Combined calorimetric and PDF study of the nanodomain structure of SixOyCz polymer-derived ceramics

摘要

SixOyCz polymer-derived ceramics (PDC's), prepared by a polymer pyrolysis route, possess very intriguing properties: (i) they resist crystallization and retain their amorphous structure to very high temperature (1300-1400 °C), show almost negligible steady-state creep at high temperature (near 1500 °C), and are very resistant to oxidation despite their excess carbon content. Recently, using high-temperature oxide melt drop solution calorimetry, we have revealed a negative enthalpy of formation for SixOyCz PDC's relative to their binary constituents and graphite. The conceptual structural model of these PDC's involves silica nanodomains surrounded by graphene layers with mixed Si-C-0 bonds forming the interface between them. Their thermodynamic stability is explained by low free energy at graphene-silica interfaces. In this work, the actual nanodomain structure of this amorphous material is characterized using pair distribution function (PDF) analysis of synchrotron x-ray scattering data, and discussed in the light of earlier results.