High pressure synthesized Ca-filled CoSb3 skutterudites with enhanced thermoelectric properties

•n-type CaxCo4Sb12 was synthesized with high pressure synthesis method.•Maximal filling fraction of Ca was substantially increased due to high pressure.•Power factor as high as 5400 μWm−1K−2 was reached in Ca0.31Co4Sb12.•The highest ZT of 1.15 was achieved in the optimal Ca0.31Co4Sb12 at 840 K.

Ca-filled CoSb3 skutterudites were synthesized under high pressure. The structural, electrical, and thermoelectric properties were investigated. CaxCo4Sb12 samples show the skutterudite structure of Im3¯ symmetry. The maximum filling fraction of calcium was substantially increased in the high-pressure synthesized samples compared with the ambient-pressure synthesized samples. As a result, the power factor was greatly increased and a maximal PF value of ca. 5400 μW m−1K−2 was reached in Ca0.31Co4Sb12. The highest ZT of 1.15 was achieved in the optimal Ca0.31Co4Sb12 at 840 K. Compared with the traditional solid state reaction method, high pressure synthesis can substantially shorten the reaction duration and extend fillable elements (or increase filling fraction), thus provide us an effective pathway for thermoelectric materials fabrication.