Length and density changes of amorphous Pd40Cu30Ni10P20 alloys due to structural relaxation

The density changes of bulk amorphous Pd₄₀Cu₃₀Ni₁₀P₂₀ due to structural relaxation under isothermal heat treatment were measured using the buoyancy method. The corresponding length changes of amorphous Pd₄₀Cu₃₀Ni₁₀P₂₀ ribbons applying non-isothermal heat treatment are determined applying dilatometry. The measured density changes Δρ(T=const.,t)/ρ_o as a function of isothermal heat treatment increase close to the glass transition up to 0.18%. The measured density changes as a function of temperature and time are furthermore reversible. The experimental data validate the model predictions of the free volume model for length and density changes of amorphous alloys due to structural relaxation applying isothermal and non-isothermal heat treatment.     

Diffusion and viscosity in molten Pd40Ni40P20 and Pd40Cu30Ni10P20 alloys

The self diffusion of ⁶²Ni and the shear viscosity in liquid Pd₄₀Ni₄₀P₂₀ and Pd₄₀Cu₃₀Ni₁₀P₂₀ have been measured. The used methods were the long-capillary technique for diffusion measurement and the gas-film-levitation for viscosity measurement. The temperature dependence of diffusion in the equilibrium melt follows the prediction of the mode-coupling theory. The Stokes-Einstein relation describes well the momentum and mass transport in both melts. The ⁶²Ni diffusion is equal in both alloys whereas the normalized bulk viscosity is higher in Pd₄₀Cu₃₀Ni₁₀P₂₀. Thermodynamic and structural considerations are invoked to propose a qualitative explanation for this behavior.     

Thermally modulated differential scanning calorimetry of a glass of composition 45Na2O-40B2O3-10Al2O3-5In2O3

The kinetics of structural relaxation and of glass transition of the 45Na₂O-40B₂O₃-10Al₂O₃-5In₂O₃ glassforming melt is studied by means of standard DSC and of temperature modulated DSC. In this way the dependence of the fictive temperature on cooling rate is determined simultaneously with the determination of the dependence of the dynamic glass transition temperature on modulation frequency. Both sets of data are fitted together in terms of the equation of Ritland-Bartenev. It was found that the activation energy of the structural relaxation exhibits a moderate dependence on temperature with the dimensionless fragility parameter α=3.3 (for strong systems, α is about 1 and increases to about 8 for some very fragile polymeric systems).     

Boron-doped a-SiOx:H films prepared by photo-CVD technique

The optoelectronic and structural properties of p-type a-SiO_x:H films have been studied. The deposition parameters e.g. chamber pressure and diborane to silane ratio are optimized to get a film with dark conductivity (σ_d) 7.9×10⁻⁶ S cm⁻¹ and photoconductivity 9.3×10⁻⁶ S cm⁻¹ for an optical gap (E₀₄) of 1.94 eV. The decrease of optical gap accompanied by the increase of conductivity is due to less oxygen incorporation in the film, which is substantiated by the decrease of the intensity of SiO absorption spectra. The properties are very much effected by the chamber pressure and diborane to silane ratio.     

Glass-forming ability and crystallization of bulk metallic glass (HfxZr1−x)52.5Cu17.9Ni14.6Al10Ti5

We have produced a series of bulk metallic glasses of composition (Hf_xZr_1−x)_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (with x=0-1) by an arc melting/suction casting method. The density of these alloys increases by nearly 67% with increasing Hf content from 6.65 g/cm³ (x=0) to 11.09 g/cm³ (x=1). Over the same composition range the glass-forming ability decreases, as demonstrated by the size of the largest amorphous ingots that can be cast without crystallization. Although both the glass transition temperature and the melting temperature increase linearly with increasing Hf content, the reduced glass transition temperature (T_g/T_m) decreases, from 0.64 (x=0) to 0.62 (x=1), which suggests that the `confusion principle' correlating increased glass-forming ability with increased number of components, does not apply in this case due to the chemical similarity between Zr and Hf. A different crystallization behavior is observed for Zr-based and Hf-based glasses. The final crystalline phases are CuZr₂ and Zr₂Ni for Zr-based alloys, and Al₁₆Hf₆Ni₇ and CuHf₂ for Hf-based alloys.     

The kinetics of structural relaxation of bulk and ribbon glassy Pd40Cu30N10P20 monitored by resistance and density measurements

Density and in situ high precision electrical resistance measurements on bulk and ribbon glassy Pd₄₀Cu₃₀Ni₁₀P₂₀ in the initial state, after cold rolling and quenching from the supercooled liquid state are performed. Three relaxation stages resulting in different signs of the electrical resistance relaxation are determined. It is shown that the resistance change upon structural relaxation is predominantly controlled by the resistivity relaxation while the volume change has a minor effect on the resistance. Cold rolling has a complex impact on the electrical relaxation similar to the effect of plastic deformation on the dislocation anelasticity in crystals. Quenching of fully relaxed samples from the supercooled liquid state recovers structural relaxation and the amount of the resistance relaxation can be several times bigger than that in the initial state. It is concluded that relaxation of the electrical resistance as dependent on different conditions (bulk/ribbon samples, thermocycling, rolling and the parameters of quenching from the supercooled liquid state) is rather complex but it is unlikely that the degree of the relaxation is governed by the amount of the free volume. This conclusion agrees with the established fact of equal density of initial glassy and crystallized bulk samples and earlier findings of nearly equal shear viscosity of bulk and ribbon samples different by four orders of magnitude in the production quenching rate.