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1.
Feng Ye Chunfeng Liu Limeng Liu Yu Zhou Qingchang Meng 《Journal of the American Ceramic Society》2008,91(3):1022-1026
Sc3 + and dual Sc3+ –Lu3+ -doped α-SiAlON compositions were sintered by hot pressing, and the formation behavior, microstructure, and mechanical properties were assessed. It was found that the small cation Sc3+ could not be accommodated into the α-SiAlON structure alone. The addition of Lu2 O3 in the composition induces the Sc3+ cation to enter the α-SiAlON structure, and leads to the production of α-SiAlON with an elongated-grain microstructure. Transmission electron microscopy analysis shows that α-SiAlON grains always contain an α-Si3 N4 core, implicating heterogeneous nucleation to be in present in a mixed lutetium/scandium-doped α-SiAlON system. 相似文献
2.
Qiwei Chen Ying Shi Liqiong An Jiyang Chen Jianlin Shi 《Journal of the American Ceramic Society》2006,89(6):2038-2042
A novel co-precipitation process was adopted for the preparation of highly sinterable europium-doped lutetia powders using ammonium hydroxide (NH3 ·H2 O) and ammonium hydrogen carbonate (NH4 HCO3 ) as the mixed precipitant. The resultant powders calcined at 1000°C for 2 h showed good dispersity and excellent sinterability. Highly transparent polycrystalline lutetia ceramics with a relative density of ∼99.9% were fabricated by pressureless sintering in flowing H2 atmosphere at 1850°C for 6 h without any additives. The average grain sizes of the transparent material were estimated to be 50–60 μm. Optical in-line transmittance in the visible wavelength region for Lu2 O3 ceramics (1 mm in thickness) reached 80%. The luminescence and decay behavior of the obtained transparent plate and the corresponding nanophosphors were also investigated. 相似文献
3.
Qun Luo Xianping Fan Xvsheng Qiao Hui Yang Minquan Wang Xianghua Zhang 《Journal of the American Ceramic Society》2009,92(4):942-944
The Eu2+ -doped glass ceramics containing BaF2 nanocrystals were prepared and their luminescence properties were investigated. The excitation spectra of Eu2+ -doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED) centered at 380 nm. The 450 nm emission of Eu2+ in glass ceramics under the 385 nm excitation was much stronger than that in glass. The Eu2+ -doped glass ceramics containing BaF2 nanocrystals may be used as a potential blue-emitting phosphor for UV-LED. 相似文献
4.
Ding Zhou Ying Shi Jianjun Xie Yuying Ren Ping Yun 《Journal of the American Ceramic Society》2009,92(10):2182-2187
The fabrication of transparent Nd3+ ion-doped Lu2 O3 ceramics is investigated by pressureless sintering under a flowing H2 atmosphere. The starting Nd-doped Lu2 O3 nanocrystalline powder is synthesized by a modified coprecipitant processing using a NH4 OH+NH4 HCO3 mixed solution as the precipitant. The thermal decomposition behavior of the precipitate precursor is studied by thermogravimetric analysis and differential thermal analysis. After calcination at 1000°C for 2 h, monodispersed Nd3+ :Lu2 O3 powder is obtained with a primary particle size of about 40 nm and a specific surface area of 13.7 m2 /g. Green compacts, free of additives, are formed from the as-synthesized powder by dry pressing followed by cold isostatic pressing. Highly transparent Nd3+ :Lu2 O3 ceramics are obtained after being sintered under a dry H2 atmosphere at 1880°C for 8 h. The linear optical transmittance of the polished transparent samples with a 1.4 mm thickness reaches 75.5% at the wavelength of 1080 nm. High-resolution transmission electron microscopy observations demonstrate a "clear" grain boundary between adjacent grains. The luminescent spectra showed that the absorption coefficient of the 3 at.% Nd-doped Lu2 O3 ceramic at 807 nm reached 14 cm−1 , while the emission cross section at 1079 nm was 6.5 × 10−20 cm2 . 相似文献
5.
Shi Chen Mengjia Wu Liqiong An Yongxiang Li Shiwei Wang 《Journal of the American Ceramic Society》2007,90(2):664-666
Upconversion emission properties of Na1/2 Bi1/2 TiO3 :Er3+ ceramics prepared by the solid-state reaction method were analyzed as a function of Er3+ concentration and incident pump power. Strong green (550 nm) and red (670 nm) emission bands were observed with 980 nm excitation at room temperature. Experimental results showed that the emission bands can be tuned by changing Er3+ concentration. Upconversion processes in these samples result from not only a two-photon excited-state absorption process but also a nonradiative energy transfer and cross-relaxation process. 相似文献
6.
Youren Xu Chao M. Huang Waltraud M. Kriven Avigdor Zangvil 《Journal of the American Ceramic Society》1994,77(8):2213-2216
The microstructure of a pressureless sintered (1605°C, 90 min) O'+β' SiAlON ceramic with CeO2 doping has been investigated. It is duplex in nature, consisting of very large, slablike elongated O' grains (20–30 μm long), and a continuous matrix of small rodlike β' grains (< 1.0 μm in length). Many α-Si3 N4 inclusions (0.1–0.5 μm in size) were found in the large O' grains. CeO2 -doping and its high doping level as well as the high Al2 O3 concentration were thought to be the main reasons for accelerating the reaction between the α-Si3 N4 and the Si-Al-O-N liquid to precipitate O'–SiAlON. This caused the supergrowth of O' grains. The rapid growth of O' crystals isolated the remnant α–Si3 N4 from the reacting liquid, resulting in a delay in the α→β-Si3 N4 transformation. The large O' grains and the α-Si3 N4 inclusions have a pronounced effect on the strength degradation of O'+β' ceramics. 相似文献
7.
Debao Zhang Baoyu Chen Zhuping Liu Shunguang Li Lili Hu 《Journal of the American Ceramic Society》2004,87(12):2228-2231
Er3+ -doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO2 ·0.3Al2 O3 )· x Na2 O·8.2La2 O3 · 0.6Er2 O3 ·0.2Yb2 O3 ·1Sb2 O3 (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω t ( t = 2, 4, 6) decreases with increasing Na2 O. Ω2 decreases rapidly with increasing Na2 O while Ω4 and Ω6 decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na2 O. Fluorescence spectra of the 4 I 13/2 to 4 I 15/2 transition have been measured and the change with Na2 O content is discussed. It is found that the full width at half-maximum decreases with increasing Na2 O. 相似文献
8.
Several experiments were conducted to investigate the formation mechanisms of the magnetoplumbite phase in La3+ -doped CaO 6Fe2 O3 . It is shown that the CaO·2Fe2 O3 phase plays a crucial role in forming the magnetoplumbite phase. The formation mechanisms are proposed and verified. 相似文献
9.
Jingsong Liu Shuren Zhang Chengtao Yang Linshan Dai 《Journal of the American Ceramic Society》2005,88(1):85-88
Ferroelectric SrBi1.4 La0.6 Ta2 O9 (SBLT) thin films were grown onto Pt/Ti/SiO2 /Si substrates by pulsed-laser deposition. With the aid of X-ray diffractometry, piezoresponse scanning probe microscopy, and ferroelectric-property measurements, a correlation between microstructure, as well as domain structure and ferroelectric properties, was established. Excluding the effect of preferential orientation on ferroelectric properties, the increase in remanent polarization was attributed to distortion of the perovskite-like sublattice and atom displacement. Despite the co-instantaneous observation of a 90° domain and slight fatigue behavior in the SBLT films, the 90° domain-wall clamping did not seem to account for the fatigue in the SBLT films. Instead, strain-stress aggravation of the SBLT sublattice, due to the substitution of La3+ into Bi3+ sites, decreased the self-regulated flexibility of the (Bi2 O2 )2+ layers and caused fatigue in the SBLT. 相似文献
10.
The electronic conduction behavior above the Verwey-like transition temperature ( T v ) of Ni2+ - and Al3+ -doped LiMn2 O4 has been reassessed. The nonadiabatic small-polaron model is adopted to assess the conduction mechanism. The Jahn–Teller distortion and short-range ordering are found to play a role in the variations of the lattice parameter and conduction behavior above T v . It is also found that the effect of the dopant content on the activation energy is minor but is significant on the preexponential factor during the hopping process above T v . In simultaneously comparing the effects of the dopants with quite different chemistry on the electronic-conduction behavior in Ni2+ - and Al3+ -doped LiMn2 O4 , it indeed provides a deep sight into understanding the fundamental conduction mechanism above T v . 相似文献
11.
I. Prakash P. Muralidharan N. Nallamuthu N. Satyanarayana M. Venkateswarlu David Carnahan 《Journal of the American Ceramic Society》2006,89(7):2220-2225
NiAl2 O4 /SiO2 and Co2+ -doped NiAl2 O4 /SiO2 nanocomposite materials of compositions 5% NiO – 6% Al2 O3 – 89% SiO2 and 0.2% CoO – 4.8% NiO – 6% Al2 O3 – 89% SiO2 , respectively, were prepared by a sol–gel process. NiAl2 O4 and cobalt-doped NiAl2 O4 nanocrystals were grown in a SiO2 amorphous matrix at around 1073 K by heating the dried gels from 333 to 1173 K at the rate of 1 K/min. The formations of NiAl2 O4 and cobalt-doped NiAl2 O4 nanocrystals in SiO2 amorphous matrix were confirmed through X-ray powder diffraction, Fourier transform infrared spectroscopy, differential scanning calorimeter, transmission electron microscopy (TEM), and optical absorption spectroscopy techniques. The TEM images revealed the uniform distribution of NiAl2 O4 and cobalt-doped NiAl2 O4 nanocrystals in the amorphous SiO2 matrix and the size was found to be ∼5–8 nm. 相似文献
12.
Matthew J. Dejneka Benjamin Z. Hanson Steve G. Crigler Luis A. Zenteno John D. Minelly Douglas C. Allan William J. Miller Dmitri Kuksenkov 《Journal of the American Ceramic Society》2002,85(5):1100-1106
Single-mode semiconductor pumps have failed to keep pace with the increasing power requirements of Er-doped fiber amplifiers (EDFAs), so there is a need for high-powered 980-nm sources. Yb3+ -doped tapered fiber lasers can provide high-power output by conversion of a low-brightness, high-powered, 920-nm, multimode broad stripe laser diode to a high-brightness, 980-nm, single-mode output. The tapered fiber laser requires a fiber with high numerical aperture (NA) (>0.4), a rectangular core, and good Yb3+ spectroscopy for efficient operation. CVD-based fiber fabrication methods are incapable of delivering fibers with an NA > ∼0.3 or with good efficiency at 980 nm so a new method of high-NA fiber fabrication was developed. The core glass composition is critical for maintaining a high-NA fiber with good power extraction while avoiding phase separation, loss, and clustering. The SiO2 level controlled the NA and interdiffusion between core and clad, while the Al2 O3 /La2 O3 ratio controlled phase separation. A La2 O3 -Al2 O3 -SiO2 glass was developed that is compatible with a pure SiO2 cladding glass and has a laser slope efficiency of 70% at 980 nm. The optimized fiber composition yielded 450 mW of 980-nm power in a single-mode fiber. 相似文献
13.
Ren Jing Yang Guang Zeng Huidan Zhang Xianghua Yang Yunxia Chen Guorong 《Journal of the American Ceramic Society》2006,89(8):2486-2491
In the present work, properties of Dy3+ -doped chalcogenide glasses as a stoichiometric formula of (0.9− x )GeSe2 – x AsSe3/2 –0.1GaSe3/2 ( x =0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were investigated as a comparison with the previously studied Ge–Ga–Se system. Property measurements include differential thermal analysis, density, Vis-NIR and IR transmission spectra, and fluorescent emission spectra. Judd–Ofelt analysis was performed using the calculated oscillator strengths of glasses. All properties of glasses show obvious dependence on compositions. Especially, the improved devitrification resistance and the longer fluorescence life at 1.34 μm emission were observed with the increasing As content. Noticeably, abnormal changes in some properties occurred to the glass whose average coordination number corresponds to the threshold of two-dimensional–three-dimensional topological phase transition. 相似文献
14.
Effects of a liquid-phase-sintering aid, BaCuO2 + CuO (BCC), on densification and microwave dielectric properties of (Zr0.8 Sn0.2 )TiO4 (ZST) ceramics have been investigated. The densification kinetics of ZST are greatly enhanced with the presence of 2.5–5 wt% BCC, but become retarded when the amount of BCC increases further. At a given BCC content, moreover, slower densification kinetics are observed with a larger particle size of ZST. The above results are attributed to a chemical reaction taking place at the interface of BCC/ZST during firing. The ZST dissolves into BCC, forming crystalline phases of ZrO2 , SnO2 , CuO, and BaTi8 O16 which reduce the amount of BCC flux available for liquid-phase sintering. The crystallization kinetics become more significant, compared with densification kinetics, with increasing the amount of BCC and the particle sizes of ZST. For samples with 2.5–5 wt% BCC, a high relative sintered density is obtained at 1000°C and the resulting microwave ceramics have a dielectric constant and a value of Q at 7 GHz in the ranges of 35–38 and 2800–5000, respectively. 相似文献
15.
Robert C. Pullar Jonathan D. Breeze Neil McN. Alford 《Journal of the American Ceramic Society》2005,88(9):2466-2471
This paper details the investigation of the quality factor ( Q ), dielectric permittivity (ɛr ) and temperature coefficient of resonant frequency (τf ) of the TE01δ mode of the columbite binary niobate ceramics, with the formula MNb2 O6 where M=2+ cation, in relation to their degree of sintering, microstructure and phase composition. The ceramics were made from a mixed oxide preparative route and fired over a range of temperatures from 800° to 1400°C, and most formed the columbite structure. A comprehensive study was made of the niobates containing the transition metal cations M=Mn2+ , Co2+ , Ni2+ , Cu2+ , and Zn2+ , and the group II metal cations M=Mg2+ , Ca2+ , Sr2+ , and Ba2+ . All columbite niobates were found to have ɛr between 17 and 22 and negative τf values between –45 and –76 ppm/°C, and ZnNb2 O6 , MgNb2 O6 , CaNb2 O6 , and CoNb2 O6 had high Q f values of 84 500, 79 600, 49 600, and 41 700 GHz, respectively. The Q f of MgNb2 O6 was found to rise to over 95 000 GHz when heated at 1300°C for 50 h. 相似文献
16.
La2 Ti2 O7 powders were prepared using three different techniques. Single-phase material was obtained at 1150°C by calcination of mixed oxides, at 1000°C by molten salt synthesis, and at 850°C by evaporative decomposition of solutions. Particle sizes and morphologies of the powders differed substantially, as did the sintered microstructures and dielectric properties. Very dense (99%), translucent, grain-oriented lanthanum titanate was fabricated by hot-forging at 1300°C under a 200-kg load. Anisotropy was demonstrated by X-ray diffraction, scanning electron microscopy, thermal expansion, and dielectric measurements. 相似文献
17.
18.
Eun Jin Kim Sung-Woo Choi Seong-Hyeon Hong 《Journal of the American Ceramic Society》2007,90(9):2795-2798
Eu3+ -doped (1–12 mol%) calcium hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) powders were synthesized by a precipitation method and their photoluminescence (PL) properties were investigated. Eu has a limited solubility in HA and Eu2 O3 was detected by X-ray diffraction above 3% doping, whereas a nearly single β-phase was obtained up to 6% doping in TCP but EuPO4 appeared in the 12% Eu-doped specimen. Electron spin resonance measurement confirmed that europium ions exist as Eu3+ in both samples. Eu3+ -doped HA exhibited a strong emission at 575 nm with several minor peaks at 610–640 nm and Eu3+ -doped TCP had an intense emission at 613 nm with secondary peaks at 590–600 nm, which were consistent with the earlier reports determined at low temperatures. In Eu-doped TCP, the PL intensity increased with increasing calcination temperature without phase transformation. The more the Eu added, the higher the PL intensity obtained in both cases. 相似文献
19.
Zhiyong Zhou Xianlin Dong Heng Chen Haixue Yan 《Journal of the American Ceramic Society》2006,89(5):1756-1760
High-temperature piezoceramics based on W6+ -doped Bi3 TiNbO9 (BTNO) were prepared by solid-state reaction sintering. A study of the donor doping effects on the structure, microstructure, and electrical properties was conducted. The Curie point ( T c ) decreased in the range of 860°–910°C with increasing amount of W6+ doping. W6+ donor dopant decreased the conductivity in BTNO by as much as two orders of magnitude. The increased resistivity in W6+ -doped BTNO induced the materials to be polarized under a high enough field. The highest piezoelectric constant, d 33 , of 12.0 pC/N was achieved with the composition of Bi3 Ti0.99 W0.01 NbO9 . Also, this composition had a good thermal depoling resistance property. 相似文献
20.
Doo-Hee Cho Kazuyuki Hirao Koji Fujita Naohiro Soga 《Journal of the American Ceramic Society》1996,79(2):327-332
Photochemical hole burning (PHB) not only can be applied for data storage systems but also serves as a powerful method for studying the local structure around optical centers. The present work investigated the effects of aluminum, magnesium, and silicon ions on hole burning and the phonon sideband for borate glasses that exhibit PHB at room temperature. Hole burning was measured for the 5 D 0−7 F 0 transition of Sm2+ and the phonon sideband spectrum for the 5 D 0 -7 F 0 transition of Eu3+ . The hole width was closely related to local structural change, especially as it seemed to decrease with decreases in the number of nonbridging oxygens produced around the rare-earth ions. In the case of sodium aluminoborate glasses, the hole width decreased considerably with increasing alumina content. The ratio Γih /Γh for 85B2 O3·10Al2 O3 ·5Na2 O·1Sm2 O3 glass, then, was 80 at room temperature, the largest value ever reported. 相似文献