Grain size effects on the transport properties of Li₃V₂(PO₄)₃ glass–ceramic nanocomposites for lithium cathode batteries

The effect of grain size on the structural and transport properties of glass–ceramic nanocomposites consisting of Li₃V₂(PO₄)₃ crystals were investigated by differential scanning calorimeter, X-ray diffraction (XRD), transmission electron micrograph (TEM), density (d) and dc conductivity. XRD patterns exhibit the formation of Li₃V₂(PO₄)₃ with monoclinic structure. It was shown by XRD and TEM studies that by appropriate heat-treatment glasses can be turned into glass–ceramic nanocomposites consisting of crystallites smaller than 56 nm embedded in the glassy matrix. Density was found to increase with increasing grain size while the molar volume decreases. The dc conductivity measured in high temperature range increased with decreasing of the grain size while the activation energy decreased. The calculated dc conductivity at 400 K for the present glass was 5.77 × 10⁻⁷ S/cm, while in its glass–ceramic nanocomposites was in the range of 1.712 × 10⁻⁵–2.10 × 10⁻⁶ S/cm. On the other hand, the calculated activation energy for the present glass was 0.542 eV, while in its glass–ceramic nanocomposites was in the range of 0.165–0.468 eV. The increase in electrical conductivity in the glass–ceramic nanocomposite annealed at 450 °C for 4 h compared to that annealed at 450 °C for 2, 8, 24 h can be attributed to the decrease in grain boundary scattering due to the reduction in grain size. The conduction was confirmed to obey non-adiabatic small polaron hopping. The electron–phonon interaction coefficient (γ _p) was calculated and found to be in the range of 5.09–16.64.