Effect of ferroic domain pattern changes on the Raman spectra of some ferroic crystals

The influence of changes in the pattern of ferroic domain structure on the Raman spectra of β-LiNH₄SO₄ and (NH₄)₃H(SO₄)₂ single crystals were studied. It was shown that the Raman spectra of β-LiNH₄SO₄ passed from the ferroelastic phase differ from those of “as-grown” crystal and those of the crystal, which was in the paraelectric phase. Significant changes could be observed in the Raman bands related to triply degenerated ν₃ and ν₄ vibrations of the SO₄ tetrahedron. Detailed temperature studies of the Raman spectra of β-LiNH₄SO₄ close to the paraelectric–ferroelectric phase transition, exhibit anomaly of some internal vibrations of SO₄ in the temperature range where a regular large-scale structure is observed. Different types of evolution of the ferroelastic domain structure and temperature behaviour of the donor and acceptor vibrations were shown while heating and cooling the (NH₄)₃H(SO₄)₂ crystal. Different values of temperature hysteresis were found in temperature studies of the ferroelastic domain structure (ΔT_S  3–5 K) and in Raman spectra studies (ΔT_S  12 K). No changes were observed in the pattern of ferroelastic domain structure at the temperature T_II–III  265 K, at which C2/c → P2/n structural phase transition takes place. On the other hand, at T_III–IV  135 K additional domains with W′-type of domain wall orientation were found.     

Ag glasses based on Zn-phosphate

The partial substitution of Zn²⁺ for Ag⁺ in Ag₄P₂O₇ leads to the formation of a wide glassy domain of composition [Ag₄P₂O₇] _(1−y) [Zn₂P₂O₇] _(y) with 0.20y0.87. The introduction of AgI in these materials results in a new series of glasses of formula [(Ag₄P₂O₇)_(1−y) (Zn₂P₂O₇)_(y)] _(1−X) [AgI] _(x), which domain for the composition y = 0.25 corresponds to 0x 0.64. The structure as well as the thermal and electrical properties of these materials are compared with those of the [AgPO₃] _(1−X) [AgI] _(x) and [Ag₄P₂O₇] _(1−x) [AgI] _(x) glasses.     

Stress relaxation in the interface between creep particle and elastic matrix-strengthening mechanism

The effect of a power law creep particle on interface behavior between the particle and elastic matrix is investigated by stress analysis. Using the results obtained through the stress analysis, the forces due to interaction of an applied stress and stress concentration with an edge dislocation are determined. The direct interaction between the edge dislocation and the creeping particle is studied under fully relaxed stress conditions. Through the investigation the following results are derived. Stress relaxation in the interface can be caused by power law creep along or by diffusion, or a combination of both mechanisms. The degree of stress relaxation caused by diffusion can be defined in terms of the relaxation time for both boundary diffusion and volume diffusion. The amount of stress relaxation caused by the power law creep particle is characterized by the quantity ₂ which is a function of Γ₀ = 2(1/√3)^{1 + m} × (σ_∞/2μ)^m(σ₀/σ_∞t^m), where m is strain rate hardening exponent, σ_∞ is applied stress, μ is the shear modulus, σ₀ is the material constant of the power law creep particle, and t is elapsed time. The value ₂ = 1.0 corresponds to the fully relaxed condition and ₂ = −0.6 corresponds to the initial state. The time to reach a fully relaxed condition is very sensitive to the strain rate exponent, with the smaller m values leading to longer times. The stress state of complete relaxation in the elastic matrix is equivalent to the solution of a void in an elastic matrix superposed on the solution of positive surface traction on the void. This result is identical to that obtained by Srolovitz et al. [Acta. Metall.32, 1979 (1984)]. When the stress is completely relaxed in the particle, all stress components (σ_r, σ_θand σ_rθ) are relaxed, while in the matrix relaxations are observed only for σ_rand σ_θ. The critical resolved shear stress and critical stress to climb the dislocation in the neighborhood of the particle exceed the Orowan stress. Also, the particle attracts the dislocation. Therefore the strengthening of a power law creep particle in an elastic matrix is caused by the Orowan mechanism and by attraction of the dislocation.     

Measurement of continuous damage parameter

The present paper introduces several measuring methods of continuous damage parameter derived by the classical definition D = 1 − (A_e/A_a): (1) The measuring method on the basis of D = 1 − (E'/ E); (2) The measuring method on the basis of D = 1 − (ε₁/ε₂); (3) The measuring method on the basis of D = −Δρ_o/ρ_o, (4) The measuring method on the basis of D = A_d/A_a, and comments on these measuring methods.     

CO-DEPOSITION OF FULLERENES AND SULFUR FROM DILUTED SOLUTION

A new method to synthesize fullerene and sulfur compounds has been developed. Using this method, C₆₀S₁₆ and C₇₀S₁₆ compounds were grown from dilute fullerene and sulfur toluene solution. Their atomic structures were analyzed by x-ray diffraction with the single crystal. The C₆₀S₁₆ crystal is C-centered monoclinic structure of a=2.0874 nm, b=2.1139 nm, c=1.05690 nm and β=111.93°, and the C₇₀S₁₆ has a primitive monoclinic, P2₁/c, with lattice parameters of a=1.5271 nm, b=1.49971 nm, c=2.18024 nm and β=109.791°. In this compound, the structure of fullerenes is maintained and sulfur atoms form S₈ rings placed around the fullerenes.     

(1-x)K0.48Na0.52NbO3-xBi0.45Nd0.05(Na0.92Li0.08)0.5ZrO3无铅压电陶瓷相结构及压电性能

为了在获得较高压电性能的同时又不大大降低陶瓷的居里温度(T_C), 设计和制备了Bi_0.45Nd_0.05(Na_0.92Li_0.08)_0.5ZrO₃改性的K_0.48Na_0.52NbO₃系无铅压电陶瓷((1-x)KNN-xBNNLZ), 研究了BNNLZ含量对KNN基无铅压电陶瓷相结构和电学性能的影响。研究结果表明, 所有陶瓷样品均具有较高的居里温度T_C(>300℃)。随着BNNLZ含量的增加, 陶瓷的正交-四方相变温度(T_O-T)不断向低温方向移动, 而三方-正交相变温度(T_R-O)不断向高温方向移动, 最终在陶瓷中形成了三方-四方(R-T)共存相, R-T共存相处于0.05<x<0.07范围。BNNLZ的加入引起陶瓷相结构的演化改变导致压电常数(d₃₃ )、介电常数(ε_r )、剩余极化强度 (P_r )和机电耦合系数(k_p )都先增大后减小, 当x=0.06时陶瓷具有最佳压电性能: d₃₃=313 pC/N, k_p=42%, P_r=25.48 μC/cm², ε_r=1353, tanδ=2.5%, T_C=327℃。     

Determination of the E1 and E1+Δ1 energy bands by photoreflectance in AlxGa1−xAs in the region 0<x<0.55

The E₁ and E₁+Δ₁ energy bands of metal–organic chemical vapor deposition grown Al_xGa_1−xAs, with x in the range 0–0.55, have been determined using photoreflectance technique. The aluminum composition for each sample was determined using the energy of the room-temperature photoluminescence compensated peak value and a suitable fundamental band gap formula. The positions of the E₁ and E₁+Δ₁ peaks were determined from curve-fitting an appropriate theoretical model to our experimental data by a modified downhill simplex method. Using the results, we propose new E₁ and E₁+Δ₁ cubic expressions as functions of the aluminum composition, x, and compare them with the available reported expressions.     

On the formation of radiation-induced defects in fluoroaluminate glasses

The spectra of electron paramagnetic resonance (EPR) of fluoroaluminate glass (FAG-36) based on mineral usovite Ba₂CaMgAlF₁₄ were studied. The paramagnetic centers responsible for EPR signals were induced by ion bombardment of the substrates prepared from this glass. The N⁺, O⁺, Ar⁺ and Pb + ions with energy E = 150 keV were used. The integrated dose D was 2 × 10¹⁶ ions/cm². It is shown by means of isochronal anneal experiments and computer simulation of the EPR spectra that they contain four components: broad Gaussian line (GL) with g = 2.016 and σ oscillating in the range 30–40; two anisotropic spectra with g_z = 2.016, g_y = 2.009; g_x = 2.001 (FA₁) and g_z = 2.045; g_y = 2.010; g_x = 1.98 (FA₂) as well as narrow isotropic line of Lorentzian shape with g = 2.0025 and ΔH = 0.6 mT. The comparison of obtained results with literature data for γ-irradiated fluoride glasses and ion-implanted oxide glasses of different compositions permitted to conclude that GL is due to hole defects typical of fluoride glasses and localized on several anions (fluorines and oxygen(s)); anisotropic FA₁- and FA₂-spectra are attributed to molecular 0₂⁻-ions, and narrow isotropic signal is supposedly assigned to big molecular ions (O₂O⁻, 0₄⁻ , CO⁺, CO⁻) located in voids of damaged implantation layer.     

Evaluation of neutron thermalization parameters and benchmark reactor calculations using a synthetic scattering function for molecular gases

Using a synthetic incoherent scattering function which describes the interaction of neutrons with molecular gases we provide analytical expressions for zero- and first-order scattering kernels, σ₀(E₀ → E), σ₁(E₀ → E), and total cross section σ₀(E₀). Based on these quantities, we have performed calculations of thermalization parameters and transport coefficients for H₂O, D₂O, C₆H₆ and (CH₂)_n at room temperature. Comparison of such values with available experimental data and other calculations is satisfactory. We also generated nuclear data libraries for H₂O with 47 thermal groups at 300 K and performed some benchmark calculations (²³⁵U, ²³⁹Pu, PWR cell and typical APWR cell); the resulting reactivities are compared with experimental data and ENDF/B-IV calculations.     

Optical properties of a-(Se70Te30)100−x(Se98 Bi2)x thin films

Measurements of optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary part of the dielectric constant) have been made on a-(Se₇₀Te₃₀)_100−x (Se₉₈Bi₂)_x thin films (where x=0, 5, 10, 15 and 20) of thickness 2000 Å in the wavelength range 450–1000 nm. It is found that the optical bandgap decreases with the increase of Se₉₈Bi₂ concentration in the a-(Se₇₀Te₃₀)_100−x(Se₉₈Bi₂)_x system. The value of refractive index (n) decreases, while the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states varying effective Fermi level.     

ZnO掺杂对Ca0.25(Li0.43Sm0.57)0.75TiO3陶瓷烧结性能和微波介电性能的影响

采用溶胶-凝胶法制备Ca_0.25(Li_0.43Sm_0.57)_0.75TiO₃(CLST)微波介质陶瓷纳米粉体, 研究了ZnO掺杂量和烧结温度对CLST+ xmol% ZnO陶瓷烧结性能和微波介电性能的影响。XRD分析结果表明: 随着ZnO掺杂量x的增加, 陶瓷的晶体结构从正交相变为伪立方相, 并在x≥1.5的样品中出现了杂相。CLST+ xmol% ZnO陶瓷的致密化烧结温度随x的增加而降低, x=1.0的样品的致密化烧结温度比x=0的降低了200 ℃。介电常数ε_r和频率品质因数Qf 随x增加和烧结温度的升高具有最优值, 频率温度系数则单调降低。x=1.0的样品在1100 ℃烧结时具有优异的综合性能: ρ = 4.85 g/cm³, ε_r =102.8, Qf = 5424 GHz, τ_f = -8.2×10^-6/℃。表明ZnO掺杂的CLST陶瓷是一种很有发展潜力的微波介质陶瓷。     

Solid-Phase Syntheses of Two Deacetyl-Thymosin β4 Analogues with Substitution at Position 12 and Their Effects on Impaired Blastogenic Response of T Lymphocytes of Uremic Patients

Two deacetyl-thymosin β₄ analogues containing Phe(4Br) or D-Phe(4Br) as position 12 were synthesized by the manual solid-phase method, and their immunological effects on the impaired blastogenic response of phytohemagglutinin-stimulated T lymphocytes of uremic patients with infectious diseases were studied. Bromination of the p-position of Phe¹² resulted in a marked restorative effect on the impaired blastogenic response of T lympocytes compared with that of our synthetic deacetyl-thymosin β₄ The synthetic [Phe(4Br)¹²]deacetyl-thymsin β₄ was approximately equal in potency to our synthetic [Phe(4F)¹²]deacetyl-thymosin β₄ in uremic patients, but the other analogue, [D-Phe(4Br)¹²]deacetyl-thymosin β₄, had no effect.     

Structural investigation of bulk and thin film PLZT using X-ray absorption spectroscopy

Thin film electro-optic and non-linear optical materials are of interest for applications in high-speed integrated optical devices. Materials of the system Pb_1−x/100La_x/100(Zr_y/100 Ti_1−y/100)_1−x/400O₃ or PLZT x/y/(100−y) are attractive since they can be integrated into Si and GaAs substrates using suitable deposition techniques. In this investigation we examine the structural properties of r.f. magnetron sputter-deposited PLZT using X-ray absorption near-edge spectroscopy (XANES). For XANES analysis, four samples were selected: (1) a highly oriented PLZT 28/0/100 film of ≈ 4500 Å deposited on SiO₂; (2) a highly oriented PLZT 28/0/100 film of ≈ 4500 Å deposited on a 2 ωm SiO₂ buffer layer over a Si(100) substrate; (3) a highly oriented PLZT 28/0/100 film of ≈4500 Å deposited on Al₂O₃ (1 02); and (4) a commercial ceramic wafer of PLZT 9/65/35. The XANES experiments were performed at the Stanford Synchrotron Radiation Laboratory (SSRL) using electron yield and fluorescence techniques. Data was taken at the Ti K-edge (4966.4eV) and compared to reference spectra. Of the reference spectra, the Ti K-edge spectra of the PLZT most closely resemble perovskite (SrTiO₃). The surface and bulk thin film are similar and all the 28/0/100 spectra resemble the spectra of 9/65/35, indicating similar cubic perovskite structures for these materials.     

电流密度对MgO-ZnO陶瓷薄膜结构和热控性能的影响

在Zn(H₂PO₄)₂电解液中, 利用微弧氧化技术在AZ31镁合金表面原位生长MgO-ZnO热控陶瓷薄膜, 研究了电流密度对薄膜结构组成、结合强度和热控性能的影响, 以及紫外辐照作用下薄膜太阳吸收率的变化规律。结果表明：薄膜主要由MgO、ZnO和非晶态物质组成, 随着电流密度增大, 微孔数量逐渐减少而粗糙度逐步增大, 其厚度、结合强度和发射率先增大后减小, 而太阳吸收率则先减小后增大。电流密度9 A/dm²时所得薄膜的结合强度达到最大12.6 MPa, 且热控性能最佳, 其发射率为0.872, 太阳吸收率为0.363; 且随着紫外辐照时间延长, 此薄膜太阳吸收率先升高而后趋于平缓。研究结果为制备良好结合强度和抗紫外辐照能力的低吸收高发射热控薄膜提供技术 支持。     

Influence of stress ratio at baseline loading on delayed retardation phenomena of fatigue crack growth in A553 steel and A5083 aluminium alloy

The delayed retardation phenomena of fatigue crack growth following a single application of tensile overload were investigated under the baseline loading with the stress ratio, R = σ_min/σ_max, ranging from −1 to 0.5 for A553 steel and A5083 aluminium alloy. Two different overload cycles were applied; the one is the case that the ratio of peak stress range to baseline stress range, r = Δσ₂/Δσ₁, is equal to two and the other is the case that the ratio of maximum peak stress to maximum baseline stress, σ_2max/σ_1max, is equal to two. The retardation took place stronger in aluminium than in steel. Under the condition of r = 2 the normalized number of cycles, N_D/N_C, (N_D: the number of cycles during retardation, N_C: the number of cycles required for propagation through the overload-affected-zone size) decreased slightly as the R ratio increased from −1 to 0.5, while under the condition of σ_2max/σ_1max = 2 the N_D/N_C-values increased drastically as the R ratio increased from −1 to 0 (or the overload ratio, r, increased from 1.5 to 2) in both the materials. These retardation behaviors were expressed theoretically according to the model proposed by Matsuoka and Tanaka [1, 3] by using four parameters: the overload ratio, r, the exponent in Paris equation, m, the overload-affected-zone size, ω_D, and the distance at the inflection point, ω_B.     

Rietveld refinement and spectroscopic studies of sodium lead fluoroapatite lacunaire synthesized by hydrothermal method

The structure of NaPb₉(PO₄)₆F(H₂O)_0.33, isostructural with apatite, was determined by X-ray powder diffraction methods and the result of Rietveld refinement is P6₃/m, a = 9.76396(8) Å and c = 7.27520(9) Å. The final refinement led to R_F = 5.4%, R_B = 6.6%. In the tunnel, the water molecule (O_w) and F⁻ ions appear to be located in 2b and 4e sites, with occupancies of 0.028(6) and 0.075(8), respectively. In the M(1) and M(2) sites the occupancies of Pb and Na are 0.282(3)/0.051(3) and 0.467(5)/0.033(5), respectively. The formula assigned to the compound is [Pb_3.38(4)Na_0.62(4)](1)[Pb_5.60(6)Na_0.40(6)](2)(PO₄)₆F_0.90(10)(H₂O)_0.33(7)□_0.77(17), where □ = vacancy. The assignment of the observed frequencies in the Raman and infrared spectra is discussed on the basis of a unit-cell group analysis and by comparison with fluor and chloroapatite analogs. The result of ³¹P and ²³Na magic angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopies confirmed the structural results.     

Physics and diagnostics of laser ablation plume propagation for high-Tc superconductor film growth

The formation, composition and propagation of laser-produced plasmas used for pulsed laser deposition (PLD) of Y₁Ba₂Cu₃O_7−x have been studied under film growth conditions. Four complementary spatially and temporally resolved in situ diagnostic techniques are applied to characterize the expansion of the laser plume into both vacuum and ambient gases: optical emission and absorption spectroscopy, fast ion probe measurements, and fast photography with a gated, image-intensified charge-coupled detector-array (ICCD) camera system. Transient optical absorption spectroscopy reveals large densities of ground state atoms, ions, and molecules in the plume as well as a slower component to the plume transport than is indicated by the plasma fluorescence and ion current.

Ablation into background gases results in scattering and attenuation of the laser plume. The exponential attenuation of the positive ion flux transmitted through 50–300 mTorr background oxygen is measured and used to define an overall ion-oxygen reaction cross-section σ_i−O2 = 2.3 × 10⁻¹⁶ cm² under the described film growth conditions.

The slowing of the laser plasma and formation of shock structures due to collisions with the ambient gas are described using ion probe measurements and ICCD photographic comparisons of expansion into vacuum and background oxygen. At the pressures used for PLD, distance-time R−t plots derived from the photographs and ion probe waveforms indicate that the higher pressure plume initially expands through the ambient gas in accordance with a drag model (where R = x_f[1 − exp( − βt)]), experiencing little slowing until a visible shock structure forms. Following a transition period, in which the plume appears to have two components, a single-component shock structure propagates in better agreement with a shock, or blast wave (R = ξ₀(E/₀)^1/5t^2/5) model.     

多级多孔硅酸镍微球的合成及其对碱性品红的高效吸附

层状硅酸镍因其独特的结构, 在电化学和催化等领域展现出良好的应用前景, 其合成与性能研究近年来受到广泛关注。本研究以氯化镍和正硅酸乙酯为原料, 采用水热法合成了硅酸镍微球, 并详细探究了镍硅比和碱源对产物组成、形貌及孔结构的影响。在优化条件下, 产物呈现由纳米片组装的、平均直径约为2.5 μm的微球形貌, 比表面积为119.6 m²·g^-1, 孔容为0.673 cm³·g^-1。Zeta电位分析表明, 该微球在pH=3~10范围内保持表面电负性。将硅酸镍微球用于处理碱性品红溶液, 吸附过程符合准二级动力学模型。在初始浓度为50 mg·L^-1的条件下, 吸附容量可达120.7 mg·g^-1, 脱除率达96.6%, 远优于改性粘土及近年来报道的多种材料。吸附量与平衡浓度的数据表明, 碱性品红在硅酸镍微球上的吸附符合Freundlich吸附模型, 1/n=0.1678, 表明该吸附为多层非均相吸附且吸附作用力强。     

(Ag2Se)1-x(Bi2Se3)x的热电性能研究

具有本征低晶格热导率的I-V-VI₂族三元硫属化合物在热电领域引起了广泛关注。AgBiSe₂作为这类化合物中少有的n型半导体, 成为一种有潜力的热电材料。本工作系统研究了AgBiSe₂的热电性能。基于Ag₂Se-Bi₂Se二元相图, 单相的(Ag₂Se)_1-x(Bi₂Se₃)_x的成分在x=0.4~0.62范围可调, 使得该材料载流子浓度具有可调性。结果表明, 通过组分调控获得了较宽范围的载体浓度1.0×10¹⁹~5.7×10¹⁹ cm^-3, 并基于声学声子散射的单一抛物带模型对其电传输性能进行了综合评估。本研究获得的最高载流子浓度接近理论最优值, 在700 K实现了最高ZT值0.5。本研究有助于深入理解AgBiSe₂的传输特性和决定热电性能的基本物理参数。     

Spectroscopic Evidence for Anionic Coordination Complexes of the Transition Metals with C70 and the Higher Fullerenes C76, C78, C82, C84, C86, C90, and C92

The carbonylate anions [M(CO)₅]^- (M = Mn, Re), [Co(CO)₄]^-, [CpFe(CO)₂]^-, and [CpM(CO)₃]^- (M = Mo, W) react with C₇₀ via single electron transfer processes to give, respectively, the corresponding 17-electron, metal-centered radicals Co(CO)₄, M(CO)₅ (M = Mn, Re), CpFe(CO)₂, and CpM(CO)₃ (M = Mo, W) in addition to the radical anion C₇₀^-. In secondary thermal or photochemical processes, the metal-centered radicals Co(CO)₄ and M(CO)₅ (M = Mn, Re) combine with the C₇₀^- to form the new η²-C₇₀ complexes [Co(CO)₃(η²-C₇₀)]^- and [M(CO)₄(η²-C₇₀)]^-. However, the metal-centered radicals CpM(CO)₃ (M = Mo, W) require photolysis to react with C₇₀^- to form [CpM(CO)₂(η²-C₇₀)]^-, whereas neither thermolysis nor photolysis induces reaction between CpFe(CO)₂ and C₇₀^-. The photochemical reaction of [Mn(CO)₅]^- with a mixture of higher fullerenes known to contain at least C₇₆, C₇₈, C₈₄, C₈₆, and C₉₀ resulted similarly in the formation of the higher fullerene complexes [Mn(CO)₄(η²-C_n)]^- (n = 76, 78, 80, 82, 84, 86, 88, 90, 92, 96, and 98), all identified using electrospray mass spectrometry.