学术论文

      长周期相Al5Ti3和r-Al2Ti的弹性各向异性及声子聚焦

      Elastic anisotropy and phonon focusing of long-period superstructures Al5Ti3 and r-Al2Ti

      摘要:
      为了系统研究四角长周期相Al5Ti3和r-Al2Ti的弹性各向异性及声子聚焦,采用第一性原理计算,并对表征弹性各向异性的数值参数及三维图形、慢度表面和群速度表面进行研究.压缩和剪切的百分比各向异性、最大与最小剪切波速的平方比、"普适弹性各向异性指数"以及弹性模量的三维空间图形表明,Al5Ti3和r-Al2Ti是各向异性的,而且Al5Ti3的各向异性更为显著.三个声子模式慢度表面的拓扑结构及曲率表明,纵向声子并不会产生焦散线,而两个横波慢度表面则具有焦散线,慢横波慢度表面尤为明显.慢度表面和群速度表面都呈现为非球形,其中,慢横波模式的各向异性最为明显,快横波模式次之,纵波模式具有最小的各向异性.弹性模量、慢度表面和群速度表面的平面投影图表明,在ab平面r-Al2Ti比Al5Ti3的各向异性更为显著,而在bc平面则是Al5Ti3的各向异性更加明显.
      Abstract:
      In order to systematically study the elastic anisotropy and phonon focusing of tetragonal long-period superstructures (LPSs) Al5Ti3 and r-Al2Ti, first-principles calculations are performed to investigate the numerical indicators and three dimensional images which are used to measure the elastic anisotropy, slowness surfaces and the group velocity surfaces.The percentage of elastic anisotropy in the compression and shear, squared ratio of the maximum/minimum shear wave velocity, "Universal elastic anisotropy index" and three dimensional directional representations of elastic moduli indicate that Al5Ti3 and r-Al2Ti are anisotropic and the anisotropy is slightly high for Al5Ti3.The topology and curvature of three acoustic phonon modes slowness surfaces show that there are no caustics due to the longitudinal (L) phonons, whereas two transverseslowness surfaces contain several caustics, especially for the slow transverse (ST) mode.Both of the slowness surfaces and group velocity surfaces are nonspherical.ST mode shows the highest anisotropy, and then followed by fast transverse (FT)mode and L mode.The projections ofelastic moduli, slowness surfaces and group velocity surfaces indicate that r-Al2Tipossesses more obvious anisotropy in ab plane, whereas the anisotropy in bc plane is more obviously for Al5Ti3.
      Author: TANG Ping-ying HUANG Guo-hua XIE Qing-lian HUANG Jin-li
      作者单位: 广西师范学院物理与电子工程学院,广西南宁,530023
      年,卷(期): 2017, 42(2)
      分类号: O341
      在线出版日期: 2017年5月16日
      基金项目: 国家自然科学基金资助项目,广西高校新型电功能材料重点实验室开放课题