In order to study the influence of crystal structure change due to implantation dose on the hardness and wear performance of 300M high-strength steel,samples were surface modified by Cr implantation with dosages of 5....In order to study the influence of crystal structure change due to implantation dose on the hardness and wear performance of 300M high-strength steel,samples were surface modified by Cr implantation with dosages of 5.0 × 10^16,1.5 × 10^17 and 3.0 × 10^17 ions/cm^2.X-ray diffraction method,which was already applied in studies on the microstructure of deformed and heat-treated materials,was used to study the crystal structure of the implanted steel,and the results were corrected with the hardness and wear performance.The solid solution strengthening effect and microstructure vary with increase in implantation dose.Owing to strong solid solution hardening of Cr,small average crystallite size and high dislocation density,the hardness and wear resistance of implanted steel with dose of 5.0 × 10^16 ions/cm^2 were found to be the highest compared with other samples.Moreover,although the crystal lite size of the implanted sample with dose of 3 × 10^17 ions/cm^2 was similar to that of substrate and the dislocation density was lower than that of the substrate,its higher hardness and lower specific wear rate were due to the solid solution hardening and perhaps Cr clusters reinforcement.展开更多
ZnO single crystals were grown by the innovated hydrothermal method. The crystal surfaces were polished, and then studied by atom force microscope （AFM） and wet-chemical etching （WCE）. It was found that the Zn pol...ZnO single crystals were grown by the innovated hydrothermal method. The crystal surfaces were polished, and then studied by atom force microscope （AFM） and wet-chemical etching （WCE）. It was found that the Zn polar plane was smoother than O polar plane under the same polishing conditions. The etch pit density of Zn polar plane is 4.3×10^3 cm^-2, which is consistent with the previous report, while the density of etch pit of O polar plane is more than 103cm^-2. After annealing treatment, the density of etch pit of Zn plane reduces to 5.8×102 cm^2 and is superior to the current report. This investigation reveals that the high quality ZnO single crystals with fine Zn polar plane can be obtained by the innovated hydrothermal method.展开更多
In this paper, we report the ground state properties i.e. electron momentum density and X-ray structure factors of fcc-copper are presented. The Am241 Compton spectrometer, which uses 59.54 keV gamma-rays, has been us...In this paper, we report the ground state properties i.e. electron momentum density and X-ray structure factors of fcc-copper are presented. The Am241 Compton spectrometer, which uses 59.54 keV gamma-rays, has been used for the Compton profile measurement. To compare the experimental data, the Compton profiles within the framework of linear combination of atomic orbitals (LCAO) method using Hartree–Fock (HF), density functional (DF) and hybrid B3PW schemes embodied in the CRYSTAL06 code have been computed. Among the various theoretical calculations, it is found that the present experimental data is in very good agreement with the hybrid B3PW scheme. A real-space analysis of the experimental Compton profile shows the metal-like behavior of copper The structure factors for copper are computed using hybrid B3PW scheme and compared with available experimental and theoretical data.展开更多
A large database is desired for machine learning(ML) technology to make accurate predictions of materials physicochemical properties based on their molecular structure.When a large database is not available,the develo...A large database is desired for machine learning(ML) technology to make accurate predictions of materials physicochemical properties based on their molecular structure.When a large database is not available,the development of proper featurization method based on physicochemical nature of target proprieties can improve the predictive power of ML models with a smaller database.In this work,we show that two new featurization methods,volume occupation spatial matrix and heat contribution spatial matrix,can improve the accuracy in predicting energetic materials' crystal density(ρ_(crystal)) and solid phase enthalpy of formation(H_(f,solid)) using a database containing 451 energetic molecules.Their mean absolute errors are reduced from 0.048 g/cm~3 and 24.67 kcal/mol to 0.035 g/cm~3 and 9.66 kcal/mol,respectively.By leave-one-out-cross-validation,the newly developed ML models can be used to determine the performance of most kinds of energetic materials except cubanes.Our ML models are applied to predict ρ_(crystal) and H_(f,solid) of CHON-based molecules of the 150 million sized PubChem database,and screened out 56 candidates with competitive detonation performance and reasonable chemical structures.With further improvement in future,spatial matrices have the potential of becoming multifunctional ML simulation tools that could provide even better predictions in wider fields of materials science.展开更多
Effective prevention and management of osteoporosis would require suitable methods for population screenings and early diagnosis. Current clinicallyavailable diagnostic methods are mainly based on the use of either X-...Effective prevention and management of osteoporosis would require suitable methods for population screenings and early diagnosis. Current clinicallyavailable diagnostic methods are mainly based on the use of either X-rays or ultrasound(US). All X-ray based methods provide a measure of bone mineral density(BMD), but it has been demonstrated that other structural aspects of the bone are important in determining fracture risk, such as mechanical features and elastic properties, which cannot be assessed using densitometric techniques. Among the most commonly used techniques, dual X-ray absorptiometry(DXA) is considered the current 'gold standard' for osteoporosis diagnosis and fracture risk prediction. Unfortunately, as other X-ray based techniques, DXA has specific limitations(e.g., use of ionizing radiation, large size of the equipment, high costs, limited availability) that hinder its application for population screenings and primary care diagnosis. This has resulted in an increasing interest in developing reliable pre-screening tools for osteoporosis such as quantitative ultrasound(QUS) scanners, which do not involve ionizing radiation exposure and represent a cheaper solution exploiting portable and widely available devices. Furthermore, the usefulness of QUS techniques in fracture risk prediction has been proven and, with the last developments, they are also becoming a more and more reliable approach for assessing bone quality. However, the US assessment of osteoporosis is currently used only as a pre-screening tool, requiring a subsequent diagnosis confirmation by means of a DXA evaluation. Here we illustrate the state of art in the early diagnosis of this 'silent disease' and show up recent advances for its prevention and improved management through early diagnosis.展开更多
Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on phy...Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on physical profile functions for dislocations, domain size, stacking faults and twin boundaries. Order dependence, strain anisotropy, hkl dependent broadening of planar defects and peak shape are used to separate the effect of different lattice defect types. The Marquardt-Levenberg (ML) numerical optimiza-tion procedure has been used successfully to determine crystal defect types and densities. However, in more complex cases like hexagonal materials or multiple phases the ML procedure alone reveals uncer-tainties. In a new approach the ML and a Monte-Carlo statistical method are combined in an alternative manner. The new CMWP procedure eliminates uncertainties and provides globally optimized parameters.展开更多
Two compounds, Dy_2(WO_4)_3 and GdY(WO_4)_3, were synthesized by using thestandard solid state reaction technique. The crystal structure was determined by powder X-raydiffraction and Rietveld refinement method. It is ...Two compounds, Dy_2(WO_4)_3 and GdY(WO_4)_3, were synthesized by using thestandard solid state reaction technique. The crystal structure was determined by powder X-raydiffraction and Rietveld refinement method. It is found that both compounds have Eu_2(WO_4)_3-typemonoclinic structure, with space group C 2/c, Z = 4. The unit cell parameters of Dy_2(WO_4)_3 are a= 0.75981(1) nm, b = 1.13220(1) nm, c = 1.13254(1) nm, and beta = 109.8001(3) deg, and those ofGdY(WO_4)_3 arc a = 0.76175(1) nm, b = 1.13543(1) nm, c = 1.13496(2) nm, and beta = 109.8015(13)deg. Each W atom has four oxygen nearest neighbors, while each rare-earth atom is surrounded byeight oxygen atoms. WO_4 tetrahedra share their four vertices with REO_8 (RE = Dy, Gd, or Y)trigondodecahedra and some REO_8 trigondodecahedra share an edge with each other. The phasetransition and the magnetic properties were investigated by differential thermal analysis (DTA) anddc superconducting quantum interference device (SQUID) magnetometer.展开更多
The compound NdAlSi was studied using X-ray powder diffraction technique and refined by the Rietveld method. The compound NdAlSi has tetragonal α-ThSiE-type structure, space group I41/amd （No. 141）, Z = 4, and the ...The compound NdAlSi was studied using X-ray powder diffraction technique and refined by the Rietveld method. The compound NdAlSi has tetragonal α-ThSiE-type structure, space group I41/amd （No. 141）, Z = 4, and the lattice parameters a = 0.41991（1） nm, c = 1.44916（3） nm. The Smith and Snyder figure of merit FN is F30= 103.1（36）. The R-factors of Rietveld refinement are Rp= 0.113 and Rwp= 0.148, respectively. The X-ray powder diffraction data is presented in this article.展开更多
Spherical cobalt carbonate with high tap density, good crystallization and uniform particle size was prepared by controlled chemical crystal method using cobalt chloride and ammonium bicarbonate as cobalt source and p...Spherical cobalt carbonate with high tap density, good crystallization and uniform particle size was prepared by controlled chemical crystal method using cobalt chloride and ammonium bicarbonate as cobalt source and precipitator. The effects of pH value and reaction time on crystallization and physical properties of cobalt carbonate were studied. The results show that the key factors influencing the preparation process of spherical cobalt carbonate with high tap density and good crystallization are how to control pH value (7.25±0.05) and keep some reaction time (about 10 h). Co4O3 was prepared by sintering spherical morphology CoCO3 samples at varied temperatures. The results show that as the decomposition temperature increases, the as-obtained Co4O3 products with porous structure transform into polyhedral structure with glazed surface, and simultaneously the cobalt content and tap density increase. However, the specific surface area shows a trend of decrease.展开更多
Plasma density and temperature can be diagnosed by x-ray line emission measurement with crystal,and bent crystals such as von Hamos and Hall structures are proposed to improve the diffraction brightness.In this study,...Plasma density and temperature can be diagnosed by x-ray line emission measurement with crystal,and bent crystals such as von Hamos and Hall structures are proposed to improve the diffraction brightness.In this study,a straightforward solution for the focusing schemes of flat and bent crystals is provided.Simulations with XOP code are performed to validate the analytical model,and good agreements are achieved.The von Hamos or multi-cone crystal can lead to several hundred times intensity enhancements for a 200μm plasma source.This model benefits the applications of the focusing bent crystals.展开更多
A new laser crystal Nd0.05La0.95Sc3(BO3)4 up to 50mm(38mm(7 mm was grown by top-seeded solution growth method from a Li6B4O9 flux. The grown crystal was characterized by X-ray powder diffraction. Its crystal structure...A new laser crystal Nd0.05La0.95Sc3(BO3)4 up to 50mm(38mm(7 mm was grown by top-seeded solution growth method from a Li6B4O9 flux. The grown crystal was characterized by X-ray powder diffraction. Its crystal structure is monoclinic with space group Cc and the unit cell dimensions: a=12.066(5), b=9.864(2), c=7.740(3) ?,β= 105.48(5)(, V=887.8(6)?3, Z=4, Dc=3.81g/cm3, which belongs to low-temperature phase. The optical absorption of the crystal shows that NLSB has a strong absorption band at 807.7 nm, which is suitable for laser-diode pumping.展开更多
Pure bisthiourea cadmium bromide (BTCB) and 1 mole % L-alanine mixed bisthiourea cadmium bromide (LABTCB) single crystals have been grown by slow evaporation method. The grown crystals have been characterized by singl...Pure bisthiourea cadmium bromide (BTCB) and 1 mole % L-alanine mixed bisthiourea cadmium bromide (LABTCB) single crystals have been grown by slow evaporation method. The grown crystals have been characterized by single crystal XRD analysis, powder XRD analysis, FTIR analysis, UV-Vis-NIR analysis and SHG studies. XRD analysis confirms the crystalline nature of the materials. The addition of L-alanine changes the crystal structure from orthorhombic to tetragonal. The presence of various functional groups present in the pure BTCB and LABTCB crystals have been confirmed by FTIR analysis. The UV-Vis-NIR spectrum shows the transmission characteristics of the crystals. The SHG study depicts the nonlinear optical efficiency of the crystals.展开更多
The nonlinear optical crystals of cobalt (Co2+) mixed copper mercury thiocyanate have been grown by slow evaporation method using water and ethanol as solvents. The grown crystals have been subjected to different char...The nonlinear optical crystals of cobalt (Co2+) mixed copper mercury thiocyanate have been grown by slow evaporation method using water and ethanol as solvents. The grown crystals have been subjected to different characterization analyses and the results were compared with pure copper mercury thiocyanate crystal (CMTC), which has been already reported. The single crystal X-ray diffraction shows that the addition of metallic impurity does not alter the basic structure of the parent crystal, but increases the cell volume markedly. The presence of functional groups has been identified using FT-IR analysis. Further the grown crystal is characterized by optical transmission analysis and thermal analysis. The thermal stability of the grown crystal is high, compared to pure CMTC crystal. The optical transparency of the grown crystal is studied by UV-Vis-NIR analysis. This study reveals that Co2+ mixed CMTC crystal has wider transparent waveband than pure CMTC crystal. The relative second harmonic generation efficiency of the Co2+ mixed CMTC crystal has been tested by Kurtz-Perry powder technique.展开更多
Crystal structures and thermal expansion properties of Yb2-xFexMo3O12（x=0.0,0.6,1.0,1.1,1.4） solid solutions have been studied by X-ray powder diffraction（XRPD） at different temperatures.Rietveld analysis of the X...Crystal structures and thermal expansion properties of Yb2-xFexMo3O12（x=0.0,0.6,1.0,1.1,1.4） solid solutions have been studied by X-ray powder diffraction（XRPD） at different temperatures.Rietveld analysis of the XRPD data shows that Yb2-xFexMo3O12 solid solutions adopt orthorhombic structure and have variable thermal expansion coefficients controlled by the ratio of Yb^3＋ to Fe^3＋.Yb2Mo3O12 shows anisotropic negative thermal expansion property,induced by the reductions in average Yb-O-Mo angle and average apparent Mo2-O bond length with increasing temperatures.As more Yb^3＋ substituted by Fe^3＋,the linear thermal expansion coefficients of Yb2-xFexMo3O12 increase from negative to positive.A near-zero thermal expansion coefficient of 0.55×10^-6K^-1 for Yb0.6Fe1.4Mo3O12 is observed in the temperature range of 573-873 K.展开更多
In this paper, we propose a method to improve anti-radiation capability by coating heavy metal X-ray protection glass with compound photonic crystal layers, based on the unique property of photonic crystal that light ...In this paper, we propose a method to improve anti-radiation capability by coating heavy metal X-ray protection glass with compound photonic crystal layers, based on the unique property of photonic crystal that light cannot be propagated within the range of band gaps. Using the plane wave expansion method,we made a theoretical study of parameters affecting the band gap structures of one-dimensional photonic crystals. Based on the findings, we chose appropriate materials and compound structure of photonic crystal so as to get high X-ray reflection coating photonic crystal layers. By this method, the reflection rate within X-ray wavelength can reach the maximum value of 100%, and the average value of over 90%. Even low-cost heavy metal X-ray protection glass of absorption coefficient value can achieve the desired effect. Thus, this method greatly decreases the anti-radiation requirements of heavy X-ray protection glass.展开更多
A uranyl compound, K_4UO_2(CO_3)_3 has been characterized by powder X-ray diffraction method. M. W.=606.46, monoclinic, C2/c (No. 15), a=1.0240(7), b=0.9198(4), c=1.2222(12)nm, β=95.12(4)°,V=1.1466(5)nm^3, Z=4, ...A uranyl compound, K_4UO_2(CO_3)_3 has been characterized by powder X-ray diffraction method. M. W.=606.46, monoclinic, C2/c (No. 15), a=1.0240(7), b=0.9198(4), c=1.2222(12)nm, β=95.12(4)°,V=1.1466(5)nm^3, Z=4, D_m=3.468g/cm^3, D_c=3.513g/cm~, λ(Cu Kα_1)=O.1540598nm, T=298K. The structure was solved by heavy atom method and Fourier synthesis, and refined by full- matrix least-squares method to R=0.1185 for 275 reflections. The uranium (Ⅵ) atom is in an eight-coordinate distorted hexagonal-bipyramidal environment with creasy fan shape. The linear uranyl group approaches to perpendicular to the equatorial plane in which three carbonate groups are chelated. U(Ⅵ) has two linear oxygen atoms closer to it (U-O=0.1767 (5) nm) than six other neighbours (U-O ranging from 0.2516 to 0.2568nm). The distances between carbon atoms and uncoordinated oxygen atoms are 0.122 (1) and 0.123(1) nm, which are distinctly different from those between carbon and coordinated oxygen atoms (mean 0.134(6) nm). This fact reveals the non-eq- uivalence of one oxygen atom to the other two in each carbonate. In K_4UO_2(CO_3)_3, the O-O dis- tance for the adjacent carbonate groups is 0.2794(4)nm approaching to the sum of Van der Waals radii of two oxygen atoms. The K-O distances vary between 0.2667 and 0.3131nm, and each anion is immediately surrounded by six potassium ions, only four of which can be considered to belong to the same structural formula unit, and they are symmetrically located above and below the equatorial plane.展开更多
密度是决定含能材料爆轰性能的重要参数。为评估现有CHON类含能材料密度的计算方法,对等电子密度面法、分子表面静电势法、基团加和法、晶体堆积法、定量构效关系法、经验公式法等进行分析和归类。结果表明,基于分子体积预测方法的精度...密度是决定含能材料爆轰性能的重要参数。为评估现有CHON类含能材料密度的计算方法,对等电子密度面法、分子表面静电势法、基团加和法、晶体堆积法、定量构效关系法、经验公式法等进行分析和归类。结果表明,基于分子体积预测方法的精度取决于分子间和分子内相互作用对密度影响描述的准确度。其中,准确描述氢键和van der Waals作用充满了挑战性。基于晶体体积计算密度的核心在于晶体结构的准确预测,结构搜索要面对巨大的状态空间和高度复杂的能量曲面的困难,预测效率是亟待解决的问题。体积加和法和经验公式法存在无法区分同分异构体和晶型的缺点,且对新发现的具有特殊结构的分子由于缺乏实验数据难以获得准确的经验参数,计算结果偏差较大。引入人工神经网络、遗传算法以及支持向量机等机器学习算法后,定量构效关系法在含能化合物性能与结构关系研究中取得很大成就,模型精度进一步提高将为基于材料基因组模式的含能材料设计研发奠定基础,这也是今后密度预测方法发展的主要方向。展开更多
基金This project was supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions,Chinathe Jiangsu Province Graduate Cultivation Innovative Project(Grant No.KYLX16_0347)+4 种基金Natural Science Foundation for Excellent Young Scientists of Jiangsu Province,China(Grant No.BK20180068)China Postdoctoral Science Foundation funded project,China(Grant No.2018M630555)the Fundamental Research Funds for the Central Universities,China(Grant No.NS2018039)the China Scholarship CouncilChina(Grant No.201706830071,awarded to Xiao-hu Chen for 1 year of study at the Department of Mechanical and Aerospace Engineering,Carleton University).The raw/processed data required to reproduce these findings cannot be shared at this time due to contractual issues.
文摘In order to study the influence of crystal structure change due to implantation dose on the hardness and wear performance of 300M high-strength steel,samples were surface modified by Cr implantation with dosages of 5.0 × 10^16,1.5 × 10^17 and 3.0 × 10^17 ions/cm^2.X-ray diffraction method,which was already applied in studies on the microstructure of deformed and heat-treated materials,was used to study the crystal structure of the implanted steel,and the results were corrected with the hardness and wear performance.The solid solution strengthening effect and microstructure vary with increase in implantation dose.Owing to strong solid solution hardening of Cr,small average crystallite size and high dislocation density,the hardness and wear resistance of implanted steel with dose of 5.0 × 10^16 ions/cm^2 were found to be the highest compared with other samples.Moreover,although the crystal lite size of the implanted sample with dose of 3 × 10^17 ions/cm^2 was similar to that of substrate and the dislocation density was lower than that of the substrate,its higher hardness and lower specific wear rate were due to the solid solution hardening and perhaps Cr clusters reinforcement.
基金Supported by the Knowledge Innovation Program of the Chinese Academy of SciencesSpecial Project on Science and Technology of Fujian Province (2005HZ1023)+4 种基金Knowledge Innovation Project of the Chinese Academy of Sciences (KJCX2.YW.W01)Outstanding Youth Fund (50625205)Youth Talent of Fujian Province (2006F3140)Fujian Engineering Research Center for Optoelectronic Materials (2007K02, 2005DC105003)the National Key Project of China for Basic Research (2007CB936703)
文摘ZnO single crystals were grown by the innovated hydrothermal method. The crystal surfaces were polished, and then studied by atom force microscope （AFM） and wet-chemical etching （WCE）. It was found that the Zn polar plane was smoother than O polar plane under the same polishing conditions. The etch pit density of Zn polar plane is 4.3×10^3 cm^-2, which is consistent with the previous report, while the density of etch pit of O polar plane is more than 103cm^-2. After annealing treatment, the density of etch pit of Zn plane reduces to 5.8×102 cm^2 and is superior to the current report. This investigation reveals that the high quality ZnO single crystals with fine Zn polar plane can be obtained by the innovated hydrothermal method.
文摘In this paper, we report the ground state properties i.e. electron momentum density and X-ray structure factors of fcc-copper are presented. The Am241 Compton spectrometer, which uses 59.54 keV gamma-rays, has been used for the Compton profile measurement. To compare the experimental data, the Compton profiles within the framework of linear combination of atomic orbitals (LCAO) method using Hartree–Fock (HF), density functional (DF) and hybrid B3PW schemes embodied in the CRYSTAL06 code have been computed. Among the various theoretical calculations, it is found that the present experimental data is in very good agreement with the hybrid B3PW scheme. A real-space analysis of the experimental Compton profile shows the metal-like behavior of copper The structure factors for copper are computed using hybrid B3PW scheme and compared with available experimental and theoretical data.
基金support from the Ministry of Education(MOE) Singapore Tier 1 (RG8/20)。
文摘A large database is desired for machine learning(ML) technology to make accurate predictions of materials physicochemical properties based on their molecular structure.When a large database is not available,the development of proper featurization method based on physicochemical nature of target proprieties can improve the predictive power of ML models with a smaller database.In this work,we show that two new featurization methods,volume occupation spatial matrix and heat contribution spatial matrix,can improve the accuracy in predicting energetic materials' crystal density(ρ_(crystal)) and solid phase enthalpy of formation(H_(f,solid)) using a database containing 451 energetic molecules.Their mean absolute errors are reduced from 0.048 g/cm~3 and 24.67 kcal/mol to 0.035 g/cm~3 and 9.66 kcal/mol,respectively.By leave-one-out-cross-validation,the newly developed ML models can be used to determine the performance of most kinds of energetic materials except cubanes.Our ML models are applied to predict ρ_(crystal) and H_(f,solid) of CHON-based molecules of the 150 million sized PubChem database,and screened out 56 candidates with competitive detonation performance and reasonable chemical structures.With further improvement in future,spatial matrices have the potential of becoming multifunctional ML simulation tools that could provide even better predictions in wider fields of materials science.
基金Supported by Partially funded by FESR P.O.Apulia Region 2007-2013-Action 1.2.4,No.3Q5AX31
文摘Effective prevention and management of osteoporosis would require suitable methods for population screenings and early diagnosis. Current clinicallyavailable diagnostic methods are mainly based on the use of either X-rays or ultrasound(US). All X-ray based methods provide a measure of bone mineral density(BMD), but it has been demonstrated that other structural aspects of the bone are important in determining fracture risk, such as mechanical features and elastic properties, which cannot be assessed using densitometric techniques. Among the most commonly used techniques, dual X-ray absorptiometry(DXA) is considered the current 'gold standard' for osteoporosis diagnosis and fracture risk prediction. Unfortunately, as other X-ray based techniques, DXA has specific limitations(e.g., use of ionizing radiation, large size of the equipment, high costs, limited availability) that hinder its application for population screenings and primary care diagnosis. This has resulted in an increasing interest in developing reliable pre-screening tools for osteoporosis such as quantitative ultrasound(QUS) scanners, which do not involve ionizing radiation exposure and represent a cheaper solution exploiting portable and widely available devices. Furthermore, the usefulness of QUS techniques in fracture risk prediction has been proven and, with the last developments, they are also becoming a more and more reliable approach for assessing bone quality. However, the US assessment of osteoporosis is currently used only as a pre-screening tool, requiring a subsequent diagnosis confirmation by means of a DXA evaluation. Here we illustrate the state of art in the early diagnosis of this 'silent disease' and show up recent advances for its prevention and improved management through early diagnosis.
基金support of the János Bolyai Research Fellowship of the Hungarian Academy of Sciences. T.U. is grateful for partial funding of this work by an EPSRC Leadership Fellowship [EP/I005420/1, EP/K039237/1, EP/K034650/1, EP/L018616/1 and EP/K034332/1] for the study of irradiation damage in zirconium alloys
文摘Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on physical profile functions for dislocations, domain size, stacking faults and twin boundaries. Order dependence, strain anisotropy, hkl dependent broadening of planar defects and peak shape are used to separate the effect of different lattice defect types. The Marquardt-Levenberg (ML) numerical optimiza-tion procedure has been used successfully to determine crystal defect types and densities. However, in more complex cases like hexagonal materials or multiple phases the ML procedure alone reveals uncer-tainties. In a new approach the ML and a Monte-Carlo statistical method are combined in an alternative manner. The new CMWP procedure eliminates uncertainties and provides globally optimized parameters.
文摘Two compounds, Dy_2(WO_4)_3 and GdY(WO_4)_3, were synthesized by using thestandard solid state reaction technique. The crystal structure was determined by powder X-raydiffraction and Rietveld refinement method. It is found that both compounds have Eu_2(WO_4)_3-typemonoclinic structure, with space group C 2/c, Z = 4. The unit cell parameters of Dy_2(WO_4)_3 are a= 0.75981(1) nm, b = 1.13220(1) nm, c = 1.13254(1) nm, and beta = 109.8001(3) deg, and those ofGdY(WO_4)_3 arc a = 0.76175(1) nm, b = 1.13543(1) nm, c = 1.13496(2) nm, and beta = 109.8015(13)deg. Each W atom has four oxygen nearest neighbors, while each rare-earth atom is surrounded byeight oxygen atoms. WO_4 tetrahedra share their four vertices with REO_8 (RE = Dy, Gd, or Y)trigondodecahedra and some REO_8 trigondodecahedra share an edge with each other. The phasetransition and the magnetic properties were investigated by differential thermal analysis (DTA) anddc superconducting quantum interference device (SQUID) magnetometer.
基金This project was financially supported by the Doctoral Start-up Foundation of Guangxi University.
文摘The compound NdAlSi was studied using X-ray powder diffraction technique and refined by the Rietveld method. The compound NdAlSi has tetragonal α-ThSiE-type structure, space group I41/amd （No. 141）, Z = 4, and the lattice parameters a = 0.41991（1） nm, c = 1.44916（3） nm. The Smith and Snyder figure of merit FN is F30= 103.1（36）. The R-factors of Rietveld refinement are Rp= 0.113 and Rwp= 0.148, respectively. The X-ray powder diffraction data is presented in this article.
文摘Spherical cobalt carbonate with high tap density, good crystallization and uniform particle size was prepared by controlled chemical crystal method using cobalt chloride and ammonium bicarbonate as cobalt source and precipitator. The effects of pH value and reaction time on crystallization and physical properties of cobalt carbonate were studied. The results show that the key factors influencing the preparation process of spherical cobalt carbonate with high tap density and good crystallization are how to control pH value (7.25±0.05) and keep some reaction time (about 10 h). Co4O3 was prepared by sintering spherical morphology CoCO3 samples at varied temperatures. The results show that as the decomposition temperature increases, the as-obtained Co4O3 products with porous structure transform into polyhedral structure with glazed surface, and simultaneously the cobalt content and tap density increase. However, the specific surface area shows a trend of decrease.
基金Project supported by the National Natural Science Fundation of China(Grant Nos.11775203 and 12075219)the China Academy of Engineering Physics(CAEP)Foundation(Grant No.CX20210019).
文摘Plasma density and temperature can be diagnosed by x-ray line emission measurement with crystal,and bent crystals such as von Hamos and Hall structures are proposed to improve the diffraction brightness.In this study,a straightforward solution for the focusing schemes of flat and bent crystals is provided.Simulations with XOP code are performed to validate the analytical model,and good agreements are achieved.The von Hamos or multi-cone crystal can lead to several hundred times intensity enhancements for a 200μm plasma source.This model benefits the applications of the focusing bent crystals.
基金the Natural Foundation of Fujian Province, International Collaborative Project of Fujian Science and Technology Committee.
文摘A new laser crystal Nd0.05La0.95Sc3(BO3)4 up to 50mm(38mm(7 mm was grown by top-seeded solution growth method from a Li6B4O9 flux. The grown crystal was characterized by X-ray powder diffraction. Its crystal structure is monoclinic with space group Cc and the unit cell dimensions: a=12.066(5), b=9.864(2), c=7.740(3) ?,β= 105.48(5)(, V=887.8(6)?3, Z=4, Dc=3.81g/cm3, which belongs to low-temperature phase. The optical absorption of the crystal shows that NLSB has a strong absorption band at 807.7 nm, which is suitable for laser-diode pumping.
文摘Pure bisthiourea cadmium bromide (BTCB) and 1 mole % L-alanine mixed bisthiourea cadmium bromide (LABTCB) single crystals have been grown by slow evaporation method. The grown crystals have been characterized by single crystal XRD analysis, powder XRD analysis, FTIR analysis, UV-Vis-NIR analysis and SHG studies. XRD analysis confirms the crystalline nature of the materials. The addition of L-alanine changes the crystal structure from orthorhombic to tetragonal. The presence of various functional groups present in the pure BTCB and LABTCB crystals have been confirmed by FTIR analysis. The UV-Vis-NIR spectrum shows the transmission characteristics of the crystals. The SHG study depicts the nonlinear optical efficiency of the crystals.
文摘The nonlinear optical crystals of cobalt (Co2+) mixed copper mercury thiocyanate have been grown by slow evaporation method using water and ethanol as solvents. The grown crystals have been subjected to different characterization analyses and the results were compared with pure copper mercury thiocyanate crystal (CMTC), which has been already reported. The single crystal X-ray diffraction shows that the addition of metallic impurity does not alter the basic structure of the parent crystal, but increases the cell volume markedly. The presence of functional groups has been identified using FT-IR analysis. Further the grown crystal is characterized by optical transmission analysis and thermal analysis. The thermal stability of the grown crystal is high, compared to pure CMTC crystal. The optical transparency of the grown crystal is studied by UV-Vis-NIR analysis. This study reveals that Co2+ mixed CMTC crystal has wider transparent waveband than pure CMTC crystal. The relative second harmonic generation efficiency of the Co2+ mixed CMTC crystal has been tested by Kurtz-Perry powder technique.
基金supported by the National Natural Science Foundation of China (No. 21403129)the Project of Shandong Province Higher Educational Science and Technology Program (No.J13LD13 & J15LC09)"Hundred Talents Project" of the Chinese Academy of Sciences
文摘Crystal structures and thermal expansion properties of Yb2-xFexMo3O12（x=0.0,0.6,1.0,1.1,1.4） solid solutions have been studied by X-ray powder diffraction（XRPD） at different temperatures.Rietveld analysis of the XRPD data shows that Yb2-xFexMo3O12 solid solutions adopt orthorhombic structure and have variable thermal expansion coefficients controlled by the ratio of Yb^3＋ to Fe^3＋.Yb2Mo3O12 shows anisotropic negative thermal expansion property,induced by the reductions in average Yb-O-Mo angle and average apparent Mo2-O bond length with increasing temperatures.As more Yb^3＋ substituted by Fe^3＋,the linear thermal expansion coefficients of Yb2-xFexMo3O12 increase from negative to positive.A near-zero thermal expansion coefficient of 0.55×10^-6K^-1 for Yb0.6Fe1.4Mo3O12 is observed in the temperature range of 573-873 K.
文摘In this paper, we propose a method to improve anti-radiation capability by coating heavy metal X-ray protection glass with compound photonic crystal layers, based on the unique property of photonic crystal that light cannot be propagated within the range of band gaps. Using the plane wave expansion method,we made a theoretical study of parameters affecting the band gap structures of one-dimensional photonic crystals. Based on the findings, we chose appropriate materials and compound structure of photonic crystal so as to get high X-ray reflection coating photonic crystal layers. By this method, the reflection rate within X-ray wavelength can reach the maximum value of 100%, and the average value of over 90%. Even low-cost heavy metal X-ray protection glass of absorption coefficient value can achieve the desired effect. Thus, this method greatly decreases the anti-radiation requirements of heavy X-ray protection glass.
基金This work was supported by the National Natural Science Foundation of China.
文摘A uranyl compound, K_4UO_2(CO_3)_3 has been characterized by powder X-ray diffraction method. M. W.=606.46, monoclinic, C2/c (No. 15), a=1.0240(7), b=0.9198(4), c=1.2222(12)nm, β=95.12(4)°,V=1.1466(5)nm^3, Z=4, D_m=3.468g/cm^3, D_c=3.513g/cm~, λ(Cu Kα_1)=O.1540598nm, T=298K. The structure was solved by heavy atom method and Fourier synthesis, and refined by full- matrix least-squares method to R=0.1185 for 275 reflections. The uranium (Ⅵ) atom is in an eight-coordinate distorted hexagonal-bipyramidal environment with creasy fan shape. The linear uranyl group approaches to perpendicular to the equatorial plane in which three carbonate groups are chelated. U(Ⅵ) has two linear oxygen atoms closer to it (U-O=0.1767 (5) nm) than six other neighbours (U-O ranging from 0.2516 to 0.2568nm). The distances between carbon atoms and uncoordinated oxygen atoms are 0.122 (1) and 0.123(1) nm, which are distinctly different from those between carbon and coordinated oxygen atoms (mean 0.134(6) nm). This fact reveals the non-eq- uivalence of one oxygen atom to the other two in each carbonate. In K_4UO_2(CO_3)_3, the O-O dis- tance for the adjacent carbonate groups is 0.2794(4)nm approaching to the sum of Van der Waals radii of two oxygen atoms. The K-O distances vary between 0.2667 and 0.3131nm, and each anion is immediately surrounded by six potassium ions, only four of which can be considered to belong to the same structural formula unit, and they are symmetrically located above and below the equatorial plane.
文摘密度是决定含能材料爆轰性能的重要参数。为评估现有CHON类含能材料密度的计算方法,对等电子密度面法、分子表面静电势法、基团加和法、晶体堆积法、定量构效关系法、经验公式法等进行分析和归类。结果表明,基于分子体积预测方法的精度取决于分子间和分子内相互作用对密度影响描述的准确度。其中,准确描述氢键和van der Waals作用充满了挑战性。基于晶体体积计算密度的核心在于晶体结构的准确预测,结构搜索要面对巨大的状态空间和高度复杂的能量曲面的困难,预测效率是亟待解决的问题。体积加和法和经验公式法存在无法区分同分异构体和晶型的缺点,且对新发现的具有特殊结构的分子由于缺乏实验数据难以获得准确的经验参数,计算结果偏差较大。引入人工神经网络、遗传算法以及支持向量机等机器学习算法后,定量构效关系法在含能化合物性能与结构关系研究中取得很大成就,模型精度进一步提高将为基于材料基因组模式的含能材料设计研发奠定基础,这也是今后密度预测方法发展的主要方向。
