The low-temperature solubility of helium in quartz

Technical Physics - The solubility of helium in α- and β-quartz single crystals, optical quartz crystals, and Pyrex glass has been studied by the method of thermal desorption of helium...     

Mass spectrometric investigation of low-temperature diffusion and solubility of helium in lead fluoride crystals

Thermal desorption of helium from presaturated crystals was used for mass spectrometric investigations of the diffusion and solubility of helium in lead fluoride crystals in the temperature range 606–714K which precedes the transition of the crystal to the superionic state. The experimental apparatus and measurement method are described and mechanisms for the diffusion and solubility of helium in PbF₂ are discussed. Zh. Tekh. Fiz. 68, 85–89 (December 1998)     

Diffusion and solubility of helium in lead fluoride single crystals in the superionic transition region

Temperature curves of the diffusion coefficients and solubilities of helium in pure and holmium-doped lead fluoride crystals are obtained in the superionic phase-transition range. Possible mechanisms of the interaction of helium with ions are discussed, along with mechanisms of the solubility and diffusion of helium in a crystal. Fiz. Tverd. Tela (St. Petersburg) 40, 759–760 (April 1998)     

The diffusion of silver ions in AgBr/Agi sheet crystals

Abstract

The results of the tracer diffusion of Ag⁺ by chemical microsectioning technique in AgBr/I sheet crystals up to the solubility limit in the temperature range 110–240°C are presented. The monotonic increase in the diffusivity and decrease of the activation enthalpy for diffusion with the increase of the iodide component in AgBr result from the decrease of the formation energy for Frenkel defects with the increase of elastic strain introduced by the oversized iodide ions.     

Grain-boundary diffusion and solubility of helium in submicrocrystalline palladium

The diffusion and solubility of helium in palladium with a submicrocrystalline structure are investigated by thermal desorption of helium from He-saturated specimens at temperatures T = 293–508 K and saturation pressures P = 0.1–35 MPa. As the saturation pressure rises, the effective diffusion coefficient increases, exhibits a plateau, and then decreases to its initial value. Along with the four plateaus discovered earlier, the solubility versus saturation pressure dependence in the range 25.5–35.0 MPa demonstrates a fifth plateau, where the solubility is as high as (3.0 ± 0.4) × 10¹⁷ cm⁻³. It is shown that the helium diffuses along grain boundaries, at which clusters (traps) consisting of eight to ten vacancies are localized, and dissolves in these clusters. The high value of C _eff in the fifth plateau is explained by pairwise merging of adjacent vacancy clusters. From the D _eff(P) dependences, the vacancy clusters concentration is estimated as C* = 2.32 × 10¹⁶ cm⁻³. Within the experimental error, this value coincides with that obtained from the solubility data. Calculations of the energy of helium-defect interaction in submicrocrystalline Pd that are made using the molecular dynamics method support the experimental results.     

Quantum diffusion

Basic ideas and results which characterize quantum diffusion of defects in quantum crystals like solid helium as a new phenomenon are presented. Quantum effects in such media lead to a delocalization of point defects (vacancies, impurities etc.) and they turn into quasiparticles of a new type—defectons, which are characterized not by their position in the crystal lattice but by their quasimomentum and dispersion law. Defecton-defecton and defecton-phonon scattering are considered and an interpolation formula for the diffusion coefficient valid in all interesting temperature and concentration regions is presented. A comparison with the experimental data is made. Some alternative points of view are discussed in detail and the inconsistency of the Kisvarsanyi-Sullivan theory is shown.     

Study of radiation damage in quartz single crystals irradiated with protons

The effect of proton irradiation on quartz single crystals is studied. Positron diagnostics (the angular distribution of annihilation photons (ADAP)) and acoustical and spectrophotometric methods are used to study radiation-induced defects. It is shown that a narrow component with intensity f in the ADAP spectrum is caused by parapositronium and determines the high sensitivity of the method used in studying special features of the quartz crystal structure. In this case, any process leading to a decrease in the probability of positrinium (Ps) formation (the capture of positrons by charged defects and the interaction with impurity ions and lattice distortions) decreases the intensity of the narrow component. The concentration of radiation-induced defects is estimated and their kinetics of annealing up to 873 K is studied.     

金属钛中氦团簇生长行为的分子动力学研究

运用分子动力学方法模拟了常温下金属钛中氦团簇的生长过程.从能量的角度考察了氦团簇的生长机理.研究发现,随着氦团簇的生长,在氦团簇周围逐渐形成位错环缺陷,氦团簇与氦原子的结合能有逐渐下降的趋势,当氦团簇生长到一定尺寸时会通过发射周围缺陷以使得结合能上升,从而增强了进一步吸收氦原子的能力.模拟还发现,随着氦团簇的继续生长,氦团簇的形状由原来的不规则结构逐渐变成了较为规则的棱柱形结构,在随后的生长过程中其生长仅在（001）平面进行,沿［001］轴的厚度几乎不变. 关键词： 氦团簇 缺陷发射 分子动力学模拟     

Mass-spectrometric analysis of diffusion and solubility of helium in cerium-gadolinium ceramics with a submicrocrystalline structure

Diffusion and solubility of helium in Ce_0.8Gd_0.2O_{1.9 − δ} ceramics (δ = 0, 0.015) with a submicrocrystal structure are studied by thermodesorption of helium from preliminarily saturated (in the gas phase) crystals at temperatures of 613 and 673 K in the saturated pressure range 0–21 MPa. It is shown that, in this ceramics (δ = 0), the defect-trap diffusion mechanism operates. The main positions for dissolution are neutral anion vacancies formed as a result of thermal dissociation of impurity-vacancy complexes and saturated up to ∼1 × 10¹⁹ cm⁻³ at P = 6 MPa and T = 673 K. The dissociation energy of the complex and the energy of helium dissolution in the neutral anion vacancy are estimated at ∼2 eV and below −0.3 eV, respectively.     

Analysis of dynamic dislocation-assisted penetration of helium into tin and cadmium deformed by stretching in liquid helium

Curves describing the liberation of helium from Sn single crystals deformed by stretching in liquid ³He and ⁴He and from Cd polycrystals in ⁴He are analyzed. It is found that the stress-strain diagrams for Sn are in qualitative agreement with the concentration of helium in the samples. The peaks in the amount of He liberated from Cd and Sn at temperatures both below and above the melting point are found to be of different types. The reasons for this difference are investigated, and the assumption concerning the existence of a chemical bond between helium atoms and structural defects of the metals under investigation is formulated.     

Diffusion and solubility of zinc in dislocation-free and plastically deformed silicon crystals

Floating-zone Si crystals enclosed in quartz ampoules were exposed to Zn vapour released by an elemental diffusion source. Penetration profiles of Zn in Si were recorded using the spreading-resistance technique or neutron activation analysis. Both the erfc-type distributions observed in plastically deformed specimens and the non-erfc profiles determined on dislocationfree wafers are consistently interpreted within the framework of the kick-out model. As an implication, Si self-interstitials generated in excess by interstitial-to-substitutional transitions of in-diffusing Zn atoms annihilate not only at the surface but also at dislocations. On the other hand, dislocation-induced segregation of Zn appears to be rather minor, as revealed by transition electron microscopy. Combining the Zn incorporation rate in dislocation-free Si with solubility data from saturated specimens yields the self-interstitial contribution to the Si self-diffusion coefficient.Dedicated to H.J. Queisser on the occasion of his 60th birthday     

氦在材料中基于扩散机理的热释放特征

以随机扩散理论为基础,研究该机理下材料中氦的热释放可能呈现的特征,考察了氦的初始深度分布和扩散系数等因素对氦的热释放率的影响;阐明了随机扩散模型下和脱附模型下的氦释放特征之异同;指出对实验观察到的热解析谱的分析应和基底中氦的深度分布的分析以及氦的聚集状态的分析相结合,才能对氦的热释放机理给出正确的理解和判断. 关键词： 随机扩散 热释放 氦     

Positron states and nanoobjects in proton-irradiated quartz single crystals: Positronium atom in quartz

The influence of proton bombardment and metal atom impurities on the structure of quartz single crystals has been studied. The related defects have been studied using positron annihilation spectroscopy (angular correlation of positron-annihilation photons), acoustic absorption, and optical absorption measurements. It is shown that the presence of a narrow component f in the angular distribution of annihilation photons (ADAP), which is related to the formation of parapositronium, determines a high sensitivity of this method with respect to features of the crystal structure of quartz. It is established that the defectness of the structure of irradiated quartz crystals can be characterized by the ratio f/f ₀ of the relative intensities of narrow components in the ADAP curves measured before (f ₀) and after (f) irradiation. Any process leading to a decrease in the probability of positronium formation (e.g., positron loss as a result of the trapping on defects and the interaction with impurity atoms and lattice distortions) decreases the intensity of the narrow component. Based on the ADAP data, estimates of the radii and concentrations of nanodefects in quartz have been obtained and their variation upon annealing at temperatures up to T = 873 K has been studied.     

Generation of surface-voltage by charged crystal defects and applications

Abstract

Working mainly on quartz crystals it has been found that crystal defects present inherently or generated deliberately on the surface and in the bulk give rise to surface voltage (called by us self-voltage) due to charged electron and hole traps produced by the defects, the self-voltage thus forming monitor of presenceof crystal defects. The self-voltage could be measured by FET instrumentation.

Based on the above the crystal defects (and hence self-voltage) were reduced or practically eleminated by combination of processes of etching and annealing of the quartz, allthis reseulting in improvements of electronic characteristics of quartz crystals such as resistivity and frequency stability.     

Applications of cathodoluminescence in mineralogy

Cathodoluminescence microscopy and cathodoluminescence spectrometry with the electron microprobe and the scanning electron microscope are applied to the study of some natural cassiterite, quartz and sphalerite crystals. Some examples of localization and distribution of crystalline defects revealed by cathodoluminescence microscopy are given. X-ray spectrometry and secondary ion mass analysis allow to illustrate the coincidence between the spatial variations of cathodoluminescence emission and the distribution of impurities within minerals. In order to establish a relationship between the spectral distribution of the luminescence and the nature of trace elements, comparisons are made between cathodoluminescence properties of natural and artificial zinc sulphide crystals. Particular attention is given to specimen containing copper-gallium impurities. It has been possible to distinguish between the impurities which can be responsible for the luminescence and those which are not associated with cathodoluminescence emission characteristic of the crystals. The study of cathodoluminescence intensity according to the excitation conditions led to consider the contribution of the X-ray photons generated in the specimen for the production of luminescence photons. An in-depth distribution law of generated photons similar to that used to take account of X-ray emission led to introduce an absorption function in the relation giving the measured intensity of cathodoluminescence according to the incident energy and the electron beam density.     

Behavior of impurity copper in ZnGeP2 single crystals with diffusion doping

Results from a study of electrophysical and luminescent properties of zinc-germanium diphosphide single crystals, diffusion doped with copper, are presented. The nature of the dominant defects formed upon copper diffusion in ZnGeP₂ is determined using a thermodynamic analysis of defect formation processes in ZnGeP₂ and a ZnGeP₂: Cu solid solution performed within the framework of the quasichemical analysis method. It is demonstrated that by choosing the copper diffusion method the hole concentration in the ZnGeP₂ can be varied over the range 10¹²–10¹⁶ cm^–3. A retrograde character was observed in copper solubility in ZnGeP₂ compounds. Defect formation processes in ZnGeP₂ upon copper diffusion depend on the degree of atomic ordering in the cation sublattice at the diffusion annealing temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 64–69, February, 1985.     

Optical studies of atoms and ions in superfluid helium using a ccd-camera system

The spectroscopic study ions and atoms immersed into liquid helium can contribute to the understanding of the structure of pointlike defects in helium and their interaction with the superfluid phase as well. Ions and atoms serve as microprobes in the form of so calledbubble orsnowball type defects in the quantum fluid. The optical emission of these structures is recorded. From the optical spectra of previous experiments the influence of the surrounding helium on the electronic configuration of the impurity atoms or ions was examined. In this experiment the light emitted from the defect atoms is observed by a camera. The pictures obtained yield information about the distribution and the motion of the defect particles in the superfluid. As an example the fluorescence light resulting from the recombination of magnesium, barium and thallium ions with excess electrons in superfluid helium was recorded.     

Löslichkeit,Diffusion und Ultrarotabsorption von Wassermolekülen in Alkalihalogenidkristallen

Following a former communication, further experiments of solubility, diffusion and infraredabsorption of water molecules in KCl-, KBr- and KJ-crystals are given. Substituted mono- and bivalent ions to the refined crystals strongly increase the solubility of water at lower temperatures but there is practically no increase at higher temperatures. This points to two mechanisms for solubility: An interstitial at lower temperatures and probably by vacancies at higher temperatures. — The penetration of water into crystals containing K₂O orF-centers produces a colorless layer by chemical reaction. From investigation of such layers we get diffusion constants for the diffusion of water molecules. In crystals containingF-centers we find an additionalKH- layer. — The chemical reactions in the solid state produce H^?-, OH^?- and O^??-centers of well known concentration. This allows determination of the oscillator strengths of the characteristical ultraviolett absorptions. — The absorption in the near infrared by crystals containing water shows especially at low temperatures sharp peaks from single H₂O-molecules and broad peaks from precipitated water. An interstitial lattice model is discussed for the single H₂O-molecules.     

Systematic features of diffusion and aggregation of intrinsic defects in dielectric crystals

It has been shown that the kinetics of reactions involving mobile intrinsic defects in the crystal is described by the exponential dependence in many cases. Based on this dependence and the fact that random-walk diffusion occurs in the cases under consideration, the distribution of diffusion paths traveled by mobile defects before entering into the reaction has been found. An expression for the arithmetic mean of these paths has been obtained. For lithium fluoride crystals irradiated with gamma-rays, the pre-exponential factors in the temperature dependences of the diffusion coefficients of F ₂ ⁺ color centers and anion vacancies have been determined and the diffusion coefficients of these types of defects have been estimated.     

A coupled-mode theory of heisenberg paramagnets

A new topographic method is presented using sound beams with frequencies at 24 GHz and 35 GHz for imaging crystal defects in nearly perfect dielectric crystals. Large crystals with dimensions up to 20×20×50 mm³ can be investigated. In this method the echo amplitude of longitudinal or transverse phonons is measured at low temperatures during a two-dimensional scan of a movable sound beam. The position dependent echo amplitude is presented as brightness-modulated image. The lateral resolution is limited by the effective diameter of the movable sound beam which is between 0.2 mm and 0.5 mm at present. The contrast pattern observed in natural quartz crystals can mainly be attributed to defects produced during growing time preferable at edges orr-faces andz-faces.