Microstructure and thermoelectric properties of chlorine-filled CoSb3 skutterudites synthesized by HPHT process

Filled CoSb3-based skutterudites are promising middle-temperature thermoelectric materials. However, p-type skutterudites containing electropositive fillers require additional charge compensation by doping atoms at the framework, which leads to enhanced carrier scattering. In this work, p-type filled CoSb3 materials with electronegative guest Cl were successfully prepared by high-pressure high-temperature (HPHT) process. A high filling fraction of Cl in void sites reaching similar to 23% was obtained without charge compensation. Cl filler exhibited p-type electron acceptor behavior and can increase hole concentration of pristine CoSb3 to a magnitude of 10(19) cm(-3). As the content of Cl rose, abnormal spinal morphology and fine nano grain were observed in Cl-filled skutterudites. In turn, lattice thermal conductivity of Cl0.6Co4Sb12 sample significantly reduced by 46% when compared to pristine CoSb3 at room temperature due to enhanced scattering of point defect, rattler, and grain boundary. In sum, HPHT process looks promising for using Cl as additional p-type dopant candidate to yield significantly enhanced phonon scattering.