Mass-Spectrometric Study of the Temperature Variation in the Dimer-to-Monomer Ratio in the Free-Surface Vaporization Fluxes from Alkali Halide Single Crystals

A mass-spectrometric method is used to investigate the kinetics of the vaporization of LiF (970–1070 K), NaCl (722–889 K), KCl (780–900 K), KBr (724–918 K), and CsI (656–838 K) single crystals. A dimer-to-monomer ratio, J_D/J_M, in the fluxes vaporizing from free surfaces of these crystals are calculated, using the currents of M⁺, MX⁺, and M₂X⁺ ions formed via electron impact ionization of the molecules MX and M₂X₂ (M is the alkali atom; X is the halogen). It is found that the dimer-to-monomer ratio increases with temperature at a continually increasing rate in the LiF and NaCl cases. In the KCl, KBr, and CsI cases, this rate passes through a maximum. Such a specific temperature variation in J_D/J_M is discussed through the analysis of proposed mechanisms of dimer formation in light of the terrace–ledge–kink and surface charge models.     

Mass Spectrometric Study of the Vaporization Kinetics of Potassium Bromide Single Crystals

A mass-spectrometric method was used to investigate the kinetics of the vaporization of potassium bromide single crystals. In electron-impact-ionization mass spectra of molecular fluxes vaporized from a free-surface of KBr, ions of K⁺, KBr⁺, Br⁺, and K₂Br⁺ originating from KBr and K₂Br₂ molecular precursors were detected in the temperature range 724–918 K. The temperature dependencies of ion currents, ln I_iT – 1/ T, of the most abundant ions (K⁺, KBr⁺, and K₂Br⁺) revealed a departure from the linearity. From a comparison between the equilibrium and nonequilibrium vaporization rates, it was concluded that the value of the vaporization coefficient for monomers and dimers passes through a maximum at about 800 and 825 K, respectively. An electron-impact-fragmentation pattern of KBr molecules, I(K⁺)/I(KBr⁺), was observed to pass reproducibly through a minimum at the temperatures of about 800 to 830 K. In the fluxes from a free surface and from one inside a Knudsen cell, the dimer-to-monomer ratios were found to vary with temperature in different ways. The difference in the equilibrium and nonequilibrium rates of vaporization, the temperature dependence of the fragmentation pattern, and the mechanism of association reactions are discussed in light of the terrace-ledge-kink and surface-charge models.     

La1-xNdxB6单晶的制备及热电子发射性能

以LaB_6和NdB_6粉末为原料,采用区域熔炼法成功制备了大尺寸、高质量的多元稀土六硼化物La_(1-x)Nd_xB_6(x=0.1~0.3)单晶,并测试了该系列单晶(100)晶面的热电子发射性能。本实验制备的单晶长度大于40mm,直径大于4mm。单晶衍射、劳埃照片、晶面摇摆曲线、单晶断口扫描等检测结果表明单晶质量较高,热发射测试结果表明在1 873K、4 000V下,单晶零场电流发射密度随着Nd含量增加从6.01A/cm~2降为4.83A/cm~2,有效逸出功从2.88eV增大到2.95eV。     

Mass Spectrometric Observations of Enhanced Rates of Association Reactions: nLiF = Li n F n (n = 2, 3) at LiF Single Crystal Surfaces

A mass spectrometric method was used to study the kinetics of lithium fluoride single-crystal sublimation. In electron impact ionization mass spectra, Li⁺, LiF⁺, Li₂F⁺, and Li₃ F ₂ ⁺ ions originating from monomer (LiF), dimer (Li₂F₂), and trimer (Li₃F₃) molecular precursors were detected in the temperature range 970–1070 K. The dimer-to-monomer and trimer-to-monomer flux ratios were found to increase progressively with increasing temperature and also in comparison with those measured under equilibrium of crystalline LiF with its saturated vapor. The temperature dependence of the ion current ratio I(Li₂F⁺)/I(Li⁺) measured over the interval 916–1087 K was shown to pass reproducibly through a minimum at about 975 K. The enhancement of the rate of association reactions at LiF crystal surfaces is discussed in light of the terrace-ledge-kink model of vaporization and surface charge concept.     

悬浮区域熔炼法制备Ce1-xPrxB6单晶体及其热发射性能研究

以CeB₆和PrB₆粉末为原料, 采用放电等离子烧结结合悬浮区域熔炼法成功制备了晶体质量良好的多元稀土六硼化物Ce_1-xPr_xB₆(x=0.1、0.2、0.4)单晶体, 并系统研究了该系列单晶体(100)晶面热电子发射性能。结果表明: Ce_0.8Pr_0.2B₆单晶(100)晶面具有最好的热发射性能, 在1873 K, 最大电流发射密度达到66.07 A/cm², 比CeB₆单晶的电流发射密度提高约20%。此外, Ce_0.9Pr_0.1B₆、Ce_0.6Pr_0.4B₆单晶(100)晶面的热发射电流密度分别为65.81 A/cm²和65.31 A/cm²。Ce_0.8Pr_0.2B₆单晶(100)晶面的逸出功最低, 为2.61 eV, 其它单晶(100)晶面的逸出功在2.64~2.753 eV范围内。因此, Ce_1-xPr_xB₆多元稀土六硼化物单晶具有良好的发射性能和低的逸出功, 作为热阴极材料有很好的应用前景。     

A:Al2O3（A=Cr,Fe,Ni）晶体生长及其缺陷研究

报道了A:Al2O3(A=Cr,Fe,Ni)晶体光学浮区法生长工艺,研究了旋转速率、生长速率对晶体质量的影响,制备出了φ6~8 mm、长度为60~80 mm的A:Al2O3晶体.A:Al2O3晶体的生长方向为<001>方向,X射线双晶摇摆曲线表明A:Al2O3晶体具有良好的晶体质量.通过X射线衍射、扫描电镜、偏光显微镜对晶体中的生长缺陷进行了研究,结果表明,A:Al2O3晶体的主要缺陷为小角度晶界、包裹体和溶质尾迹.研究了A:Al2O3晶体的光谱性能,并对A:Al2O3晶体的介电性能进行了测量,室温下1000 kHz时A:Al2O3晶体表现出较高的介电系数εr(12.1~15.7)和较小的介电损耗tanδ(0.0020~0.0002).     

基于小波变换的金刚石单晶生长声发射信号的降噪分析

依据小波变换的基本原理和方法,采用阈值降噪法对高温高压条件下金刚石单晶生长过程的声发射信号进行了小波降噪处理。结果表明:采用小波阈值降噪法能较好地消除金刚石单晶生长过程中声发射信号中的噪声,而且还保证了本身的声发射特性没有被破坏,从而可以更加准确地分析金刚石单晶的生长过程。     

弛豫铁电单晶及织构陶瓷的研究进展

综述了近年来弛豫铁电单晶和织构陶瓷的制备及其介电、压电性能的研究进展。弛豫铁电单晶的制备方法主要有高温溶液法、布里奇曼法和固态再结晶法，尺寸可达40mm以上，(001)切片压电常数d33最大可达3000pC／N，k3达到0.93，但是成分不均匀仍是影响晶体压电性能的一个主要因素。织构陶瓷的制备方法主要为固态再结晶法(TGG法和RTGG法)，其耗时短、成本低，压电性能可达到单晶的60％～80％，介电常数甚至可以超过部分单晶，是一个新的发展方向。     

Investigation of the Interaction of Sodium Chloride and Two Amino Sulfonic Acids,HEPES and MOPSO,by EMF Measurements

Ionic interactions in the two systems NaCl-HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid) and NaCl-MOPSO (3-(N-Morpholino)-2-hydroxypropanesulfonic acid) have been studied in terms of their mutual influence on the respective activity coefficients of each component. Activity coefficients for each component of the two systems and for corresponding buffers are calculated from emf measurements of solutions containing NaCl, the aminosulfonic acid, and its conjugate base in a NalSE/solution/AgCl-Ag cell at 5, 15, 25, and 37 °C.     

采用同步辐射X射线衍衬貌相术原位实时观察单晶Cu─Zn─Al形状记忆合金的马氏体相变过程

采用高强度同步辐射白光束ｘ射线衍衬貌相术原位实时研究了单晶Ｃｕ－Ｚｎ－Ａｌ形状记忆合金的马氏体相变，跟踪了马氏体变体随温度循环的演变过程。结果表明，马氏体变体首先在非完整晶区形核；由于马氏体变体之间及马氏体变体与母相之间的相互作用，使某些区域造成高度紊乱，经一次循环后，在这些区域留下了新的晶体缺陷，但是亚晶结构与原始状态一致。