Effect of zirconium on precursor chemistry, phase stability, and oxidation of polyvinylsilazane-derived SiCN ceramics

Structural evolution and oxidation resistance of polysilazane‐derived SiCN–HfO2 ceramics

“…42 For the PVS-1400 sample, weak peaks at ∼25.5 and 44 • 2θ angles can be observed, corresponding to the (0 0 2) and ( 1 phase separation in the amorphous SiCN pyrolyzed at 1400 • C, making it a pseudo-amorphous ceramic. 35 The SiHfCNO ceramics pyrolyzed at 900 • C (PVS-Hf-900) show a broad diffraction hump from 28 22 2), and (4 0 0) planes of t-HfO 2 . Nevertheless, the only nanocrystalline phase formed at 900-1400 • C in the SiHfCNO ceramics is t-HfO 2 .…”

“…The overall ceramic yield of the PVS-Hf precursor remains at ∼76.6 wt%, which is 6.2 wt% lower than that of the pure PVS precursor. 35 F I G U R E 2 Fourier transform infrared (FTIR) analysis of cross-linked and pyrolyzed polyvinylsilazane (PVS)-Hf samples at different temperatures.…”

“…There are no sharp peaks reported at high temperatures (above 1100 • C) as in the case of pure PVS sample. 35 This suggests that Hf-doping to the PVS precursor suppresses the phase separation and crystallization of C free in the SiCN matrix.…”

“…The size of t-ZrO 2 crystals in the SiCN matrix was reported to be 2.5-8.8 nm in the pyrolysis temperature range of 1000-1400 • C, respectively. 22,35 Slower growth of t-HfO 2 F I G U R E 5 Raman spectra of as-prepared SiHfCNO ceramics at different pyrolysis temperatures. versus t-ZrO 2 in the SiCN ceramics is primarily due to reduced Hf diffusivity.…”

“…Current investigation is an attempt to understand the oxidation resistance of the SiCN and SiO 3)-( 5); the mass gain in the Hf-containing SiCN is attributed to the oxidation of mixed bond structural units of SiC x N 4−x . 18,35 𝐶 free (𝑠) + 𝑂 2 (𝑔) → CO 2 (𝑔)…”