Size-Controlled Agl/Ag Heteronanowires in Highly Ordered Alumina Membranes: Superionic Phase Stabilization and Conductivity

Nanoscaled ionic conductors are crucial for future nanodevices. A well-known ionic conductor, AgI, exhibited conductivity greater than 1 Omega(-1) cm(-1) in alpha-phase and transformed into poorly conducting beta-/gamma-phase below 147 degrees C, thereby limiting applications. Here, we report that transition temperatures both from the beta-/gamma- to alpha-phase (T-c up arrow) and the alpha- to beta-/gamma-phase (T-c down arrow) are tuned by AgI/Ag heteronanowires embedded in anodic aluminum oxide (AAO) membranes with 10-30 nm pores. T-c up arrow and T-c down arrow to correspondingly higher and lower temperature as pore size decreases, generating a progressively enlarged thermal hysteresis. T-c up arrow and T-c down arrow specifically achieve 185 and 52 degrees C in 10 nm pores, and the final survived conductivity reaches, similar to 8.3 x 10(-3) Omega(-1) cm(-1) at room temperature. Moreover, the low-temperature stabilizing alpha-phase (down to 21 degrees C, the lowest in state of the art temperatures) is reproducible and survives further thermal cycling. The low-temperature phase stabilization and enhancement conductivity reported here suggest promising applications in silver-ion-based future nanodevices.