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Author: search.filters.author.Bongkarn, TheerachaiSubject: search.filters.subject.Optical properties

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    Structural, optical and electrical properties of the microcrystalline structure of (Ba1-xY2x/3)(Zr0.20Ti0.80)O3 ceramics
    (2020-07-01)
    Sumang, Rattiphorn
    ;
    Thongmee, Navavan
    ;
    Bongkarn, Theerachai
    ;
    Prasertpalichat, Sasipohn
    ;
    Kidkhunthod, Pinit
    Yttrium (Y<sup>3+</sup>) doped barium zirconate titanate, (Ba<inf>1-x</inf>Y<inf>2x/3</inf>)(Zr<inf>0.20</inf>Ti<inf>0.80</inf>)O<inf>3</inf>; BYZT ceramics with varying x (0 = x ≤ 0.10) were prepared by the solid-state reaction method. These samples were analyzed by X-ray diffraction (XRD) and the XRD patterns were fitted using the Rietveld refinement. The local structural changes of the BYZT ceramics were investigated by synchrotron X-ray absorption spectroscopy. The results showed that an increase in the x content in the BYZT lattice structure significantly affected the phase transition behavior and the local structure around the Ti absorbing atoms, which corresponds with the phase transition from a tetragonal to a cubic structure. SEM images showed a uniform and highly dense microstructure with increasing x values. The optical band gap (E<inf>gap</inf>) values measured from the UV–visual diffuse reflectance spectra, showed a decrease from ~3.55 eV to ~2.90 eV with increasing values of x. The modified Curie-Weiss law showed that a normal ferroelectric phase transition is observed in the unmodified BZT ceramic and as the concentration of x increased, it induces diffuseness in the phase transition behavior. The largest dielectric constant (ε<inf>r</inf> = 13,200), the highest recoverable energy-storage density (W<inf>rec</inf> = 1.76 J/cm<sup>3</sup>) with an excellent energy storage efficiency (η = 91%) under a lower electric field of 50 kV/cm and lowest dielectric loss (tanδ = 0.01) were found in the composition of Ba<inf>0.98</inf>Y<inf>0.01337</inf>Zr<inf>0.2</inf>Ti<inf>0.8</inf>O<inf>3</inf> (x = 0.02 mol.%).
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    Direct synthesis and growth mechanism of metal molybdate (AMoO4; A = Ca and Ba) fine particles via the mechanochemical method
    (2017-08-01)
    Janbua, Wanwisa
    ;
    Bongkarn, Theerachai
    ;
    Vittayakorn, Wanwilai
    ;
    Vittayakorn, Naratip
    Metal molybdate (AMoO<inf>4</inf>; Ca and Ba) fine particles were synthesized successfully in a simple way using the mechanochemical method under ambient conditions, without surfactants or any capping agents. The effect of milling time on phase formation and morphology was investigated. The functional group and phase formation analyses were carried out using Fourier transform infrared (FT-IR), Raman spectroscopy and X-ray diffraction (XRD) methods. XRD revealed that all samples were of a pure tetragonal scheelite structure. FT-IR and Raman analysis exhibited a Mo-O stretching peak of molecular [MoO<inf>4</inf>]<sup>2-</sup>, which related to the scheelite structure. Difference in growth mechanism and morphology was observed significantly in CaMoO<inf>4</inf> and BaMoO<inf>4</inf> particles. The primary CaMoO<inf>4</inf> nanocrystalline was formed in its initial state at 80–100 nm, and tended to aggregate into a peach-like shaped morphology with increasing milling time, while a space shuttle-like morphology formed directly via an oriented attachment mechanism for the BaMoO<inf>4</inf> particle. A possible mechanism for the formation of metal molybdate, with a different milling time, was discussed in detail. It is interesting that this work was able to present a simple way of synthesizing complex oxide materials on a large scale.