Co-reporter:Liang Li;Shuohui Gao;Tian Cui;Benxian Li;Qiang Zhou;Hongming Yuan
RSC Advances (2011-Present) 2017 vol. 7(Issue 56) pp:35477-35481
Publication Date(Web):2017/07/11
DOI:10.1039/C7RA05267G
The spinel Zn2TiO4 single crystals were grown via optical floating zone technology in an argon atmosphere for the first time, the as-grown crystals were dark blue and transparent. And the as-grown crystals, free of bubbles and with low angle grain boundary, grow along the a-axis direction. The annealed crystals were colorless and transparent, and the chemical valence of as-grown and annealed single crystals was characterized by X-ray photoelectron spectra. The room-temperature polarized Raman spectra of spinel Zn2TiO4 crystal were presented and the in situ temperature-dependent Raman spectra of the crystals were also described. DSC results of Zn2TiO4 were also discussed.
Co-reporter:Yipeng Gu;Hongzhi Shen;Liang Li
Chemical Research in Chinese Universities 2014 Volume 30( Issue 6) pp:879-884
Publication Date(Web):2014 December
DOI:10.1007/s40242-014-4252-2
SnO2:xEu3+(x=0, 1%, 3%, 5%, molar fraction) fibers were synthesized by electrospinning technology. The size of the as-prepared fibers is relatively uniform and the average diameter is about 200 nm with a large draw ratio. The as-prepared Eu3+ doped SnO2 nanofibers have a rutile structure and consist of crystallite grains with an average size of about 10 nm. A slight red shift of the A1g and B2g vibration modes and an additional peak at 288 nm were observed in the Raman spectra of the nanofibers. The energies of bandgaps of the SnO2 nanofiber with Eu doping of 1% and 3% are 2.64 eV, and the energy of bandgap is 2.94 eV with Eu doping of 5%(molar fraction). There is only orange emission(5D0→7F1 magnetic dipole transition) for Eu doped SnO2 nanofibers, and no red emission could be observed. The orange emission upon indirect excitation splits into three peaks and the peak intensity at the excitation wavelength of 275 nm is higher than that at the excitation wavelength of 488 nm.
Co-reporter:Jing Zhou, Guanlin Feng, Liang Li, Fengxian Huang, Hongzhi Shen, Hang Yang, Wenquan Wang, Qiang Zhou, Dapeng Xu
Journal of Alloys and Compounds 2013 Volume 579() pp:267-271
Publication Date(Web):5 December 2013
DOI:10.1016/j.jallcom.2013.06.053
•The phase transition of CaNb2O6 was investigated for the first time under high pressure.•In situ Raman spectroscopy and Synchrotron X-ray diffraction were measured.•A pressure-induced reversible phase transition was observed below 23 GPa.•The orthorhombic columbite Pbcn transforms to monoclinic structure P21/c.•The lattice parameters of the new phase were obtained by the Pawley refinements.The in situ high pressure studies of CaNb2O6 have been performed using Raman spectroscopy and Synchrotron X-ray diffraction in a DAC up to 23 GPa. Raman experiments show that most Raman peaks decrease in intensity and shift toward high wave numbers with increasing pressure. Two turn points in the slope of frequency–pressure curve of the slopes of Raman modes turn up at the pressure around 8 and 15 GPa. ADXRD results display that the old peaks disappear and some new peaks appear above 9.4 GPa, and the patterns remain unchanged above 15 GPa. Both Raman and X-ray diffraction data provide evidence of a reversible phase transition beginning from about 8 GPa and completing at 15 GPa.
Co-reporter:Liang Li, Guanlin Feng, Dejun Wang, Hang Yang, Zhongmin Gao, Benxian Li, Dapeng Xu, Zhanhui Ding, Xiaoyang Liu
Journal of Alloys and Compounds 2011 Volume 509(Issue 27) pp:L263-L266
Publication Date(Web):7 July 2011
DOI:10.1016/j.jallcom.2011.04.063
MgNb2O6 single crystals are grown by the optical floating zone method. The as-grown crystals are dark brown and have dimensions of Ø 4–6 mm × L 87 mm, with the largest crystal domain being Ø 5 mm × L 32 mm. After being annealed, the crystals fade to light brown. The powder X-ray diffraction analysis shows that the crystals have a columbite-type MgNb2O6 structure. The crystal grows along the c-axis and the cleavage plane is the (0 1 0) plane. Transmission polarized light microscopy measurements show that the crystal is free of low-angle grain boundaries and inclusions. The crystals have been characterized by Raman scattering, which reveals the change of Nb–O band in annealed and non-annealed samples. The photoluminescence spectra exhibit a broad and strong blue emission band centered at 435 nm.
Co-reporter:Liang Li;Ya Fan;Dejun Wang;Guanlin Feng
Crystal Research and Technology 2011 Volume 46( Issue 5) pp:475-479
Publication Date(Web):
DOI:10.1002/crat.201100068
Abstract
The transmittance and absorption spectra of a high-quality Zn2TiO4 single crystal have been measured along the a-axes at room-temperature in the range of 200-1000 nm. The wavelength dependent refractive index, extinction coefficient, real and imaginary parts of the complex dielectric constant of the Zn2TiO4 crystal have been derived from the measured T and α spectra. By fitting the refractive index spectrum, the Sellmeier dispersion equation of the Zn2TiO4 crystal has been obtained. The validity of Cauchy-Sellmeier equation has been evaluated in the energy range of 2.90–3.20 eV representing the Urbach tail. Applying the single-effective oscillator model, the dispersion energy Ed and the oscillator energy E0 have been determined as 18.76 and 5.05 eV, respectively. The obtained dispersion energy Ed takes on ionic crystal value. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Co-reporter:Shuang Li, Xuan Fang, Jing Leng, Hongzhi Shen, Ya Fan, Dapeng Xu
Materials Letters 2010 Volume 64(Issue 2) pp:151-153
Publication Date(Web):31 January 2010
DOI:10.1016/j.matlet.2009.10.029
Single crystalline Mg2B2O5 nanorods have been synthesized by a two-step process involving the mechano-chemical technique and sintering method. Using MgCl2·6H2O and NaBH4 powders as the starting materials, the mixture was firstly milled for 120 h, and then sintered at 800 °C for 2 h. The X-ray diffraction indicates the final product is monoclinic Mg2B2O5. SEM and TEM results show that the Mg2B2O5 is nanorod with the diameter about 200–400 nm and the length up to 5 μm. SAED analysis shows that the nanorod is single crystalline and twinned structure. The by-product NaCl is necessary for the formation of the single phase Mg2B2O5.
Co-reporter:Jing Leng, Shuang Li, Zhongshan Wang, Yanfeng Xue, Dapeng Xu
Materials Letters 2010 Volume 64(Issue 17) pp:1912-1914
Publication Date(Web):15 September 2010
DOI:10.1016/j.matlet.2010.06.005
Ultrafine one-dimensional LaFeO3 nanofibers were synthesized by electrospinning utilizing sol–gel precursors. The surface morphology, microstructure and crystal structure were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The nanofibers with smaller diameter were continuous and uniformly distributed. Typical fiber diameter was between 180 nm and 220 nm and the average diameter was 200 nm. The fibers consisted of many single-crystal LaFeO3 grains and the grain size was about 20–50 nm. The relationship between the diameter of as-synthesized fibers and the PVP concentration of the precursor was investigated. The experimental results indicated that the PVP concentration had a great impact on the fiber size and 5.89 wt.% PVP concentration in sol–gel precursors was advantageous to the formation of more uniform electrospun composite fibers with smaller diameter.
Co-reporter:Gengxin Song;Liang Li
Crystal Research and Technology 2010 Volume 45( Issue 5) pp:461-464
Publication Date(Web):
DOI:10.1002/crat.201000054
Abstract
A LaCoO3 single crystal with 4 mm in diameter and 30 mm in length has been grown by optical floating zone method. The as-grown crystal is highly crystalline with the rhombohedral perovskite structure (R3c) and grows parallel to the (121) direction. The room temperature resistivity of the as-grown crystal is 0.12 Ω·cm and the insulator-metal transition occurs around 500 K. The coercivity and the remanence of the as-grown crystal are 5 Oe and 6.61×10–5 μB/f.u. at 5 K, respectively. In 1000 Oe under zero-field cooling, the magnetic susceptibility of the as-grown crystal shows an upturn in a Curie tail fashion below 35 K, and appears a wave crest over the interval 55 K≤T≤90 K. In addition, a slope change of 1/χ(T) at about 12 K is observed in 50000 Oe under zero-field cooling. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Co-reporter:Guang-Qiang Zhang, Da-Peng Xu, Gen-Xin Song, Yan-Feng Xue, Liang Li, De-Yong Wang, Wen-Hui Su
Journal of Alloys and Compounds 2009 Volume 476(1–2) pp:L4-L7
Publication Date(Web):12 May 2009
DOI:10.1016/j.jallcom.2008.08.049
The crystallization of amorphous SiO2 with different forms of H2O under high pressure and high temperature was investigated experimentally, and it was first discovered that Si–OH could effectively promote the synthesis of coesite at lower temperature in a very short time. Using amorphous SiO2 with Si–OH as the initial material, single-phase coesite has been synthesized under 4.2 GPa and 190 °C for 30 min.
Co-reporter:Yan-feng XUE, Da-peng XU, Guang-qiang ZHANG, Xian-feng ZHOU, Zhan-hui DING, Xiao-mei LIU, Wen-hui SU
Chemical Research in Chinese Universities 2008 Volume 24(Issue 2) pp:135-137
Publication Date(Web):March 2008
DOI:10.1016/S1005-9040(08)60028-8
Abstract
ZrSiO4 and coesite were obtained under high-pressure and high-temperature from the nano precursor of a-SiO2 and ZrO2. XRD and Raman measurements indicate that ZrSiO4 was formed at a temperature higher than 920 °C under a pressure of 3.6 GPa. As the pressure increased to 3.9 GPa, the ZrSiO4 formation temperature was reduced to 815 °C. The formation temperature for coesite was 990 °C under 3.9 GPa. The lower formation temperature for ZrSiO4, as compared to that for coesite, provided an experimental evidence that the coesite in the Earth's surface usually occurs as inclusions in ZrSiO4.
Co-reporter:Liang Li, Hang Yang, Dejun Wang, Guanlin Feng, Benxian Li, Zhongmin Gao, Dapeng Xu, Zhanhui Ding, Xiaoyang Liu
Journal of Crystal Growth (1 December 2010) Volume 312(Issue 24) pp:3561-3563
Publication Date(Web):1 December 2010
DOI:10.1016/j.jcrysgro.2010.09.045
Crack-free and transparent Zn2TiO4 single crystals of 4–6 mm in diameter and 30 mm in length have been grown by the optical floating zone method. The powder X-ray diffraction (XRD) results show that the as-grown crystals have the spinel-type Zn2TiO4 structure. XRD2 measurements on Zn2TiO4 wafers cut perpendicular to the growth direction display only one peak at 42.7°, which indicates that the Zn2TiO4 single crystals grow along the 〈4 0 0〉 direction (a-axis). The formation of bubble inclusions was effectively suppressed by lowering rotation rate. Transmission polarized-light microscopy results showed that as-grown crystals were free of low angle grain boundaries.
