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The role of point defects and defect gradients in flash sintering of perovskite oxides
摘要： The present study investigates the impact of point defects and their redistribution on the flash sintering process. Strontium titanate was chosen as a model system for the group of perovskite ceramics. The characteristics of flash sintering of strontium titanate were analyzed with different acceptor dopant concentrations. The onset of flash sintering was found to be dependent on the acceptor dopant concentration, as expected by the increasing conductivity. A gradient in the microstructure was found after flash sintering with larger grain sizes at the negative electrode. TEM-EDS measurements indicated Ti enrichment at the positive electrode for undoped strontium titanate and strong acceptor segregation for doped strontium titanate. In contrast, grain boundaries at the negative electrode were found to be stoichiometric for the undoped case and the acceptor segregation was less obvious for the doped case. Based on these results and the space charge behavior of strontium titanate, we infer that a gradient of the oxygen vacancy concentration is induced by the electric field during flash sintering: at the positive electrode the oxygen vacancy concentration is higher than at the negative electrode. For strontium titanate it is well known that a high oxygen vacancy concentration reduces the space charge and, hence, acceptor segregation, which agrees well with the experimental findings. Overall, the present study highlights the importance of point defect gradients and space charge for flash sintering of strontium titanate, which may be applicable for many other functional ceramics.
关键词： Flash sintering,Space charge,Non-stoichiometry,Strontium titanate,Point defects
更新于2025-09-04 15:30:14
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Sol‐gel synthesis of strontium aluminate phosphor and its TL and OSL properties
摘要： SrAl2O4 monoclinic and Sr12Al14O33 cubic phase nanocrystals were synthesized using sol-gel route and their morphology verified with X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) to confirm the crystallinity of the samples and the crystallites nanoscale. Luminescence emissions were investigated by Optically Stimulated Luminescence (OSL) and Thermoluminescence (TL) methods in samples thermally treated at 1000 °C for 2 hours and irradiated with β particles. TL glow curve was complex with 9 individual peaks, which was analyzed by Tm-Tstop method, general order kinetic theory using Computerized Glow Curve Deconvolution (CGCD). A thermal transfer TL phenomenon was observed when the samples were pre-heated in Tm-Tstop procedure. CW-OSL decays measured at 30 oC have high intensities even in low doses region and curves were deconvoluted using general order kinetic theory suppling two components for low doses and three components for high dose.
关键词： SEM,TL,Strontium aluminate,OSL
更新于2025-09-04 15:30:14
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Semiconductor Heterojunctions for Enhanced Visible Light Photocatalytic H2 Production
摘要： Semiconductor-based heterojunctions have been shown to be effective photocatalytic materials to overcome the drawbacks of low photocatalytic efficiency that results from a high rate of electron?hole recombination and narrow photo-response range. In this paper, we report on the study of heterojunctions made from visible light active, graphitic carbon nitride, g-C3N4), and UV light active, strontium pyroniobate, Sr2Nb2O7. Heterojunctions made from a combination of g-C3N4 and nitrogen-doped Sr2Nb2O7 obtained at different temperatures were also studied to determine the effect of N doping. The photocatalytic performance was evaluated by using photocatalytic hydrogen evolution reaction (HER)from water g under visible light irradiation. It was found that the photocatalytic activities of as prepared heterojunctions are significantly higher than that of individual components under similar conditions. Heterojunction formed from g-C3N4 and N-doped Sr2Nb2O7 at 700oC (CN/SNON-700) showed better performance than heterojunction made from g-C3N4 and Sr2Nb2O7 (CN/SNO). A plausible mechanism for the heterojunction enhanced photocatalytic activity is proposed based on, relative band positions, and photoluminescence data.
关键词： graphitic carbon nitride,visible light photocatalysis,strontium pyroniobate,Semiconductor heterojunctions,hydrogen production
更新于2025-09-04 15:30:14
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Effect of Er3+ on NaSrB glass: thermoluminescence and structural analysis
摘要： The present work reports the investigations on Er3+-doped sodium–strontium–borate glasses for their structural, optical and thermoluminescence (TL) properties. While the amorphous nature of the prepared glasses is confirmed by the powdered X-ray diffraction (XRD), some interesting features were found in the structure and Fourier-transform infrared (FTIR) studies such as the nanocrystallization and the presence of BO3 and BO4 structural units. Some physical parameters such as ion concentration, polaron radius, inter-nuclear distance, and field strength are calculated and analyzed. Optical band gap was found to be sensitive to the concentration of the dopants. TL glow curve exhibits a single peak but it shifts with variation in concentration of Er2O3. Calculation of kinetic parameters show that the prepared glasses exhibit second-order kinetics. The effective atomic number (Zeff) of prepared glasses is also calculated which indicates their suitability for application in radiation dosimetry.
关键词： thermoluminescence,sodium–strontium–borate glasses,optical properties,radiation dosimetry,Er3+-doped,structural analysis
更新于2025-09-04 15:30:14
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Preparation and Characterization of Ba1-xSrxTiO3 by Sol-Gel Method
摘要： Barium strontium titanate (BST) with formula (Ba1-xSrxTiO3) has been synthesized by sol-gel method with different stoichiometric compositions (x = 0.3, 0.4, 0.5, 0.6). The raw materials which used to prepare compounds are (Ba,Sr) acetate as a source (Ba,Sr) and titanate isopropoxide source. The FE-SEM images showed that the particles size reduced from 464 to 13 nm when strontium concentration increased from 0.3 to 0.6. The X-ray diffraction studies have confirmed that Ba0.7Sr0.3TiO3 sample have the tetragonal phase while remaining samples have a cubic phase. The intensity of the major peaks were decreased and shifted toward higher 2θ angles when Sr2+ ions increases.
关键词： Barium strontium titanate,Curie Temperature,Ferroelectric materials,Perovskite structure
更新于2025-09-04 15:30:14