Pressure-Induced Structural Relaxation in AmorphousPd40Ni40P20: The Form

Abstract

Structural relaxation induced by hydrostatic pressure is experimentally observed for the metallic glass Pd 40 Ni 40 P 20 . The pressure dependence of the structural state is displayed in the shape of the glasstransition peak that is measured by means of differential scanning calorimetry after annealing treatments at 563 K and pressures up to 0.75 GPa. Quantification of the effect using the free-volume theory yields a formation volume of 5.9 6 0.5 Å 3 for defects in this glass. In combination with the previously determined pressure dependence for the Au diffusivity, a value of 5 6 4 Å 3 is derived for the migration volume for Au diffusion. [S0031-9007(97) PACS numbers: 61.43. Dq, 61.72.Hh, 62.50. + p, Structural relaxation in metallic glasses under the influence of an elevated temperature is a well-known phenomenon that has been widely studied (e.g., [1]). Within the amorphous structure, changes occur that lead to significant changes in physical properties, which are particularly pronounced in the atomic-transport properties viscosity and diffusivity [2]. Although pressure, similar to temperature, is liable to induce structural relaxation as well, experimental studies of pressure-induced structural relaxation are very few [3]. The pressure dependence of the structural state of metallic glasses is particularly of interest when regarding the diffusion process, since it can give insight into the formation volume for defects. Combined with the pressure dependence of the diffusivity, which yields the so-called activation volume, the migration volume for diffusion can also be derived. A separate determination of these two quantities adds to the understanding of the diffusion process.In the present Letter the phenomenon of structural relaxation induced by pressure will be investigated for the metallic glass Pd 40 Ni 40 P 20 . Experimental evidence obtained by means of differential scanning calorimetry (DSC) after annealing samples at hydrostatic pressures up to 0.75 GPa directly shows the occurrence of pressureinduced structural relaxation. The state of relaxation that is reached during these treatments is quantified by means of the free-volume theory [2,4]. This results in the determination of the formation volume for defects in amorphous Pd 40 Ni 40 P 20 . Combining the result with the pressure dependence of the diffusivity of gold determined previously on the same samples [5] yields a quantitative estimate for the migration volume for diffusion of Au in amorphous Pd 40 Ni 40 P 20 as well.Experiments were performed on a set of amorphous Pd 40 Ni 40 P 20 ribbons, being the very ribbons on which previously the pressure effect of the diffusivity has been measured [5]. The ribbons were first brought in metastable equilibrium, without inducing crystallization, by annealing at ambient pressure and a temperature of 563 K during 10 000 s. Under these conditions equilibrium is reached in approximately 5000 s [6]. Subsequently, the samples were annealed for 43 200 s at 563.0 6 0.1 K and hydrostatic pressures up to 0.75 GPa ͑60...

Crystallization in Pd40Ni40P20 glass

“…On the basis of our experiments, it might be true that phosphorus evaporation from the surface causes the monoclinic phase to become unstable so that it starts to decompose into phases 5 and 4 in the samples annealed in vacuum and Ar. Ruitenberg et al 31 observed pressure-induced structural relaxation in a Pd 40 Ni 40 P 20 ribbon glass. Structural relaxation might also affect the crystallization process of the glass.…”

Change of Compressiblity at the Glass Transition and Prigogine-Defay Ratio in ZrTiCuNiBe Alloys

“…From previous papers [16,17], we know that this procedure will bring the sample to an enthalpic state very close to a supercooled liquid, if it is observed on a long time scale. In other words, due to the long annealing procedure the sample relaxes into an enthalpic state that is equivalent to a state obtained after a long time scale cooling rate experiment.…”

“…No crystallization of any kind was observed in any of the samples. Differential scanning calorimetry (DSC) was performed at ambient pressure in a DSC 7 (Perkin-Elmer) under constant heating rate using a small piece of the processed material.In several recent papers, it has been shown [16,17] that the relaxation state of glassy material can be monitored by the peak height of the heat flow at the glass transition during heating at a constant heating rate. The enthalpy recovery crossing from a nonergodic to an ergodic state indicates the amount of relaxation that has taken place at T g or below.…”

“…In several recent papers, it has been shown [16,17] that the relaxation state of glassy material can be monitored by the peak height of the heat flow at the glass transition during heating at a constant heating rate. The enthalpy recovery crossing from a nonergodic to an ergodic state indicates the amount of relaxation that has taken place at T g or below.…”

Pressure effect of glass transition temperature in Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk metallic glass

“…2 For metallic systems, rare experimental data of T g vs pressure have been reported. Samwer et al 4 reported an increase of T g with pressure of 3.6 K/GPa for a Zr 46.8 Ti 8.2 Cu 7.5 Ni 10 Be 27.5 bulk metallic glass by an indirect enthalpy recovery method, 5 in which ambient-pressure differential scanning calorimetry ͑DSC͒ measurements of samples annealed under pressure were carried out. In this letter, we report a direct method, based on in situ hightemperature and high-pressure x-ray powder diffraction ͑XRD͒ measurements using synchrotron radiation, for studying the glass transition temperature under high pressure ͑above 1 GPa͒.…”