Correlation of structural, thermo-kinetic and thermo-mechanical properties of the Ge 11 Ga 11 Te 78 glass Roman Svoboda a, ⁎, Daniel Stříteský a , Zuzana Zmrhalová b,c , Daniela Brandová a , Jiří Málek a a Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentska 573, 532 10 Pardubice, Czech Republic b Joint Laboratory of Solid State Chemistry, Faculty of Chemical Technology, University of Pardubice, Studenstka 95, 532 10 Pardubice, Czech Republic c Center of Materials and Nanotechnology, Faculty of Chemical Technology, nam. Cs. Legii 565, 532 10 Pardubice, Czech Republic abstract article info Article history: Received 22 March 2016 Received in revised form 28 April 2016 Accepted 29 April 2016 Available online xxxx Cold crystallization and structural relaxation kinetic processes occurring in the Ge 11 Ga 11 Te 78 infrared bulk glass were studied using differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The complex crystallization behaviour was described as overlapping surface nucleation-growth Te precipitation and volume- located autocatalytic formation of GeTe and Ga 2 Te 5 crystallites. Similar crystallization activation energies were obtained by DSC and TMA. Direct comparison of the DSC and TMA data reveals that only a narrow temperature window of approx. 20 °C exists between the start of the glass softening and first formation of Te crystallites, which makes knowledge of crystallization kinetics crucial for the industrial glass processing and real-life com- mercial applications. Structural relaxation kinetics was described in terms of the Tool-Narayanaswamy-Moynihan (TNM) model. Good agreement between the relaxation activation energies determined by DSC and TMA was obtained. Values of the parameters of the TNM model were interpreted with respect to the molecular structures determined by Raman spectroscopy and reverse Monte Carlo simulations. The stabilizing role of Ga was explained by its preferred bond- ing to the non-bonding p electrons of Te. © 2016 Elsevier B.V. All rights reserved. Keywords: Ge11Ga11Te78 glass DSC TMA Structural relaxation Crystallization kinetics 1. Introduction Chalcogenide glasses are well known for their excellent transmit- tance in the infrared region. [1,2] However, if one considers applications requiring the transmittance window to be extended above 18 μm (e.g. self-aligning CO 2 detectors/traps fighting global warming or IR optics telescopes detecting biological life markers on exoplanets [3,4]), only very few materials exhibit such transmittance. Recently, the Ge–Ga–Te chalcogenide system was found [5,6] to be highly suitable in this regard: its fully telluride matrix provides considerable advantage over both the Ge–Se–Te glasses [7,8] (where the presence of Se narrows the transmit- tance window) and Ge–I–Te glasses [9,10] (where the volatility of io- dine makes the synthesis very difficult). Main disadvantage of the Te-based chalcogenides is their relatively low glass stability. Thus considerable effort is devoted to the search of the composition with optimum thermal properties. [5,6,11–13] The studies are, however, mostly performed by using differential scanning calorimetry (DCS) and do not provide proper information about the glass-softening and viscous flow effects, which are crucial for the pro- cessing of the glassy material (moulding, fibre-drawing etc.). In the present article the results provided by DSC will be correlated with the data from thermo-mechanical analysis (TMA); the thermo-kinetic and thermo-mechanical behaviour will be explained based on the structural information from Raman spectroscopy and X-ray diffraction (XRD). The Ge 11 Ga 11 Te 78 bulk glass will be used as a typical example of the com- mercially utilized Ge-Ga-Te glasses (it is the middle-positioned compo- sition on the most promising GaTe 3 –GeTe 4 pseudo-binary line; i.e. (GaTe 3 ) 50 (GeTe 4 ) 50 ). This composition was earlier reported to belong among the most promising materials for far-infrared optic fibres but certain difficulties regarding the glass stability during fibre-drawing were mentioned. [5,6] In the present study we will investigate this issue in detail. Both the glass transition and cold crystallization phe- nomena will be considered in the study. 2. Materials and methods The Ge 11 Ga 11 Te 78 glass was prepared by a melt-quenching tech- nique: proper amounts of elements were sealed in an evacuated fused silica ampule, annealed at 950 °C for 24 h and quenched in water. Small plates broken off from a thin glassy sheet formed inside the Journal of Non-Crystalline Solids 445–446 (2016) 7–14 ⁎ Corresponding author. E-mail address: roman.svoboda@upce.cz (R. Svoboda). http://dx.doi.org/10.1016/j.jnoncrysol.2016.04.045 0022-3093/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol