Effects of Re substitution for Mn on microstructures and properties in Re-substituted higher manganese silicide thermoelectric material

• Published in: Journal of alloys and compounds Vol. 776; pp. 8 - 15
• Main Authors: Homma, T., Kamata, T., Saito, N., Ghodke, S., Takeuchi, T.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05.03.2019; Elsevier BV
• Subjects: Crystal structure; Dislocation density; Electrical resistivity; Figure of merit; Heat conductivity; Intermetallic compounds; Lattices (mathematics); Manganese compounds; Manganese silicide; Materials substitution; Microstructure; Organic chemistry; Phonons; Powder metallurgy; Rapid quenching (metallurgy); Rhenium; Subgroups; TEM; Thermal conductivity; Thermoelectric; Thermoelectric materials; Thermoelectricity; Thermoelectric; Powder metallurgy; TEM; Phonons; Crystal structure
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2018.10.209

Effects of Re substitution for Mn on the microstructure-property relationships in Mn30.4Re6.0Si63.6 thermoelectric material have been investigated in comparison with those in Mn36.4Si63.6. The rapid quenching using the meld spinning leads to relatively uniform distribution of Re. After sintering, the Nowotny chimney ladder phases known as the higher manganese silicide (HMS) are stabilized in both the Re-free and Re-substituted HMSs, and the chemical formulae become Mn15Si26 and Mn19Si33, respectively. The Re atoms are successfully substituted for Mn in the (Mn,Re)19Si33 HMS. The number density of the sublattice dislocation in the Re-substituted HMS is 1.6 times higher than that in the Re-free HMS, that causes a decrease in lattice thermal conductivity. Due to the impurity effect of the Re substitution, the electrical conductivity is supposed to be enhanced, resulting in the highest dimensionless figure of merit (ZT) among the investigated HMSs. Identified microstructural difference in this study due to the Re addition. The grain sizes in both samples are equivalent (∼3 μm), but the local crystal structure, distribution of Re atoms and number of sublattice dislocations are different. The combinations of arc melting, melt spinning and PECS are important processes so as to disperse the heavy element of Re uniformly without oxides: as a consequence, the thermal conductivity decreases up to the half of that in the Mn36.4Si63.5 in addition to enhancement in electrical conductivity due to impurity effect of Re. [Display omitted] •The oxides are removed by arc melting before the melt spinning.•Re elements are relatively homogeneously distributed in the as-melt spun sample.•Crystal structures of HMSs are determined by electron diffraction.•Both Re atoms and sublattice dislocations diminish lattice thermal conductivity.•Theoretical interpretation of thermal and electrical conductivity has provided.