Microstructure and thermoelectric properties of B4C-SiBn-Si composites prepared by arc melting

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