田永君
个性化签名
- 姓名:田永君
- 目前身份:
- 担任导师情况:
- 学位:
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学术头衔:
博士生导师
- 职称:-
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学科领域:
材料科学基础学科
- 研究兴趣:
1、基于共价固体硬度是本征的并等于单位面积上每个化学键对压头阻抗之和的假设,建立了描述极性共价固体硬度的微观理论,进而推广到象b-BC2N这样的多元固体。与已知的极性共价固体的实验值比较,理论预测相当准确。
2、提出一个唯象理论模型,定量描述了YBCO高温超导薄膜表面颗粒数量与表面电阻的关系,并预测出YBCO本征表面电阻的上限,该工作被国际同行验证,并被广泛应用。
3、提出了Si衬底上生长YBCO薄膜时微裂纹产生的物理机制,由此计算出的YBCO薄膜临界厚度与实验值吻合,解决了理论与实验不符的问题。
4、提出了倒装片式高温超导梯度计的设计原理并实现之,其磁场梯度分辨率为目前国际最好水平。由此构成的心磁图仪成功地测得了高质量心磁图。
5、采用高温高压技术合成出多种新型B-C-N功能材料,正交结构的B2CN化合物具有良好的光致发光效应。其中两种B-C-N化合物的X射线衍射数据被收入国际ICDD卡片。
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2893
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0
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成果阅读
395
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成果数
10
【期刊论文】Hardness of Covalent Crystals
田永君, Faming Gao, Julong He, ErdongWu, Shimin Liu, Dongli Yu, Dongchun Li, Siyuan Zhang, and Yongjun Tian, , *
VOLUME 91, NUMBER 1 PHYSICAL REVIEW LETTERS 4 JULY 2003,-0001,():
-1年11月30日
Based on the idea that the hardness of covalent crystal is intrinsic and equivalent to the sum of the resistance to the indenter of each bond per unit area, a semiempirical method for the evaluation of hardness of multicomponent crystals is presented. Applied to β-BC2N crystal, the predicted value of hardness is in good agreement with the experimental value. It is found that bond density or electronic density, bond length, and degree of covalent bonding are three determinative factors for the hardness of a polar covalent crystal. Our method offers the advantage of applicability to a broad class of materials and initializes a link between macroscopic property and electronic structure from first principles calculation.
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【期刊论文】Preparation of CNx/TiNy multilayers by ion beam sputtering
田永君, D.L. Yu a, Y.J. Tian a, *, J.L. He a, F.R. Xiao a, T.S. Wang a, D.C. Lia, L. Lib, G. Zheng c, O. Yanagisawa d
Journal of Crystal Growth 233(2001)303-311,-0001,():
-1年11月30日
CNx/TiNy multilayers have been prepared by ion beam sputteringand analyzed by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray and X-ray photoemission spectroscopy. The structure analyses shows that the films may contain several different kinds of CaN crystals embedded in the amorphous matrix. These crystals have hexagonal and cubic crystalline structures. The TiNx layer in multilayers is primarily amorphous and contains only a few dispersed Ti2N crystals. The thickness of CNx and TiNy layers in the CNx/TiNy multilayers is about 20 and 30nm, respectively. The atomic ratios of [N]/([C]+[N]+[Ti]) in the multilayers vary from 20 to 41 at%. The bondingratios of CaN/C?N of the CNx layer in multilayers reach 0.447 or 0.585 as calculated from the C1s and N1s X-ray photoemission spectra, respectively.
A1., Crystal structure, A3., Polycrystalline deposition, B1., Nitrides
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【期刊论文】Orthorhombic B2CN crystal synthesized by high pressure and temperature
田永君, J.L. He a, Y.J. Tian a, *, D.L. Yu a, T.S. Wang a, S.M. Liu a, L.C. Guo a, D.C. Li a, X.P. Jia b, L.X. Chen b, G.T. Zou b, O. Yanagisawa c
Chemical Physics Letters 340(2001)431-436,-0001,():
-1年11月30日
B0.54C0.28N0.18 precursor powder with turbostratic structure was prepared by using melamine and boric acid. The precursor was transformed into orthorhombic B2CN under definite high pressure and temperature conditions. The composition of the orthorhombic B2CN powder is B0.47C0.23N0.30. Its lattice parameters are a=0.4776nm, b=0.4585nm and c=0.3629nm. A strong absorption band from 1088 to 1385cm-1 of orthorhombic B2CN was observed by infrared measurement. In the photoluminescence (PL) spectrum of orthorhombic B2CN powder measured at room temperature, a broad peak corresponding to its band-edge emission centers at 374nm.
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田永君, Y.J. Tian a, *, D.L. Yu a, J.L. He a, F.R. Xiao a, T.S. Wang a, D.C. Li a, L. Lib, G. Zhengc, O. Yanagisawad
Journal of Crystal Growth 225(2001)67-72,-0001,():
-1年11月30日
CNx/TiNy bilayers have been prepared by ion beam sputtering. Transmission electron microscopy observation of the films shows that some crystals exhibiting a polyhedron-type shape contain cores. The crystal sizes range from 100 to 300 nm. The results obtained by selected area electron diffraction reveal that the crystals belong to the cubic-C3N4 phase and their core is the Ti2N phase. Two types of heteroepitaxial matching between cubic-C3N4 and Ti2N are found in the CNx/TiNy bilayers, namely (112) cubic-C3N4k(1113) Ti2N and [423] cubic-C3N4k [110] Ti2N. The heteroepitaxial lattice misfit of 5.78% is calculated by the Bramfitt's lattice misfit method.
A1., Characterization, A1., Crystal structure, A1., Nucleation, A3., Physical vapor deposition processes, A3., Solid phase epitaxy, B1., Nitrides
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【期刊论文】Cubic-C3N4 nanoparticles synthesized in CNx/TiNx multilayer films
田永君, T.S. Wang a, b, *, D.L. Yu a, Y.J. Tian a, F.R. Xiao a, J.L. He a, D.C. Li a, W.K. Wang a, L. Li b
Chemical Physics Letters 334(2001)7-11,-0001,():
-1年11月30日
Cubic-C3N4 nanoparticles were synthesized in CNx/TiNx multilayer films by a nitrogen ion beam sputtering in situ titanium and graphite targets alternatively. The CAN bonding states within the CNx layers, the morphologies and structure of compounds in the films have been investigated by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. Two types of bonding states, NAsp2C and NAsp3C, exist predominantly in the CNx layer, and crystalline particles with sizes of 10-60nm were observed in the CNx layer of the films. Their diffraction data can be assigned to the cubic-C3N4 structure.
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【期刊论文】High-Tc dc-SQUID magnetometer and its application in eddy current non-destructive evaluation
田永君, H.H. Qi a, b, P.L. Lang b, M.J. Zhang b, T.S. Wang a, D.N. Zheng b, Y.J. Tian a, *
Cryogenics 44(2004)695-699,-0001,():
-1年11月30日
We have fabricated and tested a high-Tc dc-SQUID magnetometer patterned on a YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K showed that the magnetometer has a white noise of 333 fT/Hz1=2 without superconducting shield, corresponding to a flux sensitivity of 14.5 lU0/Hz1=2. We constructed a test system for eddy current non-destructive evaluation of conducting aluminum plates by using the magnetometer. Flaws over 10mm below the surface can be clearly identified. By mapping the magnetic field distribution, we can locate the flaw position. The signals caused by flaw were expanded due to the use of double-D type driving coil with a wider central slit. The experimental results confirmed that this test system could operate in a magnetic unshielded environment.
SQUID, Magnetometer, Non-destructive e, v, a, l, uation
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【期刊论文】Specific heat and related thermodynamic properties of an undercooled germanium melt
田永君, Q. Li, a) Y. Y. Zhu, a) R. P. Liu, b) G. Li, M. Z. Ma, J. K. Yu, J. L. He, Y. J. Tian, and W. K. Wang
APPLIED PHYSICS LETTERS VOLUME 85, NUMBER 4 26 JULY 2004,-0001,():
-1年11月30日
Embedded in a flux of dehydrated B2O3, melts of pure germanium were undercooled by repeated melting and solidification of the specimens within a differential scanning calorimeter facility. The highest undercooling obtained in this way was 190K. The specific heat of the undercooled melt was measured by calorimetric diagnostics within the facility, and showed a linear dependence on temperature. The thermodynamic properties of germanium, such as the difference of Gibbs free energy, the difference of entropy, and the difference of enthalpy between the undercooled melt and the solid state, were derived from the measured specific heat.
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【期刊论文】Optical properties of heterodiamond B2CN using first-principles calculations
田永君, Jian Sun, Hui-Tian Wang, a) and Nai-Ben Ming, Julong He and Yongjun Tian
APPLIED PHYSICS LETTERS VOLUME 84, NUMBER 22 31 MAY 2004,-0001,():
-1年11月30日
We report detailed ab initio calculations of the optical properties of a heterodiamond B2CN compound using the pseudopotential density functional method, including the dielectric function, the refractive index, the absorption, the electron energy-loss spectrum, and the reflectivity. The polarization dependencies of those optical properties are investigated. The results indicate that the electron-deficiency characteristic of B2CN gives rise to some features.
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【期刊论文】Spark discharge and high-speed impact treatment of turbostratic CNx powder
田永君, D.C. Li a, *, D.L. Yu a, J.L. He a, S.M. Liu a, Y.J. Tian a, O. Yanagisawa b, M. Kiritani c
Materials Science and Engineering A350(2003)190-194,-0001,():
-1年11月30日
CNx precursor powders (composition: 33.76 at.% C, 49.53 at.% N and 16.71 at.% H) having a turbostratic structure were obtained by pyrolyzing melamine. Following spark discharge treatment, the precursor becomes more ordered in structure. The order was increased with increasing treatment time. Photoluminescence (PL) analysis confirmed that the spark discharge had only a slight effect on the energy band of the turbostratic CNx powder, namely a blue shift of 11nm in the emission spectrum of the precursor. By contrast, the high-speed impact treatment clearly promoted the mass transfer between the CNx particles.
Melamine, Turbostrtic CNx, Spark discharge/, high-speed impact, Structural order
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【期刊论文】Chemical bond properties and Mossbauer spectroscopy in REBa2Cu3O7 (RE=Eu, Y)
田永君, FamingGao a, *, Dongchun Li a, JulongHe a, Yongjun Tian a, Dongli Yu a, Siyuan Zhang b
Physica C 371(2002)151-155,-0001,():
-1年11月30日
By using the chemical bond theory of complex crystals, the chemical bond properties of REBa2Cu3O7 (RE=Eu, Y) were calculated. The calculated covalencies for Cu(1)-O and Cu(2)-O bond in REBa2Cu3O7 compounds are 0.41 and 0.28 respectively. Mossbauer isomer shifts of 57Fe doped, and 119Sn doped in REBa2Cu3O7-x were calculated by using the chemical environmental factor, he, defined by covalency and electronic polarizability. Four valence state tin ion and iron ion sites were identified in 57Fe and 119Sn doped REBa2Cu3O7-x superconductors.
Superconductivity, Oxides, Chemical bond, Mossbauer spectroscopy
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