Spectral characteristics and force constants of irradiated α-SiO<Subscript>2</Subscript> single crystals

The IR-radiation reflectance spectra of α-SiO₂ single crystals exposed, in a reactor, to fast neutrons with fluences changing in a wide range have been investigated. The regularities of the change in spectral characteristics of the antisymmetric and degenerate vibrations of the bridge bonds of the crystals studied and in the dynamic parameters of these crystals in the process of their irradiation have been determined. The critical dynamics of the crystal lattice in the region of antisymmetric stretching and degenerate modes and the extremum radiation kinetics of the ion-polarizability parameters and the force constants of the indicated crystals were detected. The changes in some characteristics of these crystals, arising on their irradiation as a result of the damage of the substance, the rupture and extension of some silicon—oxygen bonds, and the transformation of the structure of α-SiO₂ single crystals by two mechanisms, have been considered. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 773–777, November–December, 2005.     

Spectroscopic parameters of CHFCl2, CHClF2, C2F6, and C3F8 molecules

We investigate the IR spectra of solutions of R-21,-22,-116, and R-218 in liquid argon at 90K. The frequencies, half-widths, and absolute integral intensities of all of the absorption bands recorded are obtained and interpreted. Scientific-Research Institute of Physics, 1, Ul'yanovskaya Str., Petrodvorets, St. Petersburg, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 297–301, May–June, 1997.     

Effect of neutron irradiation on optical spectra of α-Al2O3 and α-SiO2 single crystals

Using two crystal dielectrics (α-Al₂O₃ and α-SiO₂) as examples, the author studied the effect of large neutron-radiation doses on their optical spectra. The variation in IR spectra in the region of α-SiO₂ stretching and deformation vibrations is investigated; its relation to changes in the structure of the irradiated crystal is discussed. Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan, Ulugbek Settlement, Tashkent, 702132. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 135–138, January–February, 1999.     

Infrared spectral study of molecular vibrations in amorphous, nanocrystalline and AlO(OH) · αH2O bulk crystals

Amorphous, nanocrystalline, and bulk AlO(OH) · xH₂O crystals have six fundamental modes (FM) of vibration in a nonlinear AlO(OH) molecular structure. Most of them appear in groups of four IR and Raman bands. Their positions and relative intensities differ significantly in three specimens. The nanocrystals (monoclinic structure with z=8 molecules per unit cell) have four OH stretching bands at values enhanced by up to 360 cm⁻¹ at 3120, 3450, 3560 cm⁻¹ in comparison to those in bulk crystals or amorphous specimens. The first two bands are broad, bandwidth Δν_1/2200 to 350 cm⁻¹, while the other two are sharp, Δν_1/290 cm⁻¹. The sharp bands shift to 3525 and 3595 cm⁻¹ after heating the sample at 100°C. They no longer appear after heating at 300 or 500°C for 2 h (the specimen decomposes to Al₂O₃), leaving behind only two bands at 3100 and 3400 cm⁻¹. A Δν_1/2 value of 500 cm⁻¹ appears in the 3400 cm⁻¹ in a delocalized distribution of H atoms. Two bands also occur at 3098 and 3300 cm⁻¹ in bulk crystals (orthorhombic structure with z=4) or at 2990 and 3515 cm⁻¹ in an amorphous sample. More than one bands appear in a FM vibration in occurrence of sample in more than one conformers. The amorphous sample has approximately the same conformer structure as the bulk crystals. An amorphous surface structure exists in nanocrystals with a group of three bands at 1420, 1510 and 1635 cm⁻¹ in an interconnected network structure. It encapsulates the nanocrystals in an amorphous shell. Its volume fraction, 33% estimated from the integrated intensity in three bands, determines 2.2 nm thickness in the shell in spherical shape of nanocrystals in 35 nm diameter.     

Influence of microwave radiation on the association processes of rhodamine 6G molecules in aqueous solutions

The influence of the microwave radiation of two frequency ranges (2.0 mm and 6.9 dm) on the absorption spectra of the cationic dye rhodamine 6G has been investigated. A reversible decrease in the quantity of the dimers of the dye molecules after exposure of its aqueous solution to microwave radiation and also the phenomenon of destruction of the associates of the dye molecules under the influence of the microwave field have been revealed. They are discussed from the standpoint of the structural characteristic features of water.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 34–37, January–February, 2005.     

Influence of Radiative Irradiation on the Optical and Electrical Properties of Crystalline Quartz

The influence of radiation on the optical properties of quartz crystals has been investigated. Using the methods of IR and Raman spectroscopy, the lattice dynamics associated with a change in the spectral characteristics of a number of the stretching and deformation vibrations of the crystal lattice upon irradiation of samples by gamma quanta and neutrons to high doses has been determined. The regularities of radiative modification of the spectral characteristics of certain fully symmetrical and degenerate modes of the stretching vibrations of hydroxide groups are determined. To elucidate the reasons for the changes in the optical spectra, the latter were compared with the corresponding spectra obtained upon heating of wafers and with the change in the conductivity of crystals caused by irradiation. It is assumed that the changes in the optical spectra and conductivity of irradiated crystals are mainly due to the rearrangement of the quartz structure and to the stimulated migration of impurities. A possible mechanism of the process of conduction in the material is discussed in the framework of the existing models.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 224–229, March–April, 2005.     

Influence of the Change in Charges on the Atoms of the CNO2 Fragment of Nitrobenzene Derivatives Caused by Substituents on the Frequency of the Antisymmetric Stretching Vibration of the Nitro Group

The dependence of the frequency of the antisymmetric stretching vibration of the nitro group of the para-derivatives of nitrobenzene on the charges on the atoms of the CNO₂ group calculated by the PM3 method has been investigated. It is shown that a change in the position of the absorption band of the antisymmetric stretching vibration of the nitro group of para-derivatives of nitrobenzene, as well as Hammett's constants _p , can be used as a measure of the electronic effect of substituents, that is, of a change in the charges on the atoms of the nitro group.     

Conductivity relaxation parameters of some H and K conducting in the polycrystalline compound KDyHP3O10

Polycrystalline samples of KDyHP₃O₁₀ was obtained by heating for 12 hour at 553 K a mixture containing K₂CO₃, Dy₂O₃ and H₃PO₄. Samples were characterized through X-ray diffraction, examined by IR vibrational spectroscopy and impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of some H⁺ and K⁺ conducting in this compound have been determined from an analysis of ac conductivity data measured in a wide temperature range. Transport properties in this material appears as due to H⁺ and K⁺ ions hopping mechanism. The stretched exponential function exp[−(t/τ_σ)^β] has been used to describe the conductivity relaxation. The relaxation parameters have been investigated as a function of the nature of mobile ions. The results obtained are shown to be in good agreement with the predictions of the Ngai coupling model.     

弯曲振动薄圆盘的共振频率和等效电路参数研究

机电等效电路是分析复合换能器常用的一种解析方法, 但对薄圆盘而言, 由于弯曲振动的复杂性, 其等效集中参数很难获得, 该方法很少被应用. 本文从分布参数系统与集中参数系统等效角度, 根据动能相等原则和势能相等原则, 给出了弯曲振动薄圆盘的集中参数: 等效质量和等效弹性系数, 得到了共振频率方程, 并用ATILA软件模拟了其振动分布情况, 可以看出解析结果与数值结果趋于一致. 最后给出了分析复合振动系统时薄圆盘集中参数模型的等效电路. 本文的结果对弯曲振动复合换能器的设计提供了理论参考.     

Effects of temperature and impurities on electron radiation damage in the high voltage microscope

This paper describes the results of irradiation of specimens of copper and copper containing up to 2 at % beryllium in the high-voltage electron microscope. The results of irradiation at temperatures ranging from 20–500 K are described and discussed in the light of recently proposed theories of defect nucleation. Although the results are difficult to interpret because of the many diverse factors which influence the nucleation and growth of the damage it was found that the values for the volume density of defects were in general agreement with the predictions, if the effects of the foil surfaces were taken into account.

The corrected densities were used to derive values for the activation energy for motion of an interstitial in copper, E_m , and the binding energy between an interstitial and a beryllium atom, E_b . The results obtained were 0.12±0.03 eV for E_m and 0.29±0.07 eV for E_b .     

热压工艺参数对n型和p型Bi2Te3基赝三元热电材料电学性能的影响

通过熔炼/研磨/热压方法制备了n型和p型赝三元Bi₂Te₃基的热压合 金样品，测量了由不同工艺参数(热压温度、热压压力)制备的样品Seebeck系数和电导率.分析了热压参数对热电性能产生的影响.特别是发现了增加热压压力和热压温度会使n型和p型热压样品的Seebeck系数和电导率都有所提高，这与单晶和取向晶体材料的Seebeck系数和电导率变化趋势相反的规律显然不同，其结果对热压样品的电学性能提高有积极的影响. 关键词： 热电材料 热压 Seebeck系数 工艺参数     

Effect of O2 concentration in ambient mixture and multiphase radiation on pollutant formation in ECN spray-A

This study investigates the formation and evolution of soot and NO _X in a high-pressure constant-volume combustion chamber. This work focuses on the effect of multiphase thermal radiation and O₂ dilution in ambient/exhaust gases, sometimes also referred to as exhaust gas recirculation (EGR), qualitatively and quantitatively. The spray-A case (n-dodecane as fuel) from Engine Combustion Network (ECN) is used as the target condition. Two different soot modelling approaches have been considered: a semi-empirical two-equation model and a detailed method of moments with interpolative closure (MOMIC) model. A multiphase photon Monte Carlo (PMC) solver with line-by-line (LBL) spectral data is used to resolve radiative heat transfer. Results show that the effect of radiation on soot is minimal in spray-A. Inclusion of radiation modelling, on the other hand, marginally reduces NO prediction. Both peak soot and NO formation increase with O₂ content in the ambient gas. Oxygen content in ambient gas is also found to have significant effect on soot sizes as the mean soot diameter increases along with considerable widening of the diameter distribution with the increase of O₂ percentage in the ambient gas.     

Al2O3:V3+晶体局域结构及其自旋哈密顿参量研究

提出了解释掺杂离子局域结构畸变的配体平面移动模型，建立了此模型下晶体微观结构与自旋哈密顿参量之间的定量关系.在考虑自旋与自旋、自旋与另一电子轨道和轨道与轨道作用等微小磁相互作用的基础上，采用全组态完全对角化方法，对Al₂O₃晶体中V³⁺的局域结构和自旋哈密顿参量进行了系统的研究.结果表明，V³⁺掺入Al₂O₃晶体后，上下配体氧平面间距离增大了0.0060 nm.从而成功地解释了Al₂O₃:V³⁺晶体的自旋哈密顿参量.在此基础上，研究了三角晶场下3d²离子自旋哈密顿参量的微观起源.研究发现，自旋三重态对自旋哈密顿参量的贡献是主要的，微小磁相互作用对自旋哈密顿参量的贡献只与自旋三重态有关.     

Unified calculations of the optical band positions and spin-Hamiltonian parameters for V2+ ions in CdCl2 crystal

The eight optical spectral band positions and three spin-Hamiltonian parameters (g factors g_//, g_⊥ and zero-field splitting D) of V²⁺ ions in trigonal CdCl₂ crystal are calculated together from the complete diagonalisation (of energy matrix) method (CDM) based on the two-spin-orbit-parameter model (also called the cluster approach). In the model, differing from the usual one-spin-orbit-parameter model in the conventional crystal-field theory (where only the contribution to spin-Hamiltonian parameters due to the spin-orbit parameter of central dⁿ ion is considered), both the contributions from the spin-orbit parameter of central dⁿ ion and that of ligand ions are taken into account. The calculated results show reasonable agreement with the experimental values. The local lattice relaxation in the vicinity of V²⁺ ion due to the introduction of V²⁺ impurity is acquired from the calculations. The calculations of spin-Hamiltonian parameters from the CDM based on the one-spin-orbit-parameter and those from the perturbation theory method based on the two-spin-orbit-parameter model are also made for comparison. The results are discussed.     

The dissimilar twins - a comparative, site-selective in situ study of CO adsorption and desorption on Pt(3 2 2) and Pt(3 5 5)

The adsorption and desorption of CO on stepped Pt(3 2 2) = Pt(S)-[5(1 1 1) × (1 0 0)] and Pt(3 5 5) = Pt(S)-[5(1 1 1) × (1 1 1)] were investigated using in situ high-resolution X-ray photoelectron spectroscopy at BESSY II, which allows to clearly distinguish between different step and terrace adsorption sites. For the two surfaces, with the same nominal terrace width of five atomic rows, but different step orientation, significant differences are observed. While for Pt(3 5 5) CO adsorption at steps only occurs at on-top sites, on Pt(3 2 2) both step on-top and bridge sites are occupied, albeit with a significantly lower coverage (0.07 vs. 0.13 ML at 200 K). On both surfaces terrace sites are only occupied when the step sites are almost saturated confirming the enhanced binding energy at step sites. CO adsorbed at the (1 1 1) steps on Pt(3 5 5) is more strongly bound than on the (1 0 0) steps on Pt(3 2 2), which is attributed to the different electronic and geometric structure of the steps. The relative occupation of terrace and step sites at a given coverage remains the same between 120 and 290 K on Pt(3 5 5) K, but shows major changes on Pt(3 2 2), between step on-top and bridge sites as well as terrace on-top and bridge sites. On Pt(3 5 5) a smaller CO terrace coverage is found (0.36 vs. 0.40 ML on Pt(3 2 2) at 200 K), mainly due to the lower occupation of terrace bridge sites. For Pt(3 2 2), an ordered adsorbate phase is deduced from a c(4 × 2)-like LEED pattern, which indicates adsorbate order beyond the extension of a single terrace. A model for this structure is proposed.     

Influence of intense soft X-ray radiation on the parameters of tracks induced in CR-39 and PM-355 solid state nuclear track detectors

This paper presents the results of the influence of soft X-ray radiation on craters induced in SSNTDs by energetic α particles and protons of energy in the MeV range. We checked two detectors of the PM-355 and CR-39 types in order to verify and compare their resistance to the harsh conditions of high-temperature plasma experiments. To determine this effect some detector samples were first irradiated with α particles emitted from natural α particle sources and protons delivered by a particle accelerator. After that these samples were exposed to soft X ray radiation emitted from an X ray tube and also from the PF-1000 Plasma Focus facility. Doses during X ray irradiations varied from 0 up to tens of kGy. The irradiated samples were then etched in steps and track diameters were determined versus the absorbed dose and etching time and compared with those measured in samples not exposed to X ray radiation.     

Dynamic compensation temperature in the mixed spin-1 and spin-2 Ising model in an oscillating field on alternate layers of a hexagonal lattice

The dynamic behavior of a mixed spin-1 and spin-2 Ising system with a crystal-field interaction in the presence of a time-dependent oscillating external magnetic field on a hexagonal lattice is studied by using the Glauber-type stochastic dynamics. The lattice is formed by alternate layers of spins σ=1$\sigma =1$ and S=2. The Hamiltonian model includes intersublattice, intrasublattice and crystal-field interactions. The set of mean-field dynamic equations is obtained by employing the Glauber transition rates. Firstly, we study time variations of the average sublattice magnetizations in order to find the phases in the system, and the thermal behavior of the average sublattice magnetizations in a period or the dynamic sublattice magnetizations to obtain the dynamic phase transition points as well as to characterize the nature (continuous and discontinuous) of transitions. Then, the behavior of the dynamic total magnetization as a function of the temperature is investigated to find the dynamic compensation points as well as determine the type of behavior. We also present the dynamic phase diagrams for both presence and absence of the dynamic compensation temperatures in the nine different planes. According to the values of Hamiltonian parameters, besides the paramagnetic (p), antiferromagnetic (af), ferrimagnetic (i) and non-magnetic (nm) fundamental phases, eight different mixed phases and the compensation temperature or L- and N-types behavior in the Néel classification nomenclature exist in the system.     

Li mobility in Li0.5 − xNaxLa0.5TiO3 perovskites (0 ≤ x ≤ 0.5): Influence of structural and compositional parameters

The dependence of Li mobility on structure and composition of Li_0.5 − xNa_xLa_0.5TiO₃ perovskites (0 ≤ x ≤  0.5) has been investigated by means of neutron diffraction, nuclear magnetic resonance and impedance spectroscopy. At 300 K, all samples display a rhombohedral superstructure (R-3c S.G.), where octahedra are out of phase tilted along [111] direction of the ideal cubic cell. The elimination of the octahedral tilting is responsible for the rhombohedral–cubic transformation, detected near 1000 K. In these perovskites, La and Na cations are randomly distributed in A sites, but Li ions are fourfold coordinated at unit cell faces of the cubic perovskite. Lithium conductivity, σ_300 K, decreases with the sodium content, decreasing from values typical of fast ionic conductors, 10^− 3 S/cm, to those of good insulators, 10^− 10 S/cm, when the interconnectivity between vacant A sites is lost (x > 0.3). In samples with x < 0.3, dc conductivity displays a non-Arrhenius behaviour, decreasing activation energy from ~ 0.37 to 0.25 eV when the sample is heated between 77 and 500 K. The temperature dependence of B_Li factors shows the existence of two regimes for Li motion. Below 373 K, Li ions remain partially located near square oxygen windows that connect contiguous A sites, but above 400 K, extended Li motions become dominant. The additional decrease of activation energy from 0.25 to 0.16 eV (low-temperature ⁷Li NMR value), should require the full elimination of octahedral tilting which is only produced above 1000 °C.