Chesta Ruttanapun

Electrical and optical properties of p-type CuFe1-xSnxO2 (x = 0.03, 0.05) delafossite-oxide

The CuFe1-xSnxO2 (x = 0.03, 0.05) delafossite samples have been synthesized by a solid-state reaction to investigate electrical and optical properties of the transparent conducting oxide materials. Crystal structure was characterized by XRD. The electrical conductivity and Seebeck coefficient were measured in the high temperature range of 300 to 960 K, while the Hall coefficient, XPS, and UV-VIS-NIR spectra were analyzed at room temperature. The XRD peaks of the samples indicate the delafossite structure phase, and the XPS spectra reveal the stable Sn2+-doping state. The Seebeck and Hall coefficient display a positive sign indicating the p-type conducting oxide. The optical allowed direct gap is 3.45 eV as a visible-transparent material. The activation energies for polaron hopping between Sn2+ sites and Fe3+ sites of 36 and 32 meV are obtained from the samples having x = 0.03 and 0.05, respectively. The CuFe1-xSnxO2 delafossite oxide compounds, of which the Fe3+ sites in the CuFeO2 are substituted by the Sn2+ ions, are p-type transparent conducting oxide materials. The activation energy is found to decrease with an increased in Sn content.

Optical and electronic properties of delafossite CuBO2p-type transparent conducting oxide

CuBO2 delafossite was prepared by solid state reaction and calcined/sintered at 1005 °C. The optical properties of this p-type transparent conducting oxide were investigated. Its crystal structure, morphology, composition, oxygen decomposition, and optical and electronic properties were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermal gravimetric analysis (TGA), ultraviolet-visible-near-infrared (UV-VIS-NIR) and fluorescence spectroscopies, Seebeck coefficient, and electrical conductivity measurements. CuBO2 delafossite possesses a hexagonal space group R3¯m. TGA indicated a weight loss of 10%, which was attributed to excess oxygen. The positive Seebeck coefficient confirmed p-type behavior. Emission at 355 nm indicated a direct band type transition, and the UV-VIS-NIR spectrum indicated an optical direct gap of 3.6 eV. Activation energies for carrier production and electrical conduction were 0.147 and 0.58 eV, respectively, indicating the thermal...

Effects of spin entropy and lattice strain from mixed-trivalent Fe3+/Cr3+ on the electronic, thermoelectric and optical properties of delafossite CuFe1−x Cr x O2 (x = 0.25, 0.5, 0.75)

Mixed-trivalent Fe3+/Cr3+ content CuFe1−x Cr x O2 (x = 0.25, 0.5, and 0.75) compounds were synthesized to investigate the effects of spin entropy, and lattice strain on their electronic, thermoelectric and optical properties. The XPS results showed the existence of mixed Cu1+/Cu2+, Fe3+/Fe4+ and Cr2+/Cr3+ ion states in the structures. The mixed Fe3+/Cr3+ions caused a strong correlation to occur between the spin and the orbitals of the carriers in the octahedral layer of the sample, affecting the carrier degeneracy Seebeck coefficient behaviour, and the Cu2+ and Fe4+ ions caused an effect of enhancing the electric conductivity. These effects meant that CuFe0.75Cr0.25O2 had the highest electrical conductivity, an enhanced Seebeck coefficient compared to that of CuFeO2-based compounds, and the highest thermopower value. The lowest thermal conductivity was that of CuFe0.5Cr0.5O2, which was a result of the mismatched atomic radii of the mixed trivalent Fe3+(0.645 A)/Cr3+(0.615 A), which caused the lattice strain to occur in the structure and thus affected the point defect scattering of the phonon thermal conductivity. The lowest total thermal conductivity was that of CuFe0.5Cr0.5O2, because it had the maximum lattice strain. Overall, the effect of the mixed trivalent elements caused CuFe0.75Cr0.25O2 to have the highest value of the dimensionless figure of merit ZT, with a value that was four times that of CuFeO2-based compounds and six times that of CuCrO2-based compounds. With regard to optical properties, the lattice strain causes the indirect optical gap to increase with increasing x content, but has no effect on the direct optical gap. These results verified that the mixed-trivalent Fe3+/Cr3+ content of CuFe1−x Cr x O2 (x = 0.25, 0.5, and 0.75) affected the electronic, thermoelectric and optical properties of the structure by causing spin entropy and lattice strain to occur.

Optical parametric amplification in one-dimensional photonic bandgap structures.

In this paper, optical parametric amplification based on the degenerate four-wave mixing principle in a one-dimensional photonic bandgap (PBG) structure has been numerically studied. First, the multiple scale method was introduced to derive a complete set of nonlinear coupled-mode equations for a finite structure with different inhomogeneous nonlinear coefficients than those used in previous works. This finite structure is composed of 680 dielectric layers, which are alternating half-wave/eight-wave films. The wavelengths of the pump, signal, and idler pulses have been determined from the transmission spectrum, which was illustrated by using the transfer matrix method. The parametric interaction of the pump, signal, and idler pulses inside PBG structure has been numerically simulated by using the split-step Fourier transform method. The results of the simulation have shown that the intensities of the signal and idler have exponential growth with respect to the number of layers in the medium. Meanwhile, pump wavevector detuning directly affects the intensities of both pulses due to a band-edge phase-matching condition that might be achieved from only one optimal detuning parameter. Moreover, both the amplification gain and the conversion efficiency of the idler pulse have been shown to be dependent on the bandwidth of the pump pulse spectrum. A very narrow pulse, with a bandwidth much less than the relevant transmission peak, enables the highest amplification and conversion efficiency in this medium because the most efficient phase-matched condition occurs in this situation. Finally, the conversion efficiency grows exponentially with input pump intensity for several input signal intensities. Furthermore, the maximum conversion efficiencies directly vary with input signal intensity.

Preparation, Characterization and Finite Element Computation of Cu(Al1/2Fe1/2)O2 Delafossite-Oxide Themoelectric Generator Module

The CuAl1/2Fe1/2O2 delafossite oxide has been synthesized by solid state reaction method for studying thermoelectric properties and measuring thermoelectric generator output electric power. The Finite Element technique was used to compute the output voltage of thermoelectric generator in applying temperature difference on a single bar and a module model with compared to the measurement results. The measurement results of positive sign Seebeck coefficient confirm the p-type conductor of the sample. The properties of Seebeck coefficient, electrical conductivity, and thermal conductivity are range from 260 to 310μV/K, from 7 to16 S/cm and from 2.5 to 3.5 W/cm-K,respectively, in the temperature range of 300 to 960 K. The output voltage of the single bar in dimension 4.2 × 2.5 × 20 mm3 obtained 0.5 to 3 mV on applying temperature difference from 1 to 10 K closely to the Finite Element result. The computing results of the thermoelectric single bar and module in high temperature reveal the output electric voltage of CuAl1/2Fe1/2O2 oxide raises with the temperature and the number of thermoelectric leg increase. In important results, the high value of electric voltage is obtained 0.2 and 0.4 V for the single bar and the module at 950 K.

Facile, Alternative Synthesis of Spherical-Like Ca(H2PO4)2•H2O Nanoparticle by Aqueous-Methanol Media

Spherical-like calcium dihydrogenphosphate monohydrate (Ca (H2PO4)2H2O) nanostructure was successfully prepared by the mixing of calcium carbonate and phosphoric in aqueous-methanol media at ambient temperature for 30 min. Three thermal decomposition step and higher stability at over 800 °C of the prepared sample are different from the earlier works. Spherical-like Ca (H2PO4)2H2O nanostructure with diameter < 100 nm confirmed by SEM may be important for potential applications. This method of synthesis by aqueous-methanol media is a fast and simple method and it is expected to be applicable for the synthesis of other nanocrystalline calcium phosphates.

A Computational Investigation of Third-harmonic Generation in One-dimensional Photonic Band-gap Materials with Multiple-Scale Method

In this paper, we present a numerical investigation of third-harmonic (TH) generation in a one-dimensional photonic band-gap material that is doped with a nonlinear χ(3)medium. For modeling harmonic generation phenomena, a multiple-scale method has been introduced to perturb the nonlinear wave equation by a small factor with appropriate scale. So, we obtain coupled-mode equations (CMEs) with different from the conventional CMEs for this phenomenon. Then, we have solved these CMEs numerically to obtain the output amplitudes of TH waves in both forward- and backward-directions, and the conversion efficiencies. Finally, the solutions show that this photonic band-gap material can generate the TH waves whose amplitudes and the conversion efficiencies may be larger than the TH wave and the efficiency produced by an equivalent length of a phase-matched, bulk medium.

Synthesis and Thermoelectric Properties of Cu0.95Pt0.05Fe0.97Sn0.03O2 Delafossite-Oxide

The Cu0.95Pt0.05Fe0.97Sn0.03O2 delafossite sample, which is the simultaneous substitution of the Pt for Cu sites and the Sn for Fe sites of CuFeO2 delafossite, has been investigated the simultaneous effect on electrical conductivity and Seebeck Coefficient for thermoelectric materials due to the previous reports of Cu0.95Pt0.05FeO2 compound displaying high enhancement effect of electric conductivity and the CuFe0.97Sn0.03O2 exhibiting large increasing of Seebeck coefficient. The sample of Cu0.95Pt0.05Fe0.97Sn0.03O2 was synthesized by solid state reaction method. The crystal structure was characterized by XRD, and the valency oxidation state of the sample was evaluated by XPS. The electrical conductivity, Seebeck coefficient, and thermoelectric conductivity were measured in the high temperature range of 320 to 860 K. The measurement results show that, the sign of Seebeck value and result of XPS reveal the sample displaying p-type thermoelectric materials as confirming the simultaneous Pt and Sn-substituted contributing hole carrier. For the effect of simultaneous substitution, the Seebeck coefficient is enhanced in temperature lower than 650 K, while electrical conductivity displays small value in all temperature range. In surprising value, the thermal conductivity of the sample is smallest value in all temperature range. Totally, the ZT value of sample is obtained 0.07 at 860K as higher than that of the reference-based. This experiment confirms that the simultaneous Pt-doped and Sn-doped of Cu0.95Pt0.05Fe0.97Sn0.03O2 compound show high ZT value in temperature higher than 700 K.

Improvement of Thermoelectric Material by Reduction Thermal Conductivity of Sn-doped CuFeO2 Delafossite Compound

In this work, the polycrystalline CuFe1-xSnxO2 (x = 0.005, 0.01, 0.03) were synthesized by a solid state reaction method with sintering temperature at 1323K for 40 hours. The XRD pattern and TGA results showed the crystal structure of hexagonal delafossite-type structure for space group (166). Thermal conductivity was decreased because the large atomic mass of the Sn substituted to the Fe sites of CuFeO2. This caused phonon scattering by the point defect of the mass difference between Sn atom and Fe atom. The minimal value of the thermal conductivity was 2.1 W/mK at 573K for Sn = 0.03.

Optical and electronic transport properties of p-type CuCoO2 transparent conductive oxide

The CuCoO2 sample has been synthesized by a conventional solid-state reaction method to investigate electronic transport and optical properties for p-type transparent conducting oxide materials. The crystal structure was characterized by XRD. The Seebeck coefficient and electrical conductivity were measured in the high temperature. The UV-VIS-NIR and FTIR spectra were analyzed at room temperature. The XRD peaks confirm the samples forming the delafossite structure phase. The Seebeck coefficient sign confirms the samples displays the p-type conducting. The electronic transport energy for activating free carrier production and conduction contain 0.276 eV and 0.131 eV, respectively. The optical direct gap is 3.65 eV which is a visible-transparent oxide material. These results support that the CuCoO2 oxide compound is p-type transparent conducting oxide materials.