Thermo-Kinetic Anomalies across Rigidity Threshold in Ge<SUB>x</SUB>Se<SUB>1-x</SUB>

Abstract

We have investigated the glass-transition kinetics of nine Ge x Se 1−x glasses by differential scanning calorimetry. Relation between the drive (heating-rate q) and response (heatflow shift ∆H at T g ) is seen to be strictly linear only for GeSe 4 , known to signify the bulk-rigidity threshold for this series. From an Arrhenius analysis the activation energies for glassy relaxation are estimated, and point to the existence of different thermokinetic phases below and above the threshold composition. Series behaviour of the kinetic activation is conciled to a concurring one seen in the size of cooperatively diffusing regions. The anomalies are attributed to structural crossovers with Ge doping; first from the parent uniform Se-chains to that of backbones out-branching at corner-shared Ge(Se 1/2 ) 4 tetrahedral clusters, and subsequently interconnecting by edge-shared configurations to realize a random pearl-necklace 3-D covalent network.

Topological Ordering and Viscosity in the Glass-Forming Ge–Se System: The Search for a Structural or Dynamical Signature of the Intermediate Phase

“…To investigate this possibility, the MYEGA model (Mauro et al, 2009) FIGURE 4 | The dependence of the glass transition temperature Tg for the GexSe 1− x system, as measured using a variety of methods, on the composition x and mean coordination numbern = 2(1 + x). The results obtained from the total heat flow in the present work are compared to the results obtained by Avetikyan and Baidakov (1972), Awasthi and Sampath (2002), Azoulay et al (1975), Bhosle et al (2012a,b), Boolchand (2000), Boolchand and Bresser (2000), Bureau et al (2003), Dembovskii et al (1965), Feltz and Lippmann (1973), Feltz et al (1983), Feng et al (1997, Gueguen et al (2011), Guin et al (2002a, Gulbiten et al (2013), Lucas et al (2003), Nemilov (1964), Ota et al (1978), Sarrach et al (1976), Senapati and Varshneya (1996), Sharma et al (2005), Sreeram et al (1991a), Svoboda and Málek (2015), Wagner et al (1997), Wang et al (2005), Yang et al (2013), and Zhao et al (2013). The inset shows solely the results for Tg,rev as obtained in the present work and in the work of Boolchand and coworkers (Feng et al, 1997;Boolchand, 2000;Boolchand and Bresser, 2000;Wang et al, 2005;Bhosle et al, 2012a,b)-see Section 3.1 for details.…”

Analysis of Activation Energies &amp; Experimental Evidence for Energetic Phase Separation in Ge&lt;sub&gt;x&lt;/sub&gt;Se&lt;sub&gt;1-x&lt;/sub&gt;Glassy System

“…Glassy nature of the samples was confirmed by modulated differential scanning calorimetry MDSC (2910, TA Instruments). Glass transition temperature T g was determined from the inflexion point of baseline shift in their heat capacity data, obtained at heating scan rate of 5˚C/min, and modulation of ±1˚C at 80 sec period [18] [19].…”