Reactive Spark Plasma Sintering and Thermoelectric Properties of Zintl Semiconducting Ca14Si19 Compound

Abstract

We present a new reactive spark plasma sintering (RSPS) technique for synthesizing the rhombohedral Ca14Si19 phase. The RSPS approach reduces the synthesis time from several weeks to a few minutes. The RSPS was found to be sufficient for obtaining a high level of purity of the Ca14Si19 under a pressure of 100 MPa for a dwell period of 5 min at a temperature of 900 ∘C. From electrical resistivity measurements, we were able to determine the energy band gap of Ca14Si19 to Eg=0.145(15) eV. The Seebeck coefficient shows Ca14Si19 as a p-type semiconductor at room temperature. It becomes n-type with increasing temperature pointing to significant bipolar and conduction band contributions due to the narrow bandgap of the compound.