【作者】 孙云；

【导师】 王圣来；

【作者基本信息】 山东大学 ， 材料学， 2012， 博士

【摘要】 磷酸二氢钾(KH2PO4,简称KDP)晶体,是一种性能非常优良的非线性光学晶体,其生长研究已经有80多年的历史,是一种长盛不衰的多功能水溶性晶体。由于KDP晶体具有较大的非线性光学系数和较高的激光损伤阈值,从近红外到紫外波段都有很高的透过率,可对1.064μm激光实现二倍频、三倍频和四倍频,也可对染料激光器实现二倍频,因此,它可广泛的用于制作各种激光倍频器。另外,KDP晶体也是一种性能优良的电光晶体材料,同时也是大功率激光系统惯性约束核聚变工程(ICF)的首选非线性光学材料。随着ICF事业的发展,对KDP晶体尺寸、数量和质量的要求进一步提高。就我国而言,目前“神光Ⅲ”主机和点火工程已经被列入国家中长期重大工程,未来国家对大尺寸KDP(DKDP)晶体的数量和质量也将有更高的要求。KDP晶体在生长、出槽、搬运、加工等过程中和退火过程中出现开裂现象,晶体开裂成为制约KDP/DKDP晶体向更大、更完整和更高质量方向生长发展的瓶颈。目前KDP晶体的研究现状主要集中在生长技术,生长机制和光学质量这三个方面,晶体开裂的力学研究相对报道得较少。因此有必要进一步探讨KDP晶体的力学参数、开裂机制以及杂质对KDP晶体力学性能的影响等。KDP晶体的主要生长途径是通过水溶液法生长。从水溶液中生长KDP晶体时,杂质对KDP晶体的生长习性、光学质量及力学性能等有非常重要的影响。目前,国内外在围绕着杂质对KDP晶体影响的研究中,关于杂质离子对KDP晶体的力学性能的影响研究报道地较少。因此,本文选择KDP晶体生长溶液中常见的几种杂质离子：一价Na+离子、三价Cr3+离子以及作为电荷补偿存在的阴离子SO42-等,通过掺杂方式研究了它们对KDP晶体生长习性、晶体质量及力学性能的影响。本论文的主要内容如下：1.采用全自动、高精度RMT-150C力学实验系统开展了KDP晶体的力学参数测试,根据单轴压缩实验和劈裂实验从宏观角度分别测试了KDP晶体[001]和[100]晶向的弹性模量、泊松比、抗压强度和抗拉强度等。结果表明：[001]和[100]晶向的弹性模量分别为39.25MPa和16.82MPa,泊松比分别为0.24和0.16,KDP晶体为典型的横观各向同性材料；在单轴压缩试验下,晶体样品的应力应变曲线表现为严格的线性关系,当达到或接近抗压强度时,应力应变曲线徒然下降,晶体呈劈裂或粉碎性爆裂破坏,说明KDP晶体为典型弹脆性材料。KDP晶体在[001]晶向的抗压强度、抗拉强度分别为115.00MPa和8.35MPa,在[100]晶向的抗压强度、抗拉强度分别为93.25MPa和6.67MPa；因此,KDP晶体在[100]晶向更容易发生脆性破坏,同时在KDP晶体生长过程中的破坏以拉破坏为主。2.在一定的应力状态下,晶体材料的晶格应变和宏观应变是一致的；晶格应变可以通过X射线衍射技术测出,宏观应变可以根据弹性力学求得,因此从测得的晶格应变可推知宏观应力。采用高分辨X射线衍射法对KDP晶体的晶格应变进行了测试,并定量分析了其晶格应力,探讨出KDP晶体的晶格应变保持在10-3—10-2数量级,沿[010]方向受到的应力最大,因此晶体容易沿着(001)方向发生开裂,与实际工作中的开裂现象相符合；并归纳总结了晶体生长及加工过程中引入内应力而导致开裂的主要因素。3.根据KDP晶体的结构和晶系,利用坐标旋转的方法设计了测试晶体介电、压电和弹性性能的样品切型；利用谐振法详细研究了室温下KDP晶体全部介电、压电和弹性性能,并与文献中的相应数值作比较。本次实验测到KDP晶体的弹性系数s11=3.11×10-1m2/N,c11=4.6×1010N/m2,压电应变常数d14=9.51×10-12C/N,纠正了以往相关文献中的不精确报道；其他电弹系数的测试结果与文献数值相符。4.采用HXS—1000A型数字式智能显微硬度计对快速生长KDP晶体(001)面、(101)面、(100)面分别进行压痕法显微硬度测试,实验表明：KDP晶体的显微硬度具有明显的各向异性,(001)面、(101)面、(100)面的显微硬度分别为187kg/mm2、156.7kg/mm2、151.3kg/mm2；晶体各晶面的显微硬度呈现出显著的压痕尺寸效应,即硬度随载荷的增大而减小。实验发现,当载荷较小,在5—25g时,压痕区没有出现明显的裂纹；随着载荷的增大,在25—-200g时,裂纹以辐射状扩展,压痕边缘处形成崩碎状脆裂。本文确定以25g作为KDP晶体显微硬度测试的最佳载荷,此载荷下所测得的硬度为其显微硬度。5.采用Na+、Cr3+分别作为一价和三价金属离子掺杂剂,通过传统降温法和点籽晶快速生长法生长KDP晶体,系统地研究了不同杂质离子对KDP晶体生长溶液、热膨胀系数、显微硬度、结构完整性、光学均匀性、消光比等性能的影响。实验发现：随着Na掺杂浓度的增大,KDP晶体[001]向(即Z向)热膨胀系数逐步增大,[100]向(即X向)热膨胀系数变化很小；KDP晶体(001)面的硬度整体大于(100)面的硬度,随着Na掺杂浓度的增大,KDP晶体各晶面硬度显著降低；未掺杂的KDP晶体与掺杂Na离子5000ppm,105ppm的晶体半峰宽分别为：104.4”,122.4"和147.6”,晶体的半峰宽逐渐增大；Na离子高浓度掺杂时,锥光干涉图中黑十字发生了轻微畸变,晶体的光学均匀性下降。Cr3+选择性吸附在晶体柱面区；随着掺杂浓度的增大,晶体楔化增强,晶体内局部产生缺陷,结构应力增大；当Cr3+掺杂浓度为80ppm时,晶体内布满了大量平行于生长层{101)面的“发丝状”包裹体；Cr3+掺杂后的KDP晶体[100]方向和[001]方向的热膨胀系数相对低于未掺杂KDP晶体；KDP晶体(001)面的显微硬度随着掺杂浓度的增大而减小。未掺杂KDP晶体衍射峰及Cr3+离子掺杂浓度为20ppm的衍射峰均尖锐狭窄不包含任何附加峰；未掺杂KDP晶体衍射峰半峰宽为32.74",Cr3+离子掺杂浓度为20ppm的半峰宽为28.8",但衍射峰强度明显降低。当Cr3+离子掺杂浓度为40ppm时,衍射峰出现分裂,不再保持完整,半峰宽为75.6”,明显变宽；当Cr3+离子掺杂浓度为60ppm时,其(101)面的摇摆曲线出现两个衍射峰；主峰和附加峰的半峰宽分别为12.69"和11.99",两峰之间的偏离角度为19.5”6.采用传统降温法生长了掺杂S042-离子不同浓度的KDP晶体,研究分析了SO42-离子导致晶体出现的宏观缺陷及开裂形式,从晶体生长角度初步分析了硫酸盐掺杂导致KDP晶体开裂的主要原因。实验表明,随着SO42-离子掺杂浓度的增大,KDP晶体的主要开裂形式是垂直于生长层{101)面的裂纹；晶体中裂纹存在的区域都分布有大量层层平行于生长层的母液包藏。随着SO42-离子掺杂浓度的进一步增大,晶体内包藏呈云雾状分布,裂纹呈不规则的花状,晶体质量严重下降,透明度降低。测试并表征了晶体的热膨胀系数、显微硬度、结构完整性等,实验表明：SO42-离子掺杂浓度较低时(150,500ppm),X向和Z向的热膨胀系数相对于未掺杂样品均略微增大；SO42-离子掺杂浓度较高时(1000ppm),各方向的热膨胀系数明显增大。随着掺杂浓度的增大,硬度逐渐降低；当SO42-离子掺杂浓度为1000ppm时,显微硬度相对于未掺杂KDP晶体下降了近20%；摇摆曲线半峰宽随着SO42-离子掺杂浓度的增大逐渐增大,晶体结构完整性降低。7.采用Z片籽晶和锥头籽晶分别进行传统降温法生长KDP晶体,并对其高分辨摇摆曲线、锥光干涉图以及消光比进行测试研究。实验发现,KDP晶体在不同籽晶下均能实现较好的生长稳定性,采用锥头籽晶生长的KDP晶体具有相对较小的内应力以及更好的晶体质量。更多还原

【Abstract】 Potassium dihydrogen phosphate (KH2PO4, or KDP) is one the most famous nonlinear optical crystal, it has been more than80years for their growth and research, and it could be described as a kind of time-honored crystal grown from aqueous solution. KDP was found with large Nonlinear-optical Coefficient, high laser induced damage threshold (LIDT) and high transmittance from near infrared to ultraviolet, as well as frequency doublers of dye laser. Thus, it can be used to make various laser frequency doublers. KDP crystal was also an excellent electro-optical crystal material. In addition, with the application of high power laser system on the controlled nuclear fusion, large KDP crystal is the only nonlinear optical crystal which can be used in the Inertial Confinement Nuclear Fusion (ICF) for its excellent nonlinear optical property.In recent years, with the development of ICF, requirements of the KDP crystal size, quality and quantity was further enhanced. In China, the current "SG-III" host and the ignition project has been one of the national medium and long-term major projects. In the future, the size, the quantity, and the quality of KDP (DKDP) crystals will be in higher requirements.KDP crystal presents the cracking phenomenon during growth, getting out from crystallizers, transporting, machining and anneal process. The cracking phenomenon restricts the development of technology on large-size and high-quality crystal growth. At present, research actuality of KDP crystal concentrates in the growth technology, growth mechanism and optical quality, while the mechanical characteristic of cracking is reported little. Therefore it’s necessary to discover the mechanical parameters, cracking mechanism and impurity influence.The acquisition of KDP crystal is mainly through growing from solution. When grown KDP crystal from solution, the influence of impurities on growth habit, optical quality and mechanical properties of KDP crystal should be taken into consideration. Nowadays, the research about impurity ions effect on mechanical properties of KDP crystal is relative few. Accordingly, we chose Na+, Cr3+and SO42- as additives to study their influence on growth habits, crystal quality and mechanical properties of KDP crystal. The primary coverage is as follows:1. The automatic and high precision system of RMT-150C was carried to test the mechanical parameters of KDP crystal. Elastic modulus, Poission ratio, compressive strength and tensile strength in [001] and [100] were obtained by the uniaxial compressive testing and the cleavage crack testing from the macroscopical point of view. The results indicate that the elastic modulus in [001] and [100] are39.25MPa and16.82MPa while the Poission ratio are0.24and0.16and KDP crystal is transversely isotropic material. In the uniaxial compressive testing, it’s found that the stress-strain curves of crystal specimens are linear before the specimens were failure. When the compressive force attach a certain value the curves reduce immediately, the specimen bursts at the end of the test. The failure mode shows KDP crystal is brittle materials.2. Under a certain stress condition, the lattice strain of crystal material is consistent with the macroscopic strain. The lattice strain can be determined through X-ray diffraction technology, the macroscopic strain could be obtained according to the elasticity theory. Therefore the macroscopic stress could be inferred from the obtained lattice strain. Lattice strain of KDP crystal was characterized by High resolution X-ray diffraction (HRXRD) method and lattice stress was analysed quantitatively. It is concluded that KDP crystal’s lattice strain maintains at10-3—10-2magnitude, receives the tensile stress along the [001] direction,[100] and [010] direction receives the compressed stress. According to the mechanics character of KDP crystal—resistant to compression but unresistant to tensile, therefore KDP crystal may cleaves easily along (001) direction,which correspond to the crack phenomenon in the practical work.. The major factors causing crack in the crystal growth and the machining process were summarized.3. The appropriate samples for determining the dielectric/piezoelectric/elastic properties have been designed by using coordinate rotation mehod from the sight of KDP crystal structure. The dielectric, piezoelectric and elastic properties have been studied by resonance method in detail at room temperature and compare these parameters with that of the literature values. The results about the elastic constant s11=3.11×10-11m2/N, c,,=4.6×1010N/m2; The piezoelectric strain constant d14=9.51×10-12C/N, corrected the unprecise values reported in the literatures. The other values of electro-elastic constants determined in this test are consistent with the literatures.4. Potassium dihydrogen phosphate (KDP) crystal was rapidly grown by "point-seed" technique. Indentation experiments on different faces of KDP crystal were carried out at a serial of loads by HXS—1000A digital intelligent micro-hardness apparatus. The anisotropy of microhardness has been studied. The results show that the microhardnesses of KDP crystal on (001),(101) and (100) faces were187kg/mm2,156.7kg/mm2,151.3kg/mm2, respectively. The hardness indentation size effect (ISE) phenomenon was also found at loads varying from5to200g. The results show that the microhardnesses decreased with increasing of load for all crystal faces. The cracks appeared and expanded in the radiation form when the loads were higher than25g. The edges of indentation appeared cataclasms with the disintegration shape. In this paper, it was believed that25g was the optimal load for KDP crystal.5. In this paper, we use Na+、Cr3+as the univalent and trivalent metal ion dopants, respectively. The KDP crystals were grown by traditional lowering temperature method and "point seed" technique. The effects of these impurities on the crystal growth solution, thermal expansion coefficient, microhardness, structural integrity, optical uniformity and extinction radio were systematically investigated. The result reveal that the thermal expansion coefficient of [001] direction increased with the increase of Na ion concentration, while the thermal expansion coefficient of [100] direction changed a little. The microhardness of (001) face was bigger than the (100) face. The microhardness of crystal different faces reduced heavily with the Na ion concentration increasing. The full width at half maximum of dopant and undopant KDP crystals were:104.4",122.4" and147.6", respectively. It is obvious that the full width at half maximum was broadened with the increase of Na ion concentration, which suggested that the structure integrity was destroyed with the entering of Na ion into the crystal lattice. When the dopant concentration was high, the black cross of interference figure had a slight distortion, which suggested that the internal structure stress was relatively great, the crystal optical uniformity dropped.Cr3+is selectively to be absorbed onto prismatic sectors. With the increase of Cr3+concentration, the tapering because more and more serious and structural stress increase. Many "hair" mother liquor inclusions which parallel to{101} growth layer are filled in the KDP crystal when the Cr3+concentration in the solution increases to80ppm. The thermal expansion coefficient of Cr3+doped KDP crystals were lower than that pure KDP crystal both in [100] and [001] direction.The microhardness of KDP (001) face decrease with the increase of Cr3+concentration. The diffraction peaks of undoped and dopant crystal with20ppm Cr3+were narrow and incisive, without any additional peak. The full width at half maximum of undoped and dopant crystal with20ppm Cr3+were32.74" and28.8", respectively. But diffraction intensity decreased significantly. When the dopant concentration was40ppm, the diffraction peak appeared split, no longer maintained complete. The full width at half maximum was75.6". When the dopant concentration was60ppm, the rocking curve of (101) face contained two diffraction peaks. The full width at half maximum of the main peak and the low angle boundary were12.69" and11.99", respectively.6. KDP crystals doped with different concentrations of SO42-ions were grown by the traditional temperature lowing method. The macro defects and crack models have been analysis in detail. The main reasons that causing KDP crystal crack were analysis from the view point of crystal growth. The experiment indicate that, the main crack model of KDP crystal doped with SO42-ions was vertical to the growth layer of{101} face. The crystal sectors which had many cracks also had many mother liquor inclusions. With the doping concentration increase, the quality of KDP crystal decreased heavily. The crystal quality and mechanical properties, such as thermal expansion, microhardness, high-resolution X-ray diffractomery were characterized in detail. The results reveal that the thermal expansion coefficient (TEC) of the samples increased slightly at low SO42-dopant concentration (150ppm,500ppm) and increased obviously at high SO42-dopant concentration (1000ppm). The microhardness decreased with the increase of SO42-concentration, when the dopant concentration in solution reach to1000ppm, the microhardness reduced nearly20%compared with undoped crystal. The full width at half maximum (FWHM) of rocking curve increase with the increase of SO42-concentration, the scattered intensity was much more in the positive direction in comparison to that of the negative direction. This feature clearly indicated that the crystal lattice around these defects undergo compressed stress.7. KDP crystals were grown by the traditional temperature lowing method with Z-plate seed and cap-seed, respectively. The crystal properties, such as high-resolution X-ray diffractometry, optical homogeneity, extinction radio were determined in detail. The experiment shows that KDP crystals grown with cap-seed had better crystal quality.更多还原