Papers by Keyword: Self-Diffusion

Abstract: Self-diffusion of nickel and manganese has been investigated by the radiotracer technique in Ni50Mn50 alloys over a wide temperature range. Experiments were performed on disordered fcc, B2 and L10 structure phases present in the equiatomic alloy at high, intermediate, and low temperatures, respectively. The diffusivity of manganese was found to be significantly faster (factor 3 to 5) than that of nickel in the fcc and B2 phases. More than one order of magnitude diffusivity increase was observed upon the transition from the higher temperature fcc to the intermediate temperature B2 phase. The activation enthalpy from nickel self-diffusion in the disordered fcc phase is significantly higher than the corresponding value for manganese. In the B2 phase there is only a slight difference between the activation enthalpies of the components, which indicates a coupled diffusion mechanism of the two components. A comparison of the present tracer self-diffusion data with literature data on interdiffusion in the Ni-Mn system permits to estimate thermodynamic factors by using the Darken-Manning equation. The thermodynamic factor varies from 3 to 5 depending on the structure.

Abstract: Self-diffusion coefficient of 95Nb in NbHx alloys (x=0.05,0.25 and 0.3) has been determined in the temperature range from 823 to 1323 K by using a serial sputter-microsectioning technique. The self-diffusion coefficient of Nb in the NbHx alloys are larger than that in Nb, suggesting that vacancies are formed by hydrogen dissolution, that is, the formation of hydrogen-induced vacancies. The value of the pre-exponential factor for the Nb diffusion in the NbH0.05 alloy is five times larger than that in Nb, while the difference in the activation energies between the NbH0.05 alloy and pure Nb is small. The self-diffusion enhancement in the NbH0.05 alloy is mainly caused by lowering in vibrational frequencies of atoms in the immediate neighborhood of hydrogen-induced vacancies.

Abstract: Iron self-diffusion measurements in amorphous and nanocrystalline chemically homogenous multilayers (CHM) of FeZr/57FeZr, (with nm range periodicity) have been studied with neutron reflectivity technique. It has been found that both the activation energy for diffusion and the pre-factor were significantly smaller as compared with bulk alloys. Effect of compressive stress on self-diffusion reveals a significant dependence on the activation energy as a function of applied stress. On the basis of the obtained results the diffusion mechanism in amorphous and nanocrystalline CHM of FeZr/57FeZr is reviewed in this paper.

Abstract: We present a unified simulation of diffusion in silicon (Si) and silicon dioxide (SiO2) that is based on the diffusing dopant species and point defects that primarily contribute to the diffusion. We first present the simulation of phosphorus (P) diffusion in Si based on the integrated diffusion model that we have developed and elucidate the mechanism of the appearance of the anomalous P in-diffusion profile. The vacancy mechanism governs P diffusion in the plateau region, while the kick-out mechanism governs it in the deeper region, where Si self-interstitials dominate in the kink region and P interstitials dominate in the tail region. Next, we present the simulation of boron (B) diffusion and Si self-diffusion in SiO2. We examined the co-diffusion of implanted B and 30Si in thermally grown 28SiO2, which shows increasing diffusivities with decreasing distance between the diffusers and Si/SiO2 interface and with higher B concentration in SiO2. We propose a model in which SiO molecules generated at the interface and diffusing into SiO2 enhance both B diffusion and Si self-diffusion. The simulation showed that the SiO diffusion is so slow that the SiO concentration at the B and 30Si region critically depends on the distance from the interface. In addition, the simulation predicts the possibility of time-dependent diffusivities for B and Si because more SiO molecules should be arriving from the interface with time, and this time dependence was experimentally observed. Moreover, based on the B concentration dependence, the simulation result indicates that B and Si atoms in SiO2 diffuse correlatively via SiO; namely, the enhanced SiO diffusion by the existence of B enhances B diffusion and Si self-diffusion.