Various heating rates (VHR) as a method for crystallization kinetics determination and its application to Se 75.5Te 20Sb 4.5 chalcogenide glass

Abstract

A new method (VHR method) has been derived from Johnson–Mehl–Avrami (JMA) transformation rate equation to calculate the crystallization kinetic parameters of a glassy system. These parameters include the activation energy of crystallization E (kJ/mol), the kinetic exponent n and the frequency factor K o (s −1). The VHR method starts with obtaining E. Let us consider x i ( t) as the volume fractions of crystallization which are obtained at various heating rates β i (K/min). The method for obtaining E depends on finding the temperatures T i (K) and the times t i (s) which are required to produce the same values of x i ( t) at various values of β i . Next, the value of n is obtained by using the temperatures T 1 (K) and T 2 (K) and the times t 1 (s) and t 2 (s) which are extracted at two different values of the volume fraction x 1( t) and x 2( t) at the same heating rate. Finally, the value of K o may be obtained at any value of x( t) after obtaining the values of E and n, successively. The applicability and the full descriptions of the VHR method have been thoroughly tested on computer simulated crystallization curves. Also, the validity of the VHR method has been checked in the cases of n being temperature-independent and temperature-dependent parameter. The VHR technique has been used to estimate the crystallization parameters of Se 75.5Te 20Sb 4.5 chalcogenide glass under non-isothermal conditions.