Dislocation Etching Behaviour of Hydrothermal and Organic Acid Etchants on Natrolite Crystals

Studies on etching of (110) cleavages of natrolite crystals in organic acids (viz., succinic acid, formic acid, and phthalic acid) and stream under high hydrostatic pressures have been made. It is observed that on successive etching of matched cleavages in any of these organic etchants, the pits get bigger both in regard to depth as well as lateral dimensions. Study of matched cleavages etched in any of these etchants indicates 1:1 correspondence of point bottomed pits. Similar results are obtained when matched cleavages are etched by the hydrothermal method. In contrast to such results, it is observed that the etch pit density on a cleavage etched by the hydrothermal method is always higher when compared with its matched cleavage etched in any of the given organic acids. Through a series of experiments, it is found that while corresponding to every etch pit due to any of these organic acids there is a pit due to hydrothermal etching, the converse is not true. It is suggested that the hydrothermal etching is more reliable so far as dislocation density estimation on (101) cleavages of natrolite is concerned.     

Growth and Characterization of Urea-(DL) Tartaric Acid Single Crystals

A new organic UV nonlinear optical crystal urea-(DL)tartaric acid [CO(NH₂)₂₋(DL) C₄H₆O₆] (abbreviated as U(DL)T) is reported. Large single crystals have been grown from aqueous solution by the cooling method. They belong to the monoclinic space group P2₁ and the lattice parameters are: a = 7.6973 Å, b = 23.3310 Å, c = 4.8727 Å, and β = 100.82°. The structure and some of its physical properties have been determined. The crystal is transparent from 0.24 to 1.95 μm. The efficiency of powder SHG is larger by one order of magnitude than that of KDP. Thus the crystal will be a useful NLO material.     

局域共振声子晶体的离散化及其线缺陷研究

提出了一种局域共振声子晶体基本模型,将其散射体离散化,研究了二者的能带结构及隔声曲线.采用有限元法结合超原胞技术,将离散模型引入基本模型组成的超原胞中,研究了多种形式的线缺陷对能带结构及隔声曲线的影响.结果表明,离散模型比基本模型具有更宽的带隙,同时隔声效果更好;通过引入线缺陷,可以在能带结构中产生缺陷带,声波被局域在缺陷处只能沿缺陷传播,缺陷带的数量及位置受到线缺陷形式的影响;同时,线缺陷形式影响隔声效果,横向和纵向复合线缺陷隔声效果最好.研究结果可以为声子晶体的实际工程应用提供一定的理论参考.     

Unstable internal friction in Bismuth and Antimony single crystals

In the temperature range of 6 to 300 K an effect of the high amplitude ultrasound waves on amplitudedependences of decrement and modulus defects in the antimony and bismuth single crystals of different orientation is studied. The character of changes of the decrement and modulus defect amplitude dependences under the influence of the high amplitude ultrasound indicates that dislocation multiplication, obstacle break-through by dislocation pile-ups or deformation twinning may be observed in crystals depending on the ultrasound propagation direction and the temperature interval investigated.     

Preparation and Electrical Resistivity of Intercalation Compounds of Graphitized Cokes with Antimony Halides

Preparation of intercalation compounds of a graphitized electrode coke and a synthetic graphite with SbCl₅, SbCl₄F, SbCl₂F₃ and SbF₆ have been described and stages have been characterized by X-ray diffraction technique. On applying pressure a de-intercalation of antimon pentahalides have been found. The stability of intercalation compounds of graphitized cokes to pressure, temperature, organic solvents and aqueous HCI is lower than that of natural graphite compounds. Electrical resistivity of compacted intercalation compounds of different stages parallel and perpendicular to pressure direction decreases with increasing pressure, intercalant concentration and particle size. Intercalation increases anisotropy of electrical conductivity in graphitized coke and decreases it in synthetic graphite.     

Defects in LEC-grown Indium Phosphide Crystals Doped with Tin

Crystalline defects in Sn-doped LEC indium phosphide have been revealed by chemical etching and analyzed by TEM. Grown-in dislocations, various kinds of defect clusters and colonies of microdefects were found. The symmetrical defect clusters are shown to equate mostly with larger dislocation loops exhibiting shear components and/or other dislocation arrangements generated by a stress source which is positioned in the centre of the dislocation cluster. Those centres are often formed by a plate-like agglomeration composited of tiny inclusions and very small faulted dislocation loops. Such planarly arranged accumulations of microdefects lie on {111} planes. The direct vicinity of single threading grown-in dislocations is always enriched with tiny perfect dislocation loops and precipitates. Additionally, very large isolated interstitial-type perfect dislocation loops with b = a₀/2 〈110〉 have been found by TEM experiments. Mostly, the {110} habit plane of such loops is decorated with an high number of small dislocation loops and precipitates as a consequence of dislocation climb.     

Defects in specialty and container glasses

Laboratory techniques used to identify solid inclusions such as stones cords, and knots in glass will be described. Examples of defects from raw material, refractory, devitrification and miscellaneous sources will be presented. Glass melting, liquidus determination techniques, and glass-refractory corrosion testing methods can all be utilized to better define defect sources. Correlations between these laboratory tests and actual stone defects will be made.     

Defects in implanted and Czochralski silicon

Rod-like defects, a6〈114〉 and a/3〈111〉 faults, and a/2〈110〉 loops may all be generated by self-interstitial aggregation during the annealing of implanted or Czochralski silicon, and several models, intended to account for one or more of these, are compared. It is concluded that the rod-like defects are {113} faults, and that the three faulted defects form independently (i.e. they are not related in an „evolutionary”︁ sequence). The dipolelike a/2〈110〉 loops probably result from the unfaulting of {113} faults, while other perfect loops are generated by the shear of a/6〈114〉 defects. At a given temperature, the latter appear considerably more likely to unfault than the a3〈111〉 faults. The structure of the {113} fault remains uncertain.     

含反位缺陷碳化硅纳米管的电子结构和光学性质

基于第一性原理计算,对含有SiC反位缺陷或CSi反位缺陷碳化硅纳米管的电子结构和光学性质进行了研究.SiC缺陷在纳米管的表面形成了凸起,CSi缺陷在纳米管的表面形成了凹陷;这两种缺陷都导致在纳米管的导带底附近形成了缺陷能级,使得纳米管表现出n型电导;导带顶到杂质能级间的跃迁使得纳米管的光学带隙呈现了减小的趋势.这些结果对碳化硅纳米管电子器件和光学器件的研究都有较重要的参考价值.     

Dielectric Relations of Nematic 4-n-Heptylamino benzoic Acid in Mixtures with 4-Cyano benzoic Acid and 4-Fluoro benzoic Acid

Dielectric constants and the dielectric loss in the frequency range from 0.1–12 MHz were measured in the binary systems of 4-n-heptylamino benzoic acid with 4-cyano benzoic acid and 4-fluoro benzoic acid in the nematic phase. Not only the strong increase of dielectric anisotropy, but also the appearance of a Debye relaxation in the MHz range in both the mixtures proves the existence of the mixed associates. This model was proved by the temperature dependence of relaxation times and on chemical structure of the mixed associates, as well as, by the comparison with the measurements of one more binary system of acids.     

Defects and microvoids in a-Si and a-Si:H

We report the first measurements of positron-annihilation spectra of samples of both pure and hydrogenated amorphous silicon. Comparison of these spectra with that of crystalline silicon indicates that the lowest-lifetime component can be identified as the contribution mainly from valence-band electrons. Both the pure (a-Si) and the hydrogenated (a-Si:H) samples exhibit a component with intermediate lifetime, which we attribute to small vacancies consisting of about 4 missing atoms. Finally, only a-Si:H shows a significant long-lived line (τ > 5 ns), which arises from large microvoids, with ～ 100 missing atoms. The existence of these microvoids in a-Si:H is consistent with recent reports of the presence of occluded H₂ gas under high pressure in such films.     

Crystal Structure of an Adduct of Sarcosine with Sulfuric Acid (at 140 K)

The crystal structure of an adduct of sarcosine with sulfuric acid, (C₃NO₂H₈)₂SO²⁻₄, has been determined at low temperature (140 K). The crystals are triclinic, space group = P1 with the unit cell dimensions, a= 7.623(1) Å, b = 11.538(2) Å, c = 14.214(2) Å, α = 71.46(2)°, β = 74.36(2)°, γ = 86.46(2)°. Based on 4924 reflections with intensities larger than 3σ(I), the structure was refined to a conventional R factor of 0.038 giving e.s.d.s. in bond lengths and angles of 0.003 Å and 0.2°, respectively. There are two formula units in the asymmetric unit and both sulfate ions exist in two disordered orientations. The sulfate group 1 occupies the two orientations in the proportion 0.82/0.18 and sulfate group 2 in proportion 0.69/0.31. Both Orientations of the sulfate groups satisfy the hydrogen bonding scheme equally well. There is also a pseudo-symmetry element within the asymmetric unit as one half of this unit is transformcd into the other by a translation of approximately one half along the b- and c-axes. Thus, sarcosine molecule 1 is translated to sarcosine IV and sarcosine II to III. In the same manner, the sulfate group I in its main orientation is translated to the sulfate group 2 in its alternative orientation and vice versa.     

Yb：YAG晶体的生长缺陷及位错走向

用同步辐射透射白光形貌和应力双折射法研究了沿（111）方向生长的Yb:YAG晶体的生长缺陷、晶体中的位错起源和走向。Yb:YAG晶体中的生长缺陷主要有：生长条纹、核心和位错等。晶体中的位错主要起源于籽晶、杂质粒子以及生长初期的晶种和固液界面处位错成核。位错的走向垂直于生长界面,符合能量最低原理。采用凸界面生长工艺可以有效的消除晶体中的位错。     

人造金刚石晶体缺陷的同步辐射X射线衍射形貌像浅析

利用同步辐射X射线对人造金刚石晶体缺陷进行了形貌学研究,实验采用了透射(劳埃)形貌术和反射形貌术两种方法.所得的X射线透射劳埃图上大部分斑点分别分布在四条主晶带上,经分析发现,该金刚石晶体主要的晶体缺陷为位错,并推导出晶体内部存在Frank不全位错.该晶体的反射形貌像中位错呈网状分布,说明其表层缺陷多于内部缺陷.此外,由形貌像分析发现该人造金刚石晶体的晶体缺陷明显少于天然金刚石.     

Interesting Reactivity in the Thermolysis and Photolysis of 2,3-Diphenyl-1-naphthol

Abstract  2,3-Diphenyl-1-naphthol (1) undergoes two unexpected reactions under different conditions. Compound (1) was heated in DMSO-d₆ and underwent a Pummerer type thermal reaction to give two isomeric products, 1-(methylthio)methoxy-2,3-diphenyl naphthol-d₅ which crystallized in the space group with a = 7.1610(9) ?, b = 11.2795(15) ?, c = 12.8905(17) ?, α = 114.049(2)°, β = 96.589(2)°, and γ = 102.945(2)°, and 2-(methylthio)methyl-2,3-diphenyl 1(2H)-naphthalenone-d₅ which crystallized in the space group with a = 8.5981(5) ?, b = 10.4374(6) ?, c = 11.1078(6) ?, α = 78.748(2)°, β = 67.709(2)°, and γ = 83.184(2)°. Photolysis (254 nm) of (1) resulted in 2,2′,3,3′-tetraphenyl-1,1′-bi-2-naphthol which crystallized in the space group P2₁/c with a = 26.3616(11) ?, b = 10.1707(4) ?, c = 23.3376(9) ?, and β = 99.034(2)°. Graphical Abstract  When 2,3-diphenyl-1-naphthol was heated in DMSO-d₆ two unexpected isomers, 1-(methylthio)methoxy-2,3-diphenyl naphthol-d₅ and the racemate 2-(methylthio)methyl-2,3-diphenyl 1(2H)-naphthalenone-d₅ were produced. Photolysis in THF at 254 nm led to the unexpected product 2,2′,3,3′-tetraphenyl-1,1′-bi-2-naphthol. All structures were elucidated by X-ray crystallography.      

Reactivity of SiCl and SiF groups in SiO2 glass with mobile interstitial O2 and H2O molecules

Reactions of common network-bound halogens in synthetic SiO₂ glass, SiCl and SiF groups, with interstitial O₂ and H₂O molecules incorporated by thermally annealing were studied. It was found that the chemical properties are distinctly different between SiCl and SiF groups. SiCl groups react with interstitial O₂ and H₂O to form interstitial Cl₂ and HCl, respectively. In contrast, formation of interstitial F₂ and HF due to the reaction of SiF groups with interstitial O₂ and H₂O is not observed. The reactivity of SiCl and SiF groups is in accord with the properties and thermodynamic data of their respective analogous compounds, SiCl₄ and SiF₄.     

Extended Defects in O+-Implanted Si Layers and Their Luminescence

Crystallography Reports - The structure and luminescence properties of Czochralski-grown n-Si samples implanted with oxygen ions have been comprehensively analyzed using photoluminescence and...     

X-ray Topographic Assessment of Defects in Pure and Substituted Hexaferrite Crystals

Results of X-ray diffraction topography, in reflection and transmission scanning geometry, of flux grown single crystals of substituted and unsubstituted hexaferrites bearing composition SrGa_xIn_yFe_12-(x+y)O₁₉ (where x = 0, 5, 7, 9; y = 0, 0.8, 1.3, 1.0) are presented. Diffraction topographs reveal defects like misoriented grains, dislocations, cavities, inclusions, and the strain patterns in these crystals. The unsubstituted hexaferrites exhibit better perfection when compared to the substituted ones. The study is reported to support the results obtained by chemical etching and fractography, besides yielding additional information covering defects.     

Submicroscopic Defects in Metals and their Influence on HVEM In-situ Experiments

Recent high-voltage electron microscopy has provided evidence that substantial submicroscopic changes may occur in specimens examined in the HVEM under conditions where no visible radiation damage occurs. These are the introduction of vacancies by plastic deformation, rapid accumulation of invisible vacancy clusters by electron irradiation, and radiation-induced contamination and refining of materials. These processes are analysed in terms of defect interactions and the consequences for in-situ experiments are discussed.