Microstructure and Thermoelectric Properties of B₄C-SiB_n-Si Composites Prepared by Arc Melting

Abstract

B-C-Si system composites were prepared by arc melting in argon atmosphere using B₄C, B and Si powders. The composites contained three phases: B₄C, SiB_n (n≥14) and free Si. The electrical conductivity (σ) of the composites in which the main phase was B₄C decreased with increasing SiB_n content, but slightly increased with increasing the solid solution of silicon. The Seebeck coefficient (α) of almost all the composites increased with increasing temperature, but B₄C containing a small amount of Si showed a maximum at 800K. The composites in which the main phase was SiB_n containing free Si and B₄C had greater α values than B₄C. The thermal conductivity (κ) of the composites decreased with increasing temperature. The κ of the composites in which the main phase was B₄C increased and decreased by forming solid solutions of Si and B, respectively. The dimensionless figure-of-merit (ZT) increased with increasing temperature. The composites in which the main phase was SiB_n containing B₄C and several tens mol% Si had the greatest ZT value of 0.4 at 1100K. This value is the largest level among high performance boron-rich borides.