Long-term ageing behaviour in Ge–Se glasses Roman Golovchak Æ Andrzej Kozdras Æ Oleh Shpotyuk Æ Sergey Kozyukhin Æ Jean-Marc Saiter Received: 25 December 2008 / Accepted: 2 May 2009 / Published online: 21 May 2009 Ó Springer Science+Business Media, LLC 2009 Abstract Effect of long-term physical ageing (*18– 21 years) in vitreous germanium selenides is studied using differential scanning calorimetry method. It is compared with short-term physical ageing observed in these glasses earlier. Low compositional limit of the non-ageing ability determined using old samples coincides with the onset of reversibility window obtained using short-term aged sam- ples of Ge–Se system by temperature modulated differen- tial scanning calorimetry technique. Introduction The non-equilibrium metastable nature of glassy state is a reason for all glasses obtained by conventional melt-quenching technique to approach with time the equi- librium structure of corresponded undercooled liquid, this effect being known as physical ageing effect [1, 2]. The kinetics of the related structural relaxation processes, occurred during the transition of glass to a more energetically favourable state, depends essentially on the departure of ageing temperature (T a ) from a glass transition temperature (T g ) slowing down significantly with (T g -T a ) increase [2]. Thus, at normal conditions of storage, tens of years period was needed to observe natural physical ageing effect in sil- icate glasses [3, 4]. Since their T g is much higher than T g of chalcogenide glasses (ChG) [1], we can expect physical ageing effect to be recorded after few decades of natural storage in all of the investigated Ge–Se ChG where it is possible. Furthermore, time interval of 20–25 years has also a practical meaning for the applications of these materials in electronics and optoelectronics [5, 6]. Typical electronic devices are used at normal conditions and their usual lifetime is less than 20 years. So, it is quite important to have the information on physical ageing processes taking place at normal conditions during this period of time. It was shown recently that natural physical ageing effect in ChG consists of two components called short-term and long-term physical ageing, respectively [7–9]. The dis- tinction between these components is arbitrary (there are no sharp time-constraints associated with each of them), but they rely on different microstructural mechanisms. The first one (short-term) is associated with straightening/ alignment of Se polymeric chains (can be alternatively understood as transition from cis- to trans-conformations of Se atoms in chain within a so-called double-well potential) followed by shrinkage of surrounding network [9]. This is a relatively fast process, which can be activated at room temperatures. The other mechanism is associated with prolonged overall shrinkage of under-constrained R. Golovchak (&) Á O. Shpotyuk Lviv Scientific Research Institute of Materials of SRC ‘‘Carat’’, 202, Stryjska Str., Lviv 79031, Ukraine e-mail: roman_ya@yahoo.com O. Shpotyuk e-mail: shpotyuk@novas.lviv.ua A. Kozdras Department of Physics of Opole University of Technology, 75, Ozimska Str., Opole 45370, Poland O. Shpotyuk Institute of Physics of Jan Dlugosz University, 13/15, al. Armii Krajowej, Czestochowa 42201, Poland S. Kozyukhin Institute of General and Inorganic Chemistry of RAS, Leninsky Pr. 31, Moscow 199991, Russia J.-M. Saiter LECAP, FRE3101, PBS, Faculte ´ des Sciences, Institut des Mate ´riaux de Rouen, Universite ´ de Rouen, Avenue de l’Universite ´ BP 12, 76801 Saint Etienne du Rouvray, France 123 J Mater Sci (2009) 44:3962–3967 DOI 10.1007/s10853-009-3540-6