硫酸盐掺杂导致KDP晶体开裂的研究

采用传统降温法生长了掺杂不同浓度的SO42-离子KDP晶体,研究分析了晶体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,裂纹不规则,晶体质量严重下降,透明度降低。     

闪烁晶体的生长与宏观缺陷研究

用提拉法生长了Lu2Si2O7：Ce晶体，讨论了晶体生长过程中的几个问题；（1）熔体挥发；（2）晶体开裂；（3）层状包裹．生长过程中LPS和SiO2均存在挥发，其中后者占主导；LPS挥发不会造成组分偏析，因此对生长过程没有负面的影响．接种温度偏低导致晶体出现多晶化和晶体中较大的热应力是促使开裂发生的主要原因．层状包裹现象的出现主要是由于该晶体的结晶温度范围狭窄，熔体容易出现组分过冷，以及生长设备的温控系统精度不高等造成的．     

Na~+对KDP晶体热膨胀及硬度的影响

Na+是KDP原料中一种常见的杂质离子,采用"点籽晶"快速生长法生长了一系列掺杂Na+的KDP晶体,研究了不同掺杂浓度下Na+对KDP晶体热膨胀及硬度的影响。实验表明,随着Na+掺杂浓度的增大,KDP晶体Z向热膨胀系数逐步增大;KDP晶体(001)面的显微硬度整体大于(100)面的硬度,随着Na+掺杂浓度升高,KDP晶体各晶面硬度显著降低。     

铌酸钾锂晶体的生长与性能

使用坩埚下降法成功生长了尺寸为φ10mm50mm、四方钨青铜结构、透明铌酸钾锂晶体,讨论了引起晶体开裂的主要原因,研究了该晶体的光透过性能和介电性能,室温下该晶体的介电常数ε33=127,ε11=376,居里温度为380°     

新型压电晶体Li2B4O7的性能、生长和应用

本文详细介绍了我们在Ｌｉ２Ｂ４Ｏ７晶体坩埚下降法生长方面的研究进展，报道φ３、φ４无芯区、无孪晶、无云层、无开裂和无散射的Ｌｉ２Ｏ４Ｏ７晶体的生长条件与缺陷消除，包括高纯原料的制备与成型、缓慢的生长速率、微凸和平的固液界面形状和适当的自退火工序，同时还简要介绍了该晶体的基本性能，综述了近年来的研究进展以及该晶体在ＳＡＷ器件方面的应用。     

新型激光自倍频Yb:YAB晶体的性质研究

采用助熔剂法生长了不同配比的激光自倍频晶体Yb:YAl3(BO3)4(Yb:YAB).测量了晶体的室温吸收谱和荧光光谱,室温下仅存在一个吸收带,主吸收峰在976nm处,能与InGaAsLD有效耦合.在1.03μm处存在一个强荧光峰.测定了晶体的热膨胀系数,在平行与c轴方向的热膨胀系数较大,α2=9.4×10-6/K,约为a轴方向的3.5倍.在10％的Yb:YAB晶体中,以入射功率为11W,波长为977nm的光纤耦合二极管激光器泵浦得到4.3W的基频光波输出,斜效率为48％;在同样实验条件下得到了1.1w的自倍频绿光输出,总转换效率为10％.     

Cu∶KLN晶体的生长及物理性能研究

在KLN中掺进CuO ,以Czochralski法生长Cu∶KLN晶体 ,研究Cu∶KLN晶体的成分配比以及配比与生长速度的关系。采用场冷法极化Cu∶KLN晶体 ,以HF和HNO3混合液腐蚀极化晶片 ,测试Cu∶KLN晶片的红外光谱 ,研究Cu2 + 在KLN晶体中的占位情况。测试晶体的拉曼光谱 ,研究Cu∶KLN晶体的开裂和失透的因素和克服措施。生长出 6× 8× 30 (mm3)的Cu∶KLN晶体     

导模法生长微孔蓝宝石晶体工艺及性能研究

采用导模法生长了内孔径470 μm的蓝宝石晶棒和内孔径160 μm板形蓝宝石晶体。基于求解拉普拉斯方程的数值解, 得到生长界面处微孔的熔体膜轮廓曲线, 采用插入钼丝的方法设计了生长模具以形成和维持晶体内的微孔尺寸, 同时解决了微孔蓝宝石长晶生长过程中的两个难点: (1)获得高质量的蓝宝石晶体; (2)在蓝宝石晶体中形成并维持所需的内孔尺寸。所生长的晶体透明完整、无开裂、双晶摇摆曲线测定显示其衍射半峰宽为3.8°, 具有良好的结晶质量     

泡生法生长掺碳钛宝石激光晶体的研究

钛宝石激光晶体在现代高功率激光领域具有重要的应用价值, 但大尺寸、高品质的晶体生长仍是当前钛宝石应用面临的重大难题. 本文研究了泡生法技术生长大尺寸掺碳钛宝石激光晶体, 结果显示, 泡生法生长得到的直径180 mm、30 kg的钛宝石没有出现应力集中的开裂等宏观缺陷现象, 钛离子在晶体中分布均匀接近理论值, 晶体的FOM值达到200. 该研究对低红外残余吸收, 高品质因素、大尺寸钛宝石激光晶体的生长应用具有重要的现实意义.     

新型高效非线性光学晶体ZCTC宏观缺陷的研究

研究了采用蒸发法生长的新型高效紫外非线性光学晶体ZnCd(SCN)4（简称ZCTC）中的溶液包裹物、负晶、开裂、生长条纹、扇形界及直线管道等宏观缺陷的形成。利用光学显微镜观察和分析了这些缺陷的形态、分布规律和形成原因，讨论了消除或抑制ZCTC晶体中缺陷产生的措施。     

铜线材热膨胀系数的理论分析和实验研究

分析了面心立方结构晶体铜线材的热膨胀系数随温度的变化关系。采用精密仪器DIL402PC热膨胀仪测定了铜的热膨胀系数,得到在100℃到380℃之间铜的热膨胀系数基本保持在2.0836×10^-5/℃,比通常实验室条件下测得的结果稍大。温度大于380℃时,铜的热膨胀系数随温度呈线性增加。理论分析与实验测定的结果基本一致,说明应用此理论亦可以解释其它面心结构晶体的热膨胀系数。     

硫化锌热冲击试验与裂纹间距预报

重点研究了硫化锌热冲击开裂机理和热冲击裂纹间距、深度的预报。10mm厚硫化锌试块的燃气急热试验表明:裂纹间距随热冲击能量的增大而减小,热冲击过程中加热面最先出现非贯穿裂纹,停止加热后,裂纹贯穿试件。结合传热和热强度仿真分析,获得了热冲击过程中试件的瞬态温度场和应力场。基于材料性能的损伤演化理论,以裂纹间距和深度为变量,利用最小能量原理,获得了热冲击裂纹间距的理论预报方法,预测结果与试验吻合较好,进而分析了断裂韧性、热胀系数、材料初始模量对裂纹间距、裂纹深度的影响。该文的研究对深入理解硫化锌的热冲击失效机制,对其改性和研制具有重要意义。     

The Thermophysical Properties (Heat Capacity and Thermal Expansion) of Single-Crystal Silicon

Fragmentary investigations of the heat capacity and of the thermal expansion coefficient of single crystals of high-purity silicon are reported. The results of these investigations are compared with the entire body of data on these properties available to date. Generalized equations expressing the heat capacity and thermal expansion coefficient of silicon as functions of temperature are obtained for the temperature ranges of 298–1690 and 100–1400 K, respectively. The Debye temperature of crystalline silicon and the root-mean-square dynamic displacement of atoms from the equilibrium position in its crystal lattice are calculated using the available data on thermal expansion.     

Anisotropic thermal expansion of stoichiometric lithium niobate crystals grown along the normal direction of facets

In this paper, a stoichiometric lithium niobate (SLN) crystal with the size up to 20 × 20 × 18 mm³ was grown along the normal direction of the (0 1 2) facet from the 16 mol% K₂O fluxed melt by the top-seeded solution growth method. The anisotropic thermal expansion of the SLN crystal and congruent lithium niobate (CLN) crystal was measured along different directions by using a Shimadzu thermomechanical analyzer. As compared with CLN, the SLN crystal exhibited slightly larger thermal expansion along the Z-axis and slightly smaller expansion along the X-axis. Both the SLN and CLN crystals showed strong anisotropy in the thermal expansion. The thermal expansion coefficient of SLN along the X-axis (16.7 × 10⁻⁶ °C⁻¹ at 300 °C) is much larger than that along the Z-axis (2.5 × 10⁻⁶ °C⁻¹ at 300 °C). Based on the experimental data and polynomial fitting results, we calculated the thermal expansion coefficients for different directions. In the case of growing the SLN crystal along the normal direction of (0 1 2) facet, we studied the radial anisotropic thermal expansion and discussed the cracking problem of the crystal according to its actual growth morphology. It is found that the cracks of SLN can be suppressed by growing the crystal along the W-axis due to its reduced radial anisotropy in the thermal expansion.     

Preparation, Structure, and Thermal Expansion of CuIn3Se5

Homogeneous CuIn₃Se₅crystals 12 mm in diameter and up to 40 mm in length, with a tetragonal defect-chalcopyrite structure were grown by directional solidification. The structural parameters and thermal expansion of the crystals were measured by x-ray diffraction between 90 and 650 K. Throughout the temperature range studied, the c-axis thermal expansion coefficient of CuIn₃Se₅was found to be much smaller than the a-axis one.     

Effect of stoichiometry on the thermal expansion coefficients of lithium niobate single crystals

The chemical analysis of LiNbO₃ single crystals, with different melt compositions (Li/Nb) _m =0·945, 1·0, 1·1 and 1·2, grown by slow cooling technique, reveals a remarkable difference in solid and melt compositions. The thermal expansion coefficients alonga andc axes, determined by using Newton’s ring experiment, are found to increase anisotropically with increase in (Li/Nb) _m ratio. The variation in thermal expansion coefficient with increase in the (Li/Nb) _m ratio is discussed in the light of defect chemistry i.e. the partial replacement of Li⁺ by excess Nb⁵⁺ creates additional cation vacancies to attain the electro-neutrality in the crystal.     

Grain size and film thickness effect on the thermal expansion coefficient of FCC metallic thin films

Thin films are used in wide range of applications in industry, such as solar cells and LEDs. When thin films are deposited on substrates, various stresses are generated due to the mechanical difference between the film and substrate. These stresses can cause defects, such as cracking and buckling. Therefore, knowledge of the mechanical properties is important for improving their reliability and stability. In this study, the thermal expansion coefficient of FCC metallic thin films, such as Ag and Cu, which have different grain sizes and thicknesses, were calculated using the thermal cycling method. As a result, thermal expansion coefficient increased with increasing grain size. However, the film thickness had no remarkable effect.     

The Thermophysical Properties of Solid Solutions of CaLa2S4-La2S3 System

The thermal conductivity coefficient in the temperature range from 275 to 450 K and the coefficient of thermal expansion in the range from 300 to 900 K are experimentally determined for solid solutions of the CaLa₂S₄-La₂S₃ system. The mechanisms of heat transfer in CaLa₂S₄- La₂S₃ samples in the investigated temperature range are discussed, as well as the factors which define the complex concentration dependence of thermal conductivity coefficient. The correlation is treated between the value and temperature dependence of the coefficient of thermal expansion and the variation of the interatomic bond force in the case of variation of the concentration of cation vacancies in the investigated crystals.     

A criterion for convection of elementary excitations in crystalline solids

A universal method is suggested that provides empirical estimates of the kinetic coefficients in the equations of quasiparticle transfer in crystalline structures. The method is based on a criterion for the onset of Landau convection and on an analysis of experimental data on the electric and thermal resistance and the thermal expansion coefficient for crystals with different types of interatomic bonds.     

Microstructure effect on the properties of a commercial low-fusing dental porcelain

The aim of this study was to investigate the effect of firing cycle on a dental porcelain microstructure in order to correlate microstructure changes with mechanical and thermal properties. A commercial low-fusing dental porcelain powder (Omega 900, Vita) was investigated for this purpose. The powder was treated at different temperatures in the range 750–1000 °C. The fired samples were characterized in terms of their morphology and microstructure, and their mechanical and thermal properties were evaluated. The results showed that firing temperature affects porcelain microstructure influencing significantly in this way both the mechanical properties and the thermal expansion coefficient of the fired objects. Firing at 800 °C led to a homogeneous structure. After treatment at this temperature, the leucite crystals exhibit their maximum concentration and they are well dispersed into the glassy phase. As a consequence the optimum mechanical strength and the maximum thermal expansion coefficient are observed in these samples.