Pitiporn Thanomngam

First-principles Study of Antisite Defects in Orthorhombic PbZrO3

First-principles calculations based on density functional theory (DFT) within local density approximation were employed to investigate the antisite defects, including PbZr and ZrPb, in orthorhombic PbZrO3 by determining their defect formation energies. The formation energies of antisite defects were then compared with those of other dominant defects, i.e., lead Pb, zirconium Zr, and oxygen O vacancies to examine the likelihood of their existence. Our results revealed that PbZr defect in neutral charge state is the most dominant defect under O-rich or oxidizing condition in agreement with the previous work. In addition, there is a little structural relaxation when the Zr atom is replaced by Pb atom to form PbZr defect in neutral charge state. In opposite, under O-poor or reducing condition, the formation energies of antisite defects are quite high and higher than those of vacancy defects. This suggests that antisite defects are unlikely to form under reducing condition.

First Principles Calculations on Crystal and Electronic Structure of Co2P4O12

Crystal and electronic structure of violet-pink Co2P4O12 have been investigated using first principles calculations based on density functional theory. Its theoretical X-ray diffraction and X-ray absorption fine structure spectra were calculated and compared with their experimental spectra to verify its monophasic. The calculated spectra are in good agreement with the experimental data giving parameters of a = 11.993 Å, b = 8.328 Å, c = 10.150 Å and β = 118.51°. Our calculations on band structure and density of states of Co2P4O12 showed that its major electronic transition is associated with internal Co-3d. The calculations indicated that Co2P4O12 is a half metal ferromagnetic material which disagreed with the experimental knowledge.

Effect of exchange-correlation and GW approximations on electrical property of cubic, tetragonal and orthorhombic CH3NH3PbI3

ABSTRACT A first-principle calculations based on van der Waals-corrected Density Functional Theory (vdW-DFT) is performed to investigate atomic structure of methyl ammonium lead iodine (CH3NH3PbI3) which is a key material for high efficiency solid-state solar cell. A temperature dependent symmetry was previously reported which also included in this study. DFT calculation of electronic and optical properties are systematically studied with semi-local, non-local exchange-correlation and post-DFT approximation including PBE, HSE06 hybrid functional and GW. Relativistic effect in lead ion was taken into account by incorporating spin-orbit coupling (SOC) effect to obtain more accurate band gap of this material. With GW-SOC functional, our results of band gap calculations showed good agreement between DFT calculations and experimental studies which confirmed that this computational scheme is suitable for high accuracy material design, e.g. for solar cell applications.

Improvement of energy gap prediction for hybrid perovskite materials by first-principle calculation

The breakthrough discovery of pollution free renewable energy has been awarded to conversion of solar energy into electrical energy using planar heterojunction solar cell. A layer of hybrid perovskite light harvesting materials between transport layer and electrode is essential for high power conversion efficiency (PCE). In this work, first-principle calculation based on non-local van der Waals-corrected Density Functional Theory (vdW-DFT) is used to examine atomic structures of the most popular hybrid perovskite materials used in solar cell absorption layer. The optical band gaps achieved from electronic band structures were consistently studied using semi-local exchange-correlation functional (GGA-PBE) and post-DFT approximation (GW approximation). In order to improve band gap accuracy, we tried to compensate relativistic effect in metal ion using spin-orbit coupling (SOC). Our results showed that the energy gap predictions using first-principles GW calculations incorporate with SOC scheme are in good agreement with available experimental reports. Therefore, this calculation scheme is suggested for high accuracy organic-inorganic solar cell design.The breakthrough discovery of pollution free renewable energy has been awarded to conversion of solar energy into electrical energy using planar heterojunction solar cell. A layer of hybrid perovskite light harvesting materials between transport layer and electrode is essential for high power conversion efficiency (PCE). In this work, first-principle calculation based on non-local van der Waals-corrected Density Functional Theory (vdW-DFT) is used to examine atomic structures of the most popular hybrid perovskite materials used in solar cell absorption layer. The optical band gaps achieved from electronic band structures were consistently studied using semi-local exchange-correlation functional (GGA-PBE) and post-DFT approximation (GW approximation). In order to improve band gap accuracy, we tried to compensate relativistic effect in metal ion using spin-orbit coupling (SOC). Our results showed that the energy gap predictions using first-principles GW calculations incorporate with SOC scheme are in good a...

Effect of SnCl4 Concentration on Transparent and Conducting Undoped Tin Oxide Thin Films

The purpose-built pyrolysis system based on an ultrasonically generated aerosol has been successfully used for deposition of highly transparent and conductive undoped tin (IV) oxide thin films. The morphological, structural, optical and electrical properties as well as electronic structures of the films for different concentrations of SnCl4.5H2O used as the starting precursor were investigated. FE-SEM displayed the substrate surfaces were uniformly covered with the film. The film thickness varied with the precursor concentration. XRD patterns showed the deposited films were a tetragonal phase and presented random orientations. The optical transmission spectra of all films revealed highly transmittance in the visible region. Refractive index of the films was between 1.85 and 2.0. XPS spectra for the Sn 3d5/2 and Sn 3d3/2 confirmed that the films were composed of SnO and SnO2 phases. The non-stoichiometric composition decreased with increasing concentration of the precursor. The films deposited with 0.30 M showed the highest conductivity and carrier concentration of 17 W-1cm-1 and 9.5 x 1019 cm-3, respectively. The disagreement of relation between XPS and Hall measurement suggested the higher carrier concentration arose from incorporation of residual chlorine from the solution precursor during deposition into the films. The interstitially incorporated chlorine considerably influenced the electrical properties of the films.

Structural and Electronic Properties of β – CuPc: First Principles Study

Structural and electronic properties of CuPc in β structure (β - CuPc) were investigated by first principles calculations. The generalized gradient approximation (GGA) was used to describe the exchange-correlation with the projector-augmented wave (PAW) method. Under ambient pressure, the calculated structural parameters were calculated and found to be in good agreement with other experimental and theoretical values. The calculated direct band gap was found to be 0.683 eV. The results of electronic properties under various pressures were presented. To investigate the properties under pressure, β - CuPc was calculated at several reduced volumes. It was found that the energy gap decreases when the pressure increases. The behaviors of electronic properties under pressure were also discussed.

First-Principles Investigation on Structural and Electronic Properties of Ferromagnetic Fe2P4O12

Structural and electronic properties of Fe2P4O12 have been investigated using first-principles calculation technique. The results indicated that the Fe2P4O12 structure is monoclinic of C2/c with lattice parameters of a = 12.228 Å, b = 8.530 Å, c = 9.835 Å and β = 118.67°. Two nonequivalent octahedral FeO6 from the calculation have an average Fe−O distance of 2.143 Å. Both FeO6 are dominated by covalent interactions assigned to Fe3d and O2p at the valent electronic states. The DOS calculation gives well explanation on its half-metallic ferromagnetic property. These results are in very good agreement with the previous experimental reports.

Study on Optical and Electronic Properties of Sn-Doped ZnPc

Sn doped ZnPc films were deposited on intrinsic Si and glass substrates by organic source thermal co-evaporation technique with different deposition rates. Optical properties and electronic structure were characterized by UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) respectively. The UV-Vis results showed that phase transition of ZnPc from α-phase to β-phase occurred when Sn:ZnPc deposition rate is 0.3:0.7 or higher. XPS results indicated that the outer s electron of Sn atom is transferred to the ZnPc. Broadening of the C 1s spectra is observed with the increasing of Sn deposition rate. This broadening corresponds to the change of molecular environment surrounding carbon atoms in the Sn-doped ZnPc films.

Surface Morphology and Structural Investigation of TiN Nanocrystal Thin Films Grown with Different N2 Concentration

In this work, new information on surface morphology, phase and local structure of titanium nitride (TiN) nanocrystal thin films grown with different nitrogen gas concentration by direct current (DC) magnetron sputtering is provided. Surface morphology of the thin films was studied by field emission scanning electron microscope (FE-SEM). Phase and local structure of the TiN nanocrystals were determined by X-ray diffraction spectroscopy (XRD) and X-ray absorption fine structure (XAFS). The TiN nanocrystals were prepared on silicon substrates. N2/Ar gases were used as reactive gases for sputtering Ti target. The amount of these two reactive gases was varied at different ratios (N2/Ar), i.e. 100:0, 75:25, 50:50 and 25:75 respectively. Our results suggested that sputtering Ti target with high N2/Ar gas raSubscript texttio (higher than 75%) provides good TiN layer while sputtering with low N2/Ar gas ratio (lower than 25%) gives Ti layer instead of TiN. In addition, sputtering with 50% N2/Ar gas ratio gives a multiphase system between TiN and Ti. Local structure parameters of these nanocrystal thin films are reported.

First-Principles Investigation on Elastic Constants of TiN under High Pressure

Elastic constants of NaCl-type TiN under pressure were investigated by first-principles calculations within both local density approximation (LDA) and Perdew-Burke-Ernzerhof generalized-gradient approximation (PBE-GGA). At ambient pressure, the calculated lattice parameter, bulk modulus, and elastic constants of NaCl-type TiN are in well agreement with other available values. Under pressure, all elastic constants, C11, C12, and C44, are found to increase with pressure. C11, which is related to the longitudinal distortion, increases rapidly with pressure while C12 and C44 which are related to the transverse and shear distortion, respectively, are much less sensitive to pressure.