Thermal conductivity of SiC microwires: Effect of temperature and structural domain size uncovered by 0 K limit phonon scattering

A comparative study of structure and thermal properties is reported for three 3C crystalline silicon carbide (SiC) microwires, including Sylramic, Hi-Nicalon S and a sample fabricated by laser chemical vapor deposition (LCVD). Structural characterization by Raman spectroscopy and x-ray diffraction (XRD) finds that the LCVD-based sample contains excessive silicon and smallest grains of SiC but detectable free carbon. Thermal characterization from room temperature down to 20 K uncovers the effect of nanosized grain on thermal properties. The thermal properties are correlated with the structure via structural thermal domain (STD) size, defined as the grain boundary-induced phonon mean free path at the 0 K limit. The STD size of the three samples is found as 9.35, 1.42 and 1.03 nm for the Sylramic, Hi-Nicalon S and LCVD SiC fibers, proportional to and nearly one order of magnification smaller than the corresponding crystalline size determined by XRD: 67-113, 14.6-18.4, and 5.85-7.84 nm.