Journal of Physics and Chemistry of Solids 68 (2007) 850–854 Relaxation behavior of glassy selenium Roman Svoboda a,Ã , Pavla Pustkova´ b , Jirˇı´ Ma´lek a a Department of Physical Chemistry, University of Pardubice, Cs. Legii 565, 532 10 Pardubice, Czech Republic b Department of Inorganic Technology, University of Pardubice, Cs. Legii 565, 532 10 Pardubice, Czech Republic Abstract The dynamics of the glass transition of amorphous selenium was investigated by using differential scanning calorimeter. The heat capacity data were analyzed applying the phenomenological Tool–Narayanaswamy–Moynihan (TNM) model in order to describe the relaxation behavior of a-Se. The TNM parameters were evaluated by fitting the enthalpic cycles and also one isothermal experiment. Furthermore, peak-shift method and several other methods of evaluating the TNM parameters were applied to confirm the results of curve fitting. The results are compared with the other published enthalpy and viscosity data, volume and enthalpy relaxation are compared on account of our previous mercury dilatometry measurements. We found out that the pre-exponential factor A and the apparent activation energy Dh * of structural relaxation are similar for volume and enthalpy relaxation and Dh * is very close to the activation energy of viscous flow. r 2007 Published by Elsevier Ltd. Keywords: A. Chalcogenides; A. Glasses; C. Differential scanning calorimetry; D. Phase transitions 1. Introduction Wide application options of non-crystalline materials are closely related to the question of their long-term stability at various temperatures. At temperatures below the glass transition [1], the occurring phenomenon is the structural relaxation, process whereas the material changes its thermodynamic properties (e.g., enthalpy, volume, etc.) towards the local equilibrium represented by the under- cooled liquid state. The instantaneous state of the relaxing material can be described by the fictive temperature T f [2] (Fig. 1). Enthalpy relaxation belongs among important and therefore usually studied aspects of glassy dynamics. It is characterized by an endothermic effect at glass transition region during heating of an annealed glass. The peak area under this effect can be used to determine the fictive temperature of the measured material [3] and thus is used to define the enthalpy relaxation process. The quantitative description of structural relaxation nowadays frequently follows the phenomenological Tool–Narayanaswamy– Moynihan (TNM) model [3,4] involving expression for relaxation time t and expression for stretched exponential relaxation function M H called Kohlrausch–Williams– Watts [5] function: t ¼ A  exp x  Dh n R  T þ ð1  xÞ Dh n R  T f   , (1) dðtÞ¼ d 0 exp  Z t 0 dt t   b " # , (2) where d is function of the relaxing property (enthalpy) defined as d ¼ (H–H N )/H N and d 0 is then equal to d(H 0 )–both in agreement with Fig. 1, t is time, T is temperature, T f is the fictive temperature, R is the uni- versal gas constant, b is the parameter on non-exponenti- ality, A is the pre-exponential factor, x is the parameter of non-linearity and Dh * is the apparent activation energy of structural relaxation. TNM parameters (x, b, Dh * ,A) for the specific material can be evaluated either from direct numerical fit of the measured data or by using some of the non-fitting methods based on the simple data conversion. Among these methods belongs the peak-shift method [6,7] defined ARTICLE IN PRESS www.elsevier.com/locate/jpcs 0022-3697/$ - see front matter r 2007 Published by Elsevier Ltd. doi:10.1016/j.jpcs.2006.12.032 Ã Corresponding author. Tel.: +420 466 037 045. E-mail address: roman.svoboda@upce.cz (R. Svoboda).