准同型相界组分无铅钛酸盐基电光晶体的制备、表征及性能调控

The electro-optic materials have been widely used in optical fiber communication and laser modulation technology. The widely used electro-optic ceramics, such as PLZT, PMN-PT contain lots of lead element. Mixing sodium bismuth titanate and barium titanate can form lead-free ferroelectric materials (NBBT) with the morphotropic phase boundary. The transparent ceramic was synthesized by Chinese scholars, and the Kerr electro-optic coefficient gets to 7.8×-17m2/V2. The single crystal does not exist the light scattering result from grain boundaries, thus the optical transmittance is higher. We have found that the transmittance of NBBT single crystal was 70% in 0.45 ~ 6μm spectral region, the 29% reflection loss can be eliminated by anti-reflection coating. Electro-optic coefficient γ33 ~ 300pm/V, far higher than the lithium niobate (32pm/V). In this project, single crystals with different composition will be grown by top seeded solution growth method. We will investigate the effects on the crystal quality that raw material pretreatment, raw material volatile, temperature field distribution and growth process parameters. The optical properties will be characterized that include optical transmittance, extinction ratio, optical uniformity and electro-optic coefficient. We shall study the effect law of composition, orientation and defects on the optical properties. The optical properties will be improved by the growth and post-treatment process. The application scope will be expanded by doping elements. Finally, the NBBT crystals will be developed into practical electro-optic materials, to lay the foundation for the property regulation of lead-free materials and design novel electro-optic materials.

电光材料广泛应用于光纤通信与激光调制技术，常用的电光陶瓷，如PLZT、PMN-PT含有大量铅元素。钛酸铋钠与钛酸钡混合可形成具有准同型相界的无铅铁电材料(NBBT)。我国学者合成了该透明陶瓷，二次电光系数7.8×10-17m2/V2。单晶没有晶界的光散射，透过率更高。我们发现，NBBT单晶在0.45～6μm波段透光率70％，29%反射损失可通过增透膜消除，电光系数γ33~300pm/V，远高于铌酸锂晶体(32pm/V)。本项目采用顶部籽晶助熔剂法生长不同组分单晶，研究原料预处理、原料挥发、温场分布、生长工艺参数对晶体质量的影响；系统地表征透光率、消光比、光学均匀性和电光系数；研究单晶组分、取向和缺陷对光学性能的影响规律；改进生长与后处理工艺，提高晶体的光学性能，通过掺杂进一步拓展晶体应用范围。最终，将NBBT晶体发展成可以实用化的电光材料，为调控无铅电光材料性能及设计新的电光材料打下基础。

电光材料中性能较优异的为透明铁电陶瓷，其中，锆钛酸镧铅 (PLZT)和铌镁酸铅-钛酸铅(PMN-PT)热压陶瓷的应用最为广泛，它们在准同型相界（MPB）区域性能最佳。然而，这些电光材料含有大量的铅（Pb）元素，会给人类健康和环境带来损害。与含铅材料相类似，无铅材料(1-x)(Na0.5Bi0.5)TiO3-xBaTiO3 (NBBT)同样具有MPB结构。本项目研究发现该单晶除了具有非常好的压电性能之外，还具有非常优异的光学性质。优化顶部籽晶助熔剂法生长工艺，制备出不同组分NBBT单晶；研究了MPB附近单晶的组分、取向和光学性能之间的关系；研究了单晶的电畴组态、缺陷结构与光学性能之间的关系；掺杂Er、Nd和Pr等稀土元素离子，提高单晶的性能，拓展其应用范围。[001]方向极化四方相NBBT单晶透光率达到70％，晶体表面反射率大于23%。测量了室温下[001]方向极化晶体的折射率，拟合出折射率色散方程，在紫外和可见光区域，随着波长的减小折射率迅速增大。对于[001]方向极化的单晶，直接带隙随着BT含量增加而增加，而对于[111]方向极化的单晶，直接带隙的变化趋势则相反。NBBT单晶的线性电光系数γ33 ~ 300 pm/V、γ42 ~ 1300pm/V，远高于广泛应用的铌酸锂单晶 (32pm/V)。Er离子掺杂的NBBT单晶在980nm激光照射下，可以观察到BT含量的升高会显著抑制蓝绿波段的可见光发射。Nd掺杂NBT单晶的吸收谱中，805 nm处的吸收峰半高宽为15 nm，适合半导体激光器做泵浦。极化后的Pr掺杂NBT晶体材料光致发光特性得到了一定的增强，扩展了在检测分析方面的应用。NBBT单晶在电光器件中潜在的巨大应用价值，引起了国内外许多研究机构和公司的密切关注，促进了NBBT单晶在光开关、光波导和电光调制器方面的应用。有望开发出实用的高速、低功耗及微型化的电光器件。