氢稀释比与衬底温度对硅基薄膜相变及其光电性能影响的研究

采用热丝辅助微波电子回旋共振化学气相沉积法(HWAMWECR-CVD),通过改变衬底温度及氢稀释比制备了系列硅基薄膜,研究了衬底温度及氢稀释比对薄膜由非晶相转晶相相变及其光电性能的影响。研究结果表明,当采用低温制备硅基薄膜时,衬底温度和氢稀释比的提高都有利于非晶相向晶相的转变,但提高氢稀释比对相变的影响更为显著;晶化比越高并不代表薄膜光电性能越好,95%氢稀释比条件下制备的微晶硅薄膜具有优良的光电性能。     

水对食品相变的影响

水是食品材料中最重要的成分。本文介绍了食品中水的性质以及水对食品相变的影响，并从水活性、水的吸附性以及水的增塑性三方面描述了水在食品相变中所起的作用。另外，还着重分析了水对食品冻结温度的影响。     

Transient liquid phase bonding of titanium to aluminium nitride

Titanium has been successfully joined to aluminium nitride AlN at a temperature as low as 795 °C, using Ag–Cu Cusil^® commercial braze alloy. While reactive wetting and spreading proceeds at the AlN/braze alloy interface, chemical interactions develop at the titanium side rendering possible isothermal solidification of the joint. The determining factor in the solidification process is the fast formation of TiCu₄ crystals by heterogeneous nucleation and growth in the liquid phase. As a consequence, the braze alloy is depleted in Cu and solid Ag precipitates. After annealing, the re-melting temperature of the resulting joint can be increased up to about 910 °C which is nearly 130 °C higher than the melting point of the starting braze alloy.     

Local phase separation in Tl-based oxide superconductors

We present the results of the analysis of CuK-edge X-ray absorption fine structure (XAFS) on Tl₂Ba₂CuO₆, which show a complex Cu-O pair distribution function with multiple Cu-O bondlengths in the CuO₂ planes, implying local phase separation in this material. Based on these results we propose a model of the local structure of these Tl-based superconductors. We present the formalism used to extract a pair distribution function from XAFS from a model interatomic potential, associating a dynamic time scale to fluctuations between different bond lengths. These copper-oxygen bondlengths are compared with those found in Bi₂Sr₂CaCu₂O_8+y , La_1.85Sr_0.15Cu₂O₄ and YBa₂Cu₃O₇.     

Thickness dependence of the amorphous-cubic and cubic-hexagonal phase transition temperatures of GeSbTe thin films on silicon nitride

The crystallization temperature of GeSbTe thin films with thicknesses between 11 and 87 nm on silicon nitride was studied through resistance versus temperature measurements. The amorphous-cubic phase transition occurs at ~ 150 °C for all films thicknesses, whereas the cubic-hexagonal phase transition temperature increases with film thickness, from ~ 200 °C for the 20 nm film to ~ 250 °C for the 87 nm film. The cubic-hexagonal transition occurs gradually for the 11 nm film. Implications for phase-change memory devices are discussed.     

Gd5Ge4的磁结构相变和磁玻璃行为的研究

通过对温度诱导和磁场诱导的磁化强度的测量和分析，证明了Gd5Ge4在低温范围存在从反铁磁到铁磁的一级结构相变，有典型的相分离特征。为了进一步说明Gd5Ge4的磁结构相变，对不同低温的磁场诱导的磁化强度进行了两次循环测量，结果显示Gd5Ge4在低温下磁化行为具有不可逆性和对温度的依赖性。同时对磁化强度的研究揭示了Gd5Ge4在低温时存在磁玻璃态。     

Transient liquid phase bonding of AA 6082 aluminium alloy

Transient liquid phase bonding (TLP) on AA 6082 samples were performed under ambient non‐vacuum conditions, which was possible by a suitable pre‐treatment. This treatment involves a zincate treatment followed by copper plating, which is a common industrial process and can be performed in large batches. This treatment allows to remove the natural aluminium oxide layer and to protect the aluminium surface from excessive oxidation. Different bonding conditions were investigated and showed the feasibility of the transient liquid phase bonding process for AA 6082. Energy dispersive X‐ray spectroscopy (EDX) investigations showed that the isothermal solidification is already terminated after 5 min. The microstructure of the bonding zone showed no metallurgical discontinuity such as eutectic microstructure or intermetallic Al–Cu phases. However the microstructure shows numerous voids with a size of approximately 30 µm in the bonding zone. It is assumed that these voids were formed during the bonding process due to solidification shrinkage and the presence of interfacial oxide layers. The transient liquid phase bonded samples that were mechanically tested under tensile load showed an average strength of approximately 270 MPa, the minimum yield strength required for the base material according to EN 754‐2 is 255 MPa. Due to the notch effect of the voids, the tensile sample failed under forced fracture and showed no plastic deformation.     

On the unstable propagation of a phase transition in a solid

To explore a possible mechanism of deep earthquakes, this paper analyzes the unstable propagation of a stress-induced phase transition which is initiated in a homogeneous stress field. This Stephen problem is formulated as an initial-value problem for the phase boundary, and the driving force of the boundary is computed by using the solution of the boundary-value problem for a partially transformed material. The propagation of the phase transition under uniform pressure is numerically simulated. It is shown that (1) under lower pressure, the transition is terminated at a certain size, but it can propagate unstably when an initially transformed region is sufficiently large; and (2) when the pressure attains a critical value, the propagation becomes unstable, and goes in a particular direction depending on the initial shape. These results confirm the possibility of the unstable propagation of phase transition, and provide a theoretical basis for the hypothesis that the phase transition of a mantle material can trigger a deep earthquake.     

A new type face-centered cubic zirconium phase in pure zirconium

So far,only two orientation relationships (OR) between hexagonal close-packed (HCP) (α phase) and face-centered cubic (FCC) structures in zirconium and titanium alloys have been reported.Here a new type FCC phase (named γphase) with OR:< 11(2)0 >αll< 100 >γ and {0001}αll{002}γ was observed for the first time in annealed pure zirconium by means of transmission electron microscopy (TEM) technique.The α→γphase transformation can be accomplished via expansion along[1(1)00]direction and slip of Shockley partial dislocation with 1/3[1(1)00]on (0001) basal planes.     

First-principles study of zinc-blende to rocksalt phase transition in BP and BAs

The structural and electronic properties of BP and BAs are investigated by first-principles pseudopotential method. The calculations show the structural phase transition from zinc-blende (ZB) structure to rocksalt (RS) structure at the transition pressure of 142 GPa for BP and 134 GPa for BAs. The ZB phase of BP and BAs remains indirect gaps upon applying hydrostatic pressure, while RS phase of BP and BAs is semimetal at the transition pressure.     

Tetragonal to cubic phase transition in silver chlorate

Silver chlorate crystallizes in the tetragonal system at room temperature. The crystal undergoes a reversible first order phase tronsition to a cubic phase at 139°C. The transition temperature along with the enthalpy change was determined by thedsc technique and the change of enthalpy was found to be 3·12 cal/g. The high temperature form as determined by x-ray powder diffractometric method was found to be primitive cubic with a lattice constant of 6·681 Å at 145°C.     

Influence of heating rate on the hysteresis in the phase transition in silver selenide thin films

The electrical resistance of vacuum-deposited silver selenide thin films, of thickness 70 nm was measured in the temperature range from 300 to 430 K, at different heating rates and at a pressure of 2×10⁻⁵ mbar. The films were annealed at 430 K at a pressure of 2×10⁻⁵ mbar for an hour. It is found that annealed silver selenide films undergo a structural phase transition exhibiting hysteresis. The structural phase transition with hysteresis in silver selenide thin films is influenced by the heating rates of the films. The effect of the heating rate on the phase transition temperature and hysteresis are discussed taking into account the presence of potential barrier and the defects. Our studies reveal that hysteresis width decreases with decreasing heating rates.     

TiNiHfCu高温形状记忆合金的马氏体相变研究

通过差热扫描分析、X射线衍射和透射电镜等方法研究了Cu的添加对Ti36 Ni49-x Hf15 Cux(x=1,3,5,8)合金马氏体相变行为的影响.研究表明:Cu的加入可稍降低合金的相变温度(约15 ℃),但其Ms仍高于150 ℃,可作为高温形状记忆合金使用;随着Cu含量的升高,合金的B19'马氏体晶格常数a、b和c不发生明显变化,但单斜角β逐渐降低;Ti36 Ni49-x Hf15 Cux(x=1,3,5,8)合金的相组成为B19'单斜马氏体和(Ti,Hf,Cu)2Ni相,马氏体的亚结构为(001)复合孪晶.     

Diffusion of lithium ions and diffusion-induced stresses in a phase separating electrode under galvanostatic and potentiostatic operations: Phase field simulations

Phase separation in an electrode of a lithium ion battery, which is a phenomenon where an active electrode material is separated into Li-rich and Li-poor phases, exists widely in many active materials and has significant impacts on the diffusion of lithium ions and diffusion-induced stresses. A phase field model is developed to study the phase separation. Firstly, the influences of various energies, such as the free energy of uniform Li-ion concentration, gradient energy and elastic energy, on phase separation are discussed. Secondly, the impacts of charge operation, e.g. galvanostatic and potentiostatic, on Li-ion diffusion and diffusion-induced stresses in a planar phase separating electrode are investigated. Calculations are also made for single phase electrodes based on Fick’s law for comparison. The obtained simulation results show that the Li-ion diffusion in a phase separating electrode depends significantly on the phase separating profile and movement of phase boundary, but it is not sensitive to charge operation. The diffusion-induced stresses also separate into high and low stress regions. Finally, based on the diffusion process and diffusion-induced stress, it is suggested that phase separation should be avoided for the sake of fast charging and mechanical reliability.     

奥氏体不锈钢凝固相转变规律曲线(SPT曲线)建立

利用自行设计的高温凝固相转变测定实验装置,研究了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变过程,得到了凝固过程中液相（ L）到高温铁素体（δ）到奥氏体（γ）的相变温度。在此基础上分析了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变规律,从而建立了304奥氏体不锈钢的低冷速凝固相转变规律曲线—SPT（Solidification phase transforma?tion）曲线。结果表明：对试样进行液氮酒精淬火有效地保留了试样高温时各相的状态。可以清楚的显示在不同冷速下的不同温度淬火时液相和固相的各相成份比例及在不同淬火温度下各成份体积比例的变化。通过研究体积比例变化,可以得到304奥氏体不锈钢在不同冷速下的液相线、固相线及各种反应开始和结束的转变温度（即SPT曲线）。由SPT曲线也可以看出,随着冷却速度的增大,相转变模式会发生变化,相图会向左移动,各相变反应的温度区间减小。     

铁电晶体相变X-Y模型的蒙特卡罗计算机模拟研究

采用X－Y模型和蒙特卡罗方法对有序－无序型铁电体的自发极化行为以及相变特征进行了计算机模拟研究，得到了与实验报道及理论研究符合良好的结果。研究结果表明隧穿频率（即横场强度）对有序－无序型铁电晶体的极化和退极化过程具有显著影响，减小材料的隧穿频率（即减弱材料的横场强度）是提高这类材料的剩余极化强度、居里温度和矫顽力等指标的有效途径。     

Safety performance of traffic phases and phase transitions in three phase traffic theory

Crash risk prediction models were developed to link safety to various phases and phase transitions defined by the three phase traffic theory. Results of the Bayesian conditional logit analysis showed that different traffic states differed distinctly with respect to safety performance. The random-parameter logit approach was utilized to account for the heterogeneity caused by unobserved factors. The Bayesian inference approach based on the Markov Chain Monte Carlo (MCMC) method was used for the estimation of the random-parameter logit model. The proposed approach increased the prediction performance of the crash risk models as compared with the conventional logit model. The three phase traffic theory can help us better understand the mechanism of crash occurrences in various traffic states. The contributing factors to crash likelihood can be well explained by the mechanism of phase transitions. We further discovered that the free flow state can be divided into two sub-phases on the basis of safety performance, including a true free flow state in which the interactions between vehicles are minor, and a platooned traffic state in which bunched vehicles travel in successions. The results of this study suggest that a safety perspective can be added to the three phase traffic theory. The results also suggest that the heterogeneity between different traffic states should be considered when estimating the risks of crash occurrences on freeways.     

影响Fe-Mn-Si-Cr-Ni形状记忆合金相变点的因素

研究了变形量和回复退火温度对Fe-14Mn-5Si-8Cr-4Ni形状记忆合金相变点的影响。结果表明：当回复退火温度为673K时，Af点和Ms点都随变形量的增加而显著增加，As点增加较缓慢；303K加热前和加热后合金电阻率之差△ρ也随变形量的增加而增加，可回复变形量随变形量的变化与△ρ的变化是一致的。Fe-Mn-Si-Cr-Ni形状记忆合金的形状回复来源于应力诱发γ→ε马氏体转变及其逆转变；当变形量为10%时，Ms点随回复退火温度的增加而显著下降。     

Effect of heating rate on the hysteresis in the phase transition in silver telluride thin films

The electrical resistance of vacuum deposited silver telluride thin films was measured in the temperature range from 300 to 430 K at different heating rates. It is found that silver telluride films undergo a structural phase transition, with a hysteresis. The phase transition occurs over a wide temperature range of about 30 K and the transition temperature as well as the hysteresis width are found to be influenced by the heating rate. The effect of heating rate on the phase transition temperature and the hysteresis are discussed.