Jiraroj T-Thienprasert | Kasetsart University (original) (raw)

Papers by Jiraroj T-Thienprasert

Journal of Applied Physics, 2018

Oxygen vacancy defects (V O) in Ti-based oxides play important roles in catalytic processes despi... more Oxygen vacancy defects (V O) in Ti-based oxides play important roles in catalytic processes despite limited knowledge regarding their formation and characterization. Here, we demonstrate the use of X-ray absorption spectroscopy (XAS) measurements to compare the relative proportion of V O defects in as-grown alkali hexatitanate A 2 Ti 6 O 13 (A = Li, Na, K). Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions were studied. The similarity of measured XANES spectra of Ti K-edge in all samples indicates the presence of (Ti 4+)O 6 units in good agreement with reported X-ray diffraction results. The small influence of cations A at the tunnel was observed and can be well reproduced in the simulated spectra. In addition, we present a semi-quantitative approach to intuitively determine the content of V O defects in oxygen-deficient K 2 Ti 6 O 13-x by in situ time-resolved XAS measurements under reducing conditions (10%H 2 /Ar, 50-650°C). The in situ XANES measurements indicate that the oxidation state of bulk Ti remains the same as the as-grown sample, i.e., 4+, at elevated temperatures. By in situ EXAFS measurements, the relative number of V O defects is highest at a reduction temperature of ∼550°C and slightly decreases after that. To confirm the formation of V O defects, first-principles calculations were independently carried out using a 126-atom K 2 Ti 6 O 13 supercell with V O at various positions. Based on calculated EXAFS, the removal of the oxygen atom nearest to the tunnel, which is the lowest energy structure, provides a good match to the experimental spectra.

Physical Review B, 2017

The absorption peaks at ∼3200−3300 cm −1 in α-Al 2 O 3 crystal that were previously observed and ... more The absorption peaks at ∼3200−3300 cm −1 in α-Al 2 O 3 crystal that were previously observed and assigned to hydrogen interstitial were reinvestigated by first-principles local vibration mode calculations. Based on our calculations, we found that the vibration of hydrogen interstitial is not consistent with the observed polarized IR absorption peaks at ∼3200−3300 cm −1 for two reasons: (1) the orientation of the O-H bond is not aligned with the direction of the oscillator observed and (2) the calculated vibrational frequency is much lower than the observed values. The calculated formation energies showed that interstitial hydrogen can strongly bind with aluminum vacancy, forming [H n-V Al ] complex defects. The complexes have the O-H bond in the direction aligned with the direction of the oscillator. The vibration frequencies of the complex defects are also close to the observed value. Therefore, we assign the experimentally observed ∼3200−3300 cm −1 modes to [H n-V Al ] complex defects.

Computational Materials Science, 2016

Lead zirconate PbZrO 3 (PZO) is one of the most important ceramic materials due to its antiferroe... more Lead zirconate PbZrO 3 (PZO) is one of the most important ceramic materials due to its antiferroelectric property, which can be used in many technological applications. Due to the toxicity of Pb, there is an attempt to replace Pb with other non-toxic elements. It has been reported that doping orthorhombic-PZO with Bi and Al atoms could stabilize the antiferroelectric property in a wide temperature range and reduce the lead content in the material. In this work, we used first-principles calculations based on density functional theory to investigate the microscopic and electronic structures of Bi and Al defects in orthorhombic-PZO. Our calculated defect formation energies revealed that Bi atom can substitute on either Pb site (A-site) or Zr site (B-site); depending on the Fermi-level as well as the crystal growth condition. On the other hand, Al atom is likely to substitute only on the Zr site. In addition, our calculations revealed that there is only a small binding between Bi Pb and adjacent Al Zr or Bi Zr with the binding energies of $0.2 eV. This indicates that Bi Pb and Al Zr (or Bi Zr) are unlikely to form complexes.

Physical review letters, 2013

The synchrotron x-ray absorption near edge structures (XANES) technique was used in conjunction w... more The synchrotron x-ray absorption near edge structures (XANES) technique was used in conjunction with first-principles calculations to characterize Al-doped ZnO films. Standard characterizations revealed that the amount of carrier concentration and mobility depend on the growth conditions, i.e. H 2 ðor O 2 Þ=Ar gas ratio and Al concentration. First-principles calculations showed that Al energetically prefers to substitute on the Zn site, forming a donor Al Zn , over being an interstitial (Al i ). The measured Al K-edge XANES spectra are in good agreement with the simulated spectra of Al Zn , indicating that the majority of Al atoms are substituting for Zn. The reduction in carrier concentration or mobility in some samples can be attributed to the Al Zn -V Zn and 2Al Zn -V Zn complex formations that have similar XANES features. In addition, XANES of some samples showed additional features that are the indication of some -Al 2 O 3 or nAl Zn -O i formation, explaining their poorer conductivity.

Physical review letters, 2012

In a recent Letter [1] Scanlon and Watson (SW) reported their first principles results on hydroge... more In a recent Letter [1] Scanlon and Watson (SW) reported their first principles results on hydrogen in Cu2O. They find that (1) an interstitial H in Cu2O prefers to occupy the tetrahedral site (H tet i), which is coordinated with four Cu cations, in all three charge states (+ 1, neutral, and J1), and (2) H will bind with a Cu vacancy and form an electrically active HV Cu defect complex, which is amphoteric with (+= 0) and (0= J) transition levels at Ev+ 0: 1 and Ev+ 1: 1 eV, respectively. However, these two findings contradict two generally ...

Computational Materials Science, 2010

Chen et al. [Phys. Rev. Lett. 96 (2006) 035508] experimentally observed vibrational signatures re... more Chen et al. [Phys. Rev. Lett. 96 (2006) 035508] experimentally observed vibrational signatures related to defects in oxygen-doped CdTe using ultrahigh resolution Fourier transform infrared (FTIR) spectroscopy. They observed an absorption peak at 350 cm À1 . In addition, for samples grown under certain conditions, they observed two higher frequency peaks (1097 and 1108 cm À1 ) at low temperature that merged into one at room-temperature. They attributed the low-frequency peak (350 cm À1 ) to the vibration of O Te and the two higher frequency peaks to the vibrational modes of a O Te -V Cd complex. Subsequently, they reported similar modes around 1100 cm À1 in O-doped CdSe [Phys. Rev. Lett. 101 (2008) 195502] which were attributed to an O Se -V Cd complex. We employed first-principles DFT calculations to calculate the vibrational modes of O Te and O Te -V Cd complex in CdTe. Our calculations show that the 350 cm À1 mode is consistent with O Te . However, the frequencies of the modes around 1100 cm À1 are more than twice the expected frequencies for O Te -V Cd complexes in CdTe (or O Se -V Cd in CdSe), indicating that the O Te -V Cd complex cannot be the cause of the observed 1100 cm À1 modes. A search for a new defect model is in order.

Physical Chemistry Chemical Physics, 2010

A combination of X-ray absorption spectroscopy (XAS) measurements and quantum mechanical/molecula... more A combination of X-ray absorption spectroscopy (XAS) measurements and quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations has been applied to elucidate detailed information on the hydration structures of Ca 2+ and Cl À . The XAS spectra (extended X-ray absorption fine structure, EXAFS, and X-ray absorption near-edge structure, XANES) measured from aqueous CaCl 2 solution were analyzed and compared to those generated from snapshots of QM/MM MD simulations of Ca 2+ and Cl À in water. With regard to this scheme, the simulated QM/MM-EXAFS and QM/MM-XANES spectra, which correspond to the local structure and geometrical arrangement of the hydrated Ca 2+ and Cl À at molecular level show good agreement with the experimentally observed EXAFS and XANES spectra. From the analyses of the simulated QM/MM-EXAFS spectra, the hydration numbers for Ca 2+ and Cl À were found to be 7.1 AE 0.7 and 5.1 AE 1.3, respectively, compared to the corresponding values of 6.9 AE 0.7 and 6.0 AE 1.7 derived from the measured EXAFS data. In particular for XANES results, it is found that ensemble averages derived from the QM/MM MD simulations can provide reliable QM/MM-XANES spectra, which are strongly related to the shape of the experimental XANES spectra. Since there is no direct way to convert the measured XANES spectrum into details relating to geometrical arrangement of the hydrated ions, it is demonstrated that such a combined technique of XAS experiments and QM/MM MD simulations is well-suited for the structural verification of aqueous ionic solutions.

Journal of Physics: Conference Series, 2009

Abstract. Both synthetic and natural α-Al2O3 samples with different Cr concentrations were invest... more Abstract. Both synthetic and natural α-Al2O3 samples with different Cr concentrations were investigated by XANES. The Cr contents were analyzed using LA-ICP-MS technique prior to this experiment. XANES spectra combined with first principle calculations showed the transformation from α-Al2O3: Cr3+ to α-Al2O3: Cr3+, Cr3+ or α-Cr2O3 as the Cr-Cr content increased. The absorption transformation could be resulted from the change of environment around Cr3+ ions, ie, the Al-O-Cr bonds decreased while the Cr-O-Cr bonds increased. ...

Journal of Physics: Conference Series, 2009

Current Applied Physics, 2011

The local structures of cobalt in Co-doped TiO2 were studied by combining K-edge x-ray absorption... more The local structures of cobalt in Co-doped TiO2 were studied by combining K-edge x-ray absorption near edge structures (XANES) measurements with first-principles calculations. The Co/TiO2 samples were prepared by (1) sol-gel and (2) co-precipitation methods. To identify the local structure around Co, the measured spectra are compared against the spectra measured from Co3O4, CoO and Co foil standard samples as well as first principles XANES based on several atomic models. For the sample prepared by the co-precipitation ...

Physical Review Letters, 2009

Computational Materials Science, 2010

To investigate the local structure of InN, In 2 O 3 and their alloys, synchrotron (In L 3 -edge) ... more To investigate the local structure of InN, In 2 O 3 and their alloys, synchrotron (In L 3 -edge) X-ray absorption near edge structures (XANES) of indium oxynitride samples with varied O contents are used in conjunction with first-principles calculations. A good agreement between the measured and simulated spectra is obtained. It is found that the spectra are sensitive to the coordination number of the In atoms, i.e., fourfold for InN-like structures and sixfold for In 2 O 3 -like structures. Moreover, the spectra are quite insensitive to the species (N or O) around In. The calculated band structures and density of states are also presented and discussed.

Physica B-condensed Matter

Recently, the vibrational signatures related to oxygen defects in oxygen-doped CdSe were measured... more Recently, the vibrational signatures related to oxygen defects in oxygen-doped CdSe were measured using ultrahigh resolution Fourier transform infrared (FTIR) spectroscopy by [1]. They observed two absorption bands centered at $ 1991.77 and 2001.3 cm À 1 , which they attributed to the LVMs of O Cd , in the samples grown with the addition of CdO and excess Se. For the samples claimed to be grown with even more excess Se, three high-frequency modes (1094.11, 1107.45, and 1126.33) were observed and assigned to the LVMs of O Se -V Cd complex. In this work, we explicitly calculated the vibrational signatures of O Cd and O Se -V Cd complex defects based on first principles approach. The calculated vibrational frequencies of O Cd and O Se -V Cd complex are inconsistent with the frequencies observed by Chen et al., indicating that their observed frequencies are from other defects. Potential defects that could explain the experimentally observed modes are suggested.

Analytical and Bioanalytical Chemistry, 2011

Glass has been used in ornaments and decorations in Thailand for thousands of years, being discov... more Glass has been used in ornaments and decorations in Thailand for thousands of years, being discovered in several archeological sites and preserved in museums throughout the country. To date only a few of them have been examined by conventional methods for their compositions and colorations. In this work we report for the first time an advanced structural analysis of Thai ancient glass beads using synchrotron X-ray absorption spectroscopy (XAS) and energy-dispersive X-ray (EDX) spectrometry. Four samples of ancient glass beads were selected from four different archeological sites in three southern provinces (Ranong, Krabi and Pang-nga) of Thailand. Archaeological dating indicated that they were made more than 1,300 years ago. A historically known method for obtaining a red color is to add compounds containing transition elements such as gold, copper, and chromium. For our samples, EDX spectrometry data revealed existing fractions of iron, copper, zinc, and chromium in ascending order. Thus, copper was selectively studied by XAS as being potentially responsible for the red color in the glass beads. K-shell X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) of copper were recorded in fluorescence mode using an advanced 13-element germanium detector. Comparisons with XANES spectra of reference compounds identified two major forms of copper, monovalent copper and a metallic cluster, dispersed in the glass matrix. The cluster dimension was approximated on the basis of structural modeling and a theoretical XANES calculation. As a complement, EXAFS spectra were analyzed to determine the first-shell coordination around copper. XAS was proven to be an outstanding, advanced technique that can be applied to study nondestructively archaeological objects to understand their characteristics and how they were produced in ancient times.

Physical Review Letters, 2009

Physical Review B, 2012

For over three decades, the infrared spectroscopy peaks of around 3500 cm −1 observed in hydrogen... more For over three decades, the infrared spectroscopy peaks of around 3500 cm −1 observed in hydrogen-doped SrTiO 3 samples have been assigned to an interstitial hydrogen (H i ) attached to a lattice oxygen with two possible configuration models: the octahedral edge (OE) and the cubic face (CF) models. Based on our first-principles calculations of H i around O, both OE and CF configurations are not energetically stable. Starting from either configuration, the H i would spontaneously relax into an off axis (OA) site; lowering the energy by 0.25 eV or more. The calculated vibrational frequency of 2745 cm −1 for OA invalidates the assignment of H i to the observed 3500 cm −1 peak. In addition, the calculated diffusion barrier is low, suggesting that H i can be easily annealed out. We propose that the observed peaks around 3500 cm −1 are associated with defect complexes. A Sr vacancy (V Sr ) can trap H i and form a H-V Sr complex which is both stable and has the frequency in agreement with the observed main peak. The complex can also trap another H i and form 2H-V Sr ; consistent with the observed additional peaks at slightly higher frequencies (3510-3530 cm −1 ).

Physica B-condensed Matter

Mixed phase TiO 2 and Ce/TiO 2 samples were synthesized by a sol-gel method using different hydro... more Mixed phase TiO 2 and Ce/TiO 2 samples were synthesized by a sol-gel method using different hydrolysis conditions. In pure TiO 2 samples, traditional X-ray diffraction (XRD) and Ti K-edge synchrotron X-ray absorption near edge structures (XANES) independently revealed their anatase/rutile phase ratios. XANES results further revealed a substantial amount of Ti atoms existed in other forms beside anatase and rutile TiO 2 in the sample synthesized by the low hydrolysis condition. An increase in the extent of the hydrolysis during the synthesis leads to an increased rutile ratio and a reduction in other forms. In Ce/TiO 2 samples, the crystal sizes were too small for XRD characterization. Only XANES could be used to characterize their phase ratios. It is found that adding Ce impedes rutile formation; leading to increased anatase ratio. The difference in the fundamental aspects of XRD and XANES techniques in providing the phase ratios is discussed.

Applied Physics Letters, 2008

Synchrotron x-ray absorption near edge structures ͑XANES͒ measurements of In L 3 edge is used in ... more Synchrotron x-ray absorption near edge structures ͑XANES͒ measurements of In L 3 edge is used in conjunction with first principles calculations to characterize rf magnetron sputtered indium oxynitride at different O contents. Good agreement between the measured and the independently calculated spectra are obtained. Calculations show that the XANES spectra of this alloy are sensitive to the coordination numbers of the In atoms, i.e., fourfold for indium nitride-like structures and sixfold for indium oxide-like structures, but not to the substitution of nearest neighbor N by O or vice versa.

Journal of Applied Physics, 2018

Physical Review B, 2017

Computational Materials Science, 2016

Physical review letters, 2013

Physical review letters, 2012

Computational Materials Science, 2010

Physical Chemistry Chemical Physics, 2010

Journal of Physics: Conference Series, 2009

Current Applied Physics, 2011

Physical Review Letters, 2009

Computational Materials Science, 2010

Physica B-condensed Matter

Analytical and Bioanalytical Chemistry, 2011

Physical Review Letters, 2009

Physical Review B, 2012

Physica B-condensed Matter

Applied Physics Letters, 2008