High-pressure densified solid solutions of alkaline earth hexaborides (Ca/Sr, Ca/Ba, Sr/Ba) and their high-temperature thermoelectric properties

• Solid solutions of alkaline earth hexaborides were synthesized.
• High-temperature thermoelectric properties of mixed calcium borides are excellent.
• Spark plasma source densification results in high ZT values.
• Borides are rare-earth free and refractory materials.

Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB6, SrB6, BaB6 and the ternary hexaborides CaxSr1−xB6, CaxBa1−xB6, SrxBa1−xB6 (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB6 (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process.

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