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Article
Investigation of Amorphous to Crystalline Transition in Glassy Se80Te20 and Se70Te20M10 (M = Ag, Cd, Sb) Alloys

Authors: N. Mehta --- A. Kumar
Journal: Iraqi Journal of Applied Physics المجلة العراقية للفيزياء التطبيقية ISSN: 18132065 23091673 Year: 2005 Volume: 1 Issue: 3 Pages: 7-13
Publisher: iraqi society for alternative and renewable energy sources and techniques الجمعية العراقية لمصادر وتقنيات الطاقة البديلة والمستجدة

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Abstract

Calorimetric measurements have been performed in binary Se80Te20 and ternary Se70Te20M10 (M=Ag, Cd, Sb) alloys to study the effect of metallic additives (Ag, Cd, Sb) on the crystallization kinetics in Se80Te20 alloy. Three different non-isothermal methods Kissinger’s method, Matusita-Sakka theory and Augis-Bennett approximation method have been used in the present study. Different kinetic parameters such as the activation energy of crystallization (EC), the order parameter(n), the growth morphology parameter (m), the rate constant (K) and its frequency factor (Ko) have been determined. The effect of third element on crystallization temperature of binary Se80Te20 is explained in terms of Arrhenius dependence of rate constant K(T). The increasing sequence of activation energy of crystallization in ternary Se70Te20M10 (M=Ag, Cd, Sb) alloys is explained in terms of their average bond strength.


Article
Crystallization and Glass Transition Kinetics in Se90Sb10-xAgx Glassy Alloys

Authors: A. Kumar --- D. Kumar --- N. Mehta --- S. Srivastava
Journal: Iraqi Journal of Applied Physics المجلة العراقية للفيزياء التطبيقية ISSN: 18132065 23091673 Year: 2013 Volume: 9 Issue: 1 Pages: 7-13
Publisher: iraqi society for alternative and renewable energy sources and techniques الجمعية العراقية لمصادر وتقنيات الطاقة البديلة والمستجدة

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Abstract

Alloys of Se100-xSb10-xAgx (x=2, 4, 8) glassy system are obtained with rapid quenching. Calorimetric studies have been performed at different heating rates under non-isothermal conditions. Well defined endothermic and exothermic peaks are obtained at glass transition (Tg) and crystallization temperatures (Tc). In the present study, the glassy alloys are found to have double glass transition and crystallization temperatures. From the dependence of the glass transition temperature on the heating rate β, the activation energy of glass transition has been calculated on the basis of Moynihan and Kissinger models. The value of (Tc–Tg) and stability parameters have also been calculated for each composition for both the phases. Value of Eg is found to be decreased with increase in concentration of Ag. The values of (Tc-Tg) is highest for the sample with 8 at % of Ag. Activation energy of crystallization (Ec) has also been calculated using the well-known Kissinger’s relation, Matusita–Sakka theory and the method of Augis and Bennett. A good agreement has been found in all the three methods. The activation energy of crystallization is found to decrease with increasing concentration of Ag.


Article
Optical Investigations of CdSe1-x Tex Thin Films
الاستقصاء البصري لاغشيةCdSe1-xTex الرقيقة

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Abstract

The alloys of CdSe1-xTex compound have been prepared from their elements successfully with high purity (99.9999%) which mixed stoichiometry ratio (x=0.0, 0.25, 0.5, 0.75 and 1.0) of (Cd, Se and Te) elements. Films of CdSe1-xTex alloys for different values of composition with thickness(0.5m) have been prepared by thermal evaporation method at cleaned glass substrates which heated at (473K) under very low pressure (4×10-5mbar) at rate of deposition (3A˚/s), after that thin films have been heat treated under low pressure (10-2mbar) at (523K) for two hours.The optical studies revealed that the absorption coefficient (α) is fairly high. It is found that the electronic transitions in the fundamental absorption edge tend to be allowed direct transition. It was also found that the optical energy gap vary non-linearly with composition (x) and have a minimum value at x=0.5 and increases after heat treatment.It is found that the optical constants vary non-linearly with composition, and the behavior inverse at x=0.5, and affected by heat treatment. The behavior of 1 is similar to the behavior of n, while the behavior of 2 is similar to the behavior of k.

تم تحضير سبائك المركب CdSe1-xTex بنجاح من عناصرها الأولية بنقاوة عالية (%99.9999) بخلط نسب العناصر (x = 0.0, 0.25, 0.5, 0.75, 1.0) من (Cd, Se, Te)، واستخدم تحليل مطياف الامتصاص الذري لمعرفة تركيز العناصر في السبيكة. وكذلك أجريت فحوصات حيود الأشعة السينية ولوحظ أن السبائك تملك تركيباً متعدد البلورات. حضرت أغشية رقيقة من سبائك CdSe1-xTex لقيم مختلفة من التراكيز بسمك (0.5μm) بطريقة التبخير الحراري على قواعد نظيفة من الزجاج المسخن بدرجة حرارة 473K تحت ضغط واطئ جدا (4×10-5mbar) بمعدل تبخير (ِs 3 A) وبعد ذلك تمت معاملة الأغشية حراريا تحت ضغط واطئ (10-2mbar) بدرجة حرارة 523K لمدة ساعتين.من الدراسة البصرية تبين أن قيم معامل الامتصاص (α) عالية بعض الشيء، ووجد ان الانتقالات الإلكترونية عند حافة الامتصاص الأساسية كانت من نوع الانتقال المباشر المسموح، وان فجوة الطاقة البصرية تتغير بشكل غير خطي مع التركيز (x) وتملك أوطأ قيمة لها عند x=0.5، وكذلك وجد أن فجوة الطاقة البصرية تزداد قليلا بعد المعاملة الحرارية.استخدم طيف النفاذية في إيجاد الثوابت البصرية (n, k, ε1, ε2)التي تم حسابها بوساطة طريقة سوانبل (Swanepoel) باستخدام النفاذية العظمى TM والنفاذية الصغرى Tm في تقنية الغلاف.وتبين ان الثوابت البصرية جميعها تتغير بشكل غير خطي مع التركيز وان انقلاب السلوك يكون دائما عند x=0.5، وجد انها تبدي تأثرا بعد معاملة الأغشية حراريا. وكان تصرف الجزء الحقيقي لثابت العزل مشابها لتصرف معامل الانكسار، بينما الجزء الخيالي لثابت العزل كان مماثلا لتصرف معامل الخمود.


Article
The optical properties of a- (GeS2)100-xGax thin films
الثوابت البصرية لأغشيةGeS2)100-xGax) الرقيقة

Authors: M.A.Kadhem محمد عبدالحر كاظم --- Bushra A.Hasan بشرى عباس حسن --- R.M.S.Al-Haddad رعد محمد صالح الحداد
Journal: Iraqi Journal of Physics المجلة العراقية للفيزياء ISSN: 20704003 Year: 2013 Volume: 11 Issue: 21 Pages: 28-36
Publisher: Baghdad University جامعة بغداد

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Abstract

Thin films whose compositions can be expressed by (GeS2)100-xGax (x=0, 6,12,18) formula were obtained by thermal evaporation technique of bulk material at a base pressure of ~10-5 torr. Optical transmission spectra of the films were taken in the range of 300-1100 nm then the optical band gap, tail width of localized states, refractive index, extinction coefficient were calculated. The optical constants were found to increase at low concentration of Ga (0 to12%) while they decreases with further addition of Ga. The optical band gap was found to change in opposite manner to that of optical constants. The variation in the optical parameters are explained in terms of average bond energy of the system.

تم تحضير أغشية المركب(GeS2)100-xGax وبنسب مختلفة من المحتوى0,6,12,18%)) بواسطة التبخير الحراري تحت ضغط مقداره torr 10-5 .تم الحصول على طيف النفاذ للأغشية المحضرة ضمن المدى300-1100 nm ومن ثم تم حساب فجوة الطاقة البصرية,عرض الحالات الموضعية, و الثوابت البصرية.لقد أظهرت الثوابت البصرية ازديادا عند إضافة الكاليوم بنسب واطئة (من 0 الى 12 %)لكنها تناقصت بعد زيادة نسبة الكاليوم. فجوة الطاقة البصرية أظهرت سلوكا معاكسا لسلوك الثوابت البصرية.تم تفسير تغير المعلمات البصرية بدلالة تغير طاقة آصرة المنظومة.


Article
Density of Defect States in Se90Sb10-xAgx Glassy Alloys

Authors: A. Kumar --- R.K. Shukla --- A. Kumar
Journal: Iraqi Journal of Applied Physics المجلة العراقية للفيزياء التطبيقية ISSN: 18132065 23091673 Year: 2013 Volume: 9 Issue: 4 Pages: 25-28
Publisher: iraqi society for alternative and renewable energy sources and techniques الجمعية العراقية لمصادر وتقنيات الطاقة البديلة والمستجدة

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Abstract

The present paper reports the study of density of defect states in bulk glassy alloys of Se90Sb10-xAgx (where x = 0, 2, 4, 6 and 8). Space charge limited conduction technique is used for this purpose. I-V characteristics have been measured at various fixed temperatures in the range 300 K to 380 K. An ohmic behavior is observed at low electric fields upto 102 V/cm. However, superohmic behavior is observed at high electric fields (103 - 104 V/cm). High-field conduction theory of space charge limited conduction for uniform distribution of localized states in the mobility gap fits well with the experimental data. Using this theory, the density of defect states (DOS) near Fermi level is calculated for all the glassy alloys. A maxima is observed at 4 at. % of Ag, which is explained in terms of average co-ordination number.

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