Co-reporter:Fanshun Meng;Xiaoming Lu;Yongli Liu
Journal of Materials Science 2017 Volume 52( Issue 8) pp:4309-4322
Publication Date(Web):2017 April
DOI:10.1007/s10853-016-0526-z
The atomic configurations and electronic structures of iron on CuΣ5 symmetrical tilt grain boundary (GB) have been studied based on the density functional theory. Different segregation positions of iron are considered. A weak tendency of iron segregating to GB is arrived due to the segregation energy. In addition, iron segregation shows a cohesion strengthening effect of Cu GB
according to Rice–Wang model, which is mainly contributed by the charge redistribution. Finally, an enhancement of the local magnetic moment of iron in Cu GB or bulk or surface is explored due to larger atomic volume than the FCC iron crystal and the Cu atoms surrounding iron are slightly polarized by the doped iron. This study can enrich the understanding of the effects of iron on the cohesion of Cu–Fe alloy and also might supply an indirect guidance to expand the application of Cu–Fe alloy in electronic device manufacture field.
Co-reporter:Yujie Qi, Mu Zhang, Lin Qi and Yang Qi
RSC Advances 2016 vol. 6(Issue 25) pp:20814-20823
Publication Date(Web):15 Feb 2016
DOI:10.1039/C5RA26725K
We report a new three-step mechanism for the formation and growth of carbonaceous spheres by hydrothermal carbonization of saccharides using sucrose as a precursor material. Carbonaceous spheres with small diameters and narrow size distribution were synthesized via a rapid heating route, and a notable phenomenon of a sudden drop in the mean diameter of the carbonaceous spheres at low concentration with the extension of time was observed. The morphology, chemical structure of carbonaceous spheres and the chemical composition of residual solutions were analysed by field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FT-IR) and solution 13C nuclear magnetic resonance (NMR) respectively. Based on these results, evolution of solid products is clearly revealed. The formation contains two stages, and oversaturation of primary particles attributed to autocatalysis of fructose by the yielded acid (formic acid) results in the appearance of large amounts of carbonaceous spheres in the second stage of formation, which accounts for the sudden drop in mean diameter.
Co-reporter:X.M. Zhao, J.P. Song, Y. Yu, Z.G. Zhuang, B.Z. Sun, Y. Qi
International Journal of Refractory Metals and Hard Materials 2016 Volume 57() pp:134-138
Publication Date(Web):June 2016
DOI:10.1016/j.ijrmhm.2016.03.003
•Surface topography of CVD-W coatings before and after thermal fatigue testing was characterized and investigated.•Electron beams are only absorbed by a thin layer on coating surface owing to excellent thermal conductivity.•No visible failure was found because the surface with fine grains can suppress the crack propagation.This work deals with the effects of thermal fatigue testing on the surface topography of W coatings on graphite substrate with Si intermediate layers, where W coatings were deposited by chemical vapor deposition (CVD-W coatings) and Si intermediate layers were prepared by physical vapor deposition (PVD-Si layers). The surface topography of samples both as-deposited and after thermal fatigue testing were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Comparative studies show that CVD-W coatings have so excellent thermal conductivity that electronic beams are only absorbed by a thin layer on the coating surface. The absorbed thermal loads give rise to the melting of the pyramid-like W grain tips and the formation of shallow melting pools. Meanwhile, the size of the recrystallized grains on the surface is much smaller than those of the initial grains after cooling. Since the fine recrystallized grains can undoubtedly suppress the crack propagation, no visible failure was found in sample after thermal fatigue testing.
Co-reporter:Tingting Zhang
The Journal of Physical Chemistry C 2016 Volume 120(Issue 5) pp:2777-2786
Publication Date(Web):January 12, 2016
DOI:10.1021/acs.jpcc.5b11297
Ag nanoparticles supported on well-defined perovskite orthorhombic KNbO3 nanowires are synthesized via facile photoreduction and systematically characterized by XRD, Raman, DRUV–vis, XPS, PL, TEM, HRTEM, and HAADF-STEM. The photoreactivity of Ag/KNbO3 nanocomposites as a function of Ag contents (0.4–2.8 wt %) is assessed toward aqueous rhodamine B degradation under UV- and visible-light, respectively. It is found that the UV-induced photoreactivity initially increases and then decreases with increasing Ag contents. At an optimal Ag content (ca. 1.7 wt %), the greatest photoreactivity is achieved under UV light, with the photocatalytic reaction rate of 1.7 wt % Ag/KNbO3 exceeding that of pristine KNbO3 by a factor of ca. 13. In contrast, visible light-induced photoreactivity monotonically increases with increasing Ag contents in the range of 0.4–2.8 wt %. On the basis of the detected active species and intermediate products in the photocatalytic processes, conjugated structure cleavage and N-deethylation are revealed to be the respective predominant pathway under UV and visible-light illumination. To gain an insight into the observed photoreactivity, the electronic properties of Ag/KNbO3 have been investigated using spin-polarized DFT calculations. Herein, Ag extended adlayers (1–4 ML) on the slab models of KNbO3 (101) are employed to mimic large supported Ag nanoparticles. A Bader analysis of the electron density shows a small net charge transfer (ca. 0.1 e) from KNbO3 to Ag. The electron localization function of Ag/KNbO3 (101) illustrates that Ag adlayers with thickness larger than 2 ML are essentially metallic, and weak polarization occurs at the interface. In addition, the metallic Ag adlayers generate a continuum of Ag bandgap states, which play a key role in determining different Ag content-dependent behavior between UV and visible-light illumination.
Co-reporter:Xiaoming Lu;Tianlin Wang
Journal of Sol-Gel Science and Technology 2016 Volume 77( Issue 1) pp:100-108
Publication Date(Web):2016 January
DOI:10.1007/s10971-015-3834-x
High-quality c-axis epitaxial Bi2Sr2CaCu2O8+δ (Bi2212) superconducting thin films prepared by the Pechini sol–gel method using nitrates as reactants have been grown on SrTiO3(100) single-crystal substrates. The precursor sol was deposited on the substrates via spin-coating method. Through the optimization of experimental parameters, 2.0 K min−1 was found to be the optimal heating rate of pre-sintering stage. Below this heating rate of pre-sintering stage, partial composition segregation occurred in the precursor films that resulted in dispersion of impurity phases in sintered thin films and caused the degradation of superconducting properties. Above this heating rate of pre-sintering stage, the surface morphology of thin films was destroyed, as the macroscopic defects, such as cracks and holes caused by excessive gas emissions during organic matter decomposition process and a sharp increase in roughness of precursor film was observed. Furthermore, through the optimization of heating rate at sintering stage, 3.5–3.0 K min−1 was found to be an optimal heating rate range at which Bi2212 thin films exhibited excellent phase purity and crystalline properties. In optimized growth condition, Tc,onset rose to above 95 K.
Co-reporter:Y.L. Liu, M. Babar Shahzad, Y. Qi
Journal of Alloys and Compounds 2015 Volume 628() pp:317-324
Publication Date(Web):15 April 2015
DOI:10.1016/j.jallcom.2014.12.018
•The O/Zn effect on the non-polar a-axis film growth is studied at the atomic scale.•The optimized film quality is achieved through a series of ReaxFF based MD study.•A film growth mode (singular atom → cluster → chains → continue film) is revealed.•The transformed way of the defective substrate to the perfect stacking is revealed.The understanding of the growth process and formation mechanism of non-polar ZnO films in atomic-scale is crucial in adjusting and controlling the film deposition conditions. Using the advanced reactive force field based molecular dynamics method, we theoretically studied the effect of O/Zn ratios (8/10–10/8) on the quality of ZnO films. The comprehensive investigation of energy and temperature fluctuation profile, radial distribution function, the sputtering and injecting phenomenon, and layer coverage indicated that the film grown under stoichiometric conditions possesses the optimized quality. Furthermore, the auto-transformation ability of the substrate from defective to perfect stacking was presented and discussed by comparing to the perfect structure. The instant film growth configurations, atomic layer snapshots, and the interfacial morphology evolution were provided step-by-step to reveal the defect type and initial film nucleation and growth mechanism.
Co-reporter:Dechuan Yu, Xiaogang Shi, Huameng Fu, Yan Geng, Zhengwang Zhu, Yang Qi, Haifeng Zhang
Materials Letters 2015 Volume 157() pp:299-302
Publication Date(Web):15 October 2015
DOI:10.1016/j.matlet.2015.05.142
•A new method was proposed to quickly locate good glass formers in 3D space.•Glass formers were obtained by combining clusters and mixing entropy.•Several new Zr-based glass formers with high glass forming ability were quickly discoveredAimed at developing new Ni-free Zr-based bulk metallic glasses (BMGs), a series of Ni-free Zr–Al–Fe–Cu glass formers have been developed in this work. The compositions are designed by using a combination of clusters and mixing entropy. Glass formers in this system are considered to be a mixture of Zr–Al, Zr–Fe and Zr–Cu clusters. Their coefficients were obtained by the calculation of mixing entropy. Under the guidance of this method, a series of compositions with high glass forming ability (GFA) were developed. Among the glass formers, the alloy compositions of Zr60.32Cu22.56Fe9.95Al7.17 and Zr64.08Cu18.78Fe10.02Al7.12 possess the highest GFA. Glassy rods can be fabricated at these two compositions with critical diameter up to 5 mm, which is superior to that reported for the known Zr60Cu25Fe5Al10 BMG under the same condition.
Co-reporter:B.Z. Sun, S.L. Zhou, H. Wang, Z.Y. Fei, X.M. Lu, T.L. Wang, Y. Qi
Materials Characterization 2014 Volume 87() pp:172-178
Publication Date(Web):January 2014
DOI:10.1016/j.matchar.2013.10.011
A series of compound with the nominal composition of Bi2Sr2 − xCaxCuO6 + δ (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were synthesized by the sol–gel method. Constituent phases and crystal structure of samples were analyzed by X-ray diffraction. It can be found that the Ca-doped Bi-2201 system was composed of Bi-2201 phase containing Ca and a small quantity of Bi16(Sr,Ca)14O38. For Bi-2201 unit cell containing Ca, chemical component and site preference of Ca atoms were characterized systematically by transmission electron microscopy. With the introduction of Ca atoms, Sr-sites have been occupied partially by Ca2 + in Bi-2201 unit cell, which leads to a decrease in the lattice parameters c and b of the Bi-2201 phase when the Ca-content x is below 0.6. Two types of new orthorhombic lattices are formed in the substitution. One is a lattice with space group Pma2 as the two nearest neighbor Sr-sites in the same Sr–O layer are occupied by Ca2 +. Its lattice parameters can be characterized as a = 5.402 Å, b = 5.313 Å and c = 24.272 Å, respectively. When two nearest Sr ions of the second neighboring Sr–O layers are replaced by Ca2 + ions, the lattice with the space group Pmn21 can be formed. Its lattice parameters are close to that of the previous. The modulation vector is lying in the a*–c* plane in the two new orthorhombic lattices (Pma2 and Pmn21). Bi/Ca-2201 lattice (with Ca) and Bi-2201 lattice (without Ca) coexist in the same Bi2Sr2 − xCaxCuO6 + δ grain, which can be described as an intergrowth structure.
Co-reporter:Benzhe Sun, Jiupeng Song, Yang Yu, Zhigang Zhuang, Mingjie Niu, Yan Liu, Tinghui Zhang, Yang Qi
International Journal of Refractory Metals and Hard Materials 2014 Volume 45() pp:76-79
Publication Date(Web):July 2014
DOI:10.1016/j.ijrmhm.2014.04.005
Tungsten–copper (W–Cu) composites containing 10 wt.% Cu (W–10Cu) were prepared by pressing and sintering a type of ultrafine composite powder. Constituent phases, grain size and orientation relationship between W and Cu grains were characterized and investigated. The results show that W–10Cu composites are composed of W and Cu elementary substance and orientation relationship between W and Cu grains is defined as 1¯1¯4Cu//01¯1W and (131)Cu//(200)W. The existence of the orientation relationship depends largely on the two factors. First, the grain sizes of both W and Cu were in the nanoscale range. Secondly, the interplanar spacing between both phases can match well owing to the residual stress of the W/Cu interface. Consequently, the obtained composites exhibited high density and excellent thermal conductivity.
Co-reporter:M. Babar Shahzad, Yang Qi, Hong Lu, Xiandi Wang
Thin Solid Films 2013 Volume 534() pp:242-248
Publication Date(Web):1 May 2013
DOI:10.1016/j.tsf.2013.02.126
•Effects of sol aging-time on the properties of Al-doped ZnO thin films.•Al atoms doping in to ZnO lattice increased with sol aging up to a certain time.•Films prepared from 20-24-h aged sol showed minimum surface roughness.•Optical transmittance of thin films was found sensitive to sol aging time.A series of aluminum doped zinc oxide (AZO) thin films were prepared by sol–gel method on glass substrates to investigate the behavior of Al doping with sol aging time (as-prepared to 2 weeks). X-ray diffraction analysis revealed a considerable shift in (002) diffraction peak towards higher diffraction angles with increasing sol aging time from as-prepared to 24 h which was found to be reverse with further aging. X-ray photoelectron spectroscopy and UV–vis spectroscopy were performed to investigate the change in chemical states of Al/Zn/O atoms and band gap fluctuations respectively. It was found that more Al atoms were doped into ZnO lattice with the increment of sol aging time and saturated level was achieved for ~ 20–24 h. Field emission scanning electron microscope and atomic force microscope characterization showed dense and homogeneous film morphology with decreasing relative surface roughness with sol aging time. Photoluminescence analysis and UV–vis spectroscopy revealed defect free films by exhibiting high optical transmission in the visible regime and found to improve with sol aging time. It could be concluded that solution aging time clearly influence the doping behavior and a suitable aging provides more stability which results into more Al atoms substitution for Zn in ZnO crystal lattice that affect the structural, morphological and optical properties of AZO thin films.
Co-reporter:M. Babar Shahzad, Hong Lu, Peng Wang and Yang Qi
CrystEngComm 2012 vol. 14(Issue 21) pp:7123-7126
Publication Date(Web):13 Aug 2012
DOI:10.1039/C2CE26125A
We report a successful synthesis of high quality non-polar m-plane (100) ZnO thin films via a novel and facile two step solution growth method. The reproducible growth of polarity free films is achieved by manipulating the seed/substrate characteristics, solution chemistry and growth conditions. Based on time resolved growth reaction FESEM analysis, three step growth phenomena viz. dissolution, recrystallization & primary growth and in situ nucleation/crystallization & secondary growth is proposed and explained.
Co-reporter:Huazhe Yang, Xiaoming Yu, Yang Ji, Yang Qi
Applied Surface Science 2012 Volume 258(Issue 11) pp:4852-4856
Publication Date(Web):15 March 2012
DOI:10.1016/j.apsusc.2012.01.055
Abstract
A modified degreasing-oxidization process was devised and settled to treat the surface of nickel (Ni) substrates, and BSCCO films were prepared on the treated NiO/Ni substrates by sol–gel method. X-ray diffraction (XRD) and optical microscopy were adopted to clarify the function of different treatment on phase formation and wettability of NiO/Ni substrates. Differential thermal analysis and thermal gravimetry analysis were adopted to confirm the desirable heat treatment process. XRD and scanning electron microscopy were adopted to investigate the phase constituent and surface morphology of BSCCO films. Results demonstrate that both the surface wettability of the substrate to sol and the lattice matching between the substrate and BSCCO can be improved through the modified treatment, which are favorable for the preparation of BSCCO films.
Co-reporter:Huazhe Yang, Xiaguang Sun, Xiaoming Yu, Yang Qi
Applied Surface Science 2012 Volume 261() pp:364-368
Publication Date(Web):15 November 2012
DOI:10.1016/j.apsusc.2012.08.015
Abstract
An electrochemical technique was devised and settled to prepare MgB2 films on copper cathodes in MgCl2–Mg(BO2)2–NaCl–KCl molten salts. X-ray diffraction and scanning probe microscopy were adopted to investigate the phase composition and elements distribution of sample. R–T curve of film was monitored through standard four-probe method. Transmission electron microscope and scanning electron microscope analysis were chosen to investigate the crystallization behavior and morphology of the films at different electrolytic temperatures. The results indicated that MgB2 films were successfully fabricated on the copper cathodes, and the optimal electrolytic temperature was 601 °C. It was presumed that the non-conducting MgO impurities hindered continuous growth of MgB2 grain, which may result in dendritic growth of MgB2 grain.
Co-reporter:Xiaoming Yu, Huazhe Yang, Yang Qi
Applied Surface Science 2011 Volume 258(Issue 1) pp:38-43
Publication Date(Web):15 October 2011
DOI:10.1016/j.apsusc.2011.08.002
Abstract
Bi2Sr2Ca1Cu2O8+δ (Bi-2212) films were grown on (1 0 0) oriented SrTiO3 (STO) substrate using sol–gel spin-coating method. The effects of heat treatment conditions and coating times on the phase formation and surface morphology were investigated using thermal analysis, optical microscope, X-ray diffraction, and scanning electronic microscopy. Mixed phases were formed from 820 to 840 °C, and Bi-2212 single phase was obtained at 830 °C for 3 h. c-axis epitaxial films with smooth surfaces were obtained by drying at 600 °C and coating for 5 times.
Co-reporter:Bingsen Zhang, Yang Qi
Applied Surface Science 2011 Volume 257(Issue 22) pp:9377-9381
Publication Date(Web):1 September 2011
DOI:10.1016/j.apsusc.2011.05.116
Abstract
Bi2Sr2CaCu2O8+δ (Bi2212) thin film is an important superconducting material ascribed to its high transition temperatures and low toxicity, but the application of Bi2212 thin films is limited due to the appearances of intergrowth and impurity phases. To achieve high-quality Bi2212 thin film by molecular beam epitaxy (MBE), the oxidizing gas pressure and substrate temperature are the key parameters. Here, the phase formation in Bi-based thin films grown by MBE was studied as a function of oxidizing gas pressure and substrate temperature. Furthermore, the thermodynamic parameters have been investigated through enthalpy change. This study indicates that the substrate temperature was increased with the enhancing of ozone partial pressure when the composition ratio is fixed, Bi2212 single phase can be formed. Moreover, the chemical stability decreases in the order of Bi2Sr2CuO6+δ > Bi2212 > Bi2Sr2Ca2Cu3O10+δ.
Co-reporter:Bingsen Zhang
Crystal Research and Technology 2011 Volume 46( Issue 4) pp:340-344
Publication Date(Web):
DOI:10.1002/crat.201100016
Abstract
Bi-based oxide thin films are important superconducting materials because of its wide applicability, high transition temperatures, and low toxicity. To achieve high quality Bi-based oxide thin films by molecular beam epitaxy (MBE), the composition is a key parameter. Here, Bi, Cu, Cu/Sr and Cu/Ca thin films on glass substrates prepared by MBE have been examined by using both X-ray reflectivity and surface profiler. The thickness and surface roughness were obtained through calculation and simulation. In comparison with the film thicknesses measured by these two methods, they are in good agreement. The lines of thickness deposition rate (R) versus source temperature (T) are according with LogR=a+b/T based on Clausius-Clapeyron equation. Moreover, the Bi2.1CaySr1.9-yCuO6+δ thin films with different composition and thickness were successfully prepared by MBE by applying the thickness deposition rate lines. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Co-reporter:Ying Zhang, Huazhe Yang, Maolin Li, Benzhe Sun and Yang Qi
CrystEngComm 2010 vol. 12(Issue 10) pp:3046-3051
Publication Date(Web):08 Jun 2010
DOI:10.1039/B927276C
Different gel processes were devised to synthesize Bi2Sr2CaCu2O8+δ (Bi2212)powders by sol–gel method. The phase purity, grain size and crystallinity of Bi2212 powders were dramatically improved by a modified sol–gel method called Pechini. Meanwhile, the sintering time was correspondingly reduced by a half. According to the investigations of different gel mechanism on the quality of Bi2212 powders, the polymerization increased the stability of gel network which inhibited some complexes segregated from gel network before auto-combustion. Furthermore, the esterification reduced the amount of free metal ions and improved the homogeneity of gel.
Co-reporter:Maolin Li, Ying Zhang, Yang Li, Yang Qi
Journal of Non-Crystalline Solids 2010 Volume 356(50–51) pp:2831-2835
Publication Date(Web):November 2010
DOI:10.1016/j.jnoncrysol.2010.09.036
Polycrystalline Bi-2212 superconductors as granular superconductors are fascinating materials owing to their unusual electrical properties caused by defect interfaces including structure inhomogeneities and grain boundaries. In order to reveal the origin of granular superconductivity, granular superconductivity in doped superconductors (Bi1-xLax)2Sr2CaCu2O8+δ (x = 0, 0.02, 0.04, 0.06 and 0.08) is systematically investigated by resistance measurement. Normal-state resistance gradually evolves a truly-metallic state into a disordered-metallic state as La concentration increases. Characteristic two-stage transition is obviously observed in the superconducting state of all the samples. Two types of characteristic temperature decrease with increasing La concentration. According to percolation model, it can be derived from the gradual increase of both structure inhomogeneities and grain boundaries. Finally, a model about the electrical path is reflected in the relation between granular superconductivity and electrical transport properties of granular Bi-2212 by homovalent substitution.
Co-reporter:Jiaheng Wang;Nan Shi;Meilin Liu
Journal of Sol-Gel Science and Technology 2010 Volume 53( Issue 1) pp:101-106
Publication Date(Web):2010 January
DOI:10.1007/s10971-009-2063-6
ZnO hollow micro/nanostructures were fabricated by a novel fast hydrothermal method based on the microemulsion. The aqueous reverse micelles were used as templates and different amount of Zn2+ colloid was compelled to hydrolyze on its surface. Scanning electron microscopy indicates that the products grown in the solution with colloid volume concentration of 12.3 and 0.5 v.% are hollow nanospheres and hexagonal microtubes, respectively. It is believed that this difference should attribute to the initial shape of hydrolysate and the core/shell state of water/surfactant during hydrothermal treatment.
Co-reporter:Jiaheng Wang, Lei Meng, Yang Qi, Maolin Li, Guimei Shi, Meilin Liu
Journal of Crystal Growth (1 April 2009) Volume 311(Issue 8) pp:2305-2308
Publication Date(Web):1 April 2009
DOI:10.1016/j.jcrysgro.2009.02.039
We report the Al-doping contents dependence of crystal growth and energy band structure in Al:ZnO thin films on the quartz substrates by the sol–gel method. As the Al contents increase, the Al-doping in the lattice reveals a maximum while the dopant is 2 mol%. It is inferred that the doping deterioration attributes to the decrease of grain size, which might be induced by the pinning effect of amorphous Al2O3 on ZnO grains boundary. The blueshifts of optical bandgap imply the quantum size effect of crystallites and the Burstein–Moss shifts in photoluminescence spectra indicate the heavy doping level for all samples.
