Calcium aluminogermanate glasses for optical fiber applications

This study investigates the structural, thermal, optical, and mechanical properties of calcium aluminate glasses upon incremental substitution with germania (GeO 2 ). A series of glasses with the molar formula xGeO 2 ·(1− x )(0.64CaO·0.36Al 2 O 3 ), where x = 0–0.50 mole fraction, was synthesized and characterized. Germanium speciation was analyzed, showing a transition from Q 2 to Q⁴ and N 6 species with increasing GeO 2 content, which results in enhanced network connectivity. The incorporation of GeO 2 increases glass density and oxygen packing efficiency due to the germanate anomaly, with Ge shifting to higher coordination states. The liquid fragility index is observed to decrease with GeO 2 addition, indicating improved thermal stability and broader processing windows. Mechanical testing revealed a reduction in moduli and hardness with GeO 2 content, attributed to the replacement of stronger Al–O bonds with more flexible Ge–O bonds. Optical measurements showed improved ultraviolet and visible transparency, with a progressive red shift in the UV cutoff and a slight decrease in the optical band gap. Notably, infrared transmission was enhanced by GeO 2 incorporation, extending the transparency window and reducing OH − ‐related absorption. These results suggest that partially germanated calcium aluminate glasses offer a promising platform for cost‐effective mid‐IR applications, combining thermal robustness, improved processability, and expanded IR transmission with relatively low material cost.