ABSTRACT
Nanocrystals (NCs) are complex systems that offer a superior level of detailed engineering at the atomic level. The large number of novel and revolutionary applications have made nanocrystals of special interest. In particular oxide perovskites are one of the most widely investigated family of materials in solid-state chemistry, especially for their ferroelectric and superconducting properties. In addition to these well-known properties, perovskites show good electrical conductivity (close to metals), ion conductivity and mixed ionic-electronic conductivity. In that sense, controlled synthesis of nanomaterials with special care over size and shape are essential in many fields of science and technology. Although it is well-known that physical methods deliver excellent quality nanomaterials, their high production cost has increased the interest to more affordable alternative chemical processes. In this review, we focus on the preparation of sub-10 nm oxide perovskite nanocrystals and the main strategies used to control the final properties of the obtained products. In the second part, we present the methods available for nanocrystal solutions processing together with the most remarkable applications foreseen.
ABSTRACT
Recent advances in memristive nanocrystal assemblies leverage controllable colloidal chemistry to induce a broad range of defect-mediated electrochemical reactions, switching phenomena, and modulate active parameters. The sample geometry of virtually all resistive switching studies involves thin film layers comprising monomodal diameter nanocrystals. Here we explore the evolution of bipolar and threshold resistive switching across highly ordered, solution-processed nanoribbon assemblies and mixtures comprising BaZrO3 (BZO) and SrZrO3 (SZO) nanocrystals. The effects of nanocrystal size, packing density, and A-site substitution on operating voltage (VSET and VTH) and switching mechanism were studied through a systematic comparison of nanoribbon heterogeneity (i.e., BZO-BZO vs BZO-SZO) and monomodal vs bimodal size distributions (i.e., small-small and small-large). Analysis of the current-voltage response confirms that tip-induced, trap-mediated space-charge-limited current and trap-assisted tunneling processes drive the low- and high-resistance states, respectively. Our results demonstrate that both smaller nanocrystals and heavier alkaline earth substitution decrease the onset voltage and improve stability and state retention of monomodal assemblies and bimodal nanocrystal mixtures, thus providing a base correlation that informs fabrication of solution-processed, memristive nanocrystal assemblies.
