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Glass Stability from Thermal, Structural and Optical Properties for IR Lens Application

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Glass Stability from Thermal, Structural and Optical Properties for IR Lens Application Journal of the Korean Ceramic Society https://doi.org/10.4191/kcers.2017.54.6.08 Vol. 54, No. 6, pp. 484~491, 2017. Communication Evaluations of Sb20Se80-xGex (x = 10, 15, 20, and 25) Glass Stability from Thermal, Structural and Optical Properties for IR Lens Application Gun-Hong Jung*, Heon Kong*, Jong-Bin Yeo**, and Hyun-Yong Lee***,† *Department of Advanced Chemicals and Engineering, Chonnam National University, Gwangju 61186, Korea **The Research Institute for Catalysis, Chonnam National University, Gwangju 61186, Korea ***School of Chemical Engineering, Chonnam National University, Gwangju 61186, Korea (Received June 30, 2017; Revised September 24, 2017; Accepted October 22, 2017) ABSTRACT Chalcogenide glasses have been investigated in their thermodynamic, structural, and optical properties for application in vari- ous opto-electronic devices. In this study, the Sb20Se80-xGex with x = 10, 15, 20, and 25 were selected to investigate the glass sta- bility according to germanium ratios. The thermal, structural, and optical properties of these glasses were measured by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and UV-Vis-IR Spectrophotometry, respectively. The DSC results revealed that Ge20Sb20Se60 composition showing the best glass stability theoretically results due to a lower glass transi- tion activation energy of 230 kJ/mol and higher crystallization activation energy of 260 kJ/mol. The structural and optical anal- yses of annealed thin films were carried out. The XRD analysis reveals obvious results associated with glass stabilities. The values of slope U, derived from optical analysis, offered information on the atomic and electronic configuration in Urbach tails, associated with the glass stability. Key words : Glass, Thermal properties, Chalcogenide, Glass stability, Urbach tails 1. Introduction glass stability in Sb20Se80-xGex chalcogenide systems by using the thermal, structural, and optical properties. The halcogenide glasses are interesting inorganic materials thermal properties of Sb20Se80-xGex (x = 10, 15, 20, and 25) C owing to their superior optical transmittance and were investigated by differential scanning calorimetry (DSC, nonlinear refractive index in the infrared region. They can Mattler Toledo DSC823e) analysis under non-isothermal be used in IR optical devices such as IR lenses, fiber optics, conditions. DSC results were applied by theoretical models and IR detectors owing to the optical properties.1-4) They (Augis-Bennett, and Kissinger models) to calculate the have low cost, balanced optical and mechanical properties, phase transition activation energy for glass stability. The and ease of molding process owing to their glass transition amorphous to crystalline structural properties and optical properties.5-7) To optimize the chalcogenide glass molding properties were studied in X-ray diffractometry (XRD, process and the reliability about amorphous to crystalline X'pert PRO Multi Propose X-ray diffractometer) and UV- phase transition system, the glass stability in chalcogenide Vis-NIR Spectrophotometry, respectively. glasses is required owing to the stable amorphous state at the process temperature. 2. Experimental Procedure In infrared optics applications, Ge-Sb-Se system chalco- genides are used due to their suitable IR region transmit- Sb20Se80-xGex chalcogenide bulk glasses, where x = 10, 15, tance, glass stability, mechanical properties, and chemical 20 and 25, were fabricated by the well-known melt-quench- properties.8-12) In the Ge-Sb-Se system, we focused that the ing method. High purity (99.999%) constituent elements of addition of germanium (Ge) is contributed to glass stabili- Ge, Sb, and Se were weighted according to proper atomic ties due to the resistance to strong tendency for crystalliza- weight and then put into a cleaned quartz ampoule. The tion according to the Sb-Se bonds, which are one of the core quartz ampoule for the melt-quenching technique was made 11) parts about glass properties. Therefore, the investigation of SiO2 and cleaned successively using nitric acid, sulfuric of glass stability in the wide range of Ge rate is important to acid, and iso-propyl alcohol. The element-inserted quartz optimize the chalcogenide composition for amorphous IR tubes were vacuum-sealed under 10−4 Torr by oxygen weld- optic applications. ing to prevent oxidation. The sealed ampoules were heated In this study, we investigated the composition for the best in a tube furnace at 498, 698, 963, and 1233 K for 2 h in con- sideration of the melting points and the boiling points of †Corresponding author : Hyun-Yong Lee each element. Subsequently they were placed at 1273 K for E-mail : [email protected] 16 h because of the uniformity of composition. During the Tel : +82-62-530-0803 Fax : +82-62-530-1909 melting process, the quartz ampoules were stirred con- − 484 − November 2017 Evaluations of Sb20Se80-xGex (x = 10, 15, 20, and 25) Glass Stability from Thermal, Structural... 485 stantly to homogenize the constituents. The samples were quenched in cold water to get a glassy state. Thin films were deposited by thermal evaporation from the open boat at a deposition rate of ~ 3 Å/s onto chemically cleaned p-type Si (100) and quartz substrates under a vacuum of 3 × 10−5 Torr, and the thickness ratio was measured using a quartz crystal sensor. The film thickness was fixed at ~ 200 nm. The deposited thin films were iso- thermally annealed at temperatures from 450 K to 630 K with 30 K intervals. The annealing process was performed under a flow of 200 sccm N2 gas for 30 min at a heating rate of 5 K/min to prevent the oxidation of the thin films. The thermal properties of bulk samples were studied using the DSC method. The DSC curves were taken under non-isothermal conditions at different heating rates (5, 10, Fig. 2. DSC graphs of the Sb20Se70Ge10 chalcogenide glasses at different heating rates of 5, 10, 15, and 20 K/min. 15, and 20 K/min) on accurately weighted samples sealed in The glass transition and crystallization temperatures aluminum pans. Each scan was recorded from room gradually increased as increasing the heating rates, temperature to 823 K. The calorimeter was calibrated using indicated by dash-line arrows. the well-known melting temperatures and melting enthalp- ies of zinc, indium, and gallium (20 mg), crimped into alumi- = 10, 15, 20 and 25) at a heating rate of 5 K/min and Fig. 2 is num pans and scanned. To identify the amorphous-to- the DSC curves corresponding to heating rate dependences crystalline phase transition of the annealed Sb20Se80-xGex of Sb20Se70 Ge10 chalcogenide glass. The DSC curves indicate films, the annealed films were recorded by using XRD with a single glass transition endothermic slope and one or more Cu Kα radiation (λ = 1.542 Å). crystallization exothermic peaks. The single endothermic The optical properties were measured using a UV-VIS- glass transition confirmed the homogeneity. Fig. 1 shows NIR spectrophotometer in the wavelength range ~ 300- that the glass transition temperature increased with increas- 1,100 nm. The optical transmittance of the amorphous and ing Ge ratio. The crystallization temperatures increased crystalline-annealed Sb20Se80-xGex thin films was recorded until the Ge ratio was 20%, and then the value according to at room temperature. The absorption coefficient (α) for cal- 25% of Ge ratio decreased. culating optical bandgap was measured using the beer-lam- The DSC graph parameters of the glass transition tem- bert relation as α = −(1/d)ln(T), where d is the film thickness perature (Tg), glass transition endothermic peak tempera- and T is transmittance of the film. ture (Tgp), onset crystallization temperature (Tc), peak crystallization temperature (Tp), and the temperature inter- − 3. Results and Discussion val between peak crystallization and glass transition (Tp Tg) are listed in Table 1. Figure 1 shows the DSC curves of Sb20Se80-xGex glasses (x As shown in the Fig. 2 and Table 1, the temperatures Tg and Tc increased gradually as the heating rate (β) increased. This phenomenon according to the Tg is explained using the empirical equation shown in Eq. (1), suggested by Lassocka et al.13) β Tg = A + B ln (1) Where A consists of Tg at a heating rate of 1 K/min, and B is the cooling rate which is taken by the system to reduce the glass transition temperature when the heating rate decreased from 10 K/min to 1 K/min. The plots of Tg versus ln β exhibited a linear relationship, as shown in Fig. 3. The values of A and B are listed in Table 2. What is the glass transition is one of the issues in the non- crystalline solids. Some authors have given the glass transi- tion as the glass-to-amorphous transition.14,15) The chalco- genide glass can, therefore, be divide in ‘glass’ phase and Fig. 1. DSC graphs of the Sb20Se80-xGex (x = 10, 15, 20, and ‘amorphous’ phase around the point of Tg according to the 25) glasses under non-isothermal condition at 5 K/ non-crystal solids. The glass transition region consists of min heating rate. Points of Glass transition (●) and crystallization peak (○) are revealed well in the DSC various metastable states separated by energy barriers. The graph. atoms restricted in the metastable states tend to attain 486 Journal of the Korean Ceramic Society - Gun-Hong Jung et al. Vol. 54, No. 6 Table 1. The Transition Temperatures According to Sb20Se80-xGex Glasses at the Different Heating Rates Sample Heating rate Tg [K] Tgp [K] Tp [K] Tp−Tg [K] Ge at% [K/min] 5 435.5 445.5 567.7 131.8 10 440.8 448.8 578.2 137.8 X = 10 15 443.25 453.2 584.3 141.0 20 444.6 454.6 591.6 147.0 5 502.8 505.5 640.5 134.9 10 503.4 509.6 542.5 142.8 X =15 15 503.7 511.2 551.2 147.9 20 506.0 515.3 559.9 152.6 5 527.6 531.2 661.2 133.6 10 530.4 536.3 672.5 142.1 X = 20 15 532.9 542.0 677.2 144.2 20 533.5 544.3 679.6 146.1 5 531.5 536.5 599.2 67.7 10 535.7 542.3 605.6 69.9 X = 25 15 537.2 545.2 607.3 70.1 20 539.7 548.3 610.0 70.3 2 Fig.
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