Influence of phonon focusing on the Knudsen flow of phonon gas in single-crystal nanofilms of spintronic materials

Influence of the anisotropy of elastic energy on the phonon transport has been investigated in single- crystal nanofilms of Fe, Cu, MgO, InSb, and GaAs materials used for spintronic instruments and devices in the Knudsen flow regime of phonon gas. The dependences of the lattice thermal conductivity and lengths of free paths of phonons for all acoustic modes on the geometric parameters of the films have been considered for low temperatures with the dominance of the diffuse scattering of phonons at the boundaries. Physical aspects of the propagation of phonon modes in the films have been analyzed. It has been shown that the anisotropy of phonon transport in single-crystal films is due to the features of the propagation of phonon modes in elastically anisotropic films with a different relationship of the geometric parameters. The directions of heat flow and orientations of the film planes that yield the maximum and minimum thermal conductivity of phonons in film planes have been determined.     

Thermal conductivity of electron-doped CaMnO3 perovskites: Local lattice distortions and optical phonon thermal excitation

The thermal transport properties of a series of electron-doped CaMnO₃ perovskites have been investigated. Throughout the temperature range 5–300 K, phonon thermal conductivity is dominant, and both electron and spin wave contributions are negligible. The short phonon mean free paths in this system result in the relatively low thermal conductivities. The strong phonon scatterings stem from the A-site mismatch and bond-length fluctuations induced by local distortions of MnO₆ octahedra. The thermal conductivity in the magnetically ordered state is enhanced as a result of the decrease in spin–phonon scattering. The results also indicate that above the magnetic ordering temperature, observable thermal excitation of optical phonons occurs. The contribution of optical phonons to thermal conductivity becomes non-negligible and is proposed to play an important role in the glass-like thermal transport behavior (i.e. positive temperature dependence of the thermal conductivity) in the paramagnetic state. These features can be understood in terms of an expression of thermal conductivity that includes both acoustic and optical phonon terms.     

Filler-reduced phonon conductivity of thermoelectric skutterudites: Ab initio calculations and molecular dynamics simulations

The phonon conductivities of CoSb₃ and its Ba-filled structure Ba_x(CoSb₃)₄ are investigated using first-principle calculations and molecular dynamics (MD) simulations, along with the Green–Kubo theory. The effects of fillers on the reduction of the phonon conductivity of filled skutterudites are then explored. It is found that the coupling between filler and host is strong, with minor anharmonicity. The phonon density of states and its dispersion are significantly influenced by filler-induced softening of the host bonds (especially the short Sb–Sb bonds). Lattice dynamics and MD simulations show that, without a change in the host interatomic potentials, the filler–host bonding alone cannot lead to significant alteration of acoustic phonons or lowering of phonon conductivity. The observed smaller phonon conductivity of partially filled skutterudites is explained by treating it as a solid solution of the empty and fully filled structures.     

Optical and acoustic phonon modes confined in gallium phosphide nanoparticles

The main aim of this paper is to discuss the confinement effects on the optical and acoustic phonon vibrational modes in gallium phosphide(GaP) nanoparticles(cylindric grain).The Raman scattering from the GaP nanoparticles was investigated.It was found that the red-shifts of the longitudinal optical(LO) mode and transverse optical(TO) mode were 15 cm?1 and 13.8 cm?1,respectively.It is generally accepted that the red-shifts of the optical phonon modes are due to the presence of smaller nanosized particles(～1.2 nm) acting as the nanoclustered building blocks of the GaP nanoparticles.In the low frequency Raman spectrum,a set of Stokes lines with almost the same spacing was clearly observed.The scattering feature originates from the discrete phonon density of states of the nanoclustered building blocks.According to Lamb's vibrational theory,the Raman shift wavenumbers of the spheroidal mode and torsional mode of the lowest energy surface modes for the nanoclustered building blocks were calculated.Good agreement can be achieved between the calculated results and the observed scattering peaks.These results indicate that the corresponding Raman peaks are due to scattering from the localized acoustic phonons in the nanoclustered building blocks in the GaP nanoparticles.     

Density functional study of the mechanical and phonon properties of Al12X (X = Mo,Tc, Ru,W, Re,and Os) compounds

By means of first principles calculations, we have studied the structural, elastic, and phonon properties of the Al₁₂X (X = Mo, Tc, Ru, W, Re, and Os) compounds in cubic structure. The elastic constants of these compounds are calculated, then bulk modulus, shear modulus, Young's modulus, Possion's ratio, Debye temperature, hardness, and anisotropy value of polycrystalline aggregates are derived and relevant mechanical properties are compared with the available theoretical ones. Furthermore, the phonon dispersion curves, mode Grüneisen parameters, and thermo-dynamical properties such as free energy, entropy and heat capacity are computed and the obtained results are discussed in detail.     

异步轧制对高纯铝箔冷轧织构的影响

通过异步轧制，对高纯铝箔微取向流变行为进行了研究，结果表明，异步轧制与同步轧制的冷轧织构有较大差异，高纯铝箔在异步轧制下慢辊和快辊两侧的织构类型明显不同，尤其是旋转立方织构{001}{110}在含量上的差异更大，快辊侧随形变量的增中冷却织构主要为：S织构和{102}{uvw}织构，而慢辊侧则主要为：旋转立方织构{001}{110}，慢辊侧的旋转立方织构在相同的速比、相同的形变量下一般要大于快辊侧的旋转立方织构。     

Structural and thermoelastic properties of CaTiO3 perovskite between 7 K and 400 K

The structural and thermoelastic properties of CaTiO₃ perovskite have been studied using high-resolution powder neutron diffractometry at eighty temperatures in the range 7-400 K. The temperature variation of the unit cell volume, the thermodynamic Grüneisen parameter and the isobaric heat capacity are analysed using a two-term Debye model. Structural parameters are presented as the magnitudes of symmetry-adapted basis-vectors of seven normal modes with wavevectors that lie on the surface of the Brillouin zone of the primitive cubic aristotype phase, and a structural basis for the temperature-dependence of the bond lengths is proposed. A consistency between the vibrational Debye temperatures derived from the atomic displacement parameters and the mean values of the vibrational energies of the three atomic species calculated from the partial phonon densities of states has been found.     

异步轧制高纯铝箔冷轧织构沿板厚的分布规律

通过异步轧制，研究了高纯铝箔冷轧织构沿板厚的分布规律。在异步轧制下，快、慢速辊侧之间的各中间层的织构类型不同。速比为1．28，形变量为99．2％时，随厚度的增加，呈现出极有规律的变化：（100）丝织构含量近线性减少，而（112），（102），（123）丝织构含量近线性增加。当形变量为99．2％时，在不同速比下（400）丝织构含量沿厚度变化趋势不同：速比1．28时，呈现出近线性递减；速比1．17和1．06时，总的趋势也是递减，且在厚度d＝0．04mm处有最小值。     

CeO2的晶格动力学性质和热输运性质的第一性原理计算

采用基于密度泛函理论的有限位移法和玻尔兹曼方程,计算了CeO2的晶格动力学性质、热力学性质和热输运性质,计算结果和实验结果基本符合。通过分析CeO2所有声子模式的振动频率、Gruneisen系数和散射率,揭示了光学声子对增强晶格振动的非简谐性和声子散射率所起的重要作用。此外,还计算了不同自由程的声子模式对热导率的贡献,发现CeO2的晶格热导率主要由声子自由程在1~10 nm之间的声子所贡献。     

Texture Evolution Behavior and Its Triggered Mechanical Anisotropy of CP Ti During Severe Cold Rolling and Subsequent Annealing

The texture evolution behavior and its triggered mechanical anisotropy of commercially pure titanium(CP Ti) during severe cold rolling and subsequent annealing are discussed based on the optical microscopy and the electron backscattered diffraction analyses. Some enlightening results are found. It is shown that planar textures exist under all treatments, namely the {11–29}10–10 under rolling state, the {11–27}10–10 under 300 °C annealing state and the {11–24}10–10 under 500 °C annealing state. This indicates that the crystal plane indices of planar texture change toward {-12–10} with increasing annealing temperature, which is a result of crystal lattice rotation. Planar texture triggers anisotropy of the mechanical properties for CP Ti sheets under all treatments. In particular, CP Ti sheets exhibit severe and similar anisotropy behavior under rolling and 300 °C annealing states. Generally speaking, the rolling direction(RD) specimens get relatively low yield strength, high ultimate tensile strength and good plasticity, and RD + 45° specimens show relatively high yield strength, low ultimate tensile strength and good plasticity. The transverse direction specimens, however, usually exhibit high yield strength and low plasticity. It is proved that the above anisotropy behavior is mainly determined by the Schmid factor distribution of the(10–10)[11–20] prismatic slip system in different directions. Due to the non-negligible influence exerted by the(0001)[11–20] basal slip system after 500 °C annealing, the anisotropy behavior under this state is obviously different.     

Resonance properties of magnetically anisotropic films with various anisotropy dispersion

On the basis of a statistical model of noninteracting blocks, there is carried out an analysis of the specific features of the spectrum of ferromagnetic resonance in polycrystalline metallic magnetic films, which are connected with the presence of cubic crystallographic anisotropy and induced uniaxial magnetic anisotropy, and also with the presence of an angular dispersion of the crystallographic anisotropy. It is shown that the allowance for the angular dispersion of magnetic anisotropy leads to an asymmetry and a broadening of the integrated resonance curve and also to characteristic angular dependences of the resonance field and of the resonance linewidth.     

Short-circuit diffusion in an ultrafine-grained copper–zirconium alloy produced by equal channel angular pressing

Many unusual properties of ultrafine grain materials obtained by equal channel angular pressing (ECAP) are commonly attributed to non-equilibrium grain boundaries. Such grain boundaries are expected to exhibit higher values of energy, higher amplitude of strain fields, a larger free volume and a higher diffusivity than their relaxed counterparts. In the present study, the diffusivity of ⁶³Ni radiotracer in ECAP-processed Cu–0.17 wt.% Zr alloy was measured in the low-temperature range of 150–350 °C under conditions at which no bulk diffusion occurs. The microstructure observations after annealing indicate that alloying with Zr is essential for stabilizing the ECAP-processed alloys against grain growth and recrystallization. In all samples studied the experimentally measured diffusion profiles exhibited two distinct slopes, which are associated with “slow” and “fast” short-circuit diffusion paths. The diffusivity of “slow” diffusion paths in the ECAP-processed samples coincides with the diffusivity via relaxed grain boundaries in the coarse grain Cu measured by the same radiotracer method at similar temperatures. We associate the “fast” diffusion paths observed in this study with the non-equilibrium grain boundaries produced by ECAP.     

Textures variation of 3104 aluminum alloy sheets under different rolling conditions

1　INTRODUCTIONLargequantityoftheAl Mn Mgalloy 310 4isusedinthemanufactureofaluminumbeverage .Muchattentionwaspaidtothecontroloftextureandearinginthedeepdrawingstagesofmanufacture .Thetex tureinthecanstockwasextensivelyinvestigated .Oneearingofaluminumalloyisverycloserelatedtothetexture ,agoodassociationofthetexturescompo nentsearingdropsobviously ,inthissituationthe 4 foldearingat 0°/90°andearingat± 4 5°occursto gether[15] .Theappearanceof 4 foldearingat 0°/90°isduetothecubetext…     

Reflection and refraction of acoustic waves at the boundary between the ferromagnetic Heusler alloy and liquid

Reflection and refraction of quasi-longitudinal and quasi-transverse acoustic waves at a flat interface between a liquid and a ferromagnetic crystal of the Heusler alloy Ni_{2 + x + y} Mn_{1 ? x} Ga_{1 ? y} (in the region of its premartensitic and martensitic phase transitions) is considered. The directions of propagation and polarization and the amplitude of reflected quasi-longitudinal and quasi-transverse and of transmitted longitudinal waves in the (110) plane of the crystal are determined. In a wide region of phase transformations of this alloy, the possibility is shown of using temperature to efficiently control the angles of reflection and refraction of wave modes and the coefficients of their conversion due to a colossal acoustic anisotropy of the crystal. Beginning from a certain critical angle of the quasi-transverse wave, the quasi-longitudinal wave arising upon reflection acquires the nature of the accompanying surface vibration and at a large proximity to phase transition can be emitted into the bulk of the crystal. On the basis of the available experimental data for Ni₂MnGa crystals, numerical estimations of the above acoustic effects have been carried out.     

铝合金板织构组分单晶屈服轨迹计算

织构单晶体组分研究是分析多晶体板材塑性各向异性的基础。文章利用晶体学屈服函数CMTP方法,结合塑性力学知识计算得到6个常见单晶体织构组分产生的屈服轨迹形状,分析织构组分对板材各向异性影响,结果表明,6种织构组分在不同拉伸坐标系中产生的单晶屈服轨迹呈多边形或椭圆形,并随散布宽度增加而扩大。{001}<100>织构组分有利于多晶体板材产生各向同性,{123}<634>织构组分则易于形成各向异性。     

Heating rate effects during non-isothermal annealing of AIK steel

The effects of heating rate on microstructural size and shape parameters during annealing of cold rolled aluminum killed steel strips have been examined under non-isothermal condition. It is shown that decrease in the heating rate results in accelerated grain growth behavior compared with the prediction by quasi-isothermal based kinetics. The {111} and {112} crystallographic orientations, which enhance the normal anisotropy and deep drawability of cold rolled annealed sheets, are found to exhibit a strong correlation with the grain shape anisotropy. This grain shape anisotropy itself is strongly dependent on heating rates. Lower heating rates result in higher aspect ratios and thus better drawability of the cold rolled sheets. A Hall-Petch type relationship is observed between grain size and hardness of the annealed samples.     

Thermodynamic functions from lattice dynamic of KMgH3 for hydrogen storage applications

The dynamic and the thermodynamic properties of KMgH₃ have been investigated by density functional theory (DFT). We have found that the calculated lattice parameters differ from the experimental data by less than 0.6% and the electronic density of states (DOS) reveals that the KMgH₃ is an insulator. The formation energy of KMgH₃ from binary hydrides (MgH₂ and KH) has been calculated. Using density-functional perturbation theory, we have calculated the phonon dispersion curves, the phonon density of states, the Born effective charge tensors, the dielectric permittivity tensors and the phonon frequencies at the center of the Brillouin zone of KMgH₃. Also we have assigned the calculated phonon frequencies at the gamma point for Infrared-active and Raman-active modes. For the first time, the thermodynamic functions are computed using the phonon density of states.     

In-plane anisotropy of 1545 aluminum alloy sheet

1　INTRODUCTIONThe in plane anisotropy of mechanical proper ties brings the limitation to the use of alloy sheet.At the same time, during the material processing,the difficulties of contour machining will also be in creased. For this reason, when designing high performance aluminum alloy sheets, the in planeanisotropy is an important performance parameterthat must be considered. Studies have shown thatminor Sc and Zr in the Al Mg Mn alloy can refinegrains of cast ingot, inhib…     

密排六方金属的塑性变形

综述了密排六方金属可能的滑移和孪生变形方式。滑移面包括：（０００１）基面，（１１００）柱面和〈ｃ〉型及〈ｃ＋ａ〉型锥面。（１０１２）、（１１２１）和（１１２２）是其主要的孪生类型，在Ｔｉ和Ｚｒ中还可能出现（１０１１）、（１１２４）和（１１２３）型孪晶。进一步分析了塑变过程中滑移和孪生之间的关系。着重讨论了Ｔｉ和Ｚｒ的滑移方式与试验温度之间的关系，其滑移面开动按由易到难的排列顺序为：柱面、锥面和基面     

Role of mechanical strain on thermal conductivity of nanoscale aluminum films

Thin film components of conventional and flexible solid-state devices experience mechanical strain during fabrication and operation. At the bulk scale, small values of strain do not affect thermal conductivity, but this may not true for grain sizes comparable with the electron and phonon mean free paths and for higher volume fraction of grain boundaries. To investigate this hypothesis, thermal and electrical conductivity of nominally 125-nm-thick aluminum films (average grain size 50 nm) were measured as functions of tensile thermo-mechanical strain, using a modified version of the 3-ω technique. Experimental results show pronounced strain–thermal conductivity coupling, with ～50% reduction in thermal conductivity at ～0.25% strain. The analysis shows that mechanical strain decreases the mean free path of the thermal conduction electrons, primarily through enhanced scattering at the moving grain boundaries. This conclusion is supported by similar effects of mechanical loading observed on the electrical conduction in the nanoscale aluminum specimens.