Banjong Boonchom

Non-isothermal kinetics of the thermal decomposition of sodium oxalate Na2C2O4

The thermal transformation of Na2C2O4 was studied in N2 atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na2C2O4 and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS) methods. The activation energies (Eα) of Na2C2O4 decomposition were found to be consistent. Decreasing Eα at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated through the Liqing–Donghua method was ‘cylindrical symmetry (R2 or F1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy pathway and revealed a very hard mechanism.

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.

Dielectric properties and phase transition behaviors in (1−x)PbZrO3–xPb(Mg1/2W1/2)O3 ceramics

The solid solution of lead zirconate [PbZrO3 (PZ)] and lead magnesium tungstate [Pb(Mg1/2W1/2)O3 (PMW)] has been synthesized by the wolframite precursor method. The crystal structure, phase transformations, dielectric and thermal properties of (1−x)PZ-xPMW, where x=0.00–0.10, were investigated. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. Phase-pure perovskite was obtained for all compositions. Furthermore, a change from orthorhombic to rhombohedral symmetry was observed as the mole fraction of increased PMW. As a result, it was found that PbZrO3–Pb(Mg1/2W1/2)O3 undergoes successive transitions from the antiferroelectric phase to the ferroelectric phase to the paraelectric state. The coexistence of orthorhombic and rhombohedral phases in this binary system is located near the composition x=0.1.

Effect of Pb(Y1/2Nb1/2)O3 Additions on Thermal and Electrical Properties of PbZrO3 Ceramics

The solid solution of a (1–x)PbZrO3 – xPb(Y1/2Nb1/2)O3 (PZ – PYN) system, with x = 0.00 – 0.08, was synthesized by the wolframite precursor method. The effects of PYN content on crystal structure, and electrical and thermal properties of PbZrO3 ceramic were investigated. The crystal structure of sintered ceramics was characterized by X-ray diffraction. The pure perovskite phase was obtained for all compositions. The transition temperatures of the AFE to PE phase become lower with PYN increase. The dielectric properties of PZ were improved by the addition of PYN.

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.

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.

Study on thermal transformation of CuHPO4·H2O obtained by acetone-mediated synthesis at ambient temperature

Copper hydrogenphosphate monohydrate, CuHPO4·H2O, was synthesized for the first time through simple and rapid method using the mixing of copper carbonate and phosphoric acid in acetone medium at ambient temperature. The obtained CuHPO4·H2O decomposed in three stages via dehydration and deprotonated hydrogenphosphate reactions, revealed by TG/DTG and DSC techniques. The kinetic triplet parameters (Ea, A, and n) and thermodynamic functions (ΔH*, ΔG*, and ΔS*) for the first two decomposed steps were calculated from DSC data. All the obtained functions indicate that the deprotonated HPO42− reaction for the second step occurs at a higher energy pathway than the dehydration reaction for the first step. The calculated wavenumbers based on DSC peaks were comparable with FTIR results, which support the breaking bonds of OH (H2O) and P-OH (HPO42−) according to decomposed mechanisms. All the calculated results are consistent and in good agreement with CuHPO4·H2O’s thermal transformation mechanisms.

Synthesis, characterization, vibrational spectroscopy, and factor group analysis of partially metal-doped phosphate materials

A simple precipitating method was used to synthesize effectively a partially metal-doped phosphate hydrate (Mn0.9Mg0.1HPO4·3H2O), whereas the thermal decomposition process of the above hydrate precursor was used to obtain Mn1.8Mg0.2P2O7 and LiMn0.9Mg0.1PO4 compounds under different conditions. To separate the overlapping thermal decomposition peak, a deconvolution technique was used, and the separated peak was applied to calculate the water content. The factor group splitting analysis was used to exemplify their vibrational spectra obtained from normal vibrations of HPO42-, H2O, P2O74- and PO43- functional groups. Further, the deconvoluted bending mode of water was clearly observed. Mn0.9Mg0.1HPO4·3H2O was observed in the orthorhombic crystal system with the space group of Pbca (D2h15). The formula units per unit cell were found to be eight (Z = 8), and the site symmetric type of HPO42- was observed as Cs. For the HPO42- unit, the correlation filed splitting analysis of type C3v - Cs - D2h15 was calculated and had 96 internal modes, whereas H2O in the above hydrate was symbolized as C2v - Cs - D2h15 and had 24 modes. The symbol C2v - Cs - C2h3 was used for the correlation filed splitting analysis of P2O74- in Mn1.8Mg0.2P2O7 (monoclinic, C2/m (C2h3), Z = 2, and 42 modes). Finally, the symbol Td - Cs - D2h16 was used for the correlation filed splitting analysis of PO43- in LiMn0.9Mg0.1PO4 (orthorhombic, Pnma (D2h16), Z = 4, and 36 modes).

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.

Sonochemical Synthesis of Zn3(PO4)2.4H2O and Zn3(PO4)2 Powders

Zn3(PO4)2.4H2O, which is an important component of biomedical zinc phosphate cement, was synthesized from an aqueous solution of zinc oxide and orthophosphoric acid by the sonochemical method. This synthesis method yielded best results with respect to high purity and crystallinity. Structural characteristics of the compound were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM). FT-IR spectra indicated the presences of different crystallographic PO43 ion and H2O molecules for the Zn3(PO4)2.4H2O and Zn3(PO4)2 structures. The resulting XRD patterns showed the purity phases of orthorhombic Zn3(PO4)2.4H2O and the monoclinic for its final decomposed Zn3(PO4)2 product. The thermal stability, crystallite size, and plate-like microparticles of Zn3(PO4)2.4H2O and Zn3(PO4)2 are different in this work from those in previous reports, which may be caused by the starting reagents and reaction condition for the sonochemical method.