Crystallization processes of Ag-Ge-Se superionic glasses

MARIA ANDREA UREÑA; FONTANA, M.; ARCONDO, B.; MORA, M. T.

JOURNAL OF NON-CRYSTALLINE SOLIDS

Año: 2003 vol. 320 p. 151 - 167

0022-3093

The interest on the superionic systems has increased in recent years because of the potential application of these materials as solid electrolytes. In this field, the amorphous materials present important advantages when compared to the crystalline solids: larger conductivity, isotropy and absence of grain border. In this work, amorphous alloys of compositions (Ge25Se75)100-y Agy with y=10, 15, 20 and 25 atomic % have been studied. Amorphous samples in bulk were obtained from the liquid by water quenching (melt-quenching technique). The crystallization kinetics of the amorphous alloys has been studied under continuous heating and isothermal calorimetric regimes by means of differential scanning calorimetry. A glass transition and two exothermic transformations were observed in all the samples. The quenched samples and the crystallization products have been characterized by X-ray diffraction. The primary crystallization of the ternary phase Ag8GeSe6 and the secondary phase GeSe2 was observed. The glass and crystallization temperatures, the activation energy and the crystallization enthalpy are reported. The first step of the crystallization of the Ag8GeSe6 phase in all the (Ge25Se75)100-yAgy samples is modelled taking into account the Johnson-Mehl-Avrami-Kolmogorov theory (JMAK) and considering that the changes on the composition only modify the viscosity of the undercooled liquid. The transformation diagrams (TTT and THrT) are calculated and the glass forming ability is analyzed. The experimental results are discussed and correlated with the structures proposed for the glass. The present results and conclusions are also compared with those reported by other authors.