Effects of Zr on the precursor architecture and high-temperature nanostructure evolution of SiOC polymer-derived ceramics

SiOC and SiZrOC ceramics were obtained starting from the hydrosilane system without and with zirconium n-propoxide (Zr(OⁿPr)₄) by sol-gel route. The precursor architectures indicated that the presence of SiH bonds leads to a different cross-linking mechanism of SiZrOC precursor, where the SiH bonds were involved in the formation of SiOZr bonds. The presence of Zr caused a lower content of sp³ carbon in SiZrOC ceramics. At above 1400°C, the sp3-C/Si ratio in both ceramics increased due to carbothermal reduction, especially rapidly for SiOC ceramics, suggesting the carbothermal reduction in SiZrOC ceramics has been strongly suppressed with the presence of ZrO₂. Raman spectroscopy showed the graphitization degree of free carbon increased with temperature in both ceramics, but was always lower in SiZrOC ceramics. The SiZrOC ceramics has been found to exhibit remarkably high temperature stability with respect to carbothermal decomposition up to 1600°C in comparison with the SiOC ceramics.