High Rate Growth of Large Diameter and High Quality Li_2B_4O_7 Piezoelectric Crystals and Practical Research on SAW Devices

采用ADC（Automatic Diameter control）控制的Czochralski方法，以38.5rpm的转速和3mm/h的生长速度，成功生长出透明、无芯、高质量的Li_2B_4O_7单晶。为了改善Li_2B_4O_7生长速度相对较低的问题，提出了调整生长过程中rf输出功率与晶体旋转速率关系的晶体生长新方法。测量了所有介电常数、弹性常数和压电常数及其一、二阶温度系数。通过计算机分析预测了零延迟温度系数（TCD）取向的存在，并通过实验证实了这一点。对于TCD为零的SAW器件，在（0,78,90）附近有一些有用的衬底取向，其中K_S^2约为1%。对于具有小TCD和1.8%左右（0,75,75）的大耦合的漏形SAW器件，也有一个有用的衬底取向。在Li_2B_4O_7晶体上制备了900MHz SAW谐振滤波器。采用相同的Czochralski技术，成功地生长了LiNbO_3和BaTiO_3单晶。研究了这些晶体的光折变效应，并将其应用于光相共轭发生器和光联想存储器。

Transparent, core free and high quality single crystals of Li_2B_4O_7 were successfully grown from a congruent melt at rotation rate of 38.5rpm and growth rate of 3mm/h by the ADC(Automatic Diameter Con-trol) controlled Czochralski method. New Crystal growth methods adjusting the relationship between the rf-output power and the crystal rotation rate during the growth were proposed in order to improve the relatively low growth rate of Li_2B_4O_7. All the dielectric, elastic and piezoelectric constants and their first and second-order temperature coefficients have been measured.The existence of an orientation with zero TCD(Temperature Coefficient of Delay) was predicted by a computer analysis and confirmed experimentally for the Raleigh and leaky SAW and BAW. There are useful substrate orientations for SAW devices with zero TCD around(0ﾟ,78ﾟ,90ﾟ), where K_S^2 is approximately 1%. There is also a useful substrate orientation for the leaky SAW devices with a small TCD and a large coupling of 1.8% around(0ﾟ,75ﾟ,75ﾟ). 900MHz SAW resonator filters were fabricated on Li_2B_4O_7 crystals.Using the same Czochralski technique, LiNbO_3 and BaTiO_3 single crystals were successfully grown. The Photorefractive effect in these crystals were investigated for applications to phase conjugate genarator and optical associative memory.