الفهرس | Only 14 pages are availabe for public view |
Abstract Chalcogenide glasses with chemical formula InxTe20−xSe80 (x = 5, 10 and 15 at %) and SbyTe20−ySe80 (y = 5, 10 and 15 at %) were prepared using melt quenching method. X-ray diffraction analysis showed that all samples contain crystalline phases. Detected phases were generally identified as trigonal In2Se3 and trigonal Se for In-system and orthorhombic Sb2Se3, trigonal Sb2Te3 and trigonal Se for Sb-system. Thermal behavior of prepared samples was investigated by using differential scanning calorimetry at different heating rates, 5, 10, 15 and 20 °C/min. Investigation asserted that all samples contain amorphous phases. All scans exhibited three well known transitions of chalcogenides, glass, crystallization and melting. Homogeneity of amorphous phases was reflected by appearing single glass and crystallization transition peaks. Obtained values of transition temperatures of all samples shifted generally to higher values as heating rate increased. Lasocka relation was used to study heating rate dependence of glass and crystallization temperatures. Glass and crystallization temperatures and Lasocka parameters decreased with increasing compositions x and y. It was observed that glass temperature Tg and crystallization temperature Tc values of In-system samples are lower than those of Sb-system samples. Kissinger and Mahadevan models were used to determine glass and crystallization activation energies. Results obtained from both models were close to each other. Glass activation energy increased with increasing compositions x and y, while crystallization activation energy decreased in general. It was found that glass activation energy Eg and crystallization activation energy Ec values of In-system samples are generally higher than those of Sb-system samples. Isothermal crystallization was studied by measuring time dependence of ac conductivity at 1 kHz at different annealing temperatures, 75, 80, 85 and 90 °C. All runs manifested well known sigmoidal shape curves of amorphous materials. Avrami exponent n and rate constant K were determined by applying JMA equation. Avrami exponent values obtained revealed that crystallization process in studied samples occurs through contribution of different mechanisms suggesting that dominant process may be surface nucleation with one dimensional growth. Crystallization activation energy Ec and frequency factor K0 were determined from temperature dependence of rate constant K using Arrhenius relation. Values of crystallization activation energy Ec obtained agreed with those determined from non-isothermal methods. Frequency factor K0 decreased with increasing concentrations of In and Sb. It was found that lnK0 values of In-system samples are higher than those of Sbsystem samples. AC conductivity σ, dielectric constant κ and loss tangent tanδ were measured using two probe method in frequency range from 100 Hz to 5 MHz and temperature range from 26 to 100 °C. All graphs exhibited usual dispersion and temperature variation of chalcogenide glasses. Conduction activation energy E was determined from temperature dependence of conductivity using Arrhenius relation. Conductivity, dielectric constant and loss tangent decreased with increasing In-content and increased with increasing Sb-content, but activation energy decreased with increasing both. It was found that E values of In-samples are lower than those of Sbsamples, while σ, κ and tanδ values are generally higher. |