Temperature cycling effect on structural, optical and electrical properties of nanostructured sodium titanates

Abstract

Sodium titanates represent a promising alternative for the construction of anodes for sodium-ion batteries. To study the electrical response of nanostructured sodium titanate samples under plausible temperature conditions, we evaluate the electrical impedance in the range of temperatures from −30 ∘C to 50 ∘C, and the effect of consecutive temperature cycling. Strong changes in electrical properties are observed during the first temperature cycle, followed by a stabilization in the consecutive cycles. This behavior is reversible when the sample is exposed to external conditions and room temperature for less than an hour. Probably a structural and surface water removal and a surface water reabsorption occur, affecting the charge carriers and with it the impedance. Structurally, no differences are detected before and after the cycles, nor when evaluating only the vacuum process. However, when the optical properties are evaluated we find non-reversible changes after the temperature cycles. The optical behavior after the temperature cycling becomes uniform, the same type of electronic defects become predominant and similar direct and indirect band gap values are obtained, regardless of the starting synthesis condition. These results have significant implications for potential technological applications of these materials.