is the professor of Materials Science at the Faculty of Chemical Technology of the University of Pardubice, Czech Republic. In the 80th he was involved in the studies of chalcogenide glasses, especially their structure, using the methods of vibrational spectroscopy. From the 90th he studies phosphate and borophosphate glassy and crystalline materials and their structure by Raman and NMR spectroscopy. He organized International Conference on Borate and Phosphate Glasses in Pardubice, Czech Republic in 2014. From 2011 he is a vice-chairman of the Czech Glass Society.
Ladislav Koudelka*, Petr Kalenda & Petr Mošner
Tungsten oxide is able to form large glass-forming regions in phosphate glasses. Moreover, glasses containing WO3 offer prospective applications for their electrochromic properties. In this contribution we prepared and studied homogeneous glasses in the compositional series 40K2O-xWO3-(60-x)P2O5 with x = 10-50 mol% WO3. These glasses were prepared at temperatures of 800-900°C in platinum crucibles and cooled freely in the air. An increase in the WO3 content resulted in an increase of the glass transition temperature from 214°C up to 423°C for the glass with 40 mol% WO3. Glasses with a higher content of WO3 are usually blue coloured due to the presence of tungsten in the oxidation state W5+, but in the studied series these glasses were transparent and slightly green coloured. The reason is a high value of optical basicity stabilizing higher oxidation states . Our results are in agreement with the theory of J.A. Duffy , showing on the stabilization of the higher oxidation state of metal ions in glasses with increasing basicity of the glass composition. Nevertheless, in our glasses the ratio of W5+/W6+ can be also changed by the melting time and temperature. Raman spectra of these glasses are dominated by the vibrational bands of tungstate structural units. The observed shift of the maximum of the dominant vibrational band from 955 to 933 cm-1 for WO3-doped glasses is ascribed to changes in the coordination of tungsten from octahedral WO6 to tetrahedral WO4 as the dominant vibration (υ1) in of crystalline Na2WO4 with containing WO4 tetrahedra is placed at 928 cm-1.
- J.A. Duffy, Geochim. Cosmochim. Acta, 57 (1993) 3961.