Rapid synthesis of thermoelectric compounds by laser melting

• Laser melting was used to synthesize thermoelectric compounds including alloys, intermetallic compounds, and oxides.
• The binary alloy compositions were identical with the nominal ones.
• The resulting phases agreed well with the phase diagrams, in which high temperature phases were preferentially formed.
• Pseudo binary systems of Mn-Al alloys and Si were required to produce stoichiometric ternary Mn-Al-Si compounds.
• The heating was primary determined by light absorptance, rather than the thermal conductivity or absorption mechanism.

The synthesis of thermoelectric compounds, including Bi-Sb and Mn-Si binary systems, Mn-Al-Si ternary system, and rare-earth doped SrTiO3, has been successfully demonstrated using a continuous laser diode with a 940 nm light source. Owing to the high power density of the laser (60 W/mm2 at the maximum), the precursor powders immediately melted and reacted when irradiated by the laser. Subsequent quenching led to the stabilization of high temperature phases in the resultant compounds. Any compositional differences between the laser treated compounds and the starting materials were negligible. The thermoelectric properties varied according to the composition, as expected, demonstrating the feasibility of laser melting as a rapid synthesis tool for thermoelectric compounds. Several advantages and limitations of the synthesis conditions are also discussed.

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