Phason strains on growth, stability and structure of icosahedral phases

Growth, stability and structure of icosahedral (i-) phases have been studied by electron diffraction and X-ray diffraction in relation with the phason strains. Three alloy systems; AlPdCr, AlPdMn and AlCuV were chosen in this study. An i- Al₇₂Pd₂₅Cr₃ grain has been analysed to have a phason matrix toward to a tetragonal or orthorhombic structure. Stability of the i-phases correlated with the phason relaxation was discussed in Al-Pd-Mn system. A quenched i-Al₇₄Pd₁₇Mn₉ close to but containing significant phason strains, revealed that the phason relaxation induced by precipitation of crystalline phases upon annealing. Phason disorder dominated by the chemical composition was evidenced in a composition study in Al-Pd-Mn system. A high density random phasons characterized the icosahedral glass phase was observed in AlCuV alloys.     

Magnetic and electric properties of the ternary alloys AB

The results of experimental studies of the electrophysical and magnetic properties of solid solutions based on the AB compounds with anion (Zn₃(P_xAs_1−x)₂ and cation (Zn_xCd_1−x)₃ P₂ substitution are reported. The Zn₃(As_xP_1−x)₂ solid solutions are characterized by p-type conductivity (∼ 10¹⁵  10¹⁷ cm⁻³), low Hall mobility and conductivity of ∼ 10⁻² — 10⁻³ ohm⁻¹ cm⁻¹. In the (Zn_xCd_1−x)₃P₂ solid solutions the samples rich in zinc are p-type, those rich in cadmium — n-type, the carrier concentration is ∼ 10¹⁶ — 10¹⁸ cm⁻³. From the measurements of the magnetic properties of the above mentioned alloys it is shown that in the investigated solid solutions a transition from the structure with direct optical transition to those with indirect optical transition occurs.     

Magnetic properties of liquid 3d transition metal–Si alloys

The magnetic susceptibility has been measured for liquid transition metal–Si alloys (TM_1−cSi_c, TM = Ni, Co, Fe, Mn) as a function of temperature. The magnetic susceptibilities of liquid Ni_1−cSi_c with c ⩾ 0.3, liquid Co_1−cSi_c with c ⩾ 0.4 and liquid Fe_1−cSi_c with c ⩾ 0.6 were found to be almost independent of temperature, which suggests that the Ni, Co and Fe ions on the Si side are in the non-magnetic state. Liquid Ni_1−cSi_c with c ⩽ 0.2, liquid Co_1−cSi_c with c ⩽ 0.3 and liquid Fe_1−cSi_c with c ⩽ 0.5 show the Curie–Weiss behavior with a reasonable value of effective Bohr magnetic number. Liquid Mn_1−cSi_c with c ⩽ 0.2 and c ⩾ 0.6 were found to be in their non-magnetic state. However, the Curie–Weiss behavior was observed for liquid Mn_1−cSi_c with c = 0.3, 0.4 and 0.5. The magnetic susceptibility of their liquid alloys in the non-magnetic state has been studied by using Anderson model. The density of 3d states at the Fermi level can be estimated from the data of magnetic susceptibility.     

Evaluation of the volume fraction of nanocrystals devitrified in Al-based amorphous alloys

An evaluation of fcc-Al volume fractions (V_f) in Al₉₀Ni₅Nd₅ and Al₈₅Ni₅Y₆Co₂Fe₂ nanostructured composites has been made by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) methods. For the Al₉₀Ni₅Nd₅ alloy, there exhibited lower V_f values obtained by DSC than that by XRD due to increased interface energy and the overlapping of primary crystallization and structural relaxation features during nanocrystallization process. For the Al₈₅Ni₅Y₆Co₂Fe₂ alloy, the V_f values calculated by both methods showed good agreements at low crystallinities, but apparent differences are observed at high crystallinities. This is due to compositional variations in the remaining amorphous matrix during devitrification.     

Experimental investigation of the atomic dynamics of amorphous and icosahedral alloys

Most recent results from the experimental investigation of the single particle dynamics and the collective atomic motions in amorphous metals and in icosahedral alloys using neutron inelastic scattering techniques are briefly presented. The extension of the dispersion curve of short wavelength collective motions into the first pseudo Brillouin zone by neutron Brillouin scattering and the investigation of crystal field excitations in an amorphous metal and its dependence on structural relaxation are discussed. Comparative studies of the atomic dynamics of polydomain icosahedral alloys, approximant polycrystals, and polycrystals with similar chemical composition but different structure are discussed. It is shown that the generalized vibrational density of states and the total dynamic structure factor of the icosahedral alloys investigated so far are rather different from any crystalline sample except for the case of higher order approximants with very large units cells.     

Effects of Nb on the formation of icosahedral quasicrystalline phase in Ti-rich Ti-Zr-Ni-Cu-Be glassy forming alloys

As-cast (Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈)_100−xNb_x (0 ? x ? 5) (Ф3) glassy forming alloys were investigated in order to clarify the role of Nb on the formation of icosahedral quasicrystalline phase (I-phase) in Ti-rich Ti-Zr-Ni-Cu-Be glassy system. It is found that an I-phase is formed in Ti-Zr-Ni-Cu-Be glassy alloy by addition of Nb element; however, the nucleation rate of I-phase increases, whereas the grain growth rate decreases with increasing Nb content. Moreover, with increasing Nb content, the thermal stability against crystallization increases, while the temperature range of stability of the I-phase decreases.     

Liquid properties of Pd-Ni alloys

Liquid properties of Pd-Ni metal alloys are computed by molecular dynamics (MD) simulation with the use of quantum Sutton-Chen potential (Q-SC) model. The thermodynamical, structural, and transport properties of the alloy are investigated. The melting temperatures for Pd-Ni system are predicted. The temperature and concentration dependence of diffusion coefficient and viscosity are reported. The transferability of the potential is tested by simulating the liquid state. The values of melting point are in excellent agreement with the experiment. Comparison of calculated structural and dynamical properties with the available experiments and other calculations shows satisfactory consistency.     

Twinning of quasicrystals and related crystals

Electron microscopy and electron diffraction have been employed to bring out the intimate relationship between icosahedral quasicrystal and various types of crystalline phases with emphasis on aluminium transition metal alloys. The relationship between quasicrystal and twinned rational approximant structures will be treated in the context of irrational twinning. The twinned aggregates show an icosahedral like symmetry in electron diffraction patterns. The crystallography of irrational twins has been discussed in terms of various ways of representing a twin relationship in a cubic lattice.     

Structural properties of liquid Fe-Si alloys

The atomic structure of liquid Fe-Si alloys within the whole concentration range (including pure components) was investigated at the temperature of 1550 °C by means of X-ray diffraction. Analysis of the reported data on physical properties of Fe-Si melts has been carried out. Interrelation between liquid-state structure and solid-state properties was considered. Fe-Si alloys in the liquid state are shown to be micro-inhomogeneous and they contain atomic micro-formations (clusters) that differ by atomic composition and packing. There are five types of clusters: two of them consist of atoms of one kind (Fe or Al); the composition of the other clusters depends on the stoichiometry of solid Fe₃Si, FeSi and Fe₂Si₅ phases. The entire concentration range of the Fe-Si system consists of four concentration intervals. Within each interval melts are constituted of the clusters of two kinds. The variation of the component concentrations in Fe-Si alloys results in changing of volume fraction of each type clusters, whereas the atomic composition and arrangement inside the clusters remains constant.     

Magnetic properties of amorphous metals

Neutron scattering has provided unique information about the nature of magnetism in amorphous alloys. This paper reviews some of the results obtained principally on two ribbon-form metallic glass systems - (Fe_xNi_1?x)₇₅P₁₆B₅Al₃ and Fe_xB_1?x. The former exhibits three states depending on composition: pure ferromagnetism, re-entrant spin glass, and ordinary spin glass. The neutron results provide evidence for the coexistence of spin glass and ferromagnetic correlations in the intermediate regime. The alloys of Fe and B show Invar phenomena which result in anomalously small values of the effective spin-wave stiffness calculated from low-temperature magnetization and Mössbauer data. The long-wavelength spin waves as measured by the neutrons do not reflect the rapid demagnetization found in the bulk results, implying the presence of excitation processes other than long-wave-length spin waves.     

GHz microwave properties of melt spun Fe-Si alloys

The structural and microwave properties of melt spun Fe_100−xSi_x (x = 10, 20, 30) nanocomposites were investigated. The phases varied with Si content in FeSi alloys. It is found that the Fe₃Si and FeSi phases could be obtained with Si content up to 20 at.%. The X-ray absorption fine structure (XAFS) spectra of Fe K-edges show that the local structures around Fe atoms in melt spun Fe-Si alloys become more disordered with increasing Si content when compared with that of α-Fe. The complex permittivity-frequency and permeability-frequency properties were determined in the microwave frequency regime of 2-18 GHz by vector network analysis. It is found that flake-like FeSi powder composite has the largest values of μ′ and μ″ at 2 GHz. The reflection loss shifts to the higher frequency with the Si content increasing for melt spun FeSi alloys. A minimum reflection loss of −16.5 dB is obtained at 13.9 GHz for composition Fe₇₀Si₃₀ with the thickness of 1.5 mm. However, for composition Fe₇₀Si₃₀, the minimum reflection loss shifts to lower frequency and larger value with the thickness increasing. The results suggest a new design for microwave absorbers based on electromagnetic wave-absorbing materials.     

Electronic properties of vitreous and liquid AsSe alloys (II). Liquid alloys

Conductivity and thermopower data of liquid AsSe alloys with the same compositions as the vitreous alloys discussed in paper I (30–50% As) are presented and analysed assuming that the liquids can be regarded as ‘hot’ amorphous solids. The limitations of such an approach, as shown by the thermopower results, are discussed and improvements, based on structural and bonding arguments, suggested.     

Magnetic properties of field annealed Ni-rich microwires

We report on the temperature evolution of the magnetic behavior of Ni-riched microwires obtained by the well-known Taylor–Ulitovsky method, with nominal compositions of Ni₈₀Si₆B₁₄ and Ni₇₈Si₈B₁₄, respectively. We study the Differential Scanning Calorimetry curves in the temperature range between RT to 600 °C, and the thermomagnetic evolution up to 800 °C at the two applied magnetic field values of 0.1 and 0.5 T for both, glass-coated microwires and uncovered microwires with the coating removed by selective etching in HF solution. We also correlate our measurements with magnetic domain pattern obtained by means of Bitter technique and RT VSM axial hysteresis loops. The evolutions of the magnetic and hysteresis properties for the as-quenched and annealed microwires are compared as a function of their thermo-magnetic history.     

Magnetic properties of TiCx/C nanocomposites

The magnetic properties of nanocrystalline titanium carbide dispersed in a carbon matrix (TiC_x/C) prepared by the non-hydrolytic sol–gel process have been studied by dc magnetization measurements. The superconducting phase of titanium carbide has been observed at low temperatures with the onset of the superconducting transition temperature T_c at about 3.5 K, superimposed on a ferromagnetic component. At T > T_c the magnetic response of TiC_x/C is determined by the interplay of the ferromagnetic contribution with the paramagnetic/diamagnetic signal of the metallic system and the contribution of exchange coupled paramagnetic ions. Moreover, significant differences are observed in the magnetic response for samples of the same preparation batch, indicative of the magnetic/electronic inhomogeneity of nanocrystalline titanium carbide which is important for its practical applications.     

Magnetic and magnetoimpedance properties of Mn-doped FINEMET

In this study, the effect of substituting Mn for Fe on the magnetic and magnetoimpedance (MI) properties of amorphous and nanocrystalline Fe_73.5?xMn_xCu₁Nb₃Si_13.5B₉ (x = 1, 3, 5, 7) alloys has been investigated. A higher Mn content causes a decrease in the saturation magnetization and Curie temperature. For as-received Fe_73.5?xMn_xCu₁Nb₃Si_13.5B₉ (x = 0, 1, 3, 5, 7) ribbons, the measured values of the MI are 11%, 12%, 16%, 12% and 15% for x = 0, 1, 3, 5, 7, respectively. The magnitude of the MI ratio increases in annealed samples, indicating that they are magnetically softened by nanocrystallisation. The change in MI is found to be ～70% for the x = 3 sample annealed at 550 °C. It is also found that replacing a small amount of Fe by Mn improves the magnetic softness of Fe_73.5?xMn_xCu₁Nb₃Si_13.5B₉ alloys.     

Chemical ordering and thermodynamic properties of HgNa liquid alloys

We have studied the thermodynamic properties and microscopic structures of HgNa liquid alloy at 673 K on the basis of regular associated solution model. The concentrations of ApB type complex in a regular associated solution of Hg and Na have been determined. We have then used the concentration of complex to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity, concentration fluctuations in long wavelength limit S_CC(0) and the Warren-Cowley short-range parameter α₁. The analysis suggests that heterocoordination leading to the formation of complex Hg₄Na is likely to exist in the liquid and is of a strongly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Hg-rich region.     

Synthesis and mechanical properties of Zr-based bulk amorphous alloys

Design and characterization of bulk amorphous alloys has been an active area of research due to their promising thermal and mechanical properties. An alloy composition Z₆₅Cu₁₇Ni₁₀Al₈ was designed and synthesized by Cu mold casting. In the base alloy 2 at.% Gd was added to study its effect on thermal and mechanical properties. Characterization of the alloys was done by techniques of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and field emission scanning electron microscopy (FESEM). Many thermal parameters were evaluated to investigate the thermal stability and glass-forming ability of the alloys. In addition, the mechanical properties like nanohardness, elastic modulus and elastic recovery were measured. Thermal properties and activation energy reduced while mechanical properties like nanohardness, elastic modulus and percentage elastic recovery (% R) increased with Gd addition.     

The electrical and optical properties of amorphous germanium-gallium alloys

The paper extends an earlier study of the far infrared properties of a series of evaporated amorphous GeGa alloys. The results of temperature dependent dc resistivity and near infrared and visible optical experiments are presented. Since the properties of amorphous films are dependent on the preparation conditions, a technique has been developed in which four samples of varying composition are prepared in the same evaporation. The far infrared data indicate that a significant fraction of Ga atoms dissolve in a-Ge with four-fold coordination. However, there is also indirect evidence of mixed valence.     

Electronic properties of liquid noble metal–Si alloys

The electrical resistivity, ρ, of liquid noble metal–Si alloys (M_1−cSi_c, M = Cu, Ag, Au) increases rapidly with the addition of Si to liquid noble metals. The composition dependence of ρ exhibits a maximum at the composition c = 0.3, 0.4 and 0.4 for liquid Cu–Si, Ag–Si and Au–Si, respectively. A positive to negative transition of thermoelectric power, S, is observed at c = 0.3, 0.15 and 0.1 for liquid Cu–Si, Ag–Si and Au–Si, respectively. Their composition dependence of S reaches a minimum value in the composition range c = 0.6–0.8. The experimental results of ρ and S have been analyzed using the Faber–Ziman theory. The composition dependence of χ for liquid Cu–Si and Au–Si alloys exhibits a clear deviation from a straight line on the noble metal-rich side. As a result, liquid Cu–Si and Au–Si alloys have a minimum in the composition dependence of paramagnetic susceptibility.