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31.
White-light-emitting phosphors based on phosphate host matrix, KSrPO_4 doped with Dy~(3+), were prepared by solid state reaction and their VUV luminescent properties were firstly investigated. The excitation band peaking at 125-153 nm corresponding to the absorption of PO_4~(3-) group exhibits very strong absorption. The phosphors emit warm-white luminescence under vacuum ultraviolet excitation of 147 nm, which consists of three main emission peaks located at 475, 570 and 662 nm, respectively.According to the luminescence and color chromaticity of the optimal sample KSrPO_4:1 mol%Dy~(3+),1.3 mol%Li~+, it can be a potential candidate for mercury-free fluorescent lamps. 相似文献
32.
Yang-huan ZHANG Ya-qin LI Hong-wei SHANG Zhong-hui HOU Yan QI Dong-liang ZHAO 《中国有色金属学会会刊》2018,28(4):711-721
The La-Mg-Ni-Co-Al-based AB2-type La0.8–xCe0.2YxMgNi3.4Co0.4Al0.1 (x=0, 0.05, 0.1, 0.15, 0.2) alloys were prepared via melt spinning. The analyses of the X-ray diffraction (XRD) and scanning electron microscopy (SEM) proved that the experimental alloys contain the main phase LaMgNi4 and the second phase LaNi5. Increasing Y content and spinning rate lead to grain refinement and obvious change of the phase abundance without changing phase composition. Y substitution for La and melt spinning make the life-span of the alloys improved remarkably, which is attributed to the improvement of anti-oxidation, anti-pulverization and anti-corrosion abilities. In addition, the discharge capacity visibly decreases with increasing the Y content, while it firstly increases and then decreases with increasing spinning rate. The electrochemical kinetics increases to the optimum performance and then reduces with increasing spinning rate. Moreover, all the alloys achieve to the highest discharge capacities just at the initial cycle without activation. 相似文献
33.
《Ceramics International》2020,46(4):4610-4618
Series of SrNbxYxFe12-2xO19 (0.00 ≤ x ≤ 0.05) hexaferrites (HFs) were fabricated via citrate sol-gel approach. Structural and magneto-optical properties of ensembles were investigated in detail. The structural and morphological analyses revealed the formation of M-type Sr hexaferrite nanoparticles. Diffuse reflectance data were registered to estimate the direct optical energy band gaps (Eg) in a range of 1.77 eV-1.87 eV. Room temperature (RT, 300 K) and low temperature (10 K) magnetic hysteresis curves were recorded by enforcing applied dc magnetic field up to ±70 kOe. Magnetic parameters were significantly tuned due to coordination of Nb3+ and Y3+ rare earth ions. Specified magnetic data reveal the strong ferromagnetic characteristics of pristine SrFe12O19 and co-doped HFs with Nb3+ and Y3+ ions at both temperatures. RT squareness ratio (SQR) has an exception only for pristine sample as 0.506, which is in the margin of theoretical limit assigning the single-domain nature with uniaxial anisotropy. However, all co-doped samples have SQR = 0.288–0.485 values that are smaller than theoretical limit of 0.50, implying multi-domain nature at RT and at 10 K. Co-doped ions cause lowering in super-exchange interactions between different sites and resulting the decrements of intrinsic magneto-crystalline anisotropy and coercivity fields. The specified magnetic characteristics make our fabricated SrNbxYxFe12-2xO19 (0.00 ≤ x ≤ 0.05) HFs good candidates as permanent magnets applications and high-density recording media. 相似文献
34.
《Ceramics International》2020,46(10):16196-16209
In this study, pure cobalt ferrite (CoFe2O4) nanoparticles and europium doped CoFe2O4 (CoFe2−xEuxO4; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe3+) ions by trivalent rare earth europium (RE-Eu3+) ions on the microstructure, optical and magnetic properties of the produced CoFe2O4 nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu2O3 phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ1 and υ2) and tetrahedral A-site (υ3) around 415 cm−1, 470 cm−1 and 600 cm−1 respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu3+ ions within CoFe2O4 host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu3+ added to CoFe2O4 in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe2−xEuxO4, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe2O4 have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu3+ in CoFe2O4 lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe2O4 samples. Substitution of Fe3+ ions in CoFe2O4 nanoparticles with RE-Eu3+ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications. 相似文献
35.
《Ceramics International》2020,46(9):13170-13179
The present work reports the structural, thermal, spectral, optical and surface analysis of rare earth metal ion (Gd3+) doped mixed Zn–Mg nano-spinel ferrites. The samples of Gd3+ doped Zn–Mg nano ferrites with equi-amount chemical composition i.e. Zn0.5Mg0.5Fe2-xGdxO4 (0.00 ≤ x ≤ 0.10 in step of 0.02) were prepared by self-ignited sol-gel route. The variance in the thermal behaviour and spinel phase development with weight loss percentage in the prepared samples was investigated by TG-DTA technique. The powder X-ray diffraction (P-XRD) patterns ensured the nanocrystalline mono-phasic formation and spinel-cubic structure of all the samples. The trend of increment in lattice constant (a) and decrement in crystallite (t) size was observed with the doping of Gd3+ ions. The appearance of two requisite vibrational stretching modes was affirmed by the FT-IR spectral studies. The UV–Vis optical analysis displayed the augmentation in absorbance and drastic decrement in energy band gap value (1.96 eV–1.83 eV) with Gd3+ doping. The photo-luminescent (PL) studies revealed the broad near band-edge emission in visible wavelength range (523 nm–528 nm) for all the samples. The surface parameters investigation was undertaken with the help of BET isotherms recorded by the N2-physisorption and BJH model. The various surface parameters such as BET surface area, volume and radius of the pores, distribution of the pore sizes etc were construed from the BET data. The enhancement in these surface parameters via Gd3+ doping was noted for all the samples. The outcomes of the present work reflects the influential doping of Gd3+ ions in Zn–Mg nano ferrites, which can be implementable for bio-applications as thermal seeds in magnetic hyperthermia or as contrast enhancer in medical MRI imaging. 相似文献
36.
《Journal of the European Ceramic Society》2020,40(15):5067-5075
The influence of Y2O3 addition on the microstructure, thermo-mechanical properties and oxidation resistance of carbon fibre reinforced ZrB2/SiC composites was investigated. Y2O3 reacted with oxide impurities present on the surface of ZrB2 and SiC grains and formed a liquid phase, effectively lowering the sintering temperature and allowing to reach full density at 1900 °C. The presence of a carbon source (fibres) led to additional reactions which resulted in the formation of new secondary phases such as yttrium boro-carbides. Mechanical properties were significantly enhanced compared to the un-doped composite. Further tests at high temperatures resulted in strength increase up to 700 MPa at 1500 °C which was attributed to stress relaxation. Oxidation tests carried out at 1500 °C and 1650 °C in air showed that the presence of the Y-based secondary phases enhanced the growth of ZrO2 grains, but offered limited protection to oxygen due to the lower availability of surficial SiO2 formed from SiC. 相似文献
37.
38.
《Ceramics International》2020,46(6):7711-7718
Phase equilibria in the CaO–SiO2–La2O3–Nb2O5 system are important for the utilization of Nb and Rare Earth resources. In the present work, phase equilibria in the CaO–SiO2–La2O3–Nb2O5 system at 1473 K in H2 (pO2 = 10−15.47atm) were studied by the equilibrium experiment. SEM, EDS and XRD analysis were employed to identify the equilibrium phase relations. The isothermal spatial phase diagram of the CaO–SiO2–La2O3–Nb2O5 system and the isothermal section of CaO–SiO2–Nb2O5-(5%, 10%) La2O3 pseudo-ternary system were constructed. A total of eight equilibrium phase regions were determined, including Liquid + CaNb2O6+CaSiO3+LaNbO4 region, Liquid + CaNb2O6+SiO2+CaSiO3 region, Liquid + CaSiO3+CaNb2O6 region, Liquid + CaSiO3+SiO2 region, Liquid + CaNb2O6+SiO2 region, Liquid + CaSiO3 region, Liquid + SiO2 region and Liquid + CaNb2O6 region. Additionally, the influence of pO2 on equilibrium composition and temperature was also investigated considering its significant effect on phase equilibria in the slag system with variable valence elements. The results indicated that higher external pO2 can increase the equilibrium O content in a slag system, while higher equilibrium temperature corresponds to higher equilibrium pO2. Besides, the relationship between phase equilibria shown in the traditional slag system and in the related generalized alloy system was also revealed. The present experimental data can help further study on Nb-bearing and RE-bearing slag systems, and the theoretical conclusions will help the development of thermodynamic models. 相似文献
39.
O.N. Kondrateva G.E. Nikiforova A.V. Tyurin M.A. Ryumin V.M. Gurevich A.P. Kritskaya K.S. Gavrichev 《Ceramics International》2018,44(15):18103-18107
The heat capacity of ytterbium orthovanadate was first measured by adiabatic calorimetry in the temperature range T?=?12.28–344.06?K. No obvious anomalies were observed on the curve obtained. The values of standard thermodynamic functions in the temperature range T?=?0–400 K were calculated. Based on low-temperature calorimetry data obtained, previously published data on the high-temperature heat capacity of ytterbium orthovanadate were corrected. The anomalous contribution to heat capacity for YbVO4 was compared with the data known for YbPO4. 相似文献
40.
Xiaojun Wang Jianjun Xie Zhengjuan Wang Guohong Zhou Ying Shi Shiwei Wang Xiaojian Mao 《Ceramics International》2018,44(8):9514-9518
Transparent Y2Ti2O7 ceramics with excess Y content were fabricated by solid state reactive sintering in vacuum using Y2O3 and TiO2 powders as the starting materials. Phase composition, microstructure, density and in-line transmittance of the Y2Ti2O7 ceramics were investigated. The detailed results indicated that as Y content increased, the density and in-line transmittance increased at first and then decreased. And the highest in-line transmittance of Y2Ti2O7 ceramics is 49.9% at 1100?nm when the excess amount of Y to Ti is 2%. The effect of Y content on densification process of Y2Ti2O7 ceramics was discussed based on an assumption that oxygen vacancy defects were the dominated defects. 相似文献