Impact of non-bridging oxygens on the thermal, electrical and optical properties of germanate glasses and exploration of the germanate anomaly

In this study, we successfully prepared quaternary germanate glasses (Bax/3Srx/3Cax/3)Ge(1-x)O3 (x = 0.1–0.5) using a containerless solidification method. The structure of the germanate amorphous materials was characterized using techniques such as XRD, SEM, TEM and Raman. We evaluated the thermodynamic properties of the amorphous materials using differential scanning calorimetry and investigated their crystallization activation energies. In terms of application performance, we measured electrical conductivity and impedance spectra for the electrical properties, while the optical properties were assessed through the refractive index and transmittance. The results revealed that the (Ba0.2/3Sr0.2/3Ca0.2/3)Ge0.8O3 system represented the germanium anomaly point. Due to the highest number of ternary rings and the most compact structure within this system, the values of density, glass transition temperature, refractive index, and bandgap all reached their maximum. As the content of alkaline earth oxides increased, the glass network structure gradually fractured, leading to an increase in non-bridging oxygens and corresponding changes in properties.