Threshold switching behavior generated by the in situ filaments formation in carbon matrix enriched by ultra-small zirconium oxide nanoparticles

Organic/inorganic nanocomposites based on pyrogallol-formaldehyde xerogel, enriched by ultra-small zirconium oxide nanopowder (PF/ZrO${}_2$), were elaborated by a sol-gel method followed by thermal treatment at different temperatures. The XRD data confirm the incorporation of ZrO${}_2$ nanoparticles into the PF carbon matrix. The prepared samples have an amorphous and disordered structure for low pyrolysis temperatures. These structures remain amorphous even at high temperatures. The XRD result manifests also that the zirconium oxide (ZrO${}_2$) particles have a nanosize in the range of 3 nm. This particle size was confirmed also by transmission electronic microscopy (TEM). The TEM image of the nanocomposite PF/ZrO${}_2$ treated at 600 °C shows well the incorporation of the ZrO${}_2$ nanoparticles in the PF matrix. Most zirconium nanoparticles are well dispersed in the prepared carbon matrix. In addition, the scanning electronic microscopy (SEM) images prove the porous nature of the nanocomposites. FTIR spectrums show the existence of C = C and C-OH bond vibrations which are related to the sp${}^2$ hybridization state that affects the electronic properties of such material. Further, the samples prepared at different pyrolysis temperatures present a percolation effect, where the behavior of our nanocomposite is changed from insulator for the low temperature to semiconductor and then to metallic for a high pyrolysis temperature. The I-V characteristic of the sample prepared at 600 °C shows nonlinear conduct with an interesting hysteresis depending on synthesis and measurement parameters. The origin of the obtained conduct is explained in terms of the Joule heating effect and the filament formation phenomenon. These behaviors are promising for threshold-switching elements which can be used as selector elements in crossbar memory arrays.