Physical properties and structural studies of lithium borophosphate glasses containing TeO2.

Abstract This work presents a study on the structure, thermal behavior and properties of (100-x)[0.5Li 2 O-0.1B 2 O 3 -0.4P 2 O 5 ]-xTeO 2 glasses prepared within the concentration range of x = 0–80 mol% TeO 2. The structure of the glasses was studied with a combined Raman, 31P and 11B MAS NMR spectroscopy. 31P MAS NMR and Raman spectrum of the pure 50Li 2 O-10B 2 O 3 -40P 2 O 5 glass indicates the co-existence of Q2 and Q1 phosphate units in the glass structure. Raman spectra of TeO 2 containing glasses revealed that TeO 2 is incorporated in the structural network in the form of TeO 3 and TeO 4 (TeO 3+1) units. The ratio of TeO 4 /TeO 3 increases with rising TeO 2 content. Apart from the formation of P‒O‒Te and Te‒O‒Te bonds, the formation of B‒O‒Te bonds in the form of mixed tetrahedral units B(OP) 4-n (OTe) n also takes place as shown by 11B MAS NMR spectroscopy. The structural studies were correlated with the thermal behavior and physical properties of glasses (density, molar volume, chemical durability and refractive index). DSC studies showed that all glasses crystallize on heating within a temperature region of 400–550 °C and the surface nucleation mechanism prevails over the internal one. The crystallization temperature decreases with increasing TeO 2 content. The compounds formed by crystallization were LiPO 3 , Li 4 P 2 O 7 , BPO 4 and α-TeO 2. Glass transition temperature and dilatometric softening temperature, estimated from thermodilatometry curves, decrease with increasing TeO 2 content, whereas the thermal expansion coefficient increases. Graphical abstract The compositional dependences of glass transition temperature, T g , dilatometric softening temperature, T d , and thermal expansion coefficient, α , of the (100-x)[0.5Li 2 O-0.1B 2 O 3 -0.4P 2 O 5 ]-xTeO 2 glasses, obtained from dilatometric curves. fx1 Highlights • Structure of Li 2 O-B 2 O 3 -P 2 O 5 -TeO 2 glasses. • Raman, 31P and 11B spectroscopy. • Thermal behavior and physical properties of Li 2 O-B 2 O 3 -P 2 O 5 -TeO 2 glasses. • Relationships between structure, thermal behavior and physical properties. [ABSTRACT FROM AUTHOR]