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1.
The influence of changes in the pattern of ferroic domain structure on the Raman spectra of β-LiNH 4SO 4 and (NH 4) 3H(SO 4) 2 single crystals were studied. It was shown that the Raman spectra of β-LiNH 4SO 4 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 SO 4 tetrahedron. Detailed temperature studies of the Raman spectra of β-LiNH 4SO 4 close to the paraelectric–ferroelectric phase transition, exhibit anomaly of some internal vibrations of SO 4 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 (NH 4) 3H(SO 4) 2 crystal. Different values of temperature hysteresis were found in temperature studies of the ferroelastic domain structure (Δ TS 3–5 K) and in Raman spectra studies (Δ TS 12 K). No changes were observed in the pattern of ferroelastic domain structure at the temperature TII–III 265 K, at which C2/ c → P2/ n structural phase transition takes place. On the other hand, at TIII–IV 135 K additional domains with W′-type of domain wall orientation were found. 相似文献
2.
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 Γ 0 = 2(1/√3) 1 + m × (σ ∞/2μ) m(σ 0/σ ∞tm), where m is strain rate hardening exponent, σ ∞ is applied stress, μ is the shear modulus, σ 0 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. 相似文献
3.
The partial substitution of Zn 2+ for Ag + in Ag 4P 2O 7 leads to the formation of a wide glassy domain of composition [Ag 4P 2O 7] (1−y) [Zn 2P 2O 7] (y) with 0.20y0.87. The introduction of AgI in these materials results in a new series of glasses of formula [(Ag 4P 2O 7) (1−y) (Zn 2P 2O 7) (y)] (1−X) [AgI] (x), which domain for the composition y = 0.25 corresponds to 0 x 0.64. The structure as well as the thermal and electrical properties of these materials are compared with those of the [AgPO 3] (1−X) [AgI] (x) and [Ag 4P 2O 7] (1−x) [AgI] (x) glasses. 相似文献
4.
The present paper introduces several measuring methods of continuous damage parameter derived by the classical definition D = 1 − ( Ae/ Aa): (1) The measuring method on the basis of D = 1 − ( E'/ E); (2) The measuring method on the basis of D = 1 − (ε 1/ε 2); (3) The measuring method on the basis of D = −Δρ o/ρ o, (4) The measuring method on the basis of D = Ad/ Aa, and comments on these measuring methods. 相似文献
5.
A new method to synthesize fullerene and sulfur compounds has been developed. Using this method, C 60S 16 and C 70S 16 compounds were grown from dilute fullerene and sulfur toluene solution. Their atomic structures were analyzed by x-ray diffraction with the single crystal. The C 60S 16 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 C 70S 16 has a primitive monoclinic, P2 1/ 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 S 8 rings placed around the fullerenes. 相似文献
6.
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( TC), 设计和制备了Bi 0.45Nd 0.05(Na 0.92Li 0.08) 0.5ZrO 3改性的K 0.48Na 0.52NbO 3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 TC(>300℃)。随着BNNLZ含量的增加, 陶瓷的正交-四方相变温度( TO-T)不断向低温方向移动, 而三方-正交相变温度( TR-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( εr )、剩余极化强度 ( Pr )和机电耦合系数( kp )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, kp=42%, Pr=25.48 μC/cm 2, εr=1353, tan δ=2.5%, TC=327℃。 相似文献
7.
The E1 and E1+Δ 1 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+Δ 1 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+Δ 1 cubic expressions as functions of the aluminum composition, x, and compare them with the available reported expressions. 相似文献
8.
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, σ 0( E0 → E), σ 1( E0 → E), and total cross section σ 0( E0). Based on these quantities, we have performed calculations of thermalization parameters and transport coefficients for H 2O, D 2O, C 6H 6 and (CH 2) n at room temperature. Comparison of such values with available experimental data and other calculations is satisfactory. We also generated nuclear data libraries for H 2O 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. 相似文献
9.
The spectra of electron paramagnetic resonance (EPR) of fluoroaluminate glass (FAG-36) based on mineral usovite Ba 2CaMgAlF 14 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 × 10 16 ions/cm 2. 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 gz = 2.016, gy = 2.009; gx = 2.001 (FA 1) and gz = 2.045; gy = 2.010; gx = 1.98 (FA 2) as well as narrow isotropic line of Lorentzian shape with g = 2.0025 and Δ H = 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 FA 1- and FA 2-spectra are attributed to molecular 0 2−-ions, and narrow isotropic signal is supposedly assigned to big molecular ions (O 2O −, 0 4− , CO +, CO −) located in voids of damaged implantation layer. 相似文献
10.
Measurements of optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary part of the dielectric constant) have been made on a-(Se 70Te 30) 100−x (Se 98Bi 2) 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 Se 98Bi 2 concentration in the a-(Se 70Te 30) 100−x(Se 98Bi 2) 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. 相似文献
11.
采用溶胶-凝胶法制备Ca 0.25(Li 0.43Sm 0.57) 0.75TiO 3(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 εr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/cm 3, εr =102.8, Qf = 5424 GHz, τf = -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。 相似文献
12.
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 Ti1−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 SiO 2; (2) a highly oriented PLZT 28/0/100 film of ≈ 4500 Å deposited on a 2 ωm SiO 2 buffer layer over a Si(100) substrate; (3) a highly oriented PLZT 28/0/100 film of ≈4500 Å deposited on Al 2O 3 (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 (SrTiO 3). 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. 相似文献
13.
Two deacetyl-thymosin β 4 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 Phe 12 resulted in a marked restorative effect on the impaired blastogenic response of T lympocytes compared with that of our synthetic deacetyl-thymosin β 4 The synthetic [Phe(4Br) 12]deacetyl-thymsin β 4 was approximately equal in potency to our synthetic [Phe(4F) 12]deacetyl-thymosin β 4 in uremic patients, but the other analogue, [D-Phe(4Br) 12]deacetyl-thymosin β 4, had no effect. 相似文献
14.
The structure of NaPb 9(PO 4) 6F(H 2O) 0.33, isostructural with apatite, was determined by X-ray powder diffraction methods and the result of Rietveld refinement is P6 3/ m, a = 9.76396(8) Å and c = 7.27520(9) Å. The final refinement led to RF = 5.4%, RB = 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)(PO 4) 6F 0.90(10)(H 2O) 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. 相似文献
15.
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 = Δσ 2/Δσ 1, 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, ND/ NC, ( ND: the number of cycles during retardation, NC: 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 ND/ NC-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. 相似文献
16.
在Zn(H 2PO 4) 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/dm 2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。 相似文献
17.
The formation, composition and propagation of laser-produced plasmas used for pulsed laser deposition (PLD) of Y1Ba2Cu3O7−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 σi−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 = xf[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)1/5t2/5) model. 相似文献
18.
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 m 2·g -1, 孔容为0.673 cm 3·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。 相似文献
19.
The carbonylate anions [M(CO) 5] - (M = Mn, Re), [Co(CO) 4] -, [CpFe(CO) 2] -, and [CpM(CO) 3] - (M = Mo, W) react with C 70 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 C 70-. In secondary thermal or photochemical processes, the metal-centered radicals Co(CO) 4 and M(CO) 5 (M = Mn, Re) combine with the C 70- to form the new η 2-C 70 complexes [Co(CO) 3(η 2-C 70)] - and [M(CO) 4(η 2-C 70)] -. However, the metal-centered radicals CpM(CO) 3 (M = Mo, W) require photolysis to react with C 70- to form [CpM(CO) 2(η 2-C 70)] -, whereas neither thermolysis nor photolysis induces reaction between CpFe(CO) 2 and C 70-. The photochemical reaction of [Mn(CO) 5] - with a mixture of higher fullerenes known to contain at least C 76, C 78, C 84, C 86, and C 90 resulted similarly in the formation of the higher fullerene complexes [Mn(CO) 4(η 2-C n)] - ( n = 76, 78, 80, 82, 84, 86, 88, 90, 92, 96, and 98), all identified using electrospray mass spectrometry. 相似文献
20.
Fe–Rh alloys of Rh concentrations ranging from 40 to 50at.% and of B2 phase were deformed by use of a compression machine capable of running tests at high speeds of impact. Induced complicated substructures and phases were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and positron annihilation spectroscopy (PAS). A characteristic arrangement of L1 0 domains was observed, along with very small transformed A1 domains and dispersed in the residual B2 matrix. On the basis of the experimental results, we suggest a coupling of a pair of shears along {112}11−1 B2 for the transformation mechanisms from B2 to L1 0 and A1 phases. 相似文献
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