Wan Fahmin Faiz Wan Ali

Phase Evolution of Yttrium Iron Garnet (YIG) Made by Solid State Sintering: Particle Size Effect

The phase evolution of yttrium iron garnet (YIG) during reaction 3Y2O3-5Fe2O3 was investigated by modifying Fe2O3 particle sizes (FPS). Five different sizes of Fe2O3, (d50) are used to prepare YIG powder. Solid state reaction (SSR) was applied at 1200 °C in order to gain insight on the effect of FPS towards the YIG formation. Rietveld refinement method was used to quantify the amount of YIG yielded (%). Larger FPS (> 50 μm) initiates only 5Fe2O3 + 3Y2O3 à 3YFeO3 + Fe2O3 + Y3Fe5O12.. However, when the fine FPS (5 μm) is used, the reaction pathway was changed into 5Fe2O3 + 3Y2O3 à 6YFeO3 + 2Fe2O3 à 2Y3Fe5O12. These behaviors is explained that the smaller FPS consumed quickly to form YIG due to the smaller particle distance between Fe2O3 and Y2O3. This shall be leading to higher reaction rates (mass-transfer kinetics).

Structural Evolution of YIG during Microwave and Conventional Sintering at 1000 ºC

Microwave heating(MH) has emerged in recent years as a new method for sintering a variety of materials against conventional sintering (CH) procedure. However,the phenomenon of microwave-materials interaction is still under debate. In this work,the effect of microwave heating on YIG phase formation was investigated at 1000oC under the electromagnetic field(2.4GHz). The phase stability fired samples were qualitative and quantitative analyzed using X-ray diffraction(XRD)techniques. The obtained data were compared with CH to track the phase evolution. XRD revealed MHhas produced, YIG with 94% faster than CS. The calculated activation energy at this temperature via diffusion control model shows that MH(39.20kJ/mol)can effectively promote the phase growth rather than CH(90.96 kJ/mol).

Dielectric properties of Al2O3/CaCu3Ti4O12 composite at high frequency range

The dielectric properties of CCTO with addition Al2O3 prepared via solid state reaction investigated and reported at 1 GHz. With addition Al2O3 from 20 wt% to 80 wt%, secondary phase starts appear in XRD analysis such as copper dialuminium oxide (CuAl2O4), calcium titanate (CaTiO3) and titanium oxide (TiO2). These secondary phases show great influence on morphology and grain size of Al2O3/ CCTO composites. Hence, the addition of only 20 wt% Al2O3, the dielectric constant of CCTO reduce almost 50% and tangent loss is in between 0.0028 to 0.0630 which is very low and this characterization is suitable to use in electronic application in high frequency range.

Investigation of YIG’s active site using density functional theory

Numerous materials characteristic including yttrium iron garnet (YIG) are directly dependent on its crystal structure; phase diversity. However, only a few examination of energy and its mechanism at atomistic scales was reported. In this article, a density functional theory (DFT) based calculations have been carried out to study electronic properties of cubic Y3Fe5O12 (YIG) at its known active sites; (0,0,4), (2,2,4) and (2,2,4). The density of state (DOS) these sites were presented at-19 eV to-14 eV for lower valance band and-6 eV to 0 for upper valance band. Both (0,0,4) and (0,2,4) planes shows highest possibility of cation substitution since the energy substitution are the lowest (~40 KeV). (2,2,4) plane composed of O-O interaction in which would contribute to the oxygen vacancy.

Study on the Effect of Dielectric Structure to the Cylindrical Dielectric Resonator Antenna (DRA)

This paper presents the effect of variation of diameter and height of DR to the resonant frequency and radiation pattern of DRA. Analysis was carried out on the DR with diameter of 10.66 mm and height of 4.4 mm. The simulated and measured resonant frequencies were 3.67 and 3.77 GHz, respectively. The E-plane radiation pattern of CDRA was bi-directional pattern. The analysis was based on the CST simulation which varied the thickness and height of DR with the same increment and decrement of 1 mm. The resonant frequency of CDRA shifts significantly when the height of DR is varied, in contrast to the variation of DR’s diameter. The radiation pattern of antenna does not change when the dimension (height or diameter) of DR were altered.

Synthesis and Characterization of Ba0.3Sr0.7ZrO3 Ceramic Thick Films Prepared by Sol-Gel Technique

This manuscript is explained and discussed the properties of ceramic thick films, [Ba0.3Sr0.7ZrO3, BSZ (0.7)] synthesized through sol-gel route. The gel decomposition was studied by thermogravinometry analysis (TGA). From thermal analysis, it had shown that BSZ (0.7) phase started formed at 800 °C and above. The crystal structure of this composite film studied exhibited highly polycrystalline materials by X-ray diffraction analysis. From high magnification observation of field emission scanning electron microscopy (FESEM), grain boundaries of BSZ (0.7) films are clearly defined meanwhile grains displayed are in flaky shape. The average diameters of the grains measured were 94.6 nm. However, grains boundaries of BSZ (0.0) films, are unclear and grains slightly look dendritic structure. Electrical characterizations of the films are carried out with impedance analyzer at 4 - 12 GHz respectively. Both of electrical permittivity and loss tangent observed are dependable with microstructural and structural of the films.