الفهرس 
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Abstract
The structural, thermal kinetics analysis, dc electrical properties, switching phenomenon, ac conductivity and dielectric properties of Se85 Te10 Sn5 and Se85 Te10 In5 compositions in bulk and thin film form were studied. The studied compositions were prepared in bulk form by melting quenching technique and by thermal evaporation technique for film forms.
X-ray diffraction analysis (XRD) revealed the amorphous nature for the prepared samples in powder and thin film forms.
Energy dispersive X-ray analysis(EDX) for the investigated compositions indicates that the real percentage of the constituent elements in the investigated compositions are the same as that prepared.
Thermal analysis for Se85Te10X5 (X= Sn or In) compositions carried out under non-isothermal condition in powder form with different methods at different heating rates. The glass transition temperatures Tg, peak crystallization temperature Tp and melting temperature Tm are measured and increase with increase heating rate for
Se85 Te10 X5 (X = Sn or In) glasses. The activation energy Eg, Ec and Avrami index n are calculated and found that , are n 4 for In content and n 3 for Sn content. Then the value of m (order of the crystallization mechanism) will be 3 for
Se85Te10 In5 and suggest three-dimensional nucleation growth during its amorphous to crystalline transformation while the value of m for Se85 Te10 Sn5 will be 2 indicating the bulk nucleation with two dimensional growth.
The temperature dependence of dc electrical conductivity were examined in the range 303-333K for the considered film compositions shows is of activated type with a single activation energy ΔEσ. It is concluded that ΔEσ is independent of film thickness in the range (263 – 1220 nm), while increases with increasing film thickness.
The obtained results of the static I-V characteristic curves for Se85 Te10 X5 (X = Sn or In) films showed that these curves are of memory switching type. The analysis of the threshold voltage Vth explored that the Vth increases linearly with film thickness and decreases with increasing temperature. It is also found that the switching process in the studied film compositions can be explained on the basis of the electro-thermal model.
Ac electrical conductivity , the dielectric constant and the dielectric loss of Se85 Te10 X5 (X = Sn or In) films were examined as a function of temperature in the range (303 – 333 K), frequency in the range (102 Hz – 105 Hz) and thickness in the range (263 – 1220 nm).
The obtained results indicate that ac conductivity depends on temperature, frequency and addition of elements (Sn5 or In5) to Se85Te10 system. Ac conductivity obeys the relation , where S is the frequency exponent. The frequency exponent S decreases with increasing temperature, in accordance with the correlated barrier hopping (CBH) model between centers forming non-intimate valence alternation pairs (NIVAP’s) for Se85 Te10 X5 (X = Sn or In).
Both dielectric constant and dielectric loss increased with temperature and decreased with frequency in the investigated ranges of temperature and frequency.
The results of the dielectric loss for the studied film compositions were discussed on the basis of Guntini equation and the obtained values of the maximum barrier height Wm are in agreement with the theory of charge carriers over a potential barrier as suggested by Elliot in case of chalcogenide glasses.