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Nano-BaTiO3 phase transition behavior in coated BaTiO3-based dielectric ceramics
摘要： In this work, the phase structure of BaTiO3 nanopowders produced by the alkoxide-hydroxide and the hydrothermal method, respectively, was systemically investigated. BaTiO3 nanopowders with cubic phase produced by the alkoxide-hydroxide method could transform to tetragonal phase when heated to about 1100oC. Cubic to tetragonal phase transformation behavior of BaTiO3 nanopowders coated with 0.3BZT-0.7BT or 0.03Nb2O5-0.01Co2O3 was studied. The internal stress within core-shell structure was proposed to explain the BaTiO3 phase transformation behaviors. The mismatch of thermal expansion coefficient between core and shell plays a crucial role in cubic to tetragonal phase transformation of BaTiO3. By tuning the composition of shell and the ratio of the shell to the core, the cubic BaTiO3 core can transform to tetragonal phase successfully after sintering at 1100oC in BaTiO3 based ceramics with core-shell structure and it is mainly resulted by the reduced internal stress between the shell and core.
关键词： Phase transitions,BaTiO3 nanopowders,Internal stress.,Core-shell structure
更新于2025-09-23 15:23:52
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Fabrication of fine-grained undoped Y2O3 transparent ceramic using nitrate pyrogenation synthesized nanopowders
摘要： Y2O3 ceramic is a promising optical material for mid-infrared (IR) windows and domes. Improvements in the mechanical and thermal performance of this material have become urgent if it is to perform adequately under extreme conditions. Herein, Y2O3 nanopowders were produced through the nitrate pyrogenation method. The final Y2O3 transparent ceramics were fabricated with a hybrid sintering method combining low temperature presintering and a subsequent hot isostatic pressing (HIP) treatment. The synthesis of nanopowders and the fabrication of the final ceramic products were investigated in detail. The Y2O3 ceramic sample that was presintered at 1350 °C provided the optimum microstructure for HIP treatment and resulted in an average grain size of 0.5 μm. Owing to the reduced grain size, the flexure strength and Vickers hardness of the sample were improved to 180 MPa and 8.4 GPa, respectively. Furthermore, the achieved pure Y2O3 ceramic demonstrated an excellent thermal conductivity at high temperature.
关键词： Nanopowders,Y2O3,Nitrate pyrogenation,Fine-grained transparent ceramic
更新于2025-09-23 15:23:52
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Europium and terbium lanthanide ions co-doping in TiO2 photoanode to synchronously improve light-harvesting and open-circuit voltage for high-efficiency dye-sensitized solar cells
摘要： In this study, we explore the effects on the incorporation of europium (Eu3+) and terbium (Tb3+) rare-earth ions into titanium dioxide (TiO2) photoanodes in dye-sensitized solar cells (DSSCs). X-ray photoelectron spectroscopy (XPS) studies affirm that the Eu3+ ions are arranged at the cationic locales of Ti4+ in the matrix whereas the site inhabitance was remunerated by Tb3+ ions, supporting that the anatase phase stays unaltered without generating any new deformities. Additionally, the Eu3+ ions decidedly changed the conduction band minimum of TiO2, actually, Tb3+ ions contrarily conversion because of various vacant trap states in the band gap. Besides, the photoinduced electron transfer estimations show an efficient interfacial charge transfer for co-doped TiO2 (kET = 3.1 ns) contrasted with the bare TiO2 (2.6 ns). DSSCs based on Eu3+/Tb3+ co-doped TiO2 display higher efficiency (9.11%) than those for the bare TiO2 (7.20%) and the exclusively Eu3+ (8.01%) or Tb3+ (7.10%) doped samples, which is ascribed to the joined impact of a faster electron transportation and longer electron lifetime in the co-doped TiO2 film. This work may open another approach to further improve the performance of DSSCs by Eu3+/Tb3+ co-doping technique, advancing the development of DSSCs toward commercial applications.
关键词： Co-doping process,Europium (Eu3+)/terbium (Tb3+) lanthanide ions,Stability,Photoanodes,DSSCs,Titanium dioxide (TiO2) nanopowders
更新于2025-09-23 15:21:01
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Low-temperature synthesis and characterisation of its photocatalytic properties of BiNbO<SUB align="right">4 by combustion method using polyvinyl alcohol
摘要： BiNbO4 nanopowders were synthesised by polyvinyl alcohol sol-gel combustion method using freshly starting material Nb2O5. nH2O. The prepared samples were characterised by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and thermal gravimetric and differential thermal analysis. The orthorhombic single phase calcined at 750°C for 2 h in the air was thoroughly studied with the highest photocatalytic properties in 25 nm average size. Methyl orange was used to evaluate the photocatalytic properties of BiNbO4 under the visible light irradiation which was degraded by 98%. The regeneration ability of the catalyst was reduced by only 1.65% from 98.85% to 97.20% after using four-times without recovery.
关键词： polyvinyl alcohol,BiNbO4 nanopowders,methylene orange degradation,combustion method
更新于2025-09-19 17:15:36
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Ammonium oxalate-assisted synthesis of Gd2O3 nanopowders
摘要： The impacts of co-precipitation reaction temperature and duration, as well as calcination temperature and duration, on the particle morphology and properties of gadolinia (Gd2O3) nanopowders were investigated. Thermogravimetric curve of thermally treated gadolinium oxalate (Gd2(C2O4)3) showed that pure stable cubic phase Gd2O3 nanopowders could be obtained by calcining at 640 °C and higher. This finding was also supported by results obtained from Fourier Transform Infrared Spectrometry (FTIR) and Raman spectrometry. This study also shows that uniform spherules of Gd2O3 nanopowders could be obtained under controlled synthesis conditions. However, with an increase in both the co-precipitation reaction temperature and duration, the extent of agglomeration of Gd2O3 nanopowders increased, as observed under a Field Emission Scanning Electron Microscope (FESEM). The FESEM images and X-ray Diffraction (XRD) patterns also revealed accelerated grain growth and increased average crystallite size at high calcination temperatures and holding times. It was determined that the most favourable Gd2O3 particle morphology was achieved when Gd2(C2O4)3 was co-precipitated at 40 °C, then thermally degraded at 650°C, for 1 h and 4 h, respectively. Estimated Scherrer’s average crystallite size of the resulting Gd2O3 nanopowders was 16.54 nm, which was further affirmed with the transmission electron microscope (TEM) image, where crystallite sizes of 3 to 27.5 nm were observed in the Gd2O3 sample. This specimen also demonstrated a considerably large specific surface area of 9.16 m2/g, as measured using a Brunauer–Emmett–Teller (BET) analyser.
关键词： Ammonium oxalate,Gadolinium oxide,Nanopowders,Co-precipitation,Gadolinia
更新于2025-09-19 17:15:36
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Production of Polycrystalline Materials by Sintering of Nanodispersed Diamond Nanopowders at High Pressure. Review
摘要： The investigations dealing with the problems of forming polycrystalline materials with a high level of physical-and-mechanical properties using the method of diamond powder sintering at high pressure have been considered. The compacting mechanism of diamond nanopowders of different genesis under exposure to high pressure and high temperature is described, special features of pore structure formations are considered, and the critical role of the specified factor in sintering is shown. The need of degassing and modification of the diamond particle surface during the preparation for sintering is noted. The effectiveness of tungsten and its compounds is shown as an activating addition for producing wear-resistant thermostable diamond nanocomposites.
关键词： high pressure,nanopowders of tungsten and its compounds,diamond nanopowders,diamond nanocomposites,sintering
更新于2025-09-10 09:29:36
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Physical properties of fluorides barium and calcium nanopowders produced by the pulsed electron beam evaporation method
摘要： The mesoporous nanocrystal powders BaF2 and CaF2 with a specific surface up to 34.8 and 88.7 sq.m/g, respectively, are produced by the pulsed electron beam evaporation method in vacuum. The influence of thermal annealing of nanoparticles on air in the range of temperature from 200 to 900°C on the size, morphology of particles and change of their magnetic and luminescent properties investigated have been investigared. The essential stoichiometric impurity (overage of metals) and significant growth in a specific surface of nanopowders (NP) BaF2 and CaF2 after annealing at the temperature of 200°C have been detected. It is established that the synthesized NP BaF2 is a paramagnetic while initial material in the bulk state is diamagnetic. After annealing at 900°C appears the small ferromagnetic contribution at NP BaF2. Produced NP CaF2 showed ferromagnetic behavior. In literature there is no information about the ferromagnetism of CaF2. Appearance of the ferromagnetic response can be explained with formation of structural and radiation defects (F-centers, etc.). The analysis of PCL and magnetization curves of samples BaF2 and CaF2 allows drawing conclusions about their connection.
关键词： CaF2,pulsed electron beam evaporation,magnetic properties,luminescent properties,nanopowders,BaF2
更新于2025-09-10 09:29:36
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Structure Analysis and Ferroelectric Response of Bi <sub/>0.5</sub> Na <sub/>0.5</sub> TiO <sub/>3</sub> Nanopowder Synthesized by Sol–Gel Method
摘要： In this work, bismuth sodium titanate, Bi0(cid:2)5 ± xNa0(cid:2)5 ± y TiO3 (BNT, x(cid:3) y = ?0(cid:2)05–0.08) nanopowders were produced using the low-temperature sol–gel technique. The effects of de?cient and excess amounts of Bi and Na on BNT structure were systemically examined through X-ray powder diffraction (XRD), energy dispersive analysis (EDS) and scanning electron microscope (SEM). The optimized composition of the BNT nanopowder was pelletized and sintered at different temperatures (950 (cid:3)C–1150 (cid:3)C). Highly dense ceramics possessing pure perovskite phase was observed for the sample sintered at an optimum sintering temperature (1100 (cid:3)C). The ferroelectric properties were found to increase with an increase in sintering temperature up to 1100 (cid:3)C and then decrease. This study justi?es that Bi and Na non-stoichiometry (proper excess), processing and sintering temperatures play important role in the successful synthesis of BNT ceramics.
关键词： Nanopowders,Sol–Gel,Ferroelectric,Calcination Temperature
更新于2025-09-09 09:28:46