Enhanced thermoelectric properties of spark plasma sintered SiC with in-situ TiB2 network structures

Abstract

SiC-based composites with in-situ TiB₂ network structures were produced by coating mechanically alloyed B₄C-TiC particle mixtures on SiC granules, and then utilizing the spark plasma sintering process to obtain bulk composites with improved thermoelectric properties. A high amount of electrically conductive secondary phase introduction is generally necessary to improve the electrical transport properties of SiC, which causes adverse effects on the Seebeck coefficient and thermal conductivity. Instead, producing a network structure of TiB₂ on SiC, rather than a SiC-TiB₂ particulate composite approach, was found to be effective in enhancing the electrical and thermal conductivity of SiC, with a minimum amount of secondary phase formation. The effects of different amounts of in-situ TiB₂ network on the temperature-dependent electrical and thermal transport properties of SiC were analyzed. Increasing amounts of TiB₂ formation resulted in simultaneously increased electrical and decreased thermal conductivities by the conductive network and increased phonon scattering, respectively. Although the Seebeck coefficients of the final composites ultimately reduced due to the metallic nature of the in-situ TiB₂ network, optimizing the composition revealed a high thermoelectric performance at high temperatures. The dimensionless figure of merit value peaked at 2.5 vol% TiB₂ content as 8.5 × 10⁻³ at 923 K, which is approximately 210 % higher than monolithic SiC.