Mechanisms controlling primary crystallisation of Ga 20 Te 80 glasses M. Fontana a,b, * , B. Arcondo a , M.T. Clavaguera-Mora c , N. Clavaguera d a Departamento de Fı ´sica, Facultad de Ingenierı ´a, Universidad de Buenos Aires, Paseo Colon 850, 1063 Buenos Aires, Argentina b CONICET, Facultad de Ingenierı ´a, Universidad de Buenos Aires, Paseo Colon 850, 1063 Buenos Aires, Argentina c Grup de Fı ´sica de Materials I, Departament de Fı ´sica, Universitat Auto ` noma de Barcelona, Edifici C, 08193 Bellaterra, Spain d Grup de Fı ´sica de l’Estat So ` lid, Departament de E.C.M., Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain Received 23 March 2006; received in revised form 28 February 2007 Available online 23 April 2007 Abstract The kinetic study of the crystallisation process of Ga 20 Te 80 glass from isothermal and continuous heating calorimetric data have been performed applying a recently developed procedure. The kinetic information was complemented with X-ray diffraction measurements. With this scope, three crystallisation patterns, with three-dimensional isotropic growth have been analysed: (i) site saturation and inter- face controlled growth. (ii) homogeneous nucleation with interface controlled growth and (iii) homogeneous nucleation with two simultaneous modes of crystal growth (interface- and diffusion-controlled). A complex model with two simultaneous modes of three- dimensional isotropic crystal growth with decreasing homogeneous nucleation and soft impingement has been applied for modelling pri- mary crystallisation of the Ga 20 Te 80 glass. The model goes beyond the isokinetic hypothesis when coupling isothermal and continuous heating kinetic data. The apparent activation energy E a = (2.06 ± 0.03) eV/at obtained for the primary crystallisation of the phase Te is shown to correspond to an activation energy for nucleation E I = (2.85 ± 0.03) eV/at and an interface controlled activation energy for growth E u = (1.90 ± 0.03) eV/at at the crystallisation onset. Ó 2007 Elsevier B.V. All rights reserved. PACS: 81.10.h; 61.43.Er; 65.60.+a; 67.80.Gb Keywords: Crystal growth; Chalcogenides; Modeling and simulation; Thermal properties; Calorimetry 1. Introduction The microscopic mechanisms for primary crystallisation of chalcogen elements in glassy alloys are the base of microstructural control to optimise semiconducting and optical properties of chalcogenide glasses. Differential scanning calorimetry (DSC) has been widely used for the determination of both the thermal stability of the glassy alloys and the apparent activation energy of crystallisation through the so-called Kissinger plot [1] or Ozawa plot [2]. More controversial is the use of the Kolmogorov–John- son–Mehl–Avrami (KJMA) model [3–7] to examine the kinetics of primary crystallisation in a glassy alloy from continuous heating DSC data, see for instance papers [8– 13], and references cited therein. Primary crystallisation gives rise to a two-phase micro- structure consisting of the primary crystals and an inter- granular glassy phase. In general, the transformation involves two basic steps: nucleation and growth. In the first stage, nuclei of the precipitated phase form due to localised compositional fluctuations that occur statistically within the supersaturated matrix. The second stage involves growth of precipitates by a process of diffusion where the rate-controlling step is transport of the atoms insoluble in the primary growing grains through the disordered matrix. The main objective of this paper is to use the recently introduced master curve method [14] to establish a solid basis for modelling primary crystallisation of Ga 20 Te 80 glasses through kinetic data obtained from DSC measurements. 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.03.007 * Corresponding author. Address: Departamento de Fı ´sica, Facultad de Ingenierı ´a, Universidad de Buenos Aires, Paseo Colon 850, 1063 Buenos Aires, Argentina. Tel.: +54 11 4343 0891; fax: +54 11 4331 1852. E-mail address: mfontan@fi.uba.ar (M. Fontana). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 2131–2142