Ferroelastic phase transition in elpasolite Tl2KInF6

A new elpasolite Tl₂KInF₆ has been synthesized. This compound undergoes at 228 K a ferroelastic phase transition from a room-temperature Fm3m variety to a monoclinic variety. X-ray, optical, calorimetric and DTA studies under hydrostatic pressure have been performed and compared with other elpasolite-type fluorides.     

三聚氰胺(C_3N_6H_6)的高压Raman与压致结构相变研究

本文在8 7GPa压力范围内研究了三聚氰胺(C3N6H6)的高压原位Raman光谱。通过内、外Raman活性模的压致效应,发现在1 5GPa和6 0GPa压力下该分子晶体发生了压致结构相变。用空间群相关原理确认在1 5GPa压力下它从单斜相转变为三斜相;在6 0GPa压力下又发生了另一次结构相变。然后在室温高压条件下对三聚氰胺进行了原位同步辐射能量散射x-ray衍射实验(EDXD),在14 7GPa压力范围内,观察到常压下为单斜晶系的三聚氰胺经历了两次压致结构相变。在1 3GPa下,三聚氰胺分子晶体从单斜相转变为三斜相;在8 2GPa又转变为正交相。本实验结果为利用三聚氰胺碳氮有机分子晶体高温高压合成超硬C3N4共价晶体的研究提供了重要信息。     

Phase transition in gauge theories

In this short review we present the consequences of the spontaneously broken gauge theories will lead to when describing matter at high temperature and density. It appears various phase transitions should occur leading to the restoration of symmetry at high temperature of the originally broken one. Symmetry behaviour in external magnetic fields and in the early universe has been briefly mentioned.     

相变与临界乳光现象

分别采用白炽聚光灯和氦氖激光器照射,观察六氟化硫在临界点附近的临界乳光现象.     

Quantum phase transition and entanglement in Li atom system

By use of the exact diagonalization method, the quantum phase transition and entanglement in a 6-Li atom system are studied. It is found that entanglement appears before the quantum phase transition and disappears after it in this exactly solvable quantum system. The present results show that the von Neumann entropy, as a measure of entanglement, may reveal the quantum phase transition in this model.     

Li-ion batteries: Phase transition

Progress in the research on phase transitions during Li+extraction/insertion processes in typical battery materials is summarized as examples to illustrate the significance of understanding phase transition phenomena in Li-ion batteries.Physical phenomena such as phase transitions(and resultant phase diagrams) are often observed in Li-ion battery research and already play an important role in promoting Li-ion battery technology. For example, the phase transitions during Li+insertion/extraction are highly relevant to the thermodynamics and kinetics of Li-ion batteries, and even physical characteristics such as specific energy, power density, volume variation, and safety-related properties.     

双轴性向列相液晶的相变理论

假设一双轴性向列相液晶分子简单相互作用模型，利用平均场理论，得到从各向同性相至单轴向列相、单轴向列相至双轴向列相的相变. 结果表明，在一定温度范围内，分子形状的非轴对称性可导致系统双轴向列相的产生. 在核磁共振实验中，导出双轴向列相序参数与谱线分裂频率间的一般关系，并讨论序参数测量性的可能性. 关键词： 向列相液晶 相变     

Landau-type pressure dependence of the order parameter: application to the ferroelectric-paraelectric pressure-induced transition in KNbO3

Following the Landau model, the pressure–temperature dependence of the order parameter is derived. Using the Lyddane–Sachs–Teller (LST) relationship, the model is applied to ferroelectricity to deduce the pressure behaviour of the soft mode driving the transition. Comparison with experiment is made using recent data obtained on KNbO₃ under pressure over a large temperature range. The results indicate that the ferroelectric–paraelectric (FE–PE) transition observed in KNbO₃ at high pressure from ～4 to ～25?GPa is of the second-order type.     

Structural transition and enhanced magnetization in Bi1−xYxFeO3

Bi_1−xY_xFeO₃ (x=0-0.2) powders were prepared to study the effect of Y substitution on their structural and magnetic properties. A structural symmetric breaking from the rhombohedral R3c to orthorhombic Pnma at around x=0.10 was identified across a ferroelectric-paraelectric phase. A parabolic dependence of the magnetization upon substitution was obtained with a maximum at the phase transition boundary and a switching behavior for x=0.20. The composition-driven magnetic structure evolution was proposed to account for the magnetic properties in Bi_1−xY_xFeO₃.     

First order phase transition of Li3 ThF7 at 281 K: A comparative study between EPR and Raman scattering

Abstract

Electron Paramagnetic Resonance (EPR) and Raman Spectroscopy were used to study the low temperature phase transition of pulled Li₃ThF₇ single crystals, occurring at 281 K. In both cases, the room temperature spectra were very broad, owing to the statistical disorder and high ionic mobility of the lithium ions, which occupy only 3/4 of their structural sites. The results are compatible with a first order ferroelastic transition from the room temperature orthorhombic D_2h ²² phase to a monoclinic C_2h ^(x) one. The symmetry rules are well respected assuming a model with four lithium ions in average per chemical formula. The EPR spectra show also the appearing of additional ferroelastic domains.     

Phase transition of shocked water up to 6 GPa:Transmittance investigation

The phase transition behaviors of the shocked water are investigated by employing an optical transmittance in-situ detection system. Based on the light scattering theory and phase transformation kinetics, the phase transition mechanism of the water under multiple shocks is discussed. The experimental data indicate that the evolution of the transmittance of the shocked water can be broadly divided into three stages: relaxation stage, decline stage, and recovery stage. In the early stage of the phase transition, the new phase particles began to form around the quartz/window interface. It should be mentioned that the water/ice phase boundary seems to move toward the liquid region in one experiment of this work. Due to the new phase core being much smaller than the wavelength of the incident light, the transmittance of the sample within the relaxation stage remains steady. The decline stage can be divided into the rapid descent stage and the slow descent stage in this work, which is considered as the different growth rates of the new phase particle under different shock loadings. The recovery stage is attributed to the emergence of the new phase particles which are bigger than the critical value. However,the influence of the size growth and the population growth of the new phase particles on the transmittance restrict each other, which may be responsible for the phenomenon that the transmittance curve does not return to the initial level.     

脉冲功率3 kW二极管激光器叠阵的相变冷却

针对二极管激光器叠阵的高效散热冷却开展了研究,设计了基于R134a制冷剂的相变冷却系统和以节流式微通道相变冷却方式工作的冷却器,完成了脉冲功率3 kW叠阵的封装,并分析了制冷剂在热沉进出口的温度对叠阵出光波长的影响。实验测试结果表明:在20%的高占空比下,电流197 A时叠阵的输出功率达到3 030 W,插座效率为39%,光谱宽度小于3.8 nm,冷却器内R134a的气化率约为50%。制冷剂R134a的流量为0.60 L/min,仅为水系统的1/5,大幅减小了冷却液流量和热管理系统的体积。     

脉冲功率3 kW二极管激光器叠阵的相变冷却

针对二极管激光器叠阵的高效散热冷却开展了研究,设计了基于R134a制冷剂的相变冷却系统和以节流式微通道相变冷却方式工作的冷却器,完成了脉冲功率3 kW叠阵的封装,并分析了制冷剂在热沉进出口的温度对叠阵出光波长的影响。实验测试结果表明:在20%的高占空比下,电流197 A时叠阵的输出功率达到3 030 W,插座效率为39%,光谱宽度小于3.8 nm,冷却器内R134a的气化率约为50%。制冷剂R134a的流量为0.60 L/min,仅为水系统的1/5,大幅减小了冷却液流量和热管理系统的体积。     

Phase transition of samarium under high pressure

Abstract

The DAC X-ray power photograph method was employed for studing the phase transition of samarium up to 26.3 GPa. The experimental results show that the dhcp and fcc high pressure phase of Sm appeared at about 4.0 and 12.5 GPa and room temperature respectively. The dhcp phase was kept until 19.6 GPa. A model for Sm-type -? dhcp -? fcc phase transition is provided in this paper.     

玻色-爱因斯坦凝聚的相变特征

研究玻色-爱因斯坦凝聚的相变特征，证明了粒子间存在弱排斥相互作用的玻色系统的玻色-爱因斯坦凝聚是二级相变。     

固液双相电流变系统流动过程的相转变特性

考虑电流变液多粒子近程相互作用，利用等效平板电导模型，研究了电流变液流动过程相转变点的特性，并设计实验观察了电流变液中的这种相转变现象.研究结果表明，电流变液在一定压力梯度作用下发生流动，此时为双相流；当外加电场达到某一值时，电流变液中颗粒不流动，由固液双相流转变为液体单相流动，发生场控相转变，理论模拟结果与实验观察结果基本相符.阈值电场随外加压力梯度的增加而加大，随颗粒浓度的增加而减小. 关键词： 电流变液 颗粒流 相转变     

高功率二极管激光器相变冷却技术

根据高功率二极管激光器的散热需求,设计了一种储能式相变冷却实验系统,并开展了喷雾相变冷却器和微通道相变冷却器的设计。采用多孔微结构的换热表面,用氨做制冷剂,实现了喷雾相变冷却器表面温度37 ℃时,散热功率密度达到了511 W/cm2。采用节流汽化原理,分别设计了背冷式相变微通道冷却器和薄片型的模块式相变微通道冷却器,背冷式相变微通道冷却器采用氨做制冷剂, 散热功率密度达到了550 W/cm2,采用R124做制冷剂,散热功率密度约270 W/cm2。采用R124做制冷剂,实现了脉冲激光功率3 kW和连续激光功率100 W的相变冷却二极管激光器模块封装。     

在单粒子尺度下用胶体研究相变

悬浮于溶液中的微米胶体粒子可以自组装成多种结构,与原子一样具有丰富的相行为,通过调节粒子的大小、形状、相互作用或密度可以驱动相变。由于胶体粒子可以在光学显微镜下直接成像并测量其热运动轨迹,因此是研究相变微观过程的一种有力的模型系统。近十几年来,作用力可调粒子、非球形粒子和活性粒子的制备有了突破性进展,并在自组装技术和相应的计算机模拟中有很大进步,因此为相变研究开辟了许多可能性。文章总结了利用胶体研究相变过程的最新进展,重点关注结晶、熔化和固—固相变,并简述胶体相变研究中存在的挑战和未来前景。