Microstructural analysis of Ga2S3–2MCl (M = K, Rb, Cs) glasses using Raman scattering

Raman scattering spectra of Ga₂S₃–2MCl (M = K, Rb, Cs) glasses have been conducted at room temperature. Based on the analysis of the local co-ordination surroundings of Cs⁺ ions, the similarities and differences of Raman spectra for the glass Ga₂S₃–2CsCl and the bridged molecular GaCl₃ were explained successfully. Through considering the effect of M⁺ ions on mixed anion units [GaS_4?xCl_x] and bridged units [Ga₂S_6?xCl_x] and the corresponding microstructural model, the Raman spectral evolution of the Ga₂S₃–2MCl (M = K, Rb, Cs) glasses was reasonably elucidated.     

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.     

Influence of Ta,Y substitutions on the thermal stability,microhardness and magnetic properties of melt spun Fe–B–Si amorphous alloys

In the present research work, thermal stability, magnetic properties and microhardness of Fe₇₂B_19.2Si_4.8M₄ (M = Ta or Y) amorphous ribbons obtained by chill block melt-spinning technique are reported. The crystallization temperatures resulted as high as 1129 K (for M = Ta) and of 1167 K (for M = Y), which indicate a considerable thermal stability for both alloys. On the other hand, the saturation polarization (μ₀M_s) together with the Curie temperature (T_c) also showed excellent combination of values, with 0.95 ± 0.12 T and 586 ± 8 K, respectively (for the Ta-containing alloy) and of 1.55 ± 0.18 T and 698 ± 6 K, respectively (for the Y-containing alloy). Additionally, the Vickers microhardness exhibited values over 1100 kg/mm² for both alloys.     

Electrical properties of A2.6+xTi1.4−xCd(PO4)3.4−x (A = Li,K; x = 0.0–1.0) phosphate glasses

Electrical properties of A_2.6+xTi_1.4−xCd(PO₄)_3.4−x (A = Li, K; x = 0.0–1.0) phosphate glasses are investigated over a frequency range from 42 Hz to 1 MHz at different temperatures. Impedance spectroscopy is used to separate the bulk conductivity from electrode effect of electrical conductivity data. The bulk dc conductivity is Arrhenius activated, with activation energies and pre-exponential factors following the Meyer–Neldel rule. The real part of ac conductivity shows universal power law feature. The variation of dielectric constant with frequency is attributed to ion diffusion and polarization occurring in the phosphate glasses. The frequency dependent imaginary part of electric modulus M″(ω) plot shows non-Debye feature in conductivity relaxation. The Kohlrausch–Williams–Watts stretched exponential function was used to describe the modulus spectra and the stretching exponent β is found to be temperature independent. Scaling in M″(ω) shows that the electrical relaxation mechanisms are independent of temperature for given composition at different temperatures.     

Bulk glassy (Fe0.474Co0.474Nb0.052)100 − x(B0.8Si0.2)x alloys prepared using commercial raw materials

The alloy compositions have been optimized by modifying the B and Si contents in (Fe_0.474Co_0.474Nb_0.052)_100 ? x(B_0.8Si_0.2)_x alloy system with commercial materials. The thermal stability of the supercooled liquid improves with the increased B and Si contents from x = 22 to 28. The composition of the alloy with x = 26 is close to a eutectic point. By copper mold casting, (Fe_0.474Co_0.474Nb_0.052)_100 ? x(B_0.8Si_0.2)_x bulk glassy alloys with diameters up to 5 mm were synthesized for the composition range of x from 22 to 28. In addition to high glass-forming ability (GFA), the (Fe_0.474Co_0.474Nb_0.052)_100 ? x(B_0.8Si_0.2)_x glassy alloys exhibit good soft magnetic properties as well, i.e., rather high saturation magnetization of 0.84–1.07 T, low coercive field of 1.8–3.2 A/m, high initial permeability of 10100–24100 at 1 kHz under a field of 1 A/m and Curie temperature of 620–730 K.     

Synthesis and characterization of bulk amorphous Zr65Cu18Ni9Al8 and [Zr0.65Cu0.18Ni0.09Al0.08]98Er2 alloys

Bulk metallic glasses (BMGs), especially Zr-based BMGs, have attracted lot of attention of materials scientists because of their very attractive physical, thermal and mechanical properties and a few unique applications. In the present study, Zr₆₅Cu₁₈Ni₉Al₈ alloy was designed according to the criterion of conduction electron/atom (e/a ratio) ∼1.395 and average atomic size of alloy (R_a) ∼0.1498 nm. Addition of 2 at.% Er was carried out in the base alloy to investigate its effect on thermal and mechanical properties. Characterization of alloys was performed using the techniques of XRD, DSC, and SEM/EDS. Mechanical properties like Vicker’s microhardness, nanohardness, elastic modulus, density and fracture strength were measured. Average shear angle was found to be ∼35 ± 1° for base alloy and about 31 ± 1° for alloy containing 2 at.% Er. Wide supercooled liquid regions of 129 K and 119 K were found for the base alloy and the alloy containing 2 at.% Er.     

Structure of molten Al–Si alloys

The temperature variation of the structure and microstructure of molten eutectic Al_1−xSi_x alloys (x = 0.122 and 0.20) have been studied by neutron diffraction and small-angle neutron scattering (SANS), as well as measurements performed on pure liquid Al. All measurements have been performed at five temperatures in a heating–cooling loop. The SANS results unambiguously show that for the eutectic alloy (x = 0.122) the microstructure changes with increasing temperature in a partly reversible way while for the hypereutectic (x = 0.20) alloy the change is almost completely irreversible. This change in microstructure also manifests itself in the shape of the static structure factor S(Q).     

Preparation and properties of chalcogenide glasses in the GeS2–Sb2S3–CdS system

In searching for new kind of photoelectric material, chalcogenide glasses in the GeS₂–Sb₂S₃–CdS system have been studied and their glass-forming region was determined. The system has a relatively large glass-forming region that is mainly situated along the GeS₂–Sb₂S₃ binary side. Thermal, optical and mechanical properties of the glasses were reported and the effects of compositional change on their properties are discussed. These novel chalcogenide glasses have relatively high glass transition temperatures (T_g ranges from 566 to 583 K), good thermal stabilities (the maximum of deference between the onset crystallization temperature, T_c, and T_g is 105 K), broad transmission region (0.57–12 μm) and large densities (d ranges from 2.99 to 3.34 g cm^?3). These glasses would be expected to be used in the field of rare earth doped fiber amplifiers and nonlinear optical devices.     

Mechanically alloyed multi-component Mo-based amorphous alloys with wide supercooled liquid region

A Mo₄₄Si₂₆Ta₅Zr₅Fe₃Co₁₂Y₅ multi-component amorphous alloy was developed via mechanically alloying (MA). It exhibits a record high glass transition temperature of 1202 K and crystallization temperature of 1324 K, an ultrahigh hardness of 18 GPa, as well as a wide supercooled liquid region (122 K) promising for processing through powder metallurgy routes. Here we present the details of the phase evolution during MA and discuss the effects of alloying elements, starting from the Mo–Co and Mo–Si binary systems, through two series of ternary alloys, eventually reaching the desired properties by selecting additional components. The propensity for glass formation and the high thermal stability were interpreted in terms of the negative heat of mixing of the elements introduced, as well as a uniform coverage spanning a wide range of atomic sizes.     

Effects of hydration,annealing, and melting on heat transport properties of fused quartz and fused silica from laser-flash analysis

Thermal diffusivity (D) at high temperature (T) was measured from 15 samples of commercial SiO₂ glasses (types I, II, and III with varying hydroxyl contents) using laser-flash analysis (LFA) to isolate vibrational transport, in order to determine effects of impurities, annealing, and melting. As T increases, D_glass decreases, approaching a constant (~ 0.69 mm²s^? 1) above ~ 700 K. From ~ 1000 K to the glass transition, the slope of D is small but variable. Increases of D with T of up to 6% correlate with either low water and/or low fictive temperature and are attributed to removal of strain and defects during annealing. Upon crossing the glass transition, D substantially decreases to 0.46 mm²s^? 1 for the anhydrous melt. Hydration decreases D_glass, makes the glass transition occur over wider temperature intervals and at lower T, and promotes nucleation of cristobalite from supercooled melt. Due to the importance of thermal history, a spread in D of about 5% occurs for any given chemical type. Combining prior steady-state, cryogenic data with our average results on type I glass provides thermal conductivity (k_lat = ρC_PD) for type I: k_lat increases from ~ 0 K, becoming nearly constant above 1500 K, and drops by ~ 30% at T_g. We find that D^? 1(T) correlates with thermal expansivity times temperature from ~ 0 K to melting due to both properties arising from anharmonicity.     

Na–Pb liquid alloy structure at low lead concentrations: Neutron-diffraction studies

Na–Pb liquid alloys with the lead concentration of 1.5 and 7.9 at.%, and pure sodium as a reference system are studied by neutron-diffraction at 700 K. A characteristic prepeak of static structure factor, S(Q), at Q ∼ 1.2 Å⁻¹, known from neutron-diffraction studies of the Na–Pb alloys with the lead concentration of 20 at.% and higher, is not observed for the alloys under consideration. The experimental S(Q) values are compared with the results of molecular-dynamics simulations.     

Molecular dynamics simulation of ternary glasses Li2S–P2S5–LiI

The structure of superionic glasses in ternary systems x(0.4Li₂S–0.6P₂S₅)–(1 − x)LiI and x(0.5Li₂S–0.5P₂S₅)–(1 − x)LiI (x = 0.9, 0.75) has been studied by molecular dynamics (MD) simulations. The configurations obtained by MD were analyzed by graph theory. Phosphorus is surrounded by sulfur and iodine atoms. Li is surrounded by sulfurs alone and LiI clusters are not present as speculated by earlier spectroscopic reports. The equilibrium configuration is made up of (Li, S) and (P, S, I) rich regions which creates wide channels for Li⁺ movement. Reported variations of glass transition temperature (T_g) and ionic conductivity (σ) with LiI addition are explained based on the simulation results.     

Effect of proton irradiation on electrical properties of a-As2S3

This paper reports the effect of proton irradiation on the electrical properties of a-As₂S₃ in the temperature range of 323–418 K and frequency range 0.1–100 kHz. The variation of transport property is studied with proton irradiation dose (1 × 10¹³ ions/cm² and 1 × 10¹⁵ ions/cm²). It has been observed that proton irradiation changes the dc conductivity (σ_dc), dc activation energy (ΔE_dc) and ac conductivity (σ_ac(ω)). The σ_dc and σ_ac(ω) increases with dose of proton irradiation. The value of frequency exponent (s) decreases with the temperature and irradiation dose. These results are explained in terms of change in density of defect states in these glasses.     

Investigation of directional solidified Al–Ti alloy

Al–1 wt% Ti alloy was directionally solidified upwards under argon atmosphere under the two conditions; with different temperature gradients (G = 2.20–5.82 K/mm) at a constant growth rate (V = 8.30 μm/s) and with different growth rates (V = 8.30–498.60 μm/s) at a constant temperature gradient (G = 5.82 K/mm) in a Bridgman furnace. The dependence of characteristic microstructure parameters such as primary dendrite arm spacing (λ₁), secondary dendrite arm spacing (λ₂), dendrite tip radius (R) and mushy zone depth (d) on the velocity of crystal growth and the temperature gradient were determined by using a linear regression analysis. A detailed analysis of microstructure development with models of dendritic solidification and with previous similar experimental works on dendritic growth for binary alloys were also made.     

Formation of bulk Pt–Pd–Ni–P glassy alloys

The thermal behavior of (Pt_0.4Pd_0.3Ni_0.3)_100−xP_x (x = 16–25 at.%) glassy alloys has been investigated. It is found that the crystallization behavior of the (Pt_0.4Pd_0.3Ni_0.3)_100−xP_x glassy alloys changes from a single-stage exothermic reaction to a two-stage exothermic reaction depending on phosphorous content. When the phosphorous content is 23 at.%, the glassy alloy exhibits the largest supercooled liquid region (ΔT_x) and a sharp single exothermic peak. Fixing the phosphorous content at 23 at.%, the Pt_77−x−yPd_xNi_yP₂₃ (x = 7.7–61.6 at.%, y = 7.7–61.6 at.%) glassy alloys have a wide composition range in which the glassy alloys exhibit a large supercooled liquid region (ΔT_x beyond 60 K). In this range, the Pt_30.8Pd_23.1Ni_23.1P₂₃ glass has the largest ΔT_x (77 K) and a high reduced glass transition temperature (T_rg) of 0.60. This alloy can be cast into fully glassy rods with a diameter of 3 mm. Under uni-axial compression, bulk Pt_30.8Pd_23.1Ni_23.1P₂₃ glassy alloy has an elastic strain of ∼2%, an ultimate strain (to fracture) of ∼6.4%, a Young’s modulus of ∼106 GPa and a failure strength of ∼1390 MPa.     

Transport properties near the magneto/structural transition of Tb5Si2Ge2

We report high resolution measurements of the electrical resistivity (ρ, dρ/dT) and thermopower (S, dS/dT) measurements near the magnetic and structural transition of the layered Tb₅Si₂Ge₂ compound, which are fairly close but not fully coupled. The analysis of the transport properties confirms a split magneto/structural transition, with T_S ～ 97 K and T_S ～ 107 K for the structural transition (on cooling and heating respectively; 1st-order transition). The magnetic transition occurs only at T_C ～ 112 K and without hysteresis (2nd-order transition). The magnetic critical behavior of resistivity is analyzed, obtaining an almost classical mean field exponent (α ～ 0.59) for T > T_C. For the structural phase, and below T_S, we obtain a rather different exponent (α ～ 1.06).     

Thermodynamic prediction of bulk metallic glass forming alloys in ternary Zr–Cu–X (X = Ag,Al, Ti,Ga) systems

Prediction of bulk metallic glass (BMG) forming compositions has always been a challenge due to thermodynamic and kinetic constraints. In the present investigation, a parameter based on the enthalpy of chemical mixing (?H_chem) and the mismatch entropy (?S_σ/k_B) has been used to correlate with glass forming ability in some Zr based BMGs. The new thermodynamic parameter, P_HS = ?H_chem × ?S_σ/k_B, is found to have strong correlation with glass forming ability in the configurational entropy (?S_config/R) range of 0.9–1.0. P_HS has been calculated for compositions in Zr–Cu–Ag, Zr–Cu–Al, Zr–Cu–Ti and Zr–Cu–Ga ternary systems. It is observed that in all the systems studied, the best BMG composition (highest critical diameter (Z_c) of glass formation) is the one that corresponds to the highest negative P_HS value. Present approach using P_HS could be road map to design new BMG forming compositions.     

Dominance of magnetic scattering in the electrical-transport of Al70.5Pd22Mn7.5 icosahedral quasicrystal

Conductivity vs. temperature (σ–T) at zero and 8-T field, magneto-resistance (Δρ/ρ), magnetization vs. temperature (M–T) and magnetization vs. field (M–H) of Al_70.5Pd₂₂Mn_7.5 quasicrystal have been studied in the temperature range of 1.4 K to 300 K. The σ–T variations in both the field conditions show a σ–T minima. In addition to this the σ–T variation at 8 T shows a maxima also at ∼6 K. Comparative analysis shows that the observed σ–T minima arises due to competing inelastic scattering events in the presence of weak-localization effect. These events are e–ph scattering in the dirty-metallic limit (τ_i ∝ T⁻²), and the Kondo-type spin-flip scattering (τ_sf). The maxima observed for the σ–T variation at 8 T, has been attributed to suppression of the spin-flip scattering in the presence of field. The magneto-resistance is found to be large and positive. It was properly accounted only when the Stoner-enhancement, found in the case of spin fluctuating systems, was taken into consideration.     

Magnetic and transport studies of σ-phase Fe50V50 alloys with different thermal history

The influence of the formation conditions of the sigma phase in an equiatomic FeV alloy on the magnetic and electric transport properties is studied. It is found that a sigma phase sample with higher resistivity (subject to a previous long annealing) has a much sharper magnetic transition than one formed after a shorter heat treatment and quenching, although both have very similar magnetic moments and ferromagnetic transition temperatures (T_c ～ 15 K from minimum dM/dT).     

Characterization of Eu3+-doped fluorophosphate glasses for red emission

Fluorescence spectra and decay curves of the ⁵D₀ level for different concentrations of Eu³⁺ (4f⁶) ions in K–Ba–Al fluorophosphate glasses have been measured at room temperature and are analyzed. The Judd–Ofelt intensity parameters Ω₂ and Ω₄ have been determined from the intensity ratios of emission peaks corresponding to ⁵D₀ → ⁷F_J (J = 2 and 4) to ⁵D₀ → ⁷F₁ transitions for 1.0 mol% glass. The intensity parameters thus obtained are in turn used to calculate the radiative properties of the fluorescent levels of Eu³⁺ ions. Second and fourth rank crystal-field parameters have been evaluated by assuming a C_2V site symmetry for the local environment of Eu³⁺ ions to estimate the crystal-field strength experienced by Eu³⁺ ions in the present host. The decay profiles of the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions in the present glasses are found to be single exponential for all the studied Eu³⁺ ion concentrations. A marginal increase in lifetime of the ⁵D₀ level has been noticed with Eu³⁺ ion concentration up to 2.0 mol% and then the lifetime marginally decreases for higher Eu³⁺ ion concentrations.