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Dive into the research topics where W. B. Wu is active.

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Featured researches published by W. B. Wu.


Journal of Physics: Condensed Matter | 2003

An intense ultraviolet photoluminescence in sol?gel ZnO?SiO2 nanocomposites

Zhengping Fu; Beifang Yang; Lin Li; Weiwei Dong; Chong Jia; W. B. Wu

We report the phenomenon that the intensity of the ultraviolet (UV) photoluminescence (PL) from ZnO was greatly enhanced by incorporating ZnO into the SiO2 matrix. PL excitation results show that both the ZnO nanoparticles and the SiO2 matrix in the nanocomposites contribute to the luminescence process for the UV band. On the basis of the x-ray photoelectron spectra, we suggest that interface energy states are formed due to the presence of Zn?O?Si bonds between ZnO nanoparticles and the SiO2 matrix. A tentative model concerning the contribution of the ZnO nanoparticles, SiO2 matrix, and ZnO?SiO2 interface is suggested to explain the PL enhancement effect.


Journal of Physics: Condensed Matter | 1999

Transport and magnetic properties in perovskite compound

Xiaojuan Fan; J H Zhang; Xiaoguang Li; W. B. Wu; J Y Wan; T J Lee; H. C. Ku

Magnetic and transport properties of the series (x = 0, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1.0) have been investigated. It was found that with increasing Co content, the Curie temperature decreases, while the spin glass transition temperature decreases first then increases. As for the sample with x = 0.3, the relation of and the merging point (for the zero-field-cooled and field-cooled magnetization curves starting to merge) with the applied magnetic field H follows a relation , ), where and are constants. The resistivity increases drastically with Co doping and a semiconductor-like behaviour is displayed in the sample x = 0.3. These facts strongly suggest that the double-exchange interaction in the perovskite materials is very fragile since a small Co content can change the magnetic and relevant transport properties of the system.


Journal of Applied Physics | 2008

Effect of anisotropic strain on the charge ordering transition in manganite films

Y. Z. Chen; J. R. Sun; Songmiao Liang; W. M. Lv; B. G. Shen; W. B. Wu

The substrate induced anisotropic strain was found to have a significant effect on the charge ordering (CO) transition and surface morphology in Bi0.4Ca0.6MnO3 films deposited on (110)- and (111)-oriented SrTiO3 substrates. Effects of film thickness t on the CO transition were further studied. The CO transition appears at TCO when t exceeds 50nm, and develops rapidly to an excellent state as t reaches 100nm. The distinctive thickness-dependent CO transition has a close relation with the anisotropic strain relaxation process.


Physica C-superconductivity and Its Applications | 2000

Growth and characterization of Bi2Sr2Ca1−xGdxCu2Oy single crystals by self-flux method

Xiaoru Zhao; X.F. Sun; Liangbing Wang; Q.F. Zhou; W. B. Wu; Xiaoguang Li

Abstract Large, high-quality Bi 2 Sr 2 Ca 1− x Gd x Cu 2 O y (Gd-doped Bi2212) single crystals for x =0–1.0 were successfully grown by a self-flux method for the first time. The structure of the crystals was examined by X-ray diffraction and Laue photographs. All the crystals possess the pure Bi 2 Sr 2 CaCu 2 O y (Bi2212) phase with the in-plane dimension up to 8×3 mm 2 . The c -axis length of the doped crystals decreases with increasing Gd concentration. The superconducting transition temperature T c of the crystals increases slightly at first and then drops rapidly upon Gd doping, which can be described well by the hole filling mechanism.


Journal of Applied Physics | 2009

Thermal history dependent photoconductivity in Pr0.5Sr0.5MnO3 thin film

Litian Hu; Y.P. Sun; Bosen Wang; Zhigao Sheng; Xiaomin Luo; X. B. Zhu; Z. R. Yang; W. H. Song; J.M. Dai; Zhizhen Yin; W. B. Wu

Thermal history dependent photoconductivity has been observed in the thermal hysteresis region of Pr0.5Sr0.5MnO3 thin film. In the cooling process, the film shows an upward resistance relaxation in darkness. Under light illumination, the transient photoconductivity effect is observed. However, it exhibits a downward resistance relaxation without illumination and persistent photoconductivity (PPC) behavior with light illumination in the warming process. The PPC ratio is 18.1% at 110 K with a light density of 1.25 mW mm−2. It is found that the external magnetic field plays a similar role as the light illumination. The persistent magnetoresistance ratio reaches 44.4% at 110 K with a low magnetic field of 0.25 T. The underlying mechanism is discussed based on phase competition and phase stability switch between ferromagnetic metal and charge- and orbital-ordered insulator states. The results may be important for practical applications in photo-/magnetic field sensitive and memory devices.


Physica C-superconductivity and Its Applications | 1999

Growth of superconducting Bi2Sr2Ca(Cu1-xMnx)2Oy single crystals

Xuefeng Sun; Xiaoru Zhao; Liangbing Wang; Q.F. Zhou; W. B. Wu; Xiaoguang Li

Abstract High-quality Bi 2 Sr 2 Ca(Cu 1− x Mn x ) 2 O y single crystals were successfully grown by the self-flux method for the first time. For starting composition x =0−10%, all the crystals possess the pure Bi2212 phase with evident difference between the nominal and actual Mn concentration. The c -axis lattice parameter decreases with increasing Mn content for both as-grown and air-annealed single crystals. The superconducting transition temperature decreases dramatically upon Mn doping, with the T c suppression rate larger than those of other 3 d transition elements doped Bi2212 reported previously.


Materials Letters | 2003

Stable ultraviolet photoluminescence from sol–gel silica containing nano-sized SiC/C powder

Zhengping Fu; Jiqiang Ning; Beifang Yang; W. B. Wu; Haibin Pan; Pengshou Xu

Abstract PL band of 340 nm has been observed from sol–gel silica with and without the addition of nano-sized SiC/C powder. With the increasing of annealing temperature, the intensity of the 340-nm PL band in pure silica decreases remarkably, while that in SiC/C powder-added silica is enhanced. Based on the Fourier-transform infrared (FTIR) absorption and X-ray photoelectron spectroscopy (XPS) spectra, the authors suggest that the addition of nano-sized SiC/C powder into porous silica (PSO) will strengthen the silica network and prevent it from shrinking during heat treatment. By this mechanism, the 340-nm PL band is stabilized by the presence of SiC/C powder.


Journal of Applied Physics | 2000

Pr-doping effect on the depinning of vortices in Bi2Sr2Ca1−xPrxCu2Oy single crystals

Xiaoguang Li; X.F. Sun; Xiaojuan Fan; Xiaoru Zhao; W. B. Wu

The irreversibility lines of Pr-doped Br2Sr2Ca1−xPrxCu2Oy single crystals have been studied systematically. It was found that for the Pr-doped samples as compared with the undoped Bi2Sr2CaCu2Oy the effective superconducting area shrinks, the irreversibility line Birr decreases, and the anisotropic parameter γ increases strongly due to Pr doping. It is evident that the substitution of Pr for Ca in the system effectively reduces the hole concentration on CuO2 layers to the underdoped state and destroys the Josephson coupling of the two superconducting regions of adjacent CuO2 layers. The vortex depinning is responsible for the irreversibility and the displacement value for vortex depinning is similar to that for vortex lattice melting, but with different physical meaning.


Physica C-superconductivity and Its Applications | 1994

Effect of γ-ray irradiation on the valence state of bismuth and copper in Bi-based superconductors

Liangbing Wang; W. B. Wu; Jingsheng Zhu; Xian-Wei Liu; X.-G. Li; Guien Zhou; Y.H. Zhang

Abstract Samples of Bi 2 Sr 2 CuO 6+χ , Bi 2 Sr 2 CaCu 2 O 8+ y and Bi 2.4− z Pb z Sr 2 CaCu 2 O 8+ w crystals have been irradiated by 648 KGy γ-rays parallel to the c -axis of the crystals. After irradiation the valence states of bismuth and copper shift to high binding energies. Also, new higher valence states occur in Bi 2 Sr 2 CaCu 2 O 8+ y and Bi 2.4− z Pb z Sr 2 CaCu 2 O 8+ w crystals, lead ding to a change in T c .


Physica C-superconductivity and Its Applications | 1994

Occurrence of metallic bismuth in Bi2Sr2CuOx crystals irradiated by N+ ions

Liangbing Wang; X.-G. Li; W. B. Wu; Xianming Liu; Jingsheng Zhu; Zuyao Chen; Guien Zhou; Y.H. Zhang

Abstract X-ray photoemission spectroscopy analyses reveal that N + ion irradiation causes the occurrence of metallic bismuth in the Bi 2 Sr 2 CuO x crystals. X-ray diffraction shows that the metallic bismuth results in the disappearance of some modulated peaks. Strontium may be replaced by other ions.

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Liangbing Wang

University of Science and Technology of China

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Xiaoguang Li

University of Science and Technology of China

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Guien Zhou

University of Science and Technology of China

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J.M. Dai

Chinese Academy of Sciences

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W. H. Song

Chinese Academy of Sciences

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X. B. Zhu

Chinese Academy of Sciences

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Xiaoru Zhao

University of Science and Technology of China

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Y.H. Zhang

University of Science and Technology of China

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Y.P. Sun

Chinese Academy of Sciences

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Z. R. Yang

Chinese Academy of Sciences

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