The present work aimed to explore a kind of microwave dielectric materials with middle-permittivity, high Qf, near-zero τf, and lower sintering temperature. A series of Y2Ti2O7 microwave dielectric ceramics were synt...The present work aimed to explore a kind of microwave dielectric materials with middle-permittivity, high Qf, near-zero τf, and lower sintering temperature. A series of Y2Ti2O7 microwave dielectric ceramics were synthesized by conventional solid-state method. For improving the dielectric properties of Y2Ti2O7 system, Bi2O3, Nd2O3 and Nb2O5 were added and their effects on phase composition, micro-structure, and dielectric properties at microwave frequencies were investigated by means of X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The queuing score method for multi-target orthogonal design was used to obtain the optimum prescription. The results showed that the Y2Ti2O7 ceramics with 8 wt.% Bi2O3 and 1 mol.% Nd2O3-Nb2O5 were well sintered at 1350 ℃, exhibiting excellent dielectric characteristics, i.e. εr≈76, Qf≈18980 GHz, τf =＋25.5 ppm/℃.展开更多
A series of Y2Ti2O7 microwave dielectric ceramics were synthesized by conventional solid-state method. The effects of rare earth oxide (La2O3, CeO2, Nd2O3, Sm2O3, Eu2O3, Gd2O3 and Dy2O3) and Nd2O3 doping content on th...A series of Y2Ti2O7 microwave dielectric ceramics were synthesized by conventional solid-state method. The effects of rare earth oxide (La2O3, CeO2, Nd2O3, Sm2O3, Eu2O3, Gd2O3 and Dy2O3) and Nd2O3 doping content on the microstructure and dielectric properties of Y2Ti2O7 ceramics were investigated. The experimental results showed that the rare earth ions were considered to dissolve in Y-sites of the pyrochlore structure, different rare earth oxides and concentration had different influences on Y2Ti2O7 cerami...展开更多
A comparative study of cascades in nanostructured ferritic alloys and pure Fe is performed to reveal the influence of Y_2Ti_2O_7 nanocluster on cascades by molecular dynamics simulations. The cascades with energies of...A comparative study of cascades in nanostructured ferritic alloys and pure Fe is performed to reveal the influence of Y_2Ti_2O_7 nanocluster on cascades by molecular dynamics simulations. The cascades with energies of primary knock-on atom（PKA） ranging from 0.5 keV to 4.0 keV and PKA＇s distances to the interface from 0 to 50 are simulated. It turns out that the Y_2Ti_2O_7 nanocluster can absorb the kinetic energy of cascade atoms, prevent the cascade from extending and reduce the defect production significantly when the cascades overlap with the nanocluster. When the cascade affects seriously the nanocluster, the weak sub-cascade collisions are rebounded by the nanocluster and thus leave more interstitials in the matrix. On the contrary, when the cascade contacts weakly the nanocluster, the interface can pin the arrived interstitials and this leaves more vacancies in the matrix. Moreover, the results indicate that the Y_2Ti_2O_7 nanocluster keeps stable upon the displacement cascade damage.展开更多
Er^（3＋） doped Y_2Ti_2O_7 phosphors were prepared by the high temperature solid state reaction method at 1500℃.X-ray diffraction and luminescence spectra were used to characterize the properties of samples.Due to t...Er^（3＋） doped Y_2Ti_2O_7 phosphors were prepared by the high temperature solid state reaction method at 1500℃.X-ray diffraction and luminescence spectra were used to characterize the properties of samples.Due to the layer distribution of Y^（3＋） ions in the pyrochlore Y_2Ti_2O_7 crystal,Er^（3＋） ions,replacing Y^（3＋） in Y_2Ti_2O_7 crystal,could realize high-concentration doping by suppressing energy migration between layers to minimize concentration quenching.Investigation on the upconversion characteristic of Y_2Ti_2O_7：Er^（3＋）showed that the optimal doping concentration of Er^（3＋） was up to 28 mol.%.Y_2Ti_2O_7：0.28 Er^（3＋） exhibited both dominating red emission under 980 and 1550 nm excitation.The brightness of Y_2Ti_2O_7：0.28Er^（3＋） were 4 times（980 nm） and 7 times（1550 nm） higher than that of Y_2Ti_2O_7：0.05Er^（3＋）.And Y_2Ti_2O_7：Er^（3＋） presented much better red emission color purity and stability under 1550 nm excitation.展开更多
基金supported by the Key University Science Research of Jiangsu Province (08KJA430002)the Priority Academic Program D velopment of Jiangsu Higher Education Institute
文摘The present work aimed to explore a kind of microwave dielectric materials with middle-permittivity, high Qf, near-zero τf, and lower sintering temperature. A series of Y2Ti2O7 microwave dielectric ceramics were synthesized by conventional solid-state method. For improving the dielectric properties of Y2Ti2O7 system, Bi2O3, Nd2O3 and Nb2O5 were added and their effects on phase composition, micro-structure, and dielectric properties at microwave frequencies were investigated by means of X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The queuing score method for multi-target orthogonal design was used to obtain the optimum prescription. The results showed that the Y2Ti2O7 ceramics with 8 wt.% Bi2O3 and 1 mol.% Nd2O3-Nb2O5 were well sintered at 1350 ℃, exhibiting excellent dielectric characteristics, i.e. εr≈76, Qf≈18980 GHz, τf =＋25.5 ppm/℃.
基金Project supported by the Key University Science Research Project of Jiangsu Province (08KJA430002)
文摘A series of Y2Ti2O7 microwave dielectric ceramics were synthesized by conventional solid-state method. The effects of rare earth oxide (La2O3, CeO2, Nd2O3, Sm2O3, Eu2O3, Gd2O3 and Dy2O3) and Nd2O3 doping content on the microstructure and dielectric properties of Y2Ti2O7 ceramics were investigated. The experimental results showed that the rare earth ions were considered to dissolve in Y-sites of the pyrochlore structure, different rare earth oxides and concentration had different influences on Y2Ti2O7 cerami...
基金Project supported by the Science Challenge Project of China(Grant No.TZ2016002)the National Natural Science Foundation of China(Grant No.50871057)
文摘A comparative study of cascades in nanostructured ferritic alloys and pure Fe is performed to reveal the influence of Y_2Ti_2O_7 nanocluster on cascades by molecular dynamics simulations. The cascades with energies of primary knock-on atom（PKA） ranging from 0.5 keV to 4.0 keV and PKA＇s distances to the interface from 0 to 50 are simulated. It turns out that the Y_2Ti_2O_7 nanocluster can absorb the kinetic energy of cascade atoms, prevent the cascade from extending and reduce the defect production significantly when the cascades overlap with the nanocluster. When the cascade affects seriously the nanocluster, the weak sub-cascade collisions are rebounded by the nanocluster and thus leave more interstitials in the matrix. On the contrary, when the cascade contacts weakly the nanocluster, the interface can pin the arrived interstitials and this leaves more vacancies in the matrix. Moreover, the results indicate that the Y_2Ti_2O_7 nanocluster keeps stable upon the displacement cascade damage.
基金supported by Research Program of Application Foundation(Main subject)of Ministry of Transport of China(2015329225090)the National Natural Science Foundation of China(11504039,51502031)Fundamental Research Funds for the Central Universities(3132015150,3132015153,3132015139,3132016349)
文摘Er^（3＋） doped Y_2Ti_2O_7 phosphors were prepared by the high temperature solid state reaction method at 1500℃.X-ray diffraction and luminescence spectra were used to characterize the properties of samples.Due to the layer distribution of Y^（3＋） ions in the pyrochlore Y_2Ti_2O_7 crystal,Er^（3＋） ions,replacing Y^（3＋） in Y_2Ti_2O_7 crystal,could realize high-concentration doping by suppressing energy migration between layers to minimize concentration quenching.Investigation on the upconversion characteristic of Y_2Ti_2O_7：Er^（3＋）showed that the optimal doping concentration of Er^（3＋） was up to 28 mol.%.Y_2Ti_2O_7：0.28 Er^（3＋） exhibited both dominating red emission under 980 and 1550 nm excitation.The brightness of Y_2Ti_2O_7：0.28Er^（3＋） were 4 times（980 nm） and 7 times（1550 nm） higher than that of Y_2Ti_2O_7：0.05Er^（3＋）.And Y_2Ti_2O_7：Er^（3＋） presented much better red emission color purity and stability under 1550 nm excitation.
文摘本文利用强场图像中的高阶微扰公式计算了Y_2Ti_2O_7:Cr^(3+)晶体的电子顺磁共振谱(EPR)参量(g因子g_(//,g⊥)和零场分裂D),计算中采用双旋-轨耦合参量模型,同时考虑了中心离子和配体的旋-轨耦合对EPR参量的贡献,计算结果与实验值很好地吻合.结果表明Cr^(3+)掺入Y_2Ti_2O_7晶体会引起O^(2-)偏向[111]方向(C_3轴)2.55°,同时,杂质中心O^(2-)-Cr^(3+)键长相对于基质晶体的O^(2-)-Ti^(4+)键长增加0.005 A.
