GeS2 crystal growth kinetics in Ge-Sb-S thin film and bulk glasses V. Podzemná, J. Barták, J. Málek Department of Physical Chemistry, University of Pardubice, Studentska 573, Pardubice 532 10, Czech Republic Corresponding author: [email protected] INTRODUCTION Chalcogenide glasses exhibit many interesting properties which can be exploited for the fabrication of photonic devices. In particulary, they posses excellent infrared transparency, large linear a nd nonlinear refractive indices, low phonon energies, and properties that are thunable through compositional tailoring. These attributes make chalcogenide glasses good candidates for near-, mid- and long-wave infrared applications as compared to oxide glasses and single crystals. despite their often limited thermal and mechanical stability [1]. EXPERIMENTAL The (GeS2)x(Sb2S3)1-x glasses were prepared by pure element synthesis in evacuated quartz ampoules at temperature of 950 °C. Synthesis was finished by rapid cooling in ice-water. The samples were prepared as a thin film by vacuum thermal evaporation and bulk samples by polishing on optical quality. The positive curvature of this dependences in Fig. 3 suggests 2D-surface nucleated growth which was observed for all studied cases. In this case, the growth rate can be expressed as equation (3). Optical measurements of crystal growth were performed using Olympus BX 51 microscope. Samples were previously heat-treated in a computer-controlled furnace at selected temperature for various times. Where B and C are constants. RESULTS The sizable difference in reflectivity between the amorphous glass and the crystalline phase enables direct observation of crystal growth. All heat treated samples were extensively examined, and the sizes of the well-developed crystals grown in thin film and bulk glassy material were measured and recorded (Fig. 1). u= u (T ) = AG ⋅ e b) (GeS2)0,9(Sb2S3)0,1 e) (GeS2)0,9(Sb2S3)0,1 (3) − EG RT (1) Where T is temperature, u is the crystal growth rate, AG is the pre-exponential factor from growth data and EG is the apparent activation energy of the crystal growth. Values of activation energies are shown in Tab. 1 Activation energy (kJ/mol) Bulk Thin film Undercooled melt d) GeS2 B exp − T ⋅ ∆T Fig. 2 Time dependence of the lenght GeS2 crystals in undercooled melt of (GeS2)0,9(Sb2S3)0,1. Tab. 1 Activation energies of GeS2 crystal growth in undercooled melts. a) GeS2 C η GeS2 (GeS2)0,9(Sb2S3)0,1 (GeS2)0,8(Sb2S3)0,2 283 ± 35 172 ± 7 191 ± 25 167 ± 8 102 ± 10 50 ± 7 The operative growth mechanism can be assessed from the reduced growth rate UR given by the following equation (2) [2]. uη UR = ∆H ⋅ ∆T − (2) R⋅T ⋅T Fig. 4 Plot of logarithm (growth rate x viscosity) versus (TΔT)-1 for crystallization of GeS2 in undercooled melt. Obtained parameters B and ln C were used for prediction of temperature dependence of crystal growth rate illustrated in Fig. 5 a-f. a) GeS2 TF b) GeS2 Bulk M 1− e M Fig. 3 demonstrates the reduced growth rate plot calculated by using our growth rate data and viscosity data [3,4] announced for GeS2. c) (GeS2)0,8(Sb2S3)0,2 f) (GeS2)0,8(Sb2S3)0,2 c) (GeS2)0,9(Sb2S3)0,1 TF d) (GeS2)0,9(Sb2S3)0,1 Bulk Fig. 1 SEM microphotography of bulk samples (a,b,c) and microphotography of thin film samples obtained by optical microscopy (d,e,f). Time dependences of the crystal length were linear for each temperature and for all studied composition (Fig. 2). This behaviour is typical for crystal growth controlled by crystal-liquid interface kinetics. e) (GeS2)0,8(Sb2S3)0,2 TF The activation energy of crystal growth was obtained from the slope of the logarithm of crystal growth rate u versus reciprocal temperature 1/T dependence, supposing the Arhenius behavior (1). Fig. 3 Reduced growth rate versus undercooling for crystallization of GeS2 in undercooled melt. f) (GeS2)0,8(Sb2S3)0,2 Bulk Fig. 5 Temperature dependence of crystal growth rate and viscosity in (GeS2)x(Sb2S3)1-x undercooled melt in thin film and bulk form. CONCLUSION REFERENCES: ACKNOWLEDGEMENTS This work was supported by Ministry of Education, Youth and Sports (project CZ.1.07/2.3.00/20.0254 - ReAdMat). [1] L. Petit et al., Mater. Chem. Phys. 97 (2006) 64. [2] K.A. Jackson et al., J. Cryst. Growth 1(1967) 1. [3] J. Shánělová et al., J. Non-Cryst. Solids 352 (2006) 3952. [4] J. Málek, J. Shánělová, J. Non-Cryst. Solids 243 (1999) 116. • Crystal growth of GeS2 was observed by optical microscopy in thin films and bulk glasses of system (GeS2)x(Sb2S3)1-x where x=1; 0.9; 0.8. • The temperature dependence of crystal growth rates of studied samples was predicted by 2Dsurface nucleated growth model. • Activation energies of GeS2 crystal growth in all studied cases were determined.
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