Mixed ionic–electronic transport and polarization-driven energy storage in WO₃-doped P₂O₅–Li₂O–Bi₂O₃ glassy systems

Abstract

Using the traditional melt-quenching method, WO₃-doped lithium bismuth phosphate glassy systems with composition xWO₃–(0.45 − x)P₂O₅–0.25Li₂O–0.30Bi₂O₃ (WPLB), where x = 0.05, 0.10, 0.15, and 0.20, were developed in order to examine their structural, thermal, electrical, dielectric, impedance, and energy-storage behaviour. Results obtained using X-ray diffraction studies show that the synthesized glasses are characterized by an amorphous nature along with the presence of weakly developed nanocrystalline phases, which proves the emergence of the glass structure with an increase in WO₃ content. The density increases from 4.03 to 4.21 g cm⁻³, while the molar volume increases slightly from 53.50 to 54.42 cm³ mol⁻¹ with increasing WO₃ content. As the WO₃ content increased, the glass transition temperature improved from 368.3 to 376.2 °C and the stability parameter ΔT increased from 133.1 to 143.4 °C, according to DSC analysis, indicating an improvement in thermal stability. Based on electrical conductivity studies, it was observed that the glasses possess thermally activated hopping conduction with a systematic reduction in DC activation energy from 0.75 eV to 0.24 eV and crossover activation energy from 0.73 eV to 0.30 eV. It suggests that the presence of lithium-ion movement along with tungsten polaron hopping, occurs in these glasses. The dielectric and electric modulus study verified the non-Debye relaxation through Havriliak-Negami modelling and broadened peaks of electric modulus. The impedance analysis indicated low semicircular loops and a drop in bulk resistance with increasing WO₃ content, suggesting better charge carrier movement and reduced barrier resistance. The P-E loops revealed an increase in recoverable energy density from 14.41 mJ/cm³ to 21.43 mJ/cm³ and efficiency from 61.78% to 72.79% as x increased from 0.05 to 0.20.