Glass - Back to the Future!

Presenting Author:
Petr Kalenda

article posted 6 April 2016

Petr Kalenda is PhD student at the University of Pardubice, Czech Republic, Faculty of Chemical Technology, Department of General and Inorganic Chemistry. His research in the work group of prof. Ladislav Koudelka is oriented on phosphate and borophosphate glasses of alkaline-earth metals, especially on the study of their thermal behaviour and relationships between their structure and properties.

BaO–Nb2O5–P2O5 glasses and their crystallization

Petr Kalenda1*, Ladislav Koudelka1, Petr Mošner1, Lionel Montagne2 & Bertrand Revel2
1 University of Pardubice, Faculty of Chemical Technology, 53210 Pardubice, Czech Republic
2 University of Lille, CNRS, ENSCL, Univ. Artois, UMR 8181 – UCCS – Unité de Catalyse et Chimie du Solide, F-59000 Lille, France

Phosphate glasses containing high amount of transition metal ions (e.g. WO3, MoO3 or Nb2O5) have optical non-linear characteristics, which make them perspective for optical devices. Nine glassy samples of the ternary system BaO-Nb2O5-P2O5 was prepared in two compositional series: 40BaO–xNb2O5–(60-x)P2O5 with x=0–40 and yBaO–20Nb2O5-(80-y)P2O5 with y=20–60. Basic physical parameters of all prepared glasses were obtained. Thermal behavior of these glasses was studied by differential thermal analysis, hot-stage microscopy and dilatometry. The glass transition temperature increases with increasing content of Nb2O5 in the first glass series from 324 to 727°C, while thermal expansion coefficient decreases in the range of 15·7–9·3 ppm/°C. In the compositional series yBaO–20Nb2O5–(80-y)P2O5 both values slightly increase with BaO content. Structure of the glasses was studied by Raman spectroscopy and 31P NMR spectroscopy. Raman spectra revealed that in the first series at low Nb2O5 content a strong vibrational band of isolated NbO6 octahedra dominates the spectra, whereas at higher Nb2O5 content new bands dominate in the Raman spectra in the glasses with 30–40 mol% of Nb2O5 that were assigned to vibrations of Nb–O–Nb bonds interconnecting NbO6 octahedra. Crystallization of these glasses was studied and the crystallization products were identified by X-ray diffraction. Raman spectroscopy results were in a good agreement with X-ray diffraction. In the samples containing low Nb2O5 content primarily crystalline barium metaphosphate BaP2O6 is formed, while in those with a higher amount of Nb2O5, several crystalline niobium phosphates, barium niobates or barium niobium phosphates were found. Moreover, two barium niobophosphate compounds lying within the glass forming region in this ternary system, with the compositions of BaNb2P2O11 (with 33·3 mol% Nb2O5) and Ba3Nb2(PO4)4O2 (with 16·6 mol% Nb2O5) were investigated. They were prepared both in glassy and crystalline form and their 31P and 93Nb NMR spectra and Raman spectra were compared and discussed.