Date of Award

6-2004

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Materials Science

First Advisor

Ossama EI-Shazly

Second Advisor

Rashed Alsaeed

Abstract

The aim of the present work is to study the crystallization kinetics of some chalcogenide glassy alloys in the Selenium-Tellurium system. Four glassy systems have been prepared: Se80Te20-xSbx (x= 0, 4, 6, 8, and 10); Se70Te30-xSbx (x= 2, 6, 8, and 10); Se80Te20-xCdx (x= 2, 4, and 10); and Se80Te20-xSnx (x= 2, 4, and 10). The starting materials of (99.999%) purity were weighted according to their atomic percentages and sealed in evacuated silica tubes, under a pressure of about 10-5 torr. The tubes were heated in a furnace at the required temperature and then quenched in ice-water mixture.

X-ray diffraction measurements indicated that all samples in the first two systems are amorphous, while all samples in the other two systems indicated the existence of some degree of crystallinity, except the only sample (Se20Te16Cd4). Therefore it was decided to confine the study on the first two systems and (Se20Te16Cd4) alloy.

From the DSC measurements, the glass transition temperature (Tg) and the onset temperature of crystallization (Tc) were determined at different heating rates. It was found that (Tg) and (Tc) shift to higher values as heating rate (α) is increased. This dependence of (Tg) and (Tc) on (α) was used to calculate the activation energy of glass transition (Et) and the activation energy of crystallization (Ec), respectively. The activation energy values of glass transition using several equations were found to be in good agreement with each other, for each glassy alloy. Similarly the activation energy for crystallization was calculated using several equations and they were in good agreement with each other.

From the value of (Tc-Tg), which gives an indication of the kinetic resistance to crystallization, it was found that the alloy with 6 at %Sb is the most stable alloy for systems (1 and 2).

Crystallization using partial area analysis were studied where the crystallization mechanism was concluded for each glassy alloy.

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