title: Thermal Transport Driven by Extraneous Nanoparticles and Phase Segregation in Nanostructured Mg2(Si,Sn) and Estimation of Optimum Thermoelectric Performance.
abstract: Solid solutions of magnesium silicide and magnesium stannide were recently reported to have high thermoelectric figure-of-merits (ZT) due to remarkably low thermal conductivity, which was conjectured to come from phonon scattering by segregated Mg2Si and Mg2Sn phases without detailed study. However, it is essential to identify the main cause for further improving ZT as well as estimating its upper bound. Here we synthesized Mg2(Si,Sn) with nanoparticles and segregated phases, and theoretically analyzed and estimated the thermal conductivity upon segregated fraction and extraneous nanoparticle addition by fitting experimentally obtained thermal conductivity, electrical conductivity, and thermopower. In opposition to the previous speculation that segregated phases intensify phonon scattering, we found that lattice thermal conductivity was increased by the phase segregation, which is difficult to avoid due to the miscibility gap. We selected extraneous TiO2 nanoparticles dissimilar to the host materials as additives to reduce lattice thermal conductivity. Our experimental results showed the maximum ZT was improved from ∼0.9 without the nanoparticles to ∼1.1 with 2 and 5 vol % TiO2 nanoparticles at 550 °C. According to our theoretical analysis, this ZT increase by the nanoparticle addition mainly comes from suppressed lattice thermal conductivity in addition to lower bipolar thermal conductivity at high temperatures. The upper bound of ZT was predicted to be ∼1.8 for the ideal case of no phase segregation and addition of 5 vol % TiO2 nanoparticles. We believe this study offers a new direction toward improved thermoelectric performance of Mg2(Si,Sn).
authors.affiliation: Department of Mechanical Engineering, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Abdullah S
authors.initials: AS
authors.lastname: Tazebay
authors.affiliation: Department of Mechanical Engineering, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Su-In
authors.initials: SI
authors.lastname: Yi
authors.affiliation: Korea Electrotechnology Research Institute , Changwon, Korea.
authors.forename: Jae Ki
authors.initials: JK
authors.lastname: Lee
authors.affiliation: School of Materials Science and Engineering, Kyungpook National University , 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea.
authors.forename: Hyunghoon
authors.initials: H
authors.lastname: Kim
authors.affiliation: Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Je-Hyeong
authors.initials: JH
authors.lastname: Bahk
authors.affiliation: Department of Mechanical Engineering, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Suk Lae
authors.initials: SL
authors.lastname: Kim
authors.affiliation: Korea Electrotechnology Research Institute , Changwon, Korea.
authors.forename: Su-Dong
authors.initials: SD
authors.lastname: Park
authors.affiliation: School of Materials Science and Engineering, Kyungpook National University , 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea.
authors.forename: Ho Seong
authors.initials: HS
authors.lastname: Lee
authors.affiliation: Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Ali
authors.initials: A
authors.lastname: Shakouri
authors.affiliation: Department of Mechanical Engineering, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Choongho
authors.initials: C
authors.lastname: Yu
keywords: magnesium silicide; magnesium stannide; phase segregation; phonon scattering; titanium dioxide