Synthesis and characterization of Sm^3＋-doped CeO2 powders

Sm^3＋-doped Ce02 （denoted as Ce1-xSmxO2） powders with different morphologies were successfully synthesized via a precursor-growth-calcination approach, in which precursor was first synthesized by a hydrothermal method and Ce1-xSmxO2 powders were finally obtained through a calcination process. The products were characterized with X-ray diffractometry（XRD）, field emission scanning electron microscopy（FE-SEM） and fluorescence spectroscopy. The results reveal that the Ce1-xSmxO2 powders obtained by calcining the precursors prepared in the absence and presence of poly（vinyl pyrrolidone） （PVP） exhibit bundle-and sphere-like morphology, respectively. The possible growth process was proposed by preparing a series of intermediate morphologies during the shape evolution of CeO2 based on the SEM image observation. It is also found that the luminescence intensity of bundle-like Ce1-xSmxO2 is enhanced in comparison with that of sphere-like one due to its special morphology.     

Effects of RE^3＋（RE=La,Ce,Pr,Sm,Dy,Ho,Er,and Tm） on the luminescence of Sr2MgSiO5：Eu^2＋ phosphors

Sr2MgSiO5:Eu2+phosphors were synthesized through a high temperature solid state reaction method.The phase and luminescence properties of the samples were characterized by X-ray diffraction(XRD) and a luminescence spectrometer.The effects of RE3+(RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) on the luminescent properties of the samples were studied.The results show that the luminescence spectrum of Sr2MgSiO5:Eu2+ is a broad band composed of two emission peaks,at 460 and at 530 nm under near-ultraviolet excitation.Rare earth ions Re3+(RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) have great influence on the emission of Sr2MgSiO5:Eu2+ phosphors.The La3+ ion in Sr2MgSiO5:Eu2+ phosphors greatly enhances the emission at 460 and 530 nm.     

Eutectic nucleation in Al-7 wt pct Si-Mg casting alloys

The nucleation of eutectic crystals of hypoeutectic Al-7 wt pct Si-Mg casting alloys modified by Ce and Sr was studied by using differential scanning calorimeter (DSC) and scanning electron microscope (SEM). DSC results were applied to calculate the values of activity energy and nucleation work of eutectic nucleation for the alloys. These values were decreased and the eutectic nucleation frequency was increased with the addition of Ce and Sr to the alloys. Moreover, the morphology of eutectic silicon in the modified alloys was partially or fully modified as fine, fibrous or coral, and DSC plots show that the eutectic undercooling of Al-7 wt pct Si-Mg alloys were increased with additions of modified agents. The mechanism of eutectic modification is combined actions of the accelerated nucleation and the restricted growth.     

Synthesis and characterization of LiFePO4／C composite used as lithium storage electrodes

LiFePO4/C composites with good rate capability and high energy density were prepared by adding sugar to the synthetic precursor, A significant improvement in electrode performance was achieved. The resulting carbon contents in the sample 1 and sample 2 are 3.06% and 4.95% (mass fraction), respectively. It is believed that the synthesis of LiFePO4 with sugar added before heating is a good method because the synthesized particles having uniform small size are covered by carbon. The performance of the cathodes was evaluated using coin cells. The samples were characterized by X-ray diffraction and scanning electron microscope observation. The addition of carbon limits the particles size growth and enables high electron conductivity. The LiFePO4/C composites show very good electrochemical performance delivering about 142 mAh/g specific capacity when being cycled at the C/10 rate. The capacity fade upon cycling is very small.     

Preparation and conductivity of nanocrystalline rare earth mixed oxides SmFe1—xCoxO3—δ

Nanocrystalline rare earth mixed oxides SmFe1-xCoxO3-δ were prepared by sol-gel method at 1073K for 2h calcination and characterized by X-ray diffraction(XRD) and scanning electron microscope(SEM).The results show that SmFe1-xCoxO3-δhas the structure of perovskite type.The conductivity of the materials increases with the temperature rising and the maximum conductivity at 1073 K is 2.6 S/cm with the best mole ratio of Fe^3 to Co^3 being 1:4.This kind of oxide is a conductive ceramic material by means of conduction of electron and oxygen anion.     

Nanosized GdVO_4 powders synthesized by sol-gel method using different carboxylic acids

Nanosized GdVO_4 powders were synthesized via a sol-gel method using different carboxylic acids as chelating agent, followed by calcination at 600 ℃ for 3 h.The effect of different carboxylic acids such as citric acid,malic acid, and tartaric acid on the characteristics of the nanosized GdVO_4 powders was investigated. The GdVO_4 powder was also synthesized without carboxylic acid for comparison. The thermal decomposition process of the carboxylate precursors was investigated by thermogravimetric differential thermal analysis(TG-DTA). X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscope(FESEM),transmission electron microscope(TEM), and surface area measurement data were used to confirm the formation of nanocrystalline GdV04 powders. It is found that the synthesis using the carboxylic acid with higher heat of combustion results in the powder with larger crystallite size. The difference in the steric effect of the acids used,which was evaluated by a computational method, also affects the degree of agglomeration of the synthesized powders.     

Microwave synthesis and characterization of new red long afterglow phosphor Sr3Al2O6：Eu

Nanoparticles of red long afterglow phosphor Sr3Al2O6： Eu^2＋ were prepared by microwave irradiation method at a power of 680 W and a processing time of 15 min. The phosphors nanoparticles were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and Fluorescence spectrophotometer techniques. The results reveal that the samples are composed of single Sr3Al2O6 phase. The resultant nanoparticles show small size （80-100 nm） and spherical shape. The excitation and emission spectra indicate that excitation broad band chiefly lies in visible range and the nanoparticles emit much strong light at 612 nm under around 473 nm excitation. And the long afterglow phosphorescence of Sr3Al2O6 doped with Eu^2＋ was observed in the dark with naked eye after the removal of the excitation light. The effect of Eu^2＋ doping concentrations of the samples on the emission intensity is studied systematically. Furthermore, the microwave method requires a very short heating-time and the energy consumption.     

Preparation,morphology and luminescence properties of Gd_2O_2S:Tb with different Gd_2O_3 raw materials

The sulfide fusion method was used to synthesize Gd_2 O_2 S:Tb phosphors using commercial Gd_2 O_3 and freshly prepared Gd_2 O_3, respectively. The freshly prepared Gd_2 O_3 was synthesized from Gd_2 O(GO_3)_2·H_2 O precursor prepared by homogeneous precipitation method.The structure and morphology of the composites were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS). The result shows that the Gd_2 O_2 S:Tb phosphor prepared by commercial Gd2 O3(GOST-A) presents agglomerated particles with average particle size of2.1 μm; however, Gd_2 O_2 S:Tb produced from as-prepared Gd_2 O_3(GOST-B) tends to form regular hexagon particles with the average particle size of 1 μm. Furthermore, Gd3+and Tb3+ contents in GOST-B are higher than that in GOST-A. In addition, fluorescent properties were analyzed by fluorescent spectrophotometer. It is indicated that similar excitation and emission spectra can be obtained from the two phosphors, but the luminescence intensity of GOST-B is higher than that of GOST-A.     

Controlled synthesis and optical properties of Ce~(3+)/Tb~(3+) co-doped BaGdF_5 nanocrystals

Based on a hydrothermal method, the Ce3+/Tb3+ co-doped Ba Gd F5 nanocrystals were synthesized by controlling the introduction concentration of Ba2+ and Gd3+. The samples were characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM) images, photoluminescence(PL) excitation, and emission spectra, as well as the photoluminescence dynamic decay curves. With the increase of the Ba2+ concentration in the synthesis procedure, the positions of diffraction peaks of XRD patterns move toward lower degree, and the case of the samples synthesized with the increase of the Gd3+ concentration is contrary, which consists well with each other. The FE-SEM images suggest that the BaGdF5 nanocrystals are in spherical morphology,and the average diameters decrease with the increase of Ba2+ or Gd3+ concentration. For the 4f–5d transition of Ce3+ is sensitive to the environment of local lattice, the PL excitation and emission spectra of the samples are different. The 4f–4f transition of Tb3+ also presents different optical properties in different host lattices. The variations of the optical properties of Ce3+ and Tb3+ as well as the lifetime of the 5D4+7F5 emission of Tb3+ are also consistent well with each other in the two series of samples.     

Effect of Sn~(4+) content on properties of indium tin oxide nanopowders

Indium tin oxide(ITO)nanopowders were prepared by a modified chemical co-precipitation process.The influence of different SnO2 contents on the decomposition behavior of ITO precursors,and on the phase and morphology of ITO precursors and ITO nanopowders were studied by X-ray diffractometry,transmission electron microscopy and differential thermal and thermogravimetry analysis methods.The TG-DSC curves show that the decomposition process of precursor precipitation is completed when the temperature is close to 600 ℃and the end temperature of decompositionis somewhat lower when the doping amount of SnO2 is increased.The XRD patterns indicate that the solubility limit of Sn4+ relates directly to the calcining temperature. When being calcined at 700℃,a single phase ITO powder with 15%SnO2(mass fraction)can be obtained.But,when the calcining temperature is higher than 800℃,the phase of SnO2 will appear in ITO nanopowders which contain more than 10%SnO2.The particle size of the ITO nanopowders is 15-25 nm.The ITO nanoparticles without Sn have a spherical shape,but their morphology moves towards an irregular shape when being doped with Sn4+.     

Phase composition and luminescent properties of strontium aluminate long persistence phosphor synthesized by combustion synthesis method with different Sr/Al ratios

Strontium aluminate long persistence phos phors are synthesized by combustion method. By control- ling the raw material ratio （Sr/Al）, the effects of phase composition on subsequent spectroscopic properties of phosphors are studied. Results show that the phase com-position changes from strontium-rich phase to aluminum- rich phase with the decrease of Sr/AI： when the rate of Al/Sr changes from 3：1 to 1：1, the main crystal phase of samples is Sr3Al206, and it exhibits the characteristic fluorescence of Eu^3＋ in the lattice of Sr3Al206; when the rate of Al/Sr is between 1：2 and 2：7, phase composition is the mixture of SrAl204 and SrAl4OT, and it emits the characteristic fluorescence of Eu^2＋ in SrAl204 but not in SrAl4OT; when Al/Sr decreases to 1：4 or even 1：12, the main crystal phase of samples transform into SrAl12019, and the characteristic emission peak is about 470 nm, which corresponds to the characteristic emission of Eu2＋ in SrAl12019. At the end of the article, the influence laws of two different synthesis methods on phase composition of samples between high-temperature solid method and combustion method are compared. Compared with the high-temperature solid method, the rule of influence is similar, but the mole ratio of Al/Sr in products is always higher than the initial ratio of the raw material, and com-pounds like Sr4Al14025 are not obtained by combustion method.     

Catalytic reduction of SO2 by CO over CeO2–TiO2 mixed oxides

The structure and catalytic desulfurization characteristics of CeO₂–TiO₂ mixed oxides were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and catalytic activity tests. According to the results, a CeO₂–TiO₂ solid solution is formed when the mole ratio of cerium to titanium n(Ce):n(Ti) is 5:5 or greater, and the most suitable n(Ce):n(Ti) is determined as 7:3, over which the conversion rate of SO₂ and the yield of sulfur at 500 °C reach 93% and 99%, respectively. According to the activity testing curve, Ce_0.7Ti_0.3O₂ (n(Ce):n(Ti)=7:3) without any pretreatment can be gradually activated by reagent gas after about 10 min, and reaches a steady activation status 60 min later. The XPS results of Ce_0.7Ti_0.3O₂ after different time of SO₂+CO reaction show that CeO₂ is the active component that offers the redox couple Ce⁴⁺/Ce³⁺ and the labile oxygen vacancies, and TiO₂ only functions as a catalyst structure stabilizer during the catalytic reaction process. After 48 h of catalytic reaction at 500 °C, Ce_0.7Ti_0.3O₂ still maintains a stable structure without being vulcanized, demonstrating its good anti-sulfur poisoning performance.     

Reinvestigation of the Phase Equilibria in the La2O3-P2O5 System

The phase equilibria between the solid phases in the La₂O₃-P₂O₅ system were reinvestigated with solid state reaction method. The existence of La₃PO₇, La₇P₃O₁₈, LaPO₄, and LaP₃O₉ was confirmed. La₇P₃O₁₈ can form only at ~1200 °C or higher possibly due to kinetic reasons, but it is stable at lower temperatures. On the other hand, three intermediate compounds proposed to exist, La₅PO₁₀, La₄(P₂O₇)₃, and La₂P₄O₁₃ were not obtained in this study. Based on the literature, La₄(P₂O₇)₃ and La₂P₄O₁₃ are considered to be metastable phases, although thermodynamic evidence is still required.     

Effect of H2O and CO2 on the Oxidation Behavior and Durability at High Temperature of ODS-FeCrAl

Cyclic oxidation testing was conducted on alloy MA956 and two different batches of alloy PM2000 at 1,100 and 1,200 °C in different atmospheres rich in O₂, H₂O and CO₂. Compared to 1 h cycles in dry O₂, exposure in air + 10 vol.% H₂O resulted in an increase of the oxidation rate and a decrease of the time to breakaway for all alloys at 1,200 °C, and a faster consumption of Al in the MA956 alloy. One hour cyclic testing in 49.25 % CO₂ + 50 % H₂O + 0.75 % O₂ had a smaller effect on the oxidation rate but led to increased formation of voids in alloy MA956, which had an impact on the alloy creep resistance. At 1,100 °C, exposure in 50 % CO₂ + 50 % H₂O resulted in significant oxide spallation compared with oxidation in air, but this was not the case when 0.75 % O₂ was added to the CO₂/H₂O mixture as a buffer. The control of impurity levels drastically improved the oxidation resistance of PM2000.     

Subsolidus Phase Relations of the CoO<Subscript>x</Subscript>-CuO-SrO System

The subsolidus phase relations of the CoO_x-CuO-SrO system were investigated in air. The samples were equilibrated at 900 °C. The pseudo-ternary section contains three stoichiometric binary oxide phases (Sr₂CuO₃, SrCuO₂ and Sr₁₄Cu₂₄O_41?δ) and a binary oxide solid solution: Sr_6+xCo₅O_15+δ (0 ≤ x ≤ 0.36). Two binary phases extend into the ternary system forming solid solutions, i.e., Sr₁₄Cu_24?xCo_xO_41?δ (0 ≤ x ≤ 5) and Sr_6+xCo_5?yCu_yO_15+δ (0 ≤ x ≤ 0.36, 0 ≤ y ≤ 1.0). The Sr_6+xCo₅O_15+δ solid solution was found to undergo a phase separation into a mixture of Sr₆Co₅O_15?δ and Sr₁₄Co₁₁O₃₃ upon annealing at 600 °C. This transformation is reversible.     

Phase Stability of Ce-Modified La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> Coatings and Chemical Compatibility with YSZ

Ce-modified La₂Zr₂O₇ powders, i.e., La₂Zr₂O₇ (LZ), La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3), and La₂(Zr_0.3Ce_0.7)₂O₇ (LZ3C7), were used to produce thermal barrier coatings by atmospheric plasma spray process. The chemical compatibility of the CeO₂-doped La₂Zr₂O₇ with the traditional YSZ was investigated in LZ-YSZ powder mixtures and LZ-YSZ bilayer coatings by x-ray diffraction and scanning electron microscope. The powder mixtures and coatings were aged at 1200 and 1300 °C for 100 h. The results showed that LZ and LZ7C3 presented single pyrochlore structure after the heat treatments at both 1200 and 1300 °C. For LZ3C7, however, fluorite structure was observed at 1300 °C, indicating a poor phase stability of LZ3C7 at the elevated temperature. The results further showed that La₂(Zr_0.3Ce_0.7)₂O₇ reacted with YSZ in the bilayer ceramic coatings due to the diffusion of cerium, zirconium, and yttrium. While for La₂Zr₂O₇(LZ) and La₂(Zr_0.7Ce_0.3)₂O₇, a better chemical compatibility with YSZ was shown.     

Partial Phase Diagram of BaO-TeO2 System

The partial phase diagram of BaO-TeO₂ system was experimentally determined in the composition range 50-100 mol% TeO₂ employing differential thermal analysis and x-ray diffraction techniques. Only three intermediate compounds BaTeO₃, BaTe₂O₅ and BaTe₄O₉ melting congruently at 1000, 658 and 599 °C respectively, were observed. Each of these three line compounds exhibited two crystallographic phase transitions with corresponding transition temperatures at 802 and 982 °C, 608 and 648 °C, 576 and 591 °C respectively. The system exhibited three eutectic reactions i.e. between BaTeO₃ and BaTe₂O₅ at 602 °C and 60 mol% TeO₂ [L = BaTeO₃(s) + BaTe₂O₅(s)], BaTe₂O₅ and BaTe₄O₉ at 596 °C and 76 mol% TeO₂ [L = BaTe₂O₅(s) + BaTe₄O₉(s)] and another one between BaTe₄O₉ and TeO₂ at 592 °C and 84.5 mol% TeO₂ [L = BaTe₄O₉(s) + TeO₂(s)].     

Synthesis and photoluminescence of Eu by co-doping Eu and Cl in Sr2P2O7 under air atmosphere

A novel phosphor Sr₂P₂O₇ co-doped with europium ion and chlorine ion was firstly synthesized by solid state reaction under air atmosphere. Its properties were systematically analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectra. The introduction of chlorine into the system was helpful and necessary to Eu³⁺ substitute Sr²⁺ site and subsequently to reduce Eu³⁺ to Eu²⁺, XPS results confirmed that some amount of Eu³⁺ ions could be reduced to Eu²⁺ ions under air atmosphere at high temperature. The reduction tendency of Eu³⁺ depends not only on the doping Cl⁻ content, but also on the sintering temperature and time. Photoluminescence spectra also revealed that europium ions were present in divalent as well as trivalent oxidation states, the emission peak at 415 nm is ascribed to the typical 5d-4f transition of Eu²⁺, 592 nm and 613 nm assigned to the characteristic transitions of ⁵D₀-⁷F_1,2 of Eu³⁺. Such abnormal reduction was attributed to the electronegative defects formed by nonequivalent substitution of Eu³⁺ on the Sr²⁺ sites in the investigated phosphors.