An electron paramagnetic resonance study of the tetragonally distorted [Formula: see text] ion in [Formula: see text] and [Formula: see text

Chromium-doped [Formula: see text] and [Formula: see text] have been studied by both EPR and ENDOR spectroscopy. [Formula: see text] ions enter the fluorite structure in distorted substitution cation sites. In both matrices the distortion observed is tetragonal. X- and Q-band EPR measurements at temperatures between 4 and 300 K allowed us to determine the ion symmetry and the following spin-Hamiltonian parameters: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]; and [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]. For [Formula: see text], the weak superhyperfine interaction of [Formula: see text] with the surrounding [Formula: see text] ions has been studied by both EPR and ENDOR techniques for [Formula: see text]. No ENDOR signals were detected for [Formula: see text]. The results are tentatively explained in terms of a Jahn - Teller effect corresponding to [Formula: see text] coupling strongly stabilized by lattice stresses, although other possible origins for the distortion cannot be completely ruled out.     

Ferroelastic domain freezing and low-frequency elastic behaviour of [Formula: see text] (ALHS)

In this work elastic measurements on [Formula: see text] (ALHS) which were carried out in the low-frequency range between 1 and 50 Hz are presented. The temperature dependence of the inverse elastic compliance [Formula: see text] has been determined between 90 K and 420 K. Distinct anomalies have been found in the temperature dependence of [Formula: see text], which are connected to the motion of domain walls in the ferroelastic phase below [Formula: see text]. Around [Formula: see text] a (partial) ferroelastic `domain freezing' phenomenon has been observed. To the knowledge of the authors this is the first time that pure ferroelastic domain freezing has been reported. However, below [Formula: see text] the domain walls seem to retain a certain vibrational degree of freedom which could be responsible for an additional anomaly of the loss modulus which was observed. The elastic behaviour of a crystal of ALHS is dependent on the `history' of the given sample. During temperature cycling [Formula: see text] shows differences between the first run of heating and cooling and later runs. Finally, some basic insights concerning the domain wall motion were obtained; it was found that the domain wall mobility decreases by three orders of magnitude in the temperature region 170 - 230 K.     

Determination of the chiral structure of [Formula: see text] using anomalous x-ray scattering near the Cs K absorption edge

A structural study of [Formula: see text], grown from aqueous solution, was performed using anomalous x-ray scattering near the Cs K absorption edge to determine an absolute configuration of constituent atoms. The sense of the helical structure of the [Formula: see text] chain was found to be predominantly right-handed through a comparison of observed Bragg Bijvoet ratios with calculated ones. Assuming that [Formula: see text] consists of the two domains (i.e. right- and left-handed helices), we estimate that the volume fraction for the right-handed helix is [Formula: see text].     

退火诱导亚稳态Fe80Cu20合金固溶体的结构相变

利用扩展x射线吸收精细结构和x射线衍射研究了机械合金化制备的体心立方(bcc)的亚稳态Fe₈₀Cu₂₀合金固溶体的结构随退火温度的变化特点.结果表明，在300—873 K温度范围内，随着退火温度的升高，bcc结构物相的晶格常数近于线性降低，这主要是由于Cu原子从bcc结构Fe₈₀Cu₂₀合金固溶体中逐渐偏析出来，生成面心立方(fcc)结构的Cu物相所致.经603K退火后，Cu原子的平均键长R_Cu—Cu增加了0.003 nm左右，大约有50%的Cu原子从bcc结构的Fe₈₀Cu₂₀合金固溶体中偏析出来.在773 K退火后，bcc结构Fe_８０Cu₂₀合金固溶体近于完全相分离，生成了bcc结构的α-Fe与fcc结构的Cu物相. 关键词： 扩展x射线吸收精细结构 x射线衍射 ８０Cu₂₀合金')" href="#">Fe_８０Cu₂₀合金 机械合金化     

Physical properties of [Formula: see text] polymer electrolytes: nuclear magnetic resonance investigation and comparison with [Formula: see text

The physical properties of the ionic conductor [Formula: see text], obtained by dissolution of lithium trifluoromethanesulphonylimide in poly(propylene oxide), have been investigated for several values of n. The glass transition temperature [Formula: see text] has been established from both DSC and NMR techniques. The diffusion coefficients of [Formula: see text]-containing species have been determined by the pulsed magnetic field gradient technique. The behaviour of the proton relaxation time [Formula: see text] versus temperature and concentration has been correlated to the glass temperature. The behaviour of the proton transverse relaxation function, obtained by the spin-echo technique, has been interpreted using a simple model in which two regimes and consequently two transverse relaxation times coexist and are assigned to the `entangled' and `non-entangled' parts of the high-molecular-weight polymer chains investigated.     

Measurements of the strong-interaction widths of the kaonic (3)He and (4)He 2p levels

The kaonic (3)He and (4)He X-rays emitted in the [Formula: see text] transitions were measured in the SIDDHARTA experiment. The widths of the kaonic (3)He and (4)He 2p states were determined to be [Formula: see text], and [Formula: see text], respectively. Both results are consistent with the theoretical predictions. The width of kaonic (4)He is much smaller than the value of [Formula: see text] determined by the experiments performed in the 70's and 80's, while the width of kaonic (3)He was determined for the first time.     

稀土La对bcc-Fe中Cu扩散行为影响的第一性原理研究

采用基于密度泛函理论的第一性原理,研究了稀土La对bcc-Fe中Cu析出行为的影响.计算了α-Fe中La原子和Cu原子与空位之间,以及La原子和Cu原子之间的点缺陷结合能;在此基础上,讨论了α-Fe中La对Cu扩散激活能的关系.结果表明:La原子与空位之间有较强的相互吸引作用,且对近邻Cu原子也有一定的束缚.此外,La的加入使Cu原子近邻的空位形成能显著升高,这表明La,Cu偏聚区形成空位较为困难.与此同时,由于La原子对近邻空位和Cu原子的吸引作用,使Cu原子向近邻空位跳跃的迁移能有所升高.迁移能与空位形成能变化的计算结果显示,La原子的加入能够使α-Fe中Cu的扩散激活能显著升高,从而延缓了铁素体区富铜相的偏聚和析出.     

The effect of Co doping on antiferromagnetic correlations in the Kondo semi-metal CeNiSn

Single-crystal neutron scattering experiments have been performed to study magnetic excitations in [Formula: see text], in which the pseudo-gap of CeNiSn is suppressed by the doping. In CeNiSn there are two inelastic excitation peaks at [Formula: see text] and 4 meV, which correspond to dynamic antiferromagnetic correlations. In [Formula: see text] the 2 meV peak is smeared out, whereas the 4 meV peak becomes very weak and broad, but preserves the same quasi-one-dimensional character as that for CeNiSn. These results suggest the strong relation between the antiferromagnetic correlations and the pseudo-gap formation.     

Anomalies in the ion transport of phosphoric acid in water and heavy-water environments

This paper presents the experimentally determined precise transport data - (tracer) diffusion coefficients in both water and heavy-water environments, together with molar conductivity and viscosity of (ortho)phosphoric acid in water over an extended concentration range at [Formula: see text]. The concentration (c) dependence of the diffusion coefficients (D), viscosity [Formula: see text] and molar conductivity [Formula: see text] have been analysed. An anomalous depression in the D - [Formula: see text] curve for both [Formula: see text] - [Formula: see text] and [Formula: see text] - [Formula: see text] systems in the neighbourhood of 0.8 M is observed, which is complementary to the sudden sharp rise observed in the [Formula: see text] curve in the neighbourhood of 0.8 M. Although the occurrence of such an anomaly could be inferred from the earlier conductance, e.m.f. and diffusion data, it was never conclusively inferred earlier. This new set of diffusion and viscosity data clearly delineates anomalies in the ion transport of phosphoric acid.     

Magnetic and structural properties of as-milled and heat-treated bcc-Fe70Cu30 alloy

A ferromagnetic solid solution with a nominal atomic composition Fe₇₀Cu₃₀ and a body-centered structure has been obtained by high-energy ball milling. The decomposition of the system is monitored by X-ray diffraction (XRD), magnetic measurements and Mössbauer spectroscopy. According to XRD, for healing temperatures below 723 K there is only a bcc phase in the material, while for heating temperatures above 723 K a new phase, with a fcc structure, appears, suggesting that the solid solution has decomposed into bcc-Fe and fcc-Cu. However, the magnetic behavior observed during the decomposition process indicates that this evolution is more complex than the simple decomposition into the equilibrium phases. This behavior can be summarized in two points: (1) a decrease in the magnetization at 5 K, and (2) drastic changes in the coercive field with the thermal treatment, soft magnetic behavior for the material in the as-milled state, superparamagnetism for low heating temperatures and a hardening of the material heated to above 723 K, for which the values of the coercive field at room temperature are several times higher than those for the as-milled sample. The Mössbauer spectroscopy performed at room temperature shows that for the heat-treated samples the Fe atoms are in two different phases: a ferromagnetic phase, which evolves to bcc-Fe, and a paramagnetic phase.     

机械合金化Cu1-xSnx系的穆斯堡尔研究

利用机械合金化方法获得了几种铜－锡合金，特别是熔融法不易获得的η-Cu₆Sn₅，Ｘ射线衍射结果显示球磨使各样品纳米化，并形成包含确定合金相的固溶体，穆斯堡尔谱表明，各固溶体中除包含合金相外，还存在富锡相及富铜相，提出在机械合金化过程中，首先铜和锡纳米化，然后两种原子相互扩散形成包含合金相、富α－锡相和富ｆｃｃ铜相的固溶体。 关键词：     

Structural evolution of FexCo1−x/NM (NM=Ag, Cu, Al2O3) discontinuous multilayers by XAS

We discuss the specific features of the K-edge X-ray absorption spectroscopy (XAS) at the Fe and Co K-edges in Fe_xCo_1−x/NM discontinuous multilayers with NM=Ag, Cu, and Al₂O₃. Thermal treatments lead to the breakup of the layers forming a heterogeneous alloy with magnetic clusters of the FeCo embedded in a nonmagnetic (NM) matrix. Stabilization of the BCC phase of the FeCo alloy is directly evidenced by XAS. Differences among Fe and Co K-edge signatures indicate a strong dependence on the chemical nature of the absorbing atom for annealed samples. The amplitude of the extended X-ray absorption fine structure signal higher at the Co K-edge than at the Fe one reflect a smaller structural disorder in the Co environment. This behavior depends neither on the composition of the alloy nor on the NM material. In the case of Al₂O₃ a higher disorder around Fe atoms is observed also in the as-deposited sample. All these results indicate that the Fe segregates at the interface of the magnetic clusters/NM matrix after thermal annealing.     

Final-state effects in neutron Compton scattering measurements on zirconium deuteride and beryllium

We report inelastic neutron scattering measurements of the neutron Compton profile, J(y), for Be and for D in polycrystalline [Formula: see text] over a range of momentum transfers, q between 27 and [Formula: see text]. The measurements were performed using the inverse geometry spectrometer eVS which is situated at the UK pulsed spallation neutron source ISIS. We have investigated deviations from impulse approximation (IA) scattering which are generically referred to as final-state effects (FSEs) using a method described by Sears. This method allows both the magnitude and the q dependence of the FSE to be studied. Analysis of the measured data was compared with analysis of numerical simulations based on the harmonic approximation and good agreement was found for both [Formula: see text] and Be. Finally we have shown how [Formula: see text], where V is the interatomic potential, can be extracted from the antisymmetric component of J(y).     

Temperature-dependent Raman scattering study of the defect pyrochlores RbNbWO6 and CsTaWO6

Lattice dynamics calculations and temperature-dependent Raman scattering experiments were performed on RbNbWO(6) and CsTaWO(6) pyrochlore oxides. The observed bands were assigned to the respective motions of atoms in the unit cell. The spectra showed the presence of additional Raman bands not allowed for by the [Formula: see text] cubic structure. We have shown that these bands appear due to both substitutional disorder in the 16c sites and displacive disorder of the A ions. Raman studies also revealed the presence of an additional 80?cm(-1) band at room temperature for RbNbWO(6), not observed for CsTaWO(6). The presence of this band has been attributed to off-center displacement of the Nb and W ions due to structural phase transition into a tetragonal ferroelectric phase. The temperature evolution of the 80?cm(-1) band intensity revealed that it disappeared at a much higher temperature (about 650?K) than the reported phase transition temperature (about 360?K). This behavior is reminiscent of chemically disordered perovskite ferroelectrics, including relaxor ferroelectrics, and was attributed to the presence of small polar regions with local tetragonal distortion embedded in the paraelectric matrix of the [Formula: see text] structure.     

Influence of ternary addition of transition elements (Cr,Si and Mn) on the microstructure and magnetic properties of nano-structured CuCo alloy

The current state of studies presents the effect of ternary addition of transition elements such as Mn, Cr and Si (10 wt%) on the mechanically driven non-equilibrium solubility of 40 wt% Co containing Cu–Co alloy. X-ray powder diffraction analysis indicates that addition of Mn has been found to be the most effective in enhancing the solubility and formation of a complete solid solution between Co and Cu in a short duration (30 h) of ball milling. The microstructure of the ball milled CuCoMn alloy was found to be stable after the isothermal annealing up to a temperature of 450 °C for 1 h. The magnetic properties such as magnetic saturation, coercivity and remanence of ball milled CuCo alloy in the presence of Mn significantly altered after annealing in the temperature range 350–650 °C for 1 h. The best combination of magnetic properties of CuCoMn alloy has been found after annealing at 550 °C for 1 h.     

Thermodynamic behaviour of two-dimensional vesicles revisited

We study pressurised self-avoiding ring polymers in two dimensions using Monte Carlo simulations, scaling arguments and Flory-type theories, through models which generalise the model of Leibler, Singh and Fisher (Phys. Rev. Lett. 59, 1989 (1987)). We demonstrate the existence of a thermodynamic phase transition at a non-zero scaled pressure [Formula: see text] , where [Formula: see text] = Np/4[Formula: see text] , with the number of monomers N [Formula: see text] ∞ and the pressure p [Formula: see text] 0 , keeping [Formula: see text] constant, in a class of such models. This transition is driven by bond energetics and can be either continuous or discontinuous. It can be interpreted as a shape transition in which the ring polymer takes the shape, above the critical pressure, of a regular N -gon whose sides scale smoothly with pressure, while staying unfaceted below this critical pressure. Away from these limits, we argue that the transition is replaced by a sharp crossover. The area, however, scales with N(2) for all positive p in all such models, consistent with earlier scaling theories.     

Magnetic properties of charged spin-1 Bose gases with ferromagnetic coupling

The magnetic properties of a charged spin-1 Bose gas with ferromagnetic interactions are investigated within mean-field theory. It is shown that a competition between paramagnetism, diamagnetism and ferromagnetism exists in this system. It is shown that diamagnetism, being concerned with spontaneous magnetization, cannot exceed ferromagnetism in a very weak magnetic field. The critical value of reduced ferromagnetic coupling of the paramagnetic phase to ferromagnetic phase transition [Formula: see text] increases with increasing temperature. The Landé-factor g is introduced to describe the strength of the paramagnetic effect which comes from the spin degree of freedom. The magnetization density [Formula: see text] increases monotonically with g for fixed reduced ferromagnetic coupling [Formula: see text] as [Formula: see text]. In a weak magnetic field, ferromagnetism makes an immense contribution to the magnetization density. On the other hand, at a high magnetic field, the diamagnetism tends to saturate. Evidence for condensation can be seen in the magnetization density at a weak magnetic field.     

Preparation of p-type CdS thin films and in situ dark conductivity in vacuum deposited CdS:Cu films

CdS:Cu thin films were prepared using a vacuum co-evaporation technique. The Hall measurements indicate that the conductivity characteristic of CdS thin films transformed from highly compensated in as-grown or weakly annealed materials to p-type conductive in strongly annealed materials. X-ray diffraction spectra show that as-deposited thin films were the hexagonal phase of CdS except the presence of copper for high Cu doping and the diffraction peaks of Cu disappeared after annealing. From the X-ray photoelectron spectroscopy we found the ionization of Cu atoms and the formation of an acceptor level. In situ dark conductivity in vacuum as-deposited CdS:Cu was performed in the temperature range between 27 and 250 °C. An abnormal temperature dependence of conductivity was observed in medium and heavily Cu-doped films. The formation of a p-type material at a certain temperature was also studied by the hot probe measurements, which indicates a complex compensation process in the Cu-doped CdS films.     

Allotropic forms of carbon in the Invar Fe–Ni–C alloy before and after plastic deformation by upsetting

The effect of cold plastic deformation by upsetting (e = 1.13) on structure and hybridised bonds of carbon in the fcc Invar Fe-30.9%Ni-1.23% C alloy was studied by means of X-ray phase analysis and X-ray photoelectron spectroscopy. Carbon precipitates along grain boundaries and inside of grains in the alloy after annealing and plastic deformation were revealed. The presence of mainly sp²- and sp³-hybridised C–C bonds attributing to graphite and amorphous carbon as well as the carbon bonds with impurity atoms and metallic Fe and Ni atoms in austenitic phase were revealed in the annealed and deformed alloy. It was shown for the first time that plastic deformation of the alloy results in partial destruction of the graphite crystal structure, increasing the relative part of amorphous carbon, and redistribution of carbon between structural elements as well as in a solid solution of austenitic phase.     

聚合氯化铝铁的红外光谱研究

用傅里叶变换红外光谱法研究了不同Al/Fe mol比的聚合氯化铝铁（PAFC）的中红外光谱。Al/Fe mol比＜3：7和6：4时，PAFC中Fe-O-H-Fe与Al-O-H-Al基团在850－880cm^-1和930－970cm^-1两个区间δ弯曲振动峰频随Al/Fe mol比的线性变化关系表明了Al(Ⅲ），Fe(Ⅲ)对两个基团的相互取代，即有Fe-O-H-Al(Al-O-H-Fe)基团存在。Al/Fe mol比相近时，位于625cm^-1的Al-O-H-Al-O-H整体弯曲振动峰与位于680cm^-1的Fe-O-H-Fe-O-H整体弯曲振动峰相互迭加形成640cm^-1而为主峰的宽峰，而Al-O-H-Al，Fe-O-H-Fe特征振动峰都大大减弱或消失。这说明Fe(Ⅲ)羟合物与Al(Ⅲ）羟合物交叉共聚的作用加强，溶液中生成了含铝水羟合铁（Aluminous Ferrihydrite）。而1610－1630cm^-1区间H－OH δ弯曲振动峰强和峰频随Al/Fe mol比的变化表明：Al/Fe mol比＞6：4后PAFC中Al-Fe羟合共聚体配位水量最高且相对稳定，它们转变成为结构水后与中心离子间的键合作用增强。这就是PAFC溶液在Al/Fe mol比＞6：4后保持稳定的原因之一。