Structural properties of strontium vanadate glasses
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Structural studies of the strontium vanadate glasses of compositions xV2O5–(100 − x)SrO are reported. X-ray diffractograms, density, and oxygen molar volume, etc., of the glasses show that single-phase and homogeneous glasses were obtained in the composition domain x ⳱ 50 to 90 mol%. The network structure for the glass compositions with 90 and 80 mol% V2O5 is built up of the VO5 polyhedra, while the other glass compositions consist of the VO4 polyhedra. Density and glass transition temperature are observed to decrease with an increase in the V2O5 content. The magnetic susceptibility of the glasses shows an increase of concentration of the reduced V4+ ion with the increase of vanadium oxide content in the compositions. The well-resolved electron spin resonance structure observed for the glass composition with 50 mol% V2O5 gradually becomes poor and reduces to a single component line, which has been attributed to the increase of the hopping rate of charge carriers with the increase of the V2O5 content in the compositions.
I. INTRODUCTION
Oxide glasses containing transition metal ions (TMI)1–5 are of continuing interest because of their applicability in memory switching, electrical threshold, and optical switching devices, etc.6–8 The semiconducting nature of these glasses arises from the presence of two valence states of the TMI.1–5,9,10 Glasses containing vanadium possess both V4+ and V5+ ions and the electrical conduction process occurs due to the hopping of an unpaired 3d1 electron from a V4+ site to a V5+ site.9,10 The unpaired electron induces a polarization of the vanadium ion around it and forms a polaron. Although a large number of studies have reported on the electrical properties of TMI glasses, surprisingly the structure of these glasses has not been studied so extensively. A study of the infrared (IR) properties of a number of vanadate glasses has been reported.11,12 It has been observed that the structure of these glasses depends on the nature of the network formers as well as on the network modifiers. In this paper, we studied glass formation domain and the composition dependence of the structure and other physical properties of the strontium vanadate glasses. Interestingly we have observed that a large composition domain with a single-phase network structure can be obtained in this glass system in which the V2O5 acts as a unique glass
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 4, Apr 2000
http://journals.cambridge.org
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network former in contrast to the vanadate glasses formed with other traditional glass formers such as P2O5, SiO2, etc.1–8 II. EXPERIMENT
Glass samples were prepared from the reagent grade chemicals V2O5 and SrCO3. The chemicals in appropriate proportions (Table I) were mixed uniformly. The mixtures were decarbonized at 450 °C for 3 h in alumina crucibles and were melted in the temperature range 850 to 1200 °C depending on the compositions. It was observed that the melting temperature decrea
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