Studies on the High-Temperature Piezoresistivity of Carbon Containing Silicon Oxycarbide Nanocomposites

• Applicants: Professor Ralf Riedel; Professor Dr.-Ing. Roland Werthschützky
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2013 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 232234385

The interdisciplinary project -Studies on the High-Temperature Piezoresistivity of Carbon-Containing Silicon Oxycarbide Nanocomposites- focuses on Polymer-Derived Ceramics, here SiOC-nanocomposites, whose piezoresistive properties have been explored only rudimentary so far. Two types of complementary studies are intended to obtain a thorough understanding of the piezoresistive effect in these materials: Firstly, structural (e.g., X-ray diffraction, SEM, TEM) and spectroscopic investigations (Raman, FTIR spectroscopy) to reveal the structure-property relationship within the materials (DF) and, secondly, application-oriented investigations to encourage the development of new force/pressure sensors with superior properties at high temperature and in harsh environments (MuST). Prerequisite for these studies is the synthesis of SiOC-nanocomposites with defined carbon content and carbon microstructure. The carbon content will be varied between 1 and 30 vol % by using different polymeric precursors; the phase composition/microstructure is adjusted by means of pressureless or hot-pressing processing techniques. In-situ Raman and force and pressure-dependent resistivity measurements are carried out to provide information on the correlation of the piezoresistive effect with the local and electronic structure of the carbon phase.The temperature dependence of the sample resistivity and of piezoresistive effect will deliver important information about the underlying basic mechanism and will be used to discriminate between different models (tunneling percolation, hopping transport, etc.).The phenomenological application-oriented second part of the project consists of the build-up of special equipment for precise assessment of the piezoresistive effect, its quantification by the Gauge-Factor and the comparison to well-established sensor arrangements. Experiments on the long term stability and reproducibility will be performed in order to determine whether these materials are potential candidates for new pressure sensing devices at unusual conditions (high temperatures, harsh environments). Due to their outstanding properties, e.g. thermal and chemical stability as well as excellent creep resistance, these materials will allow a substantial extension of the operation pressure and temperature range of piezoresistive sensors, beyond the current state-of-the-art.

• DFG Programme: Research Grants