The influence of a magnetic field on the inelastic properties of LiF crystals

The effect of weak magnetic fields (0.1–0.8 T) on the internal friction and Young’s-modulus defect of LiF crystals is investigated over a range of relative strain amplitudes ɛ ₀ from 10⁻⁶ to 10⁻⁴ at frequencies of 40 and 80 kHz. Experiments with these fields show that the internal friction increases and the effective elastic modulus decreases, indicating an increase in the plasticity of the samples. Plots are obtained of the internal friction versus the magnitude of the magnetic field at various values of the strain amplitude ɛ ₀. Fiz. Tverd. Tela (St. Petersburg) 41, 1035–1040 (June 1999)     

Young’s modulus and internal friction in porous biocarbon white pine wood precursors

This paper reports on a study performed in the temperature range 100–293 K, in air and in vacuum, for the amplitude and time dependences of the Young’s modulus and the internal friction (ultrasound damping) of biocarbon precursors prepared from white pine wood at two pyrolysis (carbonization) temperatures of 1000 and 2400°C. The measurements have been conducted by the resonance technique with a composite vibrator on samples cut along and across the tree growth direction. The desorption of molecules of the external medium at low amplitudes of ultrasonic vibrations has been found to produce the pronounced influence on the effective elastic modulus and elastic vibration decrement. The data obtained from acoustic measurements of the amplitude dependences of the elastic modulus have been used to estimate the microplastic properties of the samples. It has been shown that increasing the carbonization temperature gives rise to noticeable changes in the Young’s modulus and internal friction, as well as to reduction of the microplastic stress σ _y of the biomaterial studied. The stress σ _y of the samples cut across the growth direction has been found to be substantially smaller than that of the “longitudinal” samples. The elastic and microplastic properties of precursors prepared from white pine wood have been compared with those of the white eucalyptus wood.     

Internal friction and change in Young’s modulus in the alloy Mg-Ni-Y due to a transition from an amorphous to a nanocrystalline state

The effect on the internal friction and Young’s modulus of the evolution of the structure of the amorphous alloy Mg₈₄Ni_12.5Y_3.5 (relaxation of internal stresses, devitrification, nucleation and decay of nanocrystalline phases) was investigated as it was heated. The measurements were performed on ribbon samples by flexural oscillations. Irreversible peaks of the internal friction and anomalies in the behavior of Young’s modulus as a function of temperature were observed. The position of the anomalies correlates with the characteristic temperatures of restructurings observed by differential thermal and x-ray diffraction. Possible internal-friction mechanisms associated with various types of structural relaxation and nanocrystallization processes in the alloy are discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 561–566 (April 1999)     

Structural,electrical, magnetic,elastic, and internal friction studies of Nd1−xCaxMnO3 (x=0.2, 0.33, 0.4, and 0.5) manganites

A series of Nd_1?xCa_xMnO₃ (x=0.2, 0.33, 0.4, and 0.5) manganites was prepared by sol–gel route by sintering at 1300 °C, mainly to understand the correlation between electron, spin, and phonon couplings. The internal friction and longitudinal modulus along with electrical and magnetic properties have been measured. All the samples are found to exhibit anomalies at T_C, T_N, and T_CO transition temperatures. The anomalies in longitudinal modulus and the internal friction peak at T_CO are attributed to Jahn–Teller effect. A strong correlation between the temperature dependent elastic, anelastic, resistivity, and ac susceptibility properties has been observed and an effort has been made to explain the observed anomalous behavior by a qualitative model.     

Elasticity and inelasticity of silicon nitride/boron nitride fibrous monoliths

A study is reported on the effect of temperature and elastic vibration amplitude on Young’s modulus E and internal friction in Si₃N₄ and BN ceramic samples and Si₃N₄/BN monoliths obtained by hot pressing of BN-coated Si₃N₄ fibers. The fibers were arranged along, across, or both along and across the specimen axis. The E measurements were carried out under thermal cycling within the 20–600°C range. It was found that high-modulus silicon-nitride specimens possess a high thermal stability; the E(T) dependences obtained under heating and cooling coincide well with one another. The low-modulus BN ceramic exhibits a considerable hysteresis, thus indicating evolution of the defect structure under the action of thermoelastic (internal) stresses. Monoliths demonstrate a qualitatively similar behavior (with hysteresis). This behavior of the elastic modulus is possible under microplastic deformation initiated by internal stresses. The presence of microplastic shear in all the materials studied is supported by the character of the amplitude dependences of internal friction and the Young’s modulus. The experimental data obtained are discussed in terms of a model in which the temperature dependences of the elastic modulus and their features are accounted for by both microplastic deformation and nonlinear lattice-atom vibrations, which depend on internal stresses.     

Temperature dependence of the internal friction of polycrystalline indium

The temperature dependences of the internal friction and the elastic modulus of polycrystalline indium have been investigated in the temperature range 7–320 K at oscillatory loading frequencies of approximately 100 kHz. The effect of temperature on the amplitude dependence and the effect of high-amplitude loading at 7 K on the temperature and amplitude dependences of the internal friction of indium have been analyzed. It has been demonstrated that the thermocycling leads to microplastic deformation of indium due to the anisotropy of thermal expansion and the appearance of a “recrystallization” maximum in the spectrum of the amplitude-dependent internal friction. The conclusion has been drawn that the bulk diffusion of vacancies and impurities begins at temperatures of approximately 90 K and that, at lower temperatures, the diffusion occurs in the vicinity of dislocations. It has been revealed that the high-temperature internal friction background becomes noticeable after the dissolution of Cottrell atmospheres.     

Effect of lead on microstructure and some physical properties of Sn–Zn–Cd alloy

The effect of lead on the structure, electrical resistivity, internal friction, elastic modulus and thermal properties of Sn₈₁Zn₉Cd₁₀ ternary alloys have been investigated using different experimental techniques with their analysis. In addition, properties of this alloy were compared with other Sn–Zn or Sn–Zn–Cd alloys and commercial solder alloys. It has a higher electrical resistivity, internal friction and lower elastic modulus when compared with Sn–Zn or Sn–Zn alloys with other additions such as Cd, Bi or In. The Sn₆₁Zn₉Cd₁₀Pb₂₀ alloy has a lower melting point, electrical resistivity and internal friction when compared with the commercial Pb–Sn solder alloy, but it has a similar elastic modulus.     

Influence of x irradiation on internal friction in silicon

An investigation was made of the influence of γ irradiation on the temperature dependences of internal friction in disk-shaped silicon substrates in the kilohertz frequency range. After exposure to doses of 10⁴ and 10⁵ R, two dominant internal friction peaks were observed at ∼330 and ∼450 K with activation energies H ₁=0.6 eV and H ₂=0.9 eV, respectively. These peaks were evidently caused by reorientation of interstitial silicon atoms in dumbbell configurations. Fiz. Tverd. Tela (St. Petersburg) 40, 1257–1258 (July 1998)     

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：     

描述蠕变过程中内耗的四参量模型

实验表明:蠕变过程中的内耗兼有Maxwell二参量模型的性质和滞弹性三参量模型的性质。本文提出一个用以描述蠕变过程中内耗的四参量模型。由此模型推导出的内耗表达式为Q^-1=1/(ωτ₁)+△(ωτ₂)/(1+ω²τ₂²),式中ω为测量圆频率,τ₁和τ₂分别为粘弹性内耗和滞弹性内耗的弛豫时间,△为弛豫强度。这个内耗表达式可以满意地说明蠕 关键词：     

Anomalies in the Young modulus at structural phase transitions in rare-earth cobaltites RBaCo<Subscript>4</Subscript>O<Subscript>7</Subscript> (R = Y,Tm-Lu)

The elastic properties of rare-earth cobaltites RBaCo₄O₇ (R = Y, Tm-Lu) have been experimentally studied in the temperature range of 80–300 K. The strong softening of the Young modulus ΔE(T)/E ₀ ≈ −(0.1–0.2) of cobaltites with Lu and Yb ions has been revealed, which is due to the instability of the crystal structure upon cooling and is accompanied by an inverse jump at the second-order structural phase transition. The softening of the Young modulus and the jump at the phase transition decrease by an order of magnitude and the transition temperature T _s and hysteresis ΔT _s increase from a compound with Lu to that with Tm. A large softening of the Young modulus at the structural transition in Lu- and Yb cobaltites indicates that the corresponding elastic constant goes to zero, whereas this constant in Tm cobaltite is not a “soft” mode of the phase transition. It has been found that the structural phase transition in Lu- and Yb cobaltites is accompanied by a large absorption maximum at the phase transition point and an additional maximum in the low-temperature phase and absorption anomalies in Tm cobaltite is an order of magnitude smaller.     

The temperature dependences of electromechanical properties of PLZT ceramics

The mechanical and electrical properties in lanthanum modified lead zirconate-titanate ceramics of 5/50/50 and 10/50/50 were studied by mechanical loss Q ^{- 1}, Young's modulus E, electric permittivity ε and tangent of dielectric loss of angle tgδ measurements. The internal friction Q ^{- 1} and Young modulus E measured from 290 K to 600 K shows that Curie temperature T_C is located at 574 K and 435 K (1^st cycle of heating) respectively for ceramic samples 5/50/50 and 10/50/50. The movement of T_C in second cycle of heating to lower temperature (561 K for 5/50/50 and 420 K for 10/50/50) has been observed. Together with Q ^{- 1} and E measurements, temperature dependences of ε=f(T) and tgδ=f(T) were determinated in temperature range from 300 K to 730 K. The values of T_C obtained during ε and tgδ measurements were respectively: 560 K for 5/50/50 and 419 K for 10/50/50. These temperatures are almost as high as the temperatures obtained by internal friction Q ^{- 1} measurements in second cycle of heating. In ceramic sample 10/50/50 the additional maximum on internal friction Q ^{- 1} curve at the temperature 316 K was observed.     

A mechanical spectrum study of bilayer cuprate La1.82Sr0.18CaCu2O6+δ

The mechanical spectrum of bilayer cuprate La_1.82Sr_0.18CaCu₂O_6+δ (La2126) was measured using the vibrating reed method from 30 K to room temperature at kilohertz frequency. A clear modulus softening was observed at 223 K accompanied by a sharp internal friction peak, which evidences a phase transition. Another broad internal friction peak around 250 K was observed, accompanied by a large modulus change. This contrasts with the broad internal friction peak of Ca doped Y Ba₂Cu₃O_7−δ (Y123) for which no clear modulus change was observed. The main contribution to the broad internal friction peak of La2126 is expected to be from the glass transition of the interstitial oxygen atoms.     

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.     

Relation between the reduced and unreduced hardness in nanomicroindentation tests

Hooke’s law is generalized to the case of arbitrary elastic or plastic indentation , where ɛ=q/E _r is the elastic strain, q is the average pressure over the contact area, E _r is the reduced elastic (Young’s) modulus, A is the projected area of the contact, w ₁ is the deformation in elastic indentation by a flat punch. On this basis a relation is obtained between the reduced hardness H and unreduced hardness H _h, which depends on the ratio w _s/w₁=m _s; w _s is the elastic deformation along the perimeter of the indent, and m _s≅0.78. It is shown that the correction ΔE _r to the elastic modulus E _r determined from the condition of linearity of the initial part of the unloading diagram, is ΔE _r=0.27(ΔP/P _m), where ΔP is the value used in the calculation of E _r for the length of the linear part of the diagram, reckoned from the maximum load P _m. It is shown that for metallic construction materials of medium hardness one has q=HM, where HM is the Meyer hardness. With increasing HM and increasing angle ϕ at the tip of the indenter, the ratio HM/q grows by an exponential law. Zh. Tekh. Fiz. 69, 42–48 (July 1999)     

Internal friction in Cu6PS5Br superionic crystals and related composites

Mechanical properties of Cu₆PS₅Br single crystals and composites based on them have been investigated by the internal friction method. The measurements of the internal friction and the shear modulus have been performed in the temperature range of 80–300 K at deformation frequencies of 10–100 mHz in a mode of forced torsional vibrations. The maxima caused by the superionic and ferroelastic phase transitions have been found in temperature dependences of the internal friction. It has been shown that a more than two-fold decrease in the shear modulus with increasing temperature in the range of 150–230 K is caused by mobility unfreezing in the cation sublattice of the Cu₆PS₅Br single crystal during the superionic phase transition. An abrupt (more than threefold) increase in the shear modulus upon heating in the range of 260–270 K is caused by the ferroelastic phase transition of the Cu₆PS₅Br single crystal. Parameters of the internal friction of this single crystal in the course of mentioned phase transitions have been determined.     

Structural,electrical, magnetic,elastic and anelastic behaviour of Nd0.6Ca0.4MnO3

With a view to understanding the structural, electrical and magnetic, elastic and anelastic behaviour of charge ordered Nd_0.6Ca_0.4MnO₃, systematic investigations were undertaken. The sample was synthesized by a sol–gel route. The sample was characterized by X-ray diffraction (XRD) using a Rietveld refinement technique and was found to have orthorhombic structure with space group Pnma. A study on the variation of electrical resistivity with temperature has been carried out in the range 100–300 K and it was found to exhibit a field induced transition. The ac susceptibility studies show two transition temperatures, which are attributed to charge ordering and a Néel transition. Internal friction and longitudinal modulus studies were carried out using the composite oscillator technique. An effort has been made to explain the observed anomalous behaviour by a qualitative model.     

Phase transitions in La0.5Sr0.5FeO3−δ investigated by mechanical spectrum

The mechanical spectrum measurement was performed in ceramic La_0.5Sr_0.5FeO_3?δ from liquid nitrogen temperature to room temperature at kilohertz frequencies. From temperature dependent reduced modulus, a kink (corresponding temperature labeled as T_M) was observed which evidenced a phase transition by the mechanical spectrum at two flexural resonance frequencies. This elastic manifested phase transition is a charge disproportionation transition. Around 170 K, an internal friction peak (labeled as P1) was observed accompanied with a large modulus hardening with the decrease in temperature. Two mechanisms are proposed for P1 peak, one is elastic manifestation of magnetic freezing, and the other is the ordering or freezing of oxygen vacancies.     

Dielectric and acoustic properties of the new lead-free BiLi<Subscript>0.6</Subscript>W<Subscript>0.4</Subscript>O<Subscript>3</Subscript> ceramic

The properties of the new lead-free compound BiLi_0.6W_0.4O₃, obtained using ceramic technology, were studied by dielectric and mechanical spectroscopy. The anomalies of internal friction are, along with the elastic and dielectric properties observed experimentally at a temperature of 350°C, related to its structural phase transition. Dielectric and mechanical relaxation due to processes of interaction between crystal lattice defects was revealed in the low-temperature phase.     

Ab initio calculation of the electronic structure,Fermi surface,and elastic properties of the new 7.5-K superconductor Nb<Subscript>2</Subscript>InC

Ab initio calculations were performed to investigate electronic and elastic properties of the newly discovered 7.5 K superconductor: layered Nb₂InC. As a result, electronic bands, total and site-projected l—decomposed density of states at the Fermi level, shape of the Fermi surface for Nb₂InC were obtained for the first time. Besides, independent elastic constants, bulk modulus, compressibility, shear modulus, Young’s modulus, Poisson’s ratio together with the elastic anisotropy parameters and indicator of brittle/ductile behavior of Nb₂InC were evaluated and analyzed in comparison with the available data.