the transparency and optical properties of borate glass incorporated with β-BaB2O4

Abstract The fabrication of transparent B2O3-based glasses containing non-linear optical crystals of β-BaB2O4 particles by the incorporation method was studied. Some properties such as refractive index n, second harmonic generation (SHG) efficiency and electric resistance of the remelted glasses were measured. Tg and Tx were decreased by the addition of BBO particles. A small difference in the refractive index between matrix glasses and incorporated crystals is a significant reason for the transparency. The best efficiency for SHG was 10% of the BBO crystal for the sample remelted by mixing the 40BaO–30B2O3–25SiO2–5K2O (GPII) glass and 15 wt.% BBO content at 960°C for 3 min.

Fabrication of transparent borate glasses containing β-BaB2O4 by incorporation method

The fabrication of transparent B2O3-based glasses containing non-linear optical crystal of β-BaB2O4 (BBO) particle by incorporation method was studied. The BBO particle with a diameter of about 10 μm has been successfully incorporated into BaO–B2O3–SiO2 glasses by adjusting the melting temperature, soaking time and the amount of BBO. The β-phase could be transformed to α-phase when the remelting time and/or temperature was increased. A small difference in the refractive index n, between matrix glasses and incorporated crystals, is a significant reason for the transparency. The refractive index of the remelted sample was independent of particle size, and was increased by adding more contents of BBO. Moreover, the best efficiency for second harmonic generation (SHG) was 2.5% of the BBO crystal.