Attaphol Karaphun

Characterization and magnetic properties of BaSn1−xFexO3 nanoparticles prepared by a modified sol–gel method

BaSn1−xFexO3 (xxa0=xa00, 0.05, 0.075 and 0.1) nanoparticles were prepared by a modified sol–gel method. Phase, morphology and oxidation state of samples were characterized using X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and X-ray absorption near-edge spectroscopy. XRD results show the main reflections of the perovskite-type cubic structure for all powders calcined at 1050xa0°C for 3xa0h in air. X-ray absorption measurements indicate the substitution of Fe3+ ions on the Sn site of the BaSnO3 host. The field dependence of magnetization M–H curve measured at room temperature exhibits diamagnetic behavior for undoped sample, whereas Fe-doped samples show the clear M–H loops with saturation magnetization and coercive field in the order of 0.34–1.25xa0emu/g and 260xa0Oe, respectively. Ferromagnetic (FM) ordering is interpreted in terms of overlapping of polarons mediated through oxygen vacancy defects based on the bound magnetic polaron (BMP) model. Observed FM data are fitted well with the BMP model involving localized carriers and magnetic cations.Graphical Abstract

Investigation of structural, morphological, optical, and magnetic properties of Sm-doped LaFeO3 nanopowders prepared by sol–gel method

Pure orthorhombic phase of La1−xSmxFeO3 (xu2009=u20090, 0.1, 0.2, and 0.3) nanoparticles can be obtained by sol–gel method after calcination at 800u2009°C for 3u2009h in air. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray absorption near edge spectroscopy, ultraviolet-visible spectroscopy, and vibrating sample magnetometry were used to study the crystal structure, morphology, oxidation state, functional group, optical, and magnetic properties of samples. Pure orthorhombic phase of perovskite structure is confirmed by X-ray diffraction results. Decreasing lattice parameters, crystallite sizes, and cell volumes with increasing microstrains indicate structure distortion due to the substitution of Sm ions with small ionic radius on the La sites in the orthorhombic structure. Scanning electron microscopy and transmission electron microscopy images show a homogeneous distribution of almost spherical nanoparticles with decreasing average particle sizes ranging from 56.48u2009±u20093.22 to 23.21u2009±u20094.40u2009nm for samples of high Sm content. Fourier transform infrared spectroscopy spectra confirm the Fe–O stretching mode in octahedral FeO6 unit of a perovskite structure. X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy results indicate the oxidation states +3 of La and Fe ions. The optical band gaps are found to decrease from 2.218 to 1.880u2009eV with increasing Sm content. vibrating sample magnetometry results show the antiferromagnetic behavior of undoped sample and ferromagnetic behavior for doped samples, affecting by structure distortion and particle size reduction. Interestingly, the coercive field is significantly enhanced from 95.07u2009Oe (xu2009=u20090.1) to 13,062.79u2009Oe (xu2009=u20090.3). Curie temperature (Tc) is suggested to be above 400u2009K.Graphical AbstractThe magnetization curves of La1-xSmxFeO3 (xu2009=u20090.0, 0.1, 0.2, and 0.3) nanoparticles prepared by the sol-gel method with the inset show the comparing coercive forces (Hc) of the present work and the previous works, La0.7M0.3FeO3 (Mu2009=u2009Al and Ga). Sm-doped LaFeO3 nanoparticles can exhibit ferromagnetic behavior with the significant enhancement of Hc from 95.07 to 13,062.79 Oe.

Effect of Co cations and oxygen vacancy on optical and magnetic properties of SrTi1−xCoxO3 nanoparticles prepared by the hydrothermal method

SrTi1−xCoxO3 (xu2009=u20090, 0.05, 0.10 and 0.15) nanoparticles were synthesized by the hydrothermal method. Optical and magnetic properties based on Co cations and oxygen vacancy were studied in annealed samples. Phase and structure of all samples studied by X-ray diffraction results reveal a crystal of perovskite type with the formation of impurity phases of SrCO3 and Co3O4 in as-prepared and annealed samples of xu2009=u20090.15. Images of annealed samples obtained by scanning electron microscope and transmission electron microscope reveal cubic-like nanoparticles with the increase of average particle size from 103.85u2009±u20091.15 to 113.14u2009±u20092.27xa0nm due to the increase of Co content. In addition, the determined optical band gaps of annealed samples from the obtained ultraviolet–visible spectra are found to decrease from 3.148 to 2.417xa0eV. X-ray photoelectron spectroscopy results of annealed samples with xu2009=u20090.05 and 0.10 indicate the increase of oxygen vacancy (Vo) with increasing Co content and the existence of only Co2+ cation in a sample of xu2009=u20090.05 and both of Co2+ and Co3+ cations in a sample of xu2009=u20090.10. XANES results of annealed samples confirm the oxidation state 2u2009+u2009and 3u2009+u2009of Co cations. Magnetization (M) measurements using vibrating sample magnetometer reveal paramagnetic behavior in as-prepared samples and ferromagnetic behavior in annealed samples with saturation magnetization increases from 0.48 to 3.13xa0emu/g, owing to the increase of Co content. F-center exchange mechanism due to Co2+–Vo–Co2+ and Co3+–Vo–Co3+ couplings are proposed for the ferromagnetism. Temperature dependence of magnetization for annealed SrTi0.90Co0.10O3 sample measured in zero field-cooling and field-cooling modes indicate a Curie temperature above 280xa0K.

Characterization and dielectric properties of SrTi1−xMnxO3 ceramics

SrTi1−xMnxO3 (x = 0, 0.05, 0.10, and 0.15) ceramics can be prepared by sintering SrTi1−xMnxO3 nanopowders, synthesized by a hydrothermal method, at 1,200 °C in air for 3 h. X-ray diffraction (XRD) results for all nanopowders and unannealed ceramics indicate a cubic-perovskite structure with an impurity phase of SrCO3 in nanopowders of x = 0.10 and 0.15. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of nanopowders reveal the agglomeration of cubiclike nanoparticles with particle sizes in the range of 86–105 nm. The dielectric constant (e) at room temperature tends to increase upon Mn doping, to the maximum value of 600 at 1 kHz for a ceramic sample of x = 0.05 owing to the homogeneity of grain sizes. Annealing of ceramic samples can also increase the e values through the creation of oxygen vacancies.

Magnetic and optical properties of Cu1−xFexO nanosheets prepared by the hydrothermal method

Cu1−xFexO (xu2009=u20090, 0.025, 0.05, 0.075, and 0.1) nanosheets can be sucessfully prepared by hydrothermal method at 160u2009°C for 3u2009h in a solution of 0.5u2009M KOH. X–ray diffraction results indicated a monoclinic phase of crystalline CuO nanosheets. Crystallite sizes and lattice constants were determined by Rietveld refinements of the X–ray diffraction peaks. The crystallite sizes significantly decreased from 28.46 to 21.71u2009nm with the increase of Fe content. Scanning electron microscopy and transmission electron microscopy revealed the plate-like shapes with the estimated width and length in the range of 50–170 and 100–275u2009nm, respectively. The optical band gaps (Eg) studied by ultraviolet-visible spectroscopy are found to decrease from 3.625u2009eV for undoped sample to 3.430u2009eV in Fe–doped CuO sample of xu2009=u20090.1. The magnetic properties of samples studied by vibrating sample magnetometry indicated a paramagnetic behavior for CuO nanosheets and ferromagnetic behavior in Fe–doped CuO nanostructures with the magnetization strongly depended on the Fe content. The ferromagnetism of Fe-doped samples was discussed base on the F-center exchange mechanism via oxygen vacancy defects.Graphical AbstractThis figure shows the magnetization of Fe doped CuO nanosheets synthesized at 160u2009°C for 3u2009h in 0.5u2009M KOH with SEM micrograph, showing the plate-like morphology. It can be seen in this figure that ferromagnetic behavior of CuO nanosheets can be induced by doping with Fe ion. Moreover, the optical band gaps of Fe-doped CuO nanosheets decrease with the increase of Fe content, suggesting that Fe-doped CuO nanosheets may be applied as photocatalytic materials. Ferromagnetism is proposed to be originated from the coupling of Fe3+ with the oxygen vacancy promoted in the samples.

Influence of calcination temperature on the structural, morphological, optical, magnetic and electrochemical properties of Cu2P2O7 nanocrystals

AbstractNH4CuPO4·H2O (NCPO) powder was synthesized by the hydrothermal method. Cu2P2O7 nanocrystals (CPO NCs) were obtained by calcination of the NCPO powders at 550 (CPO5), 600 (CPO6), 700 (CPO7), and 800 (CPO8)u2009°C in argon atmosphere for 3u2009h. X-ray diffraction (XRD) results indicated a monoclinic structure of NCPO with space group P21/n, while that of CPO NCs was a monoclinic phase with space group C2/c. Moreover, CuHPO4·H2O phase with space group P21/a was found in the product calcined at 550u2009°C. The estimated crystallite sizes of CPO NCs obtained by XRD (DSh) and Williamson–Hall method (DWh) were found to increase with increasing calcination temperature, ranging from 20 to 43u2009nm. Micrographs of all CPO NCs obtained by scanning electron microscope showed irregularly large particles of flake-like shape, agglomerated and stacked over each other with micrometer size, ranging from 0.146 to 0.406u2009μm. X-ray absorption near-edge spectroscopy and X-ray photoelectron spectroscopy results revealed the presence of Cu+ and Cu2+ cations in CPO NCs. The determined optical band gaps of CPO NCs using ultraviolet–visible spectrophotometer were found to increase from 3.761 to 3.802u2009eV with the increase in calcination temperature. Magnetization measurements of CPO NCs at room temperature using vibrating sample magnetometer revealed a weak ferromagnetic behavior with the enhancement of unsaturated magnetization (M) at 10u2009kOe from 0.268 to 0.467u2009emuu2009g−1, coercive field (Hc) from 215.99 to 362.21u2009Oe, and remanent magnetization (Mr) from 0.0097 to 0.0163u2009emuu2009g−1, suggesting to originate from the superexchange interaction. The cyclic voltammetry and galvanostatic charge–discharge results of all CPO NC electrodes showed pseudocapacitor behavior associated with Faradaic redox reactions. Increasing calcination temperature could result in the decrease of both specific capacitance (Csc) and capacitance retention values. The highest Csc of 297.521u2009Fu2009g−1 at 1u2009Au2009g−1 with a good cycling stability after 1000 cycle test of 94.04% was achieved in CPO5 NC electrodes.n As shown in this figure are asymmetric redox peaks of CPO5, CPO6, CPO7, and CPO8 NCs electrodes measured at a scan rate of 5u2009mVu2009s−1, indicating a pseudocapacitor behavior of these samples. Inset of the figure shows GCD curves of these samples with their specific capacitance (Csc). The highest Csc value of 297.5u2009Fu2009g−1 at 1u2009Au2009g−1 was achieved in a cell with working electrode made of CPO5 NCs obtained by calcination of the NCPO powder at 550u2009°C for 1u2009h.HighlightsCu2P2O7 NCs (20–43u2009nm) were obtained by calcination of the NCPO powder at low temperature.Eg increases from 3.761 to 3.802u2009eV with increasing calcination temperature.Weak ferromagnetic behavior is observed in all Cu2P2O7 NCs due to SE interaction.CV and GCD results of CPO NCs show a pseudocapacitor behavior due to Faradaic reaction.The highest specific capacitance of 297.5u2009Fu2009g−1 at 1u2009Au2009g−1 is achieved in CPO5 NCs.

Influence of Ba substitution, Fe doping and annealing effect on magnetic and optical properties of Sr 0.9 Ba 0.1 Ti 1−x Fe x O 3 nanoparticles prepared by the hydrothermal method

Sr0.9Ba0.1Ti1−xFexO3 (xu2009=u20090, 0.05, 0.10 and 0.15) nanoparticles were synthesized by the hydrothermal method. Influence of Ba substitution, Fe doping and annealing effect on magnetic and optical properties of these samples was studied. X-ray diffraction (XRD) results indicated a cubic perovskite structure with the increase of lattice parameter and crystallite sizes of all samples owing to the substitution with a larger ionic radius of Ba and Fe ions at Sr and Ti sites in the crystal structure, respectively. Ba substitution could result in a pure phase of annealed samples. Magnetization of as-prepared samples measured at room temperature by vibrating sample magnetometer (VSM) revealed a diamagnetic and paramagnetic behavior of undoped and Fe-doped samples, respectively. Interestingly, annealing could significantly affect the magnetic behavior of all samples i.e. undoped sample showed paramagnetic behavior, whereas all Fe-doped samples exhibited ferromagnetic behavior with the enhancement of saturation magnetization (Ms) from 0.28 to 0.78 emu/g owing to the increase of Fe content. Ferromagnetic behavior was suggested to originate from Fe3+−VO−Fe3+ coupling in the crystal structure due to the promotion of oxygen vacancy (VO) as confirmed by the X-ray photoelectron spectroscopy (XPS) results. Moreover, coercivity (Hc) and remanent magnetization (Mr) also increased from 110–442xa0Oe to 0.01–0.15xa0emu/g, respectively. The determined optical band gaps of annealed samples determined by ultraviolet–visible (UV–vis) spectroscopy were found to decrease from 3.3907 to 3.3469xa0eV with increasing Fe content.