Growth of Piezoelectric Single Crystals and Their Applications to SAW Devices

研究结果如下：(1)化合物Ba_3Ga_2Ge_<4-x>Si_xO_14、Ba_3Ga_2Si_<4-x>Sn_xO_14、Ba_3Nb_xGa_<x+2>Si_<4-2x>O_14、Ba_3Ga_2Ge_<4-x>Sn_xO_14 （x > 0.5）、Ba_<3-x>Ca_xNbGa_3Si_2O_14 （0 <x <3）均为langasite结构。(2) Ba置换A位后，Ba_3Ga_2Ge_4O_14 （BGG）具有langasite结构和较大的晶格常数。对BGG的晶体生长进行了尝试，但没有获得高质量的晶体。布里奇曼技术可能对这种材料有效。(3)成功生长出具有langasite结构的Ca_3NbGa_3SiO_14 （CNGS）单晶。但其压电常数|d11|约为4 × 10^<-12> C/N，比预期的a/ C比小。(4)根据CNGS晶体的结果，压电常数d可能与晶格常数a成正比，而不是与a/c比成正比。大晶格材料的晶体生长方法有待改进。布里奇曼技术可能是有效的。(5)测定了La_3Ga_5SiO_14 （LGS）和La_3Ta_0.5Ga_5.5O_14 （LTG）晶体的所有弹性常数、压电常数和介电常数及其一、二次温度系数。(6)模拟了LGS晶体在（0°、140°、25°）传播方向下的瑞利声表面波特性；速度ν（自由）= 2750 m/s，机电耦合系数κ^2 = 0.36%，延迟温度系数TCD = 0，潮流角PFA = 2°。(7)计算了传播方向为（15°，151°，40.5°）的LGS晶体的瑞利声表面波特性；ν(免费)= 2860 m / s,κ^ 2 = 0.41%,TCD = 0, PFA = 0°。(8)采用声呐滤波器测量了LGS的声呐特性。实测结果与仿真结果吻合较好。(9)模拟了LTG晶体在（13°、150°、36°）传播方向下的瑞利SAW性能；ν(免费)= 2690 m / s,κ^ 2 = 0.5%,TCD = 0, PFA = 0°。

The following results were obtained in this research :(1) The compounds of Ba_3Ga_2Ge_<4-x>Si_xO_14, Ba_3Ga_2Si_<4-x>Sn_xO_14, Ba_3Nb_xGa_<x+2>Si_<4-2x>O_14, Ba_3Ga_2Ge_<4-x>Sn_xO_14 (x > 0.5), Ba_<3-x>Ca_xNbGa_3Si_2O_14 (0 < x < 3) have been regretfully not langasite structures.(2) After permuting the A site by Ba, Ba_3Ga_2Ge_4O_14 (BGG) has the langasaite structure and has large lattice constants. Crystal growth of BGG has been tried, but quality crystal was not achieved. The Bridgman technique might be effective for this material.(3) Single crystal of Ca_3NbGa_3SiO_14 (CNGS), which has the langasite structure, has been successfully grown. But its piezoelectric constant |d11| was about 4x10^<-12> C/N, that smaller than expected by a/c ratio.(4) According to the result of CNGS crystal, the piezoelectric constant d may be proportional to lattice constant a, not be proportional to a/c ratio. The crystal growth method for large lattice materials has to be modified. The Bridgman technique may be effective.(5) All elastic, piezoelectric and dielectric constants, and their first and secondary temperature coefficients of La_3Ga_5SiO_14 (LGS) and La_3Ta_0.5Ga_5.5O_14 (LTG) crystals have been measured.(6) Rayleigh SAW properties of LGS crystal with propagation direction of (0°, 140°, 25°) was simulated ; velocity ν(free) = 2750 m/s, electromechanical coupling factor κ^2 = 0.36 %, temperature coefficient of delay TCD = 0, power flow angle PFA = 2°.(7) Rayleigh SAW properties of LGS crystal with propagation direction of (15°, 151°, 40.5°) was calculated ; ν(free) = 2860 m/s, κ^2 = 0.41 %, TCD = 0, PFA = 0°.(8) The SAW properties of LGS were measured by using SAW filters. The measured results have good agreement with the simulation results.(9) Rayleigh SAW properties of LTG crystal with propagation direction of (13°, 150°, 36°) was simulated ; ν(free) = 2690 m/s, κ^2 = 0.5 %, TCD = 0, PFA = 0°.