GLASSES OF THE SYSTEM AG-GE-TE

A middle-sized vitreous domain resulting from binary glasses of the Ge-Te system has been found. DTA measurements of the glass-transition (Tg) and crystallization (Tc) temperatures have been performed which show that, for a constant value of the Ge/Te ratio, the values of these parameters do not depend on the silver content. Electrical properties of the vitreous AgxGeTe4.7 system (with 0.00 less-than-or-equal-to x less-than-or-equal-to 1.40) have been investigated by means of the complex impedance method. At 25-degrees-C, electrical conductivity and activation energies vary within 10(-5) and 10(-4) OMEGA-1.cm-1 and within 0.47 and 0.42 eV, respectively. Optical gap and e.m.f. measurements as well as the determination of the electronic transference number by means of electrochemical semipermeability flux measurements reveal a semiconductor behaviour in spite of the rather high silver content. In order to investigate the local structure around the silver and germanium atoms, an EXAFS structural approach has been undertaken. The obtained results show that in ternary glasses the arrangement of the tellurium atoms around a germanium atom is appreciably the same as that found in binary glasses. It can be noticed that Fourier transform moduli are higher for glassy phases than for crystalline ones; such a feature has previously been observed in the As-Te system. Besides, Ag+ ions appear to be tetracoordinated.