Mössbauer studies of the relaxation in the FeNiB amorphous system

Young's modulus of Fe₄₄Ni₃₈Bi₁₈ amorphous ribbons annealed at different temperatures shows an oscillating behavior depending on the annealing temperature. In a previous work, several samples were studied and the Young modulus was correlated with the hyperfine field distributions. In this work, more samples are analyzed and further Mössbauer studies are performed in order to verify the above-mentioned correlation.     

人工调控微结构压电驻极体的热稳定性和电荷动态特性

利用表面带有周期性结构的硬质模板,通过冷压工艺将周期结构图案复制到多孔聚四氟乙烯(PTFE)薄膜表面,再经过热黏合工艺与致密氟化乙丙烯共聚物(FEP)薄膜复合,制备出了高度有序的微孔结构复合膜,并用电晕充电的方法对复合膜进行极化处理,最终获得氟聚合物复合膜压电驻极体.借助对这类复合膜压电驻极体介电谐振谱的测量,得到了材料的杨氏模量.并利用等温热老化工艺对它们的压电系数d33的热稳定性进行了考察.最后通过短路热刺激放电谱的测量和分析,讨论了该复合膜在热老化处理后的电荷动态 关键词： 有序结构 压电驻极体 压电性 电荷动态特性     

Effect of deformation and heat treatment on the damping constant and shear modulus of a bulk Zr-Cu-Ni-Al-Ti metallic glass

The effect of deformation by rolling or quenching from temperatures close to the glass transition temperature on the damping constant and the shear modulus of preliminarily annealed bulk samples of a Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ metallic glass was studied. These treatments are found to result in recovery of the “irreversible” contributions to the damping constant and the shear modulus, and the deformation treatment is shown to lead to an increase in the amplitude-dependent internal friction.     

Jahn-Teller transition and electron-phonon interaction in Cr-doped manganites Sr0.9Ce0.1Mn1−yCryO3

Cr-doped manganites Sr_0.9Ce_0.1Mn_1−yCr_yO₃ (y=0, 0.05, and 0.10) have been systematically investigated by X-ray, magnetic, transport, and elastic properties measurements. For parent compound Sr_0.9Ce_0.1MnO₃, it undergoes a metal-insulator (M-I) transition at 318 K, which is suggested to originate from a first-order structural transition accompanied by Jahn-Teller (JT) transition. With increasing Cr doping content, the JT transition temperature decreases. The Cr doping suppresses the antiferromagnetic (AFM) state and makes the system spin-glass (SG) behavior at low temperatures. In the vicinity of JT transition temperatures, the softening of Young's modulus originating from the coupling of the orbital (quadrupolar) moment of the e_g orbital of Mn³⁺ ion to the elastic strain has been observed. The anomalous Young's modulus properties imply the electron-phonon coupling due to the JT effect may play an important role in the system.     

Effect of Young's modulus evolution on residual stress measurement of thermal barrier coatings by X-ray diffraction

Subjected to thermal cycling, the apparent Young's modulus of air plasma-sprayed (APS) 8 wt.% Y₂O₃-stabilized ZrO₂ (8YSZ) thermal barrier coatings (TBCs) was measured by nanoindentation. Owing to the effects of sintering and porous microstructure, the apparent Young's modulus follows a Weibull distribution and changes from 50 to 93 GPa with an increase of thermal cycling. The evolution of residual stresses in the top coating of an 8YSZ TBC system was determined by X-ray diffraction (XRD). The residual stresses derived from the XRD data are well consistent with that obtained by the Vickers indention. It is shown that the evolution of Young's modulus plays an important role in improving the measurement precision of residual stresses in TBCs by XRD.     

The structure and mechanical properties of thick rutile-TiO2 films using different coating treatments

The hardness and Young's modulus of thick rutile-TiO₂ films were determined using a continuous stiffness measurement (CSM) technique in this study. Pure rutile-TiO₂ nanopowders (TH₂O, TFeSO₄ and TCuSO₄) were prepared using a modified homogeneous-precipitation process at low temperature (MHPPLT) method. The TiO₂ films were prepared from sols using 3% (w/w) of the prepared-TiO₂ suspension solution coated onto silicon wafers. After dip-coating was completed, the coatings were further treated by natural air-drying, water-vapor exposure, and calcination, respectively. An ellipsometry with a monochromator was used to measure the thickness and refractive index of the TiO₂ films, and a scanning electron microscopy (SEM) to determine their morphology. Three coatings of TH₂O, TFeSO₄ and TCuSO₄ demonstrated their refractive indexes of around 1.60 under three treatments. Volumetric expansion and thickness of the coatings should influence their refractive index. Furthermore, the continuous stiffness measurement (CSM) technique was used to perform nanoindentation testing on the hardness and Young's modulus of prepared rutile-TiO₂ coatings. The mean hardness and Young's modulus of three coatings increased with preparation temperature. In addition, the TH₂O coatings demonstrated greater hardness and modulus than those of TFeSO₄ and TCuSO₄ coatings in the natural air-drying condition. Surface cracking observed on the calcinated TFeSO₄ should be the reason why an obvious decrease of the mean hardness and Young's modulus appeared. Finally, two mechanical properties and related nanoindentation depth of the coatings were discussed in detail.     

Effect of ending surface on energy and Young's modulus of single-walled carbon nanotubes studied using linear scaling quantum mechanical method

By using a linear scaling self-consistent charge, density functional tight-binding (SCC-DFTB) method and an ab intio Dmol3 calculation, the energy and Young's modulus as a function of tube length for (10, 0) single-walled carbon nanotubes (SWCNTs) are investigated. It was found that with increasing the length of SWCNTs the Young's modulus increases rapidly, then, there is a slow increase, which ultimately approaches a constant value after the length is increased to ~20 nm, whereas a reversed variation tendency was found for the average energy of atoms in SWCNTs with a change of the tube length. We found that the characters of the length-dependent energy and Young's modulus stem from the changed P_y-DOS of atoms in the ending region of the tube. Here one simple formula is proposed for quantitatively explaining the length-dependent energy and modulus.     

Superconductivity of niobium nitride single crystals after implantation of carbon and nitrogen

Single crystals of δ-NbN_0.85 with a superconducting transition temperature T_c of 14.3 K were implanted with nitrogen and carbon ions at room temperature and subsequently annealed at high temperatures. Implantation was also performed at high substrate temperatures. After implantation at about 920°C maximum T_c-values of 16.5 and 17.8 K were obtained with N- and C-ions respectively. Disorder observed after room temperature implantation consisted of displaced Nb-atoms which could not be completely annealed in an isochromous annealing process up to 1000°C. For annealing temperatures above 1100°C nitrogen diffusion out of the implanted layers resulted in a reduction of T_c.     

高温高压下Zr2AlC的结构及热学性质的第一性原理

利用密度泛函理论研究了高温高压下Zr₂AlC的结构和热力学性质,计算得到Zr₂AlC的晶格参数与实验值符合较好．研究了Zr₂AlC的弹性常数、体模量、剪切模量和杨氏模量等力学性质随压力变化的趋势．同时研究了维氏硬度随压力的变化趋势．通过计算得到的杨氏模量预测了Zr₂AlC的弹性各向异性．最后,基于准简谐德拜模型,成功预测了Zr₂AlC的德拜温度、热容、热膨胀系数和Grüneisen参数随着压强和温度的变化关系.     

The current-induced effect on the Jahn-Teller distortion in the La0.5Ca0.5MnO3 manganite

The influence of dc current on the resistivity ρ and the Young's modulus E of La_0.5Ca_0.5MnO₃ compound has been investigated by means of an in situ measuring method. At low temperatures, both the resistivity ρ and the relative modulus ΔE increase with the current. A relaxation behavior of ρ to the higher resistive state is observed at a fixed temperature and a constant current. After storing the sample for a few days, ρ decreases with the current, accompanying a slight drop of ΔE at low temperatures. Current-induced effects on ρ and ΔE are interpreted according to the current-induced interwinning of Mn³⁺O₆ octahedral distortion modes between Q₂- and Q₃-types, which is suggested to contribute to the variation of the resistivity.     

单相钇钡铜氧高温超导体的超导转变与内耗原位研究

在80至300K温度范围内对YBa₂Cu₃O_7-δ高温超导体的电阻、内耗和弹性模量随温度的变化进行了原位测量。在T_c附近观察到两个明显的内耗峰。从峰的特征推断,这两个内耗峰可能与电子在Cu³⁺与Cu²⁺之间的弛豫过程有关。而在160K到280K温度范围内所观察到的内耗峰及杨氏模量反常效应,可能与试样中氧空位的调整有关。 关键词：     

聚四氟乙烯和氟化乙丙烯共聚物复合膜的压电性

以多孔PTFE膜为骨架,而以致密（非多孔）FEP膜为储电介质层的孔洞结构复合压电驻极体膜的制备方法.利用正压电效应,测量了复合膜的准静态压电系数d₃₃;研究了压电系数的热稳定性和复合膜中空间电荷的动态特性;并通过介电谐振谱的分析,比较了这类复合膜的准静态和动态压电系数.结果表明：FEP和PTFE复合膜压电驻极体的准静态压电系数d₃₃可以达到300 pC/N.经90℃老化20 h 后的d₃₃仍保持在初 关键词： 压电驻极体 压电性 多孔聚四氟乙烯 致密氟化乙丙烯共聚物     

Theoretical investigations of structural, elastic and thermodynamic properties for PtN2 under high pressure

We have investigated structural and elastic properties of PtN₂ under high pressures using norm-conserving pseudopotentials within the local density approximation (LDA) in the frame of density-functional theory. Calculated results of PtN₂ are in agreement with experimental and available theoretical values. The a/a₀, V/V₀, ductility/brittleness, elastic constants C_ij, shear modulus C′, bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio σ and anisotropy factor A as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also study thermodynamic properties of PtN₂. The thermal expansion versus temperature and pressure, thermodynamic parameters X (X=Debye temperature or specific heat) with varying pressure P, and heat capacity of PtN₂ at various pressures and temperatures are estimated.     

Influence of Si-N interlayer on the microstructure and magnetic properties of γ′-Fe4N films

The (γ′-Fe₄N/Si-N)_n (n: number of layers) multilayer films and γ′-Fe₄N single layer film synthesized on Si (1 0 0) substrates by direct current magnetron sputtering were annealed at different temperatures. The structures and magnetic properties of as-deposited films and films annealed at different temperatures were characterized using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The results showed that the insertion of Si-N layer had a significant influence on the structures and magnetic properties of γ′-Fe₄N film. Without the addition of Si-N lamination, the iron nitride γ′-Fe₄N tended to transform to α-Fe when annealed at the temperatures over 300 °C. However, the phase transition from γ′-Fe₄N to ?-Fe₃N occurred at annealing temperature of 300 °C for the multilayer films. Furthermore, with increasing annealing temperature up to 400 °C or above, ?-Fe₃N transformed back into γ′-Fe₄N. The magnetic investigations indicated that coercivity of magnetic phase γ′-Fe₄N for as-deposited films decreased from 152 Oe (for single layer) to 57.23 Oe with increasing n up to 30. For the annealed multilayer films, the coercivity values decreased with increasing annealing temperature, except that the film annealed at 300 °C due to the appearance of phase ?-Fe₃N.     

Temperature compensating Elinvar character in Fe-Mn-Si alloys

Young's modulus-temperature and thermal expansion curves were measured in γ-Fe-31Mn-(0.25-8.67) Si-0.77C (at%) alloys by dynamic audio resonance method and in a light dilatometer. The results show that the anomalies in Young's modulus and thermal expansion appear near the Néel temperature. The temperature coefficient of Young's modulus, (1/E_p)(dE_p/dT), is controlled by Si content below the Néel temperature. When Si content increases to 5.31 at%, (1/E_p)(dE_p/dT) is close to zero in temperature range from 260 to 335 K, i.e. the Fe-31Mn-5.31Si-0.67C (at%) alloy shows Elinvar character. The temperature range in which the Elinvar character appears is wider than that of γ-Fe-Mn Elinvar alloys. The change in exchange energy and the ΔE effect result from the effect of Si on the antiferromagnetic behavior in γ-Fe-Mn alloys since it induces or enhances localized magnetic moment. When the increase in normal Young's modulus due to lowering temperature is compensated by the ΔE effect caused by the antiferromagnetic ordering, Elinvar character appears.     

Mössbauer study of the stability of Fe5Si95 produced by inert gas condensation

Fe₅Si₉₅ specimens with an enhanced solubility of Fe in Si by about twenty-one orders of magnitude relative to crystalline Si at room temperature were prepared by the inert gas condensation technique. The thermal stability of the Fe₅Si₉₅ sample was investigated by Mössbauer spectroscopy. The spectrum of the as-prepared Fe₅Si₉₅ exhibited a broadened many different iron sites in the sample. This material was thermal stable up to temperatures of 673k for one hour. After annealing at 773K for one hour, the intermetallic compound α-FeSi₂ was formed in the annealed sample, probably via the precipitation process. The amount of the α-FeSi₂ phase increased with the annealing temperature. No β-FeSi₂ phase was observes in any of the annealed samples up to an annealing temperature of 1273K For one hour.     

The influence of Cu and Nb on the crystallization products of annealed FeCuNbSiB

Depending on different Nb and Cu concentration, we studied the formation of nano- and microcrystalline phases in differently annealed samples of FeCuNbSiB. First, the kinetics of crystallization was explored by measuring the temperature-dependent electrical resistivity and magnetization. After this, we collected Mössbauer spectra and did an X-ray diffraction analysis of annealed samples at chosen temperatures to discover the different crystalline phases. It was found how the onset of crystallization had been shifted towards other temperatures. The analysis of Mössbauer spectra shows that building up the well-known DO₃ structure of Fe₃Si is disturbed in the alloy without Cu. At higher Nb content, we resolve two different crystallization steps in the formation of Fe₃Si and a new crystalline phase, probably being a structure like Fe₂₃B₆.     

First-principles calculation of elastic and thermodynamic properties of Ni2MnGa Heusler alloy

The equilibrium lattice parameter, heat capacity, thermal expansion coefficient and bulk modulus of Ni 2 MnGa Heusler alloy are successfully obtained using the first-principles plane-wave pseudopotential (PW-PP) method as well as the quasi-harmonic Debye model. We analyse the relationship between bulk modulus B and temperature T up to 800 K and obtain the relationship between bulk modulus B and pressure at different temperatures. It is found that the bulk modulus B increases monotonically with increasing pressure and decreases with increasing temperature. The pressure dependence of heat capacity C v and thermal expansion α at various temperatures are also analysed. Finally, the Debye temperature of Ni 2 MnGa is determined from the non-equilibrium Gibbs function. Our calculated results are in excellent agreement with the experimental data.     

Ultrasonic characterization of ceramic fibres at ambient and elevated temperatures

A non-destructive laser-generated ultrasonic inspection system has been developed to evaluate the elastic properties of ceramic fibres. The approach uses a pulsed Nd:YAG laser to excite ultrasonic signals in fibres. The signal is detected by a piezoelectric acoustic emission transducer to obtain the appropriate frequency response suitable for an elastically one-dimensional sample. By using a differential time-of-flight system, a very accurate measure of the velocity can be obtained in the fibre, with a total scatter of less than 0.5%. This approach has been used to investigate the Young's modulus of polycrystalline carbon and boron fibres as a function of stress. Both types of fibres were found to have a Young's modulus increase as greater applied loads were imposed. The carbon and boron fibres, along with silicon carbide fibres, were evaluated at elevated temperatures up to 700 °C. The carbon fibres were found to have an immediate decrease in the Young's modulus as the temperature was increased, due to oxidation of the carbon. The Young's modulus of the boron fibres decreased only at temperatures higher than 200 °C, probably the result of a microstructural transformation or relaxation. The silicon carbide fibres were found to have no significant change in the elastic properties up to 700 °C. The ultrasonic technique was also applied to polycrystalline alumina fibres and fibre tows between ambient temperature and 1200 °C in a specially designed furnace. Using this technique, it was possible to distinguish the changes in the elasticity of the alumina fibres as they were processed into -alumina. The change in the Young's modulus was readily apparent during phase transformations to -alumina. In addition, the ultrasonic velocity can be used to infer information concerning any coatings that were applied to the alumina fibres. This can be used to aid in the quantification of the coating thickness and uniformity. The application of the ultrasonic inspection system has demonstrated the ability to determine rapidly and non-destructively the elastic properties in ceramic fibres. The information gained from the measurements can be used as a quality assurance technique, or can be modified to be a real-time process control/process monitoring system.     

First-principles calculations of elasticity and thermodynamic properties of LaNi5 crystal under pressure

This paper investigates the equilibrium lattice parameters, heat capacity, thermal expansion coefficient, bulk modulus and its pressure derivative of LaNi 5 crystal by using the first-principles plane-wave pseudopotential method in the GGA-PBE generalized gradient approximation as well as the quasi-harmonic Debye model. The dependences of bulk modulus on temperature and on pressure are investigated. For the first time it analyses the relationships between bulk modulus B and temperature T up to 1000 K, the relationship between bulk modulus B and pressure at different temperatures are worked out. The pressure dependences of heat capacity C v and thermal expansion α at various temperatures are also analysed. Finally, the Debye temperatures of LaNi 5 at different pressures are successfully obtained. The calculated results are in excellent agreement with the experimental data.