Enhanced thermoelectric figure of merit by composite effects and low thermal conductivity in distrontium silicide (Sr2Si).

Abstract The thermoelectric properties of Sr 2 Si, Sr 5 Si 3 , and their composites are reported. Sr 2 Si-Sr 5 Si 3 composites were synthesized by partial decomposition of Sr 2 Si to Sr 5 Si 3 during spark plasma sintering. Semiconducting Sr 2 Si grains were surrounded by boundary regions composed of smaller grains of Sr 2 Si, metallic Sr 5 Si 3 , and semiconducting Sr 3 SiO. Addition of the Sr 5 Si 3 phase reduced the electrical resistivity from 1.69 × 10−3 Ωm to 6.45 × 10−5 Ωm at room temperature, which corresponded to the samples having no and the maximum amount of the Sr 5 Si 3 phase, respectively. The electrical resistivity decreased; however, the Seebeck coefficient slightly increased to 157 μV/K at 773 K, and the thermal conductivity was approximately constant. Therefore, the power factor and ZT monotonically increased with an increase in the amount of the Sr 5 Si 3 phase in the composite samples, which confirmed almost no effect resulted from the Sr 3 SiO phase. A low thermal conductivity was demonstrated by Sr 2 Si (ca. 1 W/mK at 776 K), which resulted from weaker atomic bonds, heavier atomic mass, greater atomic volume, and a greater number of atoms in the unit cell. A further enhancement of ZT can be achieved for higher amounts of Sr 5 Si 3 and at higher temperatures. Graphical abstract Image 1 Highlights • Thermoelectric properties of Sr 2 Si, Sr 5 Si 3 , and their composites were investigated. • Remarkable reduction in ρ was observed due to the presence of Sr 5 Si 3 phase. • Simultaneous increase in S and σ was observed. • The lower κ was largely unaffected by the presence of metallic Sr 5 Si 3 phase. • The PF and ZT increased almost linearly with an increased amount of Sr 5 Si 3. [ABSTRACT FROM AUTHOR]