Investigation Properties Of Filled CoSb₃Skutterudite Synthesized By High Pressure

Thermoelectric materials convert directly between thermal and electrical energy canbe used as power generators and refrigerators with the advantages of high safety, highreliability, environment-friendly, no moving parts and maintenance-free. CoSb₃basedfilled Skutterudites as one of the most promising thermoelectric materials have beenattracted great attentions in recent years for the high Seebeck coefficient, good electricaltransport performance and the thermal conductivity as well as the optimizableperformance followed the concept of phonon-glass electron crystal.In this works, the single phase metastable n-type filled CoSb₃Skutterudites werecalculated by ab initio density functional calculations and synthesized by high-pressuresynthesis technique. The crystal structure, thermoelectric properties and some otherphysical properties like carrier concentration were investigated. The details of our worksinclude following:1、The filling behavior of Mg atoms into CoSb₃lattice voids under pressure wasinvestigated by ab initio density functional calculations according to Filling fraction limits（FFLs） theory. Isolated impurity formation energy E1of Mg filled CoSb₃phase,formation enthalpy H2of second phases and Gibbs formation energy of the reactionincluding Mg filled CoSb₃phase and second phases were calculated. The results showMg_yCo₄Sb₁₂could not be formed unless the pressure higher than9GPa. When under9GPathe filling factor is0.62, and the filling factor increases monotonically with increasingpressure even reach1.2、According to the reaults of ab initio density functional calculations of Mg filledCoSb₃, the small ion radius atom Mg filled CoSb₃was synthesized by High-pressuresynthesis technique at5GPa. The “rattling” nature of the filler atoms was validated viaEinstein model. And the influence of high electronegatice of filled atom on thethermoelectric properties were investigated, it show the high electronegatice led to highresistivity thus limiting the ZT value. Furthermore, HPS thus provides a fast synthesismethod to effectively broaden fillable elemental species into CoSb₃voids.3、Gd_yCo₄Sb₁₂, which is inaccessible at ambient pressure, was synthesized via High-pressure synthesis technique at4GPa. Thermoelectric properties investigationsreveal the enhancement of power factor and decrease of lattice thermal conductivity afterGadolinium filling. The highest ZT value of0.52was achieved for Gd_0.12Co₄Sb₁₂at600K.The transport properties show the carrier mobility decreases slightly with increasing of Gdfilling faction. The carrier concentration and mobility of Gd_0.12Co₄Sb₁₂are respectively4×10¹⁹cm^-3 and71cm2V^-1s^-1.4、The Na filled CoSb₃was synthesized by High-pressure synthesis technique at2.5GPa. Synchrotron powder X-ray diffraction, low temperature heat capacity, electrical andthermal transport properties, and Hall Effect were measured to characterize the structural,electrical, and thermoelectric properties of Na-filled CoSb₃. Anomalously large atomicdisplacement parameters （ADPs） are found for the Na filler atoms, indicating that the Naatoms are weakly bound in the structure. For Na-filled CoSb₃, although the thermalconductivity drops less effectively compared with rare-earth metal filled CoSb₃atcomparable filling fraction, it possesses a larger power factor due to relatively largercarrier mobility. The Na0.75Co₄Sb₁₂sample achieved highest power factor of5000μWm^-1K^-2, minimum lattice thermal conductivity of0.97Wm^-1K^-1and highest ZT of1.0at880K.5、 The double-filled skutterudites Gd0.12Na0.66Co₄Sb₁₂was synthesized byHigh-pressure synthesis technique for the first time. The chemical composition measuredby Electron probe micro-analyzer （EPMA） show Gd and Na enhanced filling factionmutually compare to samples which synthesized with the same nominal composition.Thermoelectric properties indicate that the combination of Gd and Na fillers inside thevoids of the skutterudite structure provides a broad range of resonant phonon scatteringconsequently a strong suppression in the lattice thermal conductivity. And electricaltransport property is greatly improved with double elemental filling. Gd0.12Na0.66Co₄Sb₁₂get maximum power factor of4885W/m^-1K^-1, minimum lattice thermal conductivity of0.96Wm^-1K^-1, highest ZT of1.07at880K.