Development and Characterization of Langasite-type crystals for surface acoustic wave device

在本研究中，我们注意到了朗加石(La_3Ga_5SiO_5&lt；14&gt；：lgs)型晶体。LGS晶体是一种适用于压电应用的主要材料，因为它的电性能介于石英和钽酸锂(LiTaO_3)之间。然而，大量昂贵的氧化镓作为原料是大规模生产所必需的。第一年，我们合成了Al取代的LGS晶体(La_3Ga_&lt；5-x&gt；Al_xSiO_&lt；14&gt；(0&lt；x&lt；1)：LGAs)。用传统的提拉法生长出直径为20-25 mm、长度为100-150 mm的单晶。化学成分数据表明，Al在LGS中的有效偏析系数为1.03~1.07，Al的溶解极限为x&lt；1.0。单晶x射线结构分析表明，Al原子分布在所有阳离子中心…中除了La占据的十面体外，更倾向于最小的四面体。随着Al含量x的增加，材料的压电系数L d_lt；11&gt；L增大1.3%，d_t；14&gt；减小7.7%。获得最大机电耦合系数的Al含量为x=0.6。第二年，利用化学计量比原料，用提拉法合成了新的Ba3TaGa3Si2O14&gt；(BTGS)晶体。对生长过程的分析表明，BTGS晶体完全熔化。用单晶X射线衍射法对BTGS的晶体结构进行了精炼。各阳离子在各部位的分布是有序的。Y切BTGS晶片的最大机电因子k^2在X轴传播时约为0.43%。因为LGAs和BTGS晶体都可以使用较低数量的昂贵的氧化镓作为原料。因此，我们可以说，这两种晶体都是体声波和表面声波器件较好的朗加斯型结构的压电材料。较少

In this study, we paid attention to Langasite (La_3Ga_5Sio_<14>: LGS) -type crystals. The LGS crystal is a leading material suitable for piezoelectric applications, because the crystal has intermediate properties between those properties of quartz and lithium tantalate (LiTaO_3) in electricity. However, a large amount of expensive gallium oxide as the raw material is necessary for mass-production. The aims of this study are to develop new LGS-type crystals consisting of lower gallium oxides.In the first year, we have developed Al substituted LGS crystals (La_3Ga_<5-x>Al_xSiO_<14> (0<x<1): LGAS) crystals. The single crystals, with a 20-25 mm diameter and a 100-150 mm length, were grown by a conventional Czochralski technique. The chemical composition data disclosed that the effective segregation coefficient k_<eff> of Al in LGS was 1.03 to 1.07 and that the Al solubility limit was x<1.0. A single-crystal x-ray structure analysis reveals that Al atoms are distributed in all cation sites … More except for the decahedral one occupied by La, by rather favoring the smallest tetrahedral one. The piezoelectric modulus l d_<11> l increased; 1.3% and d_<14> decreased; 7.7% with the increasing Al content, x, up to 1.0. The Al-content obtaining the maximum electromechanical coupling factors (k_<12>, k_<25>, and k_<26>) was x=0.6.In the second year, new piezoelectric Ba_3TaGa_3Si_2O_<14> (BTGS) crystal was synthesized by the Czochralski technique using raw materials with stoichiometric compositions. An analysis of growing process showed that the BTGS crystal congruently melts. The crystal structure of BTGS has been refined using single-crystal X-ray diffraction data. The distribution pf each cation was found to be ordered in each site. The maximum electromechanical factors k^2 in Y-cut BTGS wafer was about 0.43% at X-axis propagation. This value was larger than those of LGS.For both LGAS and BTGS crystals enables the use of a lower amount of expensive gallium oxide as the raw material. Therefore, we can say that these two crystals are the preferable piezoelectric materials with the Langasite-type structure for both bulk- and surface-acoustic wave devices. Less