KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/123456789/1

Browse

Search Results

Now showing 1 - 10 of 10

Some of the metrics are blocked by your
consent settings
Thermally induced phase transition and dielectric relaxation in lead-free BaTi0.94Sn0.06O3 Ceramics: Insights from in-situ XRD and XAS
(2025-11-01)
Sukkha, Usa
;
Chanlek, Narong
;
Kidkhunthod, Pinit
;
Kolodiazhnyi, Taras
;
Vittayakorn, Wanwilai
Lead-free BaTi<inf>0.94</inf>Sn<inf>0.06</inf>O<inf>3</inf> (BTS) ceramics were synthesized using the conventional solid-state reaction method to investigate thermally induced phase transitions and dielectric relaxation phenomena. A combination of in-situ X-ray Diffraction (XRD) and in-situ Synchrotron X-ray Absorption Spectroscopy (XAS) was employed to examine phase transitions across the temperature range of 200–400 K. The results reveal sequential phase transitions: rhombohedral-orthorhombic (R + O) at 200 K, orthorhombic (O) at 250–300 K, tetragonal (T) at 325–359 K, and tetragonal-cubic (T + C) at 373–400 K. Dielectric measurements highlight an anomalous relaxation behavior at 70–160 K, attributed to domain wall freezing. This phenomenon follows Vogel-Fulcher behavior, with an activation energy of 14 meV, a freezing temperature of 82 K, and an attempt frequency of 4.7 × 106 Hz. X-ray Photoelectron Spectroscopy (XPS) analysis reveals oxygen deficiency on the surface of the BTS ceramic, resulting in the coexistence of Ti3+/Ti4+ and Sn2+/Sn4+ oxidation states. These defects significantly influence the dielectric and phase transition properties. This study provides comprehensive insights into the interplay between local structural changes and phase transition mechanisms in BTS ceramics. By employing a multi-technique approach, it advances the understanding of dielectric and ferroelectric behaviors, positioning BTS ceramics as promising candidates for lead-free dielectric and ferroelectric device applications.
Some of the metrics are blocked by your
consent settings
The tuning of temperature stability in ultralow loss (Ba/Sr) zirconate microwave dielectric
(2022-01-01)
Pulphol, Phieraya
;
Vittayakorn, Wanwilai
;
Bongkarn, Theerachai
;
Kolodiazhnyi, Taras
;
Pongampai, Satana
The ceramic composition of Ba<inf>1-</inf><inf>x</inf> Sr <inf>x</inf> (Zr<inf>0.96</inf>Ga<inf>0.02</inf>Nb<inf>0.02</inf>)O<inf>3</inf>, where x = 0, 0.1, 0.2, 0.4, 0.5, 0.7, 0.9 and 1, was prepared and its crystal structure, microstructure, Raman and dielectric properties are analyzed. As revealed by powder x-ray diffraction analysis, the crystal structure transforms from cubic (Pm-3m) at 0 ≤ x ≤ 0.2 via tetragonal (Cmcm) at 0.2 < x ≤ 0.5 to orthorhombic (Pbnm) at x > 0.5. This is in agreement with the structural transformations previously reported for the Ba<inf>1-</inf><inf>x</inf> Sr <inf>x</inf> ZrO<inf>3</inf> and Ba<inf>1-</inf><inf>x</inf> Ca <inf>x</inf> ZrO<inf>3</inf> solid solution systems. Raman spectroscopy consistently supports these findings. The effects of structural distortion, grain size and density of samples on the microwave dielectric properties are discussed. With increasing Sr content from x = 0 to 0.2, the Q-factor of Ba<inf>1-</inf><inf>x</inf> Sr <inf>x</inf> (Zr<inf>0.96</inf>Ga<inf>0.02</inf>Nb<inf>0.02</inf>)O<inf>3</inf> ceramics drastically decreases from 18,000 to 3,000 at 10 GHz. The ceramics with a temperature coefficient of −1.4 ppm/K, dielectric constant of 37 and Q-factor of 2,900 at the resonant frequency f = 10 GHz was obtained at x = 0.5.
Some of the metrics are blocked by your
consent settings
Dielectric relaxation behavior of BaZrO3 ceramics at low temperature
(2020-10-15)
Pulphol, Phieraya
;
Vittayakorn, Naratip
;
Vittayakorn, Wanwilai
;
Kolodiazhnyi, Taras
Dielectric behavior of nominally pure BaZrO<inf>3</inf>, Sc-doped BaZrO<inf>3</inf> and Sc + Nb-co-doped BaZrO<inf>3</inf> ceramics is reported in this paper. Several dielectric anomalies are detected in the pure and Sc-doped BaZrO<inf>3</inf> in temperature interval of 2–700 K. The Arrhenius-type dielectric relaxation has activation energies ranging from ca. 10 meV–800 meV. Annealing in Ar atmosphere at 1200 °C alters the intensity of the dielectric loss peaks especially in the Sc-doped BaZrO<inf>3.</inf> In contrast, none of the dielectric relaxation anomalies were found in Sc + Nb-co-doped BaZrO<inf>3</inf>. It is proposed that at least some of the dielectric peaks originate from the proton dynamics which includes high temperature migration, intermediate-temperature rotation and low-temperature phonon-assisted proton tunneling.
Some of the metrics are blocked by your
consent settings
Electrical conductivity, magnetism, and optical properties of reduced BaCeO 3
(2019-03-01)
Pulphol, Phieraya
;
Vittayakorn, Naratip
;
Vittayakorn, Wanwilai
;
Kolodiazhnyi, Taras
BaCeO <inf>3</inf> -based perovskites are well-known proton and oxygen ion conductors. For practical applications as electrolytes in solid oxide fuel cells, these compounds must be robust towards reduction of cerium ion. In this work, we explore the effect of reducing atmosphere on the physical properties of undoped and Nb-doped BaCeO <inf>3</inf> . The BaCeO <inf>3</inf> perovskite structure is thermodynamically stable at least up to 1450 ∘ C upon annealing in H <inf>2</inf> -containing atmosphere. Annealing at 1550 ∘ C causes a decomposition of the BaCeO <inf>3</inf> . The higher annealing temperature leads to higher concentration of Ce 3 + ions and a higher electrical conductivity. With increasing the annealing temperature from 1300 to 1450 ∘ C , the activation energy of conductivity decreases from E <inf>a</inf> = 0.31–0.263 eV. We attribute the electrical conductivity in reduced BaCeO <inf>3</inf> to the activation of the small polaron hopping in agreement with the recent first-principles calculations. However, in contrast to the theoretical predictions, we find no evidence of the Ce 3 + –Ce 3 + spin-singlet small bipolarons.
Some of the metrics are blocked by your
consent settings
Disentangling small-polaron and Anderson-localization effects in ceria: Combined experimental and first-principles study
(2019-01-23)
Kolodiazhnyi, Taras
;
Tipsawat, Pannawit
;
Charoonsuk, Thitirat
;
Kongnok, Thanundon
;
Jungthawan, Sirichok
By comparison of the electrical conductivity of ceria doped with penta- and hexavalent ions, we separate the total electron localization energy into the two contributions originating from the small polaron effects and the Coulomb interaction with the donor ions. The upper bound of the itinerant small polaron hopping energy is estimated at 66±20 meV. The binding energy of the Ce3+-M5+/6+ defect complex increases from 121 meV for M=Nb5+/Ta5+ to 243 meV for M=W6+/U6+. The first-principles simulations are in qualitative agreement with the experimental findings. At low temperatures the f electrons bound to the donor defects show dielectric relaxation with the lowest activation energy of 2.7 and 17 meV for Nb(Ta)- and W-doped ceria, respectively. Remarkably, these energies are significantly smaller than the hopping energy of the itinerant small polarons. While both the electron-lattice and the electron-defect interactions cause the f electron localization in real-case ceria, the latter effects seem to be the dominant.
Some of the metrics are blocked by your
consent settings
The modification of surface, size and shape of barium zirconate powder via salt flux
(2019-01-01)
Charoonsuk, Thitirat
;
Kolodiazhnyi, Taras
;
Vittayakorn, Naratip
The “top-down” process via direct conversion of the micro (μm)-to-submicroscale (sub-μm) particle was applied in this work by using eutectic chloride salts to prepare BaZrO<inf>3</inf>. The particle size at optimum condition could be decreased by more than 10 times from 2.1 ± 0.9 μm to 168 ± 23 nm without destroying the 1:1 of Ba:Zr stoichiometry. The uniform sub-μm-BaZrO<inf>3</inf> powder was sintered in order to obtain ~98% dense ceramic at 1400°C/10 h, which is significantly lower than the 1650°C in normal cases. The microwave dielectric constant, tan δ, and quality factor were also determined. Furthermore, this method also was applied to lead-free piezoelectric material in the 0.87BaTiO<inf>3</inf>–0.13BaZrO<inf>3</inf>–CaTiO<inf>3</inf>(0.87BT–0.13BZ–CT) system. The particle size of 0.87BT–0.13BZ–CT was reduced greatly from >10 µm to 2.8 ± 0.4 µm. It can be proved that salt flux dissolution method enables high-purity with uniform sub-micro/nanometer powder production in one step by using simple laboratory equipment and low-cost raw materials.
Some of the metrics are blocked by your
consent settings
Enhancing the densification of ceria ceramic at low temperature via the cold sintering assisted two-step sintering process
(2018-11-01)
Charoonsuk, Thitirat
;
Sukkha, Usa
;
Kolodiazhnyi, Taras
;
Vittayakorn, Naratip
The cold sintering process (CSP) in the transient aqueous environment of malonic acid is applied in this study to enhance the densification behavior of ceria ceramics at a significantly reduced sintering temperature. Dense ceria ceramics (> 98% relative density) could be achieved after CSP at 180 °C, followed by the sintering at 1100 °C/4 h. As expected, the CSP can improve the compaction of the particles before sintering, resulting in ceria ceramics with a fine microstructure of submicrometer scale of grain sizes. All samples show the single phase of cubic fluorite structure with no significant change of lattice parameter. Finally, electrical conductivity of CSP and conventionally sintered ceramics is investigated. This communication emphasizes the advantage of the CSP to reduce the sintering temperature without deterioration of the structure and properties of the final ceramics.
Some of the metrics are blocked by your
consent settings
CaTiO3 induced ferroelectric phase coexistence and low temperature dielectric relaxation in BaTiO3–BaZrO3 ceramics
(2018-05-01)
Sutapun, Manoon
;
Charoonsuk, Thitirat
;
Kolodiazhnyi, Taras
;
Vittayakorn, Naratip
The series of 0.86BaTiO<inf>3</inf>–(0.14−x)BaZrO<inf>3</inf>–xCaTiO<inf>3</inf> (abbreviated as BT–BZ–xCT) ceramics with 0.03 ≤ x ≤ 0.11 were studied to obtain high piezoelectric properties. Rietveld refinement analysis indicated that the BT–BZ–CT compositions follow a gradual rhombohedral (R) → orthorhombic (O) + R → O + tetragonal (T) → T phase transformation with increasing x. Clear evidence of the series of ferroelectric phase transitions was also found in the dielectric results. The R-O and O-T transition temperature shifted close to ambient temperature, while the Curie temperature slightly increased with increasing x. In addition to the dielectric loss peaks associated with the structural phase transitions, a broad low-temperature dielectric loss peak was detected in the R phase at T = 90-150 K. This dielectric relaxation was attributed to the domain wall freezing and fits well to the Vogel-Fulcher model with activation energy E<inf>a</inf> ≈ 60-300 meV and freezing temperature T<inf>VF</inf> ≈ 75-140 K. High piezoelectric strain coefficient (d<inf>33</inf>*) of about 1030 pm/V at 10 kV was achieved at x = 0.07, and a high Curie temperature (T<inf>C</inf>) was maintained at about 375 K.
Some of the metrics are blocked by your
consent settings
Magnetic, optical, and electron transport properties of n-type CeO2: Small polarons versus Anderson localization MAGNETIC, OPTICAL, and ELECTRON TRANSPORT ... TARAS KOLODIAZHNYI et al.
(2017-01-11)
Kolodiazhnyi, Taras
;
Charoonsuk, Thitirat
;
Seo, Yu Seong
;
Chang, Suyong
;
Vittayakorn, Naratip
We report magnetic susceptibility, electrical conductivity and optical absorption of Ce1-xMxO2 where M = Nb,Ta and 0≤x≤0.03. The dc conductivity follows a simple thermally activated Arrhenius-type behavior in the T=70-700 K range with a change in slope at T∗≈155 K. The high-temperature activation energy shows gradual increase from ≈170 to 220 meV as the dopant concentration increases. The activation energy of the low-temperature conductivity shows a broad minimum of ≈77 meV at x≈0.01. Electron transport and localization mechanisms are analyzed in the framework of the Holstein small polaron, Anderson localization, and Jahn-Teller distortion models. The fit to the small polaron mobility is dramatically improved when, instead of the longitudinal phonons, the transverse optical phonons are considered in the phonon-assisted electron transport. This serves as an indirect evidence of a strong 4f1 orbital interaction with the oxygen ligands, similar to the case of PrO2. Based on comparison of the experimental data to the models, it is proposed that the defect-induced random electric fields make the dominant contribution to the electron localization in donor-doped ceria.
Some of the metrics are blocked by your
consent settings
High piezoelectric response and polymorphic phase region in the lead-free piezoelectric BaTiO3-CaTiO3-BaSnO3 ternary system
(2017-01-01)
Janbua, Wanwisa
;
Bongkarn, Theerachai
;
Kolodiazhnyi, Taras
;
Vittayakorn, Naratip
This study attempted to replace Pb-based piezoelectric ceramics with a non-toxic lead-free (Ba,Ca)(Ti,Sn)O<inf>3</inf> substitute, according to current environmental standards. The design of the (Ba<inf>(0.825+x)</inf>Ca<inf>(0.175-x)</inf>)(Ti<inf>(1-x)</inf>Sn<inf>x</inf>)O<inf>3</inf> lead-free piezoceramics reported herein was based on chemical modifications by varying Sn concentrations (x = 0.0500-0.1250). The effect of Sn ion modifications on structural evolution and dielectric, ferroelectric and piezoelectric properties was investigated. Partial substitution of Ti with Sn yields a suitable composition with multiphase boundaries near room temperature. As a result, the composition, x = 0.1000, shows outstanding piezoelectric values of d<inf>33</inf> = 515 pC N-1 and = 1293 pm V-1 at 10 kV, which are higher than those found in commercially available soft PZT. Furthermore, anomalous dielectric relaxation is far below the rhombohedral to orthorhombic phase transition at T ≈ 90-150 K, and was found clearly in all compositions. The relaxation fitted the Vogel-Fulcher model with an activation energy of E<inf>a</inf> ≈ 20-70 meV and freezing temperature of T<inf>VF</inf> ≈ 65-85 K.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results