Abstract

During the last years the interest to study the silvercontaining glass-forming systems has increased, due to the possibility to obtain materials exhibiting high ion conductivity [1–5]. By now mainly P2O5 and B2O3 have been used as a glass former for the ionic conducting glasses. A few publications are known on the synthesis of ionic conductive tellurite glasses [6–9] and also for V2O5 containing glasses [10–15]. In our previous investigations of the system Ag2OTeO2-V2O5 [16] a wide region of glasses (Fig. 1), which are synthesized in the central part of the system up to 40 mol.% Ag2O, using low cooling rate (≤100 degree/min) has been found. Meanwhile, many glass compositions in this system rich of V2O5 exhibit semiconducting properties [17], but with increasing Ag2O content high ion conductivity [18] is revealed. By the heat treatment of glasses in the 300–350 ◦C range, they easily crystallize with fine microstructure typical for glass-crystalline materials. The phase diagram of the Ag2O-TeO2-V2O5 system was also examined in detail [19, 20]. The fields of primary crystallization of twelve phases were outlined: 2TeO2·V2O5, Ag2O·TeO2, 3Ag2O·V2O5, 2Ag2O·V2O5, Ag2O· V2O5, Ag2O·2V2O5, Ag2O·7V2O5, TeO2, V2O5, Ag2O, Ag2O·3V2O5·6TeO2, and Ag2O·V2O5·2TeO2. In the Ag2O rich area dissociation of Ag2O to elementary silver has been noticed. This variety of crystal phases is a prerequisite for the synthesis of glasses with different structure. The glass structure of some compositions was also investigated. It is proved that the three-dimensional tellurite structure is destroyed and Te-non-bridging oxygen (NBO) bonds are formed with the increase of Agion content in the glasses of the Ag2O-TeO2 system [21]. The increase of Ag2O content up to 30 mol.% leads to the formation of TeO3 groups. S. Rossignol et al. investigate the structure of glasses from the system TeO2-AgO0.5-AgI. These glasses contain deformed TeO4 groups such as TeO3+1 groups. The structure of the tellurite network is not modified by the addition of AgI [7, 9]. Our purpose is to study the thermal stability and modifications of the structure of glasses with increase of silver ions in the glass formation range of the Ag2O-TeO2-V2O5 system. The determination of specific structural units of the glass network is made by IR-spectroscopy in accordance to the concept about the independent vibrations of separate groups in the glasses. They were discussed in detail many years ago by Tarte [22, 23] and Condrate [24, 25]. Glass compositions were chosen with a different Ag2O/TeO2/V2O5 ratio along Ag2O 2TeO2·V2O5 (A) and TeO2 Ag2O·2V2O5 (B) lines (Fig. 1). The choice was made having in mind the previous investigations of the glass forming region and the type of crystal phases, which could separate according to the phase diagram, during the thermal treatment procedure. As initial precursors for the synthesis were used reagent grade TeO2, V2O5 and Ag2O. After homogenization, the bathes were melted in porcelain crucibles at 600– 800 ◦C temperature range. The melts were quenched rapidly between two polished copper plates. A twin roller quenching technique was used for the compositions with high Ag2O content beyond the traditional glass-forming region. The samples were identified by X-ray powder diffractometer Philips APD 15 (Cu Kα radiation). The thermal behavior was investigated using Perkin-Elmer DSC 4 differential scanning calorimeter. The structure of the glasses was investigated by infrared absorption spectroscopy (IR) using SPECORD-M80 spectrometer preparing powder samples dispersed in Nujol. On Fig. 2 are presented DSC-curves and in Table I are summarized some thermal parameters of the glasses along a selected line (A). The glass-forming ability of melts and the thermal stability of glasses are interpreted using some criteria [26, 27]: (Tc− Tg), Tg/Tl,

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