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uniaxial stress influence on lattice,band gap and optical properties of n-type ZnO:first-principles calculations

Chinese Physics B 2012年第1期21卷 399-403页

作者：杨平李培张立强王晓亮王欢宋喜福谢方伟 Laboratory of Advanced Manufacturing&Reliability for MEMS/NEMS/OEDS School of Mechanical EngineeringJiangsu UniversityZhenjiang 212013China

The lattice, the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by first- principles calculations. The results show that the lattice constants change linearly with stress. Band gaps are broadened linearly as the uniaxial compressive stress increases. The change of band gap for n-type ZnO comes mainly from the contribution of stress in the c-axis direction, and the reason for band gap of n-type ZnO changing with stress is also explained. The calculated results of optical properties reveal that the imaginary part of the dielectric function decreases with the increase of uniaxial compressive stress at low energy. However, when the energy is higher than 4.0 eV, the imaginary part of the dielectric function increases with the increase of stress and a blueshift appears. There are two peaks in the absorption spectrum in an energy range of 4.0-13.0 eV. The stress coefficient of the band gap of n-type ZnO is larger than that of pure ZnO, which supplies the theoretical reference value for the modulation of the band gap of doped ZnO.

关键词： uniaxial stress first-principles optical properties n-type ZnO

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Effect mechanism of nitrogen injection into fire-sealed-zone on residual-coal re-ignition under stress in goaf

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International Journal of Coal Science & Technology 2022年第5期9卷 138-149页

作者： Yongliang Xu Zejian Liu Xinglin Wen Lanyun Wang Zhiguang Lv Jindong Wu Minjie Li School of Safety Science and Engineering Henan Polytechnic University(HPU)Jiaozuo 454003China State Key Laboratory Cultivation Base for Gas Geology and Gas Control of HPU Jiaozuo 454003China Collaborative Innovation Center for Coal Safety Production and High-Efficient-Clean Utilization Jiaozuo 454003China

Coal is the one of foundations of energy and economic structure in China,while the unsealing of coal mine fres would cause a great risk of coal re-ignition.In order to explore the infuence of pressure-bearing state on the re-ignition characteristics for residual coal,the uniaxial compression equipped with a temperature-programmed device was built.The scanning electron microscope,synchronous thermal analyzer and Fourier transform infrared absorption spectrometer was applied to investigate the microscopic structure and thermal efect of the coal samples.Moreover,the microscopic efect of uniaxial stress on coal re-ignition is revealed,and the re-ignition mechanism is also obtained.As the uniaxial stress increasing,the number,depth and length of the fractures of the pre-treated coal increases.The application of uniaxial stress causes the thermal conductivity to change periodically,enhances the inhibition of injecting nitrogen on heat transfer and prolonges the duration of oxidation exothermic.The content of oxygen-containing functional groups has a high correlation with apparent activation energy,and coal samples at 6 MPa is more probability to re-ignite while the fre zone is unsealed.uniaxial stress could control the re-ignition mechanism by changing the structure of fractures and pores.The side chains and functional groups of coal structure are easier to be broken by thermal-stress coupling.The higher the·OH content,the more difcult coal samples would be re-ignited.The research results would lay a solid theoretical foundation for the safe unsealing of closed fre-areas underground,tighten the common bond between the actual industry and the experimental theory in closed fre-areas underground,and provide the theoretical guidance for coal re-ignition preventing.

关键词： Coal re-ignition Unsealed fre zone uniaxial stress Thermal efect Re-ignition mechanism

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Spatially distributed damage in sandstone under stress-freeze-thaw coupling conditions

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第6期14卷 1910-1922页

作者： Lifeng Fan Yiding Fan Yan Xi Jingwei Gao College of Architecture and Civil Engineering Beijing University of TechnologyBeijing100124China

In the present study,we tried to understand the spatially distributed damage in sandstone samples under the coupled stress-freeze-thaw(SFT)conditions.Firstly,uniaxial compressive stresses(i.e.0 MPa,10 MPa,20 MPa,and 25 MPa)were applied to the samples,and then freeze-thaw(FT)cycles(0,8,16,and 24)were performed on the uniaxially stressed samples to realize the SFT coupling.Next,real-time CT scanning was conducted to observe the induced damage.The total porosity was introduced to quantitatively evaluate the damage degree.The local porosity variation,with the distance from the center of the sandstone sample,was analyzed to understand the spatial distribution of damage.Finally,the coupling effects of SFT on the damage gradient were discussed.The results indicate that the porosity rises with FT cycles,and the applied stresses can accelerate the increase in porosity.The damage increases exponentially with the distance from the center of the sample.The damage presents a spatial gradient distribution,not the commonly used uniform distribution in various studies.The damage gradient increases with FT cycles,and the increasing rate in damage gradient decreases at uniaxial stress of 0 MPa and 10 MPa first,but the increasing rate in damage gradient increases with FT cycles then at stress increasing to 20 MPa.

关键词： Rock damage Freeze-thaw(FT)cycles uniaxial stress oupling effects

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Modeling of the Effects of uniaxial stress on the ~2E→~2T2 Absorption Lines of GaP:Ti~3+——Part Ⅰ: Theoretical Investigations

Modeling of the Effects of Uniaxial Stress on the ~2E→~2T2 ...

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2004年中国材料研讨会

作者：邱庆春广东省汕头市汕头大学医学院

＜正＞ Impurities continue to play an important role in the search for superior materials for use as electronic and optoelectronic devices. Experiments showing the effects of uniaxial stress on the structure of the zero-phonon line （ZPL） obtained in the optical absorption spectrum from a Ti3+ ion in GaP are described using electron-phonon interaction model. It is found that the components of the ZPL are split when the stress is applied along the ＜001 ＞ , ＜ 111 ＞ and ＜ 110 ＞ axes. A theoretical vibronic model is used to describe this system which includes coupling to e modes in the E ground states,tobothe and tow t2 in the excited states and to t2 mode between 2E and 2T2.

关键词： GaP impurities vibronic coupling uniaxial stress

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Unified calculation method and its application in determining the uniaxial mechanical properties of concrete

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Frontiers of Structural and Civil Engineering 2011年第3期5卷 381-393页

作者： Faxing DING Xiaoyong YING Linchao ZHOU Zhiwu YU College of Civil Engineering Central South UniversityChangsha 410004China

This paper presents a unified calculation method and its application in determining the uniaxial mechanical properties of concrete with concrete strengths ranging from 10 to 140MPa.By analyzing a large collection of test results of the uniaxial mechanicalproperties of normal-strength,high-strength and super high-strength concrete in China and performing a regression analysis,unified calculation formulas for the mechanical indexes of concrete are proposed that can be applied to various grades of concrete for determining the size coefficient,uniaxial compressive strength,uniaxial tensile strength,elastic modulus,and strain at peak uniaxial compression and tension.Optimized mathematical equations for the nonlinear stress-strain relationship of concrete,including the ascending and descending branches.under uniaxial stress,are also established.The elastic modulus is almost constant throughout the elastic stage for the ascending branches of the stress-strain relationship for concrete.The proposed stress-strain relationship of concrete was applied to the nonlinear finite element analysis of both a steel-concrete composite beam and a concrete-filled steel tubular stub column.The analytical results are in good agreement with the experiment results,indicating that the proposed stress-strain relationship of concrete is applicable.The achievements presented in this paper can be used as references for the design and nonlinear finite element analysis of concrete structures.

关键词： concrete mechanical properties stress-strain relationship uniaxial stress application

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