The role of Al+3 on the microstructural and electrical properties of Na1+xAlxTi2-x(PO4)3 NASICON glass-ceramics

Abstract Sodium-ion conducting glass-ceramics are synthesized by crystallization of Na1+xAlxTi2-x (PO4)3 (0 ≤ x ≤ 1.4) (NATP) parent glasses. The thermal characterization of glasses is performed by Differential Scanning Calorimetry (DSC) and allowed to determine the glass transition (Tg) and crystallization (Tx) temperatures. An increase in the Tx - Tg parameter is observed, indicating that the thermal stability of glasses against crystallization and also the glass-forming ability increase with the inclusion of Al2O3. The X-ray results show that the NaTi2(PO4)3 phase is the majority phase after the crystallization of the precursor glasses at Tx/ 30 min. X-ray results also confirm that the limit of solid solution is reached for x = 1.0. Electrical measurements indicate that the addition of aluminum ions promotes a decrease in activation energy resulting in the increment of the total ionic conductivity of glass-ceramics by up to five orders of magnitude when compared to the free-aluminum sample. The best sodium-conductive glass-ceramic is obtained for x = 1.0 with a total ionic conductivity of 3.2 × 10−3 S cm−1 at 300 °C and activation energy of 0.47 eV. Using the impedance data converted to the electric modulus formalism, it is analyzed the contribution of the grain and grain boundary in total ionic conductivity. Finally, an increase in the average grain size of the glass-ceramics with the addition of aluminum is also observed, which contributes to the enhancement of overall ionic conductivity.