X射线法测量石英方解石的轴面异性及其在岩体应力测量中的应用

矿物晶体的力学性质一般为各向异性。在岩体现今应力测量和残余应力测量中,国际上使用的X射线法。由于测量方法的困难,在原理上仍以岩体力学性质为各向同性的假设为前题,在技术上也以岩体各向同性弹性理论为基础,形成各国都在使用的sin^2ψ法。本文对石英和方解石晶体力学性质方向性的进一步研究。使得岩体力学性质由各向同性假设步入正交异性的新水平,成为用X射线法在正交异性岩体中进行应力测量的基本依据,使应力测量从原理到技术都建立在正交异性弹性理论的基础上,这较为符合岩体的实际情况,并提高了测量的准确性。

高温高围压下岩石压缩组构与各向异性

一、引言岩石组构可分为三种:由沉积和岩浆流动造成的原生组构;岩体变形时,间隙溶液沿易于运动的方向生长成晶体,或裂隙溶液受两壁控制结晶而成的附生组构;岩石形成后,受构造应力作用而成的后生组构。它们都是造成岩石力学性质各向异性的重要原因。岩石中造岩矿物晶粒的规则排列程度愈强,岩石力学性质的各向异性愈显著,由于岩石后生组构是在岩体一定方式的变形中形成的,因而也是鉴定构造应力场和构造运动序次的重要方法,尤其是当构造已被剥蚀难以从形象上鉴定时,更有其独特作用。岩石力学性质的各向异性,直接影响岩体强度、波速和应力的空间分布。

Restoring pristine Bi2Se3 surfaces with an effective Se decapping process

High quality thin films of topological insulators （TI） such as Bi2Se3 have been successfully synthesized by molecular beam epitaxy （MBE）. Although the surface of MBE films can be protected by capping with inert materials such as amorphous Se, restoring an atomically clean pristine surface after decapping has never been demonstrated, which prevents in-depth investigations of the intrinsic properties of TI thin films with ex situ tools. Using high resolution scanning tunneling microscopy/spectroscopy （STM/STS）, we demonstrate a simple and highly reproducible Se decapping method that allows recovery of the pristine surface of extremely high quality Bi2Se3 thin films grown and capped with Se in a separate MBE system then exposed to the atmosphere during transfer into the STM system. The crucial step of our decapping process is the removal of the surface contaminants on top of amorphous Se before thermal desorption of Se at a mild temperature （-210 ~C）. This effective Se decapping process opens up the possibility of ex situ characterizations of pristine surfaces of interesting selenide materials and beyond using cutting-edge techniques.

Polarization of plane wave propagating inside elastic hexagonal system solids

Based on the reported physical parameters for hexagonal system solids,we have calculated the effects of anisotropy on polarization of plane P-wave propagation.Herein we report the results of calculations and the newly observed physical phenomena.It is found that,for a given propagation,if the polarization is parallel to the wave vector,so also to the Poynting vector.In such a case,the phase velocity is identical to the energy velocity;the quasi P-wave degenerates to a pure P-wave along the propagation.It is also noted that if the polarization is parallel to the Poynting vector but not to the wave vector,the propagating wave cannot be a pure P-wave.Furthermore,the polarization in a quasi P-wave may deviate from the wave vector for more than 45°,but the deviation from the Poynting vector is always less than 45°.The energy velocity of a quasi SV-wave can be larger than that of the quasi P-wave in some propagation directions,even though the phase velocity of a quasi SV-wave may never be larger than either the phase velocity or energy velocity of the quasi P-wave.Finally,in case of parameters ε=0 and δ*≠0,the polarization of a quasi P-wave has an observed symmetry at a 45°phase angle.The anisotropy of a hexagonal system solid determines if a pure P-wave can be created and what the propagation direction is for a plane wave propagating inside such a hexagonal system solid.

A new barium-containing alkali metal silicate fluoride NaBa3Si2O7F with deep-UV optical property

A new silicate fluoride,NaBa3 Si207 F,has been successfully synthesized by a high-temperature solution method.It crystallizes in the orthorhombic space group Cmcm(No.63).NaBa3 Si2 O7 F is the first barium-containing alkali metal silicate fluoride with the[NaO6]polyhedra,the[BaO8 F]polyhedra and isolated[Si2 O7]units.The optical characterizations indicate that NaBa3 Si2 O7 F possesses wide transparent window and available luminescence properties.To confirm the coordination surroundings of anionic groups and its thermostability,infrared spectroscopy and thermal behaviors were also analyzed,which proved the existence of tetrahedronly coordinated silicium atoms and the good stability of NaBa3 Si2 O7 F at high temperature.First-principles calculation was also implemented for better understanding the relationship between the structure of NaBa3 Si207 F and its property.Additionally,to further explore the structural novelty of NaBa3 Si2 O7 F,the comparison of the anionic structures was carried out in mixed alkali and alkaline-earth metal silicate fluorides.Interestingly,the result indicates the isolated[Si2 O7]dimer is rare among the above systems,which enriches the structural chemistry of silicate fluorides.

Microstructure and mechanical properties of Ti Al Si N nano-composite coatings deposited by ion beam assisted deposition

TiA1SiN nano-composite coatings with Silicon contents from 4.1 to 23.9 at.% were deposited on Silicon wafers. The nano- hardness, microstructure, and adhesion force of the coatings were deeply affected by Silicon contents. The TiA1SiN with 9.0 at.% Silicon has a maximum hardness of 40.9 GPa, a highest adhesion force of 67 N and a lowest friction coefficient of 0.5. Microstructures show that Silicon doping increases the hardness of coating due to solid solution hardening effect and grain boundary enhancement effect. The amorphous Si3N4 matrix, which contains （Ti,Al）N nano-crystals, is formed as the Silicon content is increased. The matrix contributes to the nano-hardness and helps to resist surface oxidization. Especially, the matrix induces low surface roughness and decreases the friction coefficient.