Transparent glass and glass‐ceramic in the binary system NaPO3‐Ta2O5

Abstract

AbstractTransparent and homogeneous tantalum phosphate glasses were prepared in the binary system (100‐x)NaPO3‐xTa2O5 with x varying from 10 to 50 mol%. Thermal, structural, and optical properties, as well as crystallization mechanisms, were investigated by thermal analysis, X‐ray diffraction, Fourier‐transform infrared spectroscopy (FTIR) and Raman spectroscopies, optical absorption, transmission electron microscopy in terms of Ta2O5 content. FTIR and Raman results support the tantalum insertion in the phosphate chains with [TaO6] polyhedra cross‐linking the phosphate units. At higher Ta2O5 content, [TaO6] clusters are formed and connected to the phosphate network by P‐O‐Ta bonds. This structural evolution is in good agreement with the thermal features measured by differential scanning calorimetry (DSC) with a strong increase of the Tg temperatures up to 920°C, high thermal stability against crystallization for low Ta2O5 content and increasing of crystallization tendency for the most Ta‐concentrated samples. Besides, due to the progressive insertion of [TaO6] units, the precipitation of Na2Ta8O21 perovskite‐like phase was identified in the sample with 50 mol% of Ta2O5. The optimal heat treatment conditions were identified using DSC measurements and a transparent glass‐ceramic from 50NaPO3 to 50Ta2O5 composition was prepared. The obtaines glass‐ceramic has great potential for optical applications, such as host for rare‐earth ions, nonlinear optical materials, and ferroelectric domain.