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

• Published in: Journal of alloys and compounds Vol. 782; pp. 1031 - 1040
• Main Authors: Mudasar, Farhan, Katsura, Yukari, Kitahara, Koichi, Kimura, Kaoru
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.04.2019; Elsevier BV
• Subjects: Atomic properties; Bonding strength; Chemical bonds; Composite; Composite materials; Electrical resistivity; Figure of merit; Grains; Heat conductivity; Heat transfer; Microstructure; Plasma sintering; Power factor; Seebeck effect; Silicide; Silicides; Spark plasma sintering; Thermal conductivity; Thermoelectric; Thermoelectricity; Unit cell; Thermal conductivity; Thermoelectric; Silicide; Composite; Microstructure
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2018.12.037

The thermoelectric properties of Sr2Si, Sr5Si3, and their composites are reported. Sr2Si-Sr5Si3 composites were synthesized by partial decomposition of Sr2Si to Sr5Si3 during spark plasma sintering. Semiconducting Sr2Si grains were surrounded by boundary regions composed of smaller grains of Sr2Si, metallic Sr5Si3, and semiconducting Sr3SiO. Addition of the Sr5Si3 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 Sr5Si3 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 Sr5Si3 phase in the composite samples, which confirmed almost no effect resulted from the Sr3SiO phase. A low thermal conductivity was demonstrated by Sr2Si (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 Sr5Si3 and at higher temperatures. [Display omitted] •Thermoelectric properties of Sr2Si, Sr5Si3, and their composites were investigated.•Remarkable reduction in ρ was observed due to the presence of Sr5Si3 phase.•Simultaneous increase in S and σ was observed.•The lower κ was largely unaffected by the presence of metallic Sr5Si3 phase.•The PF and ZT increased almost linearly with an increased amount of Sr5Si3.