Enhanced ionic conductivity of AgI nanowires/AAO composites fabricated by a simpleapproach

Abstract

AgI nanowires/anodic aluminum oxide (AgI NWs/AAO) composites have been fabricatedby a simple approach, which involves the thermal melting of AgI powders on the surface ofthe AAO membrane, followed by the infiltration of the molten AgI inside thenanochannels. As-prepared AgI nanowires have corrugated outer surfaces and arepolycrystalline according to scanning electron microscopy (SEM) and transmission electronmicroscopy (TEM) observations. X-ray diffraction (XRD) shows that a considerableamount of 7H polytype AgI exists in the composites, which is supposed to arisefrom the interfacial interactions between the embedded AgI and the alumina. ACconductivity measurements for the AgI nanowires/AAO composites exhibit a notableconductivity enhancement by three orders of magnitude at room temperature comparedwith that of pristine bulk AgI. Furthermore, a large conductivity hysteresis andabnormal conductivity transitions were observed in the temperature-dependentconductivity measurements, from which an ionic conductivity as high as8.0 × 102 Ω−1 cm−1 was obtainedat around 70 °C upon cooling. The differential scanning calorimetry (DSC) result demonstrates a similarphase transition behavior as that found in the AC conductivity measurements. Theenhanced ionic conductivity, as well as the abnormal phase transitions, can be explained interms of the existence of the highly conducting 7H polytype AgI and the formation ofwell-defined conduction paths in the composites.