Tensile properties of phase interfaces in Mg–Li alloy：A first principles study

Employing density functional theory, we study the tensile and fracture processes of the phase interfaces in Mg–Li binary alloy. The simulation presents the strain–stress relationships, the ideal tensile strengths, and the fracture processes of three phase interfaces. The results show that the α/α and α/β interfaces have larger tensile strength than that of β/β interface. The fractures of both α/α and β/β interfaces are ductile fractures, while the α/β fractures abruptly._Further analyses show that the fracture of the α/β occurs at the interface.     

mechanical and thermodynamic properties of α-and β-Si3N4 ceramics： ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4. The ground-state parameters accord quite well with the experimental data. Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K. The α → β phase transformation would not occur in a pressure range of 0-40 （3Pa and a temperature range of 0 300 K. Actually, the α → β transition occurs at 1600 K and 7.98 GPa. For α-and β-Si3N4, the c axes are slightly more incompressible than the a axes. We conclude that β-Si3N4 is a hard material and ductile in nature. On the other hand, β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0 - 010 GPa. Besides, the thermodynamic properties such as entropy, heat capacity, and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures. Significant features in these properties are observed at high temperature. The calculated results are in good agreement with available experimental data and previous theoretical values. Many fundamental solid-state properties are reported at high pressure and high temperature. Therefore, our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.     

Effects of high-pressure heat treatment on the solid-state phase transformation and microstructures of Cu61.13Zn33.94Al4.93 alloys

The phase transformation activation energy of the Cu61.13Zn33.94Al4.93 alloys, which were treated at 4 GPa and 700℃ for 15 minutes, was calculated by means of differential scanning calorimetry curves obtained at various heating and cooling rates. Then, the effects of high-pressure heat treatments on the solid-state phase transformation and the microstructures of Cu61.13Zn33.94Al4.93 alloys were investigated. The results show that high-pressure heat treatments can refine the grains and can change the preferred orientation from (111) to (200) of α phase. Compared with the as-cast alloy, the sample with high-pressure heat treatment has finer grains, lower β′→β and β→β' transformation temperature and activation energy. Furthermore, we found that high cooling rate favours the formation of fine needle-like α phase in the range of 5-20℃/min.     

Predictions of pressure-induced structural transition, mechanical and thermodynamic properties of α-and β-Si3N4 ceramics: ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4.The ground-state parameters accord quite well with the experimental data.Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K.The α→β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 K.Actually,the α→β transition occurs at 1600 K and 7.98 GPa.For α-and β-Si3N4,the c axes are slightly more incompressible than the a axes.We conclude that β-Si3N4 is a hard material and ductile in nature.On the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 GPa.Besides,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures.Significant features in these properties are observed at high temperature.The calculated results are in good agreement with available experimental data and previous theoretical values.Many fundamental solid-state properties are reported at high pressure and high temperature.Therefore,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.     

Investigations of high-pressure and high-temperature behaviors of the newly-discovered willemite-Ⅱ and post-phenacite silicon nitrides

Using the first-principles method of the plane-wave pseudo-potential, the structural properties of the newly-discovered willemite-Ⅱ Si3N4 （wⅡ phase） and post-phenacite Si3N4 （δ phase） are investigated. The α phase is predicted to undergo a first-order α→wⅡ phase transition at 18.6 GPa and 300 K. Within the quasi-harmonic approximation （QHA）, the α→wⅡ phase boundary is also obtained. When the well-known β→γ transition is suppressed by some kinetic reasons, the β→δ phase transformation could be observed in the phase diagram. Besides, the temperature dependences of the cell volume,thermal expansion coefficient, bulk modulus, specific heat, entropy and Debye temperature of the involved phases are determined from the non-equilibrium free energies. The thermal expansion coefficients of wⅡ-Si3N4 show no negative values in a pressure range of 0-30 GPa, which implies that the wⅡ-Si3N4 is mechanically stable. More importantly, the δ-Si3N4 is found to be a negative thermal expansion material. Further experimental investigations may be required to determine the physical properties of wⅡ- and δ-Si3N4 with higher reliability.     

Predictions of pressure-induced structural transition,mechanical and thermodynamic properties of α-and β-Si₃N₄ ceramics:ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4.The ground-state parameters accord quite well with the experimental data.Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K.The α→β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 K.Actually,the α→β transition occurs at 1600 K and 7.98 GPa.For α-and β-Si3N4,the c axes are slightly more incompressible than the a axes.We conclude that β-Si3N4 is a hard material and ductile in nature.On the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 GPa.Besides,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures.Significant features in these properties are observed at high temperature.The calculated results are in good agreement with available experimental data and previous theoretical values.Many fundamental solid-state properties are reported at high pressure and high temperature.Therefore,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.     

Observation of β-Relaxation in Sub-Tg Isothermally Annealed Al-Based Metallic Glasses

Al85Ni5 Y8Ca2 and Al88Ni5 Y6Co2Fe2 metallic glasses are fabricated by melt spinning. A kink or a small exothermic peak is observed for both the samples isothermally annealed at sub-glass transition temperatures. Temperature modulated differential scanning calorimetry （TMDSC） data disapprove amorphous phase separation. The activation energies derived from Kissinger plots of the exothermic process on DSC curve around glass transition temperature are consistent with those of β-relaxation of metallic glasses.     

Relativistic Configuration Interaction Treatment of Generalized Oscillator Strength for Krypton

A fully relativistic configuration interaction method is developed to investigate the transition energies and general oscillator strengths of the lower lying states of krypton, for both optically allowed and optically forbidden transitions. The calculated results are in agreement with the recent experimental measurements. The calculated transition energies for the 5s and 5s＇ transitions are 9.970 and 10. 717eV, which agree with the experimental data of 10.033 and 10.643 eV. The calculated oscillator strengths are 0.211 and 0. 170, comparable with the experimental results 0.214（±0.012） and 0.194 （±0.012）, respectively. The momentum transfer positions （K^2 in a.u.） of the minimum and maximum GOSs in the 4s^24p^6 → 4s^24p^5 （5s ＋ 5s＇） transitions are 1.105 and 2.225, comparable with the measurements results 1.24 and 2.97 [Phys. Rev. A 67 （2003） 062708].     

Influence of Al~(3+) doping on the energy levels and thermal property of the 3.5MgO·0.5MgF_2·GeO_2:Mn~(4+) red-emitting phosphor

A series of Al3+-doped 3.5MgO·0.5MgF2·GeO2:Mn4+red-emitting phosphors is synthesized by high temperature solid-state reaction. The broad excitation band at 300 nm–380 nm, resulting from the4A2→4T1transition of Mn4+,exhibits a blue shift with the increase of Al2O3 content. The observation of the decreased Mn4+–O2-distance is explained by the crystal field theory. The temperature-dependent photoluminescence spectra with various amounts of Al2O3 content are comparatively measured and the calculation shows that the activation energy increases up to 0.41 eV at the Al2O3 content of 0.1 mol. The maximum phonon densities of state for these samples are calculated from Raman spectra and they are correlated with the thermal properties.     

The phase transition,hygroscopicity, and thermal expansion properties of Yb_2-xAl_xMo₃O₁₂

Materials with the formula Yb 2-xAlxMo3O12(x =0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.0, 1.1, 1.3, 1.5, and 1.8) were synthesized and their structures, phase transitions, and hygroscopicity investigated using X-ray powder diffrac- tion, Raman spectroscopy, and thermal analysis. It is shown that Yb2-xAlxMo3O12 solid solutions crystallize in a single monoclinic phase for 1.7 ≤ x ≤ 2.0 and in a single orthorhombic phase for 0.0 ≤ x ≤ 0.4, and exhibit the characteristics of both monoclinic and orthorhombic structures outside these compositional ranges. The monoclinic to orthorhombic phase transition temperature of Al2Mo3O12 can be reduced by partial substitution of Al 3+ by Yb3+, and the Yb2-x AlxMo3O12 (0.0 < x ≤ 2.0) materials are hydrated at room temperature and contain two kinds of water species. One of these interacts strongly with and hinders the motions of the polyhedra, while the other does not. The partial substitution of Al3+ for Yb3+ in Yb2Mo3O12 decreases its hygroscopicity, and the linear thermal expansion co- efficients after complete removal of water species are measured to be 9.1×10 6 /K, 5.5×10 6 /K, 5.74×10 6 /K, and 9.5 × 10 6 /K for Yb1.8 Al0.2 (MoO4)3 , Yb1.6Al0.4 (MoO4 )3, Yb0.4 Al1.6 (MoO4)3 , and Yb 0.2Al1.8 (MoO4)3 , respectively.     

过量Zn对β-Zn4Sb3热电性能影响的研究

采用真空熔融缓冷方法制备了单相β-Zn₄Sb₃以及含有过量Zn的β-Zn₄Sb₃块体热电材料.在300—700K的温度范围内测试了材料的电导率、Seebeck系数和热导率，研究了β-Zn₄Sb₃化合物中过量Zn的分布状态及其对材料热电性能的影响规律.结果表明：过量的Zn作为第二相较均匀的分布在β-Zn₄Sb₃的晶界上，随着Zn含量增加，材料电导率和热导率上升，Seebeck系数下降，Zn第二相的引入能有效提高材料的功率因子，Zn过量2at%的材料在700K时其ZT值达到1.10. 关键词： 4Sb₃')" href="#">β-Zn₄Sb₃ 电导率 Seebeck系数     

A comparative study on structural,morphological and luminescence characteristics of Zn3(VO4)2 phosphor prepared via hydrothermal and citrate-gel combustion routes

Comparison of structural, morphological and spectroscopic properties of zinc vanadate Zn₃(VO₄)₂ phosphor synthesized via two different methods, viz. citrate-gel combustion and hydrothermal reaction, is presented. Highly crystalline and pure phase micro-rods are achieved by citrate-gel combustion route. The hydrothermal reaction products exhibit ribbon like structures. X-ray photoelectron spectroscopic investigation reveals the presence of multiple oxidation states of vanadium in the hydrothermally synthesized phosphor. Luminescence properties have also been compared and the effect of divalent cationic substitution (Ca, Mg) is presented.     

Synthesis and characterization of Mn-doped Zn2SiO4/SiO2 phosphor particles in core-shell structure

Manganese-doped zinc silicate (Zn₂SiO₄:Mn) is a kind of phosphor material that has a photo-luminescent (PL) and cathode-luminescent (CL) properties with intensive green light emission at 520 nm. The particles consisting of SiO₂@Zn₂SiO₄:Mn (SiO₂ core-Zn₂SiO₄:Mn shell) were synthesized via colloidal process and forced precipitation. After drying, the Zn/Mn precipitates were coated on the surface of SiO₂ particles. The Zn/Mn precipitates reacted with SiO₂ and transformed to Zn₂SiO₄:Mn by suitable calcination. The microstructure, crystalline phase, and luminescent characteristics of the products were studied. Besides, a CL device consisting of the core-shell powder was characterized.     

Crystallization of Ge2Sb2Te5 phase—change optical disk media

In this paper, the crystallization behaviour of amorphous Ge₂Sb₂Te₅ thin films is investigated using differential scanning calorimetry), x-ray diffraction and optical transmissivity measurements. It is indicated that only the amorphous phase to face-centred-cubic phase transformation occurs during laser annealing of the normal phase-change structure, which is a benefit for raising the phase-change optical disk's carrier-to-noise ratio (CNR). For amorphous Ge₂Sb₂Te₅ thin films, the crystallization temperature is about 200℃ and the melting temperature is 546.87℃. The activation energy for the crystallization, E_a, is 2.25eV. The crystallization dynamics for Ge₂Sb₂Te₅ thin films obeys the law of nucleation and growth reaction. The sputtered Ge₂Sb₂Te₅ films were initialized by an initializer unit. The initialization conditions have a great effect on the reflectivity contrast of the Ge₂Sb₂Te₅ phase-change optical disk.     

A revisit of photoluminescence property for vanadate oxides AVO3 (A:K, Rb and Cs) and M3V2O8 (M:Mg and Zn)

We revisited the vanadium oxide phosphors, AVO₃ (A:K, Rb, and Cs) and M₃V₂O₈ (A:Mg and Zn) for a revaluation of possibility of these compounds for lighting applications, and the internal quantum efficiency (η) and luminescent colour properties for AVO₃ (A:K, Rb, and Cs) and M₃V₂O₈ (A:Mg, and Zn) have been presented. The AVO₃ showed the broadband emission from 380 to 800 nm, and the η for the KVO₃, RbVO₃ and CsVO₃ were 4%, 79% and 87%, respectively. The CIE colour coordinates are located at white region on the chromaticity diagram. The M₃V₂O₈ (A:Mg and Zn) also exhibited a quite broadband emission between 410 and 900 nm, indicating yellow luminescent colour. The Zn₃V₂O₈ showed high η value, 52%, compared to that of the Mg₃V₂O₈ (η=6%). This enhancement of η in the Zn₃V₂O₈ could be due to the increasing exciton diffusion assisted by the hybridizations of Zn 3d and O 2p orbitals for the valence band, and Zn 4s and Ti 3d orbitals for the conduction band.     

中子探测晶体Li6Gd(BO3)3:Ce的光谱特性研究

文章用提拉法生长出Li₆Gd(BO₃)₃:Ce晶体,并对其光谱性能与发光过程进行了探索. 借助于真空紫外-紫外透过光谱测试,发现晶体的透过光谱中存在Ce³⁺离子和Gd³⁺的特征吸收峰,同时还存在与Ce⁴⁺离子相关的电荷迁移带. 对晶体的真空紫外-紫外激发发射光谱进行研究发现,在晶体存在着Ce³⁺离子的5d→4f辐射跃迁发光与Gd³⁺离子的4f→4f辐射跃迁发光,而且存在着Gd³⁺→Ce³⁺之间的能量传递. 对Li₆Gd(BO₃)₃:Ce晶体的X射线与γ射线激发发射光谱研究可知,晶体在高能射线激发下的闪烁光主要是Ce³⁺离子的发光. 关键词： 6Gd(BO₃)₃:Ce晶体')" href="#">Li₆Gd(BO₃)₃:Ce晶体 真空紫外-紫外透过光谱 真空紫外-紫外激发发射光谱 能量传递     

Facile fabrication of Zn/Zn5(OH)8Cl2·H2O flower-like nanostructure on the surface of Zn coated with poly (N-methyl pyrrole)

Zn/Zn₅(OH)₈Cl₂·H₂O flower-like nanostructures was electrodeposited on the coated Zn with poly (N-methyl pyrrole) in 0.1 M Zn (NO₃)₂ and 0.1 M KCl solution. The morphology and the structure of the Zn/Zn₅(OH)₈Cl₂·H₂O were characterized by Field Emission Scanning Electron Microscopy (FESEM), Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction analysis (XRD). The FT-IR results showed special peaks at 908 and 728 cm⁻¹ related to Zn₅(OH)₈Cl₂·H₂O. The FESEM results indicated that Zn/Zn₅(OH)₈Cl₂·H₂O consists of a flower-like nanostructure and these flower-shaped structures contain many shaped nanopetals with the thickness of 27.8 nm. The XRD result confirmed that the major phase of electrodeposited product in 0.1 M KCl as supporting electrolyte was Zn₅(OH)₈Cl₂·H₂O. The ability of PMPy to create a thin film and the existence of several pores in its matrix act as a mold for the growth of Zn/Zn₅(OH)₈Cl₂·H₂O flower-like nanostructure. The trapping of Cl⁻ and OH⁻ within pores can be considered as the reason for the formation of flowerlike Zn/Zn₅(OH)₈Cl₂·H₂O nanostructures in 0.1 M KCl.     

Ga填充n型方钴矿化合物的结构及热电性能

用熔融退火结合放电等离子烧结(SPS)技术制备了具有不同Ga填充含量的Ga_xCo₄Sb₁₂方钴矿化合物,研究了不同Ga含量对其热电传输特性的影响规律. Rietveld结构解析表明,Ga占据晶体学2a空洞位置,Ga填充上限约为0.22,当Ga的名义组成x≤0.25时,样品的电导率、室温载流子浓度N_p随Ga含量的增加而增加,Seebeck系数随Ga含量的增加而减小. 室温下霍尔测试表明,每一个Ga授予框架0.9个电子,比Ga的氧化价态Ga³⁺小得多. 由于Ga离子半径相对较小,致使Ga填充方钴矿化合物的热导率κ及晶格热导率κ_L较其他元素填充的方钴矿化合物低. 当x＝0.22时对应的样品在300K时的热导率和晶格热导率分别为3.05Wm^-1·K^-1和 2.86Wm^-1·K^-1.在600K下Ga_0.22Co_4.0Sb_12.0样品晶格热导率达到最小,为1.83Wm^-1·K^-1,最大热电优值Z,在560K处达1.31×10^-3K^-1. 关键词： skutterudite化合物 Ga原子填充 结构 热电性能     

Hydrothermal synthesis and optical characteristics of Eu in Zn2SnO4 nanocrystals

Zn₂SnO₄:Eu³⁺ nanocrystals were one-step synthesized by hydrothermal method for the first time. All the products were systematically characterized by powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), electron probe X-ray microanalyzer (EPMA), photoluminescence (PL) and photoluminescent excitation (PLE). The characteristic peak of Eu³⁺-doped in Zn₂SnO₄ nanocrystals was also detected. The luminescent properties of blank and Eu³⁺-doped Zn₂SnO₄ nanocrystals were reported.