Abstract
Crystallization kinetics of 22.5Li2O?10Al2O3?30GeO2?37.5P2O5 (mol%) glass was studied under non-isothermal condition using the differential thermal analysis (DTA). The study was performed by using the first crystallization peak temperature (Tp1) which belongs to the precipitation of LiGe2(PO4)3 phase in the glass. The activation energy of glass crystallization (Ea) was determined using different isokinetic methods. The dependence of Ea on the degree of glass-crystal transformation (?) was studied using model-free isoconversional linear integral KAS (Kissinger-Akahira-Sunose) and FWO (Flynn-Wall-Ozawa) methods. It was shown that the Ea varies with ? and hence with temperature and consequently the glass/crystal transformation can be described as a complex process involving different mechanisms of nucleation and growth.
Highlights
Lithium germanophosphate glasses have recently emerged as multipurpose materials and have drawn great attention because of their potential applications in various solid state devices [1, 2]
As revealed previously the peak Tp1 belongs to the precipitation of LiGe2(PO4)3 crystalline phase
Unlike to isokinetic methods where the kinetic parameters of the process are assumed to be constant with respect to time and temperature, the isoconversional methods assume the transformation mechanism at constant degree of conversion as a function of temperature and provide the kinetic parameters that are varying with the degree of conversion, α
Summary
Lithium germanophosphate glasses have recently emerged as multipurpose materials and have drawn great attention because of their potential applications in various solid state devices [1, 2]. By crystallization of some glasses from the system Li2O-Al2O3-GeO2-P2O5, the LiGe2(PO4) phase which belongs to the solid solutions with general formula of Li1+xMxGe2x(PO4) (M=Al, V or Cr) is formed. This family of the crystalline phosphates is often referred to as NASICON-type materials [3, 4]. It is important to know the crystallization behavior of the parent lithium phosphate glass in order to define technological parameters for fabrication of these structured materials. The crystallization kinetics of glasses can be successfully studied using the DTA or DSC techniques and for evaluation of the kinetic parameters of crystallization several methods classified as isokinetic and isoconversional (model-free) are used. Isokinetic methods assume the transformation mechanism to be same throughout the temperature or time range and allow calculating single values of the kinetic parameters such
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