LGAS晶体的微结构及声表面波特性研究

本文采用第一性原理计算了La3Ga5-xSiAlxO14 (LGAS)压电晶体几何结构、能带和态密度.并研究了其在X、Y和Z切型的声表面波速度、机电耦合系数及能流角.当x=0.5时,构建了La3Ga4.5SiAl0.5O14晶体的1×1×2超晶胞结构,发现A1原子替代2d四面体位置的Ga原子时体系总能量最低,体积最小,因此是最稳定的状态.与石英相比,LGAS具有声表面波速度较低、机电耦合系数较大且存在能流角为零的切型等优点.掺Al元素降低了成本但对结构和声表面波特性影响不大.Y切0是较好的切型,可用于制备声表面波器件.

Study on the Micro-structure and Surface Acoustic Wave Properties of La3Ga5 -xSiAlxO14 Crystals

The geometry structure,band structure and density of states of La3Ga5-xSiAlxO14(LGAS)single crystal were investigated by the first principles method.The surface acoustic wave velocity,electromechanical coupling factor and power flow angle were calculated for LGAS single crystal at X,Y,Z cuts,respectively.The 1×1×2 supercell structure of La3Ga5-xSiAlxO14 was constructed for x=0.5.The supercell shows highest stability with the minimum energy as the 2d tetrahedron site is occupied by Al atom.It is in accordance with the experimental results.Compared with quartz,LGAS crystals are of lower phase velocities and higher electromechanical coupling factor.Doping Al atom decreases the cost of crystal growth.But it has no effect on the structure and surface acoustic wave properties.The propagation direction of 0 of Y-cut LGAS is found to be optimum direction for surface acoustic wave(SAW) device applications.