Excitation power and temperature-dependent photoluminescence（PL） spectra of the ZnTe epilayer grown on（100）Ga As substrate and ZnTe bulk crystal are investigated. The measurement results show that both the structu...Excitation power and temperature-dependent photoluminescence（PL） spectra of the ZnTe epilayer grown on（100）Ga As substrate and ZnTe bulk crystal are investigated. The measurement results show that both the structures are of good structural quality due to their sharp bound excitonic emissions and absence of the deep level structural defect-related emissions. Furthermore, in contrast to the ZnTe bulk crystal, although excitonic emissions for the ZnTe epilayer are somewhat weak, perhaps due to As atoms diffusing from the Ga As substrate into the ZnTe epilayer and/or because of the strain-induced degradation of the crystalline quality of the ZnTe epilayer, neither the donor–acceptor pair（DAP） nor conduction band-acceptor（e–A） emissions are observed in the ZnTe epilayer. This indicates that by further optimizing the growth process it is possible to obtain a high-crystalline quality ZnTe heteroepitaxial layer that is comparable to the ZnTe bulk crystal.展开更多
Two experimental single crystal superalloys with 2% Cr and 4% Cr (mass fraction) were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Cr content on...Two experimental single crystal superalloys with 2% Cr and 4% Cr (mass fraction) were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Cr content on the microstructure, phase stability, tensile properties at 1100 °C and stress rupture properties at 1070 °C and 160 MPa of the single crystal superalloy were investigated. The results show that the size ofγ′ phase particles become small and uniform, and the cubic shape turns a little regular with the increase of Cr content. Theγ′ directional coarsening and rafting were observed in the 2% Cr and 4% Cr alloys after long term aging (LTA) at 1100 °C. The rafting rate ofγ′ phase increased with increasing Cr content. Needle-shaped topologically close packed (TCP) phases precipitated and grew along fixed direction in both alloys. The precipitating rate and volume fraction of TCP phases significantly increased with the increase of Cr content. The tensile property of the alloy increased and the stress rupture properties of the alloy decreased with the increase of Cr content at high temperature. The increase of Cr content increased the partition ratio of TCP forming elements, Re, W, and Mo, and the saturation degrees of these elements inγ phases increased. Therefore, the high temperature phase stability of the alloy decreased with the increase of Cr content.展开更多
Based on a 5% （mass fraction） Re-containing single crystal nickel-based superalloy with 3% （mass fraction） Cr, the microstructural variation with Cr addition was investigated. The experimental results show that se...Based on a 5% （mass fraction） Re-containing single crystal nickel-based superalloy with 3% （mass fraction） Cr, the microstructural variation with Cr addition was investigated. The experimental results show that segregation of alloying elements was enhanced in as-cast microstructure with Cr addition; and the volume fraction of eutectic is increased. However, the solidus and liquidus temperatures are remarkably reduced. With the increase of Cr content, the average γ＇ size and volume fraction are decreased in the fully heat treated microstructure. X-ray diffraction results indicate that γ/γ＇ lattice misfit becomes more negative. According to the energy dispersive spectroscopy （EDS） results, Cr is mainly distributed in the γ matrix; and more y-forming elements, such as Re and W, enter the γ matrix, while the γ/γ＇ partition ratio of Cr is inversely decreased.展开更多
An investigation has been made into the microstructural characterization of the shear bands generated under high-strain rate （≈10^4 s^-1） deformation in Fe-15%Cr-15%Ni single crystal by EBSD-SEM （electron backscat...An investigation has been made into the microstructural characterization of the shear bands generated under high-strain rate （≈10^4 s^-1） deformation in Fe-15%Cr-15%Ni single crystal by EBSD-SEM （electron backscatter diffraction-scanning electron microscopy）, TEM （transmission electron in microscopy） and HREM （high- resolution electron microscopy）. The results reveal that the propagation of the shear band exhibits an asymmetrical behavior arising from inhomogenous distribution in plasticity in the bands because of different resistance to the collapse in different crystallographic directions; The γ-ε-α′phase transformations may take place inside and outside the bands, and these martensitic phases currently nucleate at intersections either between the twins and deformation bands or between the twins and ε-sheet. Investigation by EBSD shows that recrystallization can occur in the bands with a grain size of an average of 0.2μm in diameter. These nano-grains are proposed to attribute to the results of either dynamic or static recrystallization, which can be described by the rotational recrystallization mechanism. Calculation and analysis indicate that the strain rate inside the shear band can reach 2.50×10^6 s^-1, which is higher, by two or three orders of magnitude, than that exerted dynamically on the specimen tested.展开更多
The title complex [Cr2（8-hqn）2Cl4（H2O）2]·2（CH3）2CO （8-hqn = 8-hydroxyoxyquinolate） has been synthesized and characterized by single-crystal X-ray diffraction. It crystallizes in the triclinic system, spac...The title complex [Cr2（8-hqn）2Cl4（H2O）2]·2（CH3）2CO （8-hqn = 8-hydroxyoxyquinolate） has been synthesized and characterized by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group P^-1 with a = 8.719（1）, b = 9.226（1）, c = 9.717（1） A^°, α = 71.916（2）, β= 78.072（2）, γ = 76.014（2）°, V= 713.72（15） A^°^3, Z= 1, Dc= 1.597g/cm^3, F（000） = 350 and μ（MoKa） = 1.177 mm^-1, the final R = 0.0490 and wR = 0.1055 for 1616 observed reflections with I 〉 2σ（I）. It is a dimer constructed by two monomeric units [Cr（8-hqn）Cl2（H2O）] bridged by phenoxide-like oxygen atom from 8-hydroxyoxyquinolate, where the two six-coordinated Cr（Ⅲ）atoms exhibit an octahedral coordination geometry.展开更多
In this paper, Cr-doped LiSrAlF6 crystals are investigated using high-temperature Raman spectroscopy and the single-crystal Raman spectra of Cr：LiSrAlF6 are analysed by factor group theory and comparison with other f...In this paper, Cr-doped LiSrAlF6 crystals are investigated using high-temperature Raman spectroscopy and the single-crystal Raman spectra of Cr：LiSrAlF6 are analysed by factor group theory and comparison with other fluorides. The results indicate that Cr：LiSrAlF6 is stable below its melting point; Raman peaks located at 561,322 and 250 cm-1 are assigned to the Alg modes of AlF6, SrF6 and LiF6 octachdra, respectively; with temperature increasing, Raman peaks associated with AlF6 octahedra shift towards low frequencies, while LiF6 and SrF6 octahedra are temperature- insensitive; around the crystal melting point, three new Raman peaks occur, which are associated with the AlF6 octahedral chain structure. Finally, the microstruetural evolution of Cr：LiSrAlF6 from room temperature to its melting point is discussed based on its Raman spectra.展开更多
This paper reported the crystal growth and spectroscopy characters of Cr^3＋：Li2Mg2（MoO4）3. The refractive index of Cr^3＋：Li2Mg2（MoO4）3 crystal is 1.87 and the hardness is 270 I-IV. This crystal shows broadband...This paper reported the crystal growth and spectroscopy characters of Cr^3＋：Li2Mg2（MoO4）3. The refractive index of Cr^3＋：Li2Mg2（MoO4）3 crystal is 1.87 and the hardness is 270 I-IV. This crystal shows broadband absorption property with peak wavelength at about 495 and 699 nm. The absorption crosssection is 14.75 × 10^-20 cm^2 at 495 nm and 9.63 ×10^-20 cm^2 at 699 nm, respectively. The crystal field strength and energy levels of Cr^3＋ ion were calculated based on the spectroscopic data. The Cr^3＋：Li2Mg2（MoO4）3 crystal shows broadband emission extending from 750 to 1300 nm even excited at 10 K. The room temperature emission cross section is 72×10^-20 cm^2 at 926 nm. A discussion of the relation between the spectroscopic properties and crystal field parameters of Cr^3＋：Li2Mg2（MoO4）3 crystal was presented based on the solid state spectroscopytheory.展开更多
Diode end-pumped solid-state lasers have the potential to yield high quality laser beams with high efficiency for laser range finding and warning receiver applications as well as day and night military laser designati...Diode end-pumped solid-state lasers have the potential to yield high quality laser beams with high efficiency for laser range finding and warning receiver applications as well as day and night military laser designation systems. In this paper we presents theoretical calculations using Advanced Dynamics Professional LASCAD software and experimental studies for a high power pigtailed fiber diode laser module of 8 W operating at 808 nm with a specially designed high efficiency cooling system, end pumped high-efficiency Nd:YVO4 laser of 3 × 3 × 10 mm rod and overall cavity length of 44 mm. To the best of our knowledge a self Q-switching effects was generated in Nd:YVO4 laser by changing the cavity dimensions and the position of the intracavity KTP crystal at certain regime of operation for the first time, in which the cavity length is reduced to be 30 mm and the distance between Nd:YVO4 rod and KTP crystal is only 1mm. Self Q-switched laser pulse at 532 nm with high peak power of 96 W, pulse width of 88 ns at FWHM and repetition rate of 400 kHz was achieved. Experimental studies of a passive Q-switched Nd:YVO4 laser using Cr:YAG crystal with three different transmissions of 30%, 40% and 70% were investigated. Passive Q-switched laser pulse at 1064 nm and narrow line width of less than 1.5 nm with highest peak power of nearly 18 kW, short pulse width of less than 4 ns at FWHM and higher repetition rate of 45 kHz using Cr:YAG with transmission of 30% was achieved for the first time.展开更多
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20120131110006)the Key Science and Technology Program of Shandong Province+10 种基金China(Grant No.2013GGX10221)the Key Laboratory of Functional Crystal Materials and Device(Shandong UniversityMinistry of Education)China(Grant No.JG1401)the National Natural Science Foundation of China(Grant No.61306113)the Major Research Plan of the National Natural Science Foundation of China(Grant No.91433112)the Partnership Project for Fundamental Technology Researches of the Ministry of EducationCultureSportsScience and TechnologyJapan
文摘Excitation power and temperature-dependent photoluminescence（PL） spectra of the ZnTe epilayer grown on（100）Ga As substrate and ZnTe bulk crystal are investigated. The measurement results show that both the structures are of good structural quality due to their sharp bound excitonic emissions and absence of the deep level structural defect-related emissions. Furthermore, in contrast to the ZnTe bulk crystal, although excitonic emissions for the ZnTe epilayer are somewhat weak, perhaps due to As atoms diffusing from the Ga As substrate into the ZnTe epilayer and/or because of the strain-induced degradation of the crystalline quality of the ZnTe epilayer, neither the donor–acceptor pair（DAP） nor conduction band-acceptor（e–A） emissions are observed in the ZnTe epilayer. This indicates that by further optimizing the growth process it is possible to obtain a high-crystalline quality ZnTe heteroepitaxial layer that is comparable to the ZnTe bulk crystal.
文摘Two experimental single crystal superalloys with 2% Cr and 4% Cr (mass fraction) were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Cr content on the microstructure, phase stability, tensile properties at 1100 °C and stress rupture properties at 1070 °C and 160 MPa of the single crystal superalloy were investigated. The results show that the size ofγ′ phase particles become small and uniform, and the cubic shape turns a little regular with the increase of Cr content. Theγ′ directional coarsening and rafting were observed in the 2% Cr and 4% Cr alloys after long term aging (LTA) at 1100 °C. The rafting rate ofγ′ phase increased with increasing Cr content. Needle-shaped topologically close packed (TCP) phases precipitated and grew along fixed direction in both alloys. The precipitating rate and volume fraction of TCP phases significantly increased with the increase of Cr content. The tensile property of the alloy increased and the stress rupture properties of the alloy decreased with the increase of Cr content at high temperature. The increase of Cr content increased the partition ratio of TCP forming elements, Re, W, and Mo, and the saturation degrees of these elements inγ phases increased. Therefore, the high temperature phase stability of the alloy decreased with the increase of Cr content.
基金Projects (2010CB631200, 2010CB631206) supported by the National Basic Research Program of ChinaProject (50931004) supported by the National Natural Science Foundation of China
文摘Based on a 5% （mass fraction） Re-containing single crystal nickel-based superalloy with 3% （mass fraction） Cr, the microstructural variation with Cr addition was investigated. The experimental results show that segregation of alloying elements was enhanced in as-cast microstructure with Cr addition; and the volume fraction of eutectic is increased. However, the solidus and liquidus temperatures are remarkably reduced. With the increase of Cr content, the average γ＇ size and volume fraction are decreased in the fully heat treated microstructure. X-ray diffraction results indicate that γ/γ＇ lattice misfit becomes more negative. According to the energy dispersive spectroscopy （EDS） results, Cr is mainly distributed in the γ matrix; and more y-forming elements, such as Re and W, enter the γ matrix, while the γ/γ＇ partition ratio of Cr is inversely decreased.
文摘An investigation has been made into the microstructural characterization of the shear bands generated under high-strain rate （≈10^4 s^-1） deformation in Fe-15%Cr-15%Ni single crystal by EBSD-SEM （electron backscatter diffraction-scanning electron microscopy）, TEM （transmission electron in microscopy） and HREM （high- resolution electron microscopy）. The results reveal that the propagation of the shear band exhibits an asymmetrical behavior arising from inhomogenous distribution in plasticity in the bands because of different resistance to the collapse in different crystallographic directions; The γ-ε-α′phase transformations may take place inside and outside the bands, and these martensitic phases currently nucleate at intersections either between the twins and deformation bands or between the twins and ε-sheet. Investigation by EBSD shows that recrystallization can occur in the bands with a grain size of an average of 0.2μm in diameter. These nano-grains are proposed to attribute to the results of either dynamic or static recrystallization, which can be described by the rotational recrystallization mechanism. Calculation and analysis indicate that the strain rate inside the shear band can reach 2.50×10^6 s^-1, which is higher, by two or three orders of magnitude, than that exerted dynamically on the specimen tested.
基金supported by the National Natural Science Foundation of China (No. 10676012)
文摘The title complex [Cr2（8-hqn）2Cl4（H2O）2]·2（CH3）2CO （8-hqn = 8-hydroxyoxyquinolate） has been synthesized and characterized by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group P^-1 with a = 8.719（1）, b = 9.226（1）, c = 9.717（1） A^°, α = 71.916（2）, β= 78.072（2）, γ = 76.014（2）°, V= 713.72（15） A^°^3, Z= 1, Dc= 1.597g/cm^3, F（000） = 350 and μ（MoKa） = 1.177 mm^-1, the final R = 0.0490 and wR = 0.1055 for 1616 observed reflections with I 〉 2σ（I）. It is a dimer constructed by two monomeric units [Cr（8-hqn）Cl2（H2O）] bridged by phenoxide-like oxygen atom from 8-hydroxyoxyquinolate, where the two six-coordinated Cr（Ⅲ）atoms exhibit an octahedral coordination geometry.
基金Project supported by the Key Program of the National Natural Science Foundation of China （Grant No. 50932005） and the Open Poject of Shanghai Key Laboratory of Modern Metallurgy and Materials Processing （Grant No. SELF-2009-01）.
文摘In this paper, Cr-doped LiSrAlF6 crystals are investigated using high-temperature Raman spectroscopy and the single-crystal Raman spectra of Cr：LiSrAlF6 are analysed by factor group theory and comparison with other fluorides. The results indicate that Cr：LiSrAlF6 is stable below its melting point; Raman peaks located at 561,322 and 250 cm-1 are assigned to the Alg modes of AlF6, SrF6 and LiF6 octachdra, respectively; with temperature increasing, Raman peaks associated with AlF6 octahedra shift towards low frequencies, while LiF6 and SrF6 octahedra are temperature- insensitive; around the crystal melting point, three new Raman peaks occur, which are associated with the AlF6 octahedral chain structure. Finally, the microstruetural evolution of Cr：LiSrAlF6 from room temperature to its melting point is discussed based on its Raman spectra.
基金supported by the National Natural Science Foundation of China(Nos.61308085 and 61475158)
文摘This paper reported the crystal growth and spectroscopy characters of Cr^3＋：Li2Mg2（MoO4）3. The refractive index of Cr^3＋：Li2Mg2（MoO4）3 crystal is 1.87 and the hardness is 270 I-IV. This crystal shows broadband absorption property with peak wavelength at about 495 and 699 nm. The absorption crosssection is 14.75 × 10^-20 cm^2 at 495 nm and 9.63 ×10^-20 cm^2 at 699 nm, respectively. The crystal field strength and energy levels of Cr^3＋ ion were calculated based on the spectroscopic data. The Cr^3＋：Li2Mg2（MoO4）3 crystal shows broadband emission extending from 750 to 1300 nm even excited at 10 K. The room temperature emission cross section is 72×10^-20 cm^2 at 926 nm. A discussion of the relation between the spectroscopic properties and crystal field parameters of Cr^3＋：Li2Mg2（MoO4）3 crystal was presented based on the solid state spectroscopytheory.
文摘Diode end-pumped solid-state lasers have the potential to yield high quality laser beams with high efficiency for laser range finding and warning receiver applications as well as day and night military laser designation systems. In this paper we presents theoretical calculations using Advanced Dynamics Professional LASCAD software and experimental studies for a high power pigtailed fiber diode laser module of 8 W operating at 808 nm with a specially designed high efficiency cooling system, end pumped high-efficiency Nd:YVO4 laser of 3 × 3 × 10 mm rod and overall cavity length of 44 mm. To the best of our knowledge a self Q-switching effects was generated in Nd:YVO4 laser by changing the cavity dimensions and the position of the intracavity KTP crystal at certain regime of operation for the first time, in which the cavity length is reduced to be 30 mm and the distance between Nd:YVO4 rod and KTP crystal is only 1mm. Self Q-switched laser pulse at 532 nm with high peak power of 96 W, pulse width of 88 ns at FWHM and repetition rate of 400 kHz was achieved. Experimental studies of a passive Q-switched Nd:YVO4 laser using Cr:YAG crystal with three different transmissions of 30%, 40% and 70% were investigated. Passive Q-switched laser pulse at 1064 nm and narrow line width of less than 1.5 nm with highest peak power of nearly 18 kW, short pulse width of less than 4 ns at FWHM and higher repetition rate of 45 kHz using Cr:YAG with transmission of 30% was achieved for the first time.
