Spark plasma sintered Si(Hf)OC nanocomposites exhibiting thermally stable dielectric behavior processed through precursor route

Abstract

This work uses hafnium n tetra butoxide precursor to modify silicon oxycarbide (SiOC) with an easy, novel, and economical procedure to synthesize Si(Hf)OC nanocomposites. FTIR analysis confirmed the formation of Si–O-Hf linkages during cross-linking. The as-pyrolyzed powders were sintered using the spark plasma sintering technique. X-ray diffractograms confirmed the in-situ crystallization of tetragonal HfO2 in an amorphous SiOC matrix. The morphological features were imaged using electron microscopy. The dielectric properties of sintered Si(Hf)OC nanocomposites were investigated at varied temperatures (25 °C–250 °C) and frequency ranges (10−1 Hz–106 Hz) for the first time. At room temperature, the ε՚ value at 1 kHz is found to be 14, which is almost double the value of pure sintered SiOC (ε՚∼5). The dielectric loss (tanδ) is less than 0.07 at 1 kHz at room temperature, which is significantly less than sintered SiOC (tanδ ∼0.5). An increase in permittivity is associated with high permittivity t-HfO2 nanocrystals and additional interfacial/space charge polarization at the interfaces between the t-HfO2 and SiOC matrix. At high-frequency regions (>1 kHz), the dielectric properties of nanocomposites were found to be thermally stable (up to 250 °C). At low-frequency regions (<70 Hz), the material exhibits a rise in dielectric permittivity with increasing temperature, most likely due to charge carrier accumulation at the interfaces of t-HfO2, SiO2, and carbon in the SiOC matrix through the migration of thermally activated charge carriers.