Polymer-Derived Ceramics: A Novel Inorganic Thermoelectric Material System

Structure and Electrical Properties of Carbon-Rich Polymer Derived Silicon Carbonitride (SiCN)

“…The amorphous phase is associated with very low electrical conductivity (σ dc ), in the range of 10 −9 to 10 −2 S/cm, but a vast increase of several orders of magnitude is observed as the material transforms to crystalline state via increase in pyrolysis temperature [13,14]. Over the years, the strong increase in room temperature (RT) conductivity has been attributed to increase in pyrolysis temperature during thermal treatment of the material, which in turn leads to the following: (i) structural transformation of the carbon phase from amorphous carbon to ordered sp 2 -hybridized carbon (Note that the RT conductivity of sp 2 hybridized carbon is 10 • to 10 5 S/cm); (ii) crystallization of β-SiC (Note that only SiC and sp 2 -hybridized carbon are semiconductors in the composition, Si 3 N 4 is an insulator and does not contribute to conductivity); and (iii) Nitrogen (N) doping of the β-SiC as Si 3 N 4 (in the SiC,/Si 3 N 4 /C nanocomposite) decomposes gradually to give off N 2 gas at higher temperatures when T > ~1400 • C [9,15]. While these assertions have been proven and corroborated by various characterization techniques such as XANES spectroscopy, XRD, TEM and Raman Spectroscopy, a profound understanding of the electrical conductivity of SiCN PDCs, particularly the charge carrier transport mechanisms, remain incomplete.…”