Possible enhancement of thermoelectric performance for Si-SiO2 sintered composite by percolation effect

Abstract A sintered composite consisting of p-type Si0.99B0.01 and insulative SiO2 particles was fabricated and its thermoelectric properties were investigated. The logarithm of the thermal conductivity, κ, of the composites increases almost linearly with an increase of the volume fraction of Si0.99B0.01, but that of the electrical conductivity, σ, of the composites shows a tendency to increase rapidly when the volume fraction of Si0.99B0.01 is 40%, and then gradually increase. The behavior of the electrical conductivity for the composite can be understood as being due to the percolation phenomenon of Si0.99B0.01 particle, which is caused by the completion of connection of conductive paths of Si0.99B0.01 particles in the sintered body. The value of σ/κ increases with an increase of the volume fraction of Si0.99B0.01, and becomes almost constant when the volume fraction of Si0.99B0.01is 80% or more. A maximum dimensionless figure of merit, ZT, of 0.23 was obtained for the sample of 80% Si0.99B0.01 at 1073K. The experimental results were discussed based on the effective medium approximation which reproduces the percolation phenomenon well.