B2O3-doped borophosphate glasses with enhanced dielectric properties: Structural modifications and electrical behavior for capacitor and thermistor applications

Phosphate glasses doped with varying amounts of B 2 O 3 , 30Li 2 O-20ZnO-xB 2 O 3 -(50-x)P 2 O 5 (where x is 0, 10, or 45 mol%), were synthesized using the conventional melt-quenching technique. Building upon our previous structural validation, this study focuses on the physical, vibrational, and specifically the dielectric properties of these unique borophosphate compositions. X-ray diffraction (XRD) analysis confirmed the predominantly amorphous nature of the samples utilized for electrical measurements, consistent with the established glass-forming ability of this system. Differential scanning calorimetry (DSC) verified the thermal stability of the glass network, showing that B 2 O 3 addition enhances stability and delays transition temperatures, ensuring the material's integrity for high-temperature applications. The impact of boron oxide on the physical properties of the glass, such as density, molar volume, and oxygen packing density showed notable trends correlated with B 2 O 3 content, revealing a progressive spatial compaction of the glass matrix. Structural modifications induced by B 2 O 3 doping were further investigated using Fourier-transform infrared (FTIR) spectroscopy. Dielectric investigation reveals a marked enhancement of the relative permittivity (ε r ) with increasing B 2 O 3 content, combined with low dielectric losses, highlighting suitability for capacitor applications. This enhancement is primarily attributed to the generation of highly polarizable non-bridging oxygens due to the modifying role of boron at high concentrations. Impedance spectroscopy provided insights into the electrical behavior of the glasses, indicating the presence of both negative (NTCR) and positive (PTCR) temperature coefficients of resistance. This dual behavior suggests promising applications in NTC and PTC capacitors as well as thermistors.