Electrical conductivity change induced by porosity within polymer-derived SiCN ceramics

Polymer-derived ceramics (PDCs) which is synthesized by pyrolysis of organosilicon polymers have recently attracted an increasing attention on the electrical property with possible application in Li-ion batteries, micro electro mechanical systems (MEMS) and harsh-environmental sensors. In this paper, the chemical composition, nanostructure evolution and the electrical conductivity variation which are induced by porosity are explored systematically in polymer-derived SiCN ceramics. The SiCN ceramics with 0, 4.82%, 8.94%, 16.81% and 21.32% porosities were prepared by mixing the polymer precursors with different crosslinking degree. There are significant changes in the content of N element, free carbon, crystallization SiC and the morphology of free carbon with the increasing porosity. As the porosity increases, the electrical conductivity of the SiCN ceramics decrease gradually from 0.015 to 0.003 S cm⁻¹. By comparing the relationship between the conductivity and the porosity from experiment and model prediction (only intrinsic porosity considered), it can be concluded that the chemical composition, nanostructure evolution dramatically decrease the conductivity of SiCN ceramics with 56.41% maximum decline, and the decrease of the free carbon content is the most significant aspect influencing the electrical conductivity of SiCN ceramics. Our findings can realize the regulation of the nanostructure and electrical conductivity in polymer-derived SiCN ceramics by the control of porosity with a new insight on the design of PDCs functional materials.