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

采用自动直径控制提拉法，以38.5rpm的转速和3 mm/h的生长速率，从同组分熔体中成功地生长出透明、无核、高质量的Li_2B_4O_7单晶。为了改善Li_2B_4O_7相对较低的生长速率，提出了在生长过程中调整射频输出功率与晶体转速关系的新的晶体生长方法。测量了晶体的介电常数、弹性常数和压电常数以及它们的一阶和二阶温度系数。通过计算机分析预测了零延迟温度系数的存在，并对Raleigh和漏SAW和BAW进行了实验验证。对于零TCD值(0ﾟ，78ﾟ，90ﾟ)的SAW器件，存在有用的衬底取向，其中K_S^2约为1%。对于漏声表面波器件，也有一个有用的衬底取向，它具有小的TCD和大约1.8%的大耦合(0ﾟ，75ﾟ，75ﾟ)。在Li_2B_4O_7晶体上制作了900 MHz声表面波谐振器，并用同样的提拉法成功地生长了LiNbO_3和BaTiO_3单晶。研究了这些晶体的光折变效应在位相共轭产生器和光学联想存储器中的应用。

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.