Enhanced ZT of In_xCo₄Sb₁₂-InSb Nanocomposites Fabricated by Hydrothermal Synthesis Combined with Solid-Vapor Reaction: A Signature of Phonon-Glass and Electron-Crystal Materials

A rapid route of synthesizing pristine Co₄Sb₁₂ at relatively low temperature was previously developed. However, filling the voids using the same procedure is not successful. We develop a new route to fabricate In-filled cobalt skutterudites with InSb nanoinclusions In_xCo₄Sb₁₂-(InSb)_y via solid-vapor reaction between hydrothermally synthesized Co₄Sb₁₂ powder and the indium chunk. The nanocomposites are characterized using powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS). With the success of partial filling of In into the voids and InSb nanoinclusions, the power factor of the In_xCo₄Sb₁₂-(InSb)_y nanocomposites is significantly enhanced, and the thermal conductivity is lowered as compared with the pristine Co₄Sb₁₂. As a result, ZT with its highest value of 1.0 is attained for the hierarchical structured In_0.04Co₄Sb₁₂-(InSb)_0.05 nanocomposite at 575 K. The attained ZT value is among the highest ever reported value at T ≤ 575 K for In-filled cobalt skutterudites.