Thermoelectric properties of single- and polycrystalline RuGa3

• Single- and polycrystalline samples of RuGa3 were synthesized.
• The initial chemical composition is maintained in the samples.
• Single crystal X-ray diffraction analysis reveals RuGa3 to be stoichiometric.
• Intrinsically, thermal conductivity and thermopower show distinct features below 40 K.
• In polycrystalline RuGa3 the pronounced peaks are nearly completely suppressed.

The thermoelectric properties of the intermetallic semiconductor RuGa3 are investigated. Large single crystals were grown to study intrinsic properties. To investigate the influence of grain boundaries in this system, the single crystals were ground to powder and densified using spark plasma sintering treatment. The initial chemical composition is maintained with the introduction of grain boundaries. Electrical resistivity data show semiconducting behavior for single- and polycrystalline samples. The high thermal conductivity (>500 W K−1 m−1) obtained for single crystals at low temperatures is reduced by a factor of 10 in the polycrystalline specimen. The thermopower shows a change between n-type and p-type behavior with a sharp minimum of about −700 μV K−1 at 38 K for single crystals, which is completely suppressed by the introduction of grain boundaries. A comparison with RuIn3 shows the potential of RuGa3 as a thermoelectric material in its single- and polycrystalline form.

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