35: Variable pressure impedance spectroscopy in metal triazolate nanoparticles

Abstract: Coupled ion-electron conductivity has been a subject of growing interest in recent years due to its implications in lithium-ion battery charging/discharging rates. Although many groups have studied impedance in mixed ion-electron conductors at variable temperature, few have focused on variable pressure impedance measurements. Variable pressure impedance spectroscopy is ideal for studying mixed conductors due to the dissimilar effects increased pressure may have on the ionic and electronic contributions to conductivity. For example, increased pressure may shorten bond distances leading to greater orbital overlap, increasing band dispersion and therefore charge carrier mobility. In contrast, shorter bond distances in intercalation materials may restrict ion mobility by reducing the size of the channels the ions pass through. In this work we use variable pressure impedance spectroscopy to study mixed ion-electron conductivity in metal triazolates, a class of conductive metal organic frameworks. We focus on iron and chromium triazolate due to their mixed valence nature which give rise to high electronic conductivity by increasing the number of charge carriers and reducing the band gap. The mixed valence nature of iron and chromium triazolate also introduces mobile anions to the framework to balance the charge of the oxidized metal centers, leading to a significant ionic contribution to conductivity. We find significant increases in electronic conductivity with increased pressure as expected and the magnitude of this change varies with particle size.