[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The serious photocorrosion of silver phosphate (Ag 3 PO 4 ) has limited its practical applications. In this work, we propose a strategy to suppress its photocorrosion by the construction of a Z-Scheme photocatalytic system, which composed of reduced graphene oxide-enwrapped Ag 3 PO 4 (Ag 3 PO 4 @RGO) and La,Cr-codoped SrTiO 3 (La,Cr:SrTiO 3 ). Dramatically, this system shows superior anti-photocorrosion and photocatalytic performances in degradation of both RhB and 2,4-DNP. Especially for RhB, it can be completely degraded after only 5 min under intense sunlight irradiation. The improved photoactivity and anti-photocorrosion of Ag 3 PO 4 @RGO@La,Cr:SrTiO 3 can be attributed to the following: (i) The sufficient interfacial contact between Ag 3 PO 4 and RGO is favorable to transfer the carriers and lengthen the lifetime of it; (ii) the package of Ag 3 PO 4 with RGO could work as a sheltering layer to protect Ag 3 PO 4 from photocorrosion. (iii) The aggregation of photogenerated holes in the VB of Ag 3 PO 4 makes it a rich-hole region due to Z-Scheme electrons transport mechanism, which can protect Ag 3 PO 4 from the photo-reduction. This strategy provides a new thought of protecting photosensitive semiconductor from photocorrosion and could regard as an efficient application method for environmental cleaning under natural sunlight irradiation. Furthermore, it even could be extended to outdoor or indoor air cleaning in the future.

Silver phosphate-based Z-Scheme photocatalytic system with superior sunlight photocatalytic activities and anti-photocorrosion performance

Highly efficient microwave-assisted Fenton degradation bisphenol A using iron oxide modified double perovskite intercalated montmorillonite composite nanomaterial as catalyst.

M-type barium hexaferrite Ba 0.7 La 0.3 Fe 11.7 Co 0.3 O 19 (BaLCM) powder, synthesized using sol gel auto combustion method, heat treated at 700, 900, 1100 and 1200 °C. X ray diffraction (XRD) powder patterns of heat treated samples show the formation of pure phase of M-type hexaferrite after 700 °C. Thermo gravimetric analysis (TGA) reveals that the weight loss of BaLCM becomes constant after 680 °C. The presence of two prominent peaks, at 432 cm −1 and 586 cm −1 in Fourier Transform Infrared Spectroscopy (FT-IR) spectra, gives the idea of formation of M-type hexaferrites. The M – H curve obtained from Vibrating Sample Magnetometer (VSM) were used to calculate saturation magnetization ( M S ), retentivity ( M r ), squareness ration (SR) and coercivity (H c ). The maximum value of coercivity (5602 Oe) is found at 900 °C. The band gap dependency on temperature was studied using UV–vis NIR spectroscopy. The dielectric constant has been found to be high at low frequency but it decreases with increase in frequency. Such kind of dielectric behavior is explained on the basis of Koop׳s phenomenological theory and Maxwell Wagner theory.

Effect of calcination temperature on microstructure, dielectric, magnetic and optical properties of Ba0.7La0.3Fe11.7Co0.3O19 hexaferrites

Effect of lattice strain on structural and magnetic properties of Ca substituted barium hexaferrite

Polycrystalline SrSnO3 compounds doped with 1, 3 and 5% of Cr was synthesized by simple chemical precipitation method and the effect of doping on structural, optical and magnetic properties was investigated. Powder X-ray diffraction analysis reveals the orthorhombic structure of pure and Cr doped SrSnO3 compounds. The appearance of metal oxide vibrations were investigated by Fourier transform infra red spectroscopy analysis. Presence of active Raman modes, Sr–O and Sn–O band vibrations were examined by Raman spectral analysis. The high degree of agglomeration in pure SrSnO3 sample and formation of rod like shape of particulate system in all the Cr doped samples was identified by Electron microscopy techniques. X-ray photoelectron spectroscopy analysis discloses the oxidation states of elements and presence of oxygen vacancy in the compounds. The intriguing violet–blue emission behavior of pure and Cr doped compounds due to interaction between O 2p state and Sn 5s energy levels was observed by photoluminescence spectral studies. The magnetization studies exhibit the diamagnetic property of pure SrSnO3 compound and doping of Cr3+ in Sr–Sn–O lattice drives the carrier induced exchange interactions which results ferromagnetic phase transition in all the Cr doped compounds. From the present investigation, tunability of dia to ferromagnetism with respect to the dopant concentration (Cr3+) in SrSnO3 system at room temperature leads the material for fabrication of magneto-optical and electronic devices.

Room temperature ferromagnetism in Cr doped SrSnO3 perovskite system

Synthesis of magnetically ordered barium hexaferrite powders and the adjustment of magnetic properties for perpendicular magnetic recording media are realized through substitution of divalent cation (Ca) in the BaFe12O19 system. The Ca2+ substituted Ba1−xCaxFe12O19 (where x = 0.05, 0.1, 0.15 and 0.2) compounds have been prepared through solid state reaction technique. The powder X-ray diffraction analysis reveals that all the prepared compounds crystallized in magnetoplumbite hexagonal structure and the flat hexagonal platelet morphology of the crystallites was identified through scanning electron microscopy. The formation of magnetoplumbite structured Ba1−xCaxFe12O19 system due to mechanical activation was supported by micro-Raman measurements. Both pure and Ca substituted BaFe12O19 compounds exhibit sharp intense peaks which reveals defect free environment in the crystal lattice. From the room temperature magnetization studies, it was observed that the saturation magnetization (MS) and remanent magnetization (MR) values drastically decreases for the Ba0.95Ca0.05Fe12O19 compound which may be due to the existence of spin canting effect and leads to the reduction of super exchange fields. The increase in MS and MR values for the Ba0.9Ca0.1Fe12O19 and Ba0.85Ca0.15Fe12O19 compounds could be attributed to the enhanced hyperfine fields at 12k and 2b sites due to the strengthening of Fe3+–O–Fe3+ super exchange interactions. A large reduction in the coercivity value from 3,090 to 1,548 Gauss may be attributed to the fall in magneto crystalline anisotropy. The high temperature magnetization studies infer that while increasing substitution level of Ca in the BaFe12O19 system results in decreasing trend in Curie temperature. The room temperature dielectric measurement shows that the incorporation of Ca2+ in the BaFe12O19 system results with increase in the dielectric constant and this case substantiates the space charge polarization. The magnetically ordered BaFe particulate having higher saturation and low coercivity values with superior magnetic and dielectric behaviour exhibiting the possibility for future high-recording-density storage products.

Effect of Divalent Cation Substitution in the Magnetoplumbite Structured Bafe12o19 System

The carrier doped ferromagnetism in SrTiO3 compounds has been investigated for the importance in the field of multiferroics and spintronics. Polycrystalline pure and Cr doped SrTiO3 compounds were synthesized by glycol assisted sol–gel method. Powder X-ray diffraction (XRD) studies reveal the simple cubic perovskite structure of all the prepared compounds. The grain size and lattice strain of the compounds were estimated from the powder XRD pattern which evidences the incorporation of Cr in SrTiO3 system. The local order and disorder parameter of the compounds was investigated by laser Raman spectroscopy. The change in particles to rod like surface morphology while increasing Cr doping concentration was examined by scanning electron microscope and transmission electron microscopy. The enhancement of oxygen vacancy while increasing Cr doping concentration in SrTiO3 system and reduction in Ti4+ to Ti3+ states was identified by X-ray photoelectron spectroscopy. The UV–Vis absorption spectra evidence the distinctive shift of absorption edge exclusively for Cr doped SrTiO3 compounds. Photoluminescence (PL) spectra of the compounds reveal defective states and decrease in PL intensity due to the influence of Cr in SrTiO3. Electron paramagnetic resonance analysis of Cr doped compounds reveals the paramagnetic nature of the dopants. The magnetization studies of all the prepared compounds emphasis carrier mediated diamagnetic to ferromagnetic phase transition in due with the presence of carriers induced by Cr. It is also evident that the highest dopant concentration of Cr in SrTiO3 system exhibits reversal ferromagnetism. The enhancement of magnetization and ferromagnetic ordering has been understood in terms of carrier-mediated Ruderman–Kittel–Kasuya–Yosida interaction theory. The present work also demonstrates the influence of surface morphology on the occurrence of ferromagnetism in Cr doped SrTiO3 compounds.

Carrier mediated ferromagnetism in Cr doped SrTiO 3 compounds

Conventional synthesis and characterization of cubically ordered La2FeMnO6 double perovskite compound

Ferromagnetism induced Yb (1, 3 %) doped SrTiO3 compounds were synthesized by glycol assisted citrate sol–gel method. The cubic perovskite structure of the prepared compounds was confirmed by powder X-ray diffraction and laser Raman spectra analysis. Surface morphology of the prepared compounds was analyzed by scanning electron microscopy and transmission electron microscopy. Oxidation states with functionalization of elements were identified with X-ray photoelectron spectroscopy. The interesting optical behavior was observed for Yb doped samples, which shows violet–blue emissions in photoluminescence spectra due to interface trapping and Sr defects. The magnetization studies demonstrate that pure SrTiO3 exhibits characteristic diamagnetism at room temperature and the addition of Yb3+ in Sr2+ site drives the carrier induced exchange interactions which results the ferromagnetic behavior. Hence the occurrence of tunable diamagnetic to ferromagnetic and reversal ferromagnetic transition with respect to the concentration of dopant at room temperature was identified. From the present investigation, it was observed that the doping of Yb in SrTiO3 results with new kind of multifunctional material for fabrication of magneto-optical and electronic devices.

V. Anbarasu

Papers

Room temperature ferromagnetism in Cr doped SrSnO3 perovskite system

Effect of Divalent Cation Substitution in the Magnetoplumbite Structured Bafe12o19 System

Carrier mediated ferromagnetism in Cr doped SrTiO 3 compounds

Conventional synthesis and characterization of cubically ordered La2FeMnO6 double perovskite compound

Carrier induced ferromagnetism in Yb doped SrTiO3 perovskite system