【作者】 刘琳；

【导师】 夏盛清； 张国栋； 陶绪堂；

【作者基本信息】 山东大学 ， 无机化学， 2022， 博士

【摘要】 激光是二十世纪最伟大的发明之一,具有良好的单色性、方向性和相干性,在军事国防、现代工业和社会生活等领域均有广泛的应用。利用声光互作用可以对激光的方向、强度和频率等进行有效地调控,从而进一步拓宽激光的应用范围。声光晶体是一类性能优越的声光互作用介质,目前在紫外-可见近红外区域已有TeO2、LiNbO3和PbMoO4等商用的声光晶体材料,但在中远红外区域仍旧缺乏实用性的声光晶体。因此,开发性能优良的中远红外实用性声光晶体是目前亟待解决的问题。Hg2X2(X=Cl、Br、I)系列晶体具有宽的透光范围(0.4～30 μm)、大的声光品质因子、大的双折射、低的声速和声衰减系数,是一类性能优良的声光晶体材料。捷克、美国以及俄罗斯等国家早在上世纪就针对该系列晶体开展了相关研究,并已取得突出成果。但鉴于Hg2X2系列晶体在国防军事中的重要应用,国外针对该系列晶体对我国实施技术封锁和禁运政策。我国在Hg2X2系列晶体的研究方面起步较晚,且尚未掌握大尺寸、高质量Hg2X2系列晶体的生长技术,特别是关于Hg2Br2晶体的研究仍是空白。本论文从军事国防及社会生活领域对长波红外声光晶体的重大需求出发,在国内率先开展Hg2Br2晶体的生长、性能表征、缺陷研究以及器件制备工作。本论文的主要研究内容和结论如下:Ⅰ.Hg2Br2原料纯化及单晶生长采用升华-凝结法对Hg2Br2原料进行提纯,探索了石英坩埚构造、提纯温场、保温时间、提纯次数以及提纯方向等对原料提纯效果和效率的影响。明确了 Hg2Br2原料的最佳提纯温场为高温区265℃,低温区225℃。在最优提纯工艺下水平提纯5次,随后竖直升华提纯可以有效去除Hg5Br2O4、HgO等杂质组分,从而获得高纯的Hg2Br2原料,为生长高质量晶体奠定了坚实的基础。自主研发设计了适用于Hg2Br2晶体生长的透明物理气相传输炉,探索了坩埚构造、温场、坩埚下降速率以及降温时间对晶体形核、界面演化以及质量的影响。在高/低温区温度分别为380/350 ℃的温场下,采用0.2 mm/h的坩埚下降速率和5 r/min的坩埚旋转速率进行晶体生长,成功获得Φ 35×40 mm3内部无条纹、表面光滑的Hg2Br2晶体,实现了国内该领域关键技术零的突破。高分辨X射线衍射仪、ZYGO激光平面干涉仪以及X射线劳埃衍射仪测试结果表明生长所得Hg2Br2晶体具有高质量。Ⅱ.Hg2Br2单晶性能表征及声光可调滤波器制备在获得大尺寸、高质量Hg2Br2晶体的基础上,对晶体的密度、力学、光学、热学、声学以及电学性能进行系统表征,为声光器件的制备提供了基础数据。测试结果表明Hg2Br2晶体的透光范围为0.4～35 μm,且透光范围内透过率最高可达80%。Hg2Br2晶体具有大的双折射,在1μm处的双折射高达0.97。Hg2Br2晶体沿[001]方向的横波声速和声衰减系数分别为1061.41 m/s和0.005 dB/cm,低的声速和声衰减系数对于制备高衍射效率的声光器件十分有利。Hg2Br2晶体的硬度、杨氏模量、热膨胀和热导率存在较大各向异性,[001]向晶体拥有更好的力学与热学性能,第一性原理计算结果表明这与Hg2Br2晶体特殊的一维链状结构有关。与此同时,Hg2Br2晶体在低温下仍然呈现出优异的综合性能,-140℃时晶体热导率为150℃时的两倍以上,这保证了实际应用中声光器件在低温封装环境下的性能稳定性。此外,制备了基于Hg2Br2晶体的声光可调滤波器,并测试了不同入射角下AOTF的衍射效率随驱动频率的变化情况。Ⅲ.Hg2Br2晶体加工、缺陷研究及退火改性采用X射线定向仪结合多个(110)自然面对Hg2Br2晶体进行精准定向,研究了切割速度、切割机转速、研磨垫、研磨液、研磨时间、抛光液、抛光垫以及抛光时间对Hg2Br2晶体表面损伤、粗糙度和划痕的影响,初步明确了 Hg2Br2晶体的最优加工工艺。全面识别分析了 Hg2Br2晶体中的开裂、生长条纹和位错等典型缺陷,并提出了有效的缺陷抑制措施。研究了退火温度对Hg2Br2晶体结晶质量和应力的影响,明确了在150℃下退火60 h后,Hg2Br2晶体的结晶性明显提高,应力降低,晶体质量得到明显提升。Ⅳ.Hg2Br2晶体的环境交互性探究了 Hg2Br2晶体的光致变色特性,其在波长小于450 nm的蓝紫光辐照下变暗,在160℃下退火72 h或高功率红外光辐照后暗化晶体可恢复至初始状态。利用X射线光电子能谱仪阐明了 Hg2Br2晶体光照暗化和退火恢复的机理,即紫外光辐照下Hg2Br2分解为HgBr2和Hg,退火后Hg和HgBr2重新复合。透过光谱、紫外可见漫反射谱、折射率以及高分辨XRD测试结果表明,紫外光辐照后Hg2Br2晶体的光学性能和结晶质量均下降,而经过退火晶体的光学性能和结晶质量均可恢复至与光辐照前相当水平。此外,研究了在超声或磨抛等外界作用下甲醇和无水乙醇诱发Hg2Br2晶体变色的原因。拉曼光谱、透光光谱及显微镜观察结果表明,超声条件下甲醇和无水乙醇对Hg2Br2晶体的腐蚀是造成晶体颜色暗化的主要原因。更多还原

【Abstract】 Laser is one of the greatest inventions in the twentieth century.It is widely used in military defense,modern industry and social life owing to the good monochromaticity,directionality and coherence.The direction,intensity and frequency of the laser can be effectively regulated by the acousto-optic interaction,thereby further broadening the application scope of the laser.Acousto-optic crystals are a class of acousto-optic interaction media with excellent performance.At present,the commercialized acousto-optic crystals such as TeO2,LiNbO3 and PbMoO4 have been widely applied in the ultraviolet-visible and near-infrared regions.However,acousto-optic crystals suitable for the mid and far infrared region are rare.Therefore,the exploitation of commercialized acousto-optic crystals with excellent performance in the mid and far infrared region is an urgent problem to be solved.Hg2X2(X=Cl,Br,I)series crystals are a class of potential acousto-optic materials with excellent performance,which have a wide transmission range(0.4～30 μm),large figure of merit,large birefringence,low acoustic velocity and attenuation coefficient.Some countries such as the Czech Republic,the United States and Russia have carried out relevant researches on Hg2X2 series crystals as early as the last century,and have achieved outstanding results.However,in view of the significant application of Hg2X2 series crystals in national defense and military,foreign countries have implemented technical blockade and embargo policies on our country.Our country started late in the research of Hg2X2 series crystals,and has not mastered the growth technology of large-size Hg2X2 series crystals with high-quality.Especially,no researches have been carried out on Hg2Br2 crystals.The growth,performance characterization,defect and device fabrication of Hg2Br2 crystals based on the great demand for far infrared acousto-optic crystals in the field of military defense and social life were investigated in this thesis for the first time in China.The main research contents and conclusions of this thesis are as follows:Ⅰ.Feedstocks purification and crystal growth of Hg2Br2 crystalThe purification of Hg2Br2 feedstocks is carried out by sublimation-condensation method.The effects of the quartz ampoule structure,the temperature field,the holding time,the purification times and the purification directions on the purification efficiency of feedstocks were explored.It is clear that the best purification temperature field of Hg2Br2 feedstocks is 265℃ at high temperature and 225℃ at low temperature.The impurities such as Hg5Br2O4 and HgO,can be effectively removed and Hg2Br2 feedstocks with high-purity can be obtained by horizontal purification for 5 times under the optimal purification process,followed by vertical sublimation purification,which lays a solid foundation for the growth of high-quality crystals.A home-designed transparent physical vapor transport furnace is used for the growth of Hg2Br2 crystals,and the effects of ampoule structure,temperature field,ampoule descent speed and cooling time on crystal nucleation,interface evolution and quality are explored.Under the temperature field of 380/350℃ in the high/low temperature region,the crystal growth was carried out with the ampoule descending rate of 0.2 mm/h and the ampoule rotating rates of 5 r/min,and the Φ 35×40 mm3 Hg2Br2 crystals with smooth surface were successfully obtained,which achieved a zero breakthrough of key technology in this field in China.High-resolution X-ray diffraction,ZYGO optical interferometer and X-ray Laue diffraction reflect that the as-grown Hg2Br2 crystals are of high quality.Ⅱ.Properties characterization and acousto-optic tunable filter fabrication of Hg2Br2 single crystalThe density,mechanical,optical,thermal,acoustic and electrical properties of the crystals were systematically characterized on the basis of obtaining large size Hg2Br2 crystals with high-quality,which provided basic data for the fabrication of acousto-optic devices.The results show that Hg2Br2 crystals exhibit high transmittance in a broad region(0.4～35 μm)with the maximum transmittance is around 80%.The Hg2Br2 crystal has a large birefringence,which is as high as 0.97 at 1 μm.The shear wave acoustic velocity and attenuation coefficient of Hg2Br2 crystal along the[001]direction are 1061.41 m/s and 0.005 dB/cm,respectively.Hg2Br2 crystal has low acoustic velocity and attenuation coefficient,which is beneficial to the fabrication of acousto-optic devices with high diffraction efficiency.The hardness,Young’s modulus,thermal expansion and thermal conductivity of Hg2Br2 crystal are quite anisotropic,and[001]oriented crystal has better mechanical and thermal properties.The large anisotropy could be explained by the first-principles calculation,which is attributed to the special one-dimensional chain structure of the Hg2Br2 crystal.At the same time,Hg2Br2 crystal still shows excellent comprehensive properties at low temperature,and the thermal conductivity of the crystal at-140℃ is more than twice that at 150℃,which ensures the performance stability of acousto-optic devices in low temperature packaging environment in practical applications.In addition,an acousto-optic tunable filter based on Hg2Br2 crystal was prepared,and the diffraction efficiency of AOTF at different incident angles was measured with the driving frequency.Ⅲ.The crystal processing,defects characterization and annealing modification of Hg2Br2 crystalThe orientation of Hg2Br2 crystal is accurately determined by the X-ray orientation instrument combined with multiple(1 10)natural planes.The effects of cutting speed,rotating speed of the cutting machine,grinding pad,grinding liquid,grinding time,polishing liquid,polishing pad and time on the surface damage,roughness and scratches of Hg2Br2 crystal were systematically investigated,and the optimal processing technology was preliminarily determined.Typical defects such as cracking,growth striations and dislocations in Hg2Br2 crystals are comprehensively identified and analyzed,and effective measures to suppress defect are proposed.The effects of annealing temperature on the crystallinity and stress of Hg2Br2 crystal were investigated.It was confirmed that after annealing at 150℃ for 60 h,the crystallinity of Hg2Br2 crystal was significantly improved,the stress was reduced,and the crystal quality was significantly improved.Ⅳ.Environmental interactivity of Hg2Br2 crystalsThe photochromic properties of Hg2Br2 crystal are explored.The Hg2Br2 crystal darkens under the irradiation of UV light shorter than 450 nm,and the darkened crystals can be restored after annealing at 160℃ for 72 h or irradiation of high-power infrared light.The mechanism of photo-darkening and annealing recovery of Hg2Br2 crystals was determined by X-ray photoelectron spectroscopy.Hg2Br2 decomposed into HgBr2 and Hg under the irradiation of UV light,and Hg and HgBr2 recombined after annealing.The results of transmission spectrum,UV-visible diffuse reflectance spectrum,refractive index and high-resolution XRD indicated that the optical properties and crystalline quality of Hg2Br2 crystals decreased after the irradiation of UV light,while these properties could be restored after annealing.In addition,the reason of Hg2Br2 crystal darkening induced by methanol and absolute ethanol under external action such as ultrasonic or polishing was studied.The results of Raman spectrum,transmission spectrum and microscopic observation indicated that the corrosion of Hg2Br2 crystal by methanol and absolute ethanol under ultrasonic condition is the main reason for the darkening of crystal color.更多还原